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HOW TO DESIGN AN EXPLORATION SURFACE SOIL GAS GEOCHEMICAL SURVEY: ILLUSTRATED BY APPLICATION EXAMPLES FROM THE HUGOTON EMBAYMENT OF SOUTHEAST COLORADO AND SOUTHWEST KANSAS Rufus J. LeBlanc, Jr., and Victor T. Jones, III Exploration Technologies, Inc. AAPG Annual Convention, April 18-21, 2004 Dallas, Texas Aerial Photograph of a modern-day incised valley in the Lower Jurassic Navajo Sandstone of east-central Utah. This is an excel- lent analog for the Morrow incised valley-fill sandstones of the Stateline Trend of eastern Colorado and western Kansas. Image: Cover photograph of September 2002 AAPG Bulletin
Transcript
Page 1: HOW TO DESIGN AN EXPLORATION SURFACE SOIL GAS GEOCHEMICAL … · 2019. 8. 23. · How to Design an Exploration Surface Soil Gas Geochemical Survey Page 3 BASICS OF SURFACE SOIL GAS

HOW TO DESIGN AN EXPLORATION SURFACE SOIL GAS GEOCHEMICAL SURVEY: ILLUSTRATED BY APPLICATION EXAMPLES FROM THE HUGOTON EMBAYMENT OF SOUTHEAST COLORADO AND

SOUTHWEST KANSAS

Rufus J. LeBlanc, Jr., and Victor T. Jones, IIIExploration Technologies, Inc.

AAPG Annual Convention, April 18-21, 2004Dallas, Texas

Aerial Photograph of a modern-day incised valley in the Lower Jurassic Navajo Sandstone of east-central Utah. This is an excel-lent analog for the Morrow incised valley-fill sandstones of the Stateline Trend of eastern Colorado and western Kansas.Image: Cover photograph of September 2002 AAPG Bulletin

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Page 2How to Design an Exploration Surface Soil Gas Geochemical Survey

HOW TO DESIGN AN EXPLORATION SURFACE SOIL GAS GEOCHEMICAL SURVEY: ILLUSTRATED BY APPLICATION EXAMPLES FROM THE HUGOTON

EMBAYMENT OF SOUTHEAST COLORADO AND SOUTHWEST KANSAS

Rufus J. LeBlanc, Jr., and Victor T. Jones, III

ABSTRACT

Three regional surface geochemical soil gas surveys covering areas of 150, 53, and 209 square miles were conducted in the Hugoton Embayment of southeast Colorado and southwest Kansas. The three surveys exhibit different sampling densities and comprise both reconnaissance and detailed grids. The surveys were conducted over the prolific Pennsylvanian Morrow Stateline Trend and the Permian Chase Carbonate Gas Trend.

The stratigraphic entrapment of oil and gas in these two plays, relatively shallow depth, and highly variable porosity and permeability of the reservoirs are factors which favor the application of surface soil gas surveys as an important exploration method to reduce risk in exploration, exploitation, or development efforts in these two plays. Examples of actual reconnaissance and detailed surface soil gas surveys in this petroleum province are discussed.

The surveys were conducted from 1987 to 1992 before there was the widespread development drilling as witnessed today. Both the benefits and limitations of a reconnaissance survey over the Stateline Trend from Frontera to Second Wind Fields are discussed. A detailed survey in the Moore-Johnson Field area illustrates the benefits of surface geochemistry in risk reduction in this stratigraphicly complex area. An example of a detailed soil gas survey over Byerly Field in Greeley County, Kansas is presented which depicts the complex porosity and permeability variations in the Chase Carbonate.

The paper is a retrospective analysis of soil gas surveys conducted in this complex area in light of new geologic knowledge of the area that has been revealed in the past decade.

INTRODUCTION

The hypothesis that natural soil gas microseeps detected at the surface from underlying hydrocarbon deposits could continue to be useful as an exploration method is a natural extension of the mapping of macroseeps, which led to the very early discovery of many oil and gas fields in petroleum basins all over the world (Link, 1952). A history of the development of surface soil gas geochemistry may be found in Jones et al. (2000).

Twenty years ago, in 1983, Jones and Drozd published a paper in the AAPG, which improved our understanding of two important basic concepts of surface soil gas geochemistry – magnitude and composition as relating to subsurface reservoirs, significantly improving the viability of surface geochemical prospecting as a viable exploration method.

One of the primary reasons for past failures in the application of surface geochemical surveys is a lack of a proper design of the sampling grid. Few explorationists have adequate knowledge on how to design a surface soil gas survey, and as a result do not accrue nor appreciate the benefits that can be expected

from a properly designed survey. The factors listed in Table 1 are critical for the successful design, employment, and interpretation of a soil gas survey Another reason for past failures may have been in the sample technique used in the collection of the soil gas samples (Jones, 2004, in review).

The considerations for sample spacing presented in this paper are not only the result of the authors work with exploration surveys in the area over a 16-year period, but also the result of having concurrently employed surface soil gas geochemistry in environmental assessments of petroleum contaminated sites. Reservoir heterogenities in shallow sedimentary rock units of shallow vadose zones and aquifers are very readily apparent from the surface microseep anomalies observed from the extremely high-density soil gas grids used in these applications. An example of such an application is provided in Agostino, LeBlanc, and Jones (2002).

Exploration soil gas surveys may be designed so that they are very inexpensive and regional in nature, with very few soil gas samples, or they may be designed so that they are more detailed, with dense spacing of soil gas sample sites. As will be demonstrated with application examples, there is a critical balance in the design of surface geochemical surveys that must be met if useful results are to be attained.

Measuring natural gas microseepage, like any scientific analytical method dealing with nature is not perfect. Interpretations of soil gas geochemistry should always be used in conjunction with subsurface geology and geophysics. Another important concept to remember is that there is no direct relationship between the magnitude of a surface microseep and the resultant volumetric hydrocarbon production or economics of a corresponding well or field. Soil gas microseepage, measured at the surface, is the result of light hydrocarbon gases in a reservoir being pressure-driven upward to the surface along natural fractures in the subsurface.

A general rule-of-thumb concerning soil gas surveys is that more soil gas sites per unit area are required in stratigraphic fairways than in structural fairways. However, some caution should be taken in this generalization, as there are few structural hydrocarbon accumulations that do not also have some stratigraphic variations in the reservoir.

Three regional surface geochemical soil gas surveys covering areas of 150, 53, and 209 square miles were conducted in the Hugoton Embayment of southeast Colorado and southwest Kansas. The surveys were conducted from 1987 to 1992 before there was the widespread development drilling as witnessed today. This paper describes various configurations for soil gas surveys that may be designed and discusses the type of exploration information that can be expected from each survey design from reconnaissance to detailed soil gas surveys. Examples will be drawn from the actual soil gas surveys in these areas.

The Hugoton Embayment provides an excellent petroleum basin with which to illustrate these methods for the following reasons: (1) simple tectonics with little faulting, (2) the gas microseepage is vertical, (3) shallow to intermediate depth productive horizons, (4) wide range of types of soil gas surveys, (5) the area contains both oil and gas trends, each having different unit spacing, (6) the resultant oil and gas production in these trends is in the “giant field” category, (7) the actual concentrations of the free soil gas microseepage in these areas has very low magnitudes so that the background concentrations approach zero, and (8) the oil and gas accumulations are predominantly stratigraphic, providing an additional impetus to use geochemical data in this type of high-risk exploration play.

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Page 3How to Design an Exploration Surface Soil Gas Geochemical Survey

BASICS OF SURFACE SOIL GAS SURVEYS

In its simplest mode, soil gas samples can be collected from a depth of four feet by means of a hand-held collection probe into a small volume (125 ml) glass sample bottle. These simple collection techniques do not require elaborate logistics, in addition to providing low collection costs, enabling rapid collection, and being generally unobtrusive to the environment.

The general objective of soil gas surveys is to collect and measure microscopic concentrations (microseeps) of methane, ethane, propane, and butane found in the void spaces of near-surface soils that overlie subsurface petroleum reservoirs. These gases are the lightest and most volatile constituents in crude oil, condensate, and natural gas reservoirs and because of this characteristic are the most important components to quantify and map..A most important requirement for mapping these natural seeps is that the laboratory analytical instruments must have the capability to detect very low concentrations, in the parts per billion (ppb) range, for methane, ethane, propane, and butanes.

Soil gas surveys may be used at any stage of exploration in a petroleum basin – whether in the frontier stage of an unexplored basin or in the development stage of a mature basin. An excellent summary that illustrates the variety of different stages in the application of soil gas geochemistry has been discussed by Boleneus (Figure 1). If employed very early in basin exploration, soil gas surveys can provide justification for purchasing “trend acreage”, or if geophysical data is lacking, can be used as further criteria for strengthening a subsurface lead.

Soil gas surveys may be classified as reconnaissance, detailed, regional, or local. The particular survey conducted must be tailored to the exploration objectives.

Regional surface geochemical soil gas surveys may be conducted at any stage in basin exploration – frontier, semi-mature, or mature. Local soil

gas surveys have been employed in the explotation or development stages of a play or field. Soil gas surveys have also been documented to be beneficial during the secondary recovery efforts in a particular field much like the current employment of 3-D and 4-D seismic surveys for these purposes.

Soil gas sample density per unit area determines whether a regional soil gas survey is a reconnaissance survey or a detailed survey. In a detailed survey the sample density should be commensurate with the expected prospect areal extent or well spacing of a particular play. Special high-density soil gas spacing has been used in surveys conducted for the development drilling of fields and later in secondary recovery efforts.

Reconnaissance surveys are typically employed in the frontier or semi-mature exploration stages of a concession or basin. There is less justification for a reconnaissance survey in a mature basin. Because reconnaissance soil gas surveys are the least costly exploration technique, they should be applied in series fashion with the more costly exploration techniques (gravity, magnetics, reconnaissance 2-D seismic) following later. However, exceptions do occur. A reconnaissance survey conducted across the Powder River basin in 1976 resulted in the discovery of the Hartzog Draw field (second largest field in this mature basin).

Detailed soil gas surveys are used in later exploration stages to acquire additional exploration information in areas of interest delineated by a reconnaissance survey. Detailed soil gas surveys are typically applied in a parallel fashion with other exploration methods (wildcat wells, detailed 2-D seismic grids, 3-D seismic).

An additional benefit of soil gas surveys is the capability to differentiate (using compositional ratios) between oil-prone or gas-prone fairways in a particular concession or basin or whether certain areas are thermally over-mature or immature. The concept and application of compositional ratios has been discussed in detail by Jones and Drozd (1983) and Jones et al. (2000).

Interpretation of soil gas data involves presenting the geochemical dataset within the most current and detailed geological and geophysical framework available. The magnitudes of the four light gases may be presented many different ways for interpretational presentations:

(1) Presenting the microseep magnitudes in a profile graphic.(2) Presenting the microseep profile in conjunction with a subsurface geologic cross-section

or a seismic line.(3) Presenting a group of microseep profiles as a fence-diagram graphic.(4) Presenting the microseep magnitudes in the form of an interpretative contour map.(5) Presenting the microseep magnitudes in the form of a dot map where the diameter of the

dots (at each soil gas site) is directly related to the light gas magnitudes. This presentation gives an unbiased interpretation as opposed to a contour map.

(6) If compositional ratios of the microseeps are used, then the predicted hydrocarbon (oil, condensate, gas) is indicated by color-coding within the magnitude dot maps mentioned above.

(7) Presenting the microseep magnitudes in the form of a Pixler Plot.

Anomalous concentrations of methane, ethane, propane, and butanes detected at the surface are always real seeps, since active flux is necessary to overcome near surface interfering effects.

A B C D

GEOCHEMISTRY(7) SURFACE

GEOCHEMISTRY(5, 6) SURFACE

GEOCHEMISTRY(4) SURFACE

(1, 2, 3) SURFACEGEOLOGY

Figure 1

field development.7. To define the areal extent of an oil accumulation to assist orderly

in one or more of a series of wells.6. To assist a drilling partner to decide to participate/not participate

geochemical characteristics.5. To rank drilling prospects on the basis of their most favorable

4. To identify drilling prospects; usually used in conjunction withgeophysics.

Objectives:

It is usually applied in "series/or parallel" fashion with other tools.identified by other methods (geophysics, leasing, and geochemistry).Geochemistry can be applied to known interest areas previously

ToolB. Surface Geochemistry as a Detail Exploration

areas.

immature areas.3. To differentiate oil-prone from gas-prone or thermally-mature versus

2. To select most valuable concessions; focus exploration in frontier

a low cost per square mile.1. To identify interest areas, based on gross hydrocarbon character, at

Objectives:

more costly tools used later.concessions, and plays. It is applied in "series" fashion with theGeochemistry can be applied to LARGE areas - such as basins,

Exploration ToolA. Surface Geochemistry as a Reconnaissance

Boleneus, David, 1994. Guidelines, etc. Oil & Gas Journal, June 6, pp 59-64

WILDCAT

FIELD DEVELOPMENT

DISCOVERY

PROSPECTS ARE DRILLEDMOST FAVORABLE

PROSPECTS

GEOLOGY, GEOPHYSICS

LEASING

CONCEPT

BASICGEOLOGY

LEASING

GEOPHYSICS

APPLICATIONS FOR SURFACE GEOCHEMICAL SURVEYS

INTEREST AREA

GEOLOGY

IDENTIFIEDPROSPECTS

GEOPHYSICS

FURTHER EVALUATIONOR DRILLING

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Page 4How to Design an Exploration Surface Soil Gas Geochemical Survey

GENERAL GEOLOGY OF THE HUGOTON EMBAYMENT

The Hugoton Embayment of southwest Kansas and southeast Colorado, shown in Figure 2A, is a wide, southward-plunging Paleozoic syncline of about 12,000 square miles that is bounded on the west, north, and east by uplifted areas. The Hugoton Embayment is the shallower, northward extension of the deeper Anadarko Basin of western Oklahoma and the Texas Panhandle. The Hugoton Embayment is bounded on the west by the Las Animas Arch, on the north by the Transcontinental Arch, and on the east by the Central Kansas Uplift. Sedimentary rocks thicken towards the center of the basin and southward to about 9000 feet near the Kansas-Oklahoma border.

The USGS has recognized 25 different petroleum plays in the Hugoton Embayment and Anadarko Basin (USGS, 1995). Every Paleozoic system that is represented in both these basins has produced some hydrocarbons. The province overall produces primarily gas. According to recent production data, compiled by the USGS, the province has produced more than 2.3 BBO and 65.5 TCFG since the early 1900’s. Stratigraphic trapping mechanisms are the most common, combination types less common, and structural types the least common. Pennsylvanian and Permian reservoirs have produced the largest volumes of hydrocarbons to date.

The two petroleum plays discussed in this paper are the Pennsylvanian Morrow Sand Oil Trend and the Permian Chase Carbonate Gas Trend illustrated in Figures 2B and 2C, respectively.

Contours in ft

Amarillo Uplift

Hugoton

EmbaymentApishapa Uplift

EXPLANATION

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GENERAL GEOLOGY OF HUGOTON EMBAYMENT

A. LOCATION MAP HUGOTON EMBAYMENT

Figure 2

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Page 5How to Design an Exploration Surface Soil Gas Geochemical Survey

Pennsylvanian Morrow Sand Oil Trend

Pennsylvanian Morrow fluvial sand channels developed both within and along the margins of the Morrow paleobasin during major regressive events in Early Pennsylvanian time (Figure 2B). There are five recognized regressive-transgressive cycles within the Upper Morrow Formation (Bowen and Weimer, 2003). River valleys were incised into either underlying Lower Morrow or Upper Mississippian limestones and were subsequently progressively filled with fluvial sands, estuarine sands, and finally, marine muds. The distribution of Morrow Sand channels within the incised valleys is commonly very complex, sometimes involving cross-cutting relationships. Later channel stages are frequently incised into earlier ones. The portion of the Morrow Trend mentioned in this paper is commonly referred to as the Stateline Trend and the complex of fields extends for about 60 miles in a north-south direction along the Colorado and Kansas state boundary (Figure 2B). The collection of fields in this complex will have an ultimate recovery of more than 100 MMBO and 500 BCFG.

Regional dip at the top of the Morrow is to the east-southeast. Drill depths to the Morrow reservoirs ranges from 5000 to 5500 feet. Average cumulative production from wells in this trend has ranged from 40,000 to 155,000 BO per well.A comprehensive compilation of 23 papers on the fields within the Morrow oil trend over the Las Animas Arch and Hugoton Embayment was published by the RMAG (Sonnenberg et al., 1990). Further details of the area may be found in Bowen, 2001. Recently, an excellent summary of the Morrow sequence stratigraphic framework and the relational aspects to reservoir geometry and geology and reservoir performance was presented by Bowen and Weimer (2003).

Permian Chase and Council Grove Carbonate Gas Trend

The Permian Carbonate Gas Trend (Chase and Council Grove Groups) in the Hugoton Embayment is the most prolific and important hydrocarbon play in this petroleum province. The major gas fields of this area – Hugoton, Panoma, Greenwood, Bradshaw, and Byerly have produced a total cumulative of 27 TCFG. The natural gas accumulations in these fields are due to stratigraphic entrapment caused by a facies change in the Permian Chase and Council Grove Carbonate reservoirs where they grade from limestones and dolomites in the east to nonmarine red beds in the west (Figure 2C). The upper seal for the gas reservoirs are provided by anhydrites and shales of the overlying Sumner Group.

Regional dip of the Permian Carbonates is to the east-southeast. Average drill depths of the gas reservoir at Byerly Field, in the extreme north of the Hugoton Embayment, range from about 2750 to 2900 feet. Cumulative gas production from individual wells in Byerly Field has ranged from 30 MMCFG to 3,572 MMCFG.

The stratigraphic entrapment of oil and gas in these two plays, relatively shallow depth, and highly variable porosity and permeability of the reservoirs are factors which favor the application of surface soil gas surveys as an important exploration method to reduce risk in exploration, exploitation, or development efforts in these two plays. Examples of actual reconnaissance and detailed surface soil gas surveys in this petroleum province are discussed below.

Additional information on the Chase Carbonate may be obtained from the Kansas Geological Survey website and Bebout et al. (1993).

Central Kansas Uplift

Cam

bridge Arch

Kansas

Nebraska

AbandonedHighstandPosition

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ron

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ang

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Lowstand Shorelines

Colorado

Texas

OklahomaUpliftSierra Grande

PositionHighstand

AbandonedAmarillo Uplift

Wichita Uplift160 km

100 mi

MARINE SHALE

MISSISSIPPIAN

SUBCROPLIMESTONE

CHANNELSSAND

MORROW

10km0

10mi0

KA

NS

AS

CO

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Greeley Co.

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Mount Sunflower

Second Wind

Stockholm SW

Frontera

Arapahoe

Harker Ranch

Moore-Johnson

Jace

Lookout

C. PERMIAN CHASE CARBONATE TREND

B. PENNSYLVANIAN MORROW SAND OIL TREND

MORROW PALEOGRAPHY INCISED MORROW VALLEYS

DISTRIBUTION OF OIL FIELDSIN MORROW TREND

Council Grove

Gas-Water Contact

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STEVENS

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STRATIGRAPHIC ENTRAPMENT IN CHASE CARBONATE

DISTRIBUTION OF GAS FIELDSIN CHASE TREND

A’A

Figure 2

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Page 6How to Design an Exploration Surface Soil Gas Geochemical Survey

A. 1979 Oil and Gas Fields in Stockholm Area B. 1987 Oil and Gas Field Development and New Discoveries in Stockholm Area

C. November 1987 Reconnaissance Soil Gas Profile

Eth

ane

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e (p

pb

)

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K235K234K233K232K231K230K229K228K227K226K225

SOIL GAS PROFILE ETHANE MAGNITUDE

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K225 K226 K227 K228 K229 K230 K231K232 K233 K234 K235

Soil Gas Anomaly

ENCAPMENTField

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MISSISSIPPI OILENCAPMENT

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Soil Gas Profile

Mull Drlg.Stateline Ranch #1

TXOWallace # 1-R

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Figure 3

RECONNAISSANCE SOIL GAS SURVEYS

Reconnaissance soil gas surveys typically are conducted over a large area with wide spacing between soil gas sample sites. The soil gas samples may either be collected along single line profiles or in a regular grid pattern. Examples of surveys conducted over oil fields in the Stateline Trend of the Morrow oil fairway will be used to demonstrate these concepts.

In 1979, TXO drilled the discovery well for SW Stockholm Field (and the Stateline Trend) at the location shown on Figure 3A. At this time, there were only four fields in the immediate area (Figure 3A). There were two one-well abandoned Mississippian oil Fields (Funk and Encampment Fields) and two Morrow gas fields (Arapahoe and W Stockholm Fields).

These four fields were discovered as a result of various exploration plays on low-relief structures.

By the end of 1986, SW Stockholm Field had been developed to the extent shown on Figure 3B. The field contained 53 wells and extended for four miles along the arcuate axis of the field. A history of field development was discussed by Shumard (1991). During 1987 there were three significant developments in the area: (1) TXO completed a one-half mile field-extension in March with the Wallace # 1-R. (2) In April 1987, Medallion drilled a Morrow oil new field discovery with the Arapahoe # 27-1 eight miles to the north of SW Stockholm Field. (3) In July 1987, Mull Drilling established a Morrow oil new field discovery with the Stateline Ranch # 1 well four miles north of SW Stockholm Field. These three wells, along with the wells of SW Stockholm Field had, in general terms, defined a Morrow sand oil fairway for a distance of 10 miles in a north-south direction (Figure 3B). A decision was made to conduct a reconnaissance surface soil gas survey in the area using 11 samples per section. A profile line of samples taken from this low-density grid will be used to illustrate the differences between profile versus surveys conducted on a grid pattern.

Profile Line

Eleven soil gas sites collected in a single east-west profile, 3.5 miles long, along a highway that was north of the well established Morrow oil production at SW Stockholm Field and about half way between the two new field discoveries is shown in Figure 3B. Typically, such a soil gas profile would have been placed along the trace of a geophysical seismic line if one was available. The ethane magnitudes shown on this profile indicate a possibility that the Morrow oil production fairway also extended between the two Morrow oil new field discoveries. On the soil gas profile (Figure 3C) the ethane concentrations range from nine to forty parts per billion (ppb). Background concentrations of ethane occur at sites 225, 227, 228, and 235. The anomalous ethane magnitude at site 226 on the profile appears to be the result of gas microseepage from the one-well abandoned Encampment Oil Field (Mississippian). Anomalous ethane magnitudes at site 229 through site 234 (six sites) represent gas microseepage that appears to be from the subsurface Morrow oil reservoir. The anomalous ethane concentrations extend for a distance of 8800 feet (1.7 miles). This width is consistent with the maximum width of SW Stockholm field.

At this stage, an exploration well could have been drilled within the anomalous area, provided that the geochemical anomaly was supported by geology and/or geophysics, or a reconnaissance soil gas survey could be conducted on a uniform grid pattern in order to more rigidly define the suggested Morrow oil trend trend. Based on this encouraging data, a reconnaissance soil gas survey conducted over this area is discussed below.

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Page 7How to Design an Exploration Surface Soil Gas Geochemical Survey

January 1987A. Stateline Complex Development B. Soil Gas Survey Conducted - November 1987

Ethane Magnitude Contour Map August 1990C. Stateline Complex Development

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18

7

6

36

25

24

13

31

30

19

18

28293025

21201924

16171813

98712

4561

33323136

28293025

21201924

16171813

15S

41W

14S

42W

14S

41W

15S

43W

14S

43W

14S

42W

15S

42W

15S

42W

CO

LO

RA

DO

KA

NS

AS

1718

87

6 5

36 31

33323136

17181314

871211

561216

S42

W

16S

41W

16S

43W

16S

42W

27 26

2322

1415

1110

3 2

3534

2627

22 23

15 14

14 13

1211

12

34 35

K048 K049 K050 K051 K052K053 K054 K055

K056 K057 K058 K059 K060

K067 K068 K069 K070 K071 K072 K073 K074K075 K076 K077

K078 K079 K080 K081 K082 K083 K084 K085

K092 K093K094

K095 K096K097 K098 K099 K100

K101 K102 K103 K104 K105

K118 K119 K120 K121 K122 K123 K124 K125K126 K127 K128

K129 K130 K131 K132

K133

K133A

K134

K135 K136 K137

K145 K146 K147 K148 K149 K150 K151 K152K153 K154 K155 K156 K157 K158 K159

K170 K171 K172 K173 K174 K175 K176 K177 K178 K179 K180K181 K182 K183 K184 K185 K186 K187 K188 K189 K190

K197 K198 K199 K200 K201 K202 K203 K204K205 K206 K207 K208 K209

K210 K211

K221 K222 K223 K224 K225 K226 K227 K228 K229 K230 K231K232 K233 K234 K235 K236 K237 K238 K239 K240 K241

K249 K250 K251K252

K253K254 K255 K256 K257 K258 K259 K260 K261 K262 K263

K273 K274 K275 K276 K277 K278 K279 K280 K281 K282 K283K284 K285 K286 K287 K288 K289 K290 K291 K292 K293

K301 K302 K303 K304 K305 K306 K307 K308K309 K310 K311 K312 K313

K314K315

K324 K325 K326 K327 K328 K329 K330 K331 K332 K333 K334

K335 K336 K337 K338 K339 K340 K341 K342 K343 K344

K353 K354 K355 K356 K357 K358 K359 K360

K361 K362 K363 K364K365 K366 K367

K376 K377 K378 K379 K380 K381 K382 K383 K384 K385 K386

K387 K388 K389 K390 K391 K391A K392 K393 K394 K395 K396

K406K407 K408 K409 K410 K411 K412

K413 K414K415 K416 K417 K418 K419 K420

K428 K429 K430 K431 K432 K433 K434 K435 K436 K437 K438

K439 K440 K441 K442 K443 K444 K445 K446 K447 K448

K458K459

K460 K461 K462 K463 K464K465 K466 K467 K468 K469 K470 K471 K472

K480 K481 K482 K483 K484 K485 K486 K487 K488 K489 K490

K491 K492 K493 K494 K495 K496 K497 K498 K499 K500

K511 K512 K513 K514 K515 K516 K517K518

K519 K520 K521 K522 K523 K524 K525

K532 K533 K534 K535 K536 K537 K538 K539 K540 K541 K542

K543 K544 K545 K546 K547 K548 K549 K550 K551 K552

K564 K565 K566 K567 K568 K569 K570 K571 K572K573

K574 K574A K575 K576 K577 K578 K580 K581

K589 K590 K591 K592 K593K594

K595 K596 K597 K598 K599 K600 K601 K602 K603 K604 K60

K617 K618 K619 K620 K621 K622 K623 K624

K625 K626 K627 K628 K629 K630K631 K632

K641 K642 K643 K644 K645 K646

K647 K648 K649 K650 K651 K652 K653 K654 K655 K656 K657

K671 K672 K673 K674 K675 K676 K677

K678 K679 K680

K681

K682 K683 K684 K685

K699 K700 K701 K702 K703 K704 K705 K706 K707 K708 K709

K764A K765A

< 1515 - 2020 - 2525 - 30

(ppb)CONCENTRATIONS

ETHANE

> 30

1 Mile

25

24

13

12

1

30

19

18

7

6

36

25

24

13

31

30

19

18

28293025

21201924

16171813

98712

4561

33323136

28293025

21201924

16171813

15S

41W

14S

42W

14S

41W

15S

43W

14S

43W

14S

42W

15S

42W

15S

42W

CO

LO

RA

DO

KA

NS

AS

1718

87

6 5

36 31

33323136

17181314

871211

5612

16S

42W

16S

41W

16S

43W

16S

42W

27 26

2322

1415

1110

3 2

3534

2627

22 23

15 14

14 13

1211

12

34 35

K235K234K233K232K231K230K229K228K227K226K225

STOCKHOLMSW

MORROW GASW STOCKHOLM

MISSISSIPPI OILFUNK

MORROW GASARAPAHOE

MISSISSIPPI OILENCAPMENT

MedallionArapahoe #27-1

Soil Gas Profile

Mull Drlg.Stateline Ranch #1

TXOWallace # 1-R

Figure 4

Reconnaissance Soil Gas Survey on a Uniform Grid

A reconnaissance soil gas survey was conducted in November 1987 over an area of 150 square miles as shown in Figure 4A. The soil gas sample grid used (11 sites per section or square mile) was selected, both to make sample collection rapid by using the existing road network, and to limit the number of sites over such a large area. Because the well spacing of 80 acres per well had been established at SW Stockholm Field, the particular sample density used for this survey requires defining this survey as a reconnaissance survey. The area of the survey was also chosen to include other recent Morrow discoveries to the north of SW Stockholm Field, so that the soil gas data could be calibrated to the oil production with respect to magnitude and composition. A total of 798 soil gas sites were collected over this 150 square mile area. The interpreted soil gas data over the productive trend is illustrated by the ethane magnitude contour map shown in Figure 4B. It can be clearly seen that as early as 1987 (and prior to), the soil gas survey had accurately defined the general areal extent of the productive Morrow incised valley as would be confirmed by development drilling three years later in 1990 (Figure 4C). It can also be discerned that, at this sample density, that the soil gas data is inadequate for use in determining 80-acre drilling sites. Thus, the selected density for this survey conducted in 1987 was at the minimum threshold required to provide useful exploration information. This portion of the Morrow Stateline Trend, to date, has produced a total of 34 MMBO from 299 development wells. A retrospective analysis of this soil gas survey was previously discussed by Dickinson et al. (1994)

A number of untested soil gas anomalies still exist in the remainder of the survey area to the east of the Stateline Trend. These untested soil gas anomalies exhibit similar magnitudes and areal extents as the anomalies mapped within the Stateline Trend.Substantiation that these untested soil gas anomalies do indeed outline areas of additional Morrow oil potential may be seen in the recent development of the Mount Sunflower and Sidney Morrow oil fields in Wallace and Greeley Counties, Kansas. As shown in Figure 5, these two Morrow oil fields now contain a total of 40 oil wells and have produced a total of 2.85 MMBO. Development drilling in these two new fields progressed from 1990 through 1999 and has been conducted by 13 different independent oil companies. The significance of this new Morrow oil production is that, together, the two fields have defined a new Morrow oil productive fairway that is about two miles wide and extends for seven miles in a north-south direction (Figure 5). The new fairway is four miles east of the older Stateline Trend Morrow oil production. Although the productive area of these two fields is predominantly outside of the area of the 1987 reconnaissance soil gas survey, there are soil gas anomalies that border the current production at these two fields and suggest the possibility of even further extension of this newly established production in the Morrow oil trend. This is an excellent example of an area where a later detailed soil gas survey could be conducted and combined with an earlier reconnaissance survey. A detailed soil gas survey in this area would greatly enhance the explotation/development efforts in this new Morrow oil trend.

Other important factors for consideration in dealing with soil gas surveys can also be shown and discussed from this data: (1) Calibration with established production, (2) Width of productive fairway in relation to sample density of the reconnaissance survey, and (3) Delineation of Morrow gas fairways.

AREA OFDETAIL MAP

0 mi 10

0 km 10

"STA

TELIN

E TR

EN

D"

Cheyenne County

Greeley County

Lookout

ianna

Jace

Moore-Johnson

McClave

Harker Ranch

Arapahoe

Frontera

Stockholm SW

Second Wind

Mount Sunflower

Arrowhead

Sidney

FIELD

Wallace Co.Greeley Co.

MT. SUNFLOWER

SIDNEY

FIELD

4 3 2 1 6 5

9 10 11 12 7 8

16 15 14 13 18 17

21 22 23 24 19 20

28 27 26 25 30 29

22 23 24 19 20 21

27 26 25 30 29 28

34 35 36 31 32 33

16S

41W

16S

42W

15S

41W

15S

42W

1 Mile

Figure 5

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Page 8How to Design an Exploration Surface Soil Gas Geochemical Survey

17

8

5

31

30

19

33323136

28293025

21201924

181314

71211

612

16S

41W

15S

41W

15S

43W

16S

43W

16S

42W

15S

42W

15S

42W

K385 K386

K387 K388 K389 K390 K391 K391A K392 K393 K394 K395

K412K413 K414

K415 K416 K417 K418 K419

36 K437 K438

K439 K440 K441 K442 K443 K444 K445 K446 K44

K464K465 K466 K467 K468 K469 K470 K471

K489 K490

K491 K492 K493 K494 K495 K496 K497 K498 K49

K517K518

K519 K520 K521 K522 K523 K524

K541 K542

K543 K544 K545 K546 K547 K548 K549 K550 K55

K571 K572K573

K574 K574A K575 K576 K577 K578 K580

3K594

K595 K596 K597 K598 K599 K600 K601 K602 K603

K623 K624

K625 K626 K627 K628 K629 K630 K631

5 K646

K647 K648 K649 K650 K651 K652 K653 K654 K655

K676 K677

K678 K679 K680

K681

K682 K683 K684

< 1515 - 2020 - 2525 - 30

(ppb)CONCENTRATIONS

ETHANE

> 30

Scale - Feet

1000 20000

17

8

5

31

30

19

33323136

28293025

21201924

181314

71211

612

16S

41W

15S

41W

15S

43W

16S

43W

16S

42W

15S

42W

15S

42W

Scale - Feet

1000 20000

1982

LEGENDYear Well Completed

1983198419851986

1987-1988(Modified after Schumard, 1991)

Calibration With Established Production

Figure 6 illustrates ethane soil gas concentrations over SW Stockholm Field and shows why caution should be used when selecting productive areas for calibration purposes. The production at SW Stockholm Field, as shown in Figure 6A, was first established in the southern portion of the field where wells were completed between 1982 and 1984 (Shumard, 1991). The area had reached the end of primary recovery and was in initial stages of waterflood when the soil gas survey was conducted in 1987. This means that the original reservoir pressures had been greatly reduced (from 1038 psi to 300 psi) in the southern area and the light gases that did reach the surface in this area were very low magnitude. In contrast, the wells in the central part of the field were completed during 1985 and 1986. Compare the soil gas magnitudes (Figure 6B) in the southern portion of the field with those in the central part of SW Stockholm Field where the wells had been producing a much shorter period of time. The low ethane magnitudes observed over the north part of the field are discussed in the following section.

Figure 6

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Page 9How to Design an Exploration Surface Soil Gas Geochemical Survey

A. Contour Map of Ethane Concentrations (ppb) B. SW Stockholm Field Width of Incised Valley

17

8

5

31

30

19

33323136

28293025

21201924

181314

71211

612

16S

41W

15S

41W

15S

43W

16S

43W

16S

42W

15S

42W

15S

42W

K385 K386

K387 K388 K389 K390 K391 K391A K392 K393 K394 K39

K412K413 K414

K415 K416 K417 K418 K419

K437 K438

K439 K440 K441 K442 K443 K444 K445 K446 K44

K464K465 K466 K467 K468 K469 K470 K471

K489 K490

K491 K492 K493 K494 K495 K496 K497 K498 K49

K517K518

K519 K520 K521 K522 K523 K524

K541 K542

K543 K544 K545 K546 K547 K548 K549 K550 K55

K571 K572K573

K574 K574A K575 K576 K577 K578 K580

K594

K595 K596 K597 K598 K599 K600 K601 K602 K603

K623 K624

K625 K626 K627 K628 K629 K630K631

K646

K647 K648 K649 K650 K651 K652 K653 K654 K655

K676 K677

K678 K679 K680

K681

K682 K683 K684

< 1515 - 2020 - 2525 - 30

(ppb)CONCENTRATIONS

ETHANE

> 30

Scale - Feet

1000 20000

2000 FTWIDE

WIDE6500 FT

1760 FT

2460 FT

17

8

5

31

30

19

33323136

28293025

21201924

181314

71211

612

16S

41W

15S

41W

15S

43W

16S

43W

16S

42W

15S

42W

15S

42W

Scale - Feet

1000 20000

LocationSiteSoil Gas

LEGEND

Width of Productive Fairway in Relation to Sample Density of a Reconnaissance Survey

As discussed in the previous section, low soil gas magnitudes were observed over the north part of SW Stockholm Field, however, this was not due to depleted reservoir pressures. The wells in this part of the field were completed in 1987 and 1988 (Figure 6A) which was during and after the time the soil gas survey was conducted. Figure 7 illustrates one way that a reconnaissance survey, with widely spaced soil gas sites, can fail to detect gas microseepage from a subsurface petroleum accumulation. The width of the incised Morrow valley at the extreme north end of SW Stockholm Field is only about 2000 feet (0.38 miles) wide compared to 6500 feet (1.23 miles) wide in the central part of the field. The spacing between the soil gas sites in this area is 1760 feet in an east-west direction and 2640 feet apart in north-south directions. Additionally, the orientation of the north end of the field is northwest-southeast which caused the field to transect the survey grid at the point of widest spacing between sample sites.

Because of both the width and the orientation of the north end of SW Stockholm Field, compared to the sample spacing of the reconnaissance soil gas survey, there were only low to moderate soil gas concentrations detected at sample sites over the field in the north area. These same circumstances also occurred at Second Wind Field to the southwest of SW Stockholm Field.

Figure 7

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Page 10How to Design an Exploration Surface Soil Gas Geochemical Survey

A. Location Map

B. Frontera Oil Field (1987) and W. Stockholm Gas Field (1979)

C. Ethane Concentrations (ppb) Contour Map

DISCOVERY WELLSMORROW OILMORROW GAS

19871979

ULTIMATE RESERVES

W. STOCKHOLM FIELDFRONTERA FIELD 6,200,000 BO

283 MMCFG

FUNK

ARAPAHOE

FRONTERA

STOCKHOLM WEST

STOCKHOLM

STATELINE TREND

16 157 14 13

12119 10

15 234

1718

87

6 5

34 3532 33 36

2825

29 27 26

2024232221

14 131517 16

121198 10

4513 2

31

30

19

18

7

6

32 3533 3634

252629 2728

22 242320 21

1517 131416

1211108 9

4 3 25 1

31

30

19

18

7

6

3433323136

2728293025

2221201924

1516171813

1098712

34561

3433323136

2728293025

2221201924

1516171813

1098712

34561

17181314

871211

5612

16S

42W

16S

41W

15S

41W

14S

42W

14S

41W

15S

43W

14S

43W

14S

42W

16S

43W

16S

42W

15S

42W

15S

42W

CO

LO

RA

DO

KA

NS

AS

K4K495K494

K469K468K467K466K465K464K463K46261

KK443K442K441K440K439

K438K437K436K435K434K433

K417K416K415K414K413

K412K411K41009

K391AK391K390K389K388K387

K386K385K384K383K382K381

K364K363K362K361

K360K359K358K3576

K339K338K337K336K335

K334K333K332K331K330K329

K312K311K310K309K308K307K306K30504

K287K286K285K284K283K282K281K280K279K278

CO

LO

RA

DO

KA

NS

AS

25

24

13

12

30

19

18

7

293025

201924

171813

8712

15S

41W

15S

43W

15S

42W

15S

42W

CO

LO

RA

DO

KA

NS

AS

FRONTERAOIL FIELD

W. STOCKHOLMGAS FIELD

25

24

13

12

30

19

18

7

293025

201924

171813

8712

15S

41W

15S

43W

15S

42W

15S

42W

Figure 8

Delineation of Morrow Gas Fairways

About a decade before the discovery and development of the Morrow Stateline Trend, TXO had conducted an exploration effort which targeted Morrow gas on low-relief Morrow structures in the general vicinity of the Las Animas Arch. One of the subsequent TXO Morrow gas discoveries in 1979 was the W. Stockholm (Morrow) gas field shown in Figures 3A and 8A.

TXO completed the discovery well for the field in April 1979. The Morrow gas reservoir was encountered at 5042 feet with 16 feet of net pay. The four-well gas field was developed on 640-acre spacing (Figure 8B). It appears that four dry holes were also drilled to delineate the limits of the field. Cumulative production, since 1979, from the four wells in this field has only been 283 MMCFG. The last reported production was in 1998. This gas field, considering the marginal cumulative gas production over a 21-year period and the eight wells drilled to define the field, would be considered as a non-commercial venture by most oil company economic guidelines.

Figure 8C shows a contour map of the ethane soil gas magnitudes over the field area. The anomalous ethane microseeps very clearly defined the limits of the subsurface gas accumulation. Although this is not very significant production, it is interesting to note that the 1987 reconnaissance soil gas survey (designed for Morrow oil exploration) also clearly detected gas microseepage from this structural accumulation, even eight years after production had commenced. It is intriguing to postulate that if TXO had conducted this reconnaissance soil gas survey in 1979, not only would they have detected the W Stockholm gas field, but, also would have had an indication of Morrow oil potential (from the Stateline Trend soil gas anomalies) a full eight years before actual discovery and development of SW Stockholm Field.

This example illustrates two important points: (1) The spacing of the soil gas survey was considered a reconnaissance grid for targeting Morrow oil fairways, however, in a gas fairway with 640-acre gas units, this particular spacing would be considered a detail grid. (2) There is no direct relationship between the magnitude of a surface seep and the resultant volumetric hydrocarbon production or economics of a corresponding well or field. Compare the soil gas anomaly over W Stockholm Field to the soil gas anomaly over Fronterra Field one mile to the west. Both soil gas anomalies exhibit similar ethane magnitudes and areal extent (Figure 8C), however, the resultant hydrocarbon production from the two subsurface reservoirs is very different. W. Stockholm Field has a cumulative production of only 283 MMCFG and is a depleted field. The average per well gas recovery was only 71 MMCFG. Fronterra Field, on the other hand, has a cumulative production of 3.7 MMBO. To date, the average per well oil recovery is 107,000 BO. Secondary recovery efforts are still underway at Fronterra Field.

Critique of Soil Gas Survey

As early as 1987, the soil gas survey accurately defined the general areal extent of the productive Morrow incised valley fairway, as would be confirmed by development drilling three years later in 1990. It can also be discerned that, at the particular sample density, the soil gas data could not have been used to determine 80-acre drilling sites. Additionally, because of the selected sample density, the very narrow portions of the incised valley (north part SW Stockholm and Second Wing) were not readily discernable. Therefore, the selected sample density was at the minimum threshold required to provide useful exploration information. The soil gas survey also appears to have detected microseepage from the Morrow gas and Mississippian oil fields in the area.

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Page 11How to Design an Exploration Surface Soil Gas Geochemical Survey

Figure 9

FUNK

ARAPAHOE

FRONTERAWallace Co.

STOCKHOLM WEST

Greeley Co.

STOCKHOLMSOUTHWEST

MOORE-JOHNSON

MT. SUNF

SIDNEY

JACE

SURVEYSOUTH STATELINE

NORTHSTATELINE

SURVEY

Area of Moore-Johnson Field

501

502 503

504

505

506 507

508 509

510 511

512

513514

515516

517 518

519 520

521522

523

524 525

526527

528 529

530531

532533

534

535 536 537 538

539540541542

543544

545 546

547548

549 550551

552553

554

555

556

557

558

559560

561

562

563

564

565 566

567568

569 570

571572573

574

575576577578

579 580 581

582583584585

586 587 588 589

590591

592

593

594595596

597

598 599

600

601 602

603604

605 606

607 608

609610

611

612613

614615

616617

618619

620 621

622

623 624 625 626

627628629630

631 633 634

635636637638

639640

641 642

643

644645

646

647

648

649

650

651

652

653

654655

656

657

658

659

660

661

662 663

664665666667

668 669 670 671

672673674675676677

678

679

680681

682683684

685 686 687

688 689

690691

692 693

694 695

696

697 698

699 700 701

702703704

705 706

707708

709

710

711

712

713 714 715

716 717

718 719 720

721722723

724

725

726 727

728729

730 731

732

733

734

001 002

003

004

005

006007

008009

010

011012

013

014015

016 017

018

019

020021

022023

024025

026 027

028

029

030 031

032 033

034 035

036037

038

039 040

041 042

043 044

045

046

047048

049050

051052

053

054 055 056 057

058059

060061

062 063

064

065

066

067068

069 070

071

072

073074

075

076

077078

079080

081082

083

084

085 086087088089090091

092 093 094 095 096 097

098

099 100

101102

103104

105

106 107 108

109110

111

112

112A

113

113A

114

114A

115116117

118

119 120

121122123

124 125

126

127

128

129 130

131 132

133

134

135

136137

138 139

140

141

142143

144 145

146

147

148

149

150

151

152

153154

155156

157

158

159

160

161162

163

164165166167

168

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170171172

173

174 175

176177178179

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182 183

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186 187

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244 245

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252253

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266 267

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270271

272

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274 275

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280 281

282 283

284

285 286

287288

289

290291

292

293 294

295296 297

298

299

300

301 302

303304

305 306

307 308

309310

311 312

313

314315

316317

318319

320 321

322323324

325 326

327

328

329330

331332

333 334

335

336

337 338

339

340

341

342343344

345 346347 348 349

350351352

353 354 355

356357358

359 360 361

362363364

365

366

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368 369

370

371 372

374

375 376

377

378379

380 381

382

383

384

385

386

387

388

389

390

391

392 393

394

395396397

398

399400

401 402 403

404405

406

407

408

409

410

411412413 413A

414 414A 415 416

417418419

420 421 422

423

424425426

427 428

429

430

431

432 433

434

435 436

437438

439 440

001002

003004

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123 124

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140141

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150 151 152

153154155

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162163

164165

166 167

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176177 178

179180

181 182

183184185186

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188

189190

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201202

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206207

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231232233

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241242243

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254

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260 261

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269270

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272273

274

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276

277

278

279

280

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284

285

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292293

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298299

300

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302 303

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313 314 315

316317

318 319

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321 322 323

SJ01

SJ02SJ03

SJ04SJ05

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SJ08

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SJ12SJ13SJ14

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30 29 28

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987

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R 4

2 W

R 4

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T 18 S

T 17 S

T 17 S

T 16 S

R 4

2 W

R 4

3 W

R 4

1 W

R 4

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-101:57:3038:37:

-101:57:3038:27:

GR

EE

LEY

CO

KIO

WA

CO

KA

NS

AS

CO

LOR

AD

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KIOWA CO

GR

EE

LEY

CO

CHEYENNE CO

DETAILED SOIL GAS SURVEYS OVER THE SOUTH STATELINE OIL TREND

Detailed soil gas surveys typically are conducted over a large area with a much denser spacing between soil gas sample sites than in a reconnaissance survey. The soil gas samples in a detailed survey may either be collected as infill in an area with previous sampling collected on a reconnaissance grid spacing or they may be collected in a new area with no previous sampling. Soil gas data collected years apart in the same area have been documented to be fully compatible with one another (Jones et al., 1985, Dickinson and Matthews, 1993). The example discussed in this case was conducted over the southern portion of the Morrow Stateline Trend in 1992.

Surface Soil Gas Geochemistry

A Denver-based independent oil company decided to explore for Morrow oil in the Stateline Trend on a regional level and attempt to increase the drilling success rate by using surface soil gas geochemistry. The company first purchased a reconnaissance soil gas data set in the north part of the trend and later conducted a new detailed soil gas survey in the south area as shown in Figure 9A. At the time of the new survey (April 1992), the development drilling had been completed at Second Wind field and there were only three development wells at Moore-Johnson field in the south. The two combined soil gas surveys provided soil gas microseep data consisting of 1817 samples covering a total area in the Morrow Trend of 203 square miles.

The detailed soil gas survey in the south part of the trend, consisting of 1034 sites, was conducted over a very large area (53 square miles) from just southeast of Second Wind field in Cheyenne County, Colorado to two miles south and five miles southeast of Moore-Johnson field in Greeley County, Kansas (Figures 9A and 9B).

Realizing the limitations of the northern reconnaissance survey spacing (11 sites per section), this company increased the basic sample density in the southern survey to 16 sites per section (40-acre spacing). In addition as shown in Figure 9B, the company already had several prospects in the survey area and elected to increase the sample density in these areas over the standard spacing of 16 sites per section.The high-density soil gas survey in the vicinity of Moore-Johnson field (Figure 9B) consisted of 106 sample sites over a four square mile area (24-acre spacing). It is this area which will be the focus of this paper.

The purpose of the regional detailed soil gas survey was threefold: (1) calibration of the soil gas survey to the production at Moore-Johnson field, (2) to aid in further exploitation and development drilling at Moore-Johnson field, and (3) to determine other areas along trend that exhibited similar anomalous soil gas microseepage and therefore would have Morrow exploration potential.

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Page 12How to Design an Exploration Surface Soil Gas Geochemical Survey

JACE FIELD

01020

30

2010

0

30

3013

12

1

18 17

87

56

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03/90BREWER 1

BREWER 205/90

LAWSON #102/90

MO-JO 209/90

LINN 110/90

SELL 103/90

AMOCO

AMOCO

AMOCO

AMOCOAMOCO

AMOCO

AMOCO

AMOCO

AMOCOAMOCO

17

8

5

1314

1211

12

18S

43W

18S

41W

CO

LO

RA

DO

KA

NS

AS

Scale - Feet

1000 20000

10km0

10mi0

"STA

TELIN

E TR

EN

D"

Sherman County

Greeley County

Kiowa County

Wallace County

Cheyenne County

Cheyenne County

nty

Co

lora

do

Kan

sas

Sidney

Arrowhead

Mount Sunflower

Second Wind

Stockholm SW

Frontera

Arapahoe

Harker Ranch

Castle Peak

Sorrento Field

Mt. Pearl

Speaker

McClave

Moore-Johnson

Jace

Salt Lake/Haswell

Sianna

Bledsoe Ranch

Lookout

Smokey Hill

Wildfire

Discovery of Moore-Johnson Field and Early Development Drilling in 1990

Moore-Johnson field in Greeley Co., Kansas was discovered by Amoco in October 1989 (Adams, 1990). At the time of the discovery, the Stateline Trend had been developed to the extent shown in (Figure 10A). The Amoco Moore-Johnson #1 was the discovery well for the field and was completed for 522 BOPD (Figures 10B and 10C). The well was completed in the sands of the V-7 valley fill sequence of the Morrow Formation. This equivalent interval in the Morrow Formation was initially named the Stockholm Sand during development of SW Stockholm field to the north. The sequence stratigraphy of the Morrow in relation to reservoir geology in the vicinity of Moore-Johnson field has been more recently discussed by Bowen and Weimer (1997, 2003).

The Amoco combined geological and seismic conceptual model was that of a northwest-southeast oriented Morrow sand body (Figure 10B). The location for the discovery well was determined by identification of the basal upper Morrow fluvial incised valley on 2-D seismic lines supplemented by data from available well control (Adams, 1990). By May 1990, Amoco had extended the field to include three wells (Figure 10C). The Brewer #1 and Brewer #2 flowed at rates of 670 and 350 BOPD, respectively. In the first four months, the Moore-Johnson #1 produced 30,000 BO.

This was a very significant Morrow discovery in that it extended Morrow production for a distance of 10 miles to the south from Second Wind field of the Stateline Trend. Amoco attempts at further development drilling was another story, however.

As shown in Figure 10C, attempts to extend the field to the south by Amoco in 1990 resulted in three dry holes (Moore-Johnson #2, Linn #1, Sell #1). Two successful Morrow development wells were completed by Amoco to the northwest of the discovery well in March and May of 1990 (Brewer #1, Brewer #2). Attempts by Amoco to extend the field farther to the northwest resulted in three more dry holes (Keller #1, Keller #2, Brewer #3). Amoco also drilled another dry hole to the northeast in February 1990 with the Lawson #1.

The overall success rate, at the end of 1990, for development drilling in the Moore-Johnson field area was a disappointing 33%. This was considerably below previous industry standards in the Morrow Trend. Success rates for development of Frontera, SW Stockholm and Second Wind fields of the Stateline Trend were 73%, 68%, and 56%, respectively. There was no further drilling in the field area during all of 1991.

As will be shown later in the paper, had Amoco used soil gas geochemistry, in conjunction to seismic and subsurface geology, the six dry holes could have been avoided.

Figure 10

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Page 13How to Design an Exploration Surface Soil Gas Geochemical Survey

> 125

ETHANECONCENTRATIONS

(ppb)

110 - 12590 - 11075 - 9065 - 75

< 65

AXEM/MURFIN LEASES

001 002

003

004

005

036037038

039

042

043

044

045

046

047

048

049 050051052

053

063

066

067068069070

071

072

073 074

075

076

077 078 079

080

081 082

083

084

085

087

088 089

090091

092

093

094

095

115

116117

118

119

121

124

127

128

129

130

040A 041A

230

037A

049A052A

090A

115A

276

277

278

279

280

281282283

284

285

286

291

292293

294

295

296

297

300

301

302 303

304

309

310

311

312

313 314

316317

318 319

320

321

88 113

124

197

217

11062

42

40

103

58

113

839677

78

40

77

483065

95

52 47

34

215

49 61 42

97

59 36

88

51

109

42

65 71

4647

36

35

22

143

8343

101

71

58

41

53

75

76

73

94

39 42 76 124

69

203115

148

20

161

87

50

75

23

1356341

37

121

34

75

5945

197

26

84

47

80

99

76 70

106

48

54

26

29

36 65

4775

200 76

19

83

35

65

44

123

62

83

108

38

30

57

061

17

8

5

1314

1211

12

18S

43W

18S

41W

CO

LO

RA

DO

KA

NS

AS

Scale - Feet

1000 20000

57

061

27

115

73

76

22

35

36

51

88

59

97

426149

215

34

4752

95

65 30 48

77

40

78

96 83

113 103113

052A

130

129

095

094

093

092

084

083

081

080

079078077

076

075

074073

072

069 068 067

066

063

053

051 049

048 046002

AMOCOAMOCO

AMOCO

AMOCO

AMOCO

AMOCOAMOCO

AMOCO

AMOCO

SELL 1LINN 1

MO-JO 2

BREWER 2

BREWER 1

KELLER #2

KELLER #1

MO-JO 1

BREWER #3

17

8

5

1314

1211

12

18S

43W

18S

41W

CO

LO

RA

DO

KA

NS

AS

Scale - Feet

1000 20000

Soil Gas Calibration Survey and Detailed Survey in Moore-JohnsonField Area

A soil gas calibration survey was first conducted over the three-well field and in the area of the 6 dry holes in April 1992 (Figure 11A). Because the field was being developed in 40-acre units, a sample density of 16 sites per section was selected. An ethane magnitude contour map of the soil gas data in the calibration area is shown in Figure 11A. As shown on the ethane magnitude contour map, low ethane magnitudes were observed in areas where the dry holes were drilled and the anomalous ethane values corresponded to the area of the three Morrow oil wells. There was no problem with reservoir pressure depletion at the time of the survey because of the limited production at that time.

The soil gas contour map for the calibration survey also indicated other areas of anomalous microseepage to the east and northeast of the three productive wells. The more detailed soil gas survey was extended into those areas to aid in further development drilling at Moore-Johnson field.

The initial sample grid of 16 sample sites per section was increased with infill soil gas sites as shown in Figure 11B. A total of 106 soil gas sites were sampled within the map area. The infill sample data significantly increased the detail of the microseepage anomaly pattern from that of the original calibration survey, as evidenced by comparing the two contour maps. Ethane magnitudes ranged from 22 ppb to 205 ppb within this area. The ethane magnitude contour map indicated anomalous microseepage over the Axem Resources and Murfin Drilling (Axem/Murfin) lease block in sections 2, 11, and 14.

The surface soil gas geochemical data was next integrated with the combined subsurface geology and seismic interpretations.

Figure 11

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Page 14How to Design an Exploration Surface Soil Gas Geochemical Survey

Limits ofIncised Valley

Limits ofMorrow Sands

ProductiveMorrow B Sand

ProductiveMorrow A Sand

Thin, Oil ShowMorrow B Sand

LeasesAxem/Murfin

LEGEND

> 125

ETHANECONCENTRATIONS

(ppb)

110 - 12590 - 11075 - 9065 - 75

< 65

27

57

30

38

108

83

62

123

44

65

35

83

19

76200

75 47

6536

29

26

54

48

106

7076

99

80

47

84

26

197

45 59

75

34

121

37

41 63 135

23

75

50

87

161

20

148

115 203

69

124764239

94

73

76

75

53

41

58

71

101

43 83

143

22

35

36

47 46

7165

42

109

51

88

3659

97

426149

215

34

4752

95

65 30 48

77

40

78

77 96 83

113

58

103

40

42

62 110

217

197

124

11388

061

321

320

319318

317 316

314313

312

311

310

309

304

303302

301

300

297

296

295

294

293 292

291

286

285

284

283 282 281

280

279

278

277

276

115A

090A

052A 049A

037A

230

041A040A

130

129

128

127

124

121

119

118

117 116

115

095

094

093

092

091 090

089088

087

085

084

083

082081

080

079078077

076

075

074073

072

071

070069 068 067

066

063

053

052 051 050049

048

047

046

045

044

043

042

039

038 037036

005

004

003

002001

A

A’

17

8

5

1314

1211

12

18S

43W

18S

41W

CO

LO

RA

DO

KA

NS

AS

Scale - Feet

1000 20000

AMOCO

AMOCO

AMOCO

AMOCO

AMOCO

AMOCOAMOCO

AMOCO

AMOCO

AMOCO

A’

A

TD 5300SELL 1

TD 5300LINN 1

TD 5300MO-JO 2

TD 5350LAWSON #1

TD 5250BREWER 2

BREWER 1TD 5330

KELLER #2TD 5290

TD 5360KELLER #1

TD 5300

TD 5290MO-JO 1Discovery Well

MO

RR

OW

SE

CT

ION

AX

IS O

F T

HIC

K

BREWER #3

Coyote #1Axem/MurfinProposed Location

REGIONAL DIP

17

8

5

1314

1211

12

18S

43W

18S

41W

CO

LO

RA

DO

KA

NS

AS

Scale - Feet

1000 20000

DATUM

-1500

-1400

-1300

-1200

-1100

-1000

AMOCOBREWER #1

AMOCOLAWSON #1

A A’

ATOKA

TOP MORROW

MORROW LM

MISSISSIPPIAN

TD 5350TD 5305

ANOMALIESSOIL GAS

Figure 12

Integration of Subsurface Geology, Seismic, and Surface Soil Gas Geochemistry

During the first half of 1992, Axem/Murfin integrated the combined subsurface geology and seismic interpretation with the surface soil gas data. The conceptual model for the Morrow trend, derived from the all the development of the northern Stateline Trend fields, was that the Morrow section (base of Atoka to top Morrow Limestone) was observed to thicken in the areas of maximum Morrow sand development and productive wells. In contrast, the Morrow section was much thinner, with non-deposition of Morrow sands, on the east and west flanks of the Morrow fields. This was the Axem/Murfin conceptual model at the Moore-Johnson area interpreted from the available well control and seismic data. The well control available at that time is shown in Figure 12A.

Subsurface data from the 10 Amoco wells in the area and seismic interpretation provided the Axem/Murfin concept of the Morrow incised valley boundaries, regional dip, and general axis of the depocenter of the Morrow valley as indicated on Figure 12A. Amoco had established production from 2 different Morrow sands (named “A sand” and “B sand”) in their three wells. The Morrow completion zones in the three wells are as indicated on Figure 12A. Additionally, the Morrow “B sand” was encountered in three other Amoco wells with oil shows, however, the porosity/permeability and thickness of the sand precluded completion attempts in those wells. The Morrow sands were not present in the other four Amoco wells. The expected areal distribution of Morrow sands was interpreted as shown on the map. Axem/Murfin had interpreted the Morrow sands to be oriented north-south in the area as opposed to the previous Amoco concept of a northwest-southeast alignment. In the new interpretation, the Amoco productive wells were interpreted to be at the west, updip limits of a Morrow stratigraphic trap (Figures 12A and 12C).

The interpretation of the soil gas survey data is shown on Figure 12B. The ethane magnitude contour map indicated that the maximum gas microseeps were observed in the central portion of the expected Morrow incised valley and within the expected Morrow sand fairway (Figures 12A and 12B). The geochemical, geological, and geophysical data were all compatible with the conceptual model for a Morrow stratigraphic trap.

The Axem/Murfin acreage position was excellent. A location was staked for the Axem/Murfin Coyote #1 in section 2. The well was spudded July, 25, 1992

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Page 15How to Design an Exploration Surface Soil Gas Geochemical Survey

> 125

ETHANECONCENTRATIONS

(ppb)

110 - 12590 - 11075 - 9065 - 75

< 65

LEGEND

OIL/GASWELL

DRYHOLE

1993-94 CompletionsPrevious Wells

DRYHOLE

WELLOIL

1989 - 1990199219931994

061

57

30

38

108

83

62

123

44

65

35

83

19

76200

75 47

6536

29

26

54

48

106

7076

99

80

47

84

26

197

45 59

75

34

121

37

41 63 135

23

75

50

87

161

20

148

115 203

69

124764239

94

73

76

75

53

41

58

71

101

43 83

143

22

35

36

47 46

7165

42

109

51

88

3659

97

426149

215

34

4752

95

65 30 48

77

40

78

77 96 83

113

58

103

40

42

62 110

217

197

124

11388

321

320

319318

317 316

314313

312

311

310

309

304

303302

301

300

297

296

295

294

293 292

291

286

285

284

283 282 281

280

279

278

277

276

115A

090A

052A 049A

037A

230

041A040A

130

129

128

127

124

121

119

118

117 116

115

095

094

093

092

091 090

089088

087

085

084

083

082081

080

079078077

076

075

074073

072

071

070069 068 067

066

063

053

052 051 050049

048

047

046

045

044

043

042

039

038 037036

005

004

003

002001

17

8

5

1314

1211

12

18S

43W

18S

41W

CO

LO

RA

DO

KA

NS

AS

Scale - Feet

1000 20000

MO-JO 4AXEM

AXEMMO-JO 3

AXEM

WENDLEBURG 3-11

WENDLEBURG 2-11

BREWER 2

COYOTE 2AXEM

WITT B-1

WITT A-2 BOBCAT 1-2AXEM

BOBCAT 2-2AXEM

BOBCAT 2-2AXEM

WITT A-1

LANG 34-35

SELL #13-3

HUDDLESTON 34-11

ABEL #1DUNCAN ENER.

WILLIAM #1YATES

HUDDLESTON 33-11

WENDLEBURG 1-11

BREWER 1

MILLER #1HGB OIL

COYOTE 1AXEM

BREWER 24-2

BLACKBIRD #1AXEM

BREWER 3

MO-JO 1

KELLER #1

KELLER #2

BREWER 1

BREWER 2

LAWSON #1

MO-JO 2

LINN 1 SELL 1

AMOCO

17

8

5

1314

1211

12

18S

43W

18S

41W

CO

LO

RA

DO

KA

NS

AS

Scale - Feet

1000 20000

1992 DRILLING - MOORE-JOHNSON FIELD

Eleven wells were drilled in 1992 by 5 oil companies (Figure 13A). Only Axem/Murfin used the integrated approach of soil gas geochemistry with geology and seismic to select well locations. The locations of the wells drilled in 1992 are shown on Figure 13A. An ethane magnitude contour map (Figure 13B) illustrates the geochemical basis of Axem/Murfin decisions in selecting well sites. The following is the order in which the 1992 wells were drilled:

1 In April and May 1992, MW Pet. drilled two Morrow dry holes with the Brewer #24-2 and Sell #13-31 wells. Both wells were 4000-foot step-outs. Both well locations are in areas of background soil gas concentrations. No further wells were drilled by this company in this area

2 In August 1992, Axem/Murfin drilled their first well and completed the Coyote # 1 as a Morrow oil well (Figures 13A and 13B). This was a very significant well in that it was a 4700-foot step-out extension for Moore-Johnson field. The well location was supported by a strong soil gas anomaly. The well confirmed the conceptual model established by integrating geochemistry with geology and geophysics.

3 Duncan Energy completed two direct offsets in October and November to the Amoco Brewer #1 and #2 producing Morrow wells. These two wells were only 1500-foot offset locations.

4 In November 1992, Axem/Murfin completed two Morrow wells with the Wendleburg #1-11 and Blackbird #1 wells. The Wendleburg #1-11 location was supported by a strong soil gas anomaly.

5 In December 1992, HGB Oil completed the Brewer #1 as a Morrow oil well. This location had been proven by the preceding surrounding wells to the west, east, and south.

6 HGB Oil, Yates, and Duncan Energy each drilled a Morrow dry hole in Colorado attempting to extend field production updip and to the west. There were now five dry holes in Colorado to the west of the field. All five well locations are in areas of low magnitude soil gas data.

By the end of 1992, Moore-Johnson field had produced 512,714 BO.

Figure 13

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Page 16How to Design an Exploration Surface Soil Gas Geochemical Survey

1993 and 1994 DRILLING - MOORE-JOHNSON FIELD

The locations of all the wells previously drilled through 1992 are shown on Figure 13A. An ethane magnitude contour map (Figure 7B) illustrates the basis of Axem/Murfin decisions in selecting well sites. The following are the 1993 wells that were drilled:

1 Marathon completed the Wendleburg #2-11 as a Morrow oil well in February 1993. This well was a direct offset to the Axem/Murfin Wendleburg #1-11 drilled three months previously in November 1992. This was the only lease Marathon held in the field area.

2 HGB Oil drilled three Morrow oil completions from March through July 1993 (Witt #A2, Witt #B1, Brewer #2). The wells were on the updip, west side of the field. The Witt #B1 only produced 1745 BO and is considered to be a dry hole.

3 Axem/Murfin drilled three Morrow oil wells in the north area with the Bobcat #1-2, Coyote #2, and Wendleburg #3-11. The Bobcat and Wendleburg well locations were in areas of anomalous microseeps.

4 Axem/Murfin drilled two Morrow oil wells in the south area with the Mooore-Johnson #3 and Moore-Johnson #4 wells. The Moore-Johnson #3 well was completed in August 1993 and was located in an area of anomalous ethane concentrations.

By the end of 1993, Moore-Johnson field contained 17 Morrow oil wells and extended for 11,000 feet in a north-south direction and 3000 feet in width. Axem/Murfin had completed seven successful Morrow wells without a dry hole. At the end of 1993, cumulative production at the field was 780,549 BO.

In 1994, four wells were drilled by three oil companies in the north area of the field. The following are the 1994 wells that were drilled:

5 HGB Oil drilled the Witt #A1 as a Morrow oil well in January 1994. The well location was on trend and 1500 feet from their Witt #A2 completion 6 months earlier.

6 Axem/Murfin drilled their first dry hole in the Bobcat #2-2 in January 1994. A 700-foot offset to the southwest, however, resulted in a Morrow oil completion. The Bobcat lease, to date, has produced a total cumulative of 170,646 BO from two wells.

7 Duncan Energy completed a marginal Morrow well with the Lang #34-35 in March 1994. After only producing 477 BO, the well was converted to an injection well.

Moore-Johnson field was fully defined by 34 wells. The major extension of the field only took 24 months. This is one of the shortest development periods for a comparative size field in the whole Morrow trend.

By the end of 1994, the cumulative production from the 19 Morrow wells in Moore-Johnson field was 980,152 BO.

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Page 17How to Design an Exploration Surface Soil Gas Geochemical Survey

V7b

V7c

V7d

Limits and Dimensions of Morrow V7 SandsAreal Extent Completion Zones

Morrow Well

V7c

V7b

V7d

Thickness

0 - 30 ft.

0 - 18 ft.

0 - 24 ft.

Width

1800 - 2700 ft.

1300 - 2300 ft.

2300 - 3200 ft.

-1500

-1400

-1300

-1200

-1100

DATUM-1000

FLOODING SURFACE

V3 INCISED VALLEY

MORROW SH V7 INCISED VALLEY

ST. LOUIS LM

2/90TD 5350

11/92TD 5205

12/93TD 5294

11/92TD 5270

10/92TD 5300

3/90TD 5350

ST. GENEVIEVE LM

A’

LAWSON #1AMOCO

KB 3897

MURFIN DRLG.BLACKBIRD #1-1

SEC. 11KB 3907

AXEM RES.WENDLEBURG #3-11

SEC. 11KB 3918

MURFIN DRLG.WENDLEBURG #1-11

SEC. 11KB 3917

HUDDLESTON #33-11DUNCAN ENER.

SEC. 11KB 3898SEC. 11

V7dV7b

V7c

MISSISSIPPIAN

MORROW LM

V1 INCISED VALLEY

ATOKA FM

A

KB 3902 (EST)SEC. 1

BREWER #1AMOCO

Unnamed Rocks ofAtokah Age

LimestoneThirteen Fingers

?

Pen

nsy

lvan

ian Ato

kan

Mo

rro

wan

Mo

rro

w F

m.

Upper

Lower

Ch

este

rian

ChesterGroup

Ste. Genevieve Fm.

St. Louis Fm.

Spergen Fm.

Warsaw Fm.Mer

amec

ian

Osa

gea

nK

ind

.

Mis

siss

ipp

ian

ofUnnamed Rocks

OsageanAge

Kinderhookian AgeUnnamed Rocks of

(Bowen & Weimer, 2003)Nomenclature

Morrow

MorrowLimestone

V11

V9

V7

V3

V1V7dV7cV7bV7a

LINN 1

AMOCO

SELL 1

LAWSON #1

BLACKBIRD #1

COYOTE 1

WENDLEBURG 1-11

HUDDLESTON 33-11

HUDDLESTON 34-11

SELL #13-3

LANG 34-35

BOBCAT 2-2

BOBCAT 2-2

BOBCAT 1-2

COYOTE 2

WENDLEBURG 2-11

WENDLEBURG 3-11

MO-JO 3

MO-JO 4

BREWER 2

BREWER 1

KELLER #2

KELLER #1

BREWER 3

MILLER #1

WILLIAM #1

ABEL #1

WITT A-2

WITT B-1

LINN 1

MO-JO 2

MO-JO 1

BREWER 24-2

BREWER 1

WITT A-1

BREWER 2

A

A’

LIMITS OF V7INCISED

VALLEY-FILL

17

8

5

1314

1211

12

18S

43W

18S

41W

CO

LO

RA

DO

KA

NS

AS

Scale - Feet

1000 20000

Subsurface Geology and Reservoir Performance

Moore-Johnson field (Figures 14A, 14B, and 14C) has been discussed by Adams (1990) and more recently by Bowen and Weimer (1997, 2003). These last two papers document the Morrow sequence stratigraphic framework throughout the trend and relate it to the subsurface geology, reservoir geometry, and reservoir performance at Moore-Johnson field.

The reservoir sands at Moore-Johnson field were deposited as fluvial valley-fill deposits in a valley incised into the Morrow Limestone (Figure 14C). These Morrow sands have been correlated regionally to the Morrow V7 valley sequence (Figure 14B). The areal distribution of the three reservoir sands deposited within the incised valley is shown in Figure 14A. From oldest to youngest, the order of deposition was V7b, V7c, V7d valley fill-sequences.

Structural cross section A-A’ (Figure 14C) depicts the positions of the three valley-fill sequences with respect to depth. Regional dip is to the east-southeast. The various Morrow reservoirs were encountered at depths ranging from 5100 to 5150 feet. Initial reservoir pressure was 1040 psi. Other reservoir parameters are shown in Table 1.

The three reservoir sand bodies are predominantly lateral to each other and are rarely incised into one another as is the case in the northern fields. Generally, the three sand bodies are completely encased in estuarine shales (Figure 14C). Porosities range from 14% to 28 % with permeabilities from 22 to 9,990 md (Adams, 1990). The GOR was 107:1 (cu ft/bbl). Other field parameters are listed in Table 1.

Compared to the V7 valley fill reservoirs in northern fields, the reservoirs at Moore-Johnson are narrower in cross section (see legend, Figure 14A) and of smaller extent and more compartmentalized due to the dominant shale facies. Because of these conditions, oil columns are thinner and production values are somewhat lower, however, drainage efficiency is high (Bowen and Weimer, 2003). Recovery factors are variable due to, in some cases, problems with pressure maintenance.

Oil volumes produced to date from individual wells range from 32,000 BO to over 230,000 BO. The field-wide average, to date, for the 19 wells is 91,000 BO per well. These per well averages are better than the average values at Castle Peak, Harker Ranch, SW Stockholm, and Jace fields reported by Bowen and Weimer (2003).

Figure 14

Moore-Johnson Field Parameters(Revised after Adams, 1990)

Reservoir: Morrow V7Lithology: SandstoneType Trap: Stratigraphic/ structuralDiscovery: Oct. 1989Depth: 5100-5200 ft.Spacing: 40 ac.Field Size: 1290 ac.Avg. Net Pay: 16 ft.Porosity: 14 to 28%Permeability: 22 to 9,990 mdWater Sat.: 13 to 47%Pressure: 1040 psiReserv. Drive: Gas cap expansion/ solution gas driveGOR: 107:1 cu ft / bblCum. Prod: 1,729,000 BOUltimate Prod.: 2,000,000 BO

Table 1

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Page 18How to Design an Exploration Surface Soil Gas Geochemical Survey

Duncan Energy

HGB Oil

Axem Murfin

Marathon

Amoco

20031990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

1500000

1000000

500000

0

BO

YR

C. Annual Production

B. Annual ProductionSouthern Leases

A. Annual Production

2002

2002

2002

0

50000

BO

100000

150000

200000

250000

0

50000

19921990 1991 19941993 1995 199919971996YR

1998 2000 2001

19921990 1991 19941993 1995

Entire Field

199919971996YR

1998 2000 2001

BO

100000

150000

200000

250000

0

50000

BO

100000

150000

200000

250000

19921990 1991 19941993 1995 19991997YR

1996 1998 2000 2001

Northern Leases

2003

2003

D. Cumulative ProductionMoore-Johnson Field

2003

0.5

45.3

85.3

43.383.3

1.7 54.6

40.8

6.5 32.0 13.4

25.532.4

87.076.0

87.0 76.0

220229

220

SELL 1

LAWSON #1

BLACKBIRD #1

COYOTE 1

WENDLEBURG 1-11

HUDDLESTON 33-11

HUDDLESTON 34-11

SELL #13-3

LANG 34-35

BOBCAT 2-2

BOBCAT 2-2

BOBCAT 1-2

COYOTE 2

WENDLEBURG 2-11 WENDLEBURG 3-11

MO-JO 3

MO-JO 4

BREWER 2

BREWER 1

BREWER 3

ABEL #1

WITT A-2

WITT B-1

LINN 1

MO-JO 2

MO-JO 1

BREWER 24-2

BREWER 1

WITT A-1

BREWER 2

17

8

5

1314

1211

12

18S

43W

18S

41W

CO

LO

RA

DO

KA

NS

AS

CUM. BO x 1000LEGEND

> 200

80 - 90

70 - 80

50 - 60

40 - 50

30 - 40

20 - 30

10 - 20

< 10

Scale - Feet

1000 20000

Oil Production at Moore-Johnson Field

Production for Moore-Johnson field is reported by the Kansas Geological Survey (KGS). Cumulative production is reported by lease and not individual wells. To attempt to show variation in production in the individual wells, the lease production totals were divided by the appropriate number of wells in each lease. Figure 15A illustrates the variation in production among all the wells. Note the differences in cumulative production between the Witt “A” and Bobcat leases in the north part of the field.

Annual production for the northern leases (Witt, Bobcat, Coyote, Brewer, Wendleburg and Huddleston) is shown in Figure 15B. The peak in production from 1992 to 1995 reflects the addition of the new development wells. Annual production volumes for the Moore-Johnson lease are shown on Figure 15C. The peak in production from 1994 to 1998 reflects the addition of the Axem/Murfin Moore-Johnson #3 and #4 wells. Annual production volumes for the entire field are shown in Figure 15D. Total production for the field in 2002 was 45,000 BO. Since 1997, annual production volumes have been declining at a rate of about 15% per year.

The field was unitized in 1995 for pressure maintenance by gas and water re-injection. Effects of secondary recovery operations in the north leases can be seen, beginning in 1998, in Figure 15B and for the south lease in 1999 on Figure 15C.Cumulative production for the field is shown on Figure 15E. The year to date total production for the field is 1,729,000 BO. Average per well production for the 19 wells in the field is 91,000 BO. Average per well production for the eight Axem/Murfin wells is 93,750 BO.

The KGS reported seven wells still producing in 2003. Ultimate recoverable reserves for the field will be about 2,000,000 BO

Figure 15

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Page 19How to Design an Exploration Surface Soil Gas Geochemical Survey

B. Location Map, Regional Soil Gas Survey

B. Location Map, Regional Soil Gas Survey

Lane

Gray

Meade

KANSAS

Wallace Logan

Finney

Haskell

Scott

Seward

HU

GO

TON

Grant

Greeley

Stanton

Hamilton

BR

AD

SH

AW

Morton

Kearney

Stevens

Wichita

PA

NO

MA

BYERLY

GR

EE

NW

OO

D

Gove

BYERLY

UTHWEST

LEOTI GA

LEOTI GAS AREA

Wichita

BYERLY EAST

LEOTI GAS AREA

CARWO

Logan

SS129B

SS116B

SS103B

SS090B

SS077B

SS064B

SS051B

SS039B

SS028B

SS018B

B0652

B0643

B0634

B0625

B0615

B0605B0604

B0624

B0614

B0844B0843B0842B0841B0840

B0839B0838B0837B0836B0835

B0834B0833B0832B0831B0830

B0829

B0828

B0827B0826B0825

B0595B0594

B0585B0584

B0575B0574

B0564B0563

B0552B0551B0550

B0538B0537B0536

B0524B0523B0522

B0509B0508B0507B0506

B0492B0491B0490B0489B0488

B0473B0472B0471B0470B0469

B0454B0453B0452B0451B0450

B0660B0659B0658B0657B0656B0655B0654B0653

B0651B0650B0649B0648B0647B0646B0645B0644

B0642B0641B0640B0639B0638B0637B0636B0635

B0633B0632B0631B0630B0629B0628B0627B0626

B0623B0622B0621B0620B0619B0618B0617B0616

B0694

B0688

B0683

B0820B0819B0818B0817B0816B0815B0814B0813B0812B0811

B0806B0805B0804B0803B0802B0801B0800B0799B0798B0797

B0792B0791B0790B0789B0788B0787B0786B0785B0784B0783

B0778B0777B0776B0775B0774B0773B0772B0771B0770B0769

B0764B0763B0762B0761B0760B0759B0758

B0757

B0752B0751B0750B0749B0748B0747B0746

B0741B0740B0739B0738B0737B0736

B0731B0730B0729B0728B0727

B0722B0721B0720B0719

B0714B0713B0712B0711

B0706B0705B0704

B0699B0698

B0693B0692

B0687

B0613B0612B0611B0610B0609B0608B0607B0606

B0603B0602B0601B0600B0599B0598B0597B0596

B0593B0592B0591B0590B0589B0588B0587B0586

B0583B0582B0581B0580B0579B0578B0577B0576

B0573B0572B0571B0570B0569B0568B0567B0566B0565

B0562B0561B0560B0559B0558B0557B0556

B0555B0554B0553

B0548B0547B0546B0545B0544B0543B0542B0541B0540

B0539

B0534B0533B0532B0531B0530B0529B0527B0526B0525

B0519B0518B0517B0516B0515B0514B0513B0512B0511B0510

B0502B0501B0500B0499B0498B0497B0496B0495B0494B0493

B0483B0482B0481B0480B0479B0478B0477B0476B0475B0474

B0464B0463B0462B0461B0460B0459B0458B0457B0456B0455

SS161BSS160BSS159BSS158BSS157BSS156B

SS154BSS153BSS152BSS151BSS150BSS149B

SS141BSS140BSS139BSS138BSS137BSS136B

SS128BSS127BSS126BSS125BSS124BSS123B

SS115BSS114BSS113BSS112BSS111BSS110B

SS102BSS101BSS100BSS099BSS098BSS097B

SS089BSS088BSS087BSS086BSS085BSS084B

SS076BSS075BSS074BSS073BSS072BSS071B

SS063BSS062BSS061BSS060BSS059BSS058B

SS050BSS049BSS048BSS047BSS046B

SS038BSS037BSS036BSS035B

SS027BSS026BSS025B

SS017BSS016B

SS009BSS008B

SS001BSS001B

B0908

B0907B0906

B0905B0904B0903

B0902B0901B0900B0899

B0898B0897B0896B0895B0894

B0893B0892B0891B0890B0889

B0824B0823B0822B0821

B0810B0809B0808B0807

B0796B0795B0794B0793

B0782B0781B0780B0779

B0768B0767B0766B0765

B0756B0755B0754B0753

B0745B0744B0743B0742

B0735B0734B0733B0732

B0726B0725B0724B0723

B0718B0717B0716B0715

B0710B0709B0708B0707

B0703B0702B0701B0700

B0697B0696B0695

B0691B0690B0689

B0686B0685B0684

B0682B0681B0680

B0679B0678

B0549

B0535

B0521B0520

B0505

B0504B0503

B0487B0486B0485B0484

B0468B0467B0466B0465

B0301

B0300

B0855

B0392

B0381

B0370

B0359

B0358

SS185B

SS181B

SS177B

SS173B

SS169B

SS165B

SS209BSS208BSS207B

SS206BSS205BSS204B

SS203BSS202BSS201B

SS200BSS199BSS198B

SS197BSS196BSS195B

SS194BSS193BSS192B

SS191BSS190BSS189B

SS188BSS187BSS186B

SS184BSS183BSS182B

SS180BSS179BSS178B

SS176BSS175BSS174B

SS172BSS171BSS170B

SS168BSS167BSS166B

SS164BSS163BSS162B

SS155B

SS148BSS147BSS146BSS145BSS144BSS143BSS142B

SS135BSS134BSS133BSS132BSS131BSS130B

SS122BSS121BSS120BSS119BSS118BSS117B

SS109BSS108BSS107BSS106BSS105BSS104B

SS096BSS095BSS094BSS093BSS092BSS091B

SS083BSS082BSS081BSS080BSS079BSS078B

SS070BSS069BSS068BSS067BSS066BSS065B

SS057BSS056BSS055BSS054BSS053BSS052B

SS045BSS044BSS043BSS042BSS041BSS040B

SS034BSS033BSS032BSS031BSS030BSS029B

SS024BSS023BSS022BSS021BSS020BSS019B

SS015BSS014BSS013BSS012BSS011BSS010B

SS007BSS006BSS005BSS004B

SS003BSS002B

B1332B1331B1330B1329B1328

B1327B1326B1325B1324B1323

B1322B1321B1320B1319B1318

B0449B0448B0447B0446B0445B0444

B0443B0442B0441B0440B0439

B0438B0437B0436B0435B0434

B0433B0432B0431B0430B0429

B0322

B0428B0427B0426B0425B0424

B0423B0422B0421B0420B0419

B0418B0417B0416B0415

B0414

B0413B0412B0411B0410B0409

B0408B0407B0406B0405B0404

B0345B0344B0343B0342

B0341B0340B0339B0338

B0337B0336B0335B0334

B0333B0332B0331B0330

B0329B0328B0327B0326

B0325B0324B0323

B0321B0320B0319B0318

B0317B0316B0315B0314

B0313B0312B0311B0310

B0309B0308B0307B0306

B0305B0304B0303B0302

B0887B0886B0885B0884B0883B0882B0881B0880B0879B0878

B0876B0875B0874B0873B0872B0871B0870B0869B0868

B0867

B0865B0864B0863B0862B0861B0860B0859B0858B0857B0856

B0854B0853B0852B0851B0850B0849B0848

B0847B0846B0845

B0402B0401B0400B0399B0398B0397B0396B0395B0394B0393

B0391B0390

B0389B0388B0387B0386B0385B0384B0383B0382

B0380B0379B0378B0377B0376B0375B0374B0373B0372B0371

B0369B0368B0367B0366B0365B0364B0363

B0362B0361B0360

B0357B0356B0355B0354

B0353B0352B0351B0350B0349

B0348B0347

B0346

B0275

B0264

B0888

B0877

B0866

B0677B0676

B0675B0674

B0673

B0672

B0671B0670B0669B0668B0667

B0666B0665B0664B0663B0662

B0661

B0403

B0299B0298B0297B0296B0295B0294B0293

B0292B0291B0290B0289B0288B0287B0286B0285

B0284B0283B0282B0281B0280B0279B0278B0277B0276

B0274B0273B0272B0271B0270B0269B0268B0267B0266

B0263B0262B0261B0260B0259B0258B0257B0256B0255

B0252B0251B0250B0249B0248B0247B0246B0245B0244B0243

B0241B0240B0239B0238B0237B0237B0235B0234B0233B0232

B0231B0230B0229B0228B0227B0226B0225B0224B0223

B0222B0221B0220B0219B0218B0217B0216

B0215B0214B0213B0212

B0211B0210

B0265

B0254B0253

B0242

10000

KILOMETERS

15000 20000 2500050005000 0

1 0 1 2 3 4 5

1 0 1 2 3 4 5 6 7 8 9 10

MILES

FEET

DETAILED SOIL GAS SURVEYS OVER A GAS TREND

A large detailed regional soil gas survey was conducted by a major oil company in the prolific Permian Chase Carbonate Gas Trend of the Hugoton Embayment of southwest Kansas. As shown in Figure 16, the seven-foot soil gas survey covers an area of about 210 square miles and consists of 923 soil gas sites. The soil gas survey was sampled on a box grid pattern with a one-half mile distance between samples. An average section (640 acres) contains nine soil gas sample sites. Because the established well spacing in this gas trend was 640-acres, this survey, based on sample density, would constitute a detailed soil gas survey. It is noteworthy to mention, at this point, that the previously discussed soil gas survey in the north part of the Morrow Sand Trend with 11 sites per section was considered a reconnaissance survey because the unit spacing in that trend for oil wells is 80-acres.

This detailed regional soil gas survey is located in Greeley and Wichita Counties, Kansas to the west and north of Byerly (47.3 BCFG) and Bradshaw (334 BCFG) Gas Fields. A portion of the soil gas survey was conducted over the northwest half of Byerly Field for calibration purposes. The Permian Carbonate Gas Play (Chase and Council Grove Groups) in the Hugoton Embayment is the most prolific and important hydrocarbon play in this petroleum province. This area of SW Kansas is also referred to as the Hugoton gas area. The major gas fields of this area – Hugoton, Panoma, Greenwood, Bradshaw, and Byerly (Figure 16) have produced a total cumulative of 27 TCFG.

Byerly and Bradshaw Gas Fields, together, have a total cumulative production of 381 BCFG from the Chase Carbonate reservoir. Byerly Field was discovered in 1968. Development drilling at Byerly Field (Figure 17) progressed rapidly through the 1970’s up to 1985 when the field reached a maximum development of 55 wells. There was a hiatus in development drilling from 1986 until 1990. Since 1990 there have been 14 Chase Carbonate completions at Byerly Field. There are currently 46 producing gas wells in the field of which 20% have been completed since 1995. Interpretation of the analytical data from the soil gas survey within the northwest part of Byerly Field indicates that there are some additional areas that can be recommended for further development drilling within the field area.

The natural gas accumulations at Byerly Field are due to stratigraphic entrapment caused by a facies change in the Permian Chase Carbonate reservoir where it grades from limestones and dolomites in the east to nonmarine red beds in the west. The generalized geology of the gas trend is illustrated in Figure 2. Regional dip of the Chase Carbonate is to the east-southeast. The upper seal for the gas reservoirs are provided by anhydrites and shales of the overlying Sumner Group. Average drill depths of the gas reservoir at Byerly Field range from about 2750 to 2900 feet. Porosity and permeability in the Chase Carbonate are highly variable as evidenced by the cumulative gas production from individual wells as shown in Figure 17A. Cumulative gas production from wells in Byerly Field range from 30 MMCFG to 3,572 MMCFG.

Figure 16

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Page 20How to Design an Exploration Surface Soil Gas Geochemical Survey

A. Contour Map of cumulative gas production from wells in northwest part of Byerly Field B. Ethane magnitude contour map in northwest part of Byerly Field

SS129B

SS116B

SS103B

SS090B

B0694

B0688

B0683

B0820B0819

B0806B0805

B0792B0791

B0778B0777

B0764B0763

B0752B0751

B0741B0740

B0731B0730

B0722B0721

B0714B0713

B0706B0705

B0699B0698

B0693B0692

B0687

B0519B051817

B0502B050100

B0483B048281

B0464B04632

SS161BSS160BSS159BSS158BSS157BSS156B

SS154BSS153BSS152BSS151BSS150BSS149B

SS141BSS140BSS139BSS138BSS137BSS136B

SS128BSS127BSS126BSS125BSS124BSS123B

SS115BSS114BSS113BSS112BSS111BSS110B

SS102BSS101BSS100BSS099BSS098BSS097B

SS089BSS088BSS087BSS086BSS085BSS084B

B0908

B0907B0906

B0905B0904B0903

B0902B0901B0900B0899

B0898B0897B0896B0895B0894

B0893B0892B0891B0890B0889

B0824B0823B0822B0821

B0810B0809B0808B0807

B0796B0795B0794B0793

B0782B0781B0780B0779

B0768B0767B0766B0765

B0756B0755B0754B0753

B0745B0744B0743B0742

B0735B0734B0733B0732

B0726B0725B0724B0723

B0718B0717B0716B0715

B0710B0709B0708B0707

B0703B0702B0701B0700

B0697B0696B0695

B0691B0690B0689

B0686B0685B0684

B0682B0681B0680

B0679B0678

B0521B0520

B0505

B0504B0503

B0487B0486B0485B0484

B0468B0467B0466B0465

B0301

SS207B

SS204B

SS201B

SS198B

SS195B

SS155B

SS148BSS147BSS146BSS145BSS144BSS143BSS142B

SS135BSS134BSS133BSS132BSS131BSS130B

SS122BSS121BSS120BSS119BSS118BSS117B

SS109BSS108BSS107BSS106BSS105BSS104B

SS096BSS095BSS094BSS093BSS092BSS091B

8 15 20 6 6

4 4 10

5 6 9 16

9 9 35 8 8

10 6 8 10 13

47 6 9 9

5 8 9 20 6

5 5 6 28 9

1 5 9 22 12

4 14 19 12 1

12 34 12 18 40

3 9 14 36 9

6 14 26 10 16

10 3 7 16 7

7 137 13 19

30 4 16 5 11

20 21 27 2 8

8 23 14 3

4 2 201 1

4 48 15

20 6 8

12 3

4

30

10 18 15

16 16 5 11 4 2 3 11 20 9 4 4

5 3 11 6 6 130 67 8 118 9 18 20

6 10 4 4 6 4 3 10 93 11 9 4

6 7 5 3 9 5 3

6 12 4 5 9 6

0

MILES

21< 10

15 - 2020 - 2525 - 30

> 30

ETHANECONCENTRATIONS

(ppb)

10 - 15

458

722

1669

2264

511

775

222

584

68

118 641

322

58

144

527

730

68

865421

1741

504 66

14821644

1123

622 947421

226213

375502

238

447 442

431

223457

3181348

6

53430

326 2443

91

24

249

116797

564

773

695

4221116

277373 35721741

85

138

1171

7306931140

832

1099

0

MILES

21< 300

300 - 500500 - 1,000

1,000 - 1,500> 1,500

CUMULATIVE GASPRODUCTION

PER WELLMMCFG

The stratigraphic entrapment of the gas, relatively shallow depth, and highly variable porosity and permeability of the reservoir are factors which favor the application of surface soil gas surveys as an important exploration method to reduce risk in this play.

The purpose of the regional detailed soil gas survey was threefold: (1) calibration of the survey to the gas production at Byerly Field, (2) to aid in possible further exploitation/development drilling at Byerly Field, and (3) to determine other areas along trend that exhibited similar anomalous soil gas microseepage and would therefore indicate areas of exploration potential.

The variability of the cumulative gas production from individual wells in the northwest part of Byerly Field is illustrated in Figure 17A. There is a pronounced northeast-southwest orientation of porosity and permeability development in the Chase Carbonate at Byerly Field. As evidenced by the cumulative gas production contour map, there are three porosity/permeability fairways at Byerly Field. An ethane concentration contour map, constructed from soil gas magnitude analytical data in northwest half of Byerly Field, is shown in Figure 17B. There is very good correlation between areas of maximum cumulative gas production (Figure 17A) and anomalous ethane soil gas concentrations (Figure 17B) in Byerly Field. The trends of microseep anomalies, indicated by the contour map of ethane magnitudes, exhibits the same northeast-southwest orientations as seen in the contour map of cumulative gas production. Since there are many more soil gas data points than development wells at Byerly Field, the soil gas anomalies, indicated by the contour map, probably provides a more realistic depiction of the subsurface porosity/permeability trends in the Chase Carbonate at Byerly Field.

A number of untested soil gas anomalies exist in the remainder of the soil gas survey to the west and north of Byerly Field. These anomalous gas microseeps are not random, isolated points, but rather tend to cluster in groups of gas microseep points that are on trend with established Chase Carbonate gas production at Byerly and Bradshaw Fields. These untested soil gas anomalies exhibit similar soil gas magnitudes and areal extents as the soil gas anomalies mapped within Byerly Field.

Figure 17

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Page 21How to Design an Exploration Surface Soil Gas Geochemical Survey

DRY HOLE LOCATED

> 125

ETHANECONCENTRATIONS

(ppb)

110 - 12590 - 11075 - 9065 - 75

< 65

IN AREAS OFBACKGROUND ETHANEMAGNITUDES

V7b

V7c

V7d

Limits and Dimensions of Morrow V7 SandsAreal Extent

Completion ZonesMorrow Well

V7c

V7b

V7d

Thickness

0 - 30 ft.

0 - 18 ft.

0 - 24 ft.

Width

1800 - 2700 ft.

1300 - 2300 ft.

2300 - 3200 ft.

WITT "B" LEASE

BOBCAT LEASE

WITT "A" LEASE

COYOTE

LANG LEASE

< 10

10 - 20

20 - 30

30 - 40

40 - 50

50 - 60

70 - 80

80 - 90

> 200

LEGENDCUM. BO x 1000

220

229220

76.0

25.5

76.0

6.5

32.4

87.0

13.432.0

87.0

40.8

54.61.7

83.343.3

85.3

45.3

0.5

BREWER 2

WITT A-1

BREWER 1

BREWER 24-2

MO-JO 1

MO-JO 2

LINN 1

WITT B-1

WITT A-2

ABEL #1

BREWER 3

BREWER 1

BREWER 2

MO-JO 4

MO-JO 3

WENDLEBURG 3-11WENDLEBURG 2-11

COYOTE 2

BOBCAT 1-2

BOBCAT 2-2

BOBCAT 2-2

LANG 34-35

SELL #13-3

HUDDLESTON 34-11

HUDDLESTON 33-11

WENDLEBURG 1-11

COYOTE 1

BLACKBIRD #1

LAWSON #1

SELL 1

17

8

5

1314

1211

12

18S

43W

18S

41W

CO

LO

RA

DO

KA

NS

AS

Scale - Feet

1000 20000

LINN 1

AMOCO

SELL 1

LAWSON #1

BLACKBIRD #1

COYOTE 1

WENDLEBURG 1-11

HUDDLESTON 33-11

HUDDLESTON 34-11

SELL #13-3

LANG 34-35

BOBCAT 2-2

BOBCAT 2-2

BOBCAT 1-2

COYOTE 2

WENDLEBURG 2-11

WENDLEBURG 3-11

MO-JO 3

MO-JO 4

BREWER 2

BREWER 1

KELLER #2

KELLER #1

BREWER 3

MILLER #1

WILLIAM #1

ABEL #1

WITT A-2

WITT B-1

LINN 1

MO-JO 2

MO-JO 1

BREWER 24-2

BREWER 1

WITT A-1

BREWER 2

A

A’

LIMITS OF V7INCISED

VALLEY-FILL

17

8

5

1314

1211

12

18S

43W

18S

41W

CO

LO

RA

DO

KA

NS

AS

Scale - Feet

1000 20000

061

57

30

38

108

83

62

123

44

65

35

83

19

76200

75 47

6536

29

26

54

48

106

7076

99

80

47

84

26

197

45 59

75

34

121

37

41 63 135

23

75

50

87

161

20

148

115 203

69

124764239

94

73

76

75

53

41

58

71

101

43 83

143

22

35

36

47 46

7165

42

109

51

88

3659

97

426149

215

34

4752

95

65 30 48

77

40

78

77 96 83

113

58

103

40

42

62 110

217

197

124

11388

321

320

319318

317 316

314313

312

311

310

309

304

303302

301

300

297

296

295

294

293 292

291

286

285

284

283 282 281

280

279

278

277

276

115A

090A

052A 049A

037A

273 272230229228

041040A

130

129

128

127

124

121

119

118

117 116

115

095

094

093

092

091 090

089088

087

085

084

083

082081

080

079078077

076

075

074073

072

071

070069 068 067

066

063

053

052 051 050049

048

047

046

045

044

043

042

039

038 037036

005

004

003

002001

17

8

5

1314

1211

1218

S43

W18

S41

WC

OL

OR

AD

O

KA

NS

AS

Scale - Feet

1000 20000

Advantages and Limitations of Soil Gas Surveys

As previously discussed, the major advantage of soil gas surveys in the Morrow oil trend is that of risk reduction and potentially improving the success ratio. As shown on the Figure 18A, had the survey been available to all companies, then probably, 11 of the dry holes on the west side and the north and south end of the field would not have been drilled. This alone would have increased the overall success rate for the field from 56% to 82%. Had the data been available to Amoco in 1990, at least five of the dry holes could have been avoided, increasing Amoco’s success rate from 30% to 60%.

Another major advantage of soil gas surveys is the relatively low cost. Considering sample collection, laboratory analyses, and interpretation and reporting costs, the present day cost of the 106 site soil gas survey conducted at Moore-Johnson field would be about $16,000. This is only about 15% of the dry hole cost of a single Morrow well.

In this portion of the Morrow trend, the sample density of 16 sites per section is only adequate for defining a lead or prospect area and possibly acquiring acreage. This sample density is not adequate for exploitation or development drilling. A sample density of at least 30 sites per section is needed as demonstrated at the Moore-Johnson field (LeBlanc and Jones, 2004a).

Surface soil gas geochemistry will not eliminate all dry holes being drilled within a field. The example previously discussed of the Bobcat #2-2 wells is a good example to illustrate this point. As pointed out by Bowen and Weimer (2003), the V7 sands in this part of the Morrow trend are of smaller areal extent, smaller in cross section, and more compartmentalized than in the Morrow fields to the north. At the sample density of this survey, microseep anomaly patterns could not distinguish the individual trends of the V7b, V7c, and V7d reservoirs. This is because the widths only range from 1800 to 3000 feet (see legend, Figure 18B). Perhaps a denser soil gas grid could have provided the necessary resolution.

Soil gas anomaly data can not distinguish between oil reservoirs of different geologic ages. In this part of the Morrow trend, in most wells the Mississippian has been a secondary (or primary) objective. Although not productive at Moore-Johnson field, anomalous microseeps in the surrounding area could indicate Mississippian potential in addition to Morrow. Additionally, shows were reported in some wells in the Pennsylvanian Lansing-Kansas City interval.

There is no direct relationship between the magnitudes of microseeps and either the rate or total volume of hydrocarbons a well will produce, except in a very general sense. This is particularily true when comparing reservoirs having different entrapment mechanisms, such as the Stateline Morro oil and W. Stockholm gas fields. However, as can be seen comparing the ethane contour map (Figure 18A) to the production map on Figure 18C, this concept may at least potentially work when comparisons are made over the same reservoir. For example, the Bobcat lease (170,646 BO) has been more productive than the Witt “A” lease (90,575 BO) and the Lang lease (477 BO). Similarly, the Coyote lease (95,362 BO) has been more productive than the Witt “B” lease (1745 BO). The ethane magnitudes suggest differences that may be related to these production volumes. This suggests that the amount of reserves on a prospect could likely be improved by a company getting a competitive edge in early lease acquisitions based on soil gas data. One of the reasons that Axem/Murfin had such sizeable reserves at Moore-Johnson field was their excellent lease position.

Figure 18

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Page 22How to Design an Exploration Surface Soil Gas Geochemical Survey

0 mi 10

0 km 10

"STA

TELIN

E TR

EN

D"

Kan

sas

Co

lora

do

unty

Cheyenne County

Cheyenne County

Wallace County

Kiowa County

Greeley County

Sherman County

Wildfire

Smokey Hill

Lookout

Bledsoe Ranch

Sianna

Salt Lake/Haswell

Jace

Moore-Johnson

McClave

Speaker

Mt. Pearl

Sorrento Field

Castle Peak

Harker Ranch

Arapahoe

Frontera

Stockholm SW

Second Wind

Mount Sunflower

Arrowhead

Sidney

90%W/Soil Gas

No Soil Gas42%

41%

30%

56%

68%

73% 49%

66%47%

58%

FACIESTRACT

FIELD RESER-VOIRS

SUCCESS RATIO YRS. TO DEVELOP

AVG. PER WELL RESERVES BO

UPDIPSorrento V7 58% 10 YRS.

1979-1988 358,333

Mt. Pearl-Sianna V7 47% 6 YRS.1984-1990 321,429

TRANSITIONAL

Arapahoe V3V7 66% 3 YRS.

1988-1990 154,419

Frontera V7 73% 3 YRS.1988-1990 106,429

SW Stockholm V7 68% 9 YRS.1979-1988 69,892

Second Wind V3V7 54% 4 YRS.

1988-1991 139,474

SunflowerV1V3V7

49% 4 YRS.1993-1998 83,500

Sidney-KrissV1V3V7

41% 9 YRS.1990-1999 42,950

DOWNDIP

Jace V1V7 31% 5 YRS.

1989-1993 63,846

Moore-Johnson V7

42%W/O SOILGAS

SURVEY90%

W/ SOIL GAS SURVEY

2 YRS.1992-1994 91,000

Factors Affecting the Rate of Return in the Morrow Trend

Recommendations

Figure 19 and Table 2 list success rates for development drilling in representative fields in the Morrow oil trend and other factors (years to develop, per well reserves) affecting the rate of return in the Morrow trend. The fields are grouped according to the facies tracts as defined by Bowen and Weimer (2003). It is apparent that the newer fields most recently developed (Jace, Sunflower, Sidney) have the lowest success rates. As shown at Moore-Johnson field, high-density soil gas surveys could improve drilling success in these areas. Employment of soil gas surveys could also have accelerated the development drilling schedule at Sorrento and SW Stockholm fields from the 10-year period that was required for full field development. As discussed by Bowen et al. (1993) initially (1979 to 1984), an incorrect depositional model was the main reason for the rather lengthy development time frame for these two fields.

Success rates for Morrow exploration wells were reported by Bowen et al. (1993) to have been 5% in the Sorrento-Mt. Pearl-Sianna area and reported by Moriarty (1990) to have been 10% in the Stateline area. There still remain areas of untested Morrow exploration potential in the transitional and updip facies tracts where soil gas surveys could be employed to improve the exploratory success rates over those previously reported. Regional isopach maps of the upper Morrow section have been used to define other areas where Morrow V1, V3, and V7 incised valleys might exist (Bowen and Weimer, 2003, Figure 10). Regional soil gas surveys could be very useful in exploration ventures when used in conjunction with this method, especially in areas with sparse well control (LeBlanc and Jones, 2004a).

As shown in this paper, surface soil gas geochemistry has been successfully used in developing oil reserves in the Morrow V7 incised valley trend. This method would also be applicable in other Morrow incised valley trends of southeast Colorado and southwest Kansas such as the V1 and V3 Valley systems. As reported by Bowen and Weimer (1997, 2003) these two incised valley systems are transparent on 2-D or 3-D seismic due to their close proximity to the base of Atoka/top of Morrow interface. Additionally, other Morrow incised valley fill systems were outlined by Wheeler et al. (1990) in Wallace County, Kansas and farther south in Kiowa, Brent, and Powers Counties, Colorado.

Figure 19

Table 2

A high degree of compartmentalization has been observed in the V7 reservoirs in the downdip facies tract. Future soil gas surveys in this area, for development drilling purposes, should have a higher density of samples than the grid of 30 sites per section used in the 1992 survey at Moore-Johnson field. For regional exploration activities in the Morrow trend, a soil gas grid of 16 sites per section appears satisfactory only for delineating regional microseep anomalies.

Soil gas geochemistry would also be applicable in other younger Pennsylvanian incised valley systems that have been identified in central and southern Kansas and northern Oklahoma (KGS, 2003). Likewise, Cretaceous age incised valley-fill systems exist in Rocky Mountain areas such as the Denver, Powder River, and Williston basins. The generalized paleodrainage network for the Muddy Formation was illustrated by Weimer (1992, Fig. 3) over the north Colorado, Wyoming, and eastern Montana areas. A more detailed picture of paleovalleys in the Denver basin which were filled with Muddy valley-fill sandstones was also presented.

The advantages of using each of the disciplines of geology, geophysics, and soil gas geochemistry in Morrow exploration and development are well known, however the three disciplines have seldom been used in tandem. A somewhat lesser discussed topic is that of the limitations of these three sciences.

The limitations of using soil gas surveys in the Morrow oil trend have been discussed, to some extent, in this paper. Bowen et al. (1993) discussed limitations of subsurface geology and 2-D seismic in locating reservoir quality sandstones in the Sorrento-Mt. Pearl-Sianna area. Germinario et al. (1995) likewise discussed the limitations of 2-D and 3-D seismic surveys in locating both the incised valleys and reservoir sandstones in the southern Stateline Trend.The integrated, multidisciplined approach of using geology, geophysics, and soil gas geochemistry in Morrow exploration (LeBlanc and Jones, 2004b) is a superior method whereby the advantages in one of the three disciplines complement and overcome the limitations or shortcomings of another.

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Page 23How to Design an Exploration Surface Soil Gas Geochemical Survey

Summary

A high-density soil gas survey was conducted in the vicinity of Moore-Johnson field in 1992. The survey was conducted after the discovery of the field and initial development attempts, all by the same major oil company, which resulted in a total of 10 wells (3 oil wells, 7 D&A). A second attempt to extend the field, starting in 1992, was conducted by six independent oil companies. One of the companies used an integrated approach of combining subsurface geology and seismic with a detailed geochemical soil gas survey. The remainder of the companies used industry-standard Morrow exploration techniques acquired from 1978 to 1990 during development of Morrow oil fields to the north.

A high-density soil gas survey, consisting of 106 sites, was conducted over a four square mile area of interest. Integration of geochemistry, geology, and geophysics resulted in a compatible, unified interpretation that the field could be extended to the north.

The company utilizing the soil gas survey completed the first well to extend the field with a 4700-foot stepout. This company completed eight consecutive successful Morrow wells in the field before drilling a dry hole. After drilling 10 wells, the company had a 90% success rate. A total of 34 wells were drilled to both define the limits of the field and develop the Morrow reserves. By only drilling 29% of the total wells, the company utilizing soil gas geochemistry acquired 47% of the reserves produced to date. Success rates for the remainder of the other field operators were 0%, 30%, 50% and 67%

There are still areas of untested potential in the Morrow oil trend. Fields discovered to date have produced 66.5 MMBO with ultimate recoverable reserves estimated at about 110 MMBO. Fields in the southern portion of the trend are in the downdip facies tract as characterized by Bowen and Weimer (2003). The Morrow sands in these wider incised valleys are of smaller areal extent, smaller in cross section, and more compartmentalized. Correspondingly, the average reserves per well are smaller than the northern fields. Although reserves are lower in the downdip facies, employing soil gas geochemistry can improve the relatively low success rates now being encountered in this area. This could vastly improve the rate of return.

This documentation of a successful application of a detailed soil gas survey demonstrates how the method could be used to delineate other areas of Morrow incised valley-fill systems in areas of untested potential. Additionally, the method would also be applicable in incised valley-fill systems of other geologic ages in Midcontinent and Rocky Mountain basins.

Soil gas geochemistry is not a panacea for Morrow exploration, exploitation, or development drilling, but is an integral part of a thorough exploration program. Applying the recently related concepts of Morrow sequence stratigraphy will undoubtedly be a tremendous advantage in future Morrow exploration and development drilling ventures, reservoir maintenance, and in secondary recovery operations. Using soil gas geochemistry in tandem with this concept would provide a very powerful synergistic effect to Morrow exploration and development projects.

References Cited

Agostino, P.N., R.J. LeBlanc, Jr., and V.T. Jones III, 2002, Assessment of subsurface hydrocarbon contamination resulting from multiple releases at six former bulk-fuel storage and distribution terminals, Austin, Texas: A case study, in D. Schumacher and L.A. LeSchack, eds., Surface exploration case histories: Applications of geochemistry, magnetics, and remote sensing, AAPG Studies in Geology No. 48 and SEG Geophysical Reference Series No. 11, p. 299-325.

Adams, C.W., 1990, Jace and Moore-Johnson fields, in Sonnenberg, S.A., L.T. Shannon, K. Rader, W.F. Von Drehle, and G.W. Martin, eds., Morrow sandstones of southeast Colorado and adjacent areas: Rocky Mountain Assoc. of Geologists, p. 157-164.

Bebout, D.G., W.A. White, and T.F. Hentz eds., 1993, Atlas of Midcontinent gas reservoirs: Bureau of Economic Geology The University of Texas at Austin, Austin, Texas, 85 p.

Boleneus, David, 1994, Guidelines for surface geochemical surveying, Oil & Gas Jour., June 6, v. 92, p. 59-64.

Bowen, D.W., and P. Weimer, 1997, Reservoir geology of incised valley-fill sandstones of the Pennsylvanian Morrow Formation, southern Stateline trend, Colorado and Kansas, in K.W. Shanley and B.F. Perkins, eds., 18th Annual GCSSEPM Research Conference, p. 55-66.

Bowen, D.W., and P. Weimer, 2003, Regional sequence stratigrapic setting and reservoir geology of Morrow incised-valley sandstones (lower Pennsylvanian), eastern Colorado and western Kansas, AAPG Bulletin, v. 87, p. 781-815.

Bowen, D.W., P. Weimer, and A.J. Scott, 1993, The relative success of siliciclastic sequence stratigraphic concepts in exploration: examples from incised valley fill and turbidite systems reservoirs, in P. Weimer and H. Posamentier, eds., Siliciclastic sequence stratigraphy: AAPG Memoir 58, p. 15-42.

Brown, L.G., W.A. Miller, E.M. Hundley-Goff, and S.F. Veal, 1990, Stockholm Southwest field, in S.A. Sonnenberg, L.T. Shannon, K. Rader, W.F. Von Drehle, and G.W. Martin, eds., 1990, Morrow sandstones of southeast Colorado and adjacent areas: Rocky Mountain Association of Geologists, p. 117-130.

Dickinson, Roger and M.D. Matthews, 1993, Regional microseep survey of part of the productive Wyoming-Utah thrust belt, AAPG Bulletin, v. 77, p. 1710-1722.

Dickinson, Roger, D.A Uhl, M.D. Matthews, R.J. LeBlanc, Jr., and V.T Jones, 1994, A retrospective analysis of a soil gas survey over a stratigraphic trap trend on the Kansas-Colorado border: AAPG Hedberg Research Conference, Near-Surface Expression of Hydrocarbon Migration, April 24-28, 1994, Vancouver, British Columbia, Canada. Poster Session IV, April 27, 1994.

Germinario, M.P., S.R. Cronin, and J.R. Suydam, 1995, Applications of 3-D seismic on Morrow channel sandstones, Second Wind and Jace fields, Cheyenne and Kiowa Counties, Colorado, in, R.R. Ray, ed., High definition seismic 2-D, 2-D swath, and 3-D case histories, Rocky Mountain Assoc. of Geologists, p. 101-119.

Jones, V.T., and R.J. Drozd, 1983, Predictions of oil or gas potential by near-surface geochemistry, AAPG Bulletin, v. 67, n. 6, p. 932-952.

Jones, V.T., S.G. Burtell, R.A. Hodgson, T. Whelan, C. Milan, T. Ando, K. Okada, T. Agtsuma, and O. Takono, 1985, Remote sensing and surface geochemical study of Railroad Valley, Nye County, Nevada. Presented at Fourth Thematic Mapper Conference, Remote Sensing for Exploration Geology, San Francisco, California, April 1-4.

Jones, V.T., M.D. Matthews, and D.M. Richers, 2000, Light hydrocarbon for petroleum and gas prospecting, in M. Hale, ed., Handbook of exploration geochemistry, v. 7, Elsevier Science, p. 133-212.

Kansas Geologic Survey, 2003, www.kgs.ku.edu

LeBlanc, Jr., R.J. and V.T. Jones, 2004a, How to design an exploration surface soil gas geochemical survey: Illustrated by application examples from the Hugoton Embayment of SE Colorado and SW Kansas, Abstract, AAPG Annual Meeting, April 18-21, 2004, Dallas Texas.

LeBlanc, Jr., R.J., and V.T.Jones, 2004b, Criteria for a multi-disciplined approach for exploration, exploitation, and development drilling in the Morrow incised-valley oil trend of Colorado and Kansas: The 3-G method, Abstract, Rocky Mountain Section AAPG Meeting, August 9-11, 2004, Denver, Colorado.

Link, W.K., 1952, Significance of oil and gas seeps in world oil exploration, AAPG Bulletin, v. 36, p. 1505-1541.

Montgomery, S.L., 1996, Stewart field, Finney county, Kansas: Seismic definition of thin channel reservoirs, AAPG Bulletin, v. 80, p. 1833-1844.

Moriarty, B.J., 1990, Stockholm Northwest extension, effective integration of geochemical, geological, and seismic data: in: Sonnenberg, S.A., L.T. Shannon, K. Rader, W.F. Von Drehle, and G.W. Martin, eds., Morrow sandstones of southeast Colorado and adjacent areas: Rocky Mountain Assoc. of Geologists, p. 143-152.

Shumard, C.B., 1991, Stockholm southwest field – U.S.A., Anadarko basin, Kansas: AAPG Treatice of Petroleum Geology, Atlas of oil and gas fields, stratigraphic traps II, p. 269-309.

Sonnenberg, S.A., L.T. Shannon, K. Rader, W.F. Von Drehle, and G.W. Martin, eds.,1990, Morrow sandstones of southeast Colorado and adjacent areas: Rocky Mountain Assoc. of Geologists, 263p.

Weimer, R.J., 1992, Developments in sequence stratigraphy: foreland and cratonic basins, AAPG Bulletin, v. 76, n. 7, p. 965-982.

Wheeler, D.M., A.J. Scott, V.J. Coringrato, and P.E. Devine, 1990, Stratigraphy and depositional history of the Morrow formation, southeast Colorado and southwest Kansas, in: Sonnenberg, S.A., L.T. Shannon, K. Rader, W.F. Von Drehle, and G.W. Martin, eds., Morrow sandstones of southeast Colorado and adjacent areas: Rocky Mountain Assoc. of Geologists, p. 9-35.

USGS, 1995, CD disk of petroleum provinces in the United States.


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