Managed Pressure Wells – Managing the Improbable Formation Exposure – A Case Study in Bach Ho Field, Vietnam
Authors: Van Cuong Nguyen , Anh Ta Quoc , Quoc Bao Ta , Hong Duc Vu , Van Dien Nguyen , Singh Harpreet Kaur Dalgit , Kleawyothatis Thakornpol 
Published: August 2024

Abstract
Prediction of pore pressures and fracture pressures is likely to deviate to ensure drilling and completing wells safely and economically. When a well is drilled with no operational drilling window to complete drilling to the target depth (TD), frequency of well control events such as gas kicks and lost circulation rises. Despite utilization of only wellbore strengthening material (WSM) alone, these issues could not be resolved. The managed pressure wells (MPW) techniques, the advanced drilling solution is the ultimate strategy when designing a drilling program to achieve the desired outcome in these types of certain formations. During the spotting and squeezing process, MPW techniques were employed to ensure the effectiveness of injecting the WSM material into the loss zone by actively managing the wellbore pressure.
Issues were encountered during drilling 8-1/2" hole section, client expected the peak pore pressure of 1.936SG higher than at 9-5/8" casing shoe of 1.88SG (Well X) and 1.93SG (Well Y). Client approached first with pumping WSM to enhance the integrity of wellbores, deployed after drilling 9-5/8" shoe track to increase the fracture initiation pressure, to meet expectations as of 2.0SG. MPW techniques deployed with preliminary hydraulic modeling performed: (1) reducing the mud weight, (2) increasing the flow rate while maintaining an acceptable loss rate, and (3) applying surface back pressure (SBP), to help client achieve significant results, applied during mud displacement, tripping, running liner, and managed pressure cementing.
Well X was drilled with MW 1.74SG with equivalent circulating density (ECD) controlled at 1.93SG, minimizing loss rate down until 1 to 2m3/hr. To reduce loss rate due to high ECD, WSM were used, allowing increasing to 1.78SG MW. This adjustment helped reduce drilling gas and prevent well control events, leading to successful completion of the target section at 4020mMD. During the subsequent displacement process, due to increased ECD as the prolonged open hole section and whilst rising of the kill mud weight (KMW) within the annulus caused, well induced severe losses. Subsequently, a multi-stage roll-over mud program was implemented to minimize fluid losses. As an alternative solution, MPW techniques were applied. Upon running the 7" liner, the well was rolled back to a lighter MW, allowing successful execution of managed pressure cementing (MPC).
When drilling Well Y, a loss rate of 10 to 16m3/hr. was detected when drilling into the beginning of the 8-1/2" hole section. This was successfully recovered with WSM materials to seal the fractures, by applying SBP of 700 to 800psi during the pump off events with managed pressure drilling (MPD) practices. The well was drilled successfully to a total depth (TD).
With MPW techniques in conjunction with the proper application of WSM, well control events were prevented, and costs reduced by eliminating the need to run the 7" liner. These procedures overcome challenges such as controlling ECD, managing fluid loss, controlling gas levels, and successfully completing the drilling and cementing operations. In addition, other real-time monitoring, and analysis methods, such as the Dynamic Formation Integrity Test (DFIT) and Dynamic Pore Pressure Test (DPPT), were utilized to gather valuable data for analysis and future drilling designs.