scholarly journals Discrete Element Analysis for Hydraulic Fracture Propagations in Laminated Reservoirs with Complex Initial Joint Properties

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-23 ◽  
Author(s):  
Fakai Dou ◽  
J. G. Wang ◽  
Huimin Wang ◽  
Bowen Hu ◽  
Chengxuan Li
Keyword(s):  
Mechanical Properties ◽  
Hydraulic Fracture ◽  
Fracture Morphology ◽  
Fracture Network ◽  
In Situ Stress ◽  
Element Analysis ◽  
Approach Angle ◽  
Bedding Planes ◽  
Fracturing Fluids ◽  
Shale Reservoirs

Previous studies on hydraulic fracturing mainly focus on the effects of the in-situ stress state, permeability, fracturing fluids, and approach angle in homogeneous rocks, but the impacts of joint mechanical properties in laminated shale reservoirs on the propagation and formation of the fracture network are still unclear. In this study, a coupled fluid-mechanical model was developed to investigate the impacts of joint mechanical properties on hydraulic fracture propagation. Then, this model was validated with Blanton’s criterion and some experimental observations on fracture morphology. Finally, a series of numerical simulations were conducted to comparatively analyze the impacts of joint mechanical properties on the total crack number, the percentage and distribution of each fracture type, the process of crack propagation, and the final fracture morphology. Numerical results show that the cracking behaviors induced by joint mechanical properties vary with the approach angle. Joint strength has a significant influence on the generation of matrix tensile cracks. The tensile-to-shear strength ratio plays an even more important role in the shear slips of bedding planes and is conducive to the formation of complex fracture morphology.

scholarly journals Numerical modeling of complex hydraulic fracture networks based on the discontinuous deformation analysis (DDA) method

2021 ◽  
pp. 014459872098153
Author(s):  
Yanzhi Hu ◽  
Xiao Li ◽  
Zhaobin Zhang ◽  
Jianming He ◽  
Guanfang Li
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Fracture Network ◽  
Discontinuous Deformation Analysis ◽  
Deformation Analysis ◽  
Fracture Networks ◽  
Proposed Model ◽  
Discontinuous Deformation ◽  
Shale Reservoirs ◽  
Dda Method

Hydraulic fracturing is one of the most important technologies for shale gas production. Complex hydraulic fracture networks can be stimulated in shale reservoirs due to the existence of numerous natural fractures. The prediction of the complex fracture network remains a difficult and challenging problem. This paper presents a fully coupled hydromechanical model for complex hydraulic fracture network propagation based on the discontinuous deformation analysis (DDA) method. In the proposed model, the fracture propagation and rock mass deformation are simulated under the framework of DDA, and the fluid flow within fractures is simulated using lubrication theory. In particular, the natural fracture network is considered by using the discrete fracture network (DFN) model. The proposed model is widely verified against several analytical and experimental results. All the numerical results show good agreement. Then, this model is applied to field-scale modeling of hydraulic fracturing in naturally fractured shale reservoirs. The simulation results show that the proposed model can capture the evolution process of complex hydraulic fracture networks. This work offers a feasible numerical tool for investigating hydraulic fracturing processes, which may be useful for optimizing the fracturing design of shale gas reservoirs.

scholarly journals The Influence of Bedding Planes and Permeability Coefficient on Fracture Propagation of Horizontal Wells in Stratification Shale Reservoirs

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-19
Author(s):  
Yuepeng Wang ◽  
Xiangjun Liu ◽  
Lixi Liang ◽  
Jian Xiong
Keyword(s):  
Permeability Coefficient ◽  
In Situ Stress ◽  
Stress Difference ◽  
Strength Parameters ◽  
Breakdown Pressure ◽  
Permeability Coefficients ◽  
Bedding Planes ◽  
Initiation Pressure ◽  
Shale Reservoirs

The complexity of hydraulic fractures (HF) significantly affects the success of reservoir reconstruction. The existence of a bedding plane (BP) in shale impacts the extension of a fracture. For shale reservoirs, in order to investigate the interaction mechanisms of HF and BPs under the action of coupled stress-flow, we simulate the processes of hydraulic fracturing under different conditions, such as the stress difference, permeability coefficients, BP angles, BP spacing, and BP mechanical properties using the rock failure process analysis code (RFPA2D-Flow). Simulation results showed that HF spread outward around the borehole, while the permeability coefficient is uniformly distributed at the model without a BP or stress difference. The HF of the formation without a BP presented a pinnate distribution pattern, and the main direction of the extension is affected by both the ground stress and the permeability coefficient. When there is no stress difference in the model, the fracture extends along the direction of the larger permeability coefficient. In this study, the in situ stress has a greater influence on the extension direction of the main fracture when using the model with stress differences of 6 MPa. As the BP angle increases, the propagation of fractures gradually deviates from the BP direction. The initiation pressure and total breakdown pressure of the models at low permeability coefficients are higher than those under high permeability coefficients. In addition, the initiation pressure and total breakdown pressure of the models are also different. The larger the BP spacing, the higher the compressive strength of the BP, and a larger reduction ratio (the ratio of the strength parameters of the BP to the strength parameters of the matrix) leads to a smaller impact of the BP on fracture initiation and propagation. The elastic modulus has no effect on the failure mode of the model. When HF make contact with the BP, they tend to extend along the BP. Under the same in situ stress condition, the presence of a BP makes the morphology of HF more complex during the process of propagation, which makes it easier to achieve the purpose of stimulated reservoir volume (SRV) fracturing and increased production.

scholarly journals Analysis of multi-factor coupling effect on hydraulic fracture network in shale reservoirs

2015 ◽  
Vol 2 (2-3) ◽  
pp. 162-166 ◽  
Author(s):  
Yuzhang Liu ◽  
Nailing Xiu ◽  
Yunhong Ding ◽  
Xin Wang ◽  
Yongjun Lu ◽  
...  
Keyword(s):  
Hydraulic Fracture ◽  
Coupling Effect ◽  
Fracture Network ◽  
Hydraulic Fracture Network ◽  
Shale Reservoirs

scholarly journals Effect of Joint Geometrical Parameters on Hydraulic Fracture Network Propagation in Naturally Jointed Shale Reservoirs

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-23 ◽  
Author(s):  
Zhaohui Chong ◽  
Qiangling Yao ◽  
Xuehua Li
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Fracture Network ◽  
Hydraulic Fractures ◽  
Geometrical Parameters ◽  
Breakdown Pressure ◽  
Opening Mode ◽  
Hydraulic Fracture Network ◽  
Shale Reservoirs ◽  
Network Pattern

The presence of a significant amount of discontinuous joints results in the inhomogeneous nature of the shale reservoirs. The geometrical parameters of these joints exert effects on the propagation of a hydraulic fracture network in the hydraulic fracturing process. Therefore, mechanisms of fluid injection-induced fracture initiation and propagation in jointed reservoirs should be well understood to unleash the full potential of hydraulic fracturing. In this paper, a coupled hydromechanical model based on the discrete element method is developed to explore the effect of the geometrical parameters of the joints on the breakdown pressure, the number and proportion of hydraulic fractures, and the hydraulic fracture network pattern generated in shale reservoirs. The microparameters of the matrix and joint used in the shale reservoir model are calibrated through the physical experiment. The hydraulic parameters used in the model are validated through comparing the breakdown pressure derived from numerical modeling against that calculated from the theoretical equation. Sensitivity analysis is performed on the geometrical parameters of the joints. Results demonstrate that the HFN pattern resulting from hydraulic fracturing can be roughly divided into four types, i.e., crossing mode, tip-to-tip mode, step path mode, and opening mode. As β (joint orientation with respect to horizontal principal stress in plane) increases from 0° to 15° or 30°, the hydraulic fracture network pattern changes from tip-to-tip mode to crossing mode, followed by a gradual decrease in the breakdown pressure and the number of cracks. In this case, the hydraulic fracture network pattern is controlled by both γ (joint step angle) and β. When β is 45° or 60°, the crossing mode gains dominance, and the breakdown pressure and the number of cracks reach the lowest level. In this case, the HFN pattern is essentially dependent on β and d (joint spacing). As β reaches 75° or 90°, the step path mode is ubiquitous in all shale reservoirs, and the breakdown pressure and the number of the cracks both increase. In this case, β has a direct effect on the HFN pattern. In shale reservoirs with the same β, either decrease in k (joint persistency) and e (joint aperture) or increase in d leads to the increase in the breakdown pressure and the number of cracks. It is also found that changes in d and e result in the variation in the proportion of different types of hydraulic fractures. The opening mode of the hydraulic fracture network pattern is observed when e increases to 1.2 × 10−2 m.

Physics of Proppant Transport Through Hydraulic Fracture Network

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Oliver Chang ◽  
Michael Kinzel ◽  
Robert Dilmore ◽  
John Yilin Wang
Keyword(s):  
Mathematical Model ◽  
Hydraulic Fracture ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Fracture Network ◽  
Fracture Networks ◽  
Horizontal Drilling ◽  
Simulation Tools ◽  
Proppant Transport ◽  
Shale Reservoirs

Horizontal drilling with successful multistage hydraulic fracture treatments is the most widely applied and effective method to enable economic development of hydrocarbon-bearing shale reservoirs. Once fracture networks are established, they must be propped open to maintain pathways for fluid migration through the production phase. As such, the design and application of effective and efficient proppant treatment is considered a key step to successfully develop the targeted resource. Unfortunately, the available literature and simulation tools to describe proppant transport in complex fracture networks are inadequate, and some of the fundamental mechanisms of proppant transport are poorly understood. The present study provides a critical review of relevant published literature to identify important mechanisms of particle transport and related governing equations. Based on that review, a mathematical model was developed to quantitatively predict the transport behavior of proppant particles in model fracture networks. Aspects of this mathematical model are compared against computational fluid dynamic (CFD) simulation, and implications of this work are discussed.

scholarly journals Propagation of hydraulic fracture under the joint impact of bedding planes and natural fractures in shale reservoirs

2019 ◽  
Vol 7 (6) ◽  
pp. 2690-2702 ◽  
Author(s):  
Tao Gong ◽  
Binwei Xia ◽  
Lang Liu ◽  
Ziye Peng ◽  
Yugang Gao
Keyword(s):  
Hydraulic Fracture ◽  
Natural Fractures ◽  
Bedding Planes ◽  
Shale Reservoirs

Hydraulic Fracture Height Containment by Weak Horizontal Interfaces

2015 ◽  
Author(s):  
Dimitry Chuprakov ◽  
Romain Prioul
Keyword(s):  
Hydraulic Fracture ◽  
Low Viscosity ◽  
Bedding Planes ◽  
Containment Model ◽  
Fracturing Fluids ◽  
Contrast Mechanism ◽  
Fracture Height ◽  
Fracture Height Containment ◽  
Stress Contrast ◽  
The Given

Abstract Weak formation bedding planes create a unique mechanism for hydraulic fracture height containment. They arrest the vertical growth of hydraulic fracture. The propagation across them may or may not occur. To quantify this fracture behavior, first we developed an analytical model of the elastic T-shaped fracture contact with frictional and cohesional interfaces. The model evaluates the fracture blunting and the shear activation of the interfaces. It predicts the buildup of the net pressure necessary for the fracture to cross the given interface. Next we conduct numerical simulations of the 3D fracture propagation in a formation with closely spaced horizontal interfaces. These simulations manifest intermittent and decelerated fracture growth in height, especially with low-viscosity fracturing fluids. This mechanism of fracture height containment is independent of the multilayer stress-contrast mechanism used conventionally. Combined with the stress mechanism, the fracture height containment model could alleviate the problem of height growth overestimation in some fracturing simulation cases.

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