Workflow to Image Unconformities with Deep Electromagnetic LWD Measurements Enables Well Placement in Complex Scenarios

Abstract

The advent of deep-reading directional electromagnetic logging-while-drilling measurements brings opportunities in imaging complex formations around the wellbore. In this context, basing the inversions on an assumption of a layered medium is not always sufficient to decouple geometrical effects in complex formation scenarios.Rather than attempting to invert all variables of a generic 2D formation model simultaneously, we describe in this paper how the use of 2D inversions can be enabled through a robust workflow specifically designed for a class of formation models, in this case the angular unconformity. We demonstrate how the successive application of 1D inversion to subsets of tool data gradually builds a formation model for use as input to a 2D inversion, which accounts for complex couplings present in the data in such environments.The validity and the performance of the method are established through synthetic and field datasets. IntroductionSince the introduction in 2005 of deep and directional logging-while-drilling (LWD) electromagnetic (EM) measurements, thousands of wells have been geosteered based on remote boundary imaging, in a variety of reservoirs and geological environments. The standard processing applied to the measurements is a multilayer 1D inversion. Although this type of processing is valid in a large number of cases and has supported many successful operations, this paper introduces a different way of processing measurements to produce a more structured image of the formation around the wellbore and successfully address nonlayered scenarios in which the risks associated with the errors in running the standard processing might increase beyond desirable levels.We present a processing workflow running automatically through multiple inversion steps and minimizing the bias introduced by users. The steps gradually build a richer model of the subsurface, while introducing measurements with sensitivities matching the model features added at each step. The concept was implemented and tested on a specific family of nonlayered scenarios, the angular unconformity.The first sections summarize the LWD tools and the traditional 1D and 2.5D forward modeling and inversion concepts used in the workflow and throughout the industry. Then, the characteristics of the angular unconformity scenarios are defined, before some arguments are given to justify the need for an imaging workflow rather than a single inversion in the first place as is standard. The workflow steps are detailed next, and in the final sections the results and stability on synthetic and field examples are discussed.

Net pay Optimization and Improved Reservoir Mapping From Ultra-Deep Look Around LWD-measurements

“…Based on the modeling exercise, the conductivity surrounding the tool and the resistivity of the sand layers affect the depth of investigation. We believe that applying specialized workflow targeting OWC, similar to one developed to map unconformities (Dupuis et al, 2013) has a potential to better map the OWC and help resolve the structure, the resistivity distributions, and transition zones of the formation layers, which can then be used for 3D reservoir characterization. Another observation that can be made from Fig.…”

3D Reservoir Mapping While Drilling

“…The RMWD service has been run on a large number of wells in dozens of fields around the world (Beer et al 2010;Constable et al 2012;Jenkins et al 2012;Dupuis et al 2013).…”

Automatic inversion of deep-directional-resistivity measurements for well placement and reservoir description

“…Then, recognizing structure and features in the result opens the door to further, more specialized 1D, 2D, or 3D forward modeling and inversion processing (Antonsen et al, 2014;Dupuis et al, 2013; and a wide array of postprocessing methods (filtering, clustering, and so forth) based more directly on subsurface knowledge.…”