Numerical Simulation Study on Propagation of Initial Microcracks in Cement Sheath Body during Hydraulic Fracturing Process

Abstract

Microcracks caused by perforating operations in a cement sheath body and interface have the potential to further expand or even cause crossflow during hydraulic fracturing. Currently, there are few quantitative studies on the propagation of initial cement-body microcracks. In this paper, a three-dimensional finite element model for the propagation of initial microcracks of the cement sheath body along the axial and circumferential directions during hydraulic fracturing was proposed based on the combination of coupling method of fluid–solid in porous media and the Cohesive Zone Method. The influence of reservoir geological conditions, the mechanical properties of a casing-cement sheath-formation system, and fracturing constructions in the propagation of initial axial microcracks of a cement sheath body was quantitatively analyzed. It can be concluded that the axial extension length of microcracks increased with the increase of elastic modulus of the cement sheath and formation, the flow rate of fracturing fluid, and casing internal pressure, and decreased with the increase of the cement sheath tensile strength and ground stress. The elastic modulus of the cement sheath had a greater influence on the expansion of axial cracks than the formation elastic modulus and casing internal pressure. The effect of fracturing fluid viscosity on the crack expansion was negligible. In order to effectively slow the expansion of the cement sheath body crack, the elastic modulus of the cement sheath can be appropriately reduced to enhance its toughness under the premise of ensuring sufficient strength of the cement sheath.

Study on Synchronous Propagation Behavior of Hydraulic Fractures and Cementing Interfacial Cracks during Fracturing of Shale Horizontal Wells

“…Based on the fluid solid coupling method, Xu et al [69] established the axial propagation process of cracks at CFI during hydraulic fracturing, and simulated the fracture propagation process after the fracturing fluid enters CFI under actual working conditions, and it has been compared with the famous experiment reported by Lecampion et al and Bunger et al; the simulation results are in good agreement with the experimental results [37,70]. The numerical calculation results of Xu et al [69] on the extension length of CFI cracks under fracturing conditions are taken to verify the interface crack propagation law. The simulation parameters are as follows: Elasticity modulus is 20 GPa, Poisson's ratio is 0.25, injection rate is 0.027 m 3 /s, fluid viscosity is 0.1 Pa•s, initial crack length 20 mm, initial crack width 2 mm.…”