Study on multi-stage adjust mechanism of downhole stratification control tool for natural gas hydrate multi-gas combined production gas lift

Accurate control of natural gas flow and pressure is essential to achieving multi-gas combined production of the natural gas hydrates. In this study, a downhole stratification control tool for controlling natural gas flow rate and pressure with a multi-stage throttling structure was innovatively proposed. The multi-stage throttling structure combined an adjustable cage sleeve and a fixed nozzle. The numerical model of the internal flow field of the downhole stratification control tool was established. Through the computer fluid dynamics numerical simulation, the flow field change law inside the spool module of the downhole stratification control tool under different spool structures, different outlet pressures, and different spool openings was analyzed. Moreover, the spool module prototype was processed, and the indoor experiment of the spool's performance of reducing pressure and regulating production was carried out. The results show that the multi-stage throttling structure has the advantages of adjustable spool opening and moderate cooling range and the mass flow of gas inside the spool changes linearly with the opening of the spool. The spool module can accurately control the mass flow of natural gas under high-pressure conditions, and meet the needs of the downhole stratification control tool for accurate gas control.