ABSTRACT

This paper presents a detailed study of the evolution of a salt diapir from the Late Oligocene to Present based on 3-D seismic, well logs and biostratigraphic information.

There is a notable lack of faulting associated with the diapir. The only faults are a large counter-regional normal fault dissecting the diapir and a small number of synthetic and antithetic faults. This observation is in striking contrast with older interpretations of this field since its discovery in 1948. Those proposed a large number of radial faults extending outward from the diapir; in concert with the thinking of the time that all diapirs have to actively breach their overburden on their way to the surface, causing intense faulting. This study presents evidence that a diapir can reach the surface and enter a mature state without causing extensive faulting. This study suggests that the faults observed in the field are coeval with diapirism, but are related to deeper, lateral withdrawal of salt that is feeding the growing diapir. The faults are not caused by emplacement, but are related to diapir growth.

The reinterpretation of the field changes the reservoir interpretation. Missing section observed in wells high on structure does not represent normal faults, but rather unconformities caused by differential salt uplift. Individual reservoirs are not constrained laterally by faulting. Rather, complexities in their behavior are due to depositional facies variations. Most of the reservoirs are constrained updip by either salt or uplift-induced onlap. The new interpretation of the field has led to an extensive workover and development drilling program that has revitalized this mature field.

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