CT-based 3D reconstruction of the geometry and propagation of hydraulic fracturing in shale

Abstract

Abstract Hydraulic fracturing is one of the primary techniques which has been widely implemented in order to allow for the stimulation of shale gas reservoirs. To accurately distinguish the extension characteristics and the spatial distribution of fractures during the hydraulic fracturing of the Longmaxi shale reservoirs in Changning, a self-developed, multifunctional, true triaxial experimental process (utilizing a fluid-solid coupling testing system) was used to simulate the horizontal well hydraulic fracturing. The CT technique was used to scan the samples prior to and following the conduction of the experiments; the CT scanning images of internal fractures were reconstructed and visualized via 3D reconstruction. The influence of in-situ stress, the displacement of the fracturing fluid upon the fracture morphology and the resultant fractural extensions caused by hydraulic fracturing were discussed. The study shows that the reconstructed 3D model based on the different CT values corresponding to the shale matrix, minerals and fractures can accurately characterize the internal structure and fracture distribution of shale. Shale hydraulic fracturing fractures can be divided into 3 categories: single transverse fractures, main arc fractures and complex fractures. The “fluctuation phenomenon” of a water pressure curve is related to the formation and extension of reservoir fractures, and is a discernible characteristic of complex fractures formed by the volume fracturing of shale. Stress differences and the stress difference coefficient are the governing factors in terms of the complexity of shale hydraulic fracturing networks. Displacement has a particular range of influence on the manifestation of fracture complexity; a low displacement may not result in a complete fracture, but too high a displacement tends to culminate a single fracture in the formation, which to a certain extent reduces fractural complexity.