裂缝性应力敏感气藏的数值试井分析

根据裂缝性应力敏感气藏的实验数据和试井理论,建立了渗透率呈指数形式变化的双重介质试井模型,并引入了渗透率模量的概念。利用有限元方法开发了相应的数值试井软件,并分析了典型曲线特征。应力敏感双对数曲线主要分为三个阶段。在第一阶段,其特征与常规气藏情形相同,表现为斜率为1.0的直线;中间是过渡阶段,在相同的储能系数和窜流系数的条件下,过渡期的长短受渗透率模量的控制,渗透率模量越小过渡期越长;在第三阶段表现为径向流特征,压力导数值是一个小于0.5的常数,压力和压力导数曲线的开口宽度大于常规气藏。若用常规试井解释软件解释表皮系数,其结果可能很大。常规试井软件和应力敏感试井软件实际应用对比结果表明:新方法能够准确地识别异常高压应力敏感气藏的地层参数和评价酸化改造效果。

Numerical well test analysis of stress-sensitive fractured gas reservoirs

On the basis of the experimental data of stress-sensitive reservoir and well test theories, the dual media numerical well test model was established in consideration of stress sensitive permeability. The concept of permeability module was introduced to the model. The numerical well test interpretation software was developed by finite element method. The typical curves were gained and analyzed with the software. The dual logarithmic curve consists of three periods. In the first period, it has the similar characteristics as conventional gas reservoir, showing as a straight line at slope of 1.0. In the transition period, the length is controlled by permeability modulus under condition of the same storage factor and crossflow factor, the smaller the permeabitity modulus, the longer the transition period length. In the third period, the pressure of reservoir shows a semi-log straight line, and the value of derivative pressure is a constant less than 0.5. In the log-log plot, the distance of pressure curve to the pressure derivative curve of pressure sensitive reservoir is larger than that of the normal reservoir. The interpretation result of skin factor will be abnormal positive for the sensitive data interpreted by the traditional software. A field example analysis with the new numerical simulator shows that the numerical well test analysis can accurately identify the formation parameters and evaluate the acidization effectiveness of the ultra-high stress-sensitive gas reservoir contrasting the normal well test software.