Mapping Fracture Complexity of Fractured Shale in Laboratory: Three-dimensional Reconstruction From Serial-section Images

The intrinsic anisotropy of sedimentary rocks such as shale, together with the presence of natural fractures and bedding planes, make it possible for hydraulic fracturing to generate complex fracture networks in unconventional hydrocarbon formations. However, it remains unclear how the fluid driven fractures propagate and how those newly created fractures interact with the pre-existing ones. A laboratory approach is presented in this paper to three-dimensionally (3D) map the fracture complexity of a hydraulically fractured shale sample. The 3D fracture model created using the serial-section reconstruction approach has a high spatial resolution of 39 × 39 × 50 µm3, and is considered trustworthy based on the geometrical similarity to the fracture network reconstructed from the accessible X-ray micro-computed tomography (micro-CT) at a lower resolution. According to the 3D fracture model, the fracture network predominately comprises of pre-existing fractures further opened by hydraulic fracturing testing, which significantly affects the whole network geometry. The opened natural fractures appear rougher than the opened bedding planes, indicating different mechanical influences on fracture propagation. This high-resolution fracture dataset is valuable not only for the investigation of hydraulic fracturing mechanisms, but also for fracture aperture quantification and evaluation of the fluid transmissivity.