There are a lot of sandy laminations in the Triassic Yanchang Formation shale in the central and southern Ordos Basin,but their influence on hydrocarbon accumulation is not clear.In order to reveal the geological characteristics of sandy lamination and explore its favorable effect on hydrocarbon accumulation, we have studied its lithologic and porosity-permeability characteristics, fracture development as well as oil and gas accumulation, through integration of methods such as core observation,microscopic identification,and organic geochemical analysis.The result shows that,the lithology of sandy lamination is mostly siltstone,argillaceous siltstone,and silty shale; the lamination mainly appears in the form of thin lamina,thin band,and thin interbed.And the existing sandy laminations have changed the way of lithol-ogical contact: denser development of the sandy lamination promotes more intense alternation of rock lithology,which is usually more favorable for hydrocarbon expulsion from source rocks.Besides, the sandy lamination favors pore size growth,so improving the physical property of the reservoir in turn.It changes the mechanical property of rocks,resulting in the change of distribution patterns of fractures.It also provides larger reservoir space for liquid hydrocarbon,dissolved gas,and free gas.Shale with highly developed sandy lamination in the Ordos Basin is the main target for present explora-tion and development,whereas thick deep-lacustrine shale,which is abundant in hydrocarbon,but due to limitations of present developing techniques,may only be producible in the future.%鄂尔多斯(盆)地中南部地区,三叠系延长组页岩内部存在大量的砂质纹层,该类纹层的发育与油气成藏的关系还不明确.为了深入揭示砂质纹层的地质特征、探索砂质纹层的发育对油气成藏的有利作用,综合利用岩心观察、镜下识别及有机地化分析技术,对砂质纹层的岩性特征、物性特征、裂缝发育及油气赋存开展了综合性研究.结果表明,砂质纹层的岩性涵盖粉砂岩、泥质粉砂岩、粉砂质泥页岩;纹层主要呈薄纹层、薄条带及薄夹层的形式出现.砂质纹层的存在,改变了岩性的接触方式.砂质纹层越发育,岩性交互程度越强,往往越有利于排烃.砂质纹层的存在,有利于孔隙的发育,间接改善了储层物性.砂质纹层的存在,改变了岩石的力学性质,使得裂缝展布规律得以改变.砂质纹层的存在,为液态油、溶解气和游离气提供了更多的赋存空间.鄂尔多斯盆地中南部地区,富含砂质纹层的页岩是现今的油气勘探开发目标;深湖相厚层页岩尽管油气潜力巨大,但现有的工程技术尚不能进行有效开发,是未来的勘探开发目标.
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