Subsurface Temperature Anomalies as a Key to Petroleum-Producing Areas in the Cherokee and Forest City Basins, Eastern Kansas?: ABSTRACT

Abstract

The relation of subsurface temperature to `plain-type fold` structure in the Midcontinent (USA) as an exploration tool has been speculated on for a long time. Structural highs, termed `plains-type folds,` are partly the result of differential compaction of sediments over rigid crystalline fault blocks in the Precambrian basement. In the Midcontinent, bottom-hole temperature (BHT) data, temperatures measured in drillstem tests (DSTs), and structural data are abundant. In the Cherokee and Forest City Basins, we analyzed BHT data by depth and stratigraphic unit (Cambro-Ordovician Arbuckle carbonates; Mississippian carbonates; and Perm-Pennsylvanian clastics). By relating the BHTs to DSTs, it was noted that the thermal disturbance inherent in BHT by drilling is minor and comparable within a formation. Also, the signal-noise ratio of BHTs could be improved utilizing the large data set. Although the resulting BHT formation gradients show unexpected values from the thermal conductivity in the carbonates and from the evaluated temperature disturbance by the drilling process, analysis of the BHT spatial pattern shows a coincidence of structural highs and temperature anomalies both in the clastics and in the carbonates. These BHT anomalies are outlined by values higher than the regional temperature trend. We attribute the anomalies partly to the insulation effectmore » of petroleum (which may include the self-generation of heat) and partly to the movement of fluids vertically through the fracture and fault system created in the sedimentary veneer. Numerous examples from the oil- and gas-producing areas in eastern Kansas show that the nature of origin of fluids contained in a porous medium can alter local geothermal conditions.« less