Master of Science (MS)
Geology and Geophysics
Weighted average geothermal gradients in the Western Arkoma Basin, Oklahoma are estimated from bottom hole temperatures (BHT) from 158 oil and gas wells. The regional geothermal gradient is 28.8 °C/km. The central and north central portions of the basin have higher gradients than southern and northern portions, especially in large areas of Pittsburg and Haskell counties where geothermal gradients in excess of 36 °C/km exist. These gradients suggest that temperatures suitable for low temperature geothermal power exist at depths of 2-3 km. Coals have very low thermal conductivity (0.15 – 0.5 W/m°K) acting as thermal insulators. This study examines the impact of coals on the thermal regime. Desmoinesian coal thickness was mapped in the Basin using bulk density curves from 78 well logs. The maximum thickness was about 50 ft of Pennsylvanian coal. However, most wells show much lower amounts (< 20 ft). Ten of eleven wells along a north/south cross section were selected for one dimensional (1D) thermal modeling. Correlation of net coal thickness to the weighted average geothermal gradients and computer models show that coal thickness is too thin to have a significant effect on the geothermal gradient. Temperature gradients in eight wells are consistent with vertical steady state conduction, and two are not. Analytical solutions and temperature logs show that downward movement of cold water can produce the observed geothermal gradient in these two wells. Temperature log profiles from wells near the Basin center reveal thermal anomalies indicating conditions inconsistent with steady state vertical thermal conduction below the Atoka formation. These anomalies are located around major fault fairways and provide potential evidence for fluid flow and/or refraction of thermal energy. Within the Basin center, the Spiro and Cromwell Sandstones are geothermal reservoirs of interest as they are thick, aerially extensive, have moderate to good porosity, and are at depths suitable for low temperature geothermal power (~80 °C). More detailed structural analysis, aided by two dimensional modeling is needed to further assess the geothermal potential in the area.
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Freeman, Matthew, "Evaluation of thermal insulation by coal beds in the western Arkoma Basin, OK and implications for large scale geothermal resources" (2013). LSU Master's Theses. 593.