SALT STRUCTURES AS INDICATORS OF SUBSALT RIFT BASIN FAULTS AND FAULT-CONTROLLED RESERVOIRS
Improvements in base-salt and subsalt seismic data quality have made it possible to recognize a spatial relationship between numerous salt structures, base-salt faults, and major subsalt rift basin reservoirs, and to develop geoseismic models for the prediction of subsalt fault-controlled rift basin reservoirs. The spatial relationship between salt structures and base-salt faults observed in many Europe and North American basins has led to the suggestion that faults and the resulting base-salt displacement, slope variations, thermal anomalies, paleotopography, and differential subsalt sediment compaction may contribute to a base-salt fault trigger mechanism which can control the initial location, trend, and morphology of salt structures.
Consideration of the spatial salt structure-base-salt fault association in combination with a plausible base-salt fault trigger mechanism suggests that a genetic relationship may exist between many base-salt faults and salt structures which can be used to develop predictive models of subsalt structure and fault-controlled reservoir distribution. Models of initial salt structure development based on seismic and well data from Europe and North America summarize the effect of both presalt and post-salt normal, strike slip, and transverse faults that displace the base-salt, as well as faults that cut into the overburden. Similarities between the various models are integrated into a generalized model which can be used to predict the location and type of subsalt faults, and extend the interpretation of subsalt faults to poor seismic data areas and new areas. Since subsalt rift basin faults may have also controlled synrift sedimentary and diagenetic facies distribution, the salt structure-base-salt fault model can also be used to identify areas with the best subsalt synrift-postrift reservoir potential.
Drilling results have confirmed subsalt fault and reservoir predictions based on the salt structure-base-salt fault model. Given the numerous rift systems overlain by evaporites with salt structures, the model should lead to the development of a relatively low risk-high potential subsalt reservoir prediction strategy that can be applied to other rift basins with good source potential that are sealed by salt.