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Numerical and Geophysical Modelling |
Department of Geological Sciences, University of South Carolina, Columbia, SC 29208, USA
The temperature distribution through time in the subsurface influences hydrocarbon generation. It is therefore of interest to model the spatial variation of temperature through time and the causes of the variation.
The thermal conductivity of salt is a factor of two to three times higher than that of typical sediments. Salt structures often display large vertical relief and so provide low thermal resistance paths for heat conduction to the surface, with focusing through salt at the expense of surrounding sediments. The focused heat re-enters the sediments near the salt structure apex so that local sediments are warmer than remote sediments at equal depth. Sediments close to salt base, and in secondary rim synclines, are cooler than remote sediments at equal depth. Around salt sheets, supra-salt (sub-salt) sediments are warmer (cooler) than remote sediments at equal depth.
Decreasing salt thermal conductivities with increasing temperature are shown to influence thermal anomaly patterns around salt bodies, while temperature anomalies around a laterally moving salt sheet are calculated to exemplify the relative effects of salt shape, depth of burial and heat flow. The spatial temperature history is vital for modelling timing and location of earlier onset of oil generation and maturation above salt structures, and of delay in conversion of trapped oil to gas in deeper sediments compared to the regional regime. The importance of modelling the thermal history in order to reduce exploration risk near salt structures is emphasized.
