The document provides information on prospect evaluation methodology for oil companies and governments. It discusses how prospect evaluation is used for resource assessment, contracting areas, work commitments, and investment decisions. The methodology includes volumetric and economic evaluations using seismic interpretation, mapping, cash flow analysis, and other factors. Equations and parameters involved in calculating the volumes of oil and gas in-place are also presented, such as pore volume, recovery factors, and formation properties. An example calculation of recoverable oil resources is included to demonstrate the process.

1. Prospect Evaluation
Alfred Kjemperud
The Bridge Group AS
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2. Purpose of Prospect
Evaluation
• 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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3. 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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4. The volumetric equation
STOIIP = GRV * Net/Gross Ratio * Porosity * oil
saturation * (1/Bo)
GIIP = GRV * Net/Gross Ratio * Porosity * gas
saturation * (1/Bg)
pore fluid
rock matrix
(frame, skeleton)
Recoverable oil= STOIIP * Recovery Factor for oil
Recoverable gas= GIIP * Recovery Factor for gas
From GeoKnowledge
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5. HCPV
• Hydrocarbon Pore Volume
HCPV = GRV * Net/Gross Ratio *
Porosity * HC saturation
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6. 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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7. The Trap
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8. The trap
Rock Volume
top surface
vertical
closure spill point
HC-contact
bottom surface
A A’
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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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10. Volume vs. Depth
Depth
Top map
HC water contact
Bottom map
Volume
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11. Area/depth graph
Culmination
-1900
-2200
Gross Rock Volume
Depth -2500 = Area under Graph
-2700
Spill Point
10 25 50 Area (sg km) 200
Structural
contours
Modified from Geoknowledge a.s.
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12. Anticline Geometry Corrections
(assume no internal seals)
a
Closure
Reservoir height (h)
thickness b
(a,b,c)
c
OWC/GWC
Spill point closure
a/h<<1 Large geometric multiplier
b/h = 1 Small geometric multiplier
c/h > 1 Small geometric multiplier
PhilPRA/Akj
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13. Geometry multiplier
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14. Reservoir Parameters 1
• Gross thickness (from mapping)
• Net pay
• Porosity
• Permeability
• HC satuartion
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15. Reservoir Parametrs 2
• Formation volume factor oil (Bo)
• Formation volume factor gas (Bg)
• Gas deviation factor (Z)
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16. 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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17. Exercise
Volume calculations
Length 10000 m
With 2000 m
Hight 100 m
100m Geometric Factor
Porosity 20%
So 70%
N/G 50%
RF 30%
Bo 1.3
2km
10km
1m3 = 6.29 barrels
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18. Volume calculation -
Length
Solution
10000 m
With 2000 m
Hight 100 m
Geometric Factor 0.45
GRV 900000000 m3 5661 MMbbl
N/G 50% 100m
NRV 450000000 m3 2831 MMbbl
Porosity 20%
So 70%
HCPV 63000000 m3 396.3 MMbbl
2km
Bo 1.3
STOIIP 48461538 m3 304.8 MMbbl 10km
RF 30%
Recoverable resources 14538462 m3 91.4 MMbbl
m3 - MMbbl 6.29/1000000
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