Real-Time 1D and 3D Ultra-Deep-Azimuthal-Resistivity Inversion Enabled Enhanced Geosteering Decisions and Water-Flood Monitoring, a Case Study in a Carbonate Reservoir, Offshore Abu Dhabi
Authors: Al Shehhi Noora Saeed , Al Hosani Mohamed Abdulla , Al-Ali Jamal Ahmed , Al Jaberi Salem Mubarak , Zubahar Ikhsan , Manurung Vinda , Reda Ashrakat , Fares Wael 
Published: November 2024

Production wells in mature offshore fields encounter many challenges. In this study the main consideration is avoidance of early water breakthrough driven by injection/production. Encountering water complicates effective completion and production operations. Real-time understanding of the geology and fluids, particularly water saturation variance is required to optimize well placement. This case study is from a recent well in a mature field offshore UAE. Reservoir fluid mapping solution utilizing the latest technology was identified as the most effective method to confront the challenges in this well.

The well target was planned for approximately 1400 feet, targeting a specific carbonate layer in a 6″ open hole horizontal section. Precise geosteering required that a combination of logging while drilling technologies were deployed: 4-3/4″ OD Ultra-Deep-Azimuthal-Resistivity (UDAR); Triple Combo; and a borehole Imaging laterolog high-resolution resistivity-based tool (for detailed formation evaluation). In addition, advanced geosteering algorithms for processing 1D and 3D inversions were deployed in real-time for geomapping. The focus on real-time fluid mapping supported identification of any increasing proximity to the conductive water zone, highlighting areas that could cause water flooding during production. During well placement and steering operations, this focus was maintained through the whole operation from the planning stage; through the execution stage (Real-time Modelling); and post well analysis as validation of steering actions post TD.

During drilling the 6″ hole section several geological and drilling challenges were encountered. Pro-active maneuvering of the trajectory to land in the reservoir's optimum zone was required in the early interval due to setting of the previous section's casing shoe in the dense layer above the target reservoir. UDAR inversions were the main reference for both shallow-depth-based steering and mapping. The top boundary above the target formation was mapped allowing continual interpretation of formation dip, which was in the range of 1.3 – 1.8 deg up towards the toe. Simultaneously, the bottom boundary of the target reservoir was continuously mapped to TD 8 – 10 ft below trajectory and this is where the main challenge was identified with the identification of a conductive water zone with increased proximity to the wellbore. Early TD was called as both 1D and 3D inversion results identified the hazard.

Effective action by utilizing 1D and 3D UDAR Inversion in real-time had enabled the well placement in the optimum hydrocarbon bearing zone. Geosteering and geomapping services had facilitated the rapid and critical decision to stop drilling, to prevent the possibility of water entering the well. To continue drilling and completion operations without identifying nearby water movement in this section would result in significant water production. This wouldn't be possible using conventional electromagnetic tools. Operational offshore well time was successfully reduced by 2 days, equivalent up to $ 640k USD. In the later stage, production of this well had provide promising results, maximizing well life by at least 1 year. This practice will set a new standard for future appraisal and mature reservoir wells.