川西低孔低渗砂岩储层敏感性与压裂液伤害机制实验研究

Experimental Study on Sensitivity and Fracturing Fluid Damage Mechanism of Low-Porosity and Low-Permeability Sandstone Reservoirs in Western Sichuan

摘要: 低孔低渗砂岩储层已成为我国油气增储上产的核心领域，川西地区JP44、JS31-2、J3P层该类储层储量丰富，但受地质条件复杂、工程作业干扰等因素影响，储层敏感性伤害与压裂液伤害问题突出，严重制约产能释放。为明确该区域储层伤害特征与机制，以研究区钻井取心岩样为对象，通过X射线衍射(XRD)分析、敏感性评价实验、压裂液岩心伤害实验等手段，系统开展矿物成分及物性分析、6类敏感性评价及多配方压裂液伤害测试。结果表明：研究区储层以石英、长石为主，JS31-2层粘土矿物含量最高(>36%)，粘土矿物类型以伊蒙混层、绿蒙混层、伊利石为主；储层普遍存在强速敏(速敏指数 > 80%)、强应力敏感特征，水敏、酸敏、碱敏、盐敏表现出显著层位异质性；压裂液伤害程度排序为瓜胶压裂液 > 胶液 > 降阻水 > 解吸附类压裂液，解吸附降阻水对JS31-2层伤害率仅13.33%，为最优配方。研究成果为川西低孔低渗砂岩储层保护与压裂液优化提供了实验依据与技术支撑。

Abstract: Low-porosity and low-permeability sandstone reservoirs have become the core area for increasing oil and gas reserves and production in China. The JP44, JS31-2, and J3P layers in the western Sichuan region are rich in reserves of such reservoirs. However, due to factors such as complex geological conditions and engineering operation interference, issues of reservoir sensitivity damage and fracturing fluid damage are prominent, severely restricting the release of production capacity. To clarify the characteristics and mechanisms of reservoir damage in this area, drilling core samples from the study area were used as the subject. Through X-ray diffraction (XRD) analysis, sensitivity evaluation experiments, fracturing fluid core damage experiments, and other methods, systematic analyses of mineral composition and physical properties, six types of sensitivity evaluations, and multi-formulation fracturing fluid damage tests were conducted. The results indicate that the reservoirs in the study area are dominated by quartz and feldspar. The JS31-2 layer has the highest clay mineral content (>36%), with clay minerals mainly being illite-smectite mixed layer, chlorite-smectite mixed layer, and illite. The reservoirs generally exhibit strong velocity sensitivity (velocity sensitivity index >80%) and strong stress sensitivity characteristics. Water sensitivity, acid sensitivity, alkali sensitivity, and salt sensitivity show significant layer heterogeneity. The degree of fracturing fluid damage is ranked as follows: guar gum fracturing fluid > gel fluid > friction reducer > desorption-type fracturing fluid. The desorption friction reducer has a damage rate of only 13.33% for the JS31-2 layer, making it the optimal formulation. The research results provide experimental evidence and technical support for the protection of low-porosity and low-permeability sandstone reservoirs and the optimization of fracturing fluids in western Sichuan.