Performances of a novel compressed CO2 energy storage and heat storage integration system using multi-stage hydraulic fractures of horizontal well in subsurface reservoirs

Natural reservoirs represent a promising option for large-scale compressed gas energy storage in the future, owing to their extensive distribution and favorable pressure-bearing characteristics. However, the inherent seepage resistance of these reservoirs results in elevated cyclic energy consumption. Additionally, the materials currently utilized for ground-based compression heat storage exhibit limited durability and high associated costs. Therefore, this paper proposed a novel compressed CO2 energy storage and compression heat underground storage system using multi-stage hydraulic fractures of the horizontal well in depleted oil and gas reservoirs to solve the above problems. Based on the novel system numerical model considering multiphase flow processes, the unique spatiotemporal evolution of key physical fields in this new system during the cushion and circulation stages was analyzed, which is unknown from previous studies. The round-trip efficiency was preliminarily calculated, and unique advantages of this novel system were discussed. Results show that hydraulic fractures improve fluid flow performances. High saturation zones of 0.5–0.7 formed around fractures and horizontal well are main working areas, which is markedly different from the characteristic of having a well-defined boundary within the cavern, but is stable enough during simulation periods. Compression heats storage significantly improves the system efficiency to 72 %, which is comparable to or even exceeds existing systems. Such a feasible system can cooperate with energy storage and carbon reduction with a preferable development potential. The conclusion aims to provide the assistance for the compressed CO2 energy storage system design and promotion.