珠江口盆地白云凹陷地温场特征及烃源岩热演化

Geothermal Field Characteristics and Maturity History of Source Rocks in Baiyun Sag,Pearl River Estuary Basin

通过对珠江口盆地白云凹陷108口钻井的地温数据(BHT、MDT、DST)进行校正、分析,以点到面重构白云凹陷的现今地温场,再结合地质与地球化学资料,正演恢复白云凹陷烃源岩的热演化史及生烃史。研究结果显示:(1)白云凹陷具有变地温场,地温梯度分布在35~60℃/km之间,呈现出南高北低的分布特征。(2)受控于白云凹陷变地温场作用,白云凹陷不同洼陷烃源岩热史不同,主洼文昌组烃源岩处于高成熟至过成熟阶段,东洼、西洼和南洼文昌组烃源岩处于成熟至高成熟阶段。(3)在垂向上,白云凹陷高变地温场导致烃源岩具有高热快熟的演化特征,随地温梯度升高,烃源岩成熟门限快速变浅、生烃窗口变窄。(4)白云凹陷不同洼陷具有差异生烃特征,主洼文昌组烃源岩干酪根生油气早,生油阶段主要在23.03 Ma以前,生气阶段在33.9~10.0 Ma;东洼、西洼、南洼烃源岩埋藏浅,生烃较晚(23.03 Ma以来),油气共生。

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.