Formation evaluation and well log correlationSWAPNIL PAL

IMT GEOLOGICAL TECHNOLOGY

INDIAN INSTITUTE OF TEC HNOLOGY R OORKEE

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

Well logThe 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.

Basic Logs Tools and their Measurements

Gamma Ray log

Basic Logs Tools and their Measurements

Calliper log

Basic Logs Tools and their Measurements

Electrical log

Basic Logs Tools and their Measurements

Density log

Basic Logs Tools and their MeasurementsNeutron log

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.

Basic steps for quick look evaluation

ROCK

Reservoir

Non-Reservoir

Hydrocarbon bearing

Water bearing

Gas bearing

Oil bearing

Qualitative Interpretation

Identification of Reservoir or Non-reservoir

Low gamma ray(Reservoir rock)

Identification of hydrocarbon or water bearing zone

Qualitative Interpretation

Low gamma ray +High Resistivity value

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

Qualitative Interpretation

Gas bearing zone

Oil bearing zone

Water bearing zone

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.

Quantitative InterpretationEstimation of porosity

Quantitative InterpretationEstimation of porosity

Depth (m) Vsh PHID PHIdc PHIN PHInceffective (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

Quantitative InterpretationEstimation of porosity

Depth (m) Vsh PHID PHIdc PHIN PHInceffective (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

Quantitative InterpretationEstimation 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

Quantitative Interpretation

Estimation of hydrocarbon saturationCan 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

Quantitative Interpretation

Archie’s equation

Quantitative InterpretationCalculation of formation water resistivity : RwUsing 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

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

1930 1940 1950 1960 1970 1980 19900

0.2

0.4

0.6

0.8

1

1.2

Depth (m)

Sw: w

ater

satu

ratio

n

Qualitative Interpretation

Gas bearing zone

Oil bearing zone

Water bearing zone

1930 1940 1950 1960 1970 1980 19900

0.2

0.4

0.6

0.8

1

1.2

Depth (m)

Sw: w

ater

sat

urati

on

Hurray!Oil found!!

V/sQuantitative Interpretation

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).

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.

Thank you