We often face a higher level of difficulty when using conventional methods to drill through a formation with a narrow pressure window. Even slight changes to bottom hole pressure can lead to unwanted non-productive time (NPT) in the process of securing the well, such as handling a loss and/or kick in the wellbore, or even at times, an underground blowout.
Maintaining Constant Bottom Hole Pressure (CBHP) is one of Weatherford's Managed Pressure Drilling (MPD) technologies used to drill safely by keeping the well overbalanced yet below fracture gradient. This is done by applying Surface Back Pressure (SBP) through the use of a Rotating Control Device (RCD) and an Automated MPD Choke Manifold. CBHP applies precise surface back pressure into the annulus by means of automated MPD system to maintain the annulus pressure when circulating and static. CBHP is achieved during pipe connection when the drill string injection is turned off.
In the previously drilled well, the 0.5ppg pressure window caused an underground blowout while in the thief zone. The Synthetic Oil-Based Mud (SOBM) used in this well was designed to be statically under-balanced during pipe connection to keep ECD within the 220psi window while dynamic and static. The slip joint packer - the weakest link in the annulus system - restricted the MPD SBP to maximum of 350 psi after considering the margin of error. Due to high wellbore friction pressure, the Pressure-While-Drilling (PWD) signal was intentionally turned off 60 meters before Total Depth (TD) was called by reducing the pump speed from 430gpm to 300gpm.
MPD CBHP technique was successfully applied to drill the well until target depth was achieved exceeding the poor performance in the previously drilled well where target depth was not achieved and the well was abandoned due to underground blowout.
This paper describes achieving CBHP with Managed Pressure Drilling technique and the use of an automated system which enables "walk-the-line" between pore and fracture pressure gradient. As a result, the exploration well that was considered "undrillable" with conventional drilling technique in East Kalimantan area was successfully drilled to TD. The ability to precisely control the annulus pressure with statically underbalanced mud is one of distinct advantage of MPD which allow operators to reach planned target depth and retrieve subsurface information through logging operations.