Drilling a statically underbalanced well means that the hydrostatic head exerted by the fluid used for drilling is lower than the formation pressure. However, by utilizing Managed Pressure Drilling (MPD) equipment, such as a Rotating Control Device (RCD), an automated MPD choke manifold, and a downhole isolation valve (DIV), and employing MPD techniques, such as Constant Bottomhole Pressure (CBHP) and Pressurized Mud Cap Drilling PMCD), surface backpressure can be exerted during drilling and a dynamically overbalanced condition can be established during the operation, thereby preventing the constant flow of reservoir fluids to surface. The CBHP variant of MPD was initially deployed with statically underbalanced drilling fluid to minimize damage to the reservoir until severe circulation losses were encountered, once the high permeability areas being targeted for the big-bore gas wells were penetrated. Thereafter, the same drilling fluid was to be utilized to make the transition to another MPD variant, PMCD, faster and easier. PMCD was utilized in order to continue drilling the well to target depth without needing to restore circulation and pump lost circulation material (LCM) and cement, which will also impair the productivity of the gas reservoir. This paper focuses on how these combinations of MPD techniques were successfully utilized in order to drill high-rate gas wells in South Sumatra safely and efficiently. Details of how the system was safely and efficiently installed and subsequently deployed, as well as the set-up and procedures utilized will be elaborated. Further improvements to the system and to the operation are also discussed for future applications. Finally, the evolution of MPD methods used in drilling the gas reservoir is also described in relation to the changes that have occurred to the reservoir after it has already been put in production for a number of years.

Drilling through a carbonate formation characterized bymassive vugulars and fracturescreates a difficult and high-risk operation when using conventional drilling methods. Total lost of circulation, accompanied byinflux or kicks may be encountered when drilling through high volumes of pores and numerous fracture zones. Using managed pressure drilling (MPD) techniques when drilling through vugs and severely fractured formations can reduce non-productive time in combatting lost circulation problems and preventingformation fluid influxes from reaching the surface during drilling operation. The application of a pressurized mud cap drilling (PMCD) variant of MPD in a recent project in Indonesia was key in allowing the operator to reach their targeted depth. PMCD is a non-conventional drilling technique designed to maintain annular wellbore pressure when total loss of circulation occurs. With the utilization of MPD equipment and PMCD techniques, mitigation of drilling hazards caused by lost circulation or influx was successfully performed in this project without stopping the drilling operation. The decision of calling out the MPD to the rig site saved the operator drilling days followingunsuccessful attempts to cure the lost circulation by pumping cement for several days. With PMCD, the proper bullheading sequence was carried outin order to control influxes which weremigrating through the mud-cap to the surface. With applications and actual operations on location, drilling operations successfully reachedthe targeted depth with minimum NPT and optimum hazard and cost reduction. This paper will describethe planning phase, operational aspects, and results of drilling with the PMCD technique through challenging carbonate formations in a Southern Sumatra oil and gas field.

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.