Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Evaluating top and fault seal

  | chapter = Evaluating top and fault seal

  | frompg  = 10-1

  | frompg  = 10-26

  | topg    = 10-94

  | topg    = 10-28

  | author  = Grant M. Skerlec

  | author  = Grant M. Skerlec

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch10/ch10.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch10/ch10.htm

==Importance of quantitative analysis==

==Importance of quantitative analysis==

Quantitative fault seal analysis lets us predict fault seal behavior. Fault seal behavior is rarely random. Once we understand the pattern of seal behavior in existing fields, we can risk seal behavior in untested prospects.

Quantitative fault seal analysis lets us predict [[fault seal behavior]]. Fault seal behavior is rarely random. Once we understand the pattern of seal behavior in existing fields, we can risk seal behavior in untested prospects.

==Method==

==Method==

The capacity of a fault to leak or seal hydrocarbons is largely controlled by the smear–gouge ratio (SGR). The SGR is an estimate of the composition of that portion of the fault zone through which leakage or seal must occur. We calculate the SGR by measuring the cumulative shale and sand that has moved past that zone. A fault cross-leaks or dip-leaks if the sand–shale ratio is high in the zone (high SGR). A fault cross-seals or dip-seals if the sand–shale ratio is low in the zone (low SGR).

The capacity of a fault to leak or seal hydrocarbons is largely controlled by the smear–gouge ratio (SGR). The SGR is an estimate of the composition of that portion of the fault zone through which leakage or seal must occur. We calculate the SGR by measuring the cumulative shale and sand that has moved past that zone. A fault cross-leaks or [[dip]]-leaks if the sand–shale ratio is high in the zone (high SGR). A fault cross-seals or dip-seals if the sand–shale ratio is low in the zone (low SGR).

Several other algorithms for estimating gouge composition exist.<ref name=ch10r7>Bouvier, J., D., Kaars-Sijpesteigen, C., H., Kluesner, D., F., Onyejekwe, C., C., Vander Pal, R., C., 1989, Three-dimensional [[seismic interpretation]] and fault sealing investigations, Nun River field, Nigeria: AAPG Bulletin, vol. 73, no. 11, p. 1397–1414.</ref><ref name=ch10r3>Allard, D., M., 1993, Fault leak controlled trap fill, rift basin examples (abs.), in Ebanks, J., Kaldi, J., Vavra, C., eds., Seals and Traps: A Multidisciplinary Approach: AAPG Hedberg conference, Crested Butte, Colorado, June 21–23.</ref><ref name=ch10r40>Jev, B., I., Kaars-Sijpesteign, C., H., Peters, M., P., A., M., Watts, N., W., Wilkie, J., T., 1993, Akaso field, Nigeria: use of integrated 3-D seismic, fault-slicing, clay smearing and RFT pressure data on fault trapping and dynamic leakage: AAPG Bulletin, vol. 77, no. 8, p. 1389–1404.</ref><ref name=ch10r32>Gibson, R., G., 1994, [http://archives.datapages.com/data/bulletns/1994-96/data/pg/0078/0009/1350/1372.htm Fault-zone seals in siliciclastic strata of the Columbus basin, offshore Trinidad]: AAPG Bulletin, vol. 78, no. 9, p. 1372–1385.</ref><ref name=ch10r97>Yielding, G., Freeman, B., Needham, D., T., 1997, Quantitative fault seal prediction: AAPG Bulletin, vol. 81, no. 6, p. 897–917.</ref> All have established a relationship between the actual seal behavior and inferred gouge composition.

Several other algorithms for estimating gouge composition exist.<ref name=ch10r7>Bouvier, J., D., Kaars-Sijpesteigen, C., H., Kluesner, D., F., Onyejekwe, C., C., Vander Pal, R., C., 1989, Three-dimensional [[seismic interpretation]] and fault sealing investigations, Nun River field, Nigeria: AAPG Bulletin, vol. 73, no. 11, p. 1397–1414.</ref><ref name=ch10r3>Allard, D., M., 1993, Fault leak controlled trap fill, rift basin examples (abs.), in Ebanks, J., Kaldi, J., Vavra, C., eds., Seals and Traps: A Multidisciplinary Approach: AAPG Hedberg conference, Crested Butte, Colorado, June 21–23.</ref><ref name=ch10r40>Jev, B., I., Kaars-Sijpesteign, C., H., Peters, M., P., A., M., Watts, N., W., Wilkie, J., T., 1993, Akaso field, Nigeria: use of integrated 3-D seismic, fault-slicing, clay smearing and RFT pressure data on fault trapping and dynamic leakage: AAPG Bulletin, vol. 77, no. 8, p. 1389–1404.</ref><ref name=ch10r32>Gibson, R., G., 1994, [http://archives.datapages.com/data/bulletns/1994-96/data/pg/0078/0009/1350/1372.htm Fault-zone seals in siliciclastic strata of the Columbus basin, offshore Trinidad]: AAPG Bulletin, vol. 78, no. 9, p. 1372–1385.</ref><ref name=ch10r97>Yielding, G., Freeman, B., Needham, D., T., 1997, Quantitative fault seal prediction: AAPG Bulletin, vol. 81, no. 6, p. 897–917.</ref> All have established a relationship between the actual seal behavior and inferred gouge composition.

==Procedure==

==Procedure==

The following table outlines the procedure for quantitative fault seal analysis.

The following list outlines the procedure for quantitative fault seal analysis.

# Analyze logs to block out sands and shales.

# Calculate the SGR.

# Determine the SGR threshold for seal/leak.

| Analyze logs to block out sands and shales.

| Calculate the SGR.

| Determine the SGR threshold for seal/leak.

==Step 1: Analyze logs==

==Step 1: Analyze logs==

==Determine SGR threshold==

==Determine SGR threshold==

[[file:evaluating-top-and-fault-seal_fig10-25.png|300px|thumb|{{figure number|4}}See text for explanation.]]

[[file:evaluating-top-and-fault-seal_fig10-25.png|300px|thumb|{{figure number|4}}SGR threshold plot for the U.S. Gulf Coast.]]

The SGR threshold for a basin is defined by determining the SGR for known sealing and leaking faults in producing fields. The empirical threshold can then be used to assess prospects and plays and well as develop fields. SGR thresholds vary among basins.

The SGR threshold for a basin is defined by determining the SGR for known sealing and leaking faults in producing fields. The empirical threshold can then be used to assess prospects and plays and well as develop fields. SGR thresholds vary among basins.

==See also==

==See also==

* [[How fault zones affect seal]]

* [[How fault zones affect seal]]

* [[Limitations of quantitative fault seal analysis]]

* [[Limitations of quantitative fault seal analysis]]

==References==

==References==

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Evaluating top and fault seal]]

[[Category:Evaluating top and fault seal]]