Two-Dimensional Inversion of Papua New Guinea Magnetotelluric Data with Smoothness Regularization

Two-dimensional inversion has been applied to magnetotelluric data obtained for petroleum exploration in Papua New Guinea. For the inversion, an impedance tensor is rotated to the general strike direction of the area, and TM, TE and determinant impedances are calculated. Distortion-corrected data are also derived to compare the results with the inversion of the original data. The inversion method applied is the linearized least-squares scheme with smoothness regularization. The optimum smoothness is selected based on a statistical criterion, ABIC, which is derived from Bayesian statistics and the maximum entropy theorem. The forward calculation is based on the finite-element method. Topography along the survey line is included in the mesh. The start model is a homogeneous earth, and the final models, obtained by the inversions of TM data, TM and TE data, and determinant data, are generally consistent with each other. A surface high-resistivity layer of 100-1, 000 Ω· m corresponds to Miocene limestone with a thickness of approximately 1 km. It is underlain by a thick low-resistivity layer of Mesozoic sedimentary rocks which form oil reservoirs.