Changes

==Fault seal prediction==

==Fault seal prediction==

Where sealing faults are a key element controlling the fluid flow in a reservoir, they should be characterized for reservoir description and modeling.<ref name=Fisherandjolley_2007>Fisher, Q. J., and S. J. Jolley, 2007, Treatment of faults in production simulation models, in S. J. Jolley, D. Barr, J. J. Walsh, and R. J. Knipe, eds., Structurally complex reservoirs: Geological Society (London) Special Publication 292, p. 219–233.</ref> Much of the research to date has come about because of the particular importance of understanding fault behavior in deltaic reservoirs. In deltas deposited over thick and unstable mobile shale intervals, synsedimentary faults are a major element controlling reservoir continuity and size. The faults cut relatively unlithified sediments where the potential for clay smear along the fault planes is high and potentially predictable.

Where sealing faults are a key element controlling the fluid flow in a reservoir, they should be characterized for reservoir description and modeling.<ref name=Fisherandjolley_2007>Fisher, Q. J., and S. J. Jolley, 2007, Treatment of faults in production simulation models, in S. J. Jolley, D. Barr, J. J. Walsh, and R. J. Knipe, eds., Structurally complex reservoirs: Geological Society (London) Special Publication 292, p. 219–233.</ref> Much of the research to date has come about because of the particular importance of understanding fault behavior in deltaic reservoirs. In deltas deposited over thick and unstable mobile shale intervals, synsedimentary faults are a major element controlling reservoir continuity and size. The faults cut relatively unlithified sediments where the potential for clay smear along the fault planes is high and potentially predictable.

Algorithms are available for predicting the clay smear and shale gouge sealing potential of a fault. The basis for these algorithms is that the chances for clay smear to cause fault seal is controlled by the number and thickness of the shale beds displaced past a particular point on the fault. The thickness of the clay smear within the fault plane will decrease with distance from the source beds and with increasing throw of the fault.<ref name=Yieldingetal_1997>Yielding, G., B. Freeman, and D. T. Needham, 1997, [http://archives.datapages.com/data/bulletns/1997/06jun/0897/0897.htm Quantitative fault seal prediction]: AAPG Bulletin, v. 81, no. 6, p. 897–917.</ref> The method involves taking the sand and shale distribution from a well close to the fault as a template for making the fault seal analysis.

Algorithms are available for predicting the clay smear and shale gouge sealing potential of a fault. The basis for these algorithms is that the chances for clay smear to cause fault seal is controlled by the number and thickness of the shale beds displaced past a particular point on the fault. The thickness of the clay smear within the fault plane will decrease with distance from the source beds and with increasing throw of the fault.<ref name=Yieldingetal_1997>Yielding, G., B. Freeman, and D. T. Needham, 1997, [http://archives.datapages.com/data/bulletns/1997/06jun/0897/0897.htm Quantitative fault seal prediction]: AAPG Bulletin, v. 81, no. 6, p. 897–917.</ref> The method involves taking the sand and shale distribution from a well close to the fault as a template for making the fault seal analysis.

The clay smear potential is calculated for a particular point on the fault plane as a function of the distance of that point from a shale bed acting as the source for the clay smear and the shale bed thickness<ref name=Bouvieretal_1989>Bouvier, J. D., C. H. Kaars-Sijpesteijn, D. F. Kluesner, C. C. Onyejekwe, and R. C. Van der Pal, 1989, [http://archives.datapages.com/data/bulletns/1988-89/data/pg/0073/0011/1350/1397.htm Three-dimensional seismic interpretation and fault sealing investigations, Nun River field, Nigeria]: AAPG Bulletin, v. 73, p. 1397–1414.</ref> <ref name=Fulljamesetal_1996>Fulljames, J. R., L. J. J. Zijerveld, and R. C. M. W. Fransen, 1997, Fault seal processes: Systematic analysis of fault seals over geological and production time scales, in P. Moller-Petersen and A. G. Koestler, eds., Hydrocarbon seals, importance for exploration and production: Norwegian Petroleum Society Special Publication 7, p. 51–79.</ref> ([[:file:M91Ch13FG90.JPG|Figure 12]]).

The clay smear potential is calculated for a particular point on the fault plane as a function of the distance of that point from a shale bed acting as the source for the clay smear and the shale bed thickness<ref name=Bouvieretal_1989>Bouvier, J. D., C. H. Kaars-Sijpesteijn, D. F. Kluesner, C. C. Onyejekwe, and R. C. Van der Pal, 1989, [http://archives.datapages.com/data/bulletns/1988-89/data/pg/0073/0011/1350/1397.htm Three-dimensional seismic interpretation and fault sealing investigations, Nun River field, Nigeria]: AAPG Bulletin, v. 73, p. 1397–1414.</ref> <ref name=Fulljamesetal_1996>Fulljames, J. R., L. J. J. Zijerveld, and R. C. M. W. Fransen, 1997, Fault seal processes: Systematic analysis of fault seals over geological and production time scales, in P. Moller-Petersen and A. G. Koestler, eds., Hydrocarbon seals, importance for exploration and production: Norwegian Petroleum Society Special Publication 7, p. 51–79.</ref> ([[:file:M91Ch13FG90.JPG|Figure 12]]).

Gibson<ref name=Gibson_1994>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, v. 78, no. 9, p. 1372–1385.</ref> provided a case history for fault seal analysis from the Columbus Basin, offshore Trinidad. Oil and gas fields occur in upper Miocene to Pleistocene deltaic sandstones of the Columbus Basin, located offshore to the southeast of the island of Trinidad. Numerous small faults dissect these reservoirs, and fault seal appears to be a critical feature controlling the size of these petroleum pools. Allan diagrams show that juxtaposition sealing is insufficient to explain the fault control on fluid contacts.

Gibson<ref name=Gibson_1994>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, v. 78, no. 9, p. 1372–1385.</ref> provided a case history for fault seal analysis from the Columbus Basin, offshore Trinidad. Oil and gas fields occur in upper Miocene to Pleistocene deltaic sandstones of the Columbus Basin, located offshore to the southeast of the island of Trinidad. Numerous small faults dissect these reservoirs, and fault seal appears to be a critical feature controlling the size of these petroleum pools. Allan diagrams show that juxtaposition sealing is insufficient to explain the fault control on fluid contacts.

The sediments that form the reservoirs offshore are also exposed onshore along the east coast of Trinidad. Outcrops onshore and cores offshore provide control on the nature of the fault rock. In these outcrops, shale smears are found where shale beds have been displaced along the fault. The shale smears range in thickness from millimeter- to centimeter-thick shale partings to complex zones up to several meters thick ([[:file:M91Ch13FG91.JPG|Figure 13]]).

The sediments that form the reservoirs offshore are also exposed onshore along the east coast of Trinidad. Outcrops onshore and cores offshore provide control on the nature of the fault rock. In these outcrops, shale smears are found where shale beds have been displaced along the fault. The shale smears range in thickness from millimeter- to centimeter-thick shale partings to complex zones up to several meters thick ([[:file:M91Ch13FG91.JPG|Figure 13]]).