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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