页岩气储层低频脉冲水力压裂增渗机理研究

Hydraulic fracturing, the most important way, has performed very well on the application of shale gas reservoir stimulation. However, there are a few technique problems, such as high fluid volume costs and low liquid power efficiency and so on. To solve those problems, a new concept of low frequency pulsed hydraulic fracturing process is proposed. This new method with the characteristic of shock wave and cyclic loading is expected to improve the length and complexity of the artificial fractures. The study of the mechanism of low frequency pulsed hydraulic fracturing for improving the stimulation effect in shale gas play will be conducted from following three parts:1) To study the dynamic characteristic of low frequency hydraulic fracturing by implementing CFD numerical simulation thereby achieving the propagation and attenuation pattern of low frequency pulse pressure in the fracture.2) To investigate the mechanism of the fracture&damage and the permeability improving of shale plays under low frequency pulsed hydraulic fracturing by conducting the experiments under triaxial stresses. The acoustic emission, coloring and slicing techniques will be used for fracture detecting in the experiments. The above study will improve experimental and theoretical foundation for this new technology development and also can be the technical reference to similar technical study to other brittle reservoirs.

水力压裂是当前页岩气储层改造的最主要方式，获得较好推广应用的同时也存在压裂液用量大、能量利用率低、体积改造效果不理想等瓶颈问题。为此，本课题提出低频脉冲水力压裂改造页岩气储层的新思想。该方法利用低频脉冲的冲击振动及循环加载等特性，可有效提高裂缝长度和裂缝复杂程度，达到高效低能耗的体积压裂改造目的。本课题从两个方面开展低频脉冲水力压裂提高页岩气储层改造效果的机理研究：1)通过数值模拟研究低频脉冲在水力压裂过程中水动力特性，分析得出低频脉冲能量在裂缝中的传播及衰减规律；2)设计室内三轴压裂实验，采用声发射技术和染色切片等裂缝监测技术，研究低频脉冲水力压裂作用下页岩的断裂损伤和增渗机理。以上研究将为页岩气储层低频脉冲水力压裂技术研发提供必要的实验及理论依据，也可为其它脆性储层脉冲水力压裂改造技术开发作技术参考。

本项目采用室内实验、理论分析和数值模拟等多种手段，综合研究了目的层页岩的力学性能和可压裂性指标，探索了脉动水力压裂断裂损伤机理，初步形成了脉冲水力压裂技术理论。主要研究成果如下：（1）建立了二维水力脉冲应力波传播物理模型，分析了脉冲压力波传播和衰减规律；（2）建立了脉冲水力压裂多裂缝扩展力学模型和极限判据，综合分析了脉冲水力压裂页岩断裂损伤机理；（3）构建了可以模拟不同脉冲波形、脉冲压力和频率的脉动水力压裂裂缝扩展实验系统，开展了页岩脉冲水力压裂裂缝扩展实验；（4）建立了脉冲水力压裂裂缝扩展有限元数值模型，研究了水力脉动参数、物理力学性质等对复杂缝网形成和延伸的影响；（5）建立渗流模拟数值模型，进行了主控因素对页岩井筒流量变化的影响分析，研究了低频脉冲压裂增渗机理。以上研究将为页岩气储层脉冲水力压裂技术研发提供必要的实验及理论依据，也可为其它脆性储层脉冲水力压裂改造技术开发作技术参考。