Abstract
To better understand the interaction between hydraulic fracture and oriented perforation, a fully coupled finite element method (FEM)-based hydraulic-geomechanical fracture model accommodating gas sorption and damage has been developed. Damage conforms to a maximum stress criterion in tension and to Mohr–Coulomb limits in shear with heterogeneity represented by a Weibull distribution. Fracturing fluid flow, rock deformation and damage, and fracture propagation are collectively represented to study the complexity of hydraulic fracture initiation with perforations present in the near-wellbore region. The model is rigorously validated against experimental observations replicating failure stresses and styles during uniaxial compression and then hydraulic fracturing. The influences of perforation angle, in situ stress state, initial pore pressure, and properties of the fracturing fluid are fully explored. The numerical results show good agreement with experimental observations and the main features of the hydraulic fracturing process in heterogeneous rock are successfully captured. A larger perforation azimuth (angle) from the direction of the maximum principal stress induces a relatively larger curvature of the fracture during hydraulic fracture reorientation. Hydraulic fractures do not always initiate at the oriented perforations and the fractures induced in hydraulic fracturing are not always even and regular. Hydraulic fractures would initiate both around the wellbore and the oriented perforations when the perforation angle is >75°. For the liquid-based hydraulic fracturing, the critical perforation angle increases from 70° to 80°, with an increase in liquid viscosity from 10−3 Pa·s to 1 Pa·s. While for the gas fracturing, the critical perforation angle remains 62° to 63°. This study is of great significance in further understanding the near-wellbore impacts on hydraulic fracture propagation and complexity.
Highlights
Hydraulic fracturing is commonly used to improve productivity from hydrocarbon reservoirs and has been a key technique in accessing unconventional shale reservoirs
In order to fully understand fracture behavior in the field, sensitivity studies are conducted to investigate the effects of in situ hydraulic fracture behavior in the field, sensitivity studies are conducted to investigate the effects of horizontal differential stress, initial pore pressure, and fracturing fluid viscosity
To incorporate an effective stress law the D–C criterion, the geomechanical model proposed in this study correctly describes the relationship into the D–C criterion, the geomechanical model proposed in this study correctly describes the between breakdown pressure and the far-field stress in hydraulic fracturing [37]
Summary
Hydraulic fracturing is commonly used to improve productivity from hydrocarbon reservoirs and has been a key technique in accessing unconventional shale reservoirs. The transport linkage between preexisting flaws (i.e., perforations, joints, and natural fractures) are often critical to hydrocarbon production from reservoirs. These natural fractures or other flaws can induce complex fracture geometries and flow pathways resulting from both tensile and shear. Processes 2018, 6, 213 failure [3,4,5] Implicit in this is understanding fracture initiation and propagation in the near-wellbore region as of great significance for hydraulic fracture treatment and injectivity test interpretation [6,7,8]
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