With ever increasing well construction challenges associated with lithology, downhole temperatures & pressures, the need for high performance concentric hole enlargement has never been more essential to meet the clients well objectives. Hole Enlargement portrays an area of concern by multiple oil & gas operators due to the challenging nature of enlarging a hole that subjects the tool & string members to aggressive dynamic vibrations especially when combined with thermal stresses and unpredictable lithology.
While drilling a challenging deep development well in Kuwait, the drilling engineers considered enlarging a 2,000 ft 6 inch horizontal interval to 7 inch (17% beyond the bit diameter) to facilitate 5 inch liner being run to TD & mitigate restrictions which have resulted in significant NPT due to a 50% shale & 50% lime stone unstable interval. Drilling that section has encountered multiple issues associated with the high downhole temperature in terms of directional drilling motor failures costing the operator 4 tripping cycles to replace failed tools.
Defining a hole enlargement operation using a hydraulically actuated underreamer in such challenging well was supported through an extensive application engineering feasibility study from both the service provider and operator, initiating from an operational risk assessment, hydraulic optimization simulations to ensure maximum cooling and cutting delivery efficiency, Torque & Drag analysis, vibration and critical speed interpretation, stuck pipe simulations to effectively analyze jar placement performance. The underreamer was successfully operated in downhole temperatures exceeding 300 degrees Fahrenheit and the 2000 ft interval was enlarged in 2 trips. Additional PDC cutting structure work-rate modeling was utilized to optimize the positioning of the PDC cutters for an enhanced cutting efficiency in addition to real time field support that provides drilling parameter recommendations for weight on reamer, RPM, & ROP for the entire interval to mitigate additional trips and improve drilling efficiency.
Enhancing drilling efficiency while managing NPT was the defined objectives for both parties while initially designing a hole enlargement application engineering package. This was successfully implemented and saved the operator 3 days of rig time on the planned drilling time.