Thermal History Recovery and Comparative Research on Jiuquan Basin Group

Abstract

Jiuquan basin group is formed by the superposition of two-stage different property and different generation basins. It was a tensional fault basin in Late Jurassic-Early Cretaceous and a compression depression basin since Cenozoic. The present geothermal gradient and heat flow are low in Jiuquan basin group, where the present geothermal gradient is mainly between 2.5 and 3.00 °C/100m, and the heat flow value is mainly between 50 and 57mW/m2. Jiuquan basin group is tensional fault basins and their palaeothermal gradients are higher in late Mesozoic, which reached 3.75–4.50 °C/100m. Thermal gradient of Jiuquan basin group has gradually decreased since Cenozoic. Huahai basin and Shibei depression of Jiuxi basin have subsided at a small scope since Cenozoic, the palaeotemperature of Lower Cretaceous source rock is higher than present, the maturity of Lower Cretaceous source rock is controlled by paleotemperature. It only has one stage of main oil generation, which is Early Cretaceous. Qingxi depression of Jiuxi basin and Yinger depression of Jiudong basin have subsided at a big scope since Cenozoic, and the maturity of Lower Cretaceous source rock is mainly controlled by present temperature. It has two stage of main oil generation, one is late of Early Cretaceous and another is since Late Tertiary, and main stage of oil generation is since Late Tertiary. The difference of tectonic thermal history in different basin and different units of a basin results in difference of stage of main oil generation and difference of oil-gas exploration prospect.