Abstract: The Member 4 of Xujiahe Formation in Jianyang area is a key target for increasing the reserves and production of continental tight gas in Sichuan Basin. However, the substantial heterogeneity in gas-bearing properties and the undefined dominant mechanisms governing fluid mobility severely restrict the efficient exploration and development of tight gas. Based on multi-scale characterization techniques combined with an integrated framework combining Pearson correlation analysis, grey correlation, and random forest algorithm, this study systematically investigates the distribution patterns of movable fluids in micro-nano pores and quantitatively identifies their sensitive factors. The results show as follows. (1) According to pore types and fractal characteristics, the pore system can be classified into micropores (pore size ranging from 0 to 0.01 μm), small pores (pore size ranging from 0.01 to 0.10 μm), mesopores (pore size ranging from 0.10 to 1.00 μm), and macropores (pore size greater than 1.00 μm). Among them, small pores (with an average proportion of 37.12 %) and mesopores (with an average proportion of 25.82 %) constitute the main reservoir spaces in the tight sandstone, dominated by intercrystalline pores and intragranular dissolved pores in clay minerals. (2) Movable fluids are primarily hosted in small pores (with an average proportion of 19.12 %) and mesopores (with an average proportion of 18.13 %), while bound fluids are predominantly distributed in small pores (with an average proportion of 18.00 %). (3) Pore structure parameters, including the proportion of small pores, median radius of saturated pores, and fractal dimension of mesopores, are the core sensitive factors controlling fluid mobility, significantly influencing its magnitude. Illite-smectite mixed layers and carbonate minerals indirectly affect fluid mobility by controlling and modifying pore structure in reservoirs. Pore structure dominates fluid mobility, while mineral components exert indirect influences. The research results are expected to provide a new theoretical paradigm for the evaluation of fluid mobility and the prediction of high-quality reservoirs in tight sandstone reservoirs.

Key words: tight sandstone reservoir, movable fluid, sensitive factor, Xujiahe Formation, Sichuan Basin

摘要： 简阳地区须家河组四段(须四段)是四川盆地陆相致密气增储上产的关键领域,但储层的含气性差异大,流体可动性的主控机制不清,严重制约了致密气的高效勘探开发。基于多尺度表征技术,结合构建的Pearson相关分析-灰色关联法-随机森林算法多方法融合框架,系统开展了微米—纳米孔隙中可动流体分布规律及其敏感因子的定量研究。研究结果表明:①依据孔隙类型和分形特征,简阳地区须四 段致密储层的孔隙系统可划分为微孔(孔径为0~0.01 μm)、小孔(孔径为0.01~0.10 μm)、中孔(孔径为0.10~ 1.00 μm)和大孔(孔径＞1.00 μm),其中,小孔(平均占比为37.12%)与中孔(平均占比为25.82%)是致密储层的主要储集空间,且以黏土矿物晶间孔和粒内溶孔为主。②可动流体主要赋存在小孔(平均占比为19.12%)和中孔(平均占比为18.13%),而束缚流体主要分布在小孔中(平均占比为18.00%)。③孔隙结构参数(小孔占比、饱和流体中值半径、中孔分形维数等)为控制流体可动性的核心敏感因子,显著影响着流体的可动性,而伊/蒙混层、碳酸盐矿物则通过控制与改造储层的孔隙结构间接影响流体可动性;流体可动性的主控因素呈现出"孔隙结构主导,矿物组分间接影响"的特征。研究成果以期为致密砂岩储层的流体可动性评价与优质储层预测提供理论新范式。

关键词: 致密砂岩储层, 可动流体, 敏感因子, 须家河组, 四川盆地