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煤层气藏数值模拟是煤层气水平井历史数据拟合以及生产预测的有效工具,但是计算耗时长,所需参数多。为了得到一个简单而精度足够的生产预测方法,由稳态解析的产能方程结合非稳态的边界条件可以得到煤层气井在线性流下的半解析模型。根据煤层气水平井的数值计算结果以及前人的研究成果,煤层在一维(线性或径向)非稳态渗流阶段流体饱和度和压力的关系随时间、空间变化不明显。本文通过煤层渗流控制方程推导了压力和饱和度的计算模型,并给出了由地层压力近似计算含水饱和度的方法,为气水两相渗流模型提供了计算基础。通过半解析模型与数值计算结果的对比,以及对沁水盆地两口水平井的历史数据拟合,验证了半解析模型的正确性和实用性。
CBM reservoir numerical simulation is an effective tool for historical data fitting and production prediction of CBM horizontal wells. However, it takes a long time and requires many parameters. In order to obtain a simple and accurate production forecasting method, a semi-analytical model of coal-bed gas flow in linear flow can be obtained from the steady-state analytical productivity equation combined with unsteady boundary conditions. According to the numerical results of coalbed methane horizontal wells and previous research results, the relationship between fluid saturation and pressure in one-dimensional (linear or radial) unsteady seepage stage of coal seam is not obvious with time and space. In this paper, the calculation model of pressure and saturation is deduced from the coal seam seepage control equation. The method of calculating the water saturation by the formation pressure is given, which provides the basis for the gas-water two-phase seepage model. Through the comparison between the semi-analytical model and numerical calculation results and the fitting of historical data of two horizontal wells in Qinshui Basin, the correctness and practicability of the semi-analytical model are verified.