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Volume calculation
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.
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Volume calculation
- 1. Prospect Evaluation Alfred Kjemperud The Bridge Group AS 1
- 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 2
- 3. Methodology • Volumetric Evaluation – Seismic Interpretation – Mapping – Gross rock volume determination – Volume of liquid/gas at surface • Economic Evaluation – Discounted cash flow analysis 3
- 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 4
- 5. HCPV • Hydrocarbon PoreVolume HCPV = GRV * Net/Gross Ratio * Porosity * HC saturation 5
- 6. Finding the Volume •Interpretation and mapping – Seismic – Digitizing and mapping – Depth Conversion • Geometric description – Vertical closure – Spillpoint realtions – Trap fill – Uncertainties 6
- 7. The Trap 7
- 8. The trap Rock Volume top surface vertical closure spill point HC-contact bottom surface A A’ 8
- 9. The maps A bottomsurface map is not required, when: - the reservoir thickness > vertical closure - the reservoir thickness is constant 9
- 10. Volume vs. Depth Depth Top map HC water contact Bottom map Volume 10
- 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. 11
- 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 12
- 13.
- 14. Reservoir Parameters 1 •Gross thickness (from mapping) • Net pay • Porosity • Permeability • HC satuartion 14
- 15. Reservoir Parametrs 2 •Formation volume factor oil (Bo) • Formation volume factor gas (Bg) • Gas deviation factor (Z) 15
- 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% 16
- 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 17
- 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 18