10,351
edits
Changes
Jump to navigation
Jump to search
Line 22:
Line 22: − Common hydrocarbon contacts imply communication across the fault and cross leakage. The cross-leaking fault in the following figure shows 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. − + + + + + + − + − + − The following figure 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== − − [[file:evaluating-top-and-fault-seal_fig10-4.png|thumb|{{figure number|10-4}}See text for explanation.]] + + + − + − − [[file:evaluating-top-and-fault-seal_fig10-5.png|thumb|{{figure number|10-5}}See text for explanation.]]
no edit summary
==Common hydrocarbon contacts==
==Common hydrocarbon contacts==
[[file:evaluating-top-and-fault-seal_fig10-1.png|thumb|{{figure number|10-1}}See text for explanation.]]
[[file:evaluating-top-and-fault-seal_fig10-1.png|left|thumb|{{figure number|1}}See text for explanation.]]
Common hydrocarbon contacts imply communication across the fault and cross leakage. The cross-leaking fault in [[:file:evaluating-top-and-fault-seal_fig10-1.png|Figure 1]] shows 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.
==Common free-water levels==
==Common free-water levels==
[[file:evaluating-top-and-fault-seal_fig10-2.png|thumb|{{figure number|2}}See text for explanation.]]
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).
An example of a cross-leaking fault with different OWCs and a common FWL is shown in the following figure. The P<sub>d</sub> of the R<sub>d</sub> sand is greater than that of the R<sub>u</sub> sand. The fault is cross leaking despite different OWCs.
An example of a cross-leaking fault with different OWCs and a common FWL is shown in [[:file:evaluating-top-and-fault-seal_fig10-2.png|Figure 2]]. The P<sub>d</sub> of the R<sub>d</sub> sand is greater than that of the R<sub>u</sub> sand. The fault is cross leaking despite different OWCs.
[[file:evaluating-top-and-fault-seal_fig10-2.png|thumb|{{figure number|10-2}}See text for explanation.]]
[[file:evaluating-top-and-fault-seal_fig10-3.png|left|thumb|{{figure number|3}}See text for explanation.]]
==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).
==Juxtaposed lithology leak points==
[[file:evaluating-top-and-fault-seal_fig10-3.png|thumb|{{figure number|10-3}}See text for explanation.]]
[[file:evaluating-top-and-fault-seal_fig10-4.png|thumb|{{figure number|4}}See text for explanation.]]
Cross leakage commonly creates fault-dependent leak points limiting the percent.<ref name=ch10r76>Smith, D., A., 1966, 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, 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, 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, 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 the following figure. 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, 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, 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, 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, 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 the following figure. 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.
Identifying JLLPs is an important method of assessing percent fill in prospects and determining seal behavior in existing fields. JLLPs exist only if the fault is cross leaking.
Identifying JLLPs is an important method of assessing percent fill in prospects and determining seal behavior in existing fields. JLLPs exist only if the fault is cross leaking.
==Common pressures==
==Common pressures==
[[file:evaluating-top-and-fault-seal_fig10-5.png|thumb|{{figure number|5}}See text for explanation.]]
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.
In the figure below, wells 1 and 2 are separated by a cross-leaking fault. The initial pressures of both wells lie on a common, field-wide pressure depletion curve.
In [[:file:evaluating-top-and-fault-seal_fig10-5.png|Figure 5]], wells 1 and 2 are separated by a cross-leaking fault. The initial pressures of both wells lie on a common, field-wide pressure depletion curve.
==Caveat==
==Caveat==