TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAs operators continue to develop prospects in expensive, deep water environments, delivery of high rate, high capacity, long life wells become essential for economic success. Often, operators are drilling high angle, open hole wells to maximize production by capturing reserves from several sand packages in one wellbore. In many of today's deepwater applications, hole stability and shale inhibition are keys to a successful open hole completion. Nonaqueous fluid (NAF) is the preferred fluid system to optimize drilling of the open hole section, but hole stability can be problematic during displacement operations prior to gravel packing. This paper describes a gravel packing technique that allows the operator to run the gravel pack screens in NAF, gravel pack the well and displace the casing to brine, all in one trip. Running the screens in NAF significantly increases the probability of successful screen installation and the end result is consistent, cost effective delivery of high rate, low skin completions.

This paper describes the preparation and operation for the first use of a riserless mud recovery (RMR) system on the top-hole section of a well in the Gulf of Mexico. The material includes pre-well engineering and preparations including hydraulic analysis, pre-job vessel inspection, construction of new equipment, installation, pre-well planning decisions, and rationale for decisions. In addition also discussed are benefits including improved wellbore quality due to use of an engineered drilling fluid, logistics savings from reduction of drilling fluids, and minimized environmental impact. The paper also includes descriptions of equipment installation and testing onboard the drilling vessel operations during drilling, problems encountered and lessons learned from the operation. A description of all equipment is included in the paper along with specifications and operation parameters. An RMR system has application in the top-hole drilling of oil and gas wells. Using conventional methods, drilling fluid pumped down the drillstring during operations flows out onto the sea floor; this is often referred to as " Pump and Dump??. RMR collects the mud at the mud line and pumps the fluid back to the rig where it is reconditioned and reused. It allows the use of engineered drilling fluids and has possible applications for all offshore drilling. RMR was deployed on a dynamically positioned vessel, and successfully used to drill the 26-in. hole section. Drilling fluid recovered from the mud line back to the drillship was processed and reused, resulting in significant reduction in the volume of mud required for this top-hole section. RMR reduced costs through savings in drilling fluid and improved well construction. RMR is applicable to the drilling of top-holes in the entire Gulf of Mexico. It has significant potential to reduce top-hole drilling costs, eliminate casing stings, extend casing shoe depths, drill through and past problem formations and improve the wellbore by eliminating washouts and shallow hazards. Introduction Operators continue to explore and develop fields at increasing water depths. In certain offshore areas where younger sedimentary rocks are deposited, there is often a very narrow margin between formation pore pressure and fracture pressure that creates tremendous drilling challenges (Rocha and Bourgoyne, 1994). The solution to this narrow operating window is to develop techniques that extend the casing setting depths more efficiently. The use of a riserless drilling technique, dynamic kill drilling (DKD), has been instrumental in successfully pushing the casing depths deeper in deepwater applications (Johnson and Rowden, 2001). The DKD methodology employs the dual gradient drilling concept, consisting of the seawater hydrostatic above the mud line with the ability to vary the hydrostatic below the mud line by drilling fluid weight variations. This functional control of the drilling fluid density is tremendously advantageous while drilling shallow gas or water flows from over-pressured formations where large washouts, caves, formation compaction, and collapse could occur (Pelletier et al., 1999). This technique has been repeatedly employed in challenging deepwater projects where the initial upper hole sections were extended to obtain the required leak-off tests (LOTs).

This paper describes the methodology and the results of a successful partnership between operator and service companies that improved the drilling performance and economics for the development of the North Field in Qatar. Fifteen high rate gas wells were delivered within designated directional targets, ahead of schedule and under budget. The systematic use of a new methodology for bit selection, linked with an excellent level of communication and confidence between different parties involved in the drilling operations, was a major reason for the drilling success. The different sections drilled were mainly made up of limestone, marl, and shale, but also anhydrite in the top portions of the well. In the lower sections, hard and soft limestone alternates with highly compacted shales and dolomites. Penetration rates were greatly enhanced and bit performance improved by more than 100% in some instances. The optimization of the performance took into consideration three aspects:A very tight schedule, where the optimization phase had to be performed within a limited time frame: Four wells were planned to be drilled back to back with two jack up rigs from two production platforms. After this short phase, batch drilling was expected to be performed for more than 20 deviated wells.The formations to be drilled presented a high complexity and heterogeneity where hard stringers alternate with a soft or a very compacted rock, and where in the lower section of the hole, a typical pseudo plastic behavior of the rock has to be anticipated.The well designs, casing depths, and bit types had to be in harmony with the drilling environment, the formation, and provide effective performance. New bit designs, more adapted to the technology available had to be developed or identified. The use of roller cone bits and motors was planned and used in the top hole sections. The use of PDC bits associated with extended steerable motors and/or turbines was considered as potentially providing the best performance in the intermediate and bottom sections. The early bit designs were modified based on wear patterns of dull bits. These enhancements and modifications were one of the major reasons in improved drilling performance and helped reduce the total drilling time from 75 days to 56 days per well. The challenges were met successfully, the most economical options selected and carried out ahead of time and under budget. Introduction The North Field Development - Phase 2, North Field Bravo (NFB), is the second development of the giant North Field, offshore Qatar (Fig. 1). Qatar Liquefied Gas Company (Qatargas) is responsible for this development, and to date, 15 deviated production wells have been drilled from two centrally located wellhead platforms. Following the field discovery in 1971, 18 vertical exploration/appraisal wells were drilled across the field to provide information on structure/reservoir development. A further 16 deviated production wells were drilled and completed for the first phase of gas production from the North Field Alpha (NFA) Complex. Records from these latter wells were used to benchmark the drilling performance in the NFB series of wells. The NFB wells are high departure directional wells with an average inclination of 55 degrees. The well bores can be split into two main sections, the upper section consisting of 24" and 16" phases and the lower section covering the 12 1/4" and 8 1/2" hole sizes. The use of tricone bits on steerable motors was planned for the upper section, and PDC bits on turbines or extended motors were considered to provide the best performance potential in the 12 1/4" and 8 1/2 phases. P. 91^

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