1.5D BASED INVERSION OF LOGGING-WHILE-DRILLING RESISTIVITY MEASUREMENTS IN 3D FORMATIONS

Abstract

This manuscript describes an extension of a computer method developed for the fast inversion of logging-while-drilling (LWD) resistivity measurements Pardo and Torres-Verdín (2015); Bakr et al. (2016). The method enables to simultaneously invert measurements recorded at different wells using possibly different commercial LWD co-axial and tri-axial logging instruments. The original three-dimensional (3D) transversely isotropic (TI) reservoir is approximated by a sequence of several "stitched" one-dimensional (1D) TI sections. Then, multiple 1.5D semi-analytical solutions are employed for simulation and inversion. The key novel contribution presented here is the ability to invert also for bed boundary locations in addition to the previously available inversion of horizontal and vertical resistivity values. Numerical experiments performed over numerous synthetic examples show that in most of the considered realistic 3D synthetic formations, the inversion method enables to properly recover the formation model composed of resistivity values and bed boundary locations from measurements acquired at multiple wells. Thus, it provides a useful method to properly interpret LWD resistivity measurements, especially in the presence of abnormal readings such as horns, which are prone to misinterpretation. We are currently working on the extension of this method to the case of deep and extra-deep azimuthal resistivity measurements.