Quantitative analysis of the effect of salt on geothermal temperature and source rock evolution: A case study of Kuqa foreland basin, Western China

Abstract

There develop two sets of thick salt in the Kuqa foreland basin, the impact of salt thickness on geothermal temperature and thermal evolution of source rock was analyzed using transient thermal modeling method based on the two dimensional seismic profile from west to east of the basin and the related boundary condition. The results indicate that: (1) the change of salt plies will not have different impact on geothermal temperature when the total thickness of the salt body is constant; (2) the geothermal temperature of formations above the salt will increase about 0.3–0.6 °C/100 m, while the subsalt geothermal temperature will decrease about 0.6–1.0 °C/100 m in the west of the basin; the geothermal temperature of formations above the salt will increase about 1.9–2.3 °C/100 m, while the subsalt geothermal temperature will decrease about 0.2–2.6 °C/100 m in the east of the basin; (3) the value of vitrinite reflectance will be lagged about 0.02%/100 m averagely in the west of the basin, and will be lagged about 0.05%/100 m in the east. As the thermal conductivity of salt is negatively correlated with temperature, the salt body in the east has a shallower burial and lower geothermal temperature, so its overall thermal conductivity is higher, causing the changing rates of geothermal temperature and Ro are higher than the west. A case study of Dina 2 condensate field of Kuqa foreland basin indicates that the charge time of hydrocarbon there lagged about 7.5–9.0 Ma because of the delayed source rock thermal evolution caused by the salt, matching well with the formation period of trap, which is favorable for the late accumulation of hydrocarbon in this area. Key words: salt, conductivity, geothermal temperature, source rock, thermal evolution, basin modeling, Kuqa foreland basin, Tarim Basin