A Unique Engineering Approach in Horizontal Drilling Through Unconsolidated Formations to Minimize Time and Cost Using High-Build-Rate Rotary Steerable Systems in Sultanate of Oman

Drilling horizontal wells with a high dogleg severity (DLS) of 10–16 deg/30 m is the approach that one operator in Oman adopted to drill the buildup section. The 8½-in section used to be drilled with a conventional motor BHA, which took around 4 days to complete. Due to the high DLS, it was required to slide at least 80% of the time. This led to a slow drilling rate, hole cleaning issues, and difficulties running the 7-in liner afterward. For a step change to happen, a full directional drilling system had to be reengineered with an extensive study of the BHA and well design. The objective was to reduce the total drilling time in the 8½-in BUS, improve the borehole quality, and reduce flat time. Traditional rotary steerable systems (RSS) are limited with their steering capabilities. A hybrid, high-build-rate RSS with push- and point-the-bit features offers the capabilities of achieving a DLS of up to 17 deg/30 m as it is independent of outside formation. Implementing the new approach eliminated the long sliding intervals and poor borehole cleaning caused by limited surface rotation with the motor BHA. The system was modeled using finite element drilling dynamics simulation software, with multiple bits and drillstring configurations to optimize the directional results. In addition, compressive study of the mud properties enabled drilling the section safely throughout Nahr Umar shale. Later, the same system was coupled with a high-torque motor, and the results showed an even better performance, which the operator plans to consider in the future to enhance the drilling rate. The use of a hybrid RSS system with a specific bit built for the application has proven its success as an integrated engineered drilling solution. It reduced the 8½-in section drilling time by 50% with improved borehole quality and delivered an overall ROP that is approximately three times what a motor BHA would have delivered. The improvement is a result of the use of PDC over TCI bits and the elimination of slide drilling. In addition, full rotation and elimination of micro-DLS resulted in smoother liner running operation. While drilling, the 100% rotational steering improved the overall hole cleaning, and the modified mud properties and additives helped eliminate the wiper trips performed previously prior to reaching the reservoir section. The success of this integrated system led the operator to replace all the motors in the entire field. This paper emphasizes the impact of new technology together with effective well engineering in drilling efficiency. With current industry focus on cost control, high-DLS RSS technology introduces new savings when used in the right application. This particular case is very common across the industry and proves the many advantages of integrated engineering projects.