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Volume calculation

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Volume calculation

  1. 1. Prospect Evaluation Alfred Kjemperud The Bridge Group AS 1
  2. 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. 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. 4. The volumetric equationSTOIIP = 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 oilRecoverable gas= GIIP * Recovery Factor for gas From GeoKnowledge 4
  5. 5. HCPV• Hydrocarbon Pore Volume HCPV = GRV * Net/Gross Ratio * Porosity * HC saturation 5
  6. 6. Finding the Volume• Interpretation and mapping – Seismic – Digitizing and mapping – Depth Conversion• Geometric description – Vertical closure – Spillpoint realtions – Trap fill – Uncertainties 6
  7. 7. The Trap 7
  8. 8. The trap Rock Volume top surface vertical closure spill pointHC-contact bottom surface A A’ 8
  9. 9. The mapsA bottom surface map is not required, when: - the reservoir thickness > vertical closure - the reservoir thickness is constant 9
  10. 10. Volume vs. DepthDepth Top map HC water contact Bottom map Volume 10
  11. 11. Area/depth graph Culmination -1900 -2200 Gross Rock VolumeDepth -2500 = Area under Graph -2700 Spill Point 10 25 50 Area (sg km) 200 Structural contours Modified from Geoknowledge a.s. 11
  12. 12. Anticline Geometry Corrections (assume no internal seals) a ClosureReservoir 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. 13. Geometry multiplier 13
  14. 14. Reservoir Parameters 1• Gross thickness (from mapping)• Net pay• Porosity• Permeability• HC satuartion 14
  15. 15. Reservoir Parametrs 2• Formation volume factor oil (Bo)• Formation volume factor gas (Bg)• Gas deviation factor (Z) 15
  16. 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. 17. ExerciseVolume 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 2km10km 1m3 = 6.29 barrels 17
  18. 18. Volume calculation -Length Solution 10000 mWith 2000 mHight 100 mGeometric Factor 0.45GRV 900000000 m3 5661 MMbblN/G 50% 100mNRV 450000000 m3 2831 MMbblPorosity 20%So 70%HCPV 63000000 m3 396.3 MMbbl 2kmBo 1.3STOIIP 48461538 m3 304.8 MMbbl 10kmRF 30%Recoverable resources 14538462 m3 91.4 MMbblm3 - MMbbl 6.29/1000000 18

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