Conventional open-to-atmosphere mud returns systems present a challenge when attempting to obtain energy resources that have previously been deemed economically or technically impossible to drill due to narrow drilling windows. A narrow drilling window significantly reduces the possibility of drilling to targeted depth effectively and efficiently from cost and safety perspectives. However, it is not always the pore pressure and fracture pressure gradients that define the drilling window, as has been observed in a field in East[MA(1] Java Province, Indonesia. In this instance, the actual drilling window lay between the wellbore instability and mud losses pressure gradients. Having the bottom hole pressure lower than the wellbore instability pressure would risk collapse of the wellbore, resulting in stuck pipe, or worse, a fishing job and requirement to sidetrack the well. Thus, a steady bottom hole pressure within that window was deemed critical to successfully drill to the section target depth. The application of Managed Pressure Drilling (MPD) was selected to drill the narrow drilling window and has resulted in being able to successfully drill to the targeted depth without wellbore collapse. Data acquired from system-recorded drilling parameters enabled analysis of the wellbore condition and adjustment of parameters leading to a successful operation. Calculated friction pressure, ECD trend line, flow behavior and most importantly surface back pressure were compared as analysis subjects. The utilization of MPD equipment, including Rotating Control Device (RCD) and Automated MPD Choke Manifold, enables surface back pressure to be applied to create the required bottom hole pressure sufficient to maintain wellbore stability within the narrow drilling window. With real-time results being applied on site, as described further in this paper, drilling hazards related to wellbore instability were significantly minimized, if not completely eliminated.
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.
Completion phase is critical in well construction where drilling operation is achieved in static-underbalanced condition with water as circulation fluid. With utilization of Managed Pressure Drilling (MPD) equipment that consists of Rotating Control Device (RCD), Automated MPD Choke Manifold, and Downhole Isolation Valve (DIV), lower completion string can be deployed safely and efficiently. MPD technique enables safe and efficient transition after reaching target depth and prior running lower completion. The same technique allows instant and manageable bottom hole pressure upon the completion phase. This paper emphasizes the main benefits of MPD technique while running lower completion in a gas-rich well in South Sumatra. With static-underbalanced fluid presence while drilling to target depth, transition from drilling to completion phase is very crucial. The presence of DIV eliminates the needs to kill the well with heavier mud and chemical additives prior tripping out drill string to surface. DIV isolates the open-hole formation safely while drill string is pulled out and lower completion string is made up on surface. This result in easier fluid management on surface by keeping fresh water as circulation fluids, while avoids chemical settling to the pay-zone which can lead to well productivity issues. While running the completion string, prior to reaching DIV depth, RCD bearing assembly is installed to enable closed-loop and pressure-able drilling system. The DIV is then opened securely while MPD Automated Choke Manifold manages the desired bottom hole pressure by adjusting the surface back pressure accordingly. Although the fluid weight in the well is static-underbalanced, the bottom hole pressure is managed to be overbalance at all time. Lower completion string is run to bottom then its hanger and packer set subsequently to have the primary well barrier in place for further production purpose.
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.
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