Two record wells were recently drilled in the ultra-deepwater Eastern Gulf of Mexico. The wells were the fastest two wells drilled in water depths greater than 7,000 ft in the GoM. A high-performance water-based mud (WBM) was used to drill the intermediate sections. The fluid had comparable performance to a synthetic-based mud (SBM), with the advantage of cuttings disposal permission in this environmentally sensitive offshore area. Significant savings were realized by not carrying the cuttings to shore for disposal. Other advantages included (a) no losses while running and cementing casing and (b) easier displacements. The fluid was re-used on two consecutive wells and then stored for further applications. The authors will detail the careful planning that coupled with fit-for-purpose solutions allowed setting these records while reducing the overall well cost. The wells were drilled in the Lloyd Ridge area of the Eastern Gulf of Mexico, categorized as "zero-discharge" for SBM cuttings. The use of the high-performance WBM saved the hauling and disposing of approximately 2,000 bbl of cuttings on each well. Cost savings were also accomplished by avoiding fluid losses when running and cementing the casing. On a similar project drilled completely with SBM, 2,156 bbl of mud were lost while running and cementing the 13 5/8-in. casing. Comparison of drilling and economic performance of the new water-based mud and the synthetic-based mud are included in this paper to offer a comprehensive analysis. Also presented are innovative solutions introduced to optimize hole cleaning and shale inhibition. Introduction Drilling an exploration well in the ultra-deepwater environment, generally defined as water depths greater than 7,000 ft, poses a number of difficulties not seen in less demanding applications. The comparatively unfamiliar geology of these under explored areas complicates well planning and project execution. Further, operators must confront the technical and logistical demands intrinsic of the water depth and the great distance from shore. More specifically, the technical demands inherent with engineering and applying drilling fluid systems in deep and ultra-deepwater environments are well documented in the literature.1,2,3 Much of the fluid-related problems encountered in deep water centers on the narrow operating margins between the pore pressure and fracture gradient. This situation frequently leads to major fluid losses when drilling, running casing and cementing. In an unknown geological structure, this translates to more casing strings required to reach the target depth, which leads to larger hole sizes on the initial intervals below the riser. Furthermore, these shallow formations are very reactive and may cause major problems such as shale plugging the riser and the flow line, soft cuttings accumulating into the wellbore, bit balling or even stuck pipe. With ultra-deepwater rig spread rates running between $300,000 - $400,000 / day, unplanned events such as unsuccessful casing or logging runs, extensive trips or fishing operations can magnify operating expenses considerably. In addition, these operations generate a significant amount of cuttings, which must eventually be disposed of, further elevating the importance of selecting the proper drilling fluid system. Thus, the fluid must be selected to meet both drilling and environmental performance criteria. In these and other demanding applications, invert-emulsion drilling fluids historically have generated performance advantages far superior to their water-based counterparts.4,5,6 Unfortunately, many of the cost savings resulting from higher rates of penetration, improved shale inhibition, reduced torque and drag and other performance advantages are all too often offset by the costs associated with whole losses of premium fluids and the dramatically higher costs of meeting environmental regulations. Moreover, in the Eastern Gulf of Mexico, US Environmental Protection Agency (EPA) requires all operators to obtain individual permits for the offshore discharge of cuttings generated with synthetic-base drilling fluids, a costly and time consuming proposition.
Anadarko Petroleum's Marco Polo development is located in approximately 4,300 ft. of water in Green Canyon Block 608, in the central Gulf of Mexico (GOM). The discovery and appraisal wells were drilled in 2000, and the field will ultimately be produced using a tension leg platform (TLP). The development drilling, which will be complete by 1st Quarter 2003, uses several innovative approaches to maximize project value. Some of the approaches challenge current industry trends and will be highlighted in this paper. Introduction Over the past decade, multiple fields in deepwater GOM have been developed and the region remains one of the frontier exploration areas of the world. The challenge of the Marco Polo development is the same as with most projects - to deliver maximum value. What makes this project unique is the approach. The first step was to evaluate the major components to determine the most appropriate use of current technology. Those selected technologies that significantly challenge current industry trends include: Rig Selection. The rig selected to drill the development wells is an Express-Class, dynamically positioned fifth generation semi-submersible with enhanced pipe handling capabilities. Drilling Fluid System. A newly developed water-based mud (WBM) was used in lieu of the synthetic-based drilling fluids (SBMs) traditionally used in the GOM. Cement Design. To address shallow water flow concerns, a non-foamed slurry was used on the conductor casings instead of foamed cement-the predominate slurry for cementing conductor casing in shallow water flow areas in the GOM. Additionally, a flexible slurry was used on the production casing to mitigate annular pressure buildup (APB). Both of these slurries are new developments in technology. Casing and Wellhead Design. The casing design was optimized from the exploration wells and drew on recently published casing failures in deepwater GOM1. Subsea wellheads were used and will be tied back to the surface once the TLP is installed. To meet the design criteria, the wellheads included a "thick wall extension" below the 18 3/4-in. high-pressure wellhead housing (HPWHH). The 36-in. low-pressure wellhead housing (LPWHH) and casing above the mudline was also externally insulated for flow assurance reasons. Rig Selection As with all drilling projects, rig selection plays an important role in success - particularly with batch set operations. Key issues related to rig selection for the Marco Polo project included:The ability to work in high current environments. Immediately prior to beginning the drilling program, a fourth generation, moored semi-submersible had drilled a well in an offset block where loop currents were present. As a result of these high loop currents, the drilling operation was suspended a total of 21 days.Enhanced pipe handling, which could add significant value during batch set operations.Variable deck loadLiquid mud storageBulk storage (cement and mud)Hydraulics Once qualifications were set, the rig list was narrowed down to two rigs;a fourth generation moored semi-submersible that had been used to drill the discovery and delineation wells and an immediate offset; anda fifth generation dynamically positioned (DP) semi-submersible with enhanced pipe handling capabilities. Because a batch set operation was planned, the fifth generation rig's increased variable deck load, additional bulk storage, and enhanced pipe handling capabilities delivered improved performance over the fourth generation rig. These features, combined with DP capabilities, established the fifth generation rig as the optimal choice.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper discusses one-company's experience in drilling a number of wells in 4000 to 9000 ft of water depth (WD) in the Gulf of Mexico (GOM), from the technical as well as the managerial aspects of this massive undertaking. The paper lists and discusses technologies, successes, and challenges experienced under the following headings:• Differences in technology from one area to another, as well as challenges and solution ideas to minimize trouble and flat time; • Scheduling and impacts of rig contracting, along with timing and execution; • Technical support by way of historical data analysis, benchmarking, lesson feedback into well planning and construction, and knowledge management and knowledge retention (where new technical staff are easily and quickly brought up to speed); • Mud engineering and special drilling muds -both water-based mud (WBM), and synthetic-based mud (SBM) are shown to be crucial to environmental compliance, cost control, and trouble mitigation depending on the area; • Hydraulics and cementing issues -modeling and validation, along with special considerations for the application of PWD (pressure while drilling), and other real-time data; • Technical challenges still to be addressed, and the way forward; and • Managerial challenges still to be addressed, and the way forward.
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