Investigation on the Propagation Mechanisms of a Hydraulic Fracture in Glutenite Reservoirs Using DEM

Abstract

The geometry heterogeneity induced by embedded gravel can cause severe stress heterogeneity and strength heterogeneity in glutenite reservoirs, and subsequently affect the initiation and propagation of hydraulic fractures. Since the discrete element method (DEM) can accurately describe the inter-particle interactions, the macromechanical behavior of glutenite specimen can be preciously represented by DEM. Therefore, the initiation and propagation mechanisms of hydraulic fractures were investigated using a coupling seepage-DEM approach, the terminal fracture morphologies of hydraulic fractures were determined, and the effects of stress differences, permeability, and gravel strength were studied. The results show that the initiation and propagation of hydraulic fractures are significantly influenced by embedded gravel. In addition, the stress heterogeneity and strength heterogeneity induced by the gravel embedded near the wellbore increase local initiation points, causing a complicated fracture network nearby. Moreover, due to the effect of local stress heterogeneity, gravel strength, and energy concentration near the fracture tip, four interactions of attraction, deflection, penetration, and termination between propagating fractures and encountering gravel were observed.

Research on the impact of pre‐existing geological fractures on hydraulic fracturing in high in situ stress environments

“…DEM divides the research object into multiple units, 19 links each unit together through contact, and displays the overall mechanical characteristics by analyzing the contact between each unit 20 . Therefore, DEM method has drawbacks in describing the action of fluid on solid 21,22 …”

“…20 Therefore, DEM method has drawbacks in describing the action of fluid on solid. 21,22 In addition to these mentioned, there are phase field model and cohesive element method, which have been proven effective tools for modeling fracture initiation, propagation, coalescence, and branching in solids. [23][24][25] The FDEM can not only reflect the advantages of high computational efficiency of the finite element method but also study the heterogeneous characteristics of rocks like the DEM.…”

Simulation of hydraulic fracture initiation and propagation for glutenite formations based on discrete element method

“…Due to lithology change, low porosity, poor permeability and strong heterogeneity, fracturing design and parameters optimization of glutenite formations face great challenge (Jia et al, 2017;Wang et al, 2017). For the gravels in glutenite formation, fracture distortion and multi-fracture propagation are prone to occur in the hydraulic fracturing process, resulting in sand up and affecting hydraulic fracturing effects (Meng et al, 2010;Li et al, 2013;Feng et al, 2016;Ma et al, 2017). Therefore, studies of the fracture propagation law is of great significance for the stimulation and reconstruction in glutenite formation.…”

“…Wan et al (2019); Tan et al (2021) came up with the concept of "lithology transition zone" for coal measure strata and studied the fracture propagation and penetration behavior; Zhao et al (2007) compared hydraulic fractures propagation law in different lithologies such as basalt, conglomerate, marl. For glutenite formations; Luo et al (2013) considered that particle size, content of gravel and the properties of the interface are the internal reason for irregular hydraulic fractures and pressure fluctuations based on the numerical simulation results; Meng et al (2010) analyzed the influence of gravel particle size and horizontal stress difference on fracture propagation morphology and pressure curve using artificial samples; Li et al (2013) analyzed the effects of the in situ stress and gravels on fracture propagation with RFPA-Flow, and summed up four typical fracture propagation modes at the gravel, including fracture arrest, deflection, penetration and adsorption. Based on the three-dimensional reconstructed heterogeneous glutenite model; Ju et al (2016) studied the initiation and propagation of hydraulic fractures under different horizontal stress differences by using the discrete element method, and compared with the physical simulation results.…”

Numerical Investigation of Fracture Morphology Characteristics in Heterogeneous Reservoirs

“…Li et al proposed a numerical method for constructing glutenite heterogeneity by embedding digital image technology (DIP) into a numerically coded rock failure process analysis to study the effect of gravel on hydraulic fracture propagation [39]. Tang et al established a two-dimensional numerical model based on the discrete element method to study the effects of permeability, gravel strength and stress difference on hydraulic fracture propagation in glutenite reservoirs [40]. In addition, some studies focus on the influence of single heterogeneous particles and discrete heterogeneous particles on the evolution of hydraulic fractures in heterogeneous formations based on the finite-discrete element method [12].…”