Numerical modeling of non-planar hydraulic fracture propagation in brittle and ductile rocks using XFEM with cohesive zone method

Abstract

Cite this article as: HanYi Wang, Numerical modeling of non-planar hydraulic fracture propagation in permeable medium using XFEM with cohesive zone m e t h o d , Journal of Petroleum Science and Engineering, http://dx. AbstractWith the increasing wide use of hydraulic fracturing in the petroleum industry, it is essential to accurately predict the behavior of fracture propagations based on the understanding of fundamental mechanisms governing the process. For unconventional resources exploration and development, hydraulic fracture pattern, geometry and associated dimensions are critical in determining well stimulation efficiency. In shale formations, non-planar, complex hydraulic fractures are often observed, due to the activation of pre-existing natural fractures. The propagating of turning non-planar fractures due to re-fracturing treatment and unfavorable perforation conditions have also been reported. Current numerical simulation of hydraulic fracturing generally assumes planar crack geometry and weak coupling behaviors, which severely limits the applicability of these methods in predicting fracture propagation under complex subsurface conditions. In addition, the prevailing approach for hydraulic fracture modeling also relies on Linear Elastic Fracture Mechanics (LEFM), which uses stress intensity factor at the fracture tip as fracture propagation criteria. Even though LEFM can predict hard rock hydraulic fracturing processes reasonably, but often fails to give accurate predictions of fracture geometry and propagation pressure in ductile rocks, such as poorly consolidated/unconsolidated sands and ductile shales, even in the form of simple planar geometry. In this study, a fully coupled non-planar hydraulic fracture propagation model in permeable medium based on the Extended Finite Element Method (XFEM) and Cohesive Zone Method (CZM) is developed, which is able to model fracture initiation and propagation in both brittle and ductile formations. To illustrate the capabilities of the presented model, example simulations are presented on both near wellbore and far field scale. The results indicate that the in-elastic deformations induced by propagating hydraulic fracture have significant impact on propagation pressure and fracture geometry, and the prediction of fracture propagation behaviors can be extremely erroneous if ductile formations are simply treated as soft rocks with lower Young's modulus. The method discussed in this article represents a useful step towards the prediction of non-planar, complex hydraulic fractures and can provide us a better guidance of completion design and optimizing hydraulic fracture treatment that will better drain reservoir volume in formations with complex stress conditions and heterogeneous properties.

Hydraulic fracturing process by using a modified two-dimensional particle flow code - case study

“…As shown in Figure 1, some weak points often exist around the wellbore during construction of the PFC 2D model, where may be locations of fracture initiation dependent on parameter combination applied in different cases (Table 1). Because the initial onset of fracture is influenced by wellbore geometry, local stress concentration and rock strength, if the fracture initiation is misaligned with the direction of PFP, the fracture will reorient itself to propagate in the direction of least resistance (Wang, 2015). As shown in Figures 2 and 3, fracture propagation will align or gradually reorient to the direction of maximum horizontal in-situ stress in all cases of in-situ stress ratio larger than 1.0.…”

“…With increasing fluid pressure in the domains, the aperture can reach to 1.03 × 10 -6 m when the bonding stress condition between particles is tensile. Many researches demonstrated that hydraulic fractures initiate and propagate along a preferred fracturing plane or path (PFP), which is the direction of least resistance and generally along maximum in-situ stress (Wang, 2015). As shown in Figure 1, some weak points often exist around the wellbore during construction of the PFC 2D model, where may be locations of fracture initiation dependent on parameter combination applied in different cases (Table 1).…”

“…This method has been widely used in energy industry to enhance the recovery of hydrocarbons from tight reservoir rocks, through the creation of hydraulic fractures and coupling of these new higher permeability flow paths with the natural fracture networks in the rock (Fu et al, 2013;Wang, 2015). In addition, hydraulic fracturing can be applied in fields of the disposal of radioactive waste in the underground spaces (De Laguna et al, 1968), heat production from hot dry rock geothermal reservoirs (Zimmermann et al, 2009(Zimmermann et al, , 2010, as well as the measurement of in-situ stresses (Fairhurst, 2003;Haimson and Cornet, 2003;Yokoyama et al, 2014).…”

“…An earlier study demonstrated that the main perforation parameters (e.g., length, diameter and orientation) can predict and control the variability of the fracture initiation pressure (FIP) during multistage fracturing treatment (Alekseenko et al, 2012). Based on the extended finite element method (EFEM), Wang (2015) developed a fully coupled non-planar hydraulic fracture propagation model in permeable medium, which is able to model fracture initiation and propagation around a perforated wellbore. Seen from the fracture propagation path and the induced shear stress distribution, it can be noted that the fracture first initiated along the directions of perforations, and then it gradually changes its propagation direction to align itself with the direction of maximum in-situ stress until it hits the simulation boundary.…”

Hydraulic fracturing process by using a modified two-dimensional particle flow code - method and validation

“…Chen (2012) used the commercial finite element code, ABAQUS, where the stress intensity model is replaced by a cohesive-zone fracture tip model, to simulate fracture propagation driven by fluid, and their modelling results are in good agreement with the 2D PKN and KGD solutions. Wang (2015) also used an ABAQUS embedded extended finite element method and cohesive zone method to model fracture initiation and propagation in different brittle rocks, and the results show that fluid pressure field and fracture geometry are significantly affected by the rock in-elastic deformations.…”