鄂尔多斯盆地大宁-吉县区块上古生界致密储层孔隙结构特征及其与黏土矿物的关系

Pore Structure Characteristics of Upper Paleozoic Tight Reservoir in Daning—Jixian Area of Ordos Basin and Its Relationship with Clay Minerals

为了揭示致密砂岩储层孔隙类型、孔隙赋存形态及黏土矿物对致密储层孔隙结构的影响,以鄂尔多斯盆地东缘大宁—吉县区块上古生界致密砂岩储层为例,综合高压压汞、铸体薄片和X射线全岩及黏土矿物资料,分析了致密储层孔隙和喉道组成特征,划分了孔隙结构类型,探讨了黏土矿物组成对孔隙结构的影响。结果表明:研究区致密砂岩储层孔隙结构包括5种类型,其中,Ⅰ和Ⅱ类结构以孔径(半径)100 nm~1μm孔隙为主,以溶蚀孔隙和片状喉道为主,大孔细喉;Ⅲ~Ⅴ类结构以100 nm以下孔隙(喉)为主,发育溶蚀孔隙和黏土矿物晶间孔,以弯片状和管束状喉道为主,小孔细喉。喉道和黏土矿物晶间孔以100 nm以下为主,溶蚀孔隙以100 nm~1μm为主。黏土矿物对孔径大小、孔隙组成和孔道迂曲度的影响表现为:随黏土矿物总质量分数增加,孔径100 nm以下的孔隙占比增加,孔喉半径减小,孔喉结构系数(迂曲度)变小。各类黏土矿物中,绿泥石、伊利石和伊蒙混层对孔隙结构的影响与黏土矿物总质量分数类似;高岭石是溶蚀作用的副产物,高岭石质量分数>4%,100 nm以上孔隙数量增多,孔喉半径增大。

In order to reveal the types and morphology of poresin tight sandstone reservoirs and the influence of the clay minerals on the pore structure,taking the Upper Paleozoic tight sandstone reservoir in Daning-Jixian area on the eastern margin of Ordos Basin as an example,the pore and throat composition characteristics of the tight sandstone reservoir are analyzed,the pore structure is classified,and the effect of clay mineral on pore structure is discussed based on the of mercury injection capillary pressure,thin section and XRD data.It is shown that the pore structure of the upper Paleozoic tight sandstone reservoir is divided into five types.The pore radius of type Ⅰ and Ⅱ is mainly in the range of 100 nm~1μm,with mainly secondary pores and flaky throat,and large pore-throat ratio.TypeⅢ~V are mainly composed of the pores whose radius is below 100 nm,with dissolution pores and clay mineral intercrystalline pores,bent sheet and tube bundle throat,and smaller pore-throat ratio.The radius of throat and clay mineral intercrystalline pores is mainly below 100 nm,and that of secondary pores is mainly in 100 nm~1μm.With the increase of total mass fraction of clay minerals,the proportion of pores with the radius below 100 nm increases,the pore throat radius decreases,and the pore throat structure coefficient(tortuosity)decreases.Among all kinds of clay minerals,the effect of chlorite,illite and smectite mixed layer on the pore structure is similar to the total mass fraction of clay minerals.Kaolinite is a by-product of dissolution.When the mass fraction of kaolinite is more than 4%,the number of pores above 100 nm increases,and the pore throat radius increases.