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Enhanced oil recovery (EOR) is a crucial technology in the petroleum industry, influenced by several factors, including flooding fluids and methods. The adjustment of injection strategies and the application of vibration stimulation can significantly impact oil recovery, especially residual oil. In this study, we conducted experiments using a glass micromodel to investigate the effect of pulsing water injection on oil recovery. Our results show that when the pulse frequency matches the natural frequency of the micromodel, resonance occurs during the two-phase flow of pulse driving, which causes an increase in the amplitude of oscillation, enhances the mobility of oil, and improves recovery. The efficiency of the kinetic energy of displacement is also improved. However, when the frequency is 3 Hz, the absence of resonance leads to the opposite effect. In addition, we found that a greater amplitude increases the fluidity of oil. These findings have significant implications for the design of EOR strategies and methods. Our experimental results provide insight into the effect of pulse water injection on oil recovery and offer a potential strategy for the optimization of EOR techniques.

Gas hydrates are widely distributed and abundant in nature, and are regarded as an essential clean energy for the future. Improving the development mode and promoting production efficiency is an important way to realize the commercial application of natural gas hydrate. Hydraulic fracturing has an impressive application effect in developing traditional oil and gas resources. This study proposes fracturing of radial horizontal wells to exploit oceanic hydrate reservoirs. Based on the trial production data of SH7 site in the Shenhu area, a 2D model was developed to simulate the hydrate decomposition process using fracturing of radial horizontal well. Results indicate that fractures can effectively improve the production efficiency of natural gas hydrate, and the fractures can provide high conductivity channels and effectively increase the pressure drop propagation range, thus facilitating the decomposition of hydrates. Horizontal and vertical fractures boosted gas production by 306% and 550%, respectively. Vertical fractures are more conducive to the heat replenishment from the boundary layer, thus increasing gas production more efficiently. This study provides a theoretical basis for the potential applications of radial horizontal well fracturing in field trials of gas hydrate development.

Summary Natural gas hydrate (NGH) is a potential clean energy source and is buried abundantly in seafloor sediments. Waterjet is a key technology involved in both the marine NGH solid fluidization exploitation method and the integrated radial jet drilling and completion method. To improve the efficiency of breaking and extracting NGH through a waterjet, a straight-swirling integrated jet (SSIJ) nozzle is designed based on the convergent-divergent geometry and impeller in this study. With a computational fluid dynamics method, the 3D model of SSIJ is constructed, and the characteristics of velocity field, pressure field, cavitation cloud distribution, and turbulence kinetic energy are analyzed, the results of which are compared with conical jet (CJ), convergent-divergent jet (CDJ), and swirling jet (SJ). Laboratory experiments of gas hydrate-bearing sediments (GHBS) erosion by the four kinds of jets mentioned above are conducted to evaluate the jet erosion performance based on the in-house experimental apparatus for NGH generation and cavitating jet erosion. Results indicate that the SSIJ can significantly enhance the breaking volume and efficiency of waterjet erosion on GHBS compared with the other three methods. The most important driving force for improved efficiency is the 3D velocity, which can induce axial impact stress, radial tensile stress, and circumferential shear stress on the impinged GHBS. Additionally, the insertion of an impeller with the center hole greatly improves the cavitation erosion performance of SSIJ. This paper illustrates the erosion performance of four kinds of waterjets in breaking GHBS and provides preliminary insights into the potential field applications in NGH exploitation.

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