Quantitative Characteristics of Micro Bedding Fractures in the Wufeng-Longmaxi Formation Based on High-Resolution Map Imaging Technology

The study of microfractures in shale is mainly based on qualitative description. Conversely, quantitative description of the parameters of shale microfractures can provide a quantitative basis for shale fracture characterization and shale physical properties. Nine shale reservoir samples of the Wufeng-Longmaxi Formation in the Jiaoshiba area were studied, using the backscattered two-dimensional multiscale resolution imaging technology, combined with high-resolution map imaging technology (MAPS), and thousands of images were obtained using scanning electron microscopy. Gray image analysis was used to extract microfracture information from images (2 x 2 cm multiresolution). The maximum circle method was used to calculate the length and aperture characteristics of the fractures. Parameters such as the area of the bedding fractures, the surface rate of the fractures, and the linear density of the fractures were obtained by the integration of apertures. The fracture length was between 2 similar to 7 mm, the aperture was between 1 similar to 6 mu m, the linear density was between 1 similar to 6/m and the surface rate was 1%. The bedding fractures do not contribute much to the porosity of the shale reservoir; however, shale reservoirs with high porosity have a high development of bedding fractures and good permeability. The development of a bedding fracture is controlled by the lithology within shale reservoirs. Different types of lithology contain different bedding fractures, but they have a certain regularity. Moreover, the content of organic matter and TOC (total organic content) in the shale reservoir control the development of a bedding fracture, where a high organic and TOC content are accompanied by a high number of fractures.

Automated summary

The study focuses on the quantitative description of shale microfractures, which can provide a quantitative basis for shale fracture characterization and shale physical properties. By using imaging technologies and microscopy, microfracture information was extracted and parameters such as length and aperture were calculated. It was observed that bedding fractures have limited contribution to shale porosity, but shale reservoirs with high porosity have more bedding fractures and better permeability.