A dynamic analysis model used for casing head gas assisted lift technologies

It is frequently to adopt casing head gas assisted lifting technology to reduce the adverse effects of gas on pump efficiency in the wells with high gas-liquid ratio and make full use of gas energy. A gas lift valve is lowered to the appropriate depth to re-inject the annulus gas into the tubing. In this way, the systematic efficiency is improved by using the gas lifting principle. However, the source and pressure of casing head gas cannot be controlled artificially, and gas injection pressure and injected gas volume are varied over the time. To verify the rationality of design parameters, a dynamic model was developed for the process of casing gas assisted lifting based on the flowing characteristics of each section in oil production system and the operating characteristics of oil production equipments. In this model, the volume and pressure change of casing head gas caused by downhole separators and gas lift valves are taken into account. Production parameters of oil wells with and without downhole separator and gas lift valve were compared. It is shown that after the casing head gas assisted lifting system is adopted, the pump efficiency of oil wells is improved, the casing pressure is under control and the upstroke load is reduced. It is indicated that casing head gas can be used to assist artificial lift. Finally, the effects of all parameters in the process of oil production were investigated by changing the setting depth, size and starting pressure of gas lift valves. The research results provide the basis for the design of casing head gas assisted lift technologies.