High-Resolution LWD Resistivity Images for Carbonate Facies Identification and Geosteering

Abstract

Abstract Accurate placement of the borehole within the reservoir and identification of features impacting producibility are key elements for success. Experience to date, shows that the drilling environment offers a good platform for high definition electrical borehole imaging. At the time of drilling, invasion and borehole wall rugosity are often minimal and electrical images generated by sensors that rotate with the drill string provide a full coverage of the borehole. It also provides an opportunity for real-time geological analysis while drilling and the decision making that is unavailable with wireline. Detailed analysis of images reveal discrete sedimentological and textural features aiding facies recognition in carbonate reservoirs. These facies can be up-scaled to facies associations and eventually used for depositional environment interpretation. This leads to wider prospect delineation and confirmation of the local geological model. The study also demonstrates the strength of early geological information in high-resolution for reducing geological uncertainty at an early development drilling program. We show case studies from several carbonate reservoirs in which high resolution electrical images have been acquired in conjunction with reservoir navigation (well placement). From post well analysis, we can define the key criteria that help in recognition of reservoir position; correlatable sedimentary surfaces and image facies/patterns. We test the distribution of facies and sedimentological features that can be recognised in horizontal boreholes by comparison to vertical offset wells, in addition to automated facies recognition from image log responses. The development of a Sedimentary or carbonate facies steering technique using high-resolution images with a predictive and real-time interface will reduce uncertainties related to and better aid geosteering within the desired "sweet-spot" of a variety of clastic and carbonate reservoirs.