低渗透气藏压裂井气水两相产能计算方法

Calculating method of gas-water two-phase productivity in fractured wells of low permeability gas reservoirs

存在边、底水的低渗透气藏易形成气水两相流动,无法准确预测产水气井产能。基于低渗气藏典型渗流特征,考虑气井产水影响,结合压裂气井单相渗流特征,建立了计算低渗气藏压裂气井气水两相产能计算公式,结合气水两相相渗曲线,得到求解气水两相广义拟压力以及压裂直井储层-裂缝气水两相渗流耦合模型。苏东南区A气井实例计算表明,根据线性回归方程求得无阻流量3.3709×10^4m^3/d,利用本文模型计算气井无阻流量3.2919×10^4m^3/d,与产能测试结果对比,绝对误差和相对误差仅为0.079×10^4m^3/d和2.34%,验证了新公式的准确性及适用性。同时,分析了启动压力梯度、应力敏感指数、水气体积比、裂缝半长,以及裂缝导流能力对压裂气井流入动态的影响,为低渗气藏气水两相压裂气井产能研究提供新思路。

Low permeability gas reservoirs with edge and bottom water are easy to form gas-water two-phase flow and cannot accurately predict the productivity of water-producing gas wells.Based on the typical percolation characteristics of low permeability gas reservoirs,considering the influence of water production of gas wells and the single-phase percolation characteristics of fractured gas wells,a formula for calculating gas-water two-phase productivity of fractured gas wells in low permeability gas reservoirs was established.Then combining with the gas-water two-phase permeability curve,the generalized pseudo-pressure of gas-water two-phase and the gas-water two-phase percolation coupling model of straight wells fractured were obtained.The calculation result of a gas well in southeastern of Jiangsu shows that the absolute open flow rate calculated by the linear regression equation was 3.370 9×10^4 m^3/d and the absolute open flow rate calculated by the new model was 3.291 9×10^4 m^3/d.Compared with the productivity test results,the absolute and relative errors of result calculated by the new model were only 0.079×10^4 m^3/d and 2.34%,which verified the accuracy and applicability of the new model.In addition,the effects of starting pressure gradient,stress sensitivity index,water-gas volume ratio,half-length of fracture and fracture conductivity on the inflow performance of fractured gas wells were also analyzed in this paper,which provided a new idea for the productivity study of gas-water two-phase fractured gas wells in low permeability gas reservoirs.