Abstract
Abstract Hydraulic fracturing experiments with low-viscosity fluids, such as supercritical CO2, demonstrate the formation of complex fracture networks spread throughout the rocks. To study the influence of viscosity of the fracturing fluids on hydraulic fracture propagation, a hydromechanical-coupled cohesive zone model is proposed for the simulation of mechanical response of rock grains boundary separation. This simulation methodology considers the synergistic effects of unsteady flow in fracture and rock grain deformation induced by hydraulic pressure. The simulation results indicate a tendency of complex fracture propagation with more branches as the viscosity of fracturing fluids decrease, which is in accord with experimental results. The low-viscosity fluid can flow into the microfractures with extremely small aperture and create more shear failed fracture. This study confirms the possibility of effective well stimulations by hydraulic fracturing with low-viscosity fluids.
Highlights
Hydraulic fracturing has been one of the primary engineering tools for improving well productivity especially for unconventional reservoirs, such as shale or tight sand reservoirs [1]
Hydraulic fracturing experiments with supercritical CO2 have been conducted by some research institutions [3,4,5,6,7,8]
An unsteady flow solution is embedded in cohesive zone model and implemented in ABAQUS user-defined elements (UEL) subroutine
Summary
Hydraulic fracturing has been one of the primary engineering tools for improving well productivity especially for unconventional reservoirs, such as shale or tight sand reservoirs [1]. Hydraulic fracturing experiments with supercritical CO2 have been conducted by some research institutions [3,4,5,6,7,8]. These experiment results provided valuable information to predict the initiation and propagation of artificial fracture in hydrofracturing with supercritical CO2. Fracture induced by supercritical CO2 has a large number of branches (see Figure 1 [7]). Such complex fracture networks with many microfractures make the effective development of extremely low-permeability unconventional reservoirs possible. The mechanism for the formation of complex fracture networks induced by hydrofracturing with low-viscosity supercritical CO2 is still not well studied
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