地层破裂压力液压试验数据拟合分析

Analysis on Data Fitting of Hydraulic Test for Formation Fracture Pressure

液压试验法是一种有效获取地层破裂压力的方法,但实际液压试验曲线和理想液压试验曲线差距很大,难以直接从实际液压试验曲线上确定地层漏失压力。为有效解决此问题,从对比分析理想与实际液压试验曲线特征着手,根据理想液压试验曲线与固有频率为π/2、阻尼系数为1.00时的欠阻尼振动方程具有相似的几何特征,提出了一种应用欠阻尼振动方程来拟合液压试验数据、确定地层漏失压力的方法,把利用实际液压试验曲线确定地层漏失压力的难题,转化为对欠阻尼振动方程初始振幅的求解;通过对原始液压试验数据重构分析及合理设定拟合方程参数的初始值和约束条件,有效消除了液压试验数据间的数量级差别、提高拟合计算稳定性。实例分析表明,该方法可为利用实际液压试验曲线确定地层破裂压力提供较为科学的依据。

Hydraulic test method is an effective way to obtain formation fracture pressure.But the actual hydraulic test curve and the ideal hydraulic test curve are very different,so it is difficult to determine the formation leakage pressure directly from the actual hydraulic test curve.In order to effectively solve this problem,starting from the comparison of the characteristics of ideal hydraulic test curve and the actual one,and based on the similar geometric features between the ideal hydraulic test curve and the underdamping vibration equation with the natural frequency ofπ/2and the damping coefficient of1.00,the paper proposes a method to fit the hydraulic test data by using the underdamping vibration equation to determine the leakage pressure,which could transform the problem of determining the leakage pressure based on the actual test curve into the solving of the initial amplitude of the underdamping vibration equation.Through the analysis on reconstruction of the original hydraulic test data and the reasonable setting of the initial values and the constraint conditions of the fitting equation parameters,the difference of the order of magnitude among test data is effectively eliminated and the stability of the fitting is improved.The case analysis shows that this method provides a scientific basis for formation fracture pressure determination by using the actual hydraulic test curves.