Modeling the Interaction Between Natural and Hydraulic Fractures Using Three Dimensional Finite Element Analysis

Abstract

A three dimensional geomechanical model was built using commercially available Finite Element Analysis (FEA) software to simulate propagating hydraulic fracture (HF) and its interaction with a vertical natural fracture (NF) in tight medium. The approach initially involved studying simple three dimensional single layered model followed by complex three layered model. The main area of concern was the fluid continuity at the HF-NF intersection. Different approaches were considered to model this fluid continuity. Finally, newly introduced elements were used for modeling the intersection of the NF-HF planes. These elements have ability to model the fluid continuity at HF-NF intersection. It was observed that for high stress contrast the NF activated length is smaller compared with the low stress contrast. For high stress contrast with principal horizontal stresses reversed, the HF intersects, activates and opens the NF. Increasing the injection rate results in longer and wider HF but does not significantly affect the NF activated length. Injection fluid viscosity shows an inverse relationship with HF length and a proportional relationship with HF opening or width as well as with NF length. It was observed that a weak NF plane temporarily restricts the HF propagation. On the other hand, a tougher NF or a NF with properties similar to surroundings does not show this type of restriction. The NF activated length was found maximum in the case of weaker NF and nearly zero in the case of stronger NF and NF similar to surroundings. This paper presents the results for a three layered, three dimensional geomechanical model with single HF and NF orthogonally intersecting each other, using the newly introduced cohesive elements for the first time in technical literature. Further a detailed sensitivity analysis considering the effect of stress contrast, injection rate, injection fluid viscosity and NF properties on this HF-NF interaction was conducted.

Interaction between hydraulic fractures and natural fractures: current status and prospective directions

“…In Cheng et al (2014a), a 3D displacement discontinuity method was used to describe how the HF growth intersection with NF (at 45° and 90°), and the NF failure prediction at the interface could be attempted if results obtained is compared with the Mohr-Coulomb criterion. Nikam et al (2016) integrated an advanced cohesive pore pressure (CPP) in finite element analysis (FEA) to describe the injection fluid behavior (Elwegaa et al 2019) at HF-NF intersection. Cheng et al (2014b) study was based on numerical and experimental analyses of cement block fracturing test with pre-existing fractures and validated the results with microseismic data from the lower Silurian Longmaxi shaly formation of Sichuan basin, China, to develop a new NF-HF interaction criterion.…”

“…In He et al 2015and Daneshy (2019), the propagating HF will only cross the NF when there is a very low NF tensile strength, and sufficiently high differential horizontal stress, high NF dip angle and high approach angle. At orthogonal angle, as described by Nikam et al (2016), the approaching HF crossed the NF without dilating the NF interface. As the multiple propagating HFs cross the NFs, the energy of the HF reduces thereby weakening the prospect crossing subsequent NFs.…”

“…In shale gas reservoirs, not all pre-existing NF can be reactivated with the propagation and dilation criteria (Song et al 2014). Although direct crossing will be observed at high HF-NF approach angle (60°-90°), but at low-tomedium approach angles and varying differential horizontal stresses, the HF is inclined to be arrested at a weakly bonded NF plane, or the HF can continue to propagate the tip of NF by dilation and shearing (Yildirim et al 2018a;Zhou and Xue 2011;Nikam et al 2016). The microseismic monitoring results in Williams-Stroud et al (2012a, b) showed the reactivation of pre-existing NF by shearing and dilation by induced HF in well stimulation treatment.…”

“…The microseismic monitoring results in Williams-Stroud et al (2012a, b) showed the reactivation of pre-existing NF by shearing and dilation by induced HF in well stimulation treatment. At low injection rate, low fluid viscosity, and low approach angles, the HF will tend to fuse into the NF to "expand" the NF and reactivates the NF Nikam et al 2016;Zhou et al 2016), while at orthogonal angle, the NF opening and open-zone length decreases (Akulich and Zvyagin 2008). Fracture network with greater length and width will be generated.…”

Numerical and Experimental Investigations of the Interactions between Hydraulic and Natural Fractures in Shale Formations

“…In recent years, many numerical methods, including finite element methods (FEM) [28][29][30][31][32][33], cohesive zone methods (CZM) [34][35][36][37][38][39][40][41], displacement discontinuity methods (DDM) [21,[42][43][44][45][46][47][48][49][50][51][52][53][54][55], discrete element methods (DEM) [56,57], combined finite-discrete element methods (FDEM) [58,59], rock failure process analysis (RFPA) [60,61], and extended finite element methods (XFEM) [62][63][64][65][66] have been proposed to solve the interaction problem between hydraulic and natural fractures. Additionally, the phase-field approach [67] and the peri-dynamics method [68,69] were also employed to investigate the interactions between an HF and the NF.…”