Study On Corrosion Damage And Applicability Evaluation Of Rubber Material Of Shaft Rubber

Rubber seal products play an important role in the oil and gas exploitation operations. With the development of oil and gas exploitation, the working environment of rubber seal products is more severe. While the working performance of rubber material is closely related to the environment and the rubber material is easy to be corroded in the high temperature and high pressure and high corrosive medium conditions, which leads to the decline of the performance of rubber seals, then damages the wellbore integrity and then affects the normal downhole operations, even causes safety problems. Therefore, the research of the corrosion damage and applicability of rubber material in wellbore environment is of great significance.Firstly, aiming at the shortage of previous experimental study on rubber material that not simulating the actual working conditions of wellbore rubber seals, a seal assembly which enabled the rubber O-ring under compressive stress state and a dynamic reaction kettle which realized to simulate the actual working conditions was designed. Through the feasibility study of the method and apparatus, it was found that after service in simulated wellbore conditions, the appearance of rubber material was damaged and the physical dimensions had changed, but the quality of rubber material could not accurately be judged according to these changes. So the appearance and physical dimensions were not suggested as the main investigation indexes of the corrosion damage and the applicability of rubber material. After service, the mechanical properties decreased. The tensile strength, the tensile elongation and the hardness reduced, while the compression set increased. Due to high comparability and reliability, the mechanical properties were suggested as the main investigation indexes.Then, simulating a high CO2natural gas production wellbore conditions with pressure of35MPa, temperature of140℃,5vol%CO2and95vol%CH4, the corrosion tests on fluorocarbon rubber, fluorinated silicone rubber, AFLAS, and hydrogenated nitrile rubber O-rings were performed and the applicability of the four kinds of rubber materials was evaluated. The results show that, the service performance of rubber material in compressive stress state and free state was different. Compared in free state, the corrosion damage degree of the rubber material in compressive stress state was weaker, and in free state, the liquid phase corrosion was more serious, while in compressive stress state, the gas phase corrosion was more serious. For field work, the rubber seals are in compressive stress state, so the results of the rubber material in compressive stress state were suggested as the main reference for the evaluation of the applicability of rubber material. In this simulated conditions, the hydrogenated nitrile rubber was the best. In addition, combined with EDS detection and tensile fracture morphology analysis, the corrosion damage mechanism and influence factors of rubber material in wellbore environment was explained. The study found that the tensile fractures of the four kinds of rubber materials after service mainly were brittle fracture.At last, CO2permeability tests on the four kinds of rubber materials were peformed. According to the pH of the alkaline imaging agent solution in rubber seal assembly, CO2permeability of the four kinds of rubber materials with the change of environmental temperature and pressure when the CO2content is certain was studied.