Model for Hydrocarbon Migration and Entrapment Within Faulted Structures

A model is presented that relates faults to migration and entrapment. The basic assumption of the model is that a fault is neither a seal nor a conduit. Therefore, the effect of faulting on both migration and entrapment depends on the rock properties of strata juxtaposed by the fault and on the structural attitude of the juxtaposed fault blocks. Fault-plane sections used with structure maps give a three-dimensional view of migration and trapping, and they illustrate the interplay of three critical parameters: (1) closure style, i.e., unfaulted anticline, faulted anticline, or nose, (2) cross-fault geometry, i.e., the throw and change of throw along a fault, and (3) stratigraphic geometry, i.e., the thickness and spacing of permeable and impermeable units. Cross-fault spil points define limits of trapping potential and paths for vertical migration. Synclinal spillpoints define stratigraphic tops of vertical migration paths and egress points for lateral migration. The validity and importance of the basic assumptions of the model can be evaluated by comparison with oil field characteristics in specific provinces.