This paper undertakes the application of Pressurized Mud Cap Drilling (PMCD) technique with Manage Pressure Drilling (MPD) as a new drilling approach in the Unconventional Gas Exploratory field to successfully drill through Nahr Umr & Shuaiba formations managing the risks associated with total losses due to the natural fracs and faults in the area, which if drilled conventionally instigate well control situations, large amount of drilling fluid lost into reservoir and not reaching the target depth (TD).
One of the most powerful drilling techniques to apply in unconventional wells is MPD, It's used to optimize drilling operations under critical challenges, such as narrow window between pore pressure, hole instability and fracture pressure, pressure heterogeneity when drilling different formations and severe downhole losses.
Study was carried out to mitigate challenges across 8-½" and 6″ holes based on previous conventional drilling experiences of simultaneous kick and loss events, MPD system was introduced to overcome that challenge. When severe losses were encountered at Nahr Umr & Shuaiba formations PMCD, an MPD technique, offered the ability to reach well TD despite the total losses using 3 different drilling fluids, Sacrificial fluid (SAC), Light Annular Mud (LAM) and Kill Mud Weight (KMW) in closed-loop drilling without mud returns while stablishing a mud cap in the annulus managing the wellhead pressure by bullheading to stop gas migration.
PMCD facilitated drilling under suddenly total losses minimizing the mud consumption, reduced time/cost and avoided un-controlled release of hydrocarbons. Four wells were successfully drilled, for a total of 1,183 ft, under severe Losses where LCM treatment could not heal the natural fracked formation. PMCD converted conventional drilling into close-loop drilling system by installing Rotating Control Device (RCD) on top of the annular Blow out Preventer (BOP) establishing mud-cap in the annulus and allowing constant monitoring of the well conditions via Surface Back Pressure (SBP). A positive injectivity test was performed after total losses to confirm the formation can take drilling fluid and cuttings. Drilling started with SAC injection in the string and LAM injected intermittently in the annulus through the RCD, whenever the SBP required to be managed due to gas migration effect into the mud cap. Tripping out of hole the drilling BHA and running completions were performed in PMCD mode.
This paper is the number four written (Previous: SPE-207798-MS, SPE-211775-MS & SPE-211775-MS) for the milestones achieved to develop this new area with Geo-political strategic for UAE.
Apply the PMCD, helped to reduce the time of drilling & completion in the UC wells, due to the losses control, from 35 days in average to 10 days, and saving ± 50% of the budget in the target sections (8-1/2″ & 6″).