Clay-free biodegradable wellbore fluid and method for using same fluid

Abstract

A dry mix additive, which is used to form a clay-free, i.e., non-argillaceous, inorganic salt-free, i.e., non-brine, biodegradable and chemically degradable aqueous-based wellbore fluid, which is capable of imparting non-Newtonian, pseudoplasticity and fluid loss controlling properties to aqueous systems for use in horizontal directional drilling, finding utility in horizontal environmental well installation for soil and groundwater remediation. The dry mixture comprises (1) from about 80-90 by weight of pre-gelatinized corn starch heteropolysaccharide, and (2) from about 10-20 by weight of a synthetic biopolymer such as Xanthan gum treated with a dispersing agent (glyoxal) for ease of dispersion. Sodium hypochlorite can be added, if desired, to the wellbore fluid to provide resistance to bacterial attack. The dry mixture is added to either fresh water or acidic water in amounts of 12-15 pounds of the dry mixture to a barrel (42 U.S. gallons) of water and then used as a drilling fluid in drilling horizontal wells for soil and groundwater remediation. Also, if desired, calcium hypochlorite can be circulated through the borehole following the drilling operation to accelerate the degradation of the polymers in the wellbore fluid. Following the drilling of the borehole, the contaminated formation fluids are withdrawn from the borehole.