Abstract

From the thermal-mechanical modeling of the genesis and evolution of sedimentary basins, generally two parameters can be predicted: tectonic subsidence history and thermal history, the latter being most commonly characterized by surface heat flow as a function of time. Whereas subsidence data have been analyzed and used extensively to constrain thermal-mechanical models, thermal data have received less attention in spite of their importance in estimating hydrocarbon maturation.

We consider a detailed knowledge of the present day temperature distribution within a basin to be important both as a constraint for thermal evolution models, and equally as an indication of the processes that may have governed the thermal state of the basin through time. Individual factors to be considered are: 1) basal heat flux into the basin, indicative of the thermal state of the lithosphere; 2) thermal properties (conductivity and diffusivity) of the sedimentary fill, and 3) redistribution of heat within a basin, especially by fluid migration. The relative importance of these factors, which may vary within a basin and between basins, can be determined by careful analysis of the present day thermal field.

We present a method for analyzing the thermal states of basins that integrates the types of data most commonly available: bottom hole temperatures (BHT) from exploration drillholes, conventional heat flow measurements, thermal conductivity measurements or estimates, and depths of lithological boundaries. The variation in thermal conductivity is treated as a stochastic process in space and a formal inversion of the temperature data is performed to obtain the maximum likelihood estimation of the temperature field (and associated variance) throughout the basin. Interpretation of the derived thermal field is accomplished by deterministic modeling, which simulates actual structure, conductivity heterogeneities and possible groundwater flow systems.

The method is applicable to all basins but is illustrated for the Uinta Basin, a Laramide compressional basin in the Western U.S.A., where previous studies indicate large lateral variations in the temperature field and in thermal conductivity, and significant thermal perturbations, which were the result of a regional groundwater flow system.