Abstract
Biodegradability of drilling fluid waste is essential in the development of environmentally compatible oil and gas drilling. Biodegradation is determined not only by the enzymatic potential, but also microbial tolerance to hydrocarbons. The present study investigated the hydrocarbon degradation and tolerance of Ralstonia pickettii BP20 and Alcaligenes piechandii KN1 to drilling fluids with diesel and low-aromatic continuous phases in respect to their state: non-emulsified oil, direct (O/W) and invert (W/O) emulsions; and the concentrations affecting microbial activity and viability. In general, A. piechaudii KN1demonstrated higher tolerance than R. picketti BP20 did; but, the impacts of different drilling fluids on viability and activity of both microbial strains had similar trends. Microbial growth and hydrocarbons degradation rates increased when diesel was replaced with low aromatic oil, and emulsified. The higher productivity was observed in direct (O/W) emulsions than in invert (W/O) emulsions. Similarly, viability of microorganisms in low aromatic fluids and emulsions was higher than in corresponding diesel drilling fluids. Tolerance to low aromatic fluids increased in the order: non-emulsifier oil < invert emulsion < direct emulsion. In contrast, for diesel based drilling fluids, direct emulsion enhanced, but invert emulsion reduced microbial viability compared to non-emulsified oil.
Highlights
Drilling fluids are essential for the drilling process in the oil and gas industry
The present study investigates the tolerance of two hydrocarbondegrading microorganisms Ralstonia pickettii BP20 and Alcaligenes piechandii KN1 to drilling fluids with diesel and low-aromatic continuous phases in respect to (i) their state: non-emulsified oil, direct and invert emulsions; and (ii) the concentrations affecting productivity and viability of microorganisms
The microbial tolerance is the ability of microorganisms to survive and remain active when exposed to a toxic substrate
Summary
Drilling fluids are essential for the drilling process in the oil and gas industry. Drilling fluids are used to control formation pressure, lubricate and cool the drilling bit, remove cuttings from the drilling well, and form a consolidated filter cake on the sides of the hole to prevent loss circulation. There are three major types of drilling fluids: WaterBased Fluids (WBF), non-aqueous drilling fluids (NADF with diesel, mineral or synthetic oil) and Invert Emulsion Drilling Fluids (IEDF). NADF and IEDF replace WBF to improve drilling performance with respect to higher rate of penetration, more lubrication of the drill string, stability of the sensitive and highly reactive formation, and rheological stability of the drilling fluid under high pressure and high temperature drilling conditions. Reduced toxicity and enhanced biodegradability of drilling fluids have been reported when diesel was replaced with mineral and synthetic oils [1,2]. Microbial degradation of recalcitrant compounds may be improved via emulsification and solubilization in the aqueous phase, which may be achieved through the action of surfactants [4,5,6]. Studies on the bioremediation of hydrocarbons by microorganisms observed that these compounds impaired the microbial growth and Received April 11, 2013; Accepted May 24, 2013; Published May 31, 2013
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