EFDT地层测试泵抽取样过程数值模拟分析

Numerical simulation analysis of fluid sampling process during EFDT formation testing

为提高电缆地层测试工具EFDT泵抽取样的效率,对钻井液滤液和原始地层流体分别建立质量守恒方程,采用有限体积法进行空间离散,应用全隐式格式和Newton-Raphson迭代法求解方程,建立泵抽取样过程数学模型,编制地层流体泵抽取样数值模拟程序。对不同类型探针(标准探针、大极板式探针和三维径向探针)的泵抽取样过程进行数值模拟分析。结果表明:三维径向探针可以显著增加过流面积,极大缩短抽取合格样品时间,在低渗和中高渗地层中能保持较高的作业效率,适合复杂地层采样作业。在泵抽取样过程中,标准探针和大极板式探针钻井液滤液和原始地层流体的流动呈“锥”状的两相驱替流态,原始地层流体突破较早,清理钻井液滤液、达到取样标准的时间较长。该结果为电缆地层测试地层流体泵抽取样过程中探针的选取和泵抽时间的估计提供参考。

To enhance the EFDT sampling efficiency of wireline formation testing,we developed a numerical model of the fluid sampling process.Mass conservation equations were constructed for both drilling fluid filtrate and virgin formation fluid.The finite volume approach was utilized for spatial discretization,and the solution was obtained by Newton-Raphson iterative with a fully implicit scheme.We simulated and analyzed the sampling process with different probes,namely the standard probe,elongated probe,and 3D probe.The results show that the 3D probe significantly increases the flow area and greatly shortens the sampling time of obtaining qualified samples.Besides,the 3D probe can maintain excellent operation efficiency not only in formations of intermediate to high permeability but also in low permeability formations.Hence,it proves to be more suitable for intricate formation sampling operations.The standard probe and elongated probe exhibited a conical flow pattern during fluid sampling,enabling them to withdraw the virgin formation fluid at an earlier stage,but reach the requirements comparatively more slowly.The results could serve as a valuable reference for the selection of probe and the estimation of pump-out time during wireline formation fluid sampling.