Abstract
In order to estimate the changes in fracture aperture under various long-term confining and thermal conditions, measurements of the fracture aperture are conducted using microfocus X-ray CT (µX-ray CT). Through the imaging data, the height of the fracture surface and the contact points are evaluated, and contact ratios for the fracture, the JRC and the aperture distribution are estimated. On the other hand, measurements are also conducted using a laser scan profile sensor, and some parameters are estimated. In comparing these parameters, the validity of the µX-ray CT data and an analysis of the data will be discussed. In addition, a fracture flow simulation will be conducted using the surface roughness and aperture data obtained by the µX-ray CT.
1. INTRODUCTION
It is well known that for a rock fracture under various thermal and stress conditions, a reduction in permeability occurs due to chemical and mechanical compaction. The chemical and mechanical compaction may include a pressure solution and a reduction in permeability could be explained by this pressure solution [1]-[5]. Yasuhara, et al. [6] conducted flow-through experiments on a single fracture in granite under controlled temperature and stress conditions. Specifically, two different experiments, short-term and long-term, were performed to examine the influence of the loading time on the evolution of fracture permeability. The measured changes in fracture permeability showed reversible and irreversible behaviors under short-term and long-term conditions, respectively. These results indicated that the surface roughness and the structure of a fracture may be changed by pressure solution. However, no change in the fracture structure could be directly obtained. A change in the hydraulic conductivity was indirectly obtained.
The joint surface roughness is basically measured with a non-contact laser scan profiler or a CCD camera, and then, high quality profiling data can be obtained. On the other hand, the fracture roughness and the aperture distributions of a single rock fracture under certain confining stress conditions have not been evaluated, although it is very important that a measurement system is developed to measure these parameters under confining stress conditions. Measuring the joint surface roughness and the aperture distribution is not enough to obtain the height of surface roughness, the contact conditions and the aperture distribution under confining stress conditions.
