A Novel Solution to Remove Carbonate and Sulfate Scale in Electric Submersible Pumps, Offshore Oil Wells in the Gulf of Mexico

Abstract

In the Gulf of Mexico, an important number of wells in carbonate reservoirs produce heavy oil through electric submersible pumps (ESP). The efficiency and useful life of pumps decrease due to the formation of mineral scales inside the pumps. Study of the main scale components and their origin led to look for a scale remover that is optimal for removal and that has no detrimental effect on the ESP components. Additionally, changes in the operational procedure were implemented to decrease scale formation occurrence. Inorganic scale samples were recovered from an ESP and characterized by X-ray analysis. The scale modeling software in conjunction with water analysis provided key information to predict the scale tendency and mineral composition under reservoir and operational conditions. These analyses identified the formation of two main scale minerals: calcium carbonate (CaCO3) and calcium sulfate (CaSO4). The origin of these minerals is driven by the incompatibility of formation water with water-based drilling fluids, auto-scaling due to temperature changes occurring into the ESP equipment, and the produced water flowing through the pump. Laboratory experiments were focused on finding the appropriate scale remover that could dissolve the inorganic samples that were recovered from the ESP equipment. The screening of several products allowed identifying the chelating agent with the highest activity dissolving calcium carbonate and calcium and barium sulfate scales in a single treatment. Corrosion and sensitivity tests were carried out for the metallic and nonmetallic ESP components. These results showed that the product does not have significative effect on the different parts of the ESP equipment; compatibility tests with the heavy oil and the chelant product were also satisfactory. Because of these encouraging results, a field validation test was implemented with outstanding results—the oil well production increased significantly and the temperature in the ESP equipment was improved. The implementation of this chelating agent in wells presenting scale formation significantly improved the oil production and increased the ESP run life cycle under profitable economic indicators. The operator has implemented an operational procedure for wells operating with ESP that consists in continuous monitoring to optimize the treatments.