In order to reduce gas consumption and increase the renewable energy proportion, this paper proposes a poly-generation system that couples geothermal, solar, and liquid natural gas (LNG) cold energy to produce steam, gaseous natural gas, and low-temperature nitrogen. The high-temperature flue gas is used to heat LNG; low-temperature flue gas, mainly nitrogen, can be used for cold storage cooling, enabling the staged utilization of the energy. Solar shortwave is used for power generation, and longwave is used to heat the working medium, which realizes the full spectrum utilization of solar energy. The influence of different equipment and operating parameters on the performance of a steam generation system is studied, and the multi-objective model of the multi-generation system is established and optimized. The results show that for every 100 W/m² increase in solar radiation, the renewable energy ratio of the system increases by 1.5%. For every 10% increase in partial load rate of gas boiler, the proportion of renewable energy decreases by 1.27%. The system’s energy efficiency, cooling output, and the LNG vaporization flow rate are negatively correlated with the scale of solar energy utilization equipment. The decision variables determined by the TOPSIS (technique for order of preference by similarity to ideal solution) method have better economic performance. Its investment cost is 18.14 × 10 CNY, which is 7.83% lower than that of the LINMAP (linear programming technique for multidimensional analysis of preference). Meanwhile, the proportion of renewable energy is only 0.29% lower than that of LINMAP.

Geothermal reinjection is essential for sustainable geothermal energy utilization, yet reservoir scaling triggered by water–rock interactions remains a critical obstacle to long-term operation, and the coupling mechanisms between scaling and pore-permeability evolution remain unclear. In this work, high-temperature and high-pressure reinjection experiments were conducted on natural and artificial sandstone cores, combined with ICP-OES, XRD, SEM and X-CT characterizations, to reveal scaling mechanisms and porosity-permeability evolution patterns. Temperature-ramp tests with deionized water (50–100 °C) demonstrate that thermal expansion and thermally induced clay mobilization reduce permeability by 62.52% in natural cores and 68.76% in artificial cores, verifying that temperature elevation alone can induce significant permeability impairment. Under 80 °C synthetic formation water reinjection, water–rock interaction-driven scaling decreases permeability by over 15% (natural cores) and 29.34% (artificial cores). Calcite dominates scaling products, showing dispersed distribution in natural cores and preferential pore-throat deposition in artificial cores. These findings clarify the coupling law of mineral composition and scaling deposition on pore structure evolution, and can provide a scientific reference for scaling prevention and field reinjection management of sandstone geothermal reservoirs.

Wellbore plugging has become the primary constraint on gas production for numerous oil, gas, and geothermal wells in China. To enhance productivity in mature wells, a novel straight-swirling integrated jet (SSIJ) deplugging tool was designed, incorporating a converging-diverging jet (CDJ) nozzle. A combined approach of numerical simulation and experiments was employed to optimize the tool structure and evaluate the effects of different operational parameters on its blockage-removal performance. Structural optimization identified an impeller spinning angle of 540° and an impeller thickness of 12 mm as the optimal parameters, which significantly improve the three-dimensional velocity peaks and cavitation generation capability. Compared with the CDJ nozzle, the SSIJ tool produces substantially higher tangential and radial velocity components, with peak tangential and radial velocities reaching 22 m/s and 45 m/s, respectively, under the optimized conditions. The numerical results show that the peak impact pressure reaches 2.7 MPa at a standoff distance of 12 mm, while the optimal standoff distance, considering both impact magnitude and effective coverage area, is determined to be 16 mm (4 times the outlet diameter). Furthermore, indoor validation experiments under a pump pressure of 20 MPa demonstrate that the tool completely removes the artificial scale layer from the tubing inner wall within 2 min of continuous flushing, leaving no visible residue. This study provides a quantitative reference for the design and process optimization of jet blockage-removal tools.

Natural gas hydrates are characterized by abundant reserves, wide distribution, and high energy density, while geothermal energy also holds significant development potential. Conventional hydrate dissociation methods face challenges in the later stages of production, such as insufficient driving force for dissociation and secondary hydrate formation. This study explores the approach of utilizing deep-sea geothermal energy to assist in the extraction of hydrate. The aim is to achieve efficient exploitation of hydrate while expanding the applications of geothermal energy. A field-scale coupled thermo–hydro–mechanical–chemical (THMC) injection-production numerical model is established, taking a typical hydrate reservoir in the South China Sea as the study area. The engineering feasibility of geothermal-assisted hydrate extraction is evaluated through numerical simulations. Injection temperature, extraction rate, and well layout are systematically analyzed to optimize production performance, with particular focus on the evolution of physical fields, hydrate dissociation, and geothermal formation temperature stability. The novelty of this study lies in the proposal of a closed-loop ‘in-situ geothermal extraction and reinjection’ system, and the systematic optimization of its coupled THMC responses, which has received limited quantitative investigation. The results indicate that an injection temperature of 50 °C and an injection rate of 500 m³/d provide the most favorable production performance under the investigated conditions. Compared with conventional depressurization, the optimized geothermal-assisted scheme increases cumulative gas production by approximately 40% after 600 days. Horizontal well configurations outperform vertical wells, whereas excessively close well spacing reduces thermal stimulation efficiency because of hydraulic interference. Temperature variations in the geothermal layer during the simulated extraction period are minimal, indicating favorable operational stability under the investigated conditions. In summary, geothermal-assisted depressurization enhances hydrate extraction efficiency and expands geothermal applications, offering a promising approach for future development.