A Novel Engineered Drilling Solution using a Sourceless Geosteering Bottomhole Assembly to Deliver the Longest Extended-Reach Well in a Carbonate Reservoir, Onshore Abu Dhabi, UAE

Abstract

To develop a mature onshore carbonate field in Abu Dhabi and reduce the footprint and cost, an artificial island has been built in shallow water that can accommodate drilling rigs and extended-reach wells. This paper presents a case study of the longest onshore well drilled in Abu Dhabi. Planning to drill such a deep well starts long before execution, using offset well data and extended-reach drilling (ERD) engineering. There were formation and reservoir challenges due to the uncertainty in the earth model in the horizontal section of the well. Hence, it was very challenging to maintain contact with the thin reservoir intervals, without approaching the boundaries. In addition, the limited power available to drive the drillstring and maintain circulation drove the ERD engineering team to find optimum solutions, including drillstring and bottomhole assembly (BHA) design. Furthermore, there was a known risk of differential sticking, which meant that the use of radioactive sources in the BHA was undesirable. The well was planned to be drilled in two runs, using nuclear measurements in the first run and non-nuclear measurements in the second. A well-placement methodology and workflow was developed and integrated with the geological understanding of the target layer. Analysis of offset horizontal wells resulted in the delivery of an optimized BHA design, including careful selection of logging-while-drilling (LWD) technologies, to mitigate the geological challenges. The BHA also included a new generation of intelligent, fully rotating, high-dogleg, push-the-bit rotary-steerable system, to geosteer the well in the thin target layer while maintaining the planned target trajectory with minimum borehole tortuosity by means of real-time drilling optimization. The extended-reach horizontal section was drilled successfully, and the geosteering objectives were achieved with 100% reservoir contact over a 20,000-ft interval, targeting a thin carbonate layer and overcoming the complex geological environment. The well was drilled to a record depth of 32,300 ft. The new intelligent rotary steerable system with automatic cruise control helped to eliminate any well-profile issues, minimize wellbore tortuosity, and maintain aggressive drilling parameters. The nuclear and non-nuclear LWD measurements, including NMR, helped to reinforce understanding of the reservoir properties along the entire section. This success has opened the door for drilling more challenging wells. In addition, it has proved that proper planning and execution can shift the boundaries further and gave confidence to drill even deeper.