New Acid Systems for Removing Filter Cakes Containing Manganese Tetraoxide as Non-Carbonate Weighting Agent

Abstract Reservoir fluids used to drill production or injector wells are formulated with non-damaging and easily removable additives. High density metal oxides like manganese tetraoxide (Mn3O4) and micronized ilmenite (FeTiO3) are widely used as acid-soluble weighting materials for reservoir drilling. The acid dissolution mechanisms for such metal oxide weighting materials are different from conventional acid-soluble calcium carbonate. This paper presents new acid systems to dissolve Mn3O4 as non-carbonate weighting agent in different scenarios. This paper presents the dissolution mechanisms for Mn3O4 using different types of acid including inorganic, organic acids, and chelating agents. Green additives have been developed for improving acid solubility of Mn3O4 with organic acid and esters. The solubility of Mn3O4 was also tested in high-density brines such as CaCl2, CaBr2 and ZnBr2. Testing was done to check for whether chlorine gas was developed during the removal of Mn3O4 filter cake with 15% hydrochloric acid. The removal of aqueous and non-aqueous filter cakes weighted with Mn3O4 will be illustrated. Understanding the dissolution mechanism of Mn3O4 helps design proper breaker systems for non-carbonate weighting agent. The acid solubility of Mn3O4 is a reversible chemical reaction and reaches equilibrium state under certain conditions. To maximize the dissolution output, the reaction conditions including type of acids, concentrations, temperatures, and ratio of acid to filter cake needs to be optimized. With the new acid system, complete filter cake removal is possible. Acid soluble micronized metal oxide weighting agents are suitable for reservoir fluids because they flow back easily from the formation and dissolves with acids and chelating agents. New findings reject the wrong belief that using 15% hydrochloric acid with Mn3O4 filter cake will lead to the development of chlorine gas. This paper presents an innovative, environmentally friendly acid system for removing filter cakes containing manganese tetraoxide. It provides information regarding the design of efficient breaker systems to maximize well productivity or injectivity.