Successful Deepwater MPD Application in Drilling and Cementing Through Depleted Formation with Wellbore Instability and Loss Circulation Challenge Offshore of Sabah

Abstract

Managed Pressure Drilling (MPD) has become the essential drilling technique to drill problematic zones in these past decades due to its ability to precisely manipulate downhole equivalent mud weight (EMW). This ability empowers the operator to save time and cost when drilling through loss zone with lower drilling fluid and at the same time, able to retain EMW above the wellbore instability or, if required, pore pressure gradient.

This paper describes the crucial role of MPD in a drilling operation on a horizontal deep water oil producer well in Sabah region, offshore of East Malaysia, to help the Operator recover from Wellbore Instability and Loss Circulation issues and successfully drill and cement the problematic section. The main challenge of the well is the tight drilling window between depleted sand formation and the interlayered shale formation. Therefore, the MPD Integrated Riser Joint (IRJ) was deployed along with the riser string prior drilling 12.25 in hole section. Initially, the section was drilled conventionally with wellbore strengthening techniques, only to encounter unmanageable static losses. After multiple unsuccessful attempts to cure losses, the section was cement plugged to sidetrack the well.

Considering the substantial challenges encountered, the well was sidetracked with lighter drilling fluid and applied surface back pressure (SBP) to maintain its bottom hole pressure above the wellbore instability gradient and below the fracture gradient. After the well had reached target depth, the drilling assembly was pulled out of hole in MPD mode without having to displace the well to heavier tripping mud and, once it was above the Subsea Blowout Preventor (SSBOP), the well was then isolated with blind shear rams (BSR). To continue maintaining SBP below the BSR, the MPD system was lined up on a surface loop circulation in such a way that the SBP was applied to the well via kill line. With the casing string delivered to the bottom, Managed Pressure Cementing (MPC) was utilized to cement the casing by having a schedule of SBP against pumped strokes that was formulated by software simulation to give a minimum pressure surge when the cement slurry entered the open hole.

In addition, the paper also describes the equipment setup required onboard a drillship for drilling with MPD in a deep-water setting. The MPD setup enables the application of advanced flow detection system and riser gas handling which are critical in drilling deep water wells. With all these features, MPD Deepwater application has successfully delivered the well to target depth which once was undrillable.