Zhongxian Hao

Sand deposition and gas ingestion near downhole pumps are persistent flow-assurance challenges in coalbed methane horizontal wells. A large-scale gas–water–sand flow loop was developed to investigate phase distribution, particle transport, and pump-intake behaviour under controlled gas and liquid flow rates, well inclinations, and progressing cavity pump speeds. Stratified flow dominated the horizontal configuration. Increasing gas flow generally lowered the gas–liquid interface and sand bed, while increasing pump speed increased outlet gas readings and recovered wet masses more clearly at higher gas rates. Local bed height did not consistently decrease with pump speed. Single-run comparisons at a liquid flow rate of 0.625 m³/h showed more intermittent liquid structures and lower outlet gas readings and recovered wet masses at 75° than at 90°. A four-coefficient semi-empirical model incorporated annular geometry and a pump-reference interfacial correction. Gas-group holdout RMSEs were 0.816 mm for bed height and 6.725 mm for liquid-layer thickness. Only 14 of 35 gas-held-out liquid-layer predictions were within ±10%. The model describes local phase heights within the tested horizontal geometry and operating range.

Global temperature increases and more frequent extreme climate events have intensified the challenges faced by oil-based lubricants, including environmental impact and resource depletion. In recent years, glycerol ethoxylate (GE), a non-toxic and low-cost compound, has shown promise as a water-based lubricants capable of replacing conventional oil-based systems. Boric acid (BA) is an effective additive that significantly improves the extreme pressure performance of water-based lubricants. This study demonstrates that adding BA to a GE aqueous solution decreases the friction coefficient by five times and increases extreme pressure by 12.5%. Higher concentrations of BA promote the formation of a lubricating film, enhancing the hydrodynamic pressure effect. The findings provide valuable insights into the formulation and tribological behavior of eco-friendly lubricants, promoting sustainable manufacturing, longer equipment life, and improved reliability.

To address wear failure in screw pump stator and rotor friction pairs, this study constructed a numerical model of a rhombus-like micro-dimple texture on friction pair surfaces based on the scale structure of rhombus rattlesnakes. The model was based on the fluid dynamic pressure lubrication mechanism. The CFD method was used to calculate the bearing capacity, friction coefficient, flow field pressure distribution, and flow trace distribution of an oil film carrying surface. The effects of the area rate, depth, shape, and angle of the rhombus-like dimple texture and the actual well fluid viscosity of shale oil on the surface lubrication performance of screw pump stator and rotor friction pairs were analyzed. The results demonstrated that increasing the texture area rate and the angle of the long sides and decreasing the texture angle resulted in a decrease in the oil film surface friction coefficient and an increase in the average pressure and net bearing capacity as well as the hydrodynamic lubrication performance. The average pressure increased and then decreased as the texture depth increased, while the friction coefficient of the oil film surface initially decreased and then increased. At a texture depth of 20 μm, the friction coefficient reached its lowest value while the average pressure and net bearing capacity of the oil film reached their highest value, which resulted in optimal hydrodynamic lubrication performance. When the texture depth became greater than 20 μm, vortices were gradually formed within the texture, which decreased the hydrodynamic lubrication performance. When the area rate of the rhombus-like dimple texture, depth, angle between long sides, and angle were, respectively, equal to 27%, 20 μm, 74°, and 0°, the net bearing capacity of the oil film was maximized, the friction coefficient was minimized, and the hydrodynamic lubrication performance and anti-wear effect reached their highest values. The increase in the viscosity of the actual well fluid could enhance the dynamic pressure lubrication performance and improve the bearing capacity.

This paper develops a composite weaving structure, combining hexagonal micro-bumps and hexagonal grooves, in the design of the rubber surface of the screw pump. This allows us to solve the problem of high torque and fast wear of the rubber stator during the operation of screw pump lifting oil recovery, based on the bionic hexagonal surface structure, traditional surface damping principle, and fluid dynamic pressure lubrication theory. Finite element analysis is first conducted to quantitatively analyze the impacts of the parallel side distance, groove width, and groove depth on the surface flow field and wall pressure field of the composite hexagonal structure. Based on the simulation law, the rubber surface laser structure is then designed and prepared by nanosecond laser processing. Afterward, tribological experiments are conducted under the condition of long-term immersion in the actual extraction fluid of shale oil wells. This aims at simulating the actual downhole oil production conditions and quantitatively studying the impact of the size of the composite hexagonal structure on the lubrication characteristics of the friction part of the stationary rotor, as well as the effect of abrasion reduction. The results show that, within the simulation range, the smaller the parallel side distance, the higher the load-carrying capacity. In addition, the hexagonal weave with a parallel side distance of 3 mm has a higher wall load carrying capacity than that with distances of 4 mm and 5 mm. When the groove width is equal to 0.4 mm, the oil film load carrying capacity is higher than that in the case of 0.2 mm. When the groove depth increases, the oil film pressure first increases and then stabilizes or decreases after reaching 0.3 mm. In the hexagonal weave, the friction ratio of the rotor is equal to 0.4 mm. In the tribological experiment of hexagonal weave, the smaller the parallel side distance, the smaller the friction coefficient, and the 0.5 mm weave has the highest performance.

Given the friction and drag reduction effects observed in various biological hexagonal structures in nature, a new design was implemented on the rubber surface of the stator of a submersible screw pump. This design featured a multilayer concentric hexagonal groove structure. Furthermore, a composite multilayer hexagonal structure integrating grooves and pits was also developed and applied. This study investigated the influence of groove layer number, groove depth, pit depth, and multilayer hexagonal groove texture arrangement on the rubber surface flow characteristics. Additionally, the pressure field state, the degree of influence on the oil film-bearing capacity, and the biomimetic and hydrodynamic lubrication theories were tested using the finite element analysis method. Tribological experiments were conducted on nanosecond laser-processed rubber textures under simulated liquid lubrication conditions, reflecting actual shale oil well experiments. These experiments aimed to investigate the influence of multilayer hexagonal shape parameters on the tribological characteristics of the stator-rotor friction pair of a submersible screw pump. The results indicated that with a constant overall size, a multilayer hexagonal structure with ~0.1 mm groove depth enhanced the oil film-bearing capacity, providing significant friction and drag reduction. For composite textures, a deeper pit depth within the study area enhanced the oil film-bearing capacity. Furthermore, a gradient arrangement of groove textures featuring wider outer grooves and shallower depth exhibited superior performance in terms of bearing capacity.

The effects of complex well conditions in shale oil wells on the swelling and tribological properties of high-acrylonitrile stator rubber used in screw pumps were investigated in this study. Tests were conducted considering the combined effects of immersion medium, temperature, and duration. The key parameters measured included mass change rate, volume change rate, hardness, elongation at break, tensile strength, surface micro-morphology of the rubber after thermal expansion and swelling, friction coefficient, and wear quantity. The results indicated that in the actual well fluids, the mass change rate of high-acrylonitrile rubber ranged from −1.08% to 1.29%, with a maximum volume change rate of 2.78%. In diesel oil, the greatest mass change rate of the rubber was 4.68%, and the volume change rate did not exceed ±1%, indicating superior swelling resistance. In both actual well fluids and diesel oil, the maximum decreases in hardness were 8.7% and 9.5%, respectively. Tensile strength and elongation at break decreased with increasing immersion temperature, with elongation at break in 80 °C diesel oil decreasing by over 50%, indicating a significant decline in the tensile properties of the rubber. The average friction coefficient of rubber specimens immersed in actual well fluids at three temperatures, as well as in diesel oil at 25 and 50 °C, decreased compared with the high-acrylonitrile rubber without thermal expansion and swelling. However, the average friction coefficient of rubber specimens immersed in diesel oil at 80 °C increased. The wear quantity of the rubber increased following immersion in both media. Additionally, the friction coefficient and wear quantity of the rubber increased with increasing immersion temperatures. The results of the study can offer valuable insights into assessing the durability of properties in high-acrylonitrile stator rubber under complex well conditions.