Formation evaluation and well log correlation

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A qualitative and quantitative assessment of the reservoir using well logs

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Formation evaluation and well log correlation

  1. 1. Formation evaluation and well log correlation SWAPNIL PAL IMT GEOLOGICAL TECHNOLOGY INDIAN INSTITUTE OF TECHNOLOGY ROORKEE
  2. 2. Overview Well log definition and its importance Fundamentals of qualitative and quantitative log interpretation Formation evaluation with well logs Processing and interpretation of well log data Conclusion
  3. 3. Well log The continuous recording of a geophysical parameter along a borehole produces a geophysical well log. The value of the measurement is plotted continuously against depth in the well.
  4. 4. Basic Logs Tools and their Measurements Gamma Ray log
  5. 5. Basic Logs Tools and their Measurements Calliper log
  6. 6. Basic Logs Tools and their Measurements Electrical log
  7. 7. Basic Logs Tools and their Measurements Density log
  8. 8. Basic Logs Tools and their Measurements Neutron log
  9. 9. Petrophysical Interpretation Qualitative assessment Quantitative assessment Assessment of reservoir properties, fluid type form log pattern. Numerical estimation of reservoir properties viz. % of oil, water etc.
  10. 10. Basic steps for quick look evaluation ROCK Reservoir Non-Reservoir Hydrocarbon bearing Water bearing Gas bearing Oil bearing
  11. 11. Qualitative Interpretation Identification of Reservoir or Non-reservoir Low gamma ray (Reservoir rock)
  12. 12. Identification of hydrocarbon or water bearing zone Qualitative Interpretation Low gamma ray + High Resistivity value
  13. 13. Qualitative Interpretation Low gamma ray + High Resistivity value + Large deviation in RHOB and NPHI value (cross-over region) Identification of oil or gas bearing zone
  14. 14. Qualitative Interpretation Gas bearing zone Oil bearing zone Water bearing zone
  15. 15. Quantitative Interpretation  Estimation of effective porosity & permeability.  Estimation of volume of clay fraction.  Estimation of hydrocarbon saturation.  Determination of the depth and thickness of net pay.  Estimation of reserves of hydrocarbon.
  16. 16. Quantitative Interpretation Estimation of porosity
  17. 17. Quantitative Interpretation Estimation of porosity Depth (m) Vsh PHID PHIdc PHIN PHInc effective (Gas) 1940 0.710526 0.278788 0.106539 0.46 0.175789 0.145349 1945 0.078947 0.418182 0.399043 0.09 0.058421 0.285174 1948 0.052632 0.381818 0.369059 0.07 0.048947 0.263249 1950 0.039474 0.424242 0.414673 0.06 0.044211 0.29488 1953 0.039474 0.484848 0.475279 0.14 0.124211 0.34736 1957 0.697368 0.327273 0.158214 0.33 0.051053 0.117554 1958 0.644737 0.266667 0.110367 0.41 0.152105 0.132885 gas bearing zone
  18. 18. Quantitative Interpretation Estimation of porosity Depth (m) Vsh PHID PHIdc PHIN PHInc effective (Gas) 1970 0.657895 0.236364 0.076874 0.36 0.096842 0.086858 1972 0.644737 0.218182 0.061882 0.325 0.067105 0.064494 1974 0.118421 0.272727 0.244019 0.19 0.142632 0.193325 1976 0.460526 0.272727 0.161085 0.34 0.155789 0.158437 1978 0.276316 0.254545 0.18756 0.22 0.109474 0.148517 1980 0.434211 0.272727 0.167464 0.275 0.101316 0.13439 1982 0.263158 0.284848 0.221053 0.24 0.134737 0.177895 1984 0.723684 0.254545 0.079107 0.43 0.140526 0.109817 oil bearing zone
  19. 19. Quantitative Interpretation Estimation of porosity Depth (m) Vsh PHID PHIdc 2025 0.236842 0.278788 0.212759 2028 0.565789 0.230303 0.1 2029 0.328947 0.212121 0.142344 2030 0.276316 0.260606 0.188596 2031 0.342105 0.242424 0.15949 2034 0.394737 0.278788 0.16874 2035 0.223684 0.260606 0.202313 2036 0.223684 0.260606 0.202313 2037 0.197368 0.236364 0.189713 water bearing zone
  20. 20. Quantitative Interpretation Estimation of hydrocarbon saturation Can not be measured directly but inferred from determination of WATER SATURATION (Sw) from RESISTIVITY and POROSITY logs. • Sw – Fraction of pore space occupied by water. • Sh – Fraction of pore space occupied by hydrocarbon. Sh + Sw = 1 Oil Water
  21. 21. Quantitative Interpretation Archie’s equation
  22. 22. Quantitative Interpretation Calculation of formation water resistivity : Rw Using Inverse Archie’s equation Rt 0.95 0.7 0.1 0.8 0.9 0.7 0.7 0.7 0.85 Rw 0.073837 0.037128 0.0045 0.054332 0.052893 0.054406 0.047541 0.047541 0.047488 Depth 2025 2028 2029 2030 2031 2034 2035 2036 2037 Water bearing zone Rw= 0.05, this is used in Archie’s equation to calculate water saturation in oil and gas bearing zone
  23. 23. Quantitative Interpretation Depth 1940 1945 1948 1950 1953 1957 1958 1970 1972 1974 1976 1978 1980 1982 1984 PHId 0.278788 0.418182 0.381818 0.424242 0.484848 0.327273 0.266667 0.236364 0.212121 0.272727 0.272727 0.254545 0.272727 0.290909 0.254545 Rt 0.65 15 35 48 33 0.9 0.85 1 1.5 2 4 2.9 3 1.2 0.8 Sw (Archie) 0.994843 0.138062 0.098991 0.076076 0.080283 0.720201 0.909509 0.946029 0.860707 0.579751 0.409946 0.515847 0.473365 0.701677 0.982143 Calculation of water saturation in oil and gas zones 0 0.2 0.4 0.6 0.8 1 1.2 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 Sw:watersaturation Depth (m)
  24. 24. Qualitative Interpretation Gas bearing zone Oil bearing zone Water bearing zone 0 0.2 0.4 0.6 0.8 1 1.2 1930 1940 1950 1960 1970 1980 1990 Sw:watersaturation Depth (m) Hurray! Oil found!! V/s Quantitative Interpretation
  25. 25. Conclusion Well logs contains key information about the formation drilled in different petro-physical measurements. i.e.  Prospective zones of hydrocarbon.  Reservoir type and thickness.  Estimation of Porosity, permeability.  Fluid type present in the pores and saturation level. To economically establish the existence of producible hydrocarbon reservoirs (oil & gas).
  26. 26. References Archie II: Electrical conduction in hydrocarbon bearing zone. (n.d.). In Rock Physics (Vol. 36). Archie III: Electrical conduction in shaly sand. (n.d.). In Rock Physics (Vol. 1). Archie's law: Electrical conduction in clean, water bearing rock. (n.d.). In Rock physics/History (Vol. 36). Halliburton. (n.d.). Log Interpretation Charts. M H Rider. (1991). The Geological Interpretation of well logs. Glasgow: Whittes Publishing. (1989). Open hole well logging Interpretation. Texas: Schlumberger Wireline & Testing. Serra, O. (1984). Fundamentals of well log interpretation. Amsterdam: Elsevier.
  27. 27. Thank you

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