Near Bit, Real-Time 1D and 3D Ultra-Deep Resistivity Inversion; A Case Study in the Longest Maximum-Reservoir-Contact well Offshore Abu Dhabi, UAE

Abstract

Abstract For decades, horizontal wells, offshore Abu Dhabi have been planned and executed with the objective of enhancing well productivity, injectivity, and to reduce water coning. One of the main methods of maximizing reservoir contact is through targeting two reservoir layers in one horizontal section. To enable these specific targets, the implementation of innovative geosteering solutions has a major role in securing the success of the project. Early warning and deep horizon mapping is critical, therefore we demonstrate the innovation of the placement for the Ultra-deep azimuthal resistivity (UDAR) logging while drilling (LWD) transmitter close to the bit. The subject well targets two carbonate reservoirs layers by drilling a single eight and half inch, horizontal section. The drilled footage along each formation was approximately 4000 ft of lateral length with a total length of 8000 ft measured depth. Consequently, a six- and three-quarter inch OD UDAR tool has been combined with a triple combo bottom hole assembly, in order to enhance the well placement, with the aim of simultaneous geosteering and GeoMapping using advanced 1D inversion processing in real-time. In geosteering operations early decision making allows for more gentle corrections to be made, limiting tortuosity, critical in very long wells. The latest technology, allows deployment of a UDAR transmitter close to the bit in this study ~25 ft. Providing both UDAR inversions and actual Shallow Phase / Attenuation Resistivity measurements. The Well encountered multiple geological and drilling challenges during the real time drilling operations. Despite the evident complexities in density images, which indicated the undulation of the formation, the 1D UDAR Inversions clearly identified the stratigraphic position of the well allowing for optimal well placement decisions to be made early due to the proximity of the UDAR transmitter to the bit. Additionally, the 1D inversions allowed early identification of a conductive zone below the trajectory at the heel as well as a conductive zone above the well trajectory towards the toe. This was interpreted as water coning / slumping, vividly displayed in the UDAR azimuthal resistivity image, 1D Inversion and 3D inversion, the direction of the low conductive zone was coming from the left-top side of the trajectory, indicating alignment with the nearest offset well. The 1D/3D inversion data provided has increased confidence for the completion team to finalize blanking sections and pump design in a timely manner to isolate the zone at risk from water breakthrough. This successful run with regards to both operations and safety has set a benchmark for future development for saving operation time and cost.