volume calculation
TRANSCRIPT
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Prospect Evaluation
Alfred KjemperudThe Bridge Group AS
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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
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Methodology
• Volumetric Evaluation–Seismic Interpretation–Mapping–Gross rock volume determination–Volume of liquid/gas at surface
• Economic Evaluation–Discounted cash flow analysis
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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
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HCPV
• Hydrocarbon Pore Volume
HCPV = GRV * Net/Gross Ratio * Porosity * HC saturation
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Finding the Volume
• Interpretation and mapping–Seismic–Digitizing and mapping–Depth Conversion
• Geometric description–Vertical closure–Spillpoint realtions–Trap fill–Uncertainties
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The Trap
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The trapRock Volume
bottom surface
spill point
top surfacevertical closure
HC-contact
A A’
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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
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Geometry multiplier
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Reservoir Parameters 1
• Gross thickness (from mapping)• Net pay• Porosity• Permeability• HC satuartion
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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%
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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