鄂尔多斯盆地中生界低渗透岩性油藏形成规律综述

Summary of Formation Rule for Low Permeability Lithologic Reservoir of Mesozoic in Ordos Basin

鄂尔多斯盆地中生代为典型的大型内陆坳陷湖盆,含油层系主要为三叠系延长组和侏罗系延安组。长7优质烃源岩为中生界油藏的主要源岩,异常高压为中生界低渗透储层油气大规模运移的主要动力,孔隙性砂体和裂缝系统是中生界石油运移的主要通道,多种输导体系和异常压力的有效组合控制了油藏的展布特征。利用储层成岩流体包裹体、自生伊利石测年和沥青期次等多种方法对成藏期次进行了分析,认为中生界油藏的形成为连续充注一期成藏的特点,成藏期可分为早、中、晚三个阶段,分别对应于早白垩世早期、中期和晚期,主成藏期为早白垩世中期的中期成藏阶段。总结出鄂尔多斯盆地延长组低渗透岩性油藏的形成规律,在长7优质烃源岩欠压实作用和生烃增压共同产生异常高压生的作用下,原油通过互相叠置的相对高渗砂体向上、向下运移,在长4+5、长6、长8形成大规模岩性油藏,并通过微裂缝和前侏罗纪古河输导体系,在长2及侏罗系形成了构造—岩性油藏。

Ordos Basin is the typical inland depression lake basin of Mesozoic. Yanchang Formation of Upper Triassic and Yanan Formation of Jurassic are the main oil-beating strata. Chang 7 high quality source rocks are the principal source rocks of Mesozoic oil reservoir, abnormal high pressure is the principal migration force of Mesozoic low permea- bility reservoir, porosity sandstone and fracture system are the main migration pathway of mesozoic hydrocarbon, the ef- fective combination of several carrier system and abnormal high pressure controlled the reservoir distribution. By using the methods of the diagenetic fluid inclusion of reservoirs, authigenic illite dating and bitumen with different periods, a- nalysis of the petroleum accumulation period, considered that the formation of Mesozoic oil reservoir is oil migration and accumulation. The accumulation poriod can be divided into early stage, middle stage and late stage, respectively corre- sponded to early period, middle period and late period of early cretaceous, The main accumulation stage is the middle stage of accumulation poriod in middle period of early Cretaceous. The formation rule for low permeability lithologic res- ervoir of Mesozoic in Ordos Basin has been summrized. Under the effect of abnormal high pressure which was generated by low compaction and hydrocarbon-generating pressurization of Chang 7 source rocks, hydrocarbon migrated up and down by overlying high permeability sandstone, formed large-scale lithologic reservoir in Chang 4 ＋ 5, Chang 6 and Chang 8, and by the passage system of micro fracture and anterior Jurassic paleo-river sand, formed structural lithologic reservoir in Chang 2 and Jurassic reservoir.