The estimation of porosity in Japan Trench plate boundary using low-resolution X-ray computed tomography (XCT) images and laboratory measurements

Abstract

Abstract. X-ray computed tomography (XCT) is an advanced imaging technique that has been increasingly used in the past years because it can provide valuable information on internal structures of a rock sample in a non-invasive manner. The maximum resolution of lab-based XCT facilities is ~0.5 μm, which might be sufficient to capture macropores in some rocks (i.e., sandstone), but will result in underestimation of porosity in clay-rich sediments containing micro-and nano-scale pores. Furthermore, such high-resolution XCT facilities are quite expensive and not ubiquitous. In this study, we introduce a new methodology based on the K-means clustering algorithm to process of low-resolution XCT images, illustrating its capability through porosity analysis of drillcores obtained during Integrated Ocean Drilling Program (IODP) expedition 343. The cation exchange capacity (CEC) of the squeezed samples of the same cores was also measured and used to correct shipboard measurements of Moisture and Density (MAD) porosity for the effect of the water bound in the interlayer clay particles, thereby calculating interstitial porosity. The results indicate that the porosities estimated by our method are in agreement with these MAD_derived interstitial porosities in several cores acquired from the overthrusted sediments above the Japan trench plate boundary. Also, considering interstitial porosity as a realistic measurement of porosity, the results show that our semi-automatic method improves estimations compared with a manual thresholding segmentation, as the latter suffers from user subjectivity.