一种修正的煤层气藏地层压力与含水饱和度的关系模型

A modified model for the relationship between formation pressure and water saturation in coalbed methane reservoirs

杨龙 张艺钟 徐亚飞 张茂林 鞠斌 周育瑞 王家琛

长江大学石油工程学院，湖北 武汉 430100 长江大学非常规油气湖北省协同创新中心，湖北 武汉 430100 中国石化中原油田分公司
勘探开发研究院，河南 濮阳 457001 西南石油大学石油与天然气工程学院，四川 成都 610500

煤层气藏地层压力与含水饱和度的关系模型可以应用于煤层气藏开采的多个方面，包括解吸面积的计算、流动物质平衡方程的建立、有效渗透率的评价、煤层气井产量的预测、采收率的标定等，因此准确表征地层压力与含水饱和度的关系变得尤为重要。然而目前被广泛使用的煤层气藏地层压力和含水饱和度关系的计算方法（半解析法）忽略了地层压力小于临界解吸压力时，煤基质收缩效应对孔隙压缩系数的影响，导致在地层压力较低时计算的含水饱和度偏大。为了弥补半解析法的缺陷，文中考虑煤基质收缩效应对孔隙压缩系数的影响，重新修正了地层压力与含水饱和度的关系模型。经过与数值模拟、半解析法的对比可知，在地层压力小于临界解吸压力时，半解析法的模型计算结果偏大。文中修正模型的计算结果与数值模拟结果基本吻合，验证了文中方法的准确性。从这些结果可以看出，在计算含水饱和度时不能忽略煤基质收缩效应对孔隙压缩系数的影响。文中修正的模型弥补了目前半解析法存在的缺陷，并且计算过程简单、准确，具有广泛的应用价值。

The model of the relationship between formation pressure and water saturation in coalbed methane reservoirs can be applied to many aspects of coalbed methane recovery, including the calculation of desorption area, the establishment of flowing material balance equation, the evaluation of effective permeability, the prediction of coalbed methane well production, and the calibration of recovery. It becomes particularly important to accurately characterize the relationship between formation pressure and water saturation. However, the widely used method (semi-analytical method) of calculating the relationship between formation pressure and water saturation in coalbed methane reservoirs ignores the effect of coal matrix shrinkage on the pore compression coefficient when the formation pressure is less than the critical desorption pressure, resulting in a large water saturation calculated at low formation pressure. To compensate for the defects of the semi-analytical method, the model of the relationship between formation pressure and water saturation in coalbed methane reservoir is reworked in this study by considering the effect of coal matrix shrinkage on the pore compression coefficient. After comparing with the numerical simulation and the semi-analytical method, the calculation results of the semi-analytical method is thought to be large when the formation pressure is smaller than the critical desorption pressure. The calculation results of the modified model in this paper are basically consistent with the numerical simulation results, which verifies the accuracy of the method proposed in this paper. From these results, the effect of coal matrix shrinkage on the pore compression coefficient cannot be ignored when calculating the water saturation. The modified model in this paper makes up for the defects of the current semi-analytical method, and the calculation process is simple and accurate, which can be widely applied.

10.6056/dkyqt202302015