Abstract
A two-step fracturing method is proposed to investigate the hydraulic fracture evolution behavior and the process of complex fracture network formation under multiple wells. Simulations are conducted with Rock Failure Process Analysis code. Heterogeneity and permeability of the rocks are considered in this study. In Step 1, the influence of an asymmetric pressure gradient on the fracture evolution is simulated, and an artificial structural plane is formed. The simulation results reflect the macroscopic fracture evolution induced by mesoscopic failure; these results agree well with the characteristics of the experiments. Step 2, which is based on the first step, investigates the influence of preexisting fractures (i.e., artificial structural planes) on the subsequent fracturing behavior. The simulation results are supported by mechanics analysis. Results indicated that the fracture evolution is influenced by pressure magnitude on a local scale around the fracture tip and by the orientation and distribution of pore pressure on a global scale. The constant pressure in wellbore H2 can affect fracture propagation by changing the water flow direction, and the hydraulic fractures will propagate to the direction of higher local pore pressure. Furthermore, the artificial structural planes influence the stress distribution surrounding the wellbores and the hydraulic fracture evolution by altering the induced stresses around the preexisting fractures. Finally, fracture network is formed among the artificial structural planes and hydraulic fractures when multiple wells are fractured successively. This study provides valuable guidance to unconventional reservoir reconstruction designs.
Highlights
In 1947, the first experimental hydraulic fracturing treatment in the United States occurred in the Hugoton gas field in Grant County, Kansas [1]
Many scholars have studied the hydraulic fracture evolution and the complex fracture network formation and obtained certain results that are positive to unconventional reservoir reconstruction
Ρ denotes density; σij′ is the effective stress; σij is the total stress; εij is the total strain; εv is the volume strain; α is the coefficient of the pore pressure; Ui is the displacement; p is the pore pressure; λ is the Lame coefficient; δij is the Kronecker delta; G is the modulus of shear deformation; Q is Biot’s constant; K is the permeability coefficient; K0 is the initial permeability coefficient; β is the coupling parameter, which reflects the influence of stress on the coefficient of permeability; and ξ(ξ ≥ 1) is the mutation coefficient of permeability, which accounts for the increase in permeability when the element reaches the damage state
Summary
In 1947, the first experimental hydraulic fracturing treatment in the United States occurred in the Hugoton gas field in Grant County, Kansas [1]. Many scholars have studied the hydraulic fracture evolution and the complex fracture network formation and obtained certain results that are positive to unconventional reservoir reconstruction. E results demonstrated that stress concentration around the hole would significantly increase the fracture pressure of the rock, and natural fractures in the borehole wall would eliminate stress concentration He et al [10] investigated the different hydraulic fracture extension patterns of shale through hydraulic fracturing experiments, and they believed that the typical bedding plane well developed in the shale formation plays an important role in the propagation of hydraulic fractures. E present study aims to numerically investigate how the pore pressure field can affect fracture propagation and determine how the fracture network forms when multiple wells are successively fractured in rock materials using the Rock Failure Process Analysis (RFPA)2D2.0-Flow code. Two steps in hydraulic fracturing are modeled as examples to illustrate the pore pressure distribution that affects fracture initiation and the propagation and preexisting fractures that influence the fracture behavior and stress distribution by altering the induced stresses
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