| Title | Contribution of Physical and Textural Properties of Volcanic Rock to Slip Characteristics by CO2 Injection Under Geothermal Environment |
|---|---|
| Authors | Kazumasa Sueyoshi |
| Year | 2026 |
| Conference | World Geothermal Congress |
| Keywords | CO2, Shearing, Fracture, volcanic rock |
| Abstract | The creation of an enhanced geothermal system reservoir in volcanic rock would enable increase power generation. Reservoir permeability enhancement is achieved by hydraulic stimulation to induce shearing of natural fractures, where CO2 has been proposed as the stimulating fluid due to its advantageous properties. On the other hand, shearing of fractures is affected by fluid pressure perturbation depending on permeability of the surrounding rock, and slip surface influenced by crystal or clast sizes. Therefore, we investigated the contribution of the physical properties and constituent mineral heterogeneities to CO2 injection-induced slip characteristics of a fracture in volcanic rock. Accordingly, injection experiments were conducted on dry and water-saturated andesites with low- and high-permeability, and dacitic lapilli tuffs containing a sawcut. Focusing on the results for water-saturated samples, continuous shearing with lower velocities was induced by CO2 injection in low-permeability andesite. Whereas, water injection induced shearing with sudden increases of slip velocities. By contrast, the maximum slip velocities were low in high-permeability andesite, regardless of the injected fluid. These imply that CO2 injection is effective for inducing steady shearing of natural fractures. In addition, despite the presence of unstable fluctuations in slip velocity during CO2 injection into dacitic lapilli tuff, no significant differences were observed in the fluid pressure at the onset of slip and slip velocity, compared to results for other rock types. From the above, the slip velocity reduction effect of CO2 injection is effective even when the slip surface contains lapilli and has heterogeneous contact surfaces. |