低渗透气藏产水气井稳产能力研究

Research on rate maintenance capability of water producing gas well in low permeability gas reservoir

低渗透气藏低孔、低渗特征使得气体渗流不再满足常规达西渗流原理,气井产水更进一步增加了渗流的复杂性,难以准确预测其稳产能力。基于气水两相渗流原理,考虑启动压力梯度、储层应力敏感、气体滑脱效应、气体紊流效应以及表皮效应,定义气水两相广义拟压力,推导了低渗透气藏产水气井产能公式,并结合产水气藏物质平衡方程得到低渗气藏气水同产井稳产能力预测模型。实例分析表明,理论模型与实际生产动态拟合较好,且敏感性分析表明,随着日产气量、启动压力梯度、应力敏感指数以及水气体积比的逐渐增大,气井稳产年限减小,而随着滑脱因子的不断增大,气井稳产年限增大,但启动压力梯度以及滑脱因子对气井稳产能力的影响较小,基本可忽略不计。

The characteristics of low porosity and low permeability in low permeability gas reservoir make gas seepage not follow the general Darcy percolation theory. The gas well producing water further increases the complexity of percolation, resulting in hardly predicting rate maintenance capability. Based on the percolation theory of gas and water two phase, considering the threshold pressure gradient, reservoir stress sensitivity, gas slippage effect, gas turbulence effect and skin effect, generalized pseudo pressure of gas and water two phase is defined and productivity formula of water producing gas well of low permeability gas reservoir was deduced. Combined with material balance equation of water producing gas reservoir, the rate maintenance capability prediction model of gas and producing well in low permeability gas reservoir is obtained. Practices show that theoretical model is in a good coincidence with actual production dynamic. Sensitivity analysis shows that as the increasing of daily gas production, threshold pressure gradient, stress sensitivity index and water gas volume ratio, rate maintenance life of gas wells decreases. However, as the increasing of slippage factors, rate maintenance life increases. Nevertheless, the impact of threshold pressure gradient and slippage factors on rate maintenance capability is so small that can be ignored.