The First issue: We conducted hollow cylinder tensile strength tests and Brazilian tests in Seokmo granite to measure tensile strength necesarry for estimating the magnitude of the maximum horizontal principal stress in hydraulic fracturing stress measurements. Two different pressurization rates were used in hollow cylinder tests. Tensile strengths were determined to be higher at higher pressurization rate, which suggests that tensile strength should be measurement at the same rate used in actual in situ hydraulic fracturing tests. Considering the effect of pressurization rate and specimen size on tensile strength, the hollow cylinder tests and Brazilian tests yield similar results each other. This demonstrates that Brazilian tests can be utilized to produce representative tensile strengths for interpretation of hydraulic fracturing test results.
And Secondary issue: One of the necessary information on the mechanism analysis smiling earthquake fault effect that can lead to an increase of the gap pressure due to carbon dioxide underground injection generated with it, is the friction coefficient of the discontinuity surface of my reservoir sandstone. In this study, can be directly measured in the field was tested whether it is possible to infer from the physical properties can be measured relatively easily the friction coefficient of the discontinuity surface of my difficult reservoir sandstones. Measuring the friction coefficient and physical properties of the drill core sandstone Samcheock area was analyzed whether there is any correlation. Sandstone that was used for the test is a total of 38 samples of various physical properties of 0.3-15% porosity. and is tended to samples collected by the nature that showed the distribution decreased of about 2402-5038 m/s, 1039-3043 m/s, is increased following the depth. Has measured coefficient of friction by direct shear test for discontinuities to measure various physical properties, formed artificially at rock cutter specimen respectively. Results of direct shear test, the friction coefficient tended to be greater coefficient of friction the more rocks recovered from deep showing the distribution of 0.35-0.59. Result of the comparative analysis of the friction coefficient and physical properties, as the acoustic wave velocity is increased, the coefficient of friction tended to increase certain degree linearly as the and porosity is reduced. This result suggests that we can estimate the friction coefficient of the discontinuity from the borehole geophysical data. The Critical injection pressure of carbon dioxide was calculated 2.2-10.5 MPa about virtual reservior depth condition. Injection pressure setting in excess of that can cause a faults/fractures reactivate and micro-earthquake. Many data and more results are secured of this study will be determined that it can be used as an indicator of safety analysis provides basic injection demonstration of carbon dioxide.