Active Pressure Management Maintained the Primary Well Control and Enabled to Strengthen and Drill through Naturally Fractured Carbonates Formation with Extremely Narrow Drilling Margins and Resulting in One of the Vital Hydrocarbons Discovery in Northern Pakistan – A Successful Approach of Managing Wellbore Pressure Profiles by Managed Pressure Drilling (MPD)
Authors: Ashraf Qasim , Chisti Uzma , Tashfeen Muhammad , Farooq Muhammad Umar , Rehman Muhammad Abdul 
Published: October 2023

Drilling through narrow drilling margins in wildcat wells always proves to be a challenging task where uncertainties regarding drilling windows make operators decide bottom hole equivalent circulating densities (ECDs) based on unclear data, resulting in a loss/gain scenario during drilling. This paper describes the effective use of the constant bottom hole pressure (CBHP) variant of Managed Pressure Drilling (MPD) in the wildcat well of X-1 to explain the successful drilling of the reservoir section, providing an incredibly narrow window of 0.08 SG across Lockhart & underlying formations by actively controlling the wellbore ECDs. While drilling 8 3/8" section at X -1 utilizing MW of 1.47 SG across carbonates of Lockhart formation, drilling proved to be challenging as complete losses occurred which resulted in complex well control scenario. Therefore, avoiding losses and sustaining primary control seemed to be a nearly impossible task after performing various attempts to cure losses by spotting heavy LCMs, which added to the risk by clogging the string. Hence a narrow drilling window coupled with loss/gain scenario and a plugged drilling string altogether made the operator rethink the drilling strategy.

Active bottom hole pressure management techniques, such as Managed Pressure Drilling enables to walk between the lines of pore and fracture limits with the best efficiency and integrity. Managed pressure drilling's ability to dynamically control the well enabled the operator to dynamically maintain the primary barrier and to drill through the naturally fractured loss/gain prone formation of Lockhart by utilizing underbalanced mud weight of 1.35 SG MW while maintaining ECDs ranging 1.47-1.55 SG across critical interval of Lockhart formation. Additionally, determining drilling margins through the use of dynamic pore pressure tests (DPPT) and dynamic formation integrity tests (DFIT) made the operator to make crucial choice of drilling through the Lockhart formation (Primary Reservoir) along with underlying Hangu, Kawagarh, Lumshiwal, and Chichali formations.

Effective management of annular pressure profiles resulted in successful drilling of 8 3/8" hole section without any further complications. Using low mud weight & managing ECD while drilling Lockhart formation reduced losses and thus avoided reservoir damage, which contributed to the large reservoir discovery. The discovery of a new field in Northern Pakistan using an unconventional way to control, drill, and ascertain well behavior has opened up new frontiers. This study discusses the effectiveness of MPD's CBHP technique in critical well control situations along with the design of active pressure control hydraulics, suitable for narrow margins along with all operational details, providing crucial results for comparable applications in the future.