Rolf V. Ackermann¹, Martha O. Withjack¹, Charles W. Kiven²
(1) Mobil Technology Company, Dallas, TX
(2) Mobil New Exploration and Production Ventures, Dallas, TX

Abstract: Experimental models of uplifted footwall blocks: Application to the North Sea

Footwall degradation occurs on the upthrown sides of many normal faults in sediment starved basins such as the Viking Graben. The resulting structures modify the properties of potential reservoir rocks and increase reservoir compartmentalization. We have used experimental models to better understand the structural processes and geometries associated with footwall degradation.

Our models consist of an upper, 4-cm layer of clay or sand and a lower, 1-cm layer of silicone putty, overlaying a 45°-dipping, pre-cut normal fault. All movement occurs on this fault during the first stage of the models. After the first stage, the master normal fault is dormant. During later stages, secondary normal faults develop above the footwall of the master normal fault. These faults detach above the putty layer, form near the footwall edge of the master normal fault, and are subparallel to the master normal fault. With time, these detached faults grow by propagation and linkage. New detached normal faults form behind them, farther from the footwall edge of the master normal fault. Contractional features (e.g., thrust faults, folds) develop in the hanging wall of the master normal fault, accommodating significant amouts of shortening as fault blocks adjacent to the master fault are translated down the fault plane into the hanging wall block.

The crests of many fault blocks on the west side of the North Viking Graben are modified by footwall collapse features. Seismic data from several fields display geometries strikingly similar to the models. The modeling results can be used to aid in the interpretation of these complex features.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana