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Line 33: − − [[file:evaluating-top-and-fault-seal_fig10-2.png|thumb|{{figure number|2}}Example of a cross-leaking fault with different OWCs and a common FWL.]] Line 37:
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Line 49: − − [[file:evaluating-top-and-fault-seal_fig10-5.png|thumb|{{figure number|5}}Two wells separated by a cross-leaking fault. The initial pressures of both wells lie on a common, field-wide pressure depletion curve.]]
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<gallery mode=packed heights=200px widths=200px>
<gallery mode=packed heights=200px widths=200px>
file:evaluating-top-and-fault-seal_fig10-1.png|{{figure number|1}}Two sands, R<sub>u</sub> and R<sub>d</sub>, juxtaposed by a fault. The two sands have common oil-water (OWC) and gas-water (GWC) contacts. The fault is cross leaking to both oil and gas.
file:evaluating-top-and-fault-seal_fig10-1.png|{{figure number|1}}Two sands, R<sub>u</sub> and R<sub>d</sub>, juxtaposed by a fault. The two sands have common oil-water (OWC) and gas-water (GWC) contacts. The fault is cross leaking to both oil and gas.
file:evaluating-top-and-fault-seal_fig10-2.png|{{figure number|2}}Example of a cross-leaking fault with different OWCs and a common FWL.
file:evaluating-top-and-fault-seal_fig10-3.png|{{figure number|3}}Effect of capillary properties on oil-water contacts.
file:evaluating-top-and-fault-seal_fig10-4.png|{{figure number|4}}One type of fault-dependent leak point.
file:evaluating-top-and-fault-seal_fig10-5.png|{{figure number|5}}Two wells separated by a cross-leaking fault. The initial pressures of both wells lie on a common, field-wide pressure depletion curve.
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==Common free-water levels==
==Common free-water levels==
A cross-leaking fault can have different hydrocarbon contacts across the fault. The difference in hydrocarbon contacts can be caused not by the fault zone material but by differences in the displacement pressure (P<sub>d</sub>) of the juxtaposed reservoirs. There is, however, a common free-water level (FWL).
A cross-leaking fault can have different hydrocarbon contacts across the fault. The difference in hydrocarbon contacts can be caused not by the fault zone material but by differences in the displacement pressure (P<sub>d</sub>) of the juxtaposed reservoirs. There is, however, a common free-water level (FWL).
==Capillarity and OWCs==
==Capillarity and OWCs==
[[:file:evaluating-top-and-fault-seal_fig10-3.png|Figure 3]] illustrates the effect of capillary properties on oil-water contacts. Decreasing pore throat radius, represented by three capillary tubes of decreasing diameter (left), creates a higher OWC within the reservoir. If the pore throat is large (low P<sub>d</sub>), the OWC coincides with the free water level. If the pore throat is small (high P<sub>d</sub>), the OWC is higher than the free water level. In a reservoir with a lateral facies change, a fault can be cross leaking but still separate sands with different hydrocarbon contacts (right).
[[:file:evaluating-top-and-fault-seal_fig10-3.png|Figure 3]] illustrates the effect of capillary properties on oil-water contacts. Decreasing pore throat radius, represented by three capillary tubes of decreasing diameter (left), creates a higher OWC within the reservoir. If the pore throat is large (low P<sub>d</sub>), the OWC coincides with the free water level. If the pore throat is small (high P<sub>d</sub>), the OWC is higher than the free water level. In a reservoir with a lateral facies change, a fault can be cross leaking but still separate sands with different hydrocarbon contacts (right).
==Juxtaposed lithology leak points==
==Juxtaposed lithology leak points==
Cross leakage commonly creates fault-dependent leak points limiting the percent.<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=ch10r77>Smith, D., A., 1980, [http://archives.datapages.com/data/bulletns/1980-81/data/pg/0064/0002/0100/0145.htm Sealing and non-sealing faults in the Gulf Coast Salt basin]: AAPG Bulletin, vol. 64, no. 2, p. 145–172.</ref><ref name=ch10r2>Allan, U., S., 1989, [http://archives.datapages.com/data/bulletns/1988-89/data/pg/0073/0007/0800/0803.htm Model for hydrocarbon migration and entrapment within faulted structures]: AAPG Bulletin, vol. 72, no. 7, p. 803–811.</ref><ref name=ch10r35>Hardman, R., F., P., Booth, J., E., 1989, [http://archives.datapages.com/data/bulletns/1988-89/data/pg/0073/0007/0800/0812.htm Structural interpretation of hydrocarbon traps sealed by basement normal fault block faults at stable flank of foredeep basins and at rift basins]: AAPG Bulletin, vol. 73, no. 7, p. 813–840.</ref> One type of fault-dependent leak point is illustrated in [[:file:evaluating-top-and-fault-seal_fig10-4.png|Figure 4]]. The coincidence of the hydrocarbon contact with the top of the sand juxtaposed across the fault is a juxtaposed lithology leak point (JLLP). Hydrocarbons are trapped only where there is sand/sand juxtaposition along the fault. Hydrocarbons leak across the sand/sand juxtapositions.
Cross leakage commonly creates fault-dependent leak points limiting the percent.<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=ch10r77>Smith, D., A., 1980, [http://archives.datapages.com/data/bulletns/1980-81/data/pg/0064/0002/0100/0145.htm Sealing and non-sealing faults in the Gulf Coast Salt basin]: AAPG Bulletin, vol. 64, no. 2, p. 145–172.</ref><ref name=ch10r2>Allan, U., S., 1989, [http://archives.datapages.com/data/bulletns/1988-89/data/pg/0073/0007/0800/0803.htm Model for hydrocarbon migration and entrapment within faulted structures]: AAPG Bulletin, vol. 72, no. 7, p. 803–811.</ref><ref name=ch10r35>Hardman, R., F., P., Booth, J., E., 1989, [http://archives.datapages.com/data/bulletns/1988-89/data/pg/0073/0007/0800/0812.htm Structural interpretation of hydrocarbon traps sealed by basement normal fault block faults at stable flank of foredeep basins and at rift basins]: AAPG Bulletin, vol. 73, no. 7, p. 813–840.</ref> One type of fault-dependent leak point is illustrated in [[:file:evaluating-top-and-fault-seal_fig10-4.png|Figure 4]]. The coincidence of the hydrocarbon contact with the top of the sand juxtaposed across the fault is a juxtaposed lithology leak point (JLLP). Hydrocarbons are trapped only where there is sand/sand juxtaposition along the fault. Hydrocarbons leak across the sand/sand juxtapositions.
==Common pressures==
==Common pressures==
Common pressures across a fault imply communication and cross leakage. If a new well in a separate fault compartment encounters pressures equal to the current field depleted pressures, the fault is cross leaking.
Common pressures across a fault imply communication and cross leakage. If a new well in a separate fault compartment encounters pressures equal to the current field depleted pressures, the fault is cross leaking.