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→Subseismic faults
The first part of the method involves making an estimate of the number of subseismic faults by extrapolating from statistics on the length versus frequency of known seismic faults into the subseismic region. Fractal analysis has been used on the assumption that fault-size populations approximate to fractal distributions.<ref name=Gauthierandlake_1993>Gauthier, B. D. M., and S. D. Lake, 1993, [http://archives.datapages.com/data/bulletns/1992-93/data/pg/0077/0005/0750/0761.htm Probabilistic modeling of faults below the limit of seismic resolution in Pelican field, North Sea, offshore United Kingdom]: AAPG Bulletin, v. 77, no. 5, p. 761–777.</ref> Statistics are also compiled on fault orientations, length to throw ratios, and fault densities per square kilometer. A further step is to determine those areas of the field where subseismic faults are more likely to be present than elsewhere. One method is to predict the paleostrain regime of the reservoir at the time of faulting.<ref name=Maertenetal_2006>Maerten, L., P. Gillespie, and J.-M. Daniel, 2006, [http://archives.datapages.com/data/bulletns/2006/09sep/BLTN05148/BLTN05148.HTM Three-dimensional geomechanical modeling for constraint of subseismic fault simulation]: AAPG Bulletin, v. 90, no. 9, p. 1337–1358.</ref> On this basis, a model will be made, which will include both the seismic and subseismic faults. Fault seal analysis can be applied to the subseismic faults in the model to determine whether they are sealing or not.
The first part of the method involves making an estimate of the number of subseismic faults by extrapolating from statistics on the length versus frequency of known seismic faults into the subseismic region. Fractal analysis has been used on the assumption that fault-size populations approximate to fractal distributions.<ref name=Gauthierandlake_1993>Gauthier, B. D. M., and S. D. Lake, 1993, [http://archives.datapages.com/data/bulletns/1992-93/data/pg/0077/0005/0750/0761.htm Probabilistic modeling of faults below the limit of seismic resolution in Pelican field, North Sea, offshore United Kingdom]: AAPG Bulletin, v. 77, no. 5, p. 761–777.</ref> Statistics are also compiled on fault orientations, length to throw ratios, and fault densities per square kilometer. A further step is to determine those areas of the field where subseismic faults are more likely to be present than elsewhere. One method is to predict the paleostrain regime of the reservoir at the time of faulting.<ref name=Maertenetal_2006>Maerten, L., P. Gillespie, and J.-M. Daniel, 2006, [http://archives.datapages.com/data/bulletns/2006/09sep/BLTN05148/BLTN05148.HTM Three-dimensional geomechanical modeling for constraint of subseismic fault simulation]: AAPG Bulletin, v. 90, no. 9, p. 1337–1358.</ref> On this basis, a model will be made, which will include both the seismic and subseismic faults. Fault seal analysis can be applied to the subseismic faults in the model to determine whether they are sealing or not.
General experience with inserting subseismic faults into simulation models is that they will influence the flow behavior.<ref name=Damslethetal_1998>Damsleth, E., V. Sangolt, and G. Aamodt, 1998, Sub-seismic faults can seriously affect fluid flow in the Njord field off western Norway—A stochastic fault modeling case study: Presented at the 1998 Society of Petroleum Engineers Annual Technical Conference and Exhibition, September 27–30, 1998, New Orleans, [https://www.onepetro.org/conference-paper/SPE-49024-MS SPE Paper 49024], 49 p.</ref> <ref name=Englandandtownsend_1998>England, W. A., and C. Townsend, 1998, The effects of faulting on production from a shallow marine reservoir: Presented at the 1998 Society of Petroleum Engineers Annual Technical Conference and Exhibition, September 27–30, 1998, New Orleans, [https://www.onepetro.org/conference-paper/SPE-49023-MS SPE Paper 49023], 16 p.</ref> <ref name=Ottesenetal_2005>Ottesen, S., C. Townsend, and K. M. Overland, 2005, [http://archives.datapages.com/data/specpubs/hedberg2/chapter09/CHAPTER09.HTM Investigating the effect of varying fault geometry and transmissibility on recovery: Using a new workflow for structural uncertainty modeling in a clastic reservoir], in P. Boult and J. Kaldi, eds., Evaluating fault and cap rock seals: AAPG Hedberg Series 2, p. 125–136.</ref> The critical feature seems to be whether the faults are sealing or not. Sealing faults can create an open framework of short baffles, which helps to improve sweep. The baffles increase the tortuosity of the flood front and delay water breakthrough. A large number of sealing subseismic faults in a reservoir will, on the other hand, create numerous dead ends, which will reduce the sweep efficiency of a waterflood. Nonsealing subseismic faults form cross-fault juxtapositions, which can improve vertical connectivity and enhance sweep.
General experience with inserting subseismic faults into simulation models is that they will influence the flow behavior.<ref name=Damslethetal_1998>Damsleth, E., V. Sangolt, and G. Aamodt, 1998, Sub-seismic faults can seriously affect fluid flow in the Njord field off western Norway—A stochastic fault modeling case study: Presented at the 1998 Society of Petroleum Engineers Annual Technical Conference and Exhibition, September 27–30, 1998, New Orleans, [https://www.onepetro.org/conference-paper/SPE-49024-MS SPE Paper 49024], 49 p.</ref> <ref name=Englandandtownsend_1998>England, W. A., and C. Townsend, 1998, The effects of faulting on production from a shallow marine reservoir: Presented at the 1998 Society of Petroleum Engineers Annual Technical Conference and Exhibition, September 27–30, 1998, New Orleans, [https://www.onepetro.org/conference-paper/SPE-49023-MS SPE Paper 49023], 16 p.</ref> <ref name=Ottesenetal_2005>Ottesen, S., C. Townsend, and K. M. Overland, 2005, [http://archives.datapages.com/data/specpubs/hedberg2/chapter09/CHAPTER09.HTM Investigating the effect of varying fault geometry and transmissibility on recovery: Using a new workflow for structural uncertainty modeling in a clastic reservoir], in P. Boult and J. Kaldi, eds., Evaluating fault and cap rock seals: [http://store.aapg.org/detail.aspx?id=941 AAPG Hedberg Series 2], p. 125–136.</ref> The critical feature seems to be whether the faults are sealing or not. Sealing faults can create an open framework of short baffles, which helps to improve sweep. The baffles increase the tortuosity of the flood front and delay water breakthrough. A large number of sealing subseismic faults in a reservoir will, on the other hand, create numerous dead ends, which will reduce the sweep efficiency of a waterflood. Nonsealing subseismic faults form cross-fault juxtapositions, which can improve vertical connectivity and enhance sweep.
[[file:M91Ch13FG94.JPG|thumb|300px|{{figure number|16}}Reservoir intervals thicken markedly across growth faults. They are common in areas with thick delta sequences and mobile substrates such as shale or salt. This example is from Upper Triassic deltaic sediments exposed in the coastal cliffs of Svalbard (from Edwards<ref name=Edwards_1976>Edwards, M. B., 1976, [http://archives.datapages.com/data/bulletns/1974-76/data/pg/0060/0003/0300/0341.htm Growth faults in upper Triassic deltaic sediments, Svalbard]: AAPG Bulletin, v. 60, no. 3, p. 341–355.</ref>).]]
[[file:M91Ch13FG94.JPG|thumb|300px|{{figure number|16}}Reservoir intervals thicken markedly across growth faults. They are common in areas with thick delta sequences and mobile substrates such as shale or salt. This example is from Upper Triassic deltaic sediments exposed in the coastal cliffs of Svalbard (from Edwards<ref name=Edwards_1976>Edwards, M. B., 1976, [http://archives.datapages.com/data/bulletns/1974-76/data/pg/0060/0003/0300/0341.htm Growth faults in upper Triassic deltaic sediments, Svalbard]: AAPG Bulletin, v. 60, no. 3, p. 341–355.</ref>).]]