Calculation method of multi-stage gas lift process parameters in deep offshore low-permeability oil and gas fields

To address the challenges of low drainage efficiency and structural limitations in testing deep offshore low-permeability reservoirs in the eastern South China Sea, this paper proposes an innovative semi-closed multifunctional rapid gas-lift testing technology and establishes a systematic calculation method for multi-stage gas-lift process parameters. This technology utilizes 2–3/8″ flat tubing inside a 5″ drill pipe, integrating rapid induced jetting, formation testing, fluid sampling, and efficient wellbore unloading into a single operation. Comprehensive design verification was conducted through gas-lift parameter modeling, mechanical strength checks, and sensitivity analysis. Field application results confirm that the process overcomes the limitations of traditional test strings in deep, thick reservoirs, achieving high operational efficiency and improved production recovery. Compared with conventional annular gas-lift, this method increases lifting efficiency by 25–30 %, reduces drainage time by approximately 30–40 %, and lowers gas consumption per unit liquid lifted by 15–20 %. This research provides a significant technical advancement for the testing and development of deep offshore low-permeability oil and gas fields.