Three-dimensional characterization of micro-fractures in shale reservoir rocks

Abstract

Fractures are crucial for unconventional hydrocarbon exploitation, but it is difficult to accurately observe the 3D spatial distribution characteristics of fractures. Microtomography (micro-CT) technology makes it possible to observe the 3D structures of fractures at micro-scale. In this study, micron-CT scanning is conducted on multiple mud-shale samples of source rocks in the Permian Lucaogou Formation, Junggar Basin. The Avizo® software is applied to process and segment the micron-CT images, so as to obtain the 3D fracture structure model inside rock core. Therefore, the independently-developed CTSTA program is adopted to quantitatively describe the micro-fractures inside rock core, including fracture dimension, extension direction and extension scale. Meanwhile, this study summarizes the classification characteristics of fractures and their anisotropy. On this basis, the fractal dimensions of fractures can also be extracted. Previous studies show that the geometric features of fractures have self-similarity at large and small scales, which can be described by exponential laws; and the fractal dimension is a typical exponent. Through the quantitative description or characterization of 3D fractures at micro-scale, the distribution characteristics of fractures in large scales could be known. Keywords: Tight reservoir, Microtomography, Fracture, Characterization, Fractal dimension