Overburden deformation related to the pre-piercement development of salt structures in the North Sea

Abstract

The nature of the stress regime imposed on a clastic overburden by a developing salt structure changes with time. These changes are directly related to the evolving morphology of the salt structure in a sequence of events which is now quite well understood. The stress pattern produced by initial, almost purely vertical, uplift changes rapidly into a more complex pattern as the flanks of the rising salt mass collapse progressively with flow of salt towards the crestal zone. The two main stress elements involved derive from extension within the superincumbent overburden produced by the salt uplift, and the effects of gravity that exercise an increasingly important influence as the structure develops vertically. Other factors also affecting the form taken by the overburden deformation are outlined. The discussion is illustrated with examples of migrated seismic data.