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Offshore, hydrocarbon columns up to 200 m (656 ft) thick are found within compartments interpreted as being sealed by clay smears along faults. The general observation is that the blanket of clay smear along faults only appears to be continuous and effective where the shale content of the displaced section exceeds 25%. The shale smear factor was estimated for faults from two of the fields in the basin. SSF values of between 1 and 4 were found for faults with throws more than 150 m (492 ft) that sealed the longest hydrocarbon columns. It was concluded that faults in this area could be modeled as sealing along their length provided the SSF did not exceed a value of 4.

Offshore, hydrocarbon columns up to 200 m (656 ft) thick are found within compartments interpreted as being sealed by clay smears along faults. The general observation is that the blanket of clay smear along faults only appears to be continuous and effective where the shale content of the displaced section exceeds 25%. The shale smear factor was estimated for faults from two of the fields in the basin. SSF values of between 1 and 4 were found for faults with throws more than 150 m (492 ft) that sealed the longest hydrocarbon columns. It was concluded that faults in this area could be modeled as sealing along their length provided the SSF did not exceed a value of 4.

[[file:M91Ch13FG92.JPG|thumb|300px|{{figure number|14}}Comparison between (a) depth-converted seismic interpretation from the Gullfaks field, Norwegian North Sea, and (b) a plaster model deformed by plane strain extension. The plaster model shows that many small-scale faults are expected to exist in the Gullfaks structure but are below seismic resolution (from Fossen and Hesthammer<ref name=Fossenandhesthammer_1998>Fossen, H., and J. Hesthammer, 1998, Structural geology of the Gullfaks field, northern North Sea, in M. P. Coward, H. Johnson, and T. S. Daltaban, eds., Structural geology in reservoir characterization: Geological Society Special Publication 127, p. 231–261.</ref>). Reprinted with permission from the Geological Society of London.]]

M91Ch13FG92.JPG|{{figure number|14}}Comparison between (a) depth-converted seismic interpretation from the Gullfaks field, Norwegian North Sea, and (b) a plaster model deformed by plane strain extension. The plaster model shows that many small-scale faults are expected to exist in the Gullfaks structure but are below seismic resolution (from Fossen and Hesthammer<ref name=Fossenandhesthammer_1998>Fossen, H., and J. Hesthammer, 1998, Structural geology of the Gullfaks field, northern North Sea, in M. P. Coward, H. Johnson, and T. S. Daltaban, eds., Structural geology in reservoir characterization: Geological Society Special Publication 127, p. 231–261.</ref>). Reprinted with permission from the Geological Society of London.

Only the faults that the geophysicist can pick from seismic data will be mapped, that is, those faults with vertical displacements down to the limit of seismic resolution. As mentioned in [[Data: sources]], this can be about 20–40 m for reservoirs at moderate depths. However, a significant number of subseismic faults will probably be present with vertical displacements less than this ([[:file:M91Ch13FG92.JPG|Figure 14]], [[:file:M91Ch13FG93.JPG|Figure 15]]). Thus, the true degree of the structural complexity of a reservoir will be underrepresented.

Only the faults that the geophysicist can pick from seismic data will be mapped, that is, those faults with vertical displacements down to the limit of seismic resolution. As mentioned in [[Data: sources]], this can be about 20–40 m for reservoirs at moderate depths. However, a significant number of subseismic faults will probably be present with vertical displacements less than this ([[:file:M91Ch13FG92.JPG|Figure 14]], [[:file:M91Ch13FG93.JPG|Figure 15]]). Thus, the true degree of the structural complexity of a reservoir will be underrepresented.

It is possible to input subseismic faults into a reservoir model using stochastic methods.<ref name=Muntheetal_1993>Munthe, K. L., H. Omre, L. Holden, E. Damsleth, K. Heffer, T. S. Olsen, and J. Watterson, 1993, Subseismic faults in reservoir description and simulation, Presented at the Society of Petroleum Engineers Annual Technical Conference and Exhibition, October 3–6, Houston, Texas, [https://www.onepetro.org/conference-paper/SPE-26500-MS SPE Paper 26500], 8 p.</ref> <ref name=Hollundetal_2002>Hollund, K., P. Mostad, B. F. Nielsen, L. Holden, J. Gjerde, M. G. Contursi, A. J. McCann, C. Townsend, and E. Sverdrup, 2002, Havana—A fault modelling tool, in A. G. Koestler and R. Hunsdale, eds., Hydrocarbon seal quantification: Norwegian Petroleum Society Special Publication 11, p. 157–171.</ref> In summary, this is a computerized procedure for randomly inserting shapes representing geological features into a 3-D model while still honoring predefined rules and statistics controlling the global distribution of the data.

It is possible to input subseismic faults into a reservoir model using stochastic methods.<ref name=Muntheetal_1993>Munthe, K. L., H. Omre, L. Holden, E. Damsleth, K. Heffer, T. S. Olsen, and J. Watterson, 1993, Subseismic faults in reservoir description and simulation, Presented at the Society of Petroleum Engineers Annual Technical Conference and Exhibition, October 3–6, Houston, Texas, [https://www.onepetro.org/conference-paper/SPE-26500-MS SPE Paper 26500], 8 p.</ref> <ref name=Hollundetal_2002>Hollund, K., P. Mostad, B. F. Nielsen, L. Holden, J. Gjerde, M. G. Contursi, A. J. McCann, C. Townsend, and E. Sverdrup, 2002, Havana—A fault modelling tool, in A. G. Koestler and R. Hunsdale, eds., Hydrocarbon seal quantification: Norwegian Petroleum Society Special Publication 11, p. 157–171.</ref> In summary, this is a computerized procedure for randomly inserting shapes representing geological features into a 3-D model while still honoring predefined rules and statistics controlling the global distribution of the data.