Fault Relay Structures and Their Impact on Production Behavior

Michael R. Hudec

Normal faults have traditionally been mapped as long, continuous features with throw decreasing steadily from a maximum near the center to zero at the tips. More recent work has suggested a different view, in which normal faults of all scales are composed of arrays of shorter segments, with relay zones shifting displacement between fault segments that overstep in map view. In some instances segments are linked across the relay zone, whereas in other cases the faults are unconnected, leaving a "gap" in the middle of the fault system.

Identification and correct mapping of relay zones is essential in any area where faults play a role in field segmentation. Potential relay zones can be identified by noting strike bends in the fault system, fault systems that are too long for their throw, displacement anomalies, and areas where the fault system splays into two or more strands.

The most common error in fault mapping is to interpret faults as longer and more continuous than they really are. This leads to overestimation of fault-dependent trap size and incorrect mapping of production compartments. An inaccurate compartment map can in turn lead to a less effective field development strategy, increasing the likelihood of dry holes or unnecessary wells.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California