含粉砂质层页岩储层孔隙结构和物性特征:以张家滩陆相页岩为例

鄂尔多斯盆地东南部延长组张家滩页岩储层中发育有大量粉砂质层，全面系统地理清张家滩页岩孔隙结构和物性特征，需要对比研究粉砂质纹层发育页岩、粉砂质层不发育的泥质页岩以及粉砂岩。本文选取了22块页岩样品，通过压汞法、气体吸附法和气测孔渗法等多种测试手段，结合扫描电镜观察，在对组成3种岩石类型的粉砂质层和泥质层孔隙发育类型研究的基础上，分析了3种岩石类型孔隙结构和物性特征的差异，并讨论了造成上述差异的影响因素。结果表明，粉砂质纹层发育页岩和粉砂岩孔径在100 nm以上的中-大孔孔体积较大，具有更好的储集和渗流能力。通过对比粉砂质层和泥质层的组分、沉积结构和成岩作用等的差异可知：粉砂质层中石英、长石等粉砂级刚性碎屑颗粒的富集有利于原始孔隙的形成和在物理压实过程中的保存；有机酸存在造成的酸性成岩环境有利于长石等颗粒发育溶蚀孔隙；液态烃等在颗粒表面形成的薄膜能够有效地抑制石英等胶结作用的发生。与泥质层相比，粉砂质层具有更好的孔隙形成和保存条件，使得粉砂质纹层发育页岩和粉砂岩的孔隙结构和物性特征明显优于泥质页岩。

Pore Structure and Physical Characteristics of Shale Reservoir Interbedded with Silty Layers: An Example from Zhangjiatan Lacustrine Shale

To systematically study the pore structure and physical characteristics of the shale reservoir, amounts of silty layers were investigated to compare the silty laminated shale, the clayey shale without silty laminae and the siltstone interbeds in the continental shale gas reservoir of Zhangjiatan in the Yanchang Formation, Ordos basin. SEM observation, mercury injection capillary pressure, gas adsorption, porosity and permeability tests were conducted to the 22 samples covering 3 kinds of lithologies in the shale reservoir. The pore types of the clayey layer and the silty layer in the 3 lithologies were studied,and the discrepancies in pore structure and physical properties between the 3 lithologies were analyzed. The results show that the silty laminated shale and the siltstone have larger meso-pore and macro-pore volume with the pore size larger than 100 nm,and they have better fluid storage capacity and higher permeability. Based on the comparative analysis of the compositions, sedimentary texture and diagenesis, it is concluded that the silt-sized brittle grains in the silty layers, such as quartz and feldspars, are favorable for the development of inter-particle pores,and hard to be compacted. The organic acid can also improve the development of dissolution pores in feldspars. The cementation of quartz and other minerals can be inhibited when the grains are coated by liquid hydrocarbons. The silty layer is favorable for pore development and preservation. The silty laminated shale and the siltstone have better pore structures and physical properties than the clayey shale.