Theoretical Calculation Model of Heat Transfer for Deep-derived Supercritical Fluids with a Case Study

Abstract Based on a set of equations established by Duan et al. (1992, 1996) for a geofluid system H₂O‐CO₂‐CH₄(‐N₂), a formula is obtained to calculate the heat changes. Combining the geological T‐P conditions (geothermal gradients and lithostatic and hydrostatic pressures), the enthalpy of some typical geofluids is figured out. Then the principles of heat transfer of deep‐derived supercritical fluids are discussed. The result shows that deep‐derived geofluids can bring a large amount of thermal heat and release most heat to the shallow surroundings as they move up, because the molar enthalpies vary very greatly from the deep to shallow, increasing with the increases of T and P. Generally, more than tens of kilojoules heat per molar can be released. Furthermore, the molar enthalpy is affected by the compositions of the geofluids, and the molar enthalpy of CO₂, CH₄, or N₂ is greater than that of H₂O, being twice, more than twice, and about 140% of H₂O, respectively. Finally, a case study is conducted by investigating a source rock sequence affected hydrothermally by magmatic fluids in the Huimin depression of Shengli Oilfield. The thermal heat calculated theoretically of the fluids related to a diabase intrusion is quite large, which can increase the temperature near the diabase to about 300°C, and that can, to some extent, account for the abnormal rise of the vitrinite reflectance, with the highest of about 3.8% (R_o).