塔里木盆地库车坳陷南斜坡三叠系烃源岩热演化特征及油气地质意义

Thermal evolution characteristics of Triassic source rocks and their petroleum geological significance on the southern slope of Kuqa Depression,Tarim Basin

根据最新的三维地震分层数据解释,塔里木盆地库车坳陷南斜坡地区三叠系烃源岩埋深较大,具备发育本地成熟烃源岩的可能性。通过地球化学资料及盆地模拟分析技术,对该地区三叠系烃源岩的埋藏史、热史和成熟度演化史进行模拟与分析,探讨烃源岩的成熟过程,厘定烃源岩的成熟阶段和生烃期次,进一步阐述其成藏意义。库车坳陷南斜坡三叠系克拉玛依组烃源岩分布广泛,在新和地区具有“南浅北深”的整体特征,南部地区埋深普遍在6700 m左右,向北逐渐加深,最大埋深可达8000 m以上。库车坳陷南斜坡整体沉降幅度一致,经历了早期稳定埋藏、中期持续沉降、晚期快速埋藏的演化过程。在三叠纪,该套地层稳定沉积,埋深厚度较小;白垩纪—古近纪期间,主要以陆相碎屑岩沉积为主,地层持续沉积;新近纪至今,库车坳陷南斜坡进入快速沉降阶段,埋深厚度最大。库车坳陷南斜坡三叠系烃源岩演化程度具有“北高南低”的特征。北部地区成熟早,古近纪初期达到了生烃门限(R_(o)=0.5%);古近纪末期演化至成熟阶段(R_(o)=0.7%);新近纪中期埋藏演化至高成熟阶段(R_(o)=1.0%);现今处于高成熟阶段(R_(o)=1.30%),以生气为主。南部地区成熟晚,新近纪初期才开始达到生烃门限;新近纪中期埋藏演化至成熟阶段(R_(o)=0.7%);现今处于成熟阶段(R_(o)=0.86%),以生油为主。库车坳陷南斜坡存在远源和近源两种输导体系,为圈闭成藏提供了充足的油气来源,具有“双源供烃”的特征。

According to the latest three-dimensional seismic stratification data,the Triassic source rocks are recognized to be deeply buried on the southern slope of Kuqa Depression,Tarim Basin,making it possible to develop local source rocks.Based on geochemical data and basin simulation,the burial history,thermal history and maturity evolution history of Triassic source rocks in this area were simulated and analyzed.By discussing the thermal evolution and maturity process of source rocks,the maturity stage and hydrocarbon generation stage o source rocks were proposed and their reservoir forming significance was further discussed.The source rocks of the Triassic Karamay Formation are distributed on the southern slope of Kuqa Depression.The burial depth in the southern area of Xinhe is generally about 6 700 m,which tends gradually to deepen in the north and reaches the maximum depth over 8 000 m,showing an overall characteristics of“shallowly buried in the south and deeply buried in the north”.The southern slope of Kuqa Depression has the same overall subsidence amplitude,which has experienced the tectonic evolution process of stable burial in the early stage,continuous subsidence in the middle stage and rapid burial in the late stage.During the Triassic period,the strata were deposited stably and the burial depth was small.From Cretaceous to Paleogene,continental clastic rocks were mainly deposited,and the strata continued to deposit.From Neogene to present,the southern slope of Kuqa Depression entered the stage of rapid thermal subsidence,and the burial depth reached the largest.The evolution degree of Triassic source rocks on the southern slope of Kuqa Depression is characterized by“high degree in the north and low degree in the south”.The northern region matured early,which entered the hydrocarbon generation threshold at the beginning of Paleogene (R=0.5%),evolved to mature stage by the end of Paleogene (R=0.7%) and to high maturity stage in the middle Neogene (R=1.0%) and till now (R=1.30%),mainly generating gas.The southern region matured relatively late,which entered the oil window in the early Neogene,reached mature stage in the middle Neogene (R=0.7%),and till now (R=0.86%),mainly generating oil.There are two oil and gas transportation of far-source and near-source on the southern slope of Kuqa Depression,which provides sufficient sources for oil and gas accumulation.This area has the overall characteristics of dual source hydrocarbon supply.