The Mad Dog field is located in Southern Green Canyon approximately 150-miles south of New Orleans, in 4400-ft to 6800-ft of water (Figure 1). Mad Dog wells are sub-salt and are drilled to the Lower Miocene at approximately 19000-ft true vertical depth (tvd). The discovery well for the field was drilled in 1998. Drilling in the field has been challenged by "mobile" tar. Tar has been encountered in other deepwater fields; however, other reported tar deposits have not had the mobility of the tar encountered in the Mad Dog area. Extensive work has been conducted in developing the Mad Dog tar mitigation plan and has included characterization of tar, laboratory plunger experiments with Mad Dog tar, tar shoe design optimization, investigation of solvents and catalysts to solidify tar, investigation of downhole pyrotechnic heating, investigation of coating agents and the review of drilling practices. This paper will document the theory on the origin of the tar deposits, steps taken to deal with the tar and experience with the tar. Introduction The Mad Dog spar platform was installed in Green Canyon Block 782 for producing the Mad Dog Field in 2005. To date, two grass roots wells have been drilled from the spar. Drilling operations have been conducted in the central part of the field which encompasses a graben structure, Figure 2. Mobile tar first became evident on the second appraisal well in the central part of the field. (Figure 3). The tar did not substantially affect drilling operations however it did result in lost time due to stuck wireline tools. One of the most severe mobile tar cases occurred when a Southern Flank exploration well encountered tar and was unable to meet the required total depth objective. Another severe mobile tar case occurred in the final pre-drill (pre-Spar) well drilled in the central graben. The well was side-tracked, encountered more tar and met its objective as a less-than-optimal borehole size due to the addition of several casing strings. Development of a detailed tar mitigation plan during installation of the spar rig proved fruitful as the first spar well also encountered tar and managed to deliver the required total depth and completion.

fax 01-972-952-9435. AbstractDrilling in deep water environments, such as the Gulf of Mexico (GoM), presents the potential for a variety of wellbore and operational problems.Wellbore stability, rates-ofpenetration (ROP), hole cleaning, and pressure management are but a few of the key operational parameters affected by the choice of drilling fluid for a given well. Synthetic-base muds (SBM) provide excellent wellbore stability and maximum ROP, particularly in combination with PDC bits. Conversely, management of equivalent circulating density (ECD), pump initiation and surge pressures are more difficult to control with SBM due to the effects of temperature and pressure on rheological properties. The inability to effectively control these drilling parameters can result in catastrophic lost circulation events, which negatively impact operating costs arising from non-productive time (NPT), as well as the high unit cost of the SBM. This paper highlights the development and application of a new constant-rheology synthetic-based mud (CR-SBM), designed to overcome the problems associated with pressure management when using SBM in deepwater operations. Unlike conventional SBM, this new fluid exhibits a "constant rheology" profile under the conditions encountered in deepwater operations. With the fluid's constant rheology profile, downhole surge pressures and ECD are minimized, thus reducing the frequency and severity of lost circulation events. In addition, the CR-SBM has consistently facilitated delivery of hole cleaning and barite suspension objectives in directional wells.The CR-SBM presented in this paper is unique in the sense that the near constant profile of key rheological properties was achieved using organophilic clay and without the use of special emulsifiers. In general, the components of the CR-SBM are the same as conventional SBM. Case histories are presented that demonstrate the degree to which the new CR-SBM increases deepwater operational efficiency by reducing downhole mud losses and non-productive time.

fax 01-972-952-9435. AbstractDrilling in deep water environments, such as the Gulf of Mexico (GoM), presents the potential for a variety of wellbore and operational problems.Wellbore stability, rates-ofpenetration (ROP), hole cleaning, and pressure management are but a few of the key operational parameters affected by the choice of drilling fluid for a given well. Synthetic-base muds (SBM) provide excellent wellbore stability and maximum ROP, particularly in combination with PDC bits. Conversely, management of equivalent circulating density (ECD), pump initiation and surge pressures are more difficult to control with SBM due to the effects of temperature and pressure on rheological properties. The inability to effectively control these drilling parameters can result in catastrophic lost circulation events, which negatively impact operating costs arising from non-productive time (NPT), as well as the high unit cost of the SBM. This paper highlights the development and application of a new constant-rheology synthetic-based mud (CR-SBM), designed to overcome the problems associated with pressure management when using SBM in deepwater operations. Unlike conventional SBM, this new fluid exhibits a "constant rheology" profile under the conditions encountered in deepwater operations. With the fluid's constant rheology profile, downhole surge pressures and ECD are minimized, thus reducing the frequency and severity of lost circulation events. In addition, the CR-SBM has consistently facilitated delivery of hole cleaning and barite suspension objectives in directional wells.The CR-SBM presented in this paper is unique in the sense that the near constant profile of key rheological properties was achieved using organophilic clay and without the use of special emulsifiers. In general, the components of the CR-SBM are the same as conventional SBM. Case histories are presented that demonstrate the degree to which the new CR-SBM increases deepwater operational efficiency by reducing downhole mud losses and non-productive time.

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Operators are looking at drilling for deeper gas reservoirs. There are a number of problems unique to ultra-deep drilling - greater than 20,000 feet. Well control is complicated by narrow margins and higher bottom hole pressures and temperatures. Application of tools that can assist in pore pressure prediction are limited by the depth, temperature and the high cost of errors. Well control problems can be spectacular. The depth pushes rig equipment loads to their design ratings. Maintenance, inspection and design of all components are more critical due to reduced margins. Wellbore tubulars are often designed for sour and corrosive production fluids. Those designs increase the pipe's weight and cause special handling requirements. Drilling tools are also limited by the depth, temperature and rock hardness. Two operators working in Texas, Louisiana and Wyoming drilling to depths of up to 25,000 feet have documented many of the industry's problems and current solutions. Understanding the problems and designing wells to reduce the risks is the first step to a cost effective drilling operation. Introduction This paper considers high temperature to be greater than 300° F, high pressure to require equipment rated to more than 10,000 psi, and ultra-deep to be in excess of 20,000'. The experience base is greater than 400° F, 18,000 psi and 23,000'. Interest is increasing in deep drilling. In the Gulf of Mexico (where data is readily available) the MMS estimates 5 to 20 TCF is in deep reservoirs1. Only 5% of the 35,000 wells drilled in the Gulf have been drilled deeper than 15,000'. The MMS estimates the average size of 500 discoveries from below 15,000' to be 20 BCF. The MMS has offered royalty relief on the first 20 BCF produced from deep wells. On land the deep reservoirs have not been as thoroughly drilled as the shallow basins. There is similar potential for larger reserves recovery at higher flow rates and thus, greater return on the investment. All trends indicate interest will continue to grow. Deep drilling has problems. Costs are high. Mechanical and exploratory risks are high. Smith2 documented an exponential relationship between drilling costs and depth based on API data: Cost = 80000 e 0.000255*Depth The problem of high costs is best "solved" by eliminating the "Train Wrecks." Minimize the risks inherent in deep hot wells with detailed plans and thorough communication. Most individual problems can be addressed and "solved" during the design and planning phase. Steps can be taken to minimize risks and the potential for many execution phase problems. The challenge in the design phase is addressing the problems and building flexibility into the well plan. Problems and plan changes can result in a well not achieving its objective when contingency casing strings cannot be included in the preliminary plan. Often the realization that the objectives will not be met occurs after a considerable investment. Drilling incentives on royalty relief can only pay out if discoveries are made. This paper has separated the problems of ultra-deep wells into four primary topics. The best time to address and avoid problems is during the design and planning of the well. The focus at pre-spud should be toward risk mitigation; identifying potential problems and taking steps to avoid them. Well control is the most critical problem that must be addressed by the design. A major factor in the cost is time on location due primarily to slower rates of penetration deep in the wells. These problems are addressed in drilling issues. Finally, completion problems must be addressed to provide for production. Risk/Trouble Mitigation Risk/trouble mitigation for onshore ultra-deep wells is addressed during the design, planning, drilling and operations as it is any well. However, these wells require a higher degree of investigation, conceptualizing during the planning and design and communication with a larger team and for longer periods of time.