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

We have developed a new method for the fast inversion of borehole resistivity measurements acquired in multiple wells using logging-while-drilling instruments. There are two key novel contributions. First, we approximate general 3D transversely isotropic (TI) formations with a sequence of several “stitched” 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 the inversion products. The method yields relative errors of less than 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 coaxial and/or triaxial 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, whereas conductive layers are only weakly sensitive to those effects.