煤层气井水力压裂压力曲线分析模型及应用

Hydraulic fracturing pressure curve analysis and its application to coalbed methane wells

为了确定煤层气井水力压裂裂缝参数,应用连续性方程建立了基于动态滤失系数的压力曲线分析模型.采用有效应力原理研究了有效应力影响下渗透率和孔隙度的变化对动态滤失系数的影响,应用压力曲线分析模型对使用不同黏度压裂液的煤层气井进行了研究.结果表明:综合滤失系数随有效应力减少量增大呈指数形式增加;天然裂隙闭合以前,煤储层的滤失与压力相关,拟合压力的求取应在天然裂隙闭合以后;随着压裂液黏度的增加,裂缝的半翼缝长和压裂液效率增加,裂缝宽度减少,但压裂液效率增加缓慢;煤储层表现出压裂液的高滤失和低效率特征,动态滤失系数为原始值的22.65倍,压裂液的效率仅有13.1%,计算结果与煤储层压裂易形成短宽裂缝的理论相一致.

In order to determine hydraulic fracturing crack parameters,the pressure curve analysis model which considered dynamics filtration coefficient was made by continuity equation.The effective stress principle is employed to analyze how variation in permeability and porosity affect the dynamics filtration coefficient.The pressure curve model is used to study how different viscosities of fracturing fluid affect the well.The results show that the synthetic filtration coefficient increases exponentially as the effective stress decreases.Filtration in the reservoir is associated with stress before the natural fractures close and fitting pressures should be calculated after natural fractures have closed.Crack length and fracturing fluid efficiency both increase,and crack width decreases,as the fluid viscosity increases,but the fracturing fluid efficiency increases slowly.The coal reservoir has characteristics of high filtration,and low efficiency,of the fracturing fluid.The dynamic filtration coefficient is about 22.65 times greater than the original and the fluid efficiency is 13.1 percent.These calculated results agree with the theory that short and wide cracks form easily in the coal reservoir when it is fractured.