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  = 10-44

  | topg    = 10-94

  | topg    = 10-44

  | 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

  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

}}

}}

Changes in pressure differentials across faults can change seal behavior. A [[Cross-sealing faults|cross-sealing fault]] is cross sealing to a finite column of [[hydrocarbon]]s. As the [[Buoyancy pressure|buoyant pressure]] increases at the crest of the [[hydrocarbon column]], the buoyant pressure will ultimately exceed the [[displacement pressure]] of the fault zone and the fault will [[Cross-leaking faults|cross-leak]].<ref name=ch10r76>Smith, D., A., 1966, [http://archives.datapages.com/data/bulletns/1965-67/data/pg/0050/0002/0350/0363.htm Theoretical considerations of sealing and non-sealing faults]: AAPG Bulletin, vol. 50, no. 2, p. 363–374.</ref><ref name=ch10r10>Buck, S., Robertson, G., 1996, Fault seal behavior at Beryl field, UK North Sea: observations from 20 years of production, drilling and injection data: AAPG Annual Meeting Abstracts, San Diego, May 19–22, p. A20.</ref>

Changes in pressure differentials across faults can change seal behavior. A [[cross-sealing fault]] is cross sealing to a finite column of [[hydrocarbon]]s. As the [[Buoyancy pressure|buoyant pressure]] increases at the crest of the [[hydrocarbon column]], the buoyant pressure will ultimately exceed the [[displacement pressure]] of the fault zone and the fault will [[Cross-leaking faults|cross-leak]].<ref name=ch10r76>Smith, D. A., 1966, [http://archives.datapages.com/data/bulletns/1965-67/data/pg/0050/0002/0350/0363.htm Theoretical considerations of sealing and non-sealing faults]: AAPG Bulletin, vol. 50, no. 2, p. 363–374.</ref><ref name=ch10r10>Buck, S., Robertson, G., 1996, Fault seal behavior at Beryl field, UK North Sea: observations from 20 years of production, drilling and injection data: AAPG Annual Meeting Abstracts, San Diego, May 19–22, p. A20.</ref>

==Pressure differentials and leakage==

==Pressure differentials and leakage==

[[file:evaluating-top-and-fault-seal_fig10-34.png|300px|thumb|{{figure number|1}}Pressure depletion curves for two wells separated by an initially cross-sealing fault.]]

[[file:evaluating-top-and-fault-seal_fig10-34.png|300px|thumb|{{figure number|1}}Pressure depletion curves for two wells separated by an initially cross-sealing fault.]]

[[:file:evaluating-top-and-fault-seal_fig10-34.png|Figure 1]] shows the pressure depletion curves for two wells separated by an initially cross-sealing fault. The pressure depletion curve for well A is shown in light gray (top); that for well B, in black (bottom). The buoyant pressure at the crest of the oil column against the fault seal in well A remains constant as the pressure in well B decreases. The pressure differential (AP) increases until the displacement pressure of the fault zone is exceeded and the fault begins to cross-leak. A fault in the Beryl field has broken down during production.<ref name=ch10r10 /> A fault in the Akaso field, Nigeria, may have undergone this type of breakdown with a differential pressure of [[pressure::4137 kPa]] (600 psi).<ref name=ch10r40>Jev, B., I., Kaars-Sijpesteign, C., H., Peters, M., P., A., M., Watts, N., W., Wilkie, J., T., 1993, [http://archives.datapages.com/data/bulletns/1992-93/data/pg/0077/0008/1350/1389.htm 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>

[[:file:evaluating-top-and-fault-seal_fig10-34.png|Figure 1]] shows the pressure depletion curves for two wells separated by an initially cross-sealing fault. The pressure depletion curve for well A is shown in light gray (top); that for well B, in black (bottom). The buoyant pressure at the crest of the oil column against the fault seal in well A remains constant as the pressure in well B decreases. The pressure differential (AP) increases until the displacement pressure of the fault zone is exceeded and the fault begins to cross-leak. A fault in the Beryl field has broken down during production.<ref name=ch10r10 /> A fault in the Akaso field, Nigeria, may have undergone this type of breakdown with a differential pressure of [[pressure::4137 kPa]] (600 psi).<ref name=ch10r40>Jev, B. I., C. H. Kaars-Sijpesteign, M. P. A. M. Peters, N. W. Watts, and J. T. Wilkie, 1993, [http://archives.datapages.com/data/bulletns/1992-93/data/pg/0077/0008/1350/1389.htm 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>

==See also==

==See also==

[[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]]