The success of CO2 storage, nuclear waste disposal and energy storage in rock salt depends on the ability of the formation to prevent leakage of fluids injected in the subsurface. However, fractures, either pre-existing or induced, can provide flow paths that are orders of magnitude more conductive than intact rock. This increased permeability can compromise the integrity and performance of the construction. Thus, it is essential to understand permeability evolution of rock salt fracture.
Previous studies have indicated that fracture geometry plays a dominant role in controlling fluid flow and mass transport within low permeability rocks. When fractures or faults in rock salt, which is highly soluble, are exposed to unsaturated fluid, material from the fractures walls will dissolve. If there is flow, the dissolved salt will be transported and will potentially precipitate at a distant location. This will result in a variation in permeability of the fractured zone. Limited research has focused on quantifying the interplay of reaction, diffusion, advection and even precipitation in the fracture of rock salt on the alteration of fracture surface morphology and fracture permeability. This study aims to shed light on how fluid concentration and flow rates affect the evolution of fracture geometry and permeability at the laboratory sample scale. This endeavour is critical for enhancing our understanding of the stability and long-term viability of subsurface storage projects.
With the objective of investigating these coupled mechanisms, we will perform flow-through experiments with simulated fractures in rock salt. We have constructed a model comprised of a flat glass plate placed atop a salt rock plate (4.5 cm in width, 28.0 cm in length and 4.0 cm in height) with a simplified, rectangular groove. This groove in the rock simulates a fracture within the rock salt. Two solutions of different concentrations (0.684 mol/L, 2.738 mol/L) are injected through the model fracture at 3 different flow rates (3 ml/min, 9 ml/min and 18 ml/min). The fracture geometry is tracked using a camera, while changes in fluid pressure along the fracture are monitored via a differential pressure transducer. Additionally, the dissolution rate is measured using an electrical conductivity probe. We expect that the obtained results will provide information regarding pressure differentials across the fracture, the progressive transformation of fracture morphology and total dissolved mass over time.
