基于Arps产量递减模型的页岩损失气量计算方法

A new calculation method for lost gas content of shale based on Arps production decline analysis model

含气量是页岩气储层评价的关键参数,其准确测试是计算地质储量和确定开发方案的基础。为了准确计算页岩含气量测试中的损失气量,引入经典的Arps产量递减分析方法进行了页岩含气量的分析,建立了一种基于Arps产量递减模型的页岩损失气量计算新方法。气体解析速率递减曲线与气井产量递减曲线较为类似,应用双曲递减模型、指数递减模型及调和递减模型对其进行非线性拟合,分析表明调和递减模型的拟合效果较差,双曲递减和指数递减模型拟合效果均较好。并与常用的USBM直线法和多项式法进行了对比,发现Arps指数递减模型的计算结果均介于直线法和多项式法计算结果之间,计算结果更为准确、合理。在取心方式和计算方法确定的情况下,损失时间的确定是含气量计算中最重要的影响因素,分析认为目前的损失时间确定方法是不准确的,需结合现场实际情况进一步研究。

Gas content is the key parameter for shale gas reservoir evaluation,and its accurate measurement is the basis for calculating geological reserves and determining development plans.In order to accurately calculate the lost gas content in shale gas field-test,the classical Arps production decline analysis method was introduced to analyze the gas content of shale,and a new method for calculating the lost gas based on this model was established.The curve of gas desorption rate decline is similar to that of gas well production decline curve.The nonlinear fitting of hyperbolic decreasing model,exponential decline model and harmonic decreasing model were applied for nonlinear fitting.Analysis results show that the fitting effect of harmonic decreasing model is poor,and the fitting effect of hyperbolic decreasing and exponential decreasing model is much better.Compared with the commonly used USBM linear method and polynomial method,it is found that the calculated results of the Arps exponential decline model are between the results of the USBM linear method and the polynomial method,and the calculation results are more accurate and reasonable.The determination of the lost time is the most important factor in the calculation of gas content.It is considered that the current method of determining the lost time is inaccurate,and it is necessary to be further studied under the actual situation of shale gas field.