鄂尔多斯盆地延长组成岩流体滞留效应与致密砂岩储层成因

鄂尔多斯盆地上三叠统延长组砂岩储层主要是致密低渗透储层。平缓的构造背景、储层胶结物含量及类型的差异、包裹体均一温度、碳酸盐胶结物碳氧同位素分析及地层水特征均证明，鄂尔多斯盆地上三叠统延长组砂岩储层中成岩流体存在滞留效应。尽管碎屑矿物颗粒被烃源岩生烃过程中排出的有机酸溶蚀，但由于地层平缓、成岩流体难以迁移而滞留在原来的孔隙中，形成了大量自生胶结物沉淀。孔隙度演化计算表明，除成岩压实减孔作用是导致延长组砂岩储层致密的主要因素外，成岩流体滞留效应造成延长组砂岩储层中自生黏土矿物和碳酸盐等胶结物发育，由此导致的强胶结效应是储层致密、强含油非均质性的主要原因，且其减孔作用与成岩压实作用几乎相同。

Diagenesis fluid stagnation effect and genesis of tight sandstone reservoir in Yanchang Formation,Ordos Basin

The sandstone reservoir of the Upper Triassic Yanchang Formation in Ordos Basin is mainly a low-permeability tight reservoir. The gentle tectonic setting, the difference in the content and type of reservoir cement, the homogenization temperature of inclusions, the carbon-oxygen isotope analysis of carbonate cements and formation water characteristics prove the stagnation effect in the diagenetic fluids of sandstone reservoirs, Upper Triassic Yanchang Formation, Ordos Basin. Although the detrital mineral particles are eroded by the organic acids excreted during the hydrocarbon generation of source rocks, due to the gentle formation, the diagenetic fluid is difficult to migrate and remains in the original pores to form a large amount of autogenous cement precipitation. The porosity evolution calculation shows that the pore-reducing effect of diagenetic compaction is the main cause of tight sandstone reservoirs in Yanchang Formation. Moreover, the development of authigenic clay minerals and carbonate cements in sandstone reservoirs of Yanchang Formation is caused by the stagnation effect of diagenetic fluids. Therefore, the induced strong cementation is also the main reason for forming tight reservoir with strong oil-bearing heterogeneity effect. Meanwhile, the pore-reducing effect is almost the same as diagenetic compaction.