Successful Managed Pressure Drilling Application in a Challenging Well With Crossflow in Unconventional Field
Authors: Zhang Hua , Muhammad Jamal uddin , Alhajri Naif Mutlaq 
Published: March 2023

Unconventional tight gas well encountered unexpected losses at target depth and simultaneously well control took place from water source in upper zone. Bleed off tests concluded it was kick rather than ballooning. Combining upper flow and lower loss zones resulted in downhole crossflow and near zero mud window providing high operational risks to drill next 5-7/8 inch horizontal section. Managed Pressure Drilling (MPD) was utilized to drill horizontal section, mitigate well control risk and reach reservoir target.

Prior to MPD selection, several attempts could not heal losses. The contigent 7 inch drilling liner was installed however it could not isolate the flow zone. MPD maintains constant bottom-hole pressure and enables full circulation. Under near zero mud weight (MW) window condition using same method of maintaining flow out equal to flow in would create high risk of well control as there is high possibility of influx moving up and diluting drilling fluid. It was necessary to maintain constant bottom-hole pressure during drilling and tripping by forcing influx to move down to lower fracture zone with acceptable rate of losses.

During well construction with a fully automated MPD system, as a starting point MPD static pore pressure test (PPT) precisely detected pore pressure of water flow zone, establishing the low limit of the drilling window. During successful drilling of 3,027 feet in horizontal section, the influx was forced to move down to the lower loss zone with 5 to 20 barrels per hour dynamic losses. Real-time instantaneous annular pressure adjustment with MPD system minimized losses and managed well without interrupting drilling process even under condition of losses change to gain varying by only 25 psi surface back pressure (SBP). Benefits of multi stage displacement, detection and mitigation the swab and surge by stripping in and out also proved that MPD system made the process safer. Furthermore, in such well having no mud window, early detection of gain or losses tendency was imperative, so that the remedy actions could be applied immediately before things worsened with time. MPD system had the capability to detect gain/loss relatively early than the rig pit-volume system. Moreover, the target bottomhole pressure was adjusted almost instantly by adjusting the SBP by MPD system. The well would be considered un-drillable without MPD.

MPD added safety factor during releasing stuck pipe operations where the low weight spotting fluids utilized. A fully automated MPD system provided a solution for specific risk condition such as near zero MW window and crossflow while drilling unconventional tight gas horizontal well. The precise and instant control of bottom hole pressure was the key factor of overall success.

This paper summarizes the implementation of the fully automated MPD system as a sophisticated tool to precisely control such situations instantly, saving time, associated mud costs and hence optimize the overall drilling process.