Abstract
In this study, a series of laboratory fracturing experiments were conducted on samples mined from reservoirs of the Guanyinqiao Member shale in Xishui County, Guizhou Province, using a traditional triaxial fracturing simulation system. Based on the experimental results, the breakdown pressure and effective stimulated reservoir volume were obtained for four fracturing fluids (supercritical carbon dioxide, water, NO-sand, and sand). The fracture mechanism was then analyzed using acoustic emission monitoring data. Based on the curves of pressure vs injection time for different fracturing fluids, the breakdown pressure increased with increasing fracturing fluid viscosity. When sands with different viscosities were used as the fracturing fluid, the breakdown pressure first increased and then decreased with an increase in the sand viscosity. The distribution of the tracer or proppant was not only correlated with the fracturing effect, but also promotes the filling crack of the tracer and proppant at a certain viscosity as the best fracturing effect. During sand fracturing, the proppant mainly formed shear cracks. The results provide a valuable technical reference for shale gas mining.
Highlights
Shale reservoirs are characterized by low porosity, low permeability, high brittleness, strong heterogeneity, bedding, and natural fracture development
To understand the observed differences in the breakdown pressure, it is necessary to study the fracture mechanism, which can differ based on the fracturing fluid used
Laboratory fracturing experiments were conducted with fracturing fluids possessing different viscosities under real-time acoustic emission (AE) monitoring, and the effects of the fracturing fluid viscosity on the breakdown pressure and SRVe were evaluated
Summary
Shale reservoirs are characterized by low porosity, low permeability, high brittleness, strong heterogeneity, bedding, and natural fracture development. Shale reservoirs generally do not exhibit natural productivity, and commercial development potential is only achieved through large-scale fracturing transformation, which forms a certain stimulated reservoir volume (SRV).. Many scholars have studied the initiation and propagation mechanisms of fractures through physical experiments, numerical simulations, and analytic approaches. The authors compared the fracture propagation geometry obtained by specimen splitting and computed tomography (CT) scanning with the AE monitoring results and discussed the difference in the hypocenter mechanism between hydraulically connected scitation.org/journal/adv and unconnected regions. Lou and Zhang studied the initiation and propagation of hydraulic cracks under cyclic stress conditions using indoor hydraulic fracturing tests with different fracturing fluid viscosities
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