Making Un-Drillable HPHT Well Drillable using Mud Cap Drilling

Abstract The operator of Well-A, a HPHT gas well in offshore Abu Dhabi faced a difficulty to drill ahead in a high-pressure fractured gas reservoir of "K" formation due to severe lost circulation followed by gas influx into the wellbore, namely loss/kick incident. The sudden and huge amount of mud losses at the bottom part of the reservoir led to gas flowing from the upper one observing a rapid pressure hump in the annulus between the wellbore and drill pipe. The operator then experienced complex well control situations including the burning of the entry gas to the atmosphere. The hole was finally plugged for the sidetracking due to a sticking occasion during the remedial action for the losses. The integrated drilling team recognized a little or no success of drilling to the intended well total depth in case of continuously using conventional drilling methods, began to pursue alternatives and soon initiated Mud Cap Drilling, one of the MPD methods at the multiply fractured reservoir while drilling the 8–3/8″ sidetracked hole. The application of the Mud Cap Drilling permitted efficient drilling resulting in 27 days' time saving compared with the planned duration. Furthermore, it completely prevented the well from flowing and could make the un-drillable well drillable. This successful drilling of the problematic gas reservoir using Mud Cap Drilling in the Well A has made a further encouragement of drilling HPHT gas exploration wells, which contain a lot of uncertainties in the formation pore pressure and fracture gradient profiles. The MPD as a flow control and pressure steering tool will prevent the forthcoming HPHT gas exploration wells from several drilling hazards resulting in NPT such as kick control, losses, wellbore instability, and differential sticking, slow ROP, etc. Moreover, it will allow minimizing the number of casing to be run and reducing formation damage to the gas reservoir. This paper describes the positive impacts of the application using PMCD equipment, lessons learned from the implementation and areas for the further improvement of MPD application in future.