煤层气井裸眼洞穴完井机理数值模拟研究

Numerical Simulation of CBM Open-hole Cavity Completion Mechanism

基于UDEC软件建立了煤层气井注入气体增压过程的离散元数值模型,结合离散元理论对数值模型进行分析,并利用室内实验对煤岩的力学参数进行了测定。结合煤岩储层中存在的两种天然裂缝形态——面割理和端割理模拟并分析不同地应力条件下,注入气体增压过程中井筒周围煤岩有效应力、孔隙压力和节点位移矢量分布。研究表明,煤岩的特殊结构(割理系统)对储层流体的运移和基质变形有一定的影响。流体的运移速率在面割理和端割理方向会引起应力的集中和分散,进而产生应力梯度,有利于剪切破坏的发生。在各向异性应力储层中,煤层更容易产生破裂和坍塌。煤岩内节点的位移矢量分布间接地反映了注气增压过程中不同注入压力下煤岩张性裂缝的发展趋势。

Based on UDEC, we established a numerical model by simulating the process of gas injection to coalbed methane （CBM） well. Combined with the discrete element theory, we analyzed the model, and determined the mechanical parameters of coal rock with indoor experiments. In the model, two kinds of fractures in the coal were considered---face cleat and butt cleat. Besides, the model simulated the effective stress, pore pressure and the node vector displacement near the well-bore while injecting gas are analyzed under different stresses. Study showed that the special structure of the coal rock （ cleat system） exerted certain influence on the fluid transportation and matrix transformation of the reservoir. The migration rate of the fluid in the face cleat and butt cleat, which induced stress concentration and dispersion, was helpful to the shear fail- ure. In the anisotropic stress reservoirs the anisotropic reservoir was easier to produce rupture and collapse. The displace- ment figure of the node vector was the reflection of the tendency of tensile fracture in the pressurization process under different injection.