Influence of permeability anisotropy and layering on geothermal battery energy storage. (February 2021) - Panja, Palash
Highlights: The impacts of horizontal and vertical permeability anisotropies and layering in sedimentary rocks are investigated. Pressure contours become elliptical shape with increasing horizontal anisotropy. Distributions of produced and injected waters are proportional to the permeability of the layer. Layering has an insignificant impact on cumulative heat recovery; it is possible to recover >90 % of the injected heat. Well layout and operational planning are dependent on non-symmetrical temperature and pressure profiles. Abstract: The Geothermal Battery Energy Storage concept has been proposed to provide large- scale, long-term heat storage when solar radiance is available, to be later recovered for economic benefit. The concept considers high porosity and permeability sedimentary basin formations and uses solar radiance to heat water at the ground surface which is then injected into the subsurface. This hot water elevates the ambient temperature in the reservoir, creating a high-temperature reservoir acceptable for geothermal electricity generation or for direct heating applications. The process uses produced/injected, connate formation water and thus neither a freshwater supply nor surface storage or disposal of water is required. This concept has been previously presented in several publications and presentations. Calculations show that nearly all of the heat injected can be practically recovered for certain reservoirs. Calculations of reservoir temperature and pressure profiles for injection and production in isotropic and homogeneous reservoirs have shown that a very small volume of rock mass is required for the heat storage reservoir - only of the order of 10 s of meters radius from a production/injection well for a reservoir of ∼100 m thick. With this small rock mass, locations away from fractures, faults, and inclusions are possible. Unfortunately, under natural conditions, the reservoir would not be expected to be homogeneous and isotropic. Recognizing depositional environments and superimposed tectonics, permeability may be anisotropic and heterogeneous and multiple rock layers with different properties may exist. Calculations are presented here that consider homogeneous but anisotropic reservoir permeabilities, and layered heterogeneous permeabilities (i.e., formations with horizontal layers of different permeabilities). Such reservoir properties create non-symmetrical temperature and pressure profiles away from a production/injection well. Such non-symmetrical temperature and pressure variations are important when planning the optimal spacing between production and injection wells.