ABSTRACT

We have developed an efficient inversion method to estimate layer-by-layer electric resistivity from logging-while-drilling electromagnetic induction measurements. The method assumes a 1D model based on planarly layered transversely isotropic formations with known bed boundaries, penetrated by arbitrary well trajectories. Forward simulations are based on a 1D reduced model in which borehole and mandrel effects are assumed to be negligible. The stopping criteria, regularization term, regularization parameter, the Jacobian matrix, and inversion variables are automatically estimated by the inversion algorithm, thereby minimizing the required user interaction and expertise. Numerical inversion results of challenging synthetic and field data confirmed the high stability and superior approximation properties of the developed inversion algorithm. We evaluated results indicating that triaxial induction measurements provide significantly more stable inversion results than conventional coaxial measurements, especially in the presence of anisotropic formations.

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