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GEO4270 EXERCISE 2

PROSPECT EVALUATION

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Integrated Basin Analysis and Prospect Evaluation

1. Integrated Seismic (reflection/refraction), Gravity and Magneticsand Basin Modelling

Large Scale Structures of the Basin

Tectonic Development of the Basin

Maturation of Hydrocarbons

2. Prospect Evaluation

10/14/2008 GEO4270 - Michel Heeremans2

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Prospect Evaluation

Tampen Spur:

Migration

Troll, Oseberg

,Visund, Tordis

Mature HC


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Prospect Evaluation

Prospect, n.An examination or test of the mineral

the ore, etc. is extracted

, . . .

Evaluation, The action of evaluating ordetermining the value of (a mathematical expression,

a physical quantity, etc.), or of estimating the force of(e.g. probabilities, evidence)

OED, 2.


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Course Contents

Introduction PETREL Introduction Course

Exercise: Statfjord Field a a oa ng

Interpretation

Reservoir Modelling and Prospect Evaluation

Report

Follow up meetings


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Prospect Evaluation Exercise Data

Offshore Norway Northern North Sea

What will we be using during the project: Seismic data

2D

Well data

Formation Tops

eop ys ca we ogs


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WELL LOGGING / CORRELATION

Porosity

SP

GEO4250

Short summary

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Formation Evaluation

Formation evaluation, the process of using borehole

measurements to evaluate the characteristics of subsurface

formations.

e an er, . ., . un amen a s o orma on va ua on


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Formation Evaluation Objectives

Identification of the reservoir (primary)

Reservoir properties Shape

Porosity and permeability Lithology

Well-to-well correlation

Formation dip

Surface seismic well tie


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Hydrocarbons in Place

oiSAh7758 N = initial oil in place (stb)

A = drainage area (acres)

oiB= h = productive interval thickness (ft)

= effective porosity (fraction)

Soi = initial oil saturation (fraction)

oiSAhG 560,43= B

oi= initial oil formation volume factor (reservoir

bbl/stb)

G = initial gas in place (scf)

gi Sgi = initial gas saturation (fraction)

Bgi = initial gas formation volume factor (ft3/scf)

Oil formation volume factor: Oil and dissolved gas volume at reservoir conditions divided by oil volume at

standard conditions.


Gas formation volume factor: Gas volume at reservoir conditions divided by gas volume at standard

conditions.

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Hydrocarbon Reserves

=p

e = effective porosity (fraction) So = Oil saturation (fraction)

oep

h = productive interval thickness (ft) A = drainage area (acres)

=


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Important Parameters

Saturation (S), n. [Formation Evaluation]

The relative amount of water, oil and gas in the pores of a rock, usually.formation water is assumed to contain hydrocarbons. Mathematically thiscan be expressed as:

Shc = 1 Sw

Where Shc = hydrocarbon saturation

Sw = water saturation

If Sw is low, the formation is potentially productive


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Porosity (), n. [Geology]The percentage of pore volume or void space, or that volume

within rock that can contain fluids.

Total Porosity (t): The total pore volume per unitvolume of rock

Effective Porosity (e): The interconnected pore volumeor void space in a rock that contributes to fluid flow or


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Permeability (k), n. [Geology]The ability, or measurement of a rock's ability, to transmit

fluids.

Permeability is required to calculate the flow rate at which

hydrocarbons can be produced, following Darcy law:

dkdx

u


Permeability will not be addressed in the course

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How can we measure these parameters?

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Water Saturation

Water saturation can be measured with the help of:Resistivity (R), n. [Formation Evaluation]

The ability of a material to resist electrical conduction. It is the.

resistivity is a property of the material, whereas the resistancealso depends on the volume measured.

!! Hydrocarbons are resistive while formation water isconductive !!


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Water Saturation

The Resistivity of a formation is dependent on: Presence of Formation water / Hydrocarbons

Salinity of Formation water

Temperature of Formation water Volume of water-saturated pore space

Geometry of the pore space

Mor holo and s ecies of cla minerals


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Water Saturation

Archies e uation Archie, G.E., 1942

Relation between Water Saturation and Resistivity

Sw = Water saturation

F = Formation Resistivit Factor a/ m :

ow RFR Porosity () Tortuosity factor (a)

tt

wRR Cementation factor (m)

Rw = Resistivity of the formation water Rt = Resistivity of a rock with HC, i.e.

true resistivity

= -


o saturated rock

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Porosity

Direct measurements Conventional coring

Sidewall coring

Indirect Measurements Sonic Log

Density Log

Neutron Lo


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Porosity

Sonic Log, n. [Geophysics]A type of acoustic log that displays traveltime of P-waves versus depth

(recorded in interval transit time (t), s/ft, which is the reciprocal of.

the wellbore. The tool emits a sound wave that travels from the source to theformation and back to a receiver.

og sym o :


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Porosity

Dependent on lithology and porosity

Sonic porosity derived by:

sonic = sonic derived porosity

Cptt matrixf

matrix

sonic

log

=

tmatrix = interval transit time of the matrix (table)

tlog = interval transit time of the formationtf= interval transit time of the fluid in the wellbore (fresh mud = 189; salt mud = 185)C = com action factor =

R1

R2100

Ctsh

tsh = interval transit time for adjacent shale C = a constant, normally 1.0


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Porosity

Density Log, n. [Formation Evaluation]A well log that records formation density. The logging tool consists of agamma-ray source (e.g., Cs137) and a detector shielded from the source sothat it records backscattered gamma rays from the formation (Comptonscattering). The backscattering depends on the electron density of theformation, which is roughly proportional to the bulk density.

Log symbol: RHOB, DEN


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Porosity

Density Log1. Identify evaporite minerals

2. Detect gas-bearing zones

3. Determine hydrocarbondensity

4. Evaluate shaly sand reservoirs

and complex lithologies


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Porosity

DRHO is a correction curve, if DRHO >0.20 gm/cc the RHOB curve is invalid

RHOB (formation bulk density) is afunction of matrix density, porosity anddensity of the fluids in the pores,

ere ore:

bmatrix

fmatrix

den

with:

den = density derived porosity

matrix = matrix density (table)b = orma on u ens yf= fluid density


DRHO = 0.20 og sym o :

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Porosity

Neutron Porosity, adj. [Formation Evaluation]

Referring to a log of porosity based on the effect of the formation on fast neutrons emitted.neutrons. Since hydrogen is found mainly in the pore fluids, the neutron porosity logresponds principally to porosity. However, the matrix and the type of fluid also have aneffect.

Scaled in equivalent limestone porosity units, i.e. low NPHI values represent limestone

Log symbol: NPHI, CN

y rogen n pore wa er, y rocar ons an s a es n quar z, e spars ancarbonates


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Correlation Logs

Gamma Ray Log A well log of the natural

formation radioactivity level

The log mainly reflects claycontent because clay

con a ns e ra oac ve

isotopes of K, U and Th

with the SP-log


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Correlation Logs

Spontaneous Potential Log

A record of Direct Current (DC)voltage (or Potential) that develops

moveable electrode in the well anda fixed electrode located at the

Used to Correlation

Detect boundaries of permeable beds

Determine formation-water resistivity (Rw)

Determine the volume of shale in permeablee s

Detection of hydrocarbons by the suppression ofthe SP curve


GR-log

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SEISMIC INTERPRETATION

Reservoir Identification

Seismic Attributes

GEO4240

or summary

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Phase Polarity

Amplitude

Spatial Extent

Frequency

helping to identify HC e oc y

AVO


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Minimum Phase

RC+ RC-

Zero Phase

RC+ RC-


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Seismic Attributes

An attribute is a derivative of a basic seismic measurement e or zon an orma on a r u es ava a e see g. -1) are not independent of each other but simply differentways of presenting and studying a limited amount of basicinformation

That basic information is time, amplitude, frequency and

classification

Seismic attributes may be defined as all the information,

or by logical or experience based reasoning. (Taner, 1998)


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Seismic Attributes

Time-derived attributes provide structural information-information

Frequency-derived attributes are not yet well understood but there is-

stratigraphic and reservoir information Attenuation is not used today, but there is a possibility that in the futureit will ield information on ermeabilit

Most attributes are derived from the normal stacked and migrated data

volume but variations of basic measurements as a function of an le ofincidence (and hence source to receiver offset) provides a further sourceof information. The principal examples of these pre-stack attributes is

AVO


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Seismic Attributes


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Seismic Attributes


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Seismic Attributes

Time Slice!


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Property Modeling (or Reservoir Modeling)

It is better to have a model of uncertainty

an an us on o rea y

Andre Journel

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Introduction

Goal of Property modeling: Capture geology and build realistic property models

Goal of Reservoir modeling: Predicting rock properties at unsampled locations and forecasting the future

,

12002)

y use o eos a s cs


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Why create a realistic reservoir property model?

We are making big decisions based on limited data Maximize the usage of all information optimise production

Correct upscaling of logs and a proper facies interpretation

is important Reservoir properties are critical factors affecting production


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Geostatistics

Geostatistics is a branch of applied statistics that placesemp as s on: The geological context of the data

The spatial relationship between the data

Data measured with different volumetric support and precision

us ness ee : ma e e es poss e ec s on n e ace ouncertainty. Uncertainty exists because of our incomplete

knowled e of a dataset alwa s incom lete data . One ofthe biggest uncertainties is the numerical description of thesubsurface


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Examples of Geostatistics

Analysis of variables in space Samples located close to each other are probably more

similar than samples located far from each other

The spatial coordinates of the observed samples are builtinto the statistic formulas

Examples: Gold content in ore (ppm)

Reservoir sandstone bed thickness (meter/feet)


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Incorporate the Maximum Amount of Data

Well data Seismic data Production Outcrops Other geological studies

Integrated study Structure horizon, fault

Deterministic

information

Stratigraphic correlation

Facies images Framework

Statistical

information

Conceptual

information

e men o og ca mo e

Facies description

Connectivity

s ogram

Variogram

Correlation

Trend

Variation


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Sequential Approach to Property Modeling

1. Defining the geometry and stratigraphic layering of the reservoir interval to bemodeled Involves the development of a conceptual model for the major architecture and continuity of

facies, porosity and permeability witihin each layer

2. The facies rock types are modeled by either (1) cell-based or (2) object-based

3. The porosity is modeled on a by-facies basis before permeability because thereare more reliable porosity data available

4. The 3-D models of permeability are constrained to the porosity, facies andayer ng prev ous y es a s e

5. Multiple equally likely realizations are created by repeating the entire process Each realization is equally likely to be drawn; however, some realizations are more similar to

others, hence their class has higher probability6. These models are input to a simulator or visualized and used to aid in decision

making


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Tampen Spur

Introduction

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F

Location

B

H


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Facts

Discovery well: 33/12-1

Discovery Year: 1974

. . Total production of saleable products 04.2007: 633.786214 mill. Sm3 o.e.

Recoverable reserves:

3 .

Gas: 25.70 bill Sm3

NGL: 11.40 mill tonne

a o r r o uc on

35

40

45

50

10

15

20

25

30

Sm3

0

5

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

1993

1992

1991

1990

1989

1988

1987

1986

1985

1984

1983

1982

1981

1980

1979

Year

Oil [mill Sm3] Gas [bill Sm3] Sm3o.e. [mill] Water [mill Sm3]


NGL: Natural Gas Liquids, incl. propane, butane, pentane, hexane and heptane, but not methane and ethane

1 tonne NGL: 1.9 Sm3 o.e.

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Stratigraphy

10/14/2008 GEO4270 - Michel Heeremans47From: Evans et al, 2003, Millenium Atlas

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Cross Section


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GEO4270 Prospect Evaluation

IMPORTANT! PETREL is just a tool which helps you with your interpretation and

modeling

This exercise is meant for leanin reservoir identification reservoir

evaluation and reservoir modeling

The results depend completely on your own interpretationan e accuracy o e ava a e a a


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Important links

http://www.npd.no/English/Produkter+og+tjenester/Fakta+og+statistikk/fakta-start.htm (Norway Wells)

http://www.og.dti.gov.uk/information/wells.htm (UK Wells)


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References

Asquith, G. and Krygowski, D. (2004). Basic Well LogAnalysis

Brown, A. (2004). Interpretation of Three-Dimensional

Seismic Data

Deutsch, C. (2002). Geostatistical Reservoir Modeling

Evans, D. et al. (2003). Millenium Atlas

Schlumberger (2006). Petrel Seismic to Simulation Software

roper y o e ng ourse, v.


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