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采用真三轴压裂物理模拟的方法,研究了四川页岩储层压裂过程中的水力裂缝扩展行为和裂缝形态.实验结果表明,四川页岩压裂裂缝扩展模式分为主裂缝多分支裂缝和网状复杂裂缝.在水平主应力差较高的实验条件下,压力曲线波动频率高且趋势平稳,实时声发射监测结果表明,在实验的前期压裂裂缝易穿过天然节理,并形成单一主裂缝,而在实验的后期易形成多分支裂缝;在水平应力差较低条件下,压力曲线波动频率高但是不时伴有压力陡降,声发射监测结果表明,水力裂缝扩展易沿着页岩天然裂缝系统扩展,并形成复杂裂缝形态.定义了水力裂缝垂直穿过页岩层理面时的临界摩擦系数,采用实验参数和结果,揭示了在上述条件下,水平地应力差异系数和临界摩擦系数之间的相互关系,随着水平地应力差异系数的增加,临界摩擦系数显著降低.上述研究对中国的深层页岩气开发具有一定的指导意义.
Using the method of true triaxial fracturing physical simulation, the hydraulic crack propagation behavior and fracture morphology during the fracturing of shale reservoirs in Sichuan Province are studied.The experimental results show that the fracture propagation modes of shale fractures in Sichuan are divided into multi-branch fractures And mesh-like complex fractures.Under the experimental conditions that the horizontal principal stress difference is high, the frequency of the pressure curve is high and the trend is steady. The monitoring results of real-time acoustic emission show that the fractures in the early stage of the experiment easily pass through the natural joints and form a single Main fractures, and easy to form multi-branch fractures in the later stage of the experiment. Under the condition of low horizontal stress difference, the pressure curve fluctuates frequently but is accompanied by sudden pressure drop from time to time. The acoustic emission monitoring results show that the hydraulic fractures are easy to expand along the shale The natural fracture system is extended and the complex fracture morphology is formed.The critical friction coefficient of hydraulic fractures perpendicular to shale bedding plane is defined.The experimental data and the results show that under the above conditions the horizontal stress difference coefficient and the critical friction coefficient , The critical friction coefficient decreases remarkably with the increase of the horizontal stress difference coefficient.The above studies show that the deep shale gas Hair has some significance.