In the future, there will be more and more abandoned oil-gas wells with the exploitation of onshore oilfield resources. However, the large height difference in abandoned oil-gas wells can be used as building blocks for gravity power generation, thus maximizing the economic value of abandoned oil-gas wells. In this study, a scheme of gravity power generation by virtue of the spud-in casing depth of oil-gas wells is proposed, and a gravity power generation model based on abandoned oil-gas wells is established. The parameters and economic benefits of gravity energy storage are calculated for oil-gas wells in the Huabei oilfield, the Daqing oilfield, and the Xinjiang oilfield. It is shown that the power density and discharge time of the gravity energy storage system in abandoned oil-gas wells are suitable for distributed power generation. In addition, the fast response characteristics of energy storage in abandoned oil-gas wells are verified, which makes the system suitable for correcting continuous and sudden frequency and voltage changes in the power grid but not suitable for energy arbitrage under a high number of annual cycles. Furthermore, the leveling cost of storage of the gravity system in abandoned oil-gas wells is more economical with the high number of annual cycles. The analysis of this work provides a significant investigation of the feasibility of gravity power generation by using abandoned oil-gas wells.

Inconel 625 and Hastelloy X are two commonly used solid‐solution‐strengthened superalloys, and the connection of them is inevitable in high‐temperature applications. Brazing is a commonly accepted joining method. In this study, the two alloys were vacuum brazed by sandwiching a BNi‐2 adhesive filler into them. A brazing temperature‐dependent cracking phenomenon, where the cracking ratio decreased from 50.73% to 7.09% when the brazing temperature was elevated from 1030°C to 1070°C, was observed at the junctions. It is found that the microstructures of the junctions are not uniform and are categorized into two main types, both consisting of Si‐denuded, Si‐rich, and medium Si regions. The cracks predominantly form in Type II microstructures in which the well‐aligned Si‐denuded zones are fully constrained by the surrounding Si‐rich regions. The formation of the unique microstructures is attributed to deep undercooling induced by fast diffusion of B, as supported by composition characterization and thermodynamic calculations. The cracking susceptibility and the proportion of each microstructure type are governed by the brazing temperature, which influences the extent and likelihood of deep undercooling. Critical discussion indicates that the crack initiation most likely occurs within the Si‐denuded regions rather than at the eutectic regions.

Repairing is considered as a practical and economic scheme to effectively extend the lifetime of components made of Inconel 738 (IN 738), which has been widely used in hot sections of jet engines and industrial gas turbines. In this study, the feasibility of repairing IN 738 substrates was investigated using InterPulse tungsten inert gas (TIG) welding with Inconel 625 (IN 625) and Pmet 838 as feeding materials. It was shown that single-pass deposition achieved sound metallurgical bonding under three different TIG parameters, with no cracks observed in any of the specimens. Under multi-pass repairing, γ ′ dissolution was observed in the heat-affected zone (HAZ), and cracks were observed neither in the multi-pass deposited layers nor the HAZ. The Pmet 838 deposited layer was quasi-homogeneous and entirely devoid of γ ′; the IN 625 multi-pass deposited layer, however, exhibits pronounced mesoscopic segregation with significantly lower hardness than the IN 738 substrate. The Pmet 838 deposited layer demonstrates considerably higher hardness than that of the IN 738 substrate, primarily attributed to the existence of dense cellular structures. The hardness in the HAZ of both specimens decreases with increasing the distance from the fusion line to the base metal, which may be associated with gradient variations of the cellular structures. After annealing at 920 °C for 150 h, the average Vickers hardness of the Pmet 838 multi-pass deposited layer decreased from 486.1 ± 13.9 HV _0.2 to 378.2 ± 6.2 HV _0.2 , even though copious precipitation of γ ′ was observed in it, which is attributable to the disappearance of the cellular structure; in contrast, the IN 625 deposited layer exhibited heterogeneously distributed γ ′ precipitates and needle-like δ phase, corresponding to the aforementioned mesoscopic segregation, resulting in an increase in the average Vickers hardness from 252.1 ± 6.6 HV _0.2 to 317.6 ± 17.4 HV _0.2 .