ABSTRACT:

Base fluid toxicity and chemical biodegradation in a marine environment is an important parameter in assessing the impact of discharging cuttings used in offshore drilling operations. In the last few years, the regulations to minimize environmental impact have lead the oil and gas drilling industry to generate several environmentally friendly synthetic-based drilling fluids. To further minimize environmental impact, the disposal of drill cuttings has been assessed around the world. In some cases cuttings are re-injected or shipped onshore and processed. In both cases, it burdens the cost of the drilling operations, and may still impact the environment. Preliminary published laboratory work indicated that biodegradation could be enhanced with drilling fluid additives. Since then, extensive laboratory work and research have been conducted. This has lead to the development of this increased biodegration approach designed for drilling in environmentally sensitive areas. This paper highlights a new generation of oil based fluid that is non-toxic and more readily biodegradable both under aerobic conditions. The fluid system is a response to the environmental concerns restricting the discharge of cuttings at sea, while also minimizing solids treatment and associated cost. This fluid design has stable fluid properties and provides good hole integrity, typical of those seen with invert emulsion fluids. Drilling fluid chemistry, composition and laboratory testing optimized this novel drilling fluid. This environmentally friendly invert fluid is stable to above 150°C (300°F) and is resistant to common contaminants encountered while drilling. Laboratory testing has also indicated that the treated drilling-fluid system shows return permeability rates compared to untreated systems. The primary focus of the design evaluation was to optimize biodegradation and toxicity test results. The consequential drilling fluid formulation uses an in-situ process to accelerate the rate of biodegradation of a mineral, synthetic or ester based fluid up to several fold. This process used a treatment comprised of organic nitrogen, phosphorus compounds and fatty acids. Based on design results, the system environmentally outperforms synthetic fluids presently used to drill in many sensitive offshore areas.

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