Abstract: When sulfonated surfactants are used to displace crude oil from a subterranean formation, the produced oil and water contain the surfactant and form a tight emulsion. This crude oil-water-surfactant emulsion is broken with a strong inorganic acid, for example, hydrochloric acid. The amount of acid added is sufficient to lower the pH of the water in the emulsion to 3.0 or lower. Thereafter, the oil is separated from the emulsion by conventional techniques.

Abstract: Scale deposition is inhibited with a new scale inhibitor precipitation squeeze method wherein inhibitor solution is injected at a higher first pH into a subsurface brine producing formation. Thereafter, the solution is subjected to a fluid or substance which lowers the higher first pH of the scale inhibitor solution to a lower second pH, thereby causing precipitation of scale inhibitor in the formation. The scale inhibitor is characterized by the fact that the scale inhibitor exhibits a significant solubility decrease between the higher first pH and the lower second pH. The method of this invention, therefore, is based on decreasing the pH the scale inhibitor solution to deposit the scale inhibitor and does not use prior art divalent cation precipitation methods to precipitate inhibitors. This invention lessens the chances of formation damage or plugging. The preferred scale inhibitors are the amine phosphonates of a given general structure.

Abstract: A method for removing scale and inhibiting the formation of scale in a well penetrating a subterranean formation for the production of fluids from the formation, the method comprising;(a) injecting an aqueous solution of EDTA into the well in an amount and for a time effective to remove scale from the well; and,(b) injecting a scale inhibitor through the well and into the subterranean formation surrounding the well.

Abstract: Step declines in the production rate from a well following an acid treatment, and a scale inhibitor treatment are reversed by use of an EDTA treatment.