Investigation of Relationship between In-Situ Stress and Fluid Conduits from Chinshui Geothermal Area, NE Taiwan

Recently, underground geo-engineering has been paying more and more attention as the demand of natural resources and waste disposal dramatically increases these years, such as petroleum exploitation, geothermal energy, carbon capture and sequestration, and nuclear waste disposal. In the underground geo-engineering, knowledge of in-situ stress is essential for engineering design. Furthermore, understanding the relationship between fractures and in-situ stress is one of key information to evaluate the potential of fracture seal/conduit for such projects. In this study, we summarized the results of geothermal exploration in the ChinShui Geothermal area, NE Taiwan. The results are integrated from core observation, downhole physical logging, anelastic strain recovery, paleostress analysis, and focal mechanism stress inversion around the ChinShui geothermal area, Ilan, NE Taiwan. The in-situ stress results from multi-scale observations of core-based method, local paleostress, and regionally focal mechanisms all show strike-slip faulting stress regime of NE-compression and NW-extension as recent stress state. Using the classification of non-filling and filling (closed and opened) fractures, we are able to identify no-fluid fractures, healed fractures and fluid conduits, respectively. The fluid conduits strike NE, which is consistent with the predicted orientation of open cracks based on current stress state. Accroding to the orientation distribution of fluid conduits, the stress ratio and fluid pressure ratio are estimated as 0.30 and 0.59, respectively. Furthremore, in accordance with the tensile strength of 2.56MPa and the assumption of S2 as vertical lithostatic stress, the magnitude of S1, S3 and fluid pressure at 700m can be estimated as 21.6, 17.2 and 19.8 MPa, respectively. This study provides insights into understanding the relationship between in-situ stress state and fracture sealing/conduits. The results can be applied for geo-engineering projects such as geothermal energy exploitation, CO2 sequestration and nuclear waste disposal.