伦坡拉盆地始新统牛堡组烃源岩成熟史

Maturity history of source rocks in the Eocene Niubao Formation,Lunpola Basin

伦坡拉盆地自下而上发育始新统牛堡组牛二中亚段、牛二上亚段及牛三下亚段3套烃源岩。基于钻井测试资料、地震资料及含烃流体包裹体测试分析,利用盆地模拟技术对伦坡拉盆地热史及牛堡组3套烃源岩的成熟史进行了系统分析。研究表明,伦坡拉盆地自始新统牛三段沉积以来直至渐新统丁青湖组三段沉积末期,古地温梯度总体表现为持续降低,变化介于6.67~4℃/hm,为典型热盆特征,古地温梯度升高与区域构造隆升作用具有明显的相关性。牛二中及牛二上亚段的2套烃源岩成熟较早且热演化程度高,分别于中—晚始新世（距今约46.4~37.5 Ma）及早渐新世（距今约36.6~33.5 Ma）进入生油门限,现今主体皆位于成熟生油阶段（R_o=0.7%~1.3%）,是该区主力烃源岩。西部蒋日阿错洼陷牛二中及牛二上亚段主力烃源岩现今热演化程度最高,生供烃条件较中—东部江加错、爬错洼陷更为优越。

Three sets of source rocks developed upwards in the Eocene Niubao Formation in the Lunpola Basin,i.e.,the middle part of the second member of Niubao Formation（ E_2n_2~2）,the upper part of the second member of Niubao Formation（ E_2n_3~2）,and the lower part of the third member of Niubao Formation（ E_2n_3~1）. Based on drilling,seismic and hydrocarbon fluid inclusion analyses,the thermal evolution history of the basin and the maturity history of source rocks in the Niubao Formation were systematically analyzed with basin simulation technology. From the E2n3 to the third member of the Oligocene Dingqinghu Formation,the paleogeothermal gradient in the Lunpola Basin consistently decreases from 66.7 to 40 °C / km,showing the characteristics of a typical heating basin. The growth of paleogeothermal gradient is clearly related to regional tectonic uplifting. The source rocks in the E_2n_2~2 and E_2n_3~2became mature early and have a higher maturity. They entered oil generation thresholds during the middle-late Eocene（ 46.4-37.5 Ma） and early Oligocene（ 36.6-33.5 Ma）,respectively. At present,they are mature and generating oil（ Ro= 0.7%-1.3%）,and serve as the main source rock in the study area. At present,the thermal evolution extent of E_2n_2~2 and E_2n_3~2hydrocarbon source rocks in the Jiangriacuo Sag in the west is the highest,and its hydrocarbon forming and supplying ability is superior to the Jiangjiangcuo and Pacuo sags in the center and east.