惠民凹陷基山砂体成岩作用及对油气圈闭的影响

Sandstone diagenesis and its influences on hydrocarbon traps in Jishan sand-body in Humin depression,north China

惠民凹陷基山砂体成岩作用对岩性地层圈闭的形成具有重要的控制作用。通过砂体储层结构和成岩作用分析发现,半径在0.4μm～1.5μm之间的孔喉占累计渗透率贡献值达到90%。分析表明,基山砂体主要储集空间为次生孔隙,主要是由长石等陆源碎屑矿物蚀变而成的自生高岭石晶间微孔,其孔径与压汞分析测试值吻合较好,是与之对应的岩石主要储集空间。压实作用造成的岩石物性致密带和沿砂体边缘形成的碳酸盐胶结层,构成了成藏组合中的区域盖层和局部盖层。即受成岩作用控制,基山砂体层段内致密胶结层和次生孔隙带为油气圈闭提供了有效的储盖组合。这说明成岩作用可以作为相对独立的因素控制油藏的圈闭条件,成岩相研究是连接油藏、圈闭和成岩现象的基本桥梁。

Sandstone diagenesis plays an important role in formation of stratigraphic traps of the Humin Depression, North China. A mercury injection testing result indicates that the porous radius ranging in 0.4μ m - 1.5μm can offer up to 90% permeability for the Jishan Sand-body reservoir samples of Humin Depression. This study shows that effective reservoir volume of the Jishan Sand-body is characterized by secondary porosity origin and dominantly consists of intercrystal porosity of kaolinite with porous radius similar to 0.4μm - 1.5μm. These kaolinites mostly resulted from alteration of detrital feldspars or plagioclases. On the other hand, compact and carbonate cementation layers, distributed on margin of sand-bodies, frequently constitute regional and local covers of hydrocarbon traps. Therefore compacted cementation layers and secondary porosity zones can provide effective reservoir-cover assemblages for hydrocarbon traps in Jishan Sand-body. It is also presented that diagensis may become an independent factor controlling pool-forming condition, and diagentic facies is the juncture of reservoir, trap and diagensis.