Weak Bonded Interface and Shear Block Design for Validating Fracture Caging’s Effect in Induced Seismic Mitigation

Fracture caging is an innovative approach in geothermal energy extraction, utilizing one injection well surrounded by multiple boundary wells for production. This method facilitates high-rate fluid injection at elevated pressures, while concurrently managing induced seismicity. To validate this concept, a cubic block with a designed weak layer and multiple injection/production wells will be used to simulate injection-induced shear events. A significant challenge in this process is the creation of a reliable and repeatable weak layer with the necessary bonding strength for shearing. After evaluating various materials, plaster was selected as the best option due to its light weight, ease of drilling holes, and shape adaptability. Experimental trials led to the optimal interface design: a combination of an aluminum surface, textured with 120-grit sandpaper and cured plaster. This interface consistently demonstrated a friction angle of 39° and cohesion of 0.79 MPa. Based on this optimization, we designed an experimental setup consisting of an aluminum block divided into two semi sections with a 10-mm-thick layer of plaster cured between them. Three validation tests have been conducted, and we found that injecting fluids to the simulated fault induced shearing of the block that was stable under pre-existing mechanical load. However, if we have boundary wells as producer, the fault is stable throughout the whole experiment under the same injection rate. This work not only helps validate the concept of fracture caging, but also has broader implications for civil engineering. It presents a reliable method for creating a weak bonding layer with uniform strength, a crucial element in various engineering applications.