Guoyu Hu

3D simulation of LWD directional resistivity tool response using FDFD potential formulations

*u Summary The authors present a novel finite-difference frequencydomain (FDFD) method for simulating the response of a logging-while-drilling (LWD) directional resistivity tool in three-dimensional borehole environments. This new method is based on the numerical solution of the boundaryvalue problem of the electromagnetic coupled potentials using the finite-difference approximation in a cylindrical coordinate system. Numerical simulation examples are provided to show the validity, accuracy, and efficiency of this new numerical formulation. All the results obtained by this method agreed well with 1D analytical, 2D numerical mode matching (NMM), and 3D FDTD results. The FDFD method is used to show environmental effects on a tilted antenna LWD tool.

Borehole And Invasion Effects of New Asymmetric Array Induction Tools

The equations to evaluate borehole and invasion effects of Halliburton’s new asymmetric array induction tools, ACRtTM and H-ACRtTM, have been developed according to the geometric factor theory of induction logging. To use these equations, we first examined the borehole effects. The numerical simulation confirms that when the borehole size is less than or equal to 10 inches, the three long spacing subarrays are not usually affected by the borehole conditions (mud, borehole size, and tool eccentricity). Then we investigated the invasion effects. For the fixed invasion depth and borehole conditions, the invasion effect is approximately a linear function of the conductivity difference between invaded-zone and virgin formation; for the fixed conductivity difference between the invaded-zone and bed formation, the invasion effect is a non-linear function of the invaded depth. We can also use the equations for estimating the required depth of invasion for the given log curve separation, or for estimating the maximum curve separation for the given depth of invasion.