New Well Construction Strategy Defies Challenges and Enables Successful Development of a Newly Found Oilfield Offshore Dubai

Abstract

The last marine cycle of Dubai Lower-Cretaceous has left reefal carbonate deposits on paleo-highs from deep basement faults. Those shores face deposits at the edge of the former Bab basin and developed very good reservoir but had a prolonged emersion prior to the deposition of Nahr Umr seal and are often karstified. A successful development relied on high-angle drilling through an unstable seal and advance geosteering within a complex reservoir with a thin oil leg. A unique drilling approach in the region was designed and executed to deliver these wells safely. Oil- based mud (OBM), casing while drilling (CWD), and steering assembly were deployed to build safely in unstable shale and land at a high angle within the reservoir close to the roof in a relatively slim hydrocarbon column. The reservoir presents a succession of clinoforms. Good porosity and permeability streaks are present with tighter zones. Karsts, often linked with faults, represent a threat to drilling and well completion. The new high-definition reservoir mapping while drilling (RMWD) (6-in reservoir) was introduced to accurately steer within this reservoir. Simulations of drilling dynamics revealed the best BHA and casing designs. Over seven wells, this method was optimized by using an RSS and executing the 3D trajectory with required build rate and with no compromise on ROP. CWD was used to drill up to 12,481ft MD, which is the deepest in the world for such technology. Without it, inevitable slump down to the water leg would compromise the development of the entire field. The new RMWD technology revealed the reservoir details by mapping over 100 ft thickness of structure and fluid contacts. Subseismic Karsts and the irregular shale-carbonate contacts were precisely delineated. This allowed proactive reactions while drilling and avoided costly sidetracks. Clinoforms were resolved; transition zones and oil water contact depths were mapped. Over the course of seven wells, the information gathered allowed a redefinition of the entire field model from both a geological and reservoir perspective. As result, the original oil in place (OOIP) was recalculated with a renewed field development plan. The technical execution enabled the production of dry oil wells while steering as high as possible within the most permeable layers at a high rate, mitigating karst risk. The introduction of successful CWD eliminated the need to drill the 8^-in section. Four days were saved during the well construction process, and drilling risks associated with unstable and reactive shale were greatly reduced. The new RMWD technology in the lateral section potentially saved millions in development strategies and completion plans by mapping the complete oil column, transition, and water zones while providing safe geosteering away from karstic shales.