川西地区九龙山构造砾岩储层敏感性实验分析

An experimental analysis of sensitivity of the Jiulongshan conglomerate reservoirs in West Sichuan Basin

四川盆地西北部九龙山构造下侏罗统珍珠冲组气藏的储层岩石矿物特征和孔隙结构十分特殊和复杂,颗粒大、裂缝发育且非均质性强,具有低孔隙度、低渗透率致密储层的特征,目前对开发过程中的储层伤害机理及主要伤害因素尚未掌握。为此,进行了系统的岩心实验分析,结果表明:该区储层总体表现为强速敏性和强—极强水敏性,速敏渗透率损害率为67.2%～94.1%,水敏渗透率损害率为71.3%～95.5%,渗透率越低,速敏性越强;碱敏性中等偏强—强,碱敏渗透率损害率为48.6%～90.9%,酸敏性弱,注酸前后渗透率变化不大;应力敏感性强,裂缝受压后产生闭合难于恢复,渗透率损失率大。总之,该气藏储层敏感性强,极易被伤害,主要伤害类型为水敏、速敏和应力敏感,建议气田生产中避免"强采强注",施工中采用合理矿化度的工作液,加入适当的黏土稳定剂,并控制酸碱度。

The reservoir in the Lower Jurassic Zhenzhuchong Formation of the Jiulongshan structure,northwestern Sichuan Basin,is a complex and fractured-type conglomerate reservoir,of which rock minerals and pore structures are highly special and complex.Characterized by large rock grains,developed fractures,and intense heterogeneity,this reservoir is regarded as a typical low-porosity and low-permeability tight reservoir.For lack of a better understanding of the mechanism of reservoir damage and the major factors of reservoir damage,a core sensitivity analysis is needed.The systematic core experimental analysis showed that the reservoir has strong velocity sensitivity and strong to super strong water sensitivity,the velocity-sensitivity permeability damage rate is 67.2% to 94.1%,the water-sensitivity permeability damage rate is 71.3% to 95.5%,whereas the lower the permeability is,the stronger the velocity sensitivity.The Alkali sensitivity is from moderately strong to strong,and the alkali-sensitivity permeability damage rate is 48.6% to 90.9%,but the acidic sensitivity is rather weak with no significant change in permeability rate either before or after acid injection.The stress sensitivity is strong,and the fracture closure resulting from increased confining pressure is difficult to recover,and the permeability loss is high.It is concluded that the sensitivity of the Jiulongshan reservoir is strong,prone to various types of damages including water-sensitivity,velocity-sensitivity and stress sensitivity damages.Therefore,it is suggested that the intensive injection and production should be avoided in order to reduce the velocity-sensitivity and stress-sensitivity damages.Similarly,during the construction,a liquid with a proper degree of mineralization should be adopted with a appropriate amount of clay stabilizer added,and the pH value should be carefully controlled.