Abstract:

By correcting and analyzing the geothermal data (BHT, MDT and DST) from 108 wells in the Baiyun Sag, Pearl River Estuary Basing we reconstructed the current geothermal field of the sag from spots to planes. Combined with geological and geochemical data, we forward simulated and restored the thermal evolution and hydrocarbon generation history of source rocks in the sag. The results show that: (1)the Baiyun Sag shows characteristics of varying geothermal field, and the geothermal gradient is distributed in 35-60 ℃/km, decreasing from south to north; (2)Controlled by the varying geothermal fields in the Baiyun Sag, the source rock thermal history of different depressions in the sag is different. The Wenchang Formation source rocks in the main depression are highly mature to over mature, and those in the east, west and south depressions are mature to highly mature; (3)The high varying geothermal field in the Baiyun Sag likely leads to the evolution characteristics of high heat and rapid maturity of source rocks. With increasing geothermal gradient, the maturity threshold of source rocks quickly becomes shallow, and the hydrocarbon generation window becomes narrow; (4)Different depressions in the Baiyun Sag have different hydrocarbon generation characteristics: Kerogen oil and gas generation in the Wenchang Formation source rocks in the main depression was early. The oil generation occurred mainly before 23.03 Ma, and the gas generation occurred in 33.9-10.0 Ma; Source rocks in the east, west and south depressions are buried shallow, and the hydrocarbon generation there was relatively late (since 23.03 Ma). The oil and gas are cogenetic.

Key words: Baiyun sag, temperature correction, geothermal gradient, heat flow, thermal evolution history