Volume calculation

1

Prospect Evaluation

Alfred KjemperudThe Bridge Group AS

2

Purpose of ProspectEvaluation

• Government– Integral part of resource assessment– Basis for nomination of contract areas– Basis for contractor’s work commitment– Basis for evaluation of applications

• Oil company– Integral part of resource assessment– Basis for investment decision

3

Methodology

• Volumetric Evaluation–Seismic Interpretation–Mapping–Gross rock volume determination–Volume of liquid/gas at surface

• Economic Evaluation–Discounted cash flow analysis

4

The volumetric equationSTOIIP = GRV * Net/Gross Ratio * Porosity * oil

saturation * (1/Bo)GIIP = GRV * Net/Gross Ratio * Porosity * gas

saturation * (1/Bg)

Recoverable oil= STOIIP * Recovery Factor for oilRecoverable gas= GIIP * Recovery Factor for gas

rockrock matrixmatrix(frame, skeleton)(frame, skeleton)

pore fluidpore fluid

From GeoKnowledge

5

HCPV

• Hydrocarbon Pore Volume

HCPV = GRV * Net/Gross Ratio * Porosity * HC saturation

6

Finding the Volume

• Interpretation and mapping–Seismic–Digitizing and mapping–Depth Conversion

• Geometric description–Vertical closure–Spillpoint realtions–Trap fill–Uncertainties

7

The Trap

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The trapRock Volume

bottom surface

spill point

top surfacevertical closure

HC-contact

A A’

9

The maps

A bottom surface map is not required, when:- the reservoir thickness > vertical closure- the reservoir thickness is constant

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Volume vs. Depth

Top map

Bottom mapHC water contact

Depth

Volume

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Area/depth graph

Depth

Area (sg km)

Structural contours

Spill Point

Culmination

Gross Rock Volume

= Area under Graph

-2200

-2500

-2700

-1900

10 25 50 200

Modified from Geoknowledge a.s.

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Anticline Geometry Corrections(assume no internal seals)

a

bc

Closure height (h)Reservoir

thickness(a,b,c)

Spill point closureOWC/GWC

a/h<<1 Large geometric multiplier

b/h = 1 Small geometric multiplier

c/h > 1 Small geometric multiplier

PhilPRA/Akj

13

Geometry multiplier

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Reservoir Parameters 1

• Gross thickness (from mapping)• Net pay• Porosity• Permeability• HC satuartion

15

Reservoir Parametrs 2

• Formation volume factor oil (Bo)• Formation volume factor gas (Bg)• Gas deviation factor (Z)

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Recovery Factor

• Oil– Dependant on depletion mechanism

• Natural depletion– 5-15%

• Effective water drive– 15-30%

• Pressure maintenence methods– Up to 65%

• Gas– Up to 80-85%

17

ExerciseVolume calculations

10km

100m

2km

Length 10000 mWith 2000 mHight 100 mGeometric Factor

Porosity 20%So 70%

N/G 50%

RF 30%

Bo 1.3

1m3 = 6.29 barrels

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Volume calculation -Solution

Length 10000 mWith 2000 mHight 100 mGeometric Factor 0.45GRV 900000000 m3 5661 MMbbl

N/G 50%NRV 450000000 m3 2831 MMbbl

Porosity 20%So 70%

HCPV 63000000 m3 396.3 MMbbl

Bo 1.3

STOIIP 48461538 m3 304.8 MMbbl

RF 30%

Recoverable resources 14538462 m3 91.4 MMbbl

m3 - MMbbl 6.29/1000000

10km

100m

2km