致密砂岩气井气水两相产能预测半解析模型

致密砂岩气井产能预测受气水两相流特征和裂缝渗流参数影响大,相比于数值模拟,基于解析模型的产能预测计算快、应用较广,但传统的解析模型在处理两相渗流方程非线性问题时简化过大,造成动态分析结果误差较大。针对这一问题,本文考虑了储层和裂缝中的气水两相流动特征,利用三线性流模型表征压裂缝及储层应力敏感性,建立了致密砂岩气井气水两相产能预测模型。将流动物质平衡方程与牛顿迭代法结合,利用平均地层压力逐步更新渗流模型非线性参数,并通过逐次迭代将气水两相模型线性化,获得了模型的半解析解。通过与商业数值模拟软件结果对比以及矿场实例应用验证了模型的准确性,并绘制了气水两相产能预测曲线,分析了敏感性参数对产能的影响规律。研究结果表明,所建立的半解析求解方法能够高效地处理气水两相非线性渗流问题,快速准确地获取致密气井产能预测曲线；致密储层产水严重影响了气井产能,合理的裂缝参数对提高气井产能至关重要；气藏开发过程中应合理控制生产压差,降低应力敏感效应对致密气井产能的影响。

A semi-analytical model of production prediction for tight sandstone gas wells considering gas-water two-phase flow behavior

The productivity prediction of tight sandstone gas wells is greatly affected by the characteristics of gas-water two-phase flow and fracture seepage parameters. Compared with numerical simulations, the productivity prediction based on analytical models is quicker and more widely used. However, traditional analytical models are too simplified to dealing with the nonlinear differential equations in the two-phase seepage flow models, resulting in significant error in production performance analysis. In order to solve this problem, a semi-analytical productivity prediction model of gas-water two-phase flow in tight sandstone formation and hydraulic fractures are presented in this study. A tri-linear model is used to capture the characteristic of hydraulic fracture and formation stress sensitivity. Based on the flowing material balance equation and the Newton iteration method, the semi-analytical solution is obtained using the average formation pressure to update the non-linear parameters of the seepage model gradually and by linearizing the gas-water two-phase model through successive iterations. The precision of the proposed model is validated by using the commercial numerical simulator Eclipse and field case application. Then the production prediction curves of the gas and water phase are obtained, and the effect of several parameters on transient responses is analyzed based on the new method. The results show that the production predicted with the semi-analytical method is accurate for the two-phase flow problem with high computation efficiency. Besides, the tight reservoir water production seriously affects the gas well productivity, and reasonable fracture parameters are essential to increase the productivity of gas wells. In addition, it is crucial to set reasonable producing pressure differential to reduce the negative effect of stress sensitivity on gas productivity in the development of tight gas reservoirs.