煤层气压裂中阶梯排量测试确定地层闭合压力的新方法

A New Method to Determine Formation Closure Pressure for the Step-Rate Test in Hydraulic Fracturing of Coal Bed

在煤层气水力压裂主压前进行的阶梯排量测试,主要用来确定地层闭合压力。常规方法是根据地面压力和排量之间曲线的斜率变化进行确定,存在的问题是斜率变化不明显,确定的地层闭合压力不够准确。为此,根据不稳定渗流和试井理论,推导出排量阶梯变化时的压降方程。根据该方法所作的曲线斜率变化比较明显,所确定的地层闭合压力较准确。计算实例表明该方法可以成功应用到实际现场。

Before the main hydraulic fracturing in coal-bed methane,the step-rate test is mainly used to determine the formation closure pressure.Conventionally,the determination of formation closure pressure is based on the variation in slope between ground pressure and flow rate,which has problems of no obvious variation in slope and no accurate determination of formation closure pressure.Pressure drawdown equations are derived when flow rate varies in step form based on the theories of non-steady permeable flow and well test.The variation in slope in the curve plotted by using the new method is obvious and formation closure pressure determined by this method is accurate.