Development of a Mechanistic Model for a Pneumatic Pump

Summary The rod pump is the primary artificial lift method in mature oil wells; however, it increasingly faces challenges such as mechanical wear, unintended gas emissions, and high maintenance costs. For wells in a rod pump system, the natural gas on the casing can be vented to reduce the bottomhole pressure and increase production. To avoid gas venting, a compressor could also be installed at an additional cost to inject the casing gas into the pipeline. To address these limitations, alternative pumping techniques that minimize moving parts and use natural gas as a driving force have been developed, with a pneumatic pump being the primary operating principle of the proposed method. In this study, we present the development of a mechanistic model for the pneumatic pump, formulated from transient mass balance, steady-state momentum, and force balance. A dedicated pump testing facility was constructed under controlled conditions to obtain experimental data, which were then used for model calibration and validation. Once validated, the model was applied to a sensitivity analysis of pump dimensions for design optimization. The results show that the pneumatic pump operates through alternating liquid fill-up and gas compression processes. The liquid-level transitions are governed by the chamber’s upper and lower limits, mainly determined by buoyancy and drag on the float rod. Model predictions of liquid flow rate were in strong agreement with experimental data, with errors within ±10%. The analysis further indicates that increasing injection gas or bottomhole pressure enhances production rate by raising pump cycles. Among design parameters, tubing size, gas line diameter, and stroke length were found to be the most influential, with a 10% increase in these parameters boosting production by 3–15%.