The Significance of Salt Reconstruction for Basin Modeling Results

H. Johansen, L. Bonnell, A. Andersen, and V. Blomvik

Salt structures can play a major role in the temperature history as well as in the formation of hydrocarbon traps. Salt movement through time is therefore an important process to incorporate into basin models. Based on this need, a new model for geologic reconstruction of salt geometries was incorporated into the BMT^TM basin modeling system.

The reconstruction model is based on two basic mechanisms: (1) The ability to change lithology for a polygon (a sub-domain in the cross section) at a given time (litho-switching); and (2) the ability to inflate/deflate mass in polygons. Litho-switching is used where salt diapirs penetrate overlaying strata. Inflation/deflation is used to change the shape of a salt polygon. By inflating/deflating parts of polygons, it is possible to restore the salt layer step by step back to original form.

The advantage of this approach is its applicability to geological problems that cannot be addressed by many basin modeling systems. To test the approach, we have reconstructed a cross-section from the Central Graben of the North Sea using two different geological models. One model assumes that synforms developed on the surface during Triassic deposition. These synforms were later preserved as sediment "pods". The other geological model assumes that the salt movement was passively related to eastward basin subsidence, with salt upwelling between rafted Triassic blocks. The test indicate that the approach is versatile and can be used to evaluate the thermal consequences of a number of geologic models of salt movement.

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