Modeling competing hydraulic fracture propagation with the extended finite element method

Summary The high computational costs associated with the implicit formulation of discontinuous deformation analysis (DDA) have been one of the major obstacles for its implementation to engineering problems involving jointed rock masses with large numbers of blocks. In this paper, the Newmark‐based predictor‐corrector solution (NPC) approach was modified to improve the performance of the original DDA solution module in modeling discontinuous problems. The equation of motion for a discrete block system is first established with emphasis on the consideration of contact constraints. A family of modified Newmark‐based predictor‐corrector integration (MNPC) scheme is then proposed and implemented into a unified analysis framework. Comparisons are made between the proposed approach and the widely used constant acceleration (CA) integration approach and central difference (CD) approach, regarding the stability and numerical damping features for a single‐degree‐of‐freedom model, where the implications of the proposed approach on open‐close iteration are also discussed. The validity of the proposed approach is verified by several benchmarking examples, and it is then applied to two typical problems with different numbers of blocks. The results show that the original CA approach in DDA is efficient for the simulation of quasi‐static deformation of jointed rock masses, while the proposed MNPC approach leads to improved computational efficiency for dynamic analysis of large‐scale jointed rock masses. The MNPC approach therefore provides an additional option for efficient DDA of jointed rock masses.

Section: Introductionmentioning

confidence: 99%

Modified predictor‐corrector solution approach for efficient discontinuous deformation analysis of jointed rock masses

Zheng

Leung

Zhu

et al. 2018

“…By introducing an additional slip degree of freedom to improve the performance of the finite elements in resolving the kinematics of strong discontinuity, the assumed enhanced strain method can be used for investigating the pore‐scale mechanisms leading to the brittle and ductile deformation behaviour of crystalline rocks . The extended finite element method was developed to simulate multiple hydraulic fractures, but the accuracy of the results still depends on the quality of mesh generation . Discrete element modelling does not require meshing, because it consists of discretised particles that are free to move with respect to each other .…”

Section: Introductionmentioning

confidence: 99%

Numerical analysis of the hydrofracturing behaviour of heterogeneous glutenite considering hydro‐mechanical coupling effects based on bonded particle models

Wang

Dong

et al. 2018

The heterogeneity of tight reservoirs significantly influences hydrofracturing behaviours, such as crack morphology, type, initiation, propagation, and distribution. The accurate characterisation of the influencing mechanisms has become a pivotal issue in enhancing the fracturing stimulation of tight reservoirs, as well as in the prediction of tight oil and gas production. In this study, the hydrofracturing behaviours of heterogeneous glutenites and their influencing mechanisms were numerically investigated based on bonded particle models (BPMs). The geometry and mechanical properties of the natural glutenites were obtained using microfocus computed tomography (CT) and triaxial tests and were used to construct heterogeneous BPMs. The hydrofracturing behaviours of the heterogeneous BPMs under various in-situ stresses were analysed with hydro-mechanical coupling effects considered and compared with those of homogeneous BPMs under the same conditions. The numerical results show that gravels in heterogeneous glutenites inhibit crack propagation. The shear cracks that appear in the initial stage of crack development subsequently propagate and distribute around the injection hole, and there are fewer hydraulic shear cracks than tensile cracks. The crack morphologies of BPMs are found to be consistent with the experimental forms. The numerical simulation provides a way to understand the mechanisms that govern the hydrofracturing crack types and propagation of heterogeneous reservoirs.

“…Several numerical methods have been used to model hydraulically loaded fracture problems. Comprehensive reviews on HF modeling were presented by Adachi et al, Detournay, and Lecampion et al The most used methods in this area are based on finite difference method, finite element method (FEM), extended FEM (XFEM), phase field method, element‐free method, boundary element method (BEM), discrete fracture network models, discrete element models, and peridynamics . However, FEM, XFEM, and BEM are the most used methods in hydraulic fracturing problems .…”

Section: Introductionmentioning

confidence: 99%

Analysis of refracturing in horizontal wells: Insights from the poroelastic displacement discontinuity method

Rezaei

Bornia

Rafiee³

et al. 2018

Summary In this paper, a fully coupled 2‐dimensional poroelastic displacement discontinuity method is used to investigate the refracturing process in horizontal wells. One of the objectives of refracturing is to access new reserves by adding new hydraulic fractures in zones that were bypassed in the initial fracturing attempt. Pore pressure depletion in the vicinity of old fractures directly affects the state of stress and eventually the propagation of newly created hydraulic fractures. Thus, a poroelastic analysis is required to identify guidelines for the refracturing process, in particular to understand the extension of the pore pressure depletion, and eventually, the orientation of new as well as old fractures. We propose a fully coupled approach to model the whole process of child fracture propagation in a depleted area between 2 parent fractures in the same wellbore. This approach omits the need of using multistep workflow that is regularly used to model the process. The maximum tensile stress criterion (σ criterion) is used for hydraulic fracture propagation. The proposed method is verified using available analytical solutions for total stress and pore pressure loading modes on a line fracture in drained and undrained conditions. Then, test cases of multifractured horizontal wells are studied to calculate the time evolution of the stress and pore pressure fields around old fractures and to understand the effect of these fields on the propagation path of newly created fractures. Finally, the effect of the pore pressure depletion on the propagation path of the newly created fractures in the bypassed area of the same wellbore is studied. The results show that the depleted areas around old fractures are highly affected by the extent and severity of the stress redistribution and pore pressure depletion. It is observed that a successful creation of new fractures may only happen in certain time frames. The results of this study provide new insights on the behavior of newly created fractures in depleted zones. They also clarify the relationship between stress change and pore pressure depletion in horizontal wells.