Abstract

Most extensional faults are characterized by displacement distri butions that range from zero at the fault tips to a maximum value at some point along the length of the fault. Regardless of the pattern of displacement distribution, a geometrical requirement resulting from the displacement variation along the fault is that beds must stretch parallel with the strike of the fault. It has been suggested that minor faults and fractures evolve perpendicular to the main fault to accommodate this stretch. The amount of stretch that this subpopulation of faults must accommodate is quantified here using several alternative displacement profile models. The choice of pro file model is much less significant than the ratio of maximum displacement to fault length (Dmax/L). The amount of stretch rapidly increases from about 0.7% at Dmax/L of 0.05 to about 3% at the typical upper limit for Dmax/L of 0.1. These relationships predict tens to hundreds of meters of fault-parallel stretch associated with kilometer-scale extensional faults. The size and spatial distribution of stretch accommodation faults should be incorporated in three-dimensional (3-D) fault zone models, and there are several implications for fault linkage and seal. One possible strain accommodation scenario is that a small number of faults that have displacements significant enough to generate reservoir-juxtaposition leak points could exist. Alternatively, a subseismic fault and fracture population could either significantly degrade horizontal permeability parallel with the major fault or, if open, constitute a target for high-angle exploitation drilling. The intersections between the stretch accommodation faults and the main fault could provide conduits for fault valving or low-entry pressure leak points. The most commonly observed candidate stretch accommodation faults occur in fault overlap zones in segmented fault systems, coincident with maximum displacement gradients on the fault planes. In these cases, cutoff stretch accommodation could be an integral factor in fault segment linkage.

You do not currently have access to this article.