资源环境科技发展态势分析平台

Specific storage reflects the volumetric deformation capacity of permeable media. Classical groundwater hydrology equates elastic storage to medium compressibility (plus fluid compressibility times porosity). However, it is unclear if storage behavior can be represented by a single parameter. Hydraulic gradients act as body forces that push the medium in the direction of flow causing it to deform instantaneously everywhere, i.e., even in regions where pressure would not have changed according to conventional fluid flow. Therefore, actual deformation depends not only on the mechanical properties of the medium but also on aquifer geometry and on surrounding strata, which act like constraints to displacements. Here we discuss the question and highlight the nonlocal nature of storage (i.e., the volume of water released at a point depends on the poroelastic response over the whole aquifer). Proper evaluation of transient pressure and water release from storage requires acknowledging the hydromechanical coupling, which generally involves the use of numerical methods. We propose analytical solutions to the HM problem of fluid injection (extraction) into finite aquifers with one-dimensional or cylindrical geometries. We find that pressure response is much faster (virtually instantaneous) and larger than expected from traditional purely hydraulic solutions when aquifer deformation is restrained, whereas the pressure response is reversed (i.e., pressure drop in response to injection) when the permeable medium is free to deform. These findings suggest that accounting for hydromechanical coupling may be required when hydraulic testing is performed in low permeability media, which is becoming increasingly demanded for energy-related applications.