Factors Involved in Removal of Sulphate From Drilling Muds by Barium Carbonate

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Abstract The conditions under which barium carbonate can be used to remove sulfatesfrom drilling muds are limited. The amount of sulfate remaining in solution inthe system after treatment with barium carbonate is shown to be a function ofthe concentration of the carbonate and barium ions and the concentration ofother electrolytes. Barium hydroxide may advantageously replace bariumcarbonate when the contamination is not entirely due to anhydrite (calcium inthe system is then stoichiometrically less than sulfate) or when the carbonateconcentration is high. The effect of substances such as quebracho, phosphates, and chromates, which form complexes or precipitates with barium, isdiscussed. Introduction As the complexity of the operations in drilling for oil has increased, moreattention has of necessity been directed to the problems pertaining to themaintenance of good drilling mud properties. As a result, chemical treatment ofmuds has become an important factor in recent years. Some of these treatmentshave been designed to eliminate the deleterious effects of contaminants inaqueous mud systems by precipitation or other means. The most common ofsubstances encountered during drilling include sodium chloride, cement, andcalcium sulfate while various other contaminants, usually in small amounts, maybe introduced from the water, clays, and other materials used in preparation ofthe mud. In certain cases, for example where continued salt-water flow isencountered or massive anhydrite is drilled, special muds may be used so thatthe physical properties of the mud will remain satisfactory for drilling. Inother cases, it is desirable to remove the contaminants so that solubleelectrolytes in the system are maintained at low values. For sulfate contamination, the common practice in the field is to add bariumcarbonate to precipitate the sulfate as barium sulfate. Ordinarily such aprocedure gives satisfactory results. There have been important instances, however, where addition of barium carbonate was not effective in removal ofsoluble sulfates from drilling muds, and it is to these cases that the presentpaper is directed. T.P. 2639