Achieving CO2 Emissions Reduction by Overcoming Well Integrity Challenges in High Pressure and Narrow Window Environments: A Case Study of a Giant Middle East Deep Gas Field

Abstract While drilling the 12″ section, a water bearing formation is encountered prior to reaching the target gas reservoir formation. This formation is sporadically-charged across the field requiring a KMW up to 21 ppg. This poses major well integrity challenges as it becomes critical to avoid losses in the resulting narrow mud window and ensuring proper cement placement. Inability to predict the mud window makes it impossible to define the drilling strategy to implement. To understand the drilling challenges, in-depth offset wells analysis was performed. Based on mud weights required to drill across the reference formation, the heat-map for historical KMW was created based on confirmed well control events. It was difficult to predict formation-flow potential. Field geomechanics studies was then carried out to correlate the mapping done earlier. Once possibility of encountering abnormally pressured formation is flagged, in order prevent drilling risks such as loss circulation and poor cementing placement, proactive measures such as: Improved influx monitoring, drilling/cementing fluids optimization, liner-and-tieback system implementation, Managed Pressure Drilling/Cementing, optimized casing design were put in place. The integrated approach led to quick influx detection, proper definition of mud window, i.e. Pore Pressure and Fracture Gradient together, helped to prevent the losses, design of fit-for-purpose bridging strategy to ensure full drilling fluid column at all time while avoiding the cost associated with fluid losses. Drilling the section with Managed Pressure Drilling system (MPD) and low mud weight led to achievement of high ROP leading to substantial time saving. The Liner string was run and Managed Pressure Cementing (MPC) was implemented to manage the equivalent circulating density (ECD), avoid losses and ensure good zonal isolation. Overall non-productive time was reduced by 40% as compared to the offset wells in the area. Integrated drilling approach delivers great gains when there is good understanding of the well integrity challenges and solutions are tailored to solve identified problems.