致密砂岩储层物性及非均质性特征

Physical property and heterogeneity of tight sandstone reservoirs： A case of the Upper Triassic 6 member of Xujiahe Formation， Guang’an， central Sichuan Basin

岳亮 孟庆强 刘自亮 杨威 金惠 沈芳 张军建 刘四兵

Liang Yue Qingqiang Meng Ziliang Liu Wei Yang Hui Jin Fang Shen Junjian Zhang Sibing Liu

中国西南地区四川盆地上三叠统须家河组碎屑岩地层为典型的非常规致密砂岩储集层，迄今已探明天然气储量已达万亿立方米，其中四川盆地中部广安地区须家河组六段（须六段）具有较大的勘探开发潜力。以须六段气藏段致密砂岩为研究对象，通过镜下薄片、物性和压汞等测试，结合分形理论研究，系统分析了其孔隙结构、物性特征和储层非均质性。结果表明：须六段砂岩储集层可明显划为3类。Ⅰ类储层（平均孔隙度12.27 %，平均渗透系数6.037 6 × 10 μm）以大孔或中孔为主，分形维数范围为2.42～2.59；Ⅱ类储层（平均孔隙度9.26 %，平均渗透系数1.152 3 × 10 μm）以中孔为主，小孔为次，大孔发育差，分形维数范围为2.47～2.56；Ⅲ类储层（平均孔隙度5.20 %，平均渗透系数0.351 7 × 10 μm）以小孔或中孔为主，大孔发育差或不发育，分形维数范围为2.45～2.81。孔隙类型的差异分布导致各类储层非均质性变化明显，主要表现为Ⅲ类储层非均质性强于Ⅰ类储层。相关性分析表明物性条件耦合于储层非均质性，且存在关键临界值，分形维数范围在2.45～2.60时，孔隙度与分形维数为正相关关系，渗透系数与分形维数的关系无明显规律；而分形维数大于2.60时，孔隙度与分形维数为负相关关系，渗透系数与分形维数为斜率接近0的线性关系。基于致密砂岩储层物性条件与分形特征的定量研究，探讨非常规天然气优质储层的评价标准，对指导中国非常规储层的勘探与开发研究具有重要理论与现实意义。

Unconventional tight sandstone reservoirs with proven natural gas reserves up to trillion cubic meters are typical of the Upper Triassic Xujiahe Formation of clastic rocks in the Sichuan Basin of southwestern China. The 6 member of Xujiahe Formation （Xu 6 Member） in Guang’an area， central Sichuan Basin， contains gas reservoirs with great exploration and development potential. In this study， thin section observation， physical property measurements， mercury intrusion tests and fractal theory were integrated to analyze a suite of the Xu 6 Member tight gas sandstone samples in terms of pore structure， physical property and reservoir heterogeneity. The results show that the sandstone reservoirs studied can be classified into three types. That is， TypeⅠreservoir （with an average porosity of 12.27 % and average permeability ratio of 6.037 6 × 10 μm） is dominated by macro- or meso-scale pores， and its fractal dimension varies between 2.42 and 2.59. TypeⅡreservoir （with an average porosity of 9.26 % and average permeability ratio of 1.152 3 × 10 μm） is dominated by meso-scale pores， followed by micro-scale pores， with macro-scale pores poorly developed； and its fractal dimension ranges from 2.47 to 2.56. TypeⅢreservoir （with an average porosity of 5.20 % and average permeability ratio of 0.351 7 × 10 μm） is dominated by micro- or meso-scale pores， together with poorly developed or undeveloped macro-scale pores； and its fractal dimension varies between 2.45 and 2.81. The different distribution of pore types leads to obvious changes in the heterogeneity of various types of reservoirs， which mainly shows that the heterogeneity of TypeⅢreservoir is stronger than that of TypeⅠreservoir. Differential distribution of pore types is directly related to reservoir heterogeneity， as manifested by stronger heterogeneity of TypeⅢreservoir compared with TypeⅡ. Correlation analysis reveals that differential pore types are coupled with reservoir heterogeneity， and there is a critical value. When the fractal dimension ranges between 2.45 and 2.60， the porosity and fractal dimension are in positive correlation， and the variation of permeability is irregular； when the parameter is greater than 2.60， there is a negative correlation between porosity and fractal dimension， and permeability is in linear relationship with fractal dimension with a slope close to 0. In all， the quantitative study on physical properties and fractal characteristics of tight sandstone reservoirs， is of great theoretical and practical significance to discussing the evaluation criteria of unconventional high-quality natural gas reservoirs， and guiding the exploration and development of unconventional reservoirs in China.

10.11743/ogg20220309