Thermal Stresses and Their Effects during the Deep Hot Fluids Penetrating upward in DF 1-1 Diapiric Area, Yinggehai Basin

The hot fluids are intensive and frequent in the DF1-1 diapiric area, Yinggehai basin, South China Sea. Thermal fluids penetrating the strata from the deep belt generated thermal stress, which resulted in changes to the local stress field. Moving thermal fluids are capable of transporting a large amount of heat from the deep part of the basin, resulting in thermal anomalies, which heat and expand adjacent sediments to form local thermal stress. Thermal stresses controlled the stress patterns and direction of overpressure fluid migration in some locations. The structural stress associated with thermal stress induced the fluid migration system including fractures, faults and sand folds. On the other hand, because the fluids have had thermal energy and hydrocarbon or CO₂ when penetrating strata from the deep, the obvious temperature differentia caused abnormal phenomena in a series of geochemical parameters, including transferring from smectite to illite, vitrinite reflectance rate, the temperature of fluid inclusions etc.. All those processes mean that the characteristics of the diapiric body and its surrounding rock are extremely different before diapirism and after diapirism. This research also demonstrates and analyzes the evolutional process of the thermal stress field and temperature field by comparing a quantitative dynamic simulation with field analysis. The results show that stress fields and temperature fields moved upwards over time. The thermal stress field also promoted the episodic opening of faults, and accelerated the hydrocarbon-bearing fluid flow upwards. The extent of the effect of thermal fluids depends on the proportion between thermal stress and tectonic stress.