渝东南牛蹄塘组页岩成岩作用及其对孔隙的影响

以渝科1井钻遇的下寒武统牛蹄塘组页岩为研究对象,探讨渝东南地区过成熟页岩中成岩作用对孔隙发育的影响。伊利石结晶度和等效镜质体反射率Ro测定,显示牛蹄塘组页岩处于有机质过成熟的晚成岩阶段。通过场发射扫描电镜和气体吸附实验对页岩孔隙进行了定性和定量表征。页岩孔隙主要由有机质孔隙、粒内孔隙和粒间孔隙组成,以中孔为主,平均直径为4.93nm,总孔体积平均为0.014 3cm~3/g。牛蹄塘组页岩经过强烈的压实作用和胶结作用使得粒间孔隙欠发育。黏土矿物大多已伊利石化,伊利石平均质量分数为86%,伊蒙混层平均质量分数为13%,黏土矿物中的孔隙以伊利石中的粒内孔隙为主。溶解作用使得碳酸盐矿物产生粒内孔隙和粒间孔隙,孔隙直径较大。有机质成熟作用产生了有机质孔隙,随着有机质成熟度的进一步增加,有机质内的有机质孔隙体积和孔隙直径都不断减小。页岩的孔隙因不同成岩作用的共同改造而变化。

Diagenesis and its effect on pores of the Niutitang Formation shale in southeast Chongqing,China

Samples of drilling cores from the Well Yuke 1 are studied in order to correctly recognize the diagenesis and its effect on pores of the mature shale in the Lower Cambrian Niutitang Formation, southeast Chongqing.The testing of crystallinity of illite and maturity (Ro )reveals that the Niutitang Formation shale is in the late diagenetic stage and the application of SEM and nitrogen adsorption experiments to the shale determines the characterization of pores qualitatively and quantitatively.It shows that the pores in the shale consist of organic pore,intragranular pore and intergranular pore in which mid sized pores are dominant with average diameter of 4 .9 3 nm and average pore volume of 0.014 3 cm3/g.Strong compaction and cementation in the Niutitang Formation shale lead to the decreases of intergranular pores.Study indicates that illite accounts for 86%of total clay minerals and intragranular pore is the main pore type in clay minerals.Dissolution forms intragranular pore and intergranular pore with relatively large pore size,while organic pore is resulted from the organic maturation.With the increase of maturity, pore volume and pore size in organic material are decreased.It reveals that the combined reformation by different diagenesis is an important reason for the variation of pore in the shale.