Three-Dimensional Visualization and Characterization of Cracks in Geothermal Reservoir Rock Using Image Analysis of Reconstructed μCT Images: A Preliminary Study

摘要

In most geothermal reservoirs, cracks are considered very important because of the ability to transport water vapor. In most cases, characterizations of cracks are often difficult to be performed. However, through the vast development of imaging technique, many researches have been conducted in order to obtain better understanding regarding the nature of cracks. Using micro-CT (μCT) scanning devices, i.e., the Skyscan 1173, we were able to obtain 3D images of geothermal reservoir rock from West Java. The rock sample was scanned using X-ray voltage of 130 kV and current of 61 μA. The reconstructed images have spatial resolution of 59.85 μm/pixel. Using CTVox and ImageViewer, we were able to visualize the cracks both in 2D and 3D perspective. We further performed image processing and analysis, i.e.: simple segmentation of pore-solid by thresholding the gray values and binarizing the images, de-noising (despeckling), and 3D structure analysis. From these analyses, we obtain the value of porosity of 6.27%, and from further analysis, we separate the crack from the granular pore. The fraction of the cracks is 2.35% from the total volume of the sample. This preliminary study however, still contains some errors. By visualizing the produced image from the isolation, we can still observed the existence of isolated granular pores. Nonetheless, this study has confirmed that using image processing and image analysis approach of reconstructed μCT images, we were able to isolate cracks from granular pores, and also calculate the volume fraction of the cracks.