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2D RESERVOIR IMAGING USING DEEP DIRECTIONAL RESISTIVITY MEA

Deep directional electromagnetic (EM) logging-while-drilling technology is the principal enabler of proactive well placement, relying on real-time interpretation through a 1D multilayer inversion, integrated with geological modeling software. The new-generation reservoir-scale measurements are used to map lithological boundaries and fluid contacts in excess of 30 m away from the wellbore and to optimize well placement in increasingly more-complex scenarios. As the drilling progresses, deep directional resistivity data is continuously inverted to estimate the 1D formation resistivity profile locally, and the inversion results are stacked to create a 2D reservoir map. This approach is adequate if the formation is layered and slowly varying laterally. However, in complex reservoir scenarios with locally 2D or 3D structures or where the formation changes abruptly, the 1D approximation used in real-time inversion may not be the most accurate solution.

We introduce a new, minimally biased 2D inversion to accurately map complex reservoir structures. The 2D pixel-based inversion makes no assumption about the reservoir model, and the inversion can image non-1D geological structures such as faults, sand injectites, shale lenses, and other complex geometries with arbitrary anisotropic resistivity distributions. The fully automated algorithm runs a 2.5D EM simulator in the inversion loop and requires no user input except selecting the processing interval. An adaptive regularization ensures that the most plausible resistivity distribution with the least resistivity variation is found that is consistent with the data. The algorithm is parallelized to run on a cluster. The algorithm is feasible for real-time application, provided relatively moderate computational resources are available. Runtime for typical processing of a 200-ft interval is about 2 hr on a cluster with 500 cores.

The inversion is validated on several realistic 2D synthetic multilayer models with faults and other lateral discontinuities. The inversion has been applied to multiple deep directional resistivity field data sets, demonstrating its ability to accurately map faults and sand injectite reservoirs over long intervals. The new reservoir maps derived from the 2D inversion would enable more quantitative and informed well placement decisions, deliver detailed insight about the reservoir structure, and allow a precise refinement of existing reservoir models.
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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.