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The exploitation and transportation of deep-sea and remote oil and gas fields have risen to become important components of national energy strategies. The gas–liquid separation and gas blocking caused by the large density difference between the gas and liquid phases are the primary influencing factors for the safe and reliable operation of gas–liquid mixed transportation pump systems. This paper takes the independently designed single-stage helical axial-flow mixed transportation pump compression unit as the research object. Through numerical simulation, the internal flow of the mixed transportation pump is numerically calculated to study the aggregation and conglomeration of small gas clusters in the flow passage hub caused by gas–liquid phase separation, influenced by the shear flow of phase separation, forming axial vortices at the outlet where gas clusters gather in the flow passage. The work performed by the impeller on the gas clusters is insufficient to overcome the adverse pressure gradient formed at the outlet of the flow passage due to the gathering of the liquid phase in adjacent flow passages, resulting in the phenomenon of gas blocking, with vortex gas clusters lingering near the hub wall of the flow passage. [ABSTRACT FROM AUTHOR]

Abstract: In enhanced oil recovery (EOR) operations foam has been applied to improve sweep during gas injection or for gas shut-off. Field experiences for North Sea reservoirs involve foams using hydrocarbon gas for conformance control and gas blocking in high pressure and high temperature fields. Generally foam field applications have utilized CO2 and N2 in addition to hydrocarbon gas. As reservoir conditions vary significantly it is important to understand foam properties on a broad experimental basis. The large changes in physical properties with temperature and pressure may affect CO2-foam properties and these are discussed by varying pressure from 30 to 280bar in an outcrop Berea sandstone core material at 50°C. The CO2-foam properties were compared to N2-foams. Foam was generated by co-injection of surfactant solution (AOS) and N2 or CO2 at 80% foam quality (fraction gas) at a total injection rate of 40ml/h. Strong N2-foams were generated both at 30 and 280bar. In general, N2-foams were stronger than CO2-foams. Comparing CO2-foams at different pressures showed that CO2-foams at 30bar were strong (MRF ~50–75) whereas supercritical CO2-foams gave MRFs in the range of 3–6. The visual foam structure observations from a sight glass at the core outlet showed denser N2-foams compared to CO2-foams. Injecting seawater after N2-foam showed that relative seawater permeability was low and remained low (<0.1) after injecting more than 10 pore volumes of seawater. Indeed, similar and positive results were obtained both for experiments run at 30 and 280bar. Mass transfer was found to be very important for CO2-foam stability. Results from two CO2-foam flooding experiments with equilibrated fluids at 30bar and 50°C showed improved foam strength, even though the largest improvement was observed for foams ability to block seawater. The water relative permeability was strongly reduced in the presence of foam, thus providing the reservoir engineer with another tool for water blocking. [Copyright &y& Elsevier]