− | High pore pressure has fractured the top seal and lost hydrocarbons in several basins, including the North Sea<ref name=ch10r70>Skerlec, G., M., 1982, Risking top seals in the Central Graben: Exxon Production Research Company internal report.</ref><ref name=ch10r71>Skerlec, G., M., 1990, SEALS: A short course for risking top seal and fault seal: Franklin, Pennsylvania, SEALS International, 600 p.</ref><ref name=ch10r11>Caillet, G., 1993, The caprock of the Snorre field (Norway): a possible leakage by hydraulic fracturing: Marine and Petroleum Geology, vol. 10, no. 1, p. 42–50., 10., 1016/0264-8172(93)90098-D</ref><ref name=ch10r48>Leith, T., L., Kaarshad, I., Connan, J., Pierron, J., Caillet, G., 1993, Recognition of caprock leakage in the Snorre field, Norwegian North Sea: Marine and Petroleum Geology, vol. 10, no. 1, p. 29–41., 10., 1016/0264-8172(93)90097-C</ref> the Norwegian Sea<ref name=ch10r84>Ungerer, P., Burrus, J., Doligez, B., Chenet, P., Y., Bessis, F., 1990, [http://archives.datapages.com/data/bulletns/1990-91/data/pg/0074/0003/0000/0309.htm Basin evaluation by integrated two-dimensional modeling of heat transfer, fluid flow, hydrocarbon generation, and migration]: AAPG Bulletin, vol. 74, no. 3, p. 309–335.</ref> and the Malay basin.<ref name=ch10r66>Scharr, G., 1976, The occurrence of hydrocarbons in overpressured reservoirs of the Baram delta, offshore Sarawak, Malaysia: Fifth Annual Convention, Indonesian Petroleum Association, Proceedings, p. 163–169.</ref> The process is undoubtedly more widespread. Loss of top seal integrity due to natural hydraulic fracturing also appears to control the risk economics and vertical distribution of hydrocarbons in the Gulf Coast.<ref name=ch10r30>Fertl, W., H., Leach, W., G., 1988, Economics of hydrocarbon reserves in overpressured reservoirs below 18,000 feet in south Louisiana: SPE paper 18146, 16 p.</ref><ref name=ch10r46>Leach, W., G., 1993a, Fluid migration, HC concentration in south Louisiana Tertiary sands: Oil & Gas Journal, vol. 91, no. 11, p. 71–74.</ref><ref name=ch10r47>Leach, W., G., 1993b, Maximum hydrocarbon window determination in south Louisiana: Oil & Gas Journal, vol. 91, no. 13, p. 81–84.</ref> | + | High pore pressure has fractured the top seal and lost hydrocarbons in several basins, including the North Sea<ref name=ch10r70>Skerlec, G., M., 1982, Risking top seals in the Central Graben: Exxon Production Research Company internal report.</ref><ref name=ch10r71>Skerlec, G., M., 1990, SEALS: A short course for risking top seal and fault seal: Franklin, Pennsylvania, SEALS International, 600 p.</ref><ref name=ch10r11>Caillet, G., 1993, The caprock of the Snorre field (Norway): a possible leakage by hydraulic fracturing: Marine and Petroleum Geology, vol. 10, no. 1, p. 42–50, DOI: [http://www.sciencedirect.com/science/article/pii/026481729390098D 10.1016/0264-8172(93)90098-D].</ref><ref name=ch10r48>Leith, T., L., Kaarshad, I., Connan, J., Pierron, J., Caillet, G., 1993, Recognition of caprock leakage in the Snorre field, Norwegian North Sea: Marine and Petroleum Geology, vol. 10, no. 1, p. 29–41, DOI: [http://www.sciencedirect.com/science/article/pii/026481729390097C 10.1016/0264-8172(93)90097-C].</ref> the Norwegian Sea<ref name=ch10r84>Ungerer, P., Burrus, J., Doligez, B., Chenet, P., Y., Bessis, F., 1990, [http://archives.datapages.com/data/bulletns/1990-91/data/pg/0074/0003/0000/0309.htm Basin evaluation by integrated two-dimensional modeling of heat transfer, fluid flow, hydrocarbon generation, and migration]: AAPG Bulletin, vol. 74, no. 3, p. 309–335.</ref> and the Malay basin.<ref name=ch10r66>Scharr, G., 1976, The occurrence of hydrocarbons in overpressured reservoirs of the Baram delta, offshore Sarawak, Malaysia: Fifth Annual Convention, Indonesian Petroleum Association, Proceedings, p. 163–169.</ref> The process is undoubtedly more widespread. Loss of top seal integrity due to natural hydraulic fracturing also appears to control the risk economics and vertical distribution of hydrocarbons in the Gulf Coast.<ref name=ch10r30>Fertl, W., H., Leach, W., G., 1988, Economics of hydrocarbon reserves in overpressured reservoirs below 18,000 feet in south Louisiana: [https://www.onepetro.org/conference-paper/SPE-18146-MS SPE paper 18146], 16 p.</ref><ref name=ch10r46>Leach, W., G., 1993a, Fluid migration, HC concentration in south Louisiana Tertiary sands: Oil & Gas Journal, vol. 91, no. 11, p. 71–74.</ref><ref name=ch10r47>Leach, W., G., 1993b, Maximum hydrocarbon window determination in south Louisiana: Oil & Gas Journal, vol. 91, no. 13, p. 81–84.</ref> |
− | * α = poroelastic constant, assumed to be 1 in most analyses (see <ref name=ch10r25>Engelder, T., Lacazette, A., 1990, Natural hydraulic fracturing, in Barton, N., Stephansson, O., eds., Rock Joints: Rotterdam, A., A. Balkema, p. 35–43.</ref> | + | * α = poroelastic constant, assumed to be 1 in most analyses<ref name=ch10r25>Engelder, T., Lacazette, A., 1990, Natural hydraulic fracturing, in Barton, N., Stephansson, O., eds., Rock Joints: Rotterdam, A., A. Balkema, p. 35–43.</ref> |
− | | Calculate the ratio from leak-off tests. Take care since leak-off tests may report the pressure value either prior to or after the fracture pressure point ( <ref name=ch10r23>Eaton, B., A., 1969, Fracture gradient prediction and its application in oilfield operations: Trans. AIME, October, p. 1353–1360.</ref> ). Leak-off tests are also commonly taken where casing has been set and may reflect the mechanical properties of the cement casing rather than the wall rock. Alternatively, Poisson's ratio can be estimated from available laboratory data ( <ref name=ch10r45>Lama, R., D., Vutukuri, V., S., 1978, Handbook of Mechanical Properties of Rocks: Rockport, MA, Trans. Technical Publications.</ref> ). Poisson's ratio increases with depth to approach a maximum of 0.5. | + | | Calculate the ratio from leak-off tests. Take care since leak-off tests may report the pressure value either prior to or after the fracture pressure point.<ref name=ch10r23>Eaton, B., A., 1969, Fracture gradient prediction and its application in oilfield operations: Trans. AIME, October, p. 1353–1360.</ref> Leak-off tests are also commonly taken where casing has been set and may reflect the mechanical properties of the cement casing rather than the wall rock. Alternatively, Poisson's ratio can be estimated from available laboratory data.<ref name=ch10r45>Lama, R., D., Vutukuri, V., S., 1978, Handbook of Mechanical Properties of Rocks: Rockport, MA, Trans. Technical Publications.</ref> Poisson's ratio increases with depth to approach a maximum of 0.5. |
− | Variations on this equation as well as empirical relationships are common.<ref name=ch10r39 /><ref name=ch10r55>Matthews, W., R., Kelly, J., 1967, How to predict formation pressure and fracture gradient from electric and sonic logs: Oil & Gas Journal, vol. 65, no. 8, p. 92–106.</ref><ref name=ch10r23 /><ref name=ch10r8>Breckles, I., M., Van Eekelen, H., A., M., 1982, Relationship between horizontal stress and depth in sedimentary basins: Journal of Petroleum Technology, vol. 34, no. 9, p. 2191–2199., 10., 2118/10336-PA</ref><ref name=ch10r9>Brennan, R., M., Annis, M., R., 1984, A new fracture gradient prediction technique that shows good results in Gulf of Mexico abnormal pressure: SPE paper 13210, 6 p.</ref> An alternative method of determining the principal stresses and fracture gradient is through the use of borehole deformation.<ref name=ch10r4>Bell, J., S., 1990, Investigating stress regimes in sedimentary basins using information from oil industry wireline logs and drilling records, in Hurst, A., Lovell, M., A., Morton, A., C., eds., Geological Applications of Wireline Logs: Geological Society London Special Publication 48, p. 305–325.</ref><ref name=ch10r28>Evans, C., J., Brereton, N., R., 1990, In situ crustal stress in the United Kingdom from borehole breakouts, in Hurst, A., ed., Geological Applications of Wireline Logs: Geological society Special Publication 48, p. 327–338.</ref> | + | Variations on this equation as well as empirical relationships are common.<ref name=ch10r39 /><ref name=ch10r55>Matthews, W., R., Kelly, J., 1967, How to predict formation pressure and fracture gradient from electric and sonic logs: Oil & Gas Journal, vol. 65, no. 8, p. 92–106.</ref><ref name=ch10r23 /><ref name=ch10r8>Breckles, I., M., Van Eekelen, H., A., M., 1982, Relationship between horizontal stress and depth in sedimentary basins: Journal of Petroleum Technology, vol. 34, no. 9, p. 2191–2199, DOI: [https://www.onepetro.org/journal-paper/SPE-10336-PA 10.2118/10336-PA].</ref><ref name=ch10r9>Brennan, R., M., Annis, M., R., 1984, A new fracture gradient prediction technique that shows good results in Gulf of Mexico abnormal pressure: SPE paper 13210, 6 p.</ref> An alternative method of determining the principal stresses and fracture gradient is through the use of borehole deformation.<ref name=ch10r4>Bell, J., S., 1990, [http://sp.lyellcollection.org/content/48/1/305.abstract Investigating stress regimes in sedimentary basins using information from oil industry wireline logs and drilling records], in Hurst, A., Lovell, M., A., Morton, A., C., eds., Geological Applications of Wireline Logs: Geological Society London Special Publication 48, p. 305–325.</ref><ref name=ch10r28>Evans, C., J., Brereton, N., R., 1990, In situ crustal stress in the United Kingdom from borehole breakouts, in Hurst, A., ed., Geological Applications of Wireline Logs: Geological Society of London Special Publication 48, p. 327–338.</ref> |