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.

Recent drilling operations in Southern Sumatra area, especially Jambi and South Sumatera district, have experienced various problems upon drilling the top section, intermediate section, as well as production section. Overpressures, loss circulation and narrow window between pore and fracture gradient are common problems when drilling the top hole section. In some wells, coal caving and shale sloughing are claimed to be the reason of drilling day extension in this particular section. Overpressure zone within permeable system have cornered several field operators to activate well control system. Some field operators even had to experience blow out. The upper zone of intermediate section sometimes experience tight hole and shale sloughing, which require adequate drilling fluid management. In several wells, reactive shale is identified within the lower intermediate section, which requires the operators to utilize oil based mud to avoid clay swelling. Total loss circulation inflicted with high gas content is a normal condition when penetrating the intermediate and production section. This condition increases operational days when drilled conventionally with high potential of pipe stuck, complications in formation evaluation such as cuttings recovery and well logging, or even forcing the operators to side track the well due to sloughing. Extensive well bore clean out period also have been experienced by some operators when drilled with high barite concentration within the production zone. This paper elaborates a new drilling convention that has been practiced by the operators within these areas, evolving the commonly known Managed Pressure Drilling technique into a culture when penetrating such problems. Success stories will be highlighted when drilling through the top section, intermediate, and production section presenting risks associated from economical and operational perspective.

Bottomhole pressure management is essential to address challenging issues in hostile drilling environmentsbecause of wellbore pressure disparity during pump cycles while in circulating or noncirculating modes. This disparity can cause substantial instability on equivalent circulating density (ECD). While drilling in deepwater, HPHT, or any other hostile environment, these conditions may result in costly nonproductive time, may jeopardize operational safety, or may disrupt the well drillability. One of the most advanced methods to enhance ECD management during drilling and connection is use of a sub-based uninterrupted circulating system. This technology has been proven to improve drilling performance by maintaining continuous circulation during drilling and connection to retain wellbore pressure stability without significant changes to the rig operation system. This system enables operators to improve drilling performance in wells with a slim pressure window, challenging geomechanical instability, extreme temperature (geothermal), high and long tangent section where hole cleaning is very essential, as well as in extended reach. This system also can be easily integrated with managed pressure drilling technology that exists in the present market. This system uses a small-footprint, sub-based system with an automated flow switching mechanism to eliminate personnel exposure to the high-pressure system. By maintaining steady state circulation throughout the drilling process, the CFS remedies wellbore pressure disparity to retain continuous circulation and ECD management along the entire wellbore. This condition can effectively assist the operator to reduce nonproductive time, to enhance operational safety, and to enable drilling the well to target depth in a timely and safe manner. This paper will describe the equipment design of this uninterrupted circulating system as well as the best practice and constraints during operation. Generic factory testing will also be discussed to provide comprehensive understanding the reliability of the system.