This paper evaluated dispersants for high densityinvert-emulsion drilling fluids weighted with manganese tetroxide (Mn3O4) particles for high temperature applications. Additionally, the use of dispersants to control the reaction of cleaning fluid with Mn3O4-based filter cake was studied. The dispersants selectedare non-toxic to aquatic organisms and biodegradable. Adding dispersants to the drilling fluid will result in reduced sag, rheological properties, and low fluid-loss.

Three dispersants (A, B, and C)improved the flow behavior Oil-based drilling fluids weighted mainly with manganese tetraoxide particles. They are based on ethoxylated alcohol and polyether carboxylic acid. Dispersant A was anionic and dispersants B and C were non-ionic. In addition, three dispersants (D, E, and F) showed excellent results in controlling the reaction rate of cleaning fluids with manganese tetraoxide particles. Dispersant D was based on sulfonic acid, dispersant E was based on phosphate ester, and dispersant F was based on malic acid copolymer.

Dispersant B showed improved the rheological/filtration properties and sag before/after heat aging at 400°F and 16 hours aging time for Mn3O4 oil-based drilling fluids (1.9 SG) than fluids with or without dispersants A or C. Combination of ionic and non-ionic dispersants improved the filtration properties of oil-based drilling fluids (2.1 SG) weighted mainly with manganese tetraoxide particles. Using dispersant E, the reaction rate of lactic acid/Mn3O4 system was the lowest, followed by dispersant F, and then dispersant D. Dispersants D, E, and F can be used as additives in the cleaning fluid formulation to control the reaction with Mn3O4-based filter cake.

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