塔里木盆地典型砂岩油气储层自生伊利石K-Ar同位素测年研究与成藏年代探讨

K-Ar dating of authigenic illite and its applications to study of oil-gas charging histories of typical sandstone reservoirs, Tarim basin, Northwest China

塔里木盆地共发现 8套砂岩油气储层 ,对其中的 5套典型砂岩油气储层进行了自生伊利石K Ar同位素测年分析与研究。利用该项技术对其成藏史进行初步探讨是本次研究的主要目的。中央隆起下志留统沥青砂岩的自生伊利石年龄为 383.4 5～ 2 35 .17Ma ,表明志留系古油藏形成于加里东晚期—海西晚期 ;上泥盆统东河砂岩的自生伊利石年龄为 2 6 3.82～ 2 31.34Ma ,表明东河砂岩油气藏主要形成于海西晚期 ;库车坳陷依南 2气田 (依南 2井 )下侏罗统阳霞组砂岩的自生伊利石年龄为 2 8.0 8～ 2 3.85Ma ,表明油气充注发生在中新世以来 ;喀什凹陷阿克莫木气田 (阿克 1井 )下白垩统砂岩的自生伊利石年龄为 2 2 .6 0～ 18.79Ma ,表明中新世可能有古油气运移或古油藏形成 ;库车坳陷迪那 2气藏 (迪那 2 0 1井 )古近系砂岩中的伊利石主要为碎屑成因 ,不能用于进行油气成藏史研究 ,但该气藏白垩系砂岩的自生伊利石年龄为 2 5 .4 9～ 15 .4 7Ma ,表明可能为中新世成藏。本次研究表明 ,该项技术在塔里木盆地初步显示出较好的应用效果 ,具有较为广阔的应用前景。

Eight sets of sandstone reservoirs have been discovered in Tarim basin, Northwest China, for five of them a research on reservoir hydrocarbon charging histories by applying K-Ar dating of authigenic illite has been done. The ages of the authigenic illite of the Lower Silurian bituminous sandstones in the Central Uplift range from 383.5 to 235.2 Ma, suggesting that the Silurian oil accumulations were formed from the late Caledonian to the late Hercynian. The ages of the authigenic illite of the Upper Devonian Donghe sandstone reservoirs range from 263.8 to 231.3 Ma, indicating that the hydrocarbon accumulations within the Donghe sandstone were mainly formed in the late Hercynian. The ages of authigenic illite of the Lower Jurassic Yangxia group sandstones in the Yinan-2 gas reservoir (Yinan-2, Kuqa depression), range from 28.1 to 23.9 Ma, suggesting that the initial hydrocarbon charging occurred in the Miocene. The ages of the authigenic illite of the Lower Cretaceous sandstones in the Akemomu gas field (Ake-1, Kashi Sag, the southwest depression) range from 22.6 to 18.8 Ma, indicating a probable early oil accumulations or early migration of hydrocarbon within this area. The illite of the Paleogene sandstones in the Dina 2 gas reservoir (Well Dina-201, Kuqa depression) are inferred that it have a detrital origin and can not be used for dating hydrocarbon charge. The ages of authigenic illite in the underlying Cretaceous sandstones in the well Dina-201 range from 25.5 to 15.5 Ma, indicating that the hydrocarbon charging in this reservoir probably occurred within the Miocene. This study highlights the potential of applying K-Ar dating of authigenic illite to the investigation of the timing of hydrocarbon charging histories in Tarim basin reservoir sandstones.