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致密化储层是困扰和制约低孔、特低渗储层油气勘探的重要因素.鄂尔多斯盆地南部富县地区上三叠统延长组长6三角洲前缘水下分流河道砂体中碳酸盐胶结作用较为发育,是影响储层质量的主要因素之一.本文通过岩石学、地球化学等综合研究,系统地探讨了碳酸盐致密化储层的成因,首次将碳酸盐胶结作用划分为内源碳酸盐胶结和外源碳酸盐胶结两个成岩阶段与类型,指出这两种成岩作用的本质区别是碳酸盐流体的来源和成岩作用的时期不同.借助各种薄片鉴定、电子探针、微量元素及碳氧同位素等分析结果,进一步明确了内源碳酸盐胶结的流体源自岩石内部,其胶结物形成于成岩作用早期,故矿物颗粒自形程度较好,且存在后期被溶蚀现象,使储层孔隙度提高3%～8%,从而改善了储层物性;而外源碳酸盐胶结的流体源自富含有机质的泥岩中释放出的大量二氧化碳与水的结合,由于物化条件的变化,在砂体中溶蚀、扩散、运移,并充填剩余孔隙,因此,属成岩晚期产物,且多呈基底式胶结,使岩石孔隙度骤然降低,严重地破坏了储层物性,导致该区长6储层的局部致密化,影响了油气的富集.而部分形成于砂体顶部的致密层可构成碳酸盐成岩圈闭,是油气勘探的有利区带.本文在对碎屑岩中致密化储层成因机理探讨的基础上,指出了碳酸盐致密化储层的空间分布特征,明确了该区石油勘探的方向和有利区带,对碎屑岩致密化储层油气藏的勘探开发具有重要的理论和实际指导意义.
The densification of reservoirs is an important factor that plagued and restricted oil and gas exploration in low-porosity and ultra-low permeability reservoirs.Carbonate cementation in the subaqueous distributary channel sandbodies in the Upper Triassic Yanchang Formation of the Upper Triassic in Fu County, southern Ordos Basin Which is one of the main factors that affect the reservoir quality.Based on the comprehensive study of petrology and geochemistry, the paper systematically explores the genesis of carbonate densification reservoirs, and divides the carbonate cementation into It is pointed out that the essential difference between these two diagenetic processes is the source of carbonate fluid and the diagenetic period of diagenesis.Due to the identification of various thin sections, Pin, trace elements and carbon and oxygen isotope analysis results, and further clarified that the endogenous carbonate cementing fluid from the rock, the cement was formed in the early diagenesis, so the degree of mineral particles better shape, and there is the late The erosion phenomenon improves the reservoir porosity by 3% ~ 8%, thus improving the reservoir physical properties. However, the exogenous carbonate-cemented fluid originates from the large amount of carbon dioxide released from the organic-rich mudstone and Because of the change of physical and chemical conditions, the water dissolves, diffuses, migrates and fills the remaining pores in the sand body. Therefore, it belongs to the late diagenesis and is mostly base-type cementation, causing the porosity of the rock to suddenly decrease and seriously damage The physical properties of the reservoirs led to the local densification of reservoirs in Chang 6, which affected the oil and gas enrichment, while the dense layers partly formed at the top of the sand bodies could constitute carbonate diagenetic traps, which is a favorable zone for hydrocarbon exploration Based on the discussion of the genesis mechanism of densified reservoirs in clastic rocks, the paper points out the spatial distribution characteristics of the carbonate densified reservoirs, clarifies the direction and favorable zones of oil exploration in this area, The exploration and development of densified reservoir reservoirs have important theoretical and practical significance.