含环状天线槽正交方位随钻电磁波测井仪器三维有限体积法数值模拟

针对由多环状天线槽构成的方位随钻电磁波测井仪器真实结构,基于柱坐标系下耦合势Helmholtz方程和三维有限体积法研究建立一套相应的三维电磁响应数值模拟算法.首先,采用柱坐标系下三维不规则Yee氏交错网格对计算区域进行剖分,保证了钻铤表面附近的剖分网格与非光滑刻槽钻铤表面同形;并利用电场延拓边界条件逼近钻铤表面的理想电...

Numerical simulation of the LWD orthogonal azimuth electromagnetic tool with annular antenna recesses by the 3D finite volume method

All antennas of the sensor of the LWD orthogonal azimuth electromagnetic tool (LWD-OAEMT) are installed in the annular recesses on the grooved metal drill collar. The recesses are often filled with ferrite or other magnetic materials to seal the coils. In this paper, we apply the Helmholtz equations about coupling potentials and three-dimensional finite volume method (3D FVM) with cylindrical grids to simulate the responses of the LWD tool consisting of multiple antenna recesses on the non-smooth grooved metal mandrel surface. Firstly, irregular Yee's staggered grids in cylindrical-coordinate system are used to guarantee the grid near the mandrel surface is conformal with the non-smooth grooved tool geometry. The electrical field continuation technique is employed to approximate the perfectly electric conductor (PEC) boundary condition in order to efficiently improve the discretization precision of the coupling potential on the grooved drill collar surface. On this basis, the equivalent conductivity and magnetic permeability in a heterogeneous element are determined by the standardization technique, and the 3D FVM is employed to discretize the coupling potential equations in the cylindrical coordinates and the transmitting antennas in the annular recesses. Then, the Parallel Direct Sparse Solver (PARDISO) is used to solve the discrete equations to ensure the accuracy of numerical simulation and increase the stability of solutions. Finally, the 3D FVM is validated with comparison of results by numerical model matching (NMM) algorithm in homogeneous formation. In terms of numerical results, we further examine the influence of metal drill collar and antenna recesses on the LWD tool and its response characteristics in the layered TI formation model with different borehole dipping angles.