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3D Electromagnetic Modeling and Quality Control of Ultradeep

Reliable interpretation of borehole electromagnetic (EM) measurements acquired in horizontal and high-angle wells requires fast, robust, and versatile solutions of forward and inverse problems of Maxwell’s system in complex three-dimensional (3D) anisotropic formations. Based on recent advances in numerical simulation methods, we implement 3D anisotropic EM modeling and inversion software and algorithms to simulate and quality control (QC) ultradeep azimuthal resistivity (UDAR) measurements. The combination of fast modeling and inversion under complex and anisotropic 3D earth-model conditions enables us to accurately quantify the limits of resolution and uncertainty of UDAR measurements.
The software and algorithms allow fast and robust modeling based on the finite-volume homogenization technique together with a special reduced-order gridding procedure. This modeling strategy enables the use of model-independent finite-volume grids in tool coordinates combined with a global-model grid accepting inputs from commonly used 3D earth-model rendering formats. While the tool moves along the well trajectory, the formation determined on the 3D global grid shifts and rotates in tool coordinates. Furthermore, we implement several fast direct and iterative solvers in our modeling/inversion workflow, all of which yield practically identical results. Parallel computing also allows real-time modeling.
Our modeling approach is effective for the multidimensional inversion of UDAR profiling/logging along arbitrary well trajectories. Benchmarks and examples of UDAR simulations on operator’s 3D subsurface models confirm the efficacy of our simulation method. The accompanying figure describes a benchmark example including a 3D simulation of commercial UDAR measurements acquired across a spatially complex formation model with two faults. Numerical simulation time for 3,000 couplings of logging points and tool configurations is less than 8 CPU hours on a typical laptop and less than 20 seconds on a supercomputer. The benchmark was also verified against an independent 3D EM modeling method. Our 3D fully anisotropic modeling software can be used for real-time inversion QC of commercial UDAR tool measurements. A 3D simulation based on a two-dimensional (2D) model of the well curtain section (obtained as stitched-together 1D models: results obtained from 1D inversion of commercial measurements) and comparison of this simulation to actual tool measurements identify the sections of the well trajectory where 2D-3D inversion is needed to decrease the data misfit to acceptable values (i.e., measurement noise levels).
Future endeavors include fast, fully anisotropic 2D-3D measurement simulation using adaptive upscaling of 3D models and novel 2D-3D inversion algorithms specifically designed for UDAR measurement conditions. Our goal is to develop real-time 2D and 3D inversion of UDAR measurements for well geosteering and refined 3D subsurface model rendering as additional measurements and geometrical constraints are included into the inversion by asset teams.
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Our vision is to advance the science of formation evaluation through electrical, nuclear, lithological, and other well logging techniques; to promote the proper application of these techniques to exploration for and exploitation of gas, oil and other naturally occurring substances; to maintain high ethical standards and to further the interests of persons professionally engaged in these endeavors. With the support of our Oil and Gas, Service, Software and Educational Institutions we can make a difference in the industry.