Abstract
An array of multimodal and multiscale images of fractured shale rock samples and analogs was collected with the aim of improving the numerical representation of fracture networks. 2D and 3D reconstructions of fractures and matrices span from 10−6 to 100 m. The origin of the fracture networks ranged from natural to thermal maturation to hydraulically induced maturation. Images were segmented to improve fracture identification. Then, the fractal dimension and length distribution of the fracture networks were calculated for each image dataset. The resulting network connectivity and scaling associations are discussed at length on the basis of scale, sample and order of magnitude. Fracture network origin plays an important role in the resulting fracture systems and their scaling. Rock analogs are also evaluated using these descriptive tools and are found to be faithful depictions of maturation-induced fracture networks.
Highlights
Interest in the study of unconventional rocks has significantly increased in the last decade
The power-law exponent α was calculated for each dataset. If such a fit was possible, we evaluated inequalities (3)–(5) and used the connectivity characterization model proposed in [21] to designate a connectivity regime for each of our datasets and make inferences about the scaling of the fracture networks of the shale rocks systems presented in this study
Fractal dimensions for three-dimensional datasets were converted into their two-dimensional equivalent using the following relation [21,32]: D3D = D2D + 1 (6)
Summary
Interest in the study of unconventional rocks (shales, mudstones, siltstones, marls, etc.) has significantly increased in the last decade. Shale formations were regarded as either source or seal rocks [1] while being overlooked for their energy resource potential. This drastically changed with the increase in the use of hydraulic fracturing and horizontal wells. Even though the interest in characterizing and modeling shale rock properties continues to be relevant, environmental concerns regarding the control of greenhouse gas emissions and storage have prompted research on the use of depleted shale reservoirs for CO2 storage. Shale formations can act as seals for potential subsurface hydrogen storage in conventional reservoirs [17,18]
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