Step-Change in Reducing Oil Deferment in Northern Sultanate of Oman: Successful Application of Managed Pressure Drilling Enables Drilling Nearby Online Water Injector Wells
Authors: Harrasi Nadir Ali Al , Abuawad Ahmed Soliman , Orta Cesar E , Farsi Mohammed Malallah Al , Hashmi Mohammed Salim , Mashrafi Majid Mohammed , Riyamy Khaleel Ahmed , Shehhi Saif Said 
Published: November 2024

Oil deferment is experienced when drilling wells on fields where some formations are waterflooded to increase the production. In some cases, the Power Injector Wells (PIW) must be shut down up to 2 or 14 days prior to drilling ahead, resulting in a very slow drilling campaign together with a reduction in production. The water injection also yielded high uncertainty of the downhole environment in both planning and execution phases of the drilling process, resulting in several MW adjustments when observing influxes into the wellbore.

Managed Pressure Drilling (MPD) represents an advanced technique for primary well control. It typically utilizes a closed, pressurized circulating fluid system, enabling more precise management of wellbore pressure profiles compared to adjustments based solely on mud weight or mud pump rates. The primary goal of MPD is to enhance drilling efficiency by minimizing nonproductive time (NPT) and mitigating drilling-related risks.

This paper discusses the successful trials of a new approach to drill the 8 ½" hole section through Shuaiba Lower, Hawar Shale and Kharaib formations in the Lekhwair field, to reduce the risk associated while drilling through potential high-pressure points while optimizing the drilling operations. The pressure points have been triggered by some induced fractures from the water injectors.

The team carried out a study on the existing process of drilling 8 ½" holes aiming to eliminate the need of shutting down the nearby injector wells and depressurize the field. This led to the selection of Managed Pressure Drilling (MPD) technique, specifically the applied Surface Back Pressure (SBP) and Constant Bottom Hole Pressure (CBHP) variation of MPD. MPD is a closed-loop drilling system with returns diverted away from the rig floor through a dedicated flow line and a drilling choke manifold. The well is continuously monitored, and the annulus pressure is controlled through the SBP. At the same time, the injection pressure from nearby wells was monitored and communicated to the drilling team on site for awareness.

By 2024 the team delivered 3 (three) trial wells drilled with MPD without shutting down the nearby injector wells: a vertical well and a deviated well in 2023, and a horizontal well in 2024. In all 3 (three) a hydrostatically underbalanced mud weight (MW) was used while drilling with MPD to allow the execution of dynamic pore pressure tests (DPPT) to ascertain the connectivity with nearby injector wells and to determine the required tripping MW for completion operations. The drill pipe connections while drilling were performed following CBHP procedures, adding and adjusting the required SBP to maintain the bottom hole pressure constant, this was achieved with the use of a third triplex pump dedicated to establish flow through the MPD choke manifold when performing connections.

This technology is a step change in the journey to address the risks while drilling nearby online injector wells in Sultanate of Oman. It generates a huge value by avoiding oil production deferment and enable reaching the oil productivity commitments.