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Geologic surveying

This is the oldest and first used tool fordetermining the possibility of findingunderground petroleum reservoirs.

It involves examination of the surface geology,formation outcrops, and surface rock samples.

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The collected information is used inconjunction with geologic theories todetermine whether petroleum reservoirscould be present

The rate of success of finding petroleumreservoirs using geologic surveys alone hasbeen historically low.

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Surface Geochemical Exploration:History and Application

How does it work?

Seepinghydrocarbonsmove alongfractures tothe surfacecausingdetectable soilalterationanomalies.

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Surface Geochemical Exploration:History and Application

Assume all reservoirs leak (no perfect seal) Macroseeps

Initial field discoveries Microseeps

Large body of empirical evidence Russia (research state supported) USA (research supported by commercialization) China (research state supported)

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Surface Geochemical Exploration:

Geophysical and Geochemical phenomenaassociated with hydrocarbon seepagealteration.

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Geophysical Surveys

1.gravity survey,

2.magnetic survey,

3.seismic survey, and

4.remote sensing.

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The gravity survey is the least expensivemethod and involves the use of a gravimeter,which picks up a reflection of the density ofthe subsurface rock.

For example, because salt is less dense thanrocks, it can detect the presence of saltdomes, which would indicate the presence ofan anticline structure.

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The magnetic survey involves measurement ofthe magnetic pull, which is affected by the typeand depth of the subsurface rocks.

The magnetic survey can be used to determinethe existence and depth of subsurface volcanicformations, or basement rocks, which containhigh concentrations of magnetite.

Such information is utilized to identify thepresence of sedimentary formations above thebasement rocks.

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2. Play to Prospect Level

The seismic survey Involves sending strong pressure (sound)

waves through the earth and receiving thereflected waves off the various surfaces of thesubsurface rock layers.

This determines the locations of traps that aresuitable for petroleum accumulation.

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Exploration and ProductionSeismic Surveys

Earth ScienceWorld ImageBank Image#h5inpjEarth ScienceWorld ImageBank Image#h5inor

Seismic surveys are used to locate likely rock structuresunderground in which oil and gas might be found

Shock waves are fired into the ground. These bounce off layersof rock and r eveal any structural domes that might contain oil

Drill here!

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Exploration Noise/Vibration

Dynamite Vibration Truck Air Gun Marine Vessels

Disturbance tohuman/wildlife/marine life

Low Impact/Transient

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Exploration

Methods to locate:1) Maps;2) Exploratory well cuttings; and3) Geophysical studies (gravity, magnetic, seismic reflectionsatrapping mechanism,

such as an anticline or faulted strata.18

Remote sensing is a modern technique thatinvolves using infrared, heat-sensitive, colorphotography to detect the presence ofunderground mineral deposits, water, faults,and other structural features.

The sensing device, normally on a satellite,feeds the signals into special computers thatproduces maps of the subsurface structures.

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Drilling Proposal - Exploratory Drilling

Three conditions must be present:1) source rock, ric h in organic material;2) reservoir rock, s uch as porous and permeable limestone or dolomite; and3) a trapping mechanism, such as an anticline or faulted strata.

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Drilling Operation

ISSUE #37 | N ovember 2005 Phoenix GeophysicsOntario Ministry of Natural Resources 21

Drilling Overview

1. Rig Types and Components 2. Drilling Method

Fundamentals Dangers Evaluation of sediments Logging

3. Testing

Fast & Furious

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24803

Traveling BlockTraveling Block

HookHook

SwivelSwivel

Draw WorksDraw Works

Mud PumpMud PumpRotary TableRotary Table

KellyKellyMud HoseMud Hose

Crown BlockCrown Block

inging

ill iill i

ii

CasingDrill Pipe

Bit

Drilling Rig

What doesWeight on Bit mean? 23

BARGE: Towed, Sunk, Sits on Bottom < 30 Feet of WaterJacket: 1+ Wells, Small/Cantilevere d Rig Calm/ShallowJACK-UP: Towed, Jacked-up, 15 to 650 FeetSEMI-SUBMERS IBLE Anchored over Drill Site 4000 Feet

Dynamic Positioning 6500 FeetDrill Ships: Automatic Positioning 10000+ Feet

Offshore Rig Types

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At a producing well site, active wellsmay be further categorised as:

oil producers producing predominantly liquidhydrocarbons, but mostly with some associated gas.

gas producers producing almost entirely gaseoushydrocarbons.

water injectors injecting water into the formation tomaintain reservoir pressure, or simply to dispose of waterproduced with the hydrocarbons because even aftertreatment, it would be too oily and too saline to beconsidered clean for dumping overboard offshore, let aloneinto a fresh water resource in the case of onshore wells.

Water injection into the producing zone frequently has anelement of reservoir management; however, oftenproduced water disposal is into shallower zones safelybeneath any fresh water zones.

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aquifer producers intentionally producing water for re-injection to manage pressure. If possible this water willcome from the reservoir itself. Using aquifer producedwater rather than water from other sources is topreclude chemical incompatibility that might lead toreservoir-plugging precipitates. These wells willgenerally be needed only if produced water from theoil or gas producers is insufficient for reservoirmanagement purposes.

gas injectors injecting gas into the reservoir often as ameans of disposal or sequestering for later production,but also to maintain reservoir pressure.

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aquifer producers intentionally producing water for re-injection to manage pressure. If possible this water willcome from the reservoir itself.

Using aquifer produced water rather than water fromother sources is to preclude chemical incompatibilitythat might lead to reservoir-plugging precipitates.

These wells will generally be needed only if produced

water from the oil or gas producers is insufficient forreservoir management purposes. gas injectors injecting gas into the reservoir often as a

means of disposal or sequestering for later production,but also to maintain reservoir pressure.

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Trap nomenclature:

Crest (or culmination) is the highest point ofthe trapSpill point is the lowest point at whichhydrocarbons may be contained in the trap.This lies on a horizontal contour, the spillplane Closure of the trap is a vertical distancecrest to spill plane

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A trap may contain oil, gas, or both. The oil watercontact (commonly referred to as OWC) is thedeepest level of producible oil.Similarly, the gas oil contact (GOC), is the lower limitof producible gas.Also it is important to gas overlies the oil as the gashas a lower density and water will take the lowestposition (the highest density of the three liquids).

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Petroleum System Elements & Processes

2480

120F120F

350F350F

GenerationGeneration

MigrationMigration

Seal RockSeal Rock

Reservoir RockReservoirRock

OilOil

WaterWater

Gas CapGasCap

EntrapmentEntrapment

It is ALL or nothing

Source Rock

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Fig. 1. Main geological conditions and geochemical processes requiredfor the formation of petroleum accumulations in sedimentary basins:1) petroleum generation in source rocks;2) primary migration of petroleum;3) secondary migration of petroleum;4) accumulation of petroleum in a reservoir trap;5) seepage of petroleum at the Earths surface as a consequence of a

fractured cap rock.

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Petroleum accumulation forms in sedimentarybasins and can be discovered by exploration, ifthe following geological conditions are met: Occurrence of source rocks which generate

petroleums under proper subsurfacetemperature conditions.

Sediment compaction leading to expulsion ofpetroleum from the source and into thereservoir rocks (primary migration).

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Occurrence of reservoir rocks of sufficientporosity and permeability allowing flow ofpetroleum through the pore system(secondary migration).

Structural configurations of sedimentarystrata whereby the reservoir rocks formtraps, i.e. closed containers in the subsurfacefor the accumulation of petroleum.

Traps are sealed above by impermeablesediment layers (cap rocks) in order to keeppetroleum accumulations in place.

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Correct timing with respect to the sequence bywhich the processes of petroleum generation/migration and trap formation have occurredduring the history of a sedimentary basin.

Favourable conditions for the preservation ofpetroleum accumulation during extended periodsof geologic time, i.e. absence of destructive, suchas the fracturing of cap rocks leading todissipation of petroleum accumulations, orsevere heating resulting in the cracking of oil intogas.

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The question of the origin of petroleum hasbeen hotly debated for a long time.

A great many theories, hypotheses andspeculations have been proposed.

Decades ago, various ideas on a possible

inorganic origin of petroleum were broughtforward, e.g. that it results from the reactionof iron carbide with water deep in the Earthscrust.

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The main evidence supporting these theorieswas the occasional occurrence of hydrocarbonfluid inclusions and solid bitumens in igneousrocks as well as a few cases of oil and gasfields hosted in fractured basement rocks (e.g.

granites, basalts, and metamorphic rocks).

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However, in most of these cases it could bedemonstrated that the petroleum materials wereultimately generated in sedimentary rocks and hadbeen transported, e.g. by convective flow ofmineralising aqueous fluids, into the granites, or thatthey had migrated from sedimentary strata over longdistances to accumulate in fractured basement rocks.

These cases of petroleums occurring in basement rocksare extremely rare and not commercially importantwhen compared to the vast majority of hydrocarbonreserves in sedimentary basins (Selley, 1998).

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One of the main arguments concerns theubiquitous occurrence of biological markermolecules in petroleums, such as porphyrines,steranes and hopanes.

The highly specific carbon structures of thesemolecules could not be synthesized by inorganicreactions.

They are clearly and uniquely derived frommolecular structures synthesized by livingorganisms.

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Today, the evidence in favour of an organic origin ofpetroleum is overwhelming.

One of the main arguments concerns the ubiquitousoccurrence of biological marker molecules inpetroleums, such as porphyrines, steranes andhopanes.

The highly specific carbon structures of thesemolecules could not be synthesized by inorganicreactions.

They are clearly and uniquely derived from molecularstructures synthesized by living organisms.

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A geologic environment that allows for economicallysignificant amounts of oil and gas to accumulateunderground is termed an oil/petroleum trap

Oil and gas is contained in a reservoir. A reservoir mustbe permeable to oil and gas, and contain sufficientinterconnected pore space to accommodate thepetroleum. Common examples are poorly lithifiedsandstones, carbonate reefs, diagenetic carbonates.

The roof of the trap must be made of material that isimpermeable to fluids. This is necessary to prevent theupward escape of oil and gas which are much less densethan the surrounding rock.

Common traps include anticline fold traps, fault-boundedtraps (structural traps) as well as various stratigraphictraps.

Petroleum Traps

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1. Dome-Shaped and AnticlineReservoirs

These reservoirs are formedby the folding of the rocklayers as shown in Figure 1.1.

The dome is circular inoutline, and the anticline islong and narrow

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Oil and/or gas moved or migrated upwardthrough the porous strata where it wastrapped by the sealing cap rock and the shapeof the structure.

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2. Faulted Reservoirs:

These reservoirs areformed by shearing andoffsetting of the strata(faulting), as shown inFigure 1.2.

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3. Salt-Dome Reservoirs: This type of reservoir structure, which

takes the shape of a dome, wasformed due to the upward movementof large, impermeable salt dome thatdeformed and lifted the overlyinglayers of rock.

As shown in Figure 1.3, petroleum istrapped between the cap rock and anunderlying impermeable rock layer, orbetween two impermeable layers ofrock and the salt dome.

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4. Unconformities: This type of reservoir

structure, shown inFigure 1.4, was formedas a result of anunconformity where theimpermeable cap rockwas laid down across thecut-off surfaces of thelower beds.

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5. Lense-Type Reservoirs: In this type of reservoir, the

petroleum bearing porousformation is sealed by thesurrounding, nonporous formation.

Irregular deposition of sedimentsand shale at the time theformation was laid down is theprobable cause for this abruptchange in formation porosity.

An example of this type ofreservoirs is shown in Figure 1.5.

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Stratigraphic trap

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Day 2 - Sources, Origin and Nature ofPetroleum

Oil and gas field development Production Well fluids and surface production operations Transportation

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Oil and gas field development Largest Hydrocarbon Basinsby Ultimate Potential

5 of top 10US Fields inCalifornia(>1 BBL)

Where do you look for oil?54

A Strategic Natural Resource

National Geographic, 200255

Well Development, Location, Spacing,and Production Rates

Another important function of reservoirengineering is to determine the optimumlocations of the wells to be drilled and theproduction rate from each well for the mosteffective depletion of the reservoir.

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MU

FILTR TE

What does the hole look like?

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Surface Production Operations

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GOSP J&P KSA $340m

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