Evaluation of fracture aperture using X-ray CT. 2

Understanding the influence of small scale structure and its heterogeneity onto flow through rock fractures is important for improving the reliability of performance assessment of Geologic Disposal of High Level Nuclear Waste. An established technique for measuring the fracture aperture profile is required to achieve the above purpose. There are several aperture measurement techniques: 1. estimation of aperture based on the measurement of fracture surface geometry, 2. direct measurement of the fracture from rock surface, 3. non-destructive method. The X-ray CT method is one of the non-destructive methods. In H14 study, we investigated problems associated with fracture aperture measurement using X-ray CT method, and we proposed several approaches to improve measurement accuracy. In this year, the method proposed in H14 study was applied to a natural rock fracture in a 10 cm block, which has been prepared for permeability and tracer tests in the future. The obtained results are summarized as follows: (1) stacking is effective for reducing noises in X-Ray CT profiles, (2) image difference method is also effective to distinguish and extract fractures form X-Ray CT profiles, (3) by combining these methods, it was shown that the measurement accuracy of fracture aperture is improved significantly, (4) it was shown that correction coefficient is constants on the same condition, (5) we applied this methods to rough surface, we got measurement data. (author)