Extended Reach Drilling (ERD) wells drilled nowadays can reach a step-out of 10 km (33,000 ft) and thus present many drilling challenges, including torque and drag, hole cleaning, wellbore stability, equivalent circulating density (ECD) management, lost circulation management, just to name a few. These challenges can severely limit the desired well depth or increase the operation time, particularly in deepwater environment. A new synthetic-based flat rheology drilling fluid (SBM) with new emulsifier and rheology modifier package has been designed for narrow margin ERD wells. This newly developed flat-rheology SBM utilizes a novel, single emulsifier to simplify fluid formulation, improve emulsion stability, enhance thermal stability, and provide surface wetting and fluid lubricity. This allows the system to be formulated for any ERD applications with mud weights up to 18.0 lb/gal and temperatures up to 350°F. In addition, the system uses a new rheology modifier that provides temperature-independent rheology profile for better hole cleaning, barite suspension, ECD management and lost circulation control. A recent field trial conducted in deepwater GoM indicated that the new system is easy to handle and provides good fluid performance in terms of drilling rate, ECD management, lost circulation control and hole cleaning. The SBM at one time was severely contaminated due to salt water flow but the fluid held together without any problems. Similar results on drilling performance were observed with another onshore field trial that used a non-synthetic-based fluid. This article describes the new flat-rheology SBM system with examples showing typical mud formulations, fluid properties, barite sag performance data, field test data and computer hydraulics simulation of ECD impacts.

SPE Members Abstract The first wells have been successfully completed offshore Gulf of Mexico using a new synthetic-based drilling fluid. Polyalphaolefin (PAO), the synthetic base used for these fluids, is unique to the drilling fluids industry at this time. The environmental benefits of PAO-based synthetic systems over conventional oil-based fluids and some water-based fluids has already been presented in prior papers. However, the practical benefits gained from utilizing PAO as an alternative to conventional systems can now be documented after a series of highly successful field tests in the Gulf of Mexico. The non-aqueous PAO system has been used on several wells in the Gulf of Mexico to drill problematic formations previously drilled with either inhibitive waterbased or oil-based fluids. Wells with angles up to 86 and formations from 4500 ft to 18300 ft have been successfully drilled. Direct comparisons can be made regarding performance benefits of PAO-based synthetic systems verses waterbased and oil-based systems previously used to drill in the same location. Benefits in hole stability, cuttings integrity, lubrication, and gauge wellbores, all leading to increased penetration rates and subsequent reduction in drilling days, can be seen. This paper reviews the results of the first field tests with PAO synthetic systems in the Gulf of Mexico concentrating on the practical aspects of drilling rather than the detailed environmental information which has been covered in prior literature. Introduction Drilling in certain areas of the Gulf Coast demands a great deal from a mud system. Massive sections of extremely reactive, hydratable shales commonly known as "gumbo" must be drilled at shallow depths. These often create the need for high dilution rates with waterbased muds and still create wellbore instability problems even with the most inhibitive systems. The need for weighted systems and the requirement for directional wells from platforms has lead to the use of both diesel-based and low toxicity invert oil mud systems. Although conventional oil muds have provided the best available technology in the past, the environmental constraints placed on these systems add many directly related operational problems and costs. P. 405^

fax 01-972-952-9435. AbstractA conventional oil-based drilling fluid was determined not to be applicable for drilling narrow hole annuli in a mature field offshore Norway. Drilling these wells with a very narrow hydraulic window required an oil-based drilling fluid with reduced viscosity and improved sag stability. A totally reformulated drilling fluid system was developed. The combination of base oil and selected products produced a fluid with a flatter rheological profile, resulting in reduced plastic viscosity (PV) and increased low shear rate viscosity (LSRV). This rheological profile reduced equivalent circulating density (ECD) and improved sag stability. This rheological profile also directly impacted pump pressure and hole cleaning capabilities, delivering lower pump pressure and allowing for higher pump rates and improved hole cleaning. This paper presents the experimental work performed when developing the system for this specific application. The authors also will present field data and compare the performance of the new drilling fluid system with that of conventional systems.

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