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Line 21: − + − [[file:evaluating-top-and-fault-seal_fig10-6.png|thumb|left|{{figure number|1}}A fault is cross sealing if it juxtaposes hydrocarbon-bearing sands with water-wet sands.]]+ + + + − − [[file:evaluating-top-and-fault-seal_fig10-7.png|thumb|{{figure number|2}}A fault is cross sealing if it juxtaposes sands with different hydrocarbon contacts and/or different free water levels.]] − − [[file:evaluating-top-and-fault-seal_fig10-8.png|thumb|{{figure number|3}}Two wells separated by a cross-sealing fault. Well 2 encountered virgin pressures in contrast to the lower pressures in the main field..]]
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==Hydrocarbon against water==
==Hydrocarbon against water==
<gallery mode=packed heights=300px widths=300px>
file:evaluating-top-and-fault-seal_fig10-6.png|{{figure number|1}}A fault is cross sealing if it juxtaposes hydrocarbon-bearing sands with water-wet sands.
file:evaluating-top-and-fault-seal_fig10-7.png|{{figure number|2}}A fault is cross sealing if it juxtaposes sands with different hydrocarbon contacts and/or different free water levels.
file:evaluating-top-and-fault-seal_fig10-8.png|{{figure number|3}}Two wells separated by a cross-sealing fault. Well 2 encountered virgin pressures in contrast to the lower pressures in the main field.
</gallery>
A fault is cross sealing if it juxtaposes hydrocarbon-bearing sands with water-wet sands, as illustrated in [[:file:evaluating-top-and-fault-seal_fig10-6.png|Figure 1]]. Both oil and gas are prevented from flowing into the sand in the hanging wall (R<sub>d</sub>) by the cross-sealing fault.
A fault is cross sealing if it juxtaposes hydrocarbon-bearing sands with water-wet sands, as illustrated in [[:file:evaluating-top-and-fault-seal_fig10-6.png|Figure 1]]. Both oil and gas are prevented from flowing into the sand in the hanging wall (R<sub>d</sub>) by the cross-sealing fault.
==Different hydrocarbon contacts==
==Different hydrocarbon contacts==
A fault is also cross sealing if it juxtaposes sands with different hydrocarbon contacts and/or different free water levels, as illustrated in [[:file:evaluating-top-and-fault-seal_fig10-7.png|Figure 2]]. Small differences in hydrocarbon contacts do not necessarily imply a cross-sealing fault because the capillary properties of the juxtaposed sands can create different hydrocarbon contacts even across a cross-leaking fault. Different free water levels do imply a cross-sealing fault.
A fault is also cross sealing if it juxtaposes sands with different hydrocarbon contacts and/or different free water levels, as illustrated in [[:file:evaluating-top-and-fault-seal_fig10-7.png|Figure 2]]. Small differences in hydrocarbon contacts do not necessarily imply a cross-sealing fault because the capillary properties of the juxtaposed sands can create different hydrocarbon contacts even across a cross-leaking fault. Different free water levels do imply a cross-sealing fault.
==Different pressures==
==Different pressures==
Different pressures across a fault imply cross seal. In [[:file:evaluating-top-and-fault-seal_fig10-8.png|Figure 3]], wells 1 and 2 are separated by a cross-sealing fault. Well 2 encountered virgin pressures in contrast to the lower pressures in the main field.
Different pressures across a fault imply cross seal. In [[:file:evaluating-top-and-fault-seal_fig10-8.png|Figure 3]], wells 1 and 2 are separated by a cross-sealing fault. Well 2 encountered virgin pressures in contrast to the lower pressures in the main field.