FDTD simulation of MWD electromagnetic tools in large-contrast geophysical formations

We describe numerical simulations of electromagnetic logging tools used in oil and gas exploration using a three-dimensional finite-difference time-domain (FDTD) scheme extended to cylindrical coordinates. We pay particular attention to the simulation in geophysical formations exhibiting large contrast on the conductivity values of adjacent beds. Phase and amplitude (continuous wave) information are extracted from very early time domain data. A perfectly matched layer absorbing boundary condition extended to cylindrical coordinates and modified for conductive media (diffusion regime) is employed in the FDTD method to simulate the open domains of realistic oilfields. Results from the FDTD simulations of measurement-while-drilling tools are compared against numerical mode matching results, showing good agreement for conductivity contrasts between adjacent beds in geophysical formations as large as 10 000.