Detailed Reservoir Characterization Utilizing Oil- Based Micro-Resistivity Image Logs

The use of borehole image data is an increasingly critical component in evaluating the full potential of a field prior to the initiation of the development phase. Over the years, a number of technological advances have significantly improved quality of the acquired micro-resistivity images in water-based mud systems. However, increasing use of non-conductive mud systems to limit drilling risks and improve efficiency has provided an environment that precluded the use of conventional micro-resistivity imaging devices. This is especially the case in exceptionally deep wells drilled on the edge of continental margins and on far-reach wells drilled from sub sea templates. Thus, it was imperative to develop micro-resistivity imaging technology that would operate in various oil, diesel or synthetic muds, allowing flexibility in the mud system design. This paper introduces the development and successful application of a new oil-based microresistivity imaging device for detailed reservoir characterization. One of the key factors in appraising oil field potential is the production of detailed geological reservoir models. Such models require fine-scale detail such as reservoir heterogeneities, which may act as baffles and barriers to fluid flow, to be accurately identified and populated in the model. Unfortunately conventional openhole log data only allow for identification of sand bodies, thick bedded heterolithic intervals and mudstone successions. A new generation of oil-based borehole imaging devices provides not only high-resolution directional data sets typically used for structural dip determination, but in addition images provide important information concerning sedimentary fabric and texture. This study aims to present a new approach for detailed description of lithofacies and depositional sequences, accurate determination of net-to-gross, determination of palaeocurrent direction, and sand body geometry within an non-conductive mud system that ultimately provides detailed characterization of the reservoir.