塔里木盆地库车坳陷中生界油源岩有机成熟度和生烃历史

Organic maturity and hydrocarbon generation history of the Mesozoic oil-prone source rocks in Kuqa depression, Tarim Basin

库车坳陷存在上三叠统黄山街组(T3h)和中侏罗统恰克马克组(J2q)两套湖相油源岩,从三个方面研究了这两套油源岩现今成熟度分布及其在地质历史中的演化:一是对钻孔和露头剖面两套油源岩样品镜质组反射率实测分析;二是从中下侏罗统煤系源岩,特别是煤中镜质组反射率实测数据限定分别位于中下侏罗统(J1y和J2k)煤系地层上下的两套油源岩的有机成熟度;三是从地层分层数据和地温史对人工井(中)两套油源岩成熟度的模拟分析。库车坳陷黄山街组和恰克马克组露头剖面油源岩镜质组反射率自东向西总体上呈现明显的增高趋势,在东部基本上处于临界成熟—成熟阶段,而西部则处于凝析油—湿气阶段或干气阶段。库车坳陷黄山街组油源岩主要生油阶段位于65～5Ma,生油高峰约在23～12Ma,油源灶最早(约65Ma)出现在坳陷西部,不断向东部扩展;恰克马克组湖相油源岩主要生油阶段位于12Ma至现今,生油高峰约在5～2Ma,油源灶最早(约12Ma)出现在拜城凹陷腹部,后向四周扩展。

Upper Triassic Huangshanjie Formation (T3h) and Middle Jurassic Qakemake Formation (J2q) are two sets of lacustrine oil-prone source rocks in Kuqa depression, Tarim Basin, its organic maturity and geological evolution have been measured or constrained from three aspects: firstly, vitrinite reflectances are directly measured on the lacustrine source rock samples from wells and outcrops; secondly, organic maturities have been constrained from the vitrinite reflectance data of underlying and overlying coal measures strata; thirdly, organic maturities are calculated by BasinMod software according to the data of strata and basin thermal history. The obvious incremental trend of organic maturity from the east part to the west part of Kuqa depression has been showed according to the systematical vitrinite reflectance analysis of the outcrop samples of Huangshanjie Formation and Qakemake Formation. The organic maturities of two sets of source rocks in the east part are in the marginal mature and mature phase, but most source rocks in the west part are in the condensate-wet gas or overmature-dry gas phase. The timing of oil window of Huangshanjie Formation (T3h) ranged from 65 Ma to 5 Ma, the peak of oil generation occurred about 23～12 Ma, oil source kitchen originally occurred in the west part and lately expanded to the east part of the depression. The timing of oil window of Qakemake Formation ranged from 12 Ma to the present, the peak of oil generation occurred about 5～2 Ma, oil source kitchen firstly occurred in the hinterland of Baicheng sag and lately expanded around Baicheng sag.