Response of a Gulf Coast Drilling Mud to Chemicals, Temperature and Heat-treatment

Abstract

Abstract A typical drilling mud from the Hastings oil field, Brazoria County, Texas, containing only 8 per cent (dry basis) of material of colloidal dimensions, which is largely illite, was concentrated to a density of 10.2 lb. per gal. andused in this study. The effects of water dilution, treatment with complexpolyphosphates, temperature and the time of heating upon the rheologicalproperties of the mud were investigated. It was found that water plays animportant part in chemical treatment and that sodium acid pyrophosphate andsodium tripolyphosphate were more efficient than other complex polyphosphatesfor chemical treatment. Muds treated with either of these chemicals manifestedmaximum reduction in viscosity and minimum filtration rates at lowconcentrations. Furthermore, mud treated to minimum viscosity with either ofthese two chemicals was virtually unaffected by heat-treatment. Introduction The drilling of deep wells is dependent upon the use of drilling mud, andproblems frequently arise concerning the effects on mud of temperature, prolonged heating and aging. The use of chemicals to control the rheologicalproperties of mud is a well-established practice. Salts of weak organic acidssuch as sodium tannate or gallate were used at first until the complexphosphates of sodium were found to be more efficient. Consequently, it seemed important to investigate the reactionof a mud to chemical treatment with phosphates, temperature, heat-treatment andaging, particularly since previous work in the laboratory at the University ofTexas had provided the particle-size distribution and mineral composition of Hastings mud. Properties of Mud Used in Experiments A large sample of the mud from a drilling well in the Hastings field, Brazoria County, Texas, was obtained directly from the circulatory system. Someof the general physical characteristics of the mud and other data are presentedin Table I. The Alexander mud was used for the experimental work. Comparisonwith Curkeet mud indicates a considerably greater dilution but otherwisesuggests similarity. The mineral composition and particle-size distribution ofCurkeet mud (Table 2) are available (Fancher and Oliphant). It is suggestedthat Alexander mud would have a similar composition. T.P. 1589