Improvement of a well bottomhole zone treatment applying a spent sulfuric acid solution

Abstract

Relevance. Caused by the need to ensure highly efficient distribution of spent sulfuric acid solutions during acid treatment of a production well bottomhole zone. The proposed method increases the efficiency of this process by growth of efficiency of production wells exploiting terrigenous limestone reservoirs in the wellbore zone. Aim. To develop and propose a method for using spent sulfuric acid solutions during acid treatment of a production well bottomhole zone, a methodology for its application. The essence of the method is that to increase the efficiency of production wells exploiting terrigenous reservoirs, solutions of sulfuric acid or its derivatives, in particular spent sulfuric acid, are used as an acid reagent. Objects. It was revealed that the surface activity of spent sulfuric acid in fresh water at the interface with hydrocarbon liquids is significantly greater than the activity of solutions of commercial hydrochloric and sulfuric acids. Based on physical and chemical studies, it has been established that spent sulfuric acid solutions can be used in acid treatment of the bottomhole zone of wells to increase formation fluid production. Solutions of hydrochloric (HCl) and sulfuric (H2SO4) acids, as well as waste – spent sulfuric acid, were used as experimental liquids. Compared to commercial acids, the spent sulfuric acid solutions have the greatest ability to interact in carbonate rocks.   Methods. Models of porous medium were created in experimental columns, which were pipes made of organic glass with a length of 0.5 m and a diameter of 0.025 m. The manufactured model of the porous medium was evacuated and saturated with fresh water, after which the water permeability was determined, then the water was replaced with acid solutions. After a certain time for the acid to react with the carbonates of the porous medium, the water permeability was again determined. The experiments were carried out at room temperature and a pressure gradient of 0.05...0.2 MPa/m. Moreover, after completion of the treatment of the near-wellbore zone in order to prevent the deposition of sediments formed in the pores as a result of the interaction of acid with carbonates, the well is put into operation after an eight-hour holding period with large depressions in the near-wellbore zone. Results. Visual observations shown that water filtration through the porous medium at high pressure gradients leads to a large removal of sediments from the porous medium. This is the consequence of an increase in the porous medium permeability after treating it with a 15% solution of waste sulfuric acid. Thus, laboratory experiments shown that the use of spent sulfuric acid solutions under certain conditions can increase well productivity.