深埋藏致密砂岩储层微观孔隙结构的分形表征及成因机理——以塔里木盆地顺托果勒地区柯坪塔格组为例

基于物性、铸体薄片、扫描电镜、压汞等测试分析资料，利用分形几何方法，对塔里木盆地顺托果勒地区柯坪塔格组致密砂岩储集层微观孔隙结构进行分形表征，探讨孔隙结构非均质性的成因机理。结果表明，顺托果勒地区柯坪塔格组储集空间主要为粒间溶孔、粒内溶孔和残余粒间孔，喉道类型包括缩颈型、片状、弯片状以及管束状喉道。建立了孔隙结构分形评价标准：Ⅰ类（分形维数D ≤ 2.350）、Ⅱ类（2.350 < D < 2.580）、Ⅲ类（D ≥ 2.580）和裂缝型。具有Ⅰ类孔隙结构的最有利储层主要分布在柯坪塔格组上段，Ⅱ类、Ⅲ类孔隙结构对应的储集体主要分布于柯坪塔格组下段。孔隙结构的非均质性受沉积微相的物质基础条件控制。砂岩的成分及粒径的差别是导致储集岩孔隙结构分异的主要因素。柯坪塔格组下段经历的压实作用、胶结作用强于上段，而溶蚀作用弱于上段，导致下段孔隙结构明显比上段差。构造破裂作用导致脆性矿物含量较高的柯坪塔格组上段局部发育微裂缝，改善了渗透性能，并增强了孔隙结构的非均质性；但在柯坪塔格组下段则表现为颗粒挤压破碎、压实作用强。

Fractal characterization and genetic mechanism of micro-pore structure in deeply buried tight sandstone reservoirs: a case study of Kalpintag Formation in Shuntuoguole area,Tarim Basin

Based on physical property, cast thin section, scanning electron microscope, mercury injection and other test analysis data, the pore structures of tight sandstone reservoirs were investigated in Kalpintag Formation, Shuntuoguole area, Tarim Basin. Fractal characterization is conducted on the micro-pore structure by using fractal geometry, so as to explore the genetic mechanism of pore structure heterogeneity. The results have shown that the reserving space in Kalpintag Formation, Shuntuoguole area are mainly composed of intergranular dissolved pore, intragranular dissolved pore and residual intergranular pore. The throat types include necking throat, lamellar throat, curved lamellar throat and tube-shaped throat. The fractal evaluation criteria of pore structure was established, i.e., Type I (D ≤ 2.350), Type Ⅱ (2.350 < D < 2.580), Type Ⅲ (D ≥ 2.580)and fracture type. The most favorable reservoirs with Type-I pore structure are mainly distributed in the upper member of Kalpintag Formation, while the reservoirs with Type-Ⅱ and Type-Ⅲ pore structures are mainly in the lower member. The heterogeneity of pore structures is controlled by the material basis originated from sedimentary microfacies. The different compositions and particle sizes of sandstone are the main cause for the variation of pore structures in reservoirs. In Kalpintag Formation, the lower member underwent stronger compaction and cementation but weaker dissolution than the upper member, resulting in the significantly worse pore structure in the lower member. Tectonic fracturing leads to the micro-cracks locally developed in the upper member of Kalpintag Formation with higer brittle mineral content, helps to improve the permeability and enhance the heterogeneity of pore structures, but the lower member of Kalpintag Formation shows the strong effects of particle crushing and compaction.