Fast inversion of logging-while-drilling resistivity measurements acquired in multiple wells

Abstract

This paper introduces a new method for the fast inversion of borehole resistivity measurements acquired in multiple wells using logging-while-drilling (LWD) instruments. There are two key novel contributions. First, we approximate general three-dimensional (3D) transversely isotropic (TI) formations with a sequence of several \stitched" one-dimensional (1D) planarly layered TI sections. This allows us to approximate the solution of rather complex 3D formations using only 1.5D simulations. Second, the developed method supports the simultaneous inversion of measurements acquired in different neighboring wells and/or with different logging instruments. Numerical experiments performed with realistic 3D synthetic formations confirm the flexibility of the method and the reliability of inversion products. The method yields relative errors below 5% on the model space, and it enables the interpretation of resistivity measurements acquired in multiple wells (e.g., an exploratory, an offset, and a geosteering well) and with any combination of co-axial and/or tri-axial commercial logging measurements acquired with known antennae configurations. Numerical results also indicate that thinly-bedded resistive formations are very sensitive to the presence of noise on the measurements and/or to possible errors on bed boundary locations, while conductive layers are only weakly sensitive to those effects.