Abstract
Rock yielding may well take place during hydraulic fracturing in deep reservoirs. The prevailing models based on the linear elastic fracture mechanics (LEFM) are incapable of describing the evolution process of hydraulic fractures accurately. In this paper, a hydro-elasto-plastic model is proposed to investigate the hydraulic fracture propagation in deep reservoirs. The Drucker–Prager plasticity model, Darcy’s law, cubic law and cohesive zone model are employed to describe the plastic deformation, matrix flow, fracture flow and evolution of hydraulic fractures, respectively. Combining the embedded discrete fracture model (EDFM), extended finite element method (XFEM) and finite volume method, a hybrid numerical scheme is presented to carry out simulations. A dual-layer iterative procedure is developed based on the fixed-stress split method, Picard iterative method and Newton–Raphson iterative method. The iterative procedure is used to deal with the coupling between nonlinear deformation with fracture extension and fluid flow. The proposed model is verified against analytical solutions and other numerical simulation results. A series of numerical cases are performed to investigate the influences of rock plasticity, internal friction angle, dilatancy angle and permeability on hydraulic fracture propagation. Finally, the proposed model is extended to simulate multiple hydraulic fracture propagation. The result shows that plastic deformation can enhance the stress-shadowing effect.
Highlights
With the rapid growth in the global demand for oil and gas resources and the successful development of middle–shallow formations (4500 m) [1,2]
To study fracture propagation in deep reservoirs, we extend the model to ductile formations accounting for the rock plasticity, and construct a dual-layer iterative procedure for solving the nonlinear problem caused by inelasticity and fracture propagation
A series of numerical cases are performed to investigate the influences of rock plasticity, internal friction angle, dilatancy angle and permeability on hydraulic fracture plasticity, internal friction angle, dilatancy angle and permeability on hydraulic fracture propagation
Summary
With the rapid growth in the global demand for oil and gas resources and the successful development of middle–shallow formations (4500 m) [1,2]. Hydraulic fracturing technology, which can effectively improve the permeability of reservoir rocks, plays an important role in the development of oil and gas reservoirs [3]. It is important to predict the shape and trend of hydraulic fractures accurately. The prevailing fracture propagation models based on the linear elastic fracture mechanics are no longer applicable for predicting the evolution process of hydraulic fractures in deep ductile formations. Accounting for rock plasticity, establishing an efficient model to perform accurate simulation of hydraulic fracture propagation is significant for the development of deep oil and gas resources
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