Environmentally Friendly Dispersants for HP/HT Aqueous Drilling Fluids Containing Mn3O4, Contaminated With Cement, Rock Salt, and Clay

Abstract

Abstract Dispersants are widely used in drilling fluids to prevent solids flocculation and to control the rheological properties of the fluids. There is high demand for effective, thermally stable and environmentally friendly dispersants for HPHT drilling fluids. This work was undertaken to investigate the use of environmentally friendly dispersants in HPHT aqueous drilling fluids containing manganese tetroxide (Mn3O4) as the weighting agent. The dispersants were chosen because they are non-toxic to aquatic organisms and biodegradable. The effects of cement, rock salt and clay particles as contaminants on the dispersant performance and the fluid properties were investigated. The dispersants were lab tested in high density fluids of 2.1 g/cm3 at a temperature of 200°C and pressure of 500 psi. The fluids were analyzed before and after heat-aging using rheometer, sag test, light scattering, and HPHT fluid loss. Out of over 100 dispersants tested, two dispersants showed best performance in controlling the flow behavior of the fluids in the presence of contaminants. Dispersant A is a synthetic copolymer of maleic anhydride and acrylic acid and dispersant B is an anionic lignosulfonate. They are compatible with water based drilling fluid system having manganese tetroxide as the weighting agent (SG = 2.1) and thermally stable (150-250 °C). Both dispersants lowered the rheology including plastic viscosity and yield point before and after heat aging (200°C) when compared to blank. They show also lower sag and fluid loss values in the presence of contaminants and lowered the filter cake thickness.