The development of the Kanowit Field in offshore Sarawak, Malaysia requires the drilling of two subsea development wells using a semi-sub rig. Previous experience identified the need for solids-free drilling fluid to ensure maximum reservoir productivity and so that the quality of the produced gas is within required specifications. High reservoir pressure requires the use of high-density solids-free drilling fluids, but associated costs and the high probability of losing large volumes to the fractured carbonate reservoir made this option unsuitable. A more cost-effective option was to use a less-dense solids-free drilling fluid and utilize managed pressure drilling (MPD) to be able to compensate for the difference in density with backpressure. MPD mitigated the loss circulation risk by controlling the level of overbalance to the minimum and MPD early kick and loss detection capabilities, used in conjunction with a statically underbalanced drilling fluid, also allowed for the collection of actual geopressure environment data that aided in the decision making process. Both wells were completed and tested with a maximum potential flow rate that exceeded the technical potential in initial projections. The successful deployment of MPD with solids-free drilling fluids proves its technical and economic feasibility in carrying out subsea development drilling through carbonate reservoirs prone to severe circulation losses.
Managed Pressure Drilling (MPD) has been successfully used by a number of operating companies in both onshore and offshore applications in Asia Pacific. Over 100 wells have now been drilled in the region using MPD techniques. MPD has delivered significant cost savings in almost all of the applications. The high cost of offshore drilling means that offshore MPD deliver significant cost savings when non-productive times associated with fluid losses or well control events are eliminated. MPD has now been successfully used on all the types of offshore rigs from platforms, tender rigs, jack-ups, semi-submersibles as well as drillships. Both subsea and surface stacks on floaters have been used for MPD. Drilling with a so-called "closed wellbore" using MPD equipment for drilling operations has now been proven to be beneficial on all rig types and almost all well types. All drilling, logging and completion installations can be safely executed when using MPD equipment. On most installations, only minor modifications are required to enable a closed wellbore drilling system, which in turn enables More Productive Drilling. This paper describes the experiences with MPD equipment installations on floating rigs and on fixed installations in Asia Pacific and it provides some of the lessons learned when using MPD equipment and technologies. Introduction Since 2005, over 100 wells have been drilled using MPD techniques by a number of operating companies. MPD has delivered direct cost and time savings by eliminating the non-productive time associated with losses and other related well control events. Being able to control wellbore pressures by using a closed wellbore system and introducing the application of some simple techniques has allowed previously "undrillable" wells to be successfully drilled to TD. Operators plan and budget wells for a certain number of days and then find that in the best case some 20% time spent on curing losses and kicks is added to their well times. Yet other operators have encountered losses and well control issues that double or even triple their planned well timings. Exceeding planned well times not only pushes drilling budgets past acceptable limits, but it also has a knock on effect on the rig sequence especially if the rig is shared by other operators in the region. Rigging up MPD equipment has allowed successful drilling of the fractured carbonates on all of the wells where the equipment was rigged up Not all of the wells encountered losses, and on these wells the equipment was rigged up but not used. On the wells that did encounter the loss/kick scenarios, MPD enabled all of these wells to be drilled to TD without significant delays. Reasons for MPD The main application of MPD in Asia Pacific is in the drilling of fractured carbonate formations such as Baturaja and Kujung in Indonesia. Total losses are often experienced when fractures and vugs are encountered, and once fluid hydrostatic is lost, gas in the upper part of the carbonate reservoir migrates rapidly to surface, resulting in a well control situation. Once the losses are cured and the well is brought under control, drilling resumes until the next fracture is encountered. At that point, the entire process of killing the well and curing losses often repeats itself. Curing the losses with LCM, gunk squeezes or cement can be successful, but very often this has detrimental effects on the productivity of the reservoir. Using underbalanced drilling (UBD) techniques is not suitable as delivery from a fractured carbonate reservoir can be large and handling large volumes of hydrocarbons on an offshore rig whilst drilling adds to operational complications. Furthermore, crew size and equipment spread for an offshore UBD operation becomes a further limiting factor in the application of UBD offshore. The ability to drill these wells using MPD techniques has been proven to be highly successful.
Studies have revealed that gas kicks unintentionally entrained in oil or synthetic based mud in deepwater drilling operations at water depths greater than 3000 ft are unlikely to break out of solution until they are above the subsea BOPs. The rig diverter is conventionally used to vent riser gas with minimal control and with considerable risk and environmental impact through the uncontrolled discharge of drilling fluids. Riser gas handling (RGH) systems currently being offered provide a reactive solution to the problem by supplying a riser joint equipped with additional components for this specific purpose. This joint is normally composed of a retrofitted annular BOP and a flow spool with hoses that is installed on top of the rig marine riser. An alternative and proactive approach to riser gas handling, which we prefer to call riser gas risk mitigation, is proposed by utilizing managed pressure drilling (MPD) equipment. MPD involves the use of a rotating control device (RCD) to create a closed and pressurizable drilling system where flow out of the well is diverted to an automated MPD choke manifold with a high-resolution mass flow meter that increases the sensitivity and reaction time of the system to kicks, losses and other unwanted drilling events. Experiments and field deployments have shown that the deepwater MPD system can detect a gas influx before it dissolves in oil-based mud, allowing for management of the same using conventional well control methods. Since the MPD system has already closed the well in, automatic diversion and control of gas in the riser is also possible, if required, thereby further minimizing the likelihood of an environmental discharge should a riser gas event occur. Experience gained from deepwater MPD operations in Asia Pacific will be presented to illustrate this.
Digitalisation and automation can account for massive efficiencies in wells operations. Managed Pressure Drilling (MPD) and Automated Well Control are examples of "smart" technologies that can mitigate risks and costs associated with drilling wells. The Automated Well Control system was developed to monitor the well, identify an influx, take control of the rig equipment and shut in the well. MPD provides annular pressure control, real-time information of the well parameters and conditions downhole and very accurate and immediate influx detection. However, if a high intensity influx is taken that exceeds the pre-planned operational limits of the MPD package, then secondary well control is required. Therefore, a combination of Automated Well Control and MPD has been developed to deliver both pressure control and well control in a safe, efficient and less error-prone manner. On an MPD operation, the Automated Well Control system shuts-in the well as soon as it is required to do so. With Automated Well Control in MPD mode, the MPD system decides when to shut in and the Automated Well Control technology will immediately space out, stop the mud pumps and top-drive, and shut in the well using the pre-selected blowout preventer. This interface between the two systems mitigates drilling hazards using automation. The sensitivity of MPD, combined with Automated Well Control technology enables fast identification, decision making and reaction to well control events. Consequently, this fully integrated solution improves safety and operational efficiency. The MPD and Automated Well Control systems were integrated into a test rig and several tests were efficiently performed. The tool enabled immediate action in the event of influxes, providing a valuable solution for the industry. This paper briefly describes MPD and Automated Well Control and summarises the interface between the two technologies, detailing how the integrated system works on a rig. Moreover, rig trialling results and further developments are presented.
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