Pressured Mud Cap Drilling from A Semi-Submersible Drilling Rig
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Pressurized Mud Cap Drilling (PMCD) is a drilling technique that has been used for over seven years in many wells where conventional drilling proved impossible or uneconomic 1-5 . PMCD is typically used to drill fractured carbonates, where the pore and fluid loss gradient are virtually the same, resulting in total mud losses and kicks in the same hole section. However, it is not restricted to just carbonates, it can be used on any fractured rock that is very competent in respect to wellbore stability, or formations prone to severe to total loss with good wellbore stability characteristic.Traditional PMCD typically requires the periodic injection of sometimes large volumes of weighted mud into the annulus in order to maintain a reliable mud cap. The process is highly cyclical, often unpredictable, and can be prohibitively expensive. The process also requires highly skilled and experienced people to run it properly, an increasingly rare commodity these days.Use of the Micro-Flux Control (MFC) method with PMCD could permit the process to be automated and controlled to a much higher level of accuracy, allowing less experienced people to confidently run the system. While continuously injecting across the wellhead, and using delta flow as the control variable, the casing backpressure would be monitored. Casing pressure increases, indicating a loss of mud cap fluid downhole, would be automatically controlled by precise adjustment of the continuous delta flow, together with pressure monitoring, rather than by periodic injection of large volumes of fresh mud cap fluid. This paper will briefly describe the MFC method, rig up details and operational issues. It will also describe how to apply the procedure to automate and operationally enhance PMCD, explaining the benefits when compared
Pressurized Mud Cap Drilling (PMCD) is a drilling technique that has been used for over seven years in many wells where conventional drilling proved impossible or uneconomic 1-5 . PMCD is typically used to drill fractured carbonates, where the pore and fluid loss gradient are virtually the same, resulting in total mud losses and kicks in the same hole section. However, it is not restricted to just carbonates, it can be used on any fractured rock that is very competent in respect to wellbore stability, or formations prone to severe to total loss with good wellbore stability characteristic.Traditional PMCD typically requires the periodic injection of sometimes large volumes of weighted mud into the annulus in order to maintain a reliable mud cap. The process is highly cyclical, often unpredictable, and can be prohibitively expensive. The process also requires highly skilled and experienced people to run it properly, an increasingly rare commodity these days.Use of the Micro-Flux Control (MFC) method with PMCD could permit the process to be automated and controlled to a much higher level of accuracy, allowing less experienced people to confidently run the system. While continuously injecting across the wellhead, and using delta flow as the control variable, the casing backpressure would be monitored. Casing pressure increases, indicating a loss of mud cap fluid downhole, would be automatically controlled by precise adjustment of the continuous delta flow, together with pressure monitoring, rather than by periodic injection of large volumes of fresh mud cap fluid. This paper will briefly describe the MFC method, rig up details and operational issues. It will also describe how to apply the procedure to automate and operationally enhance PMCD, explaining the benefits when compared
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.
The development drilling campaign for the Ujung Pangkah field in offshore East Java, Indonesia, began in the first quarter of 2007. To prepare for circulation losses, the field operator tendered for managed pressure drilling (MPD) services as a contingency. The first gas well was successfully drilled by relying on conventional lost circulation material (LCM) to minimize the losses encountered. However, after drilling a pilot hole, plugging back and sidetracking the second gas well, total losses were encountered, followed by the persistent migration of gas up the annulus despite seawater bullheading. After stabilizing the well, MPD equipment and personnel were then mobilized and the system was rigged up to allow for clean-out and completion operations. Total losses were again experienced, but MPD made washing and reaming down to the previous depth possible. MPD techniques also kept gas migration in check, allowing for safer tripping operations in and out of the hole. An additional 55 ft of new formation was drilled and completion was run using MPD methods. This gas well has proved to be the most productive well drilled in the field to date. In subsequent wells, MPD equipment was rigged up before drilling the hole sections where severe circulation losses are anticipated. This practice paid dividends when severe losses were again experienced while drilling the first oil well. With the MPD system already installed, drilling was able to resume immediately in MPD mode up to the target depth for the section, despite total losses. Liner running and cementing was then successfully done in MPD mode, allowing for the successful isolation of the zone where the losses were and for drilling operations for the next hole section to proceed immediately. The MPD system in the Ujung Pangkah field has proven its value as a contingency measure by allowing drilling operations to continue despite total loss of circulation and by minimizing the non-performance time involved when the eventuality occurs. Ujung Pangkah Field Development The Ujung Pangkah Field is located in shallow water off the northeastern coast of Java, Indonesia, immediately to the west of the island of Madura (see Figure 1 for the location of the field). The production sharing contract for the Pangkah block, where the field is located, was signed on May 1996. Ujung Pangkah-1, the first exploration well drilled in the area, flowed at rates of 20 mmscf/d and 987 bopd through a restricted choke. The discovery was announced in November 1998. The Ujung Pangkah appraisal program, which was completed in 2004, confirmed reserves for the field in excess of 450 bcf of rich gas with the possibility of developing additional oil from the structure. The Ujung Pangkah oil rim underlying the gas accumulation has approximately 450 million barrels mapped in place. In December 2004, it was announced that an agreement was finalized for the sale of gas from the Ujung Pangkah Field. The agreement provides for the supply of 440 billion cubic feet of natural gas from the field over a 20 year period at an expected plateau rate of 100 million cubic feet per day (gross). The gas will be delivered from the field to the Indonesian State Electricity Company's (PLN) 2,200 MW gas-fired power station, at Gresik near Surabaya, East Java.
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