Influence of permeability anisotropy on high-efficiency energy storage power generation system of geothermal battery

In the context of the current energy transition, the market for innovative technologies for clean energy utilization is growing. Geothermal battery storage power generation technology is expected to solve the problem of intermittency of renewable energy sources such as solar and wind power, and is attracting attention in the clean energy field. Geothermal battery energy storage system uses the low permeability, low porosity cap and base layers and the high permeability, high porosity intermediate reservoirs formed in the sedimentary strata to realize the storage of hot water. This hot water creates a high-temperature geothermal reservoir, and it has been shown that this stored heat can be efficiently recovered and may even enable long-term or even seasonal storage. In sedimentary structures, there are very obvious anisotropy in their physical characteristics and other aspects, among which permeability anisotropy plays an important role in the flow process of fluids. Therefore, it is crucial to study the effect of permeability anisotropy on energy storage capacity. In this study, a multi-field coupled model of temperature-percolation-stress field (THM) for geothermal energy storage was developed using TOUGHREACT-FLAC3D coupling software to simulate four permeability anisotropies and analyze the hot water flow paths, temperature and pressure distributions, and power generation efficiency. The results showed that: (1) permeability anisotropy has a strong influence on the evolution of pressure during injection and production, pressure fronts move rapidly in the direction of high permeability and the lower the anisotropy the larger equivalent permeability the lower the pressure required to inject hot water. (2) Hot water flows preferentially in the direction of large permeability, and the propagation of temperature and pressure is consistent with the direction of hot water flow, but the temperature distribution is mainly determined by the direction of fluid flow, and hot water is used to heat up the colder rocks and water in the initial environment during the flow process resulting in heat loss, so the permeability anisotropy has less effect on the distribution of temperature in the reservoir. (3) The rock of the reservoir expands under the action of high-temperature hot water, and its pore pressure recovery value is gradually higher than the initial pore pressure of the reservoir (12 MPa) with the increase of temperature. (4) At the end of the 30 injection cycles, the maximum power generated at an anisotropy of 1000 permeability can reach 5.2 MW. Therefore, when selecting the geothermal cell storage system, the reservoir with a large permeability in the horizontal direction is more efficient