Compressed Air Flow within Aquifer Reservoirs of CAES Plants

Compressed air energy storage in aquifers: basic principles, considerable factors, and improvement approaches

Compressed air energy storage in aquifers (CAESA) can be considered a novel and potential large-scale energy storage technology in the future. However, currently, the research on CAESA is relatively scarce and no actual engineering practices have yet been performed due to a lack of detailed theoretical and technical support. This article provides a summary and analysis of the current research about the key problems in CAESA. The theoretical foundation and evaluation methods are first addressed, and then the aquifer selection criteria are proposed by analyzing the impact of the main geological factors on the performance. Subsequently, the optimal design of wellbore and the operation parameters are discussed, and different possible enhanced methods are proposed for extending the application of CAESA. Finally, conclusions are made and application outlook is addressed.

New Experimental Equipment Recreating Geo-Reservoir Conditions in Large, Fractured, Porous Samples to Investigate Coupled Thermal, Hydraulic and Polyaxial Stress Processes

Use of the subsurface for energy resources (enhanced geothermal systems, conventional and unconventional hydrocarbons), or for storage of waste (CO₂, radioactive), requires the prediction of how fluids and the fractured porous rock mass interact. The GREAT cell (Geo-Reservoir Experimental Analogue Technology) is designed to recreate subsurface conditions in the laboratory to a depth of 3.5 km on 200 mm diameter rock samples containing fracture networks, thereby enabling these predictions to be validated. The cell represents an important new development in experimental technology, uniquely creating a truly polyaxial rotatable stress field, facilitating fluid flow through samples, and employing state of the art fibre optic strain sensing, capable of thousands of detailed measurements per hour. The cell’s mechanical and hydraulic operation is demonstrated by applying multiple continuous orientations of principal stress to a homogeneous benchmark sample, and to a fractured sample with a dipole borehole fluid fracture flow experiment, with backpressure. Sample strain for multiple stress orientations is compared to numerical simulations validating the operation of the cell. Fracture permeability as a function of the direction and magnitude of the stress field is presented. Such experiments were not possible to date using current state of the art geotechnical equipment.