非线性流下低渗气藏酸压井产能方程

Analysis of the productivity equation of acid fracturing well in low-permeability gas reservoir with non-linear seepage

针对酸压过程中形成的蚓孔区对气井产能影响,根据酸压裂后气体渗流规律变化,建立考虑滑脱效应、启动压力梯度、应力敏感共同影响下低渗气藏有限导流垂直酸压裂缝井产能预测模型,进行酸压井产能的影响因素敏感性分析.结果表明:启动压力梯度和应力敏感使气井产能下降,启动压力梯度和应力敏感系数越大,气井产能下降幅度越大,滑脱效应使气井产能增大,滑脱因子越大,气井产能增加幅度越大;气井产能随裂缝半长的增加而增加,增加幅度随裂缝半长的增加而减小,且在一定裂缝长度下,裂缝导流能力存在一个最佳值,其随裂缝半长增加而增加;蚓孔区系统的蚓孔长度越长,气井产能下降幅度越大,而蚓孔区渗透率越大,气井产能下降幅度越小,渗透率达到一定值后,下降幅度可忽略.

The wormholing zone is formed in the course of acid fracturing,which affects the gas well productivity.In view of the acid wormholing zone,based on the change of fluid flow rule after fracturing,using the steady seepage theory,with the influence of the start-up pressure gradient,slippage effect and stress sensitivity in the low-permeability gas reservoirs taken into account,a gas well productivity prediction model was established for the finite conductivity vertical acid fracture wells.The parameters sensitivity analysis for productivity of the acid fracturing well is analyzed by using examples.The result shows that the gas well productivity decline is caused by start-up pressure gradient and stress sensitivity and high speed non-Darcy flow effect,and along with start-up pressure gradient and deformation coefficient of permeability enlargement,the gas well production continues to decline.While the slippage effect leads to increase in gas well production,and along with slippage factor enlargement,the gas well production continues to increase.Along with the crack length enlargement,the gas well production continues to increase,and the increasing extent is decline.Under a certain crack length,there is an optimum fracture diversion capacity,which continues to increase along with the crack length enlargement.The longer the length of acidizing wormhole is in the acid wormholing zone,the more the decreasing extent of the gas well productivity.The higher the permeability is in the acid wormholing zone,the less the decreasing extent of the gas well productivity.When the permeability reaches a certain value,the decline can be ignored.