The predominant limitation to directional and extendedreach drilling is excessive torque and drag. Although torque and drag data exist for sandstone and metal surfaces, over 70% ofthe formations drilled worldwide are classified as shales. Unfortunately, data on shales are limited because ofpractical restrictions.References at the end of the paper. 501

Production from fields developed in deeper and colder waters requires that the hydrocarbons brought to the surface be at the highest possible temperature to eliminate asphaltenes, paraffins and hydrates from blocking a production line. Good insulation allows a less viscous fluid to be produced at higher rates, extend shut-in period and reduce stress during expansion and contraction of pipes. Ideally, the annular space between the riser and production line should be isolated with a special, low thermal conductivity fluid. Further, the insulation fluid must be environmentally acceptable to mitigate the effects of any spills or other unexpected events. The recent development of a lightweight hybrid riser for a deepwater completion in North Sea required a thermal insulation fluid that was both cost effective and environmentally acceptable. This paper describes a unique joint project to develop a lightweight riser and insulating fluid. The development included the building of a special test facility, which featured a 20-m long (60 ft) full size aluminum riser with electrically heated production pipe, which was filled with insulation fluid. The test piece was immersed into the sea for several months exposure. The authors will detail several formulations, both mineral oil and water-base fluids including simple techniques to measure thermal conductivity, diffusivity and heat capacity. These data are compared to a specially developed computer model and field data from long-term exposure test. Other applications of the thermal fluid is drilling through permafrost and insulating transportation lines. Introduction With the development of fields in Alaska, it was necessary to prevent the melting of permafrost. In the early 1980's thermal insulating fluids were developed1 with diesel oil as the base fluid. This fluid was used also in double-wall pipelines to transport oil at the highest possible temperature. With the development of fields in deeper and colder waters there is need for good insulation to produce hydrocarbons and prevent paraffines, asphaltenes deposits, as well as hydrates blockage, specially in shut-in situation. Insulation also reduces thermal expansion and contraction caused by temperature fluctuations. Sub-sea construction of drilling riser, top tension risers and hybrid riser towers in deep and ultra-deep waters required modern lightweight materials and better, more environmentally acceptable, thermal insulators. In deepwater applications, risers have to be supported by buoyancy in the form of distributed buoyant material, submerged tanks, or a floating structure with some form of pontoons or a hull. Lightweight materials have the advantage of minimizing the amount of buoyancy required. Steel and low-density titanium, composite and aluminum are the primary materials used for risers. Among the lighter materials, aluminum is the most cost-effective and has sufficient mechanical properties for use in riser construction.2,3 The thermal insulation fluid has to be non -corrosive for these materials. Manufacturing of an aluminum riser tube Although aluminum is the most cost-competitive material for a hybrid riser, precipitation hardenable alloys offer the highest strength. Specifically, they obtain the strength through precipitation of hardening particles formed from the alloying elements. Welding of those alloys necessitates their exposure to high temperatures where the strength is lost. Softening of the heat affected zone, change in microstructure, loss of alloying elements in the welding zone and excessive deformation during welding are major drawbacks for using aluminum alloys. However, it is possible to overcome these problems by using a solid state welding method, called Friction Stir Welding (FSW).

Silicate drilling fluids have been used for more than 60 years. While the early versions of silicate-base systems proved very inhibitive, controlling mud properties was difficult because proper polymer additives were not available for maintaining rheology and fluid loss control. Furthermore, the solids control equipment available at the time was ineffective in removing solids. During the last decade, silicate-base systems have been re-engineered to provide a state-of-the-art and environmentally acceptable, water-base system that provides the inhibition approaching that of an invert emulsion field. The proposed mechanism of inhibition is the surface adsorption and chemical reaction of the silicate polymer with the formation surface. This "coating" effectively provides a thin pressure and chemical barrier on the surface of the wellbore. This formation/silicate interaction has raised a number of concerns regarding both the lubricity and the formation damage potential of the fluid. This paper investigates systematically both the lubrication characteristics of the fluid and the effect of silicate-base systems on formation production and evaluation. The results show promise in expanding the application of silicates as reservoir drill-in fluids and in the drilling of critical high-angle wells where lubricity is a primary design criterion. The data obtained in this study utilizes purpose-built lubricity and formation damage equipment to critically look at the problems. From this investigation the authors will reveal that the coefficient of friction of silicate fluids, as observed in the laboratory and measured in the field, does not differ significantly from that of other water-base fluids. Furthermore, the thin physical and chemical barrier formed during the reaction of the silicate polymer with the formation surface prevents fluids and fine particles from migrating into the formation, thereby minimizing damage to the producing zone. Introduction Silicate-based drilling fluids are probably the most misunderstood systems in the industry. Since the introduction of sodium silicate fluids in the the 1930's, silicate chemistry has demonstrated outstanding shale and formation inhibition characteristics. However, rheology and filtration properties had been difficult to control. Over the past few years, the development of modern polymer technology provided fluid design tools that proved effective in controlling both the rheological and filtration properties of silicate systems. Complementing advanced polymer technology was the design of new solids control and process technology that made silicate-base products effective well-bore stabilizing agents. Improvement in inhibition not only contributes to wellbore stability but also to minimizing dilution volumes, minimizing costs. The low dilution rates and toxicity of the system also provide an excellent fluid with minimal environment impact. In the 1980's, Wingrave's research on shale stability found that silicates, used in conjunction with the potassium ion and specific polymers, combined for an effective shale-stabilizing package.1 During the last decade the industry has effectively used sodium silicate in conventional polymer fluid formulations to provide an effective water-base shale stabilizing system.2,3,4,5 High-performance polymers and efficient solids removal equipment can now provide the required fluid performance and maintenance necessary for efficient and cost-effective silicate chemistry. Furthermore, its capacity to provide inhibition competitive with invert emulsion fluids makes silicate systems an ideal alternative for optimum wellbore stability, without the environmental limitations of an invert emulsion fluid.

There are ample incentives and opportunities to improve current mud-testing equipment and to develop new instruments to measure mu~ prope~ies not previously' tested. This paper discusses three innovative devices for testing drilling muds: the automatic s~ea~ometer umt, the high-temp~rature/high-pressure (HTHP) dynamic filtration tester, and the filter-cake penetrometer. Each discus-SIon mcludes a summary of preVIOUS technology, current API standards (if available), equipment description, and selected case studies.

The technical demands placed on drilling fluids used in the deep waters of Norway differ dramatically from those encountered in any other deepwater basin. Unlike the deepwater of the Gulf of Mexico, West Africa or Brazil, seafloor temperatures here can dip as low as -2.5° C (27.5°F), with low ambient surface temperatures the year round. These characteristics combined with constantly changing sea conditions and some of the world's most stringent environmental restrictions, makes the engineering of drilling fluid systems for Norwegian North Sea wells an arduous effort. This paper describes the innovative development and qualification of a water-base drilling fluid system engineered for a well to be drilled in 837 meters (2745 ft) of water off Norway. The pre-qualified fluid was required to inhibit hydrates under normal drilling conditions and possess excellent shale inhibition characteristics to support hole stability and avoid bit balling. Since the primary objective was to obtain a non-contaminated formation water sample, the system must possess superb fluid loss control so the operator could avoid a full drill stem test, thereby saving some US$8 million. Furthermore, the qualified system would have to meet local environmental regulations for offshore discharge of cuttings and excess fluids. The authors will discuss the development protocol, the qualification of the novel fluid system and its application in the technically demanding Norwegian well. During the development phases, two hydrate testers were qualified and employed in both designing the fluid and to monitor its hydrate inhibitive tendencies during drilling. In addition, the particle size distribution and polymer concentration were engineered to reduce the filtrate invasion, while polymers were specially selected for improved rheological parameters to cope with the cold temperatures. The behavior of a number of glycols and salts were characterized prior to the start of drilling. The practical approach to qualify the novel fluid system will be explained in detail, emphasizing its use as a guideline to help non-fluid specialists design drilling fluids for this unique deepwater environment. Introduction The exceptional technical requirements associated with engineering drilling fluid systems for the deepwater environment have been well documented in the literature1,2,3,4. Regardless of the location, wells constructed in water depths exceeding 458 meters (1,500 ft) present a host of distinctive concerns that must be addressed early in the planning stages and monitored constantly during the drilling operation. If left unchecked, these troublesome phenomenon pose serious safety, environmental and economic risks and in some cases can even jeopardize the project itself. Among the most threatening of the fluid-related concerns in the deepwater environment are the constant risk of lost circulation, intrinsically low pore pressure to fracture gradient differentials, ineffective hole cleaning in young gumbo shales, unique environmental and logistics considerations, wellbore stability, mud density and the potentially disastrous formation of gas hydrates in the cold water atmosphere, among others.