Simulation of Multiple Hydraulic Fracturing in Non-Uniform Pore Pressure Field

2005 ◽  
Vol 9 ◽  
pp. 163-172 ◽  
Author(s):  
Lian Chong Li ◽  
Chun An Tang ◽  
Leslie George Tham ◽  
Tian Hong Yang ◽  
Shao Hong Wang
Keyword(s):  
Hydraulic Fracturing ◽  
Pore Pressure ◽  
Process Analysis ◽  
Failure Process ◽  
Fracture Initiation ◽  
Global Scale ◽  
Breakdown Pressure ◽  
Failure Evolution ◽  
Rock Failure Process ◽  
Fracturing Experiments

A series of numerical simulations of hydraulic fracturing were performed to study the initiation, propagation and breakdown of fluid driven fractures. The simulations are conducted with a flow-coupled Rock Failure Process Analysis code (RFPA2D). Both heterogeneity and permeability of the rocks are taken into account in the studies. The simulated results reflect macroscopic failure evolution process induced by microscopic fracture subjected to porosity pressure, which are well agreeable to the character of multiple hydraulic fracturing experiments. Based on the modeling results, it is pointed out that fracture is influenced not only by pore pressure magnitude on a local scale around the fracture tip but also by the orientation and the distribution of pore pressure gradients on a global scale. The fracture initiation, the orientation of crack path, the breakdown pressure and the stress field evolution around the fracture tip are influenced considerably by the orientation of the pore pressure. The research provides valuable guidance to the designers of hydraulic fracturing engineering.

scholarly journals A Crack Propagation Control Study of Directional Hydraulic Fracturing Based on Hydraulic Slotting and a Nonuniform Pore Pressure Field

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Yugang Cheng ◽  
Zhaohui Lu ◽  
Xidong Du ◽  
Xuefu Zhang ◽  
Mengru Zeng
Keyword(s):  
Crack Initiation ◽  
Hydraulic Fracturing ◽  
Pore Pressure ◽  
Pressure Field ◽  
Process Analysis ◽  
Failure Process ◽  
Horizontal Stress ◽  
Directional Hydraulic Fracturing ◽  
Rock Failure Process ◽  
Initiation Pressure

Hydraulic fracturing techniques for developing deeply buried coal reservoirs face routine problems related to high initial pressures and limited control over the fracture propagation direction. A novel method of directional hydraulic fracturing (DHF) based on hydraulic slotting in a nonuniform pore pressure field is proposed. A mechanical model is used to address crack initiation and propagation in a nonuniform pore pressure field, where cracks tend to rupture and propagate towards zones of high pore pressure for reducing the effective rock stress more. The crack initiation pressure and propagation morphology are analyzed by rock failure process analysis software. The numerical results show that the directional propagation of hydraulic fracturing cracks is possible when the horizontal stress difference coefficient is less than or equal to 0.5 or the slotting deviation angle is less than or equal to 30°. These findings are in good agreement with experimental results, which support the accuracy and reliability of the proposed method and theory.

scholarly journals A Numerical Investigation on the Hydraulic Fracturing Effect of Water Inrush during Tunnel Excavation

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Quan Zhang ◽  
Bingxiang Huang ◽  
Manchao He ◽  
Shan Guo
Keyword(s):  
Stress Concentration ◽  
Hydraulic Fracturing ◽  
Process Analysis ◽  
Failure Process ◽  
Water Inrush ◽  
Water Source ◽  
Stress Concentrations ◽  
Karst Cavity ◽  
Effect Of Water ◽  
Rock Failure Process

When a high-pressure water source is located near a tunnel under excavation, water inrush is commonly associated with a hydraulic fracturing effect. To study the hydraulic fracturing effect of water inrush (HFEWI), flow-rock failure process analysis (F-RFPA2D) was adopted to simulate the water inrush process. The simulated results indicated that a stress disturbance area formed in front of the excavation face and that a hydraulic fracture zone formed in front of the karst cavity. Similarly, stress concentrations formed in front of the excavation face and the karst cavity. The hydraulic fracturing effect was characterized by stress concentration, and the local hydraulic crack propagation was the result of stress concentration. In addition, a pore pressure gradient formed in the crack-free area of the surrounding rock, and the occurrence of hydraulic cracking was the root cause of the significant change in water flow. When the hydraulic cracks initially formed and expanded, the zone of crack activity was large. As the cracks continued to expand, the range of activity decreased and finally concentrated directly in front of the excavation face. Additionally, the shapes of the water inrush channel obtained by the experimentation and numerical simulation were basically the same: semielliptical. During the evolution of hydraulic crack initiation, expansion, and penetration, the bottom of the excavated borehole was initially dry and then experienced seepage and water inrush. Finally, the minimum safe thickness of the rock wall was calculated to provide a safety guideline for this type of water inrush.

scholarly journals Numerical Simulation on the Basic Rules of Multihole Linear Codirectional Hydraulic Fracturing

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14 ◽  
Author(s):  
Weiyong Lu ◽  
Yonglong Wang ◽  
Xin Zhang
Keyword(s):  
Hydraulic Fracturing ◽  
Principal Stress ◽  
Process Analysis ◽  
Failure Process ◽  
Water Injection ◽  
Fracture Initiation ◽  
Rock Breaking ◽  
Hydraulic Fractures ◽  
Basic Law ◽  
The Difference

Directional rupture is one of the most important and common problems in rock breaking engineering. The purpose of directional rock breaking can be effectively realized by using multihole linear codirectional hydraulic fracturing. In this paper, realistic failure process analysis (RFPA) software is used to verify the experimental results of multihole linear codirectional hydraulic fracturing and investigate its basic law. The following results are demonstrated: (1) RFPA software can be very helpful to study the basic law of multihole linear codirectional hydraulic fracturing; (2) the process of multihole linear codirectional hydraulic fracturing can be divided into four stages: water injection boost, fracture initiation, stable fracture propagation, and fracture connection; and (3) multihole linear codirectional hydraulic fractures propagate along the direction of borehole distribution. Multihole codirectional hydraulic fracturing is influenced by the angle between the direction of the hole distribution and maximum principal stress, the difference of the principal stress, and the spacing of the boreholes. The smaller the angle, the difference value of the principal stress, and the hole spacing, the better the multihole codirectional hydraulic fracturing effect.

Numerical Analysis of Faults on Deep-Buried Tunnel Surrounding Rock Damaged Zones

2011 ◽  
Vol 90-93 ◽  
pp. 74-78 ◽  
Author(s):  
Jun Hu ◽  
Ling Xu ◽  
Nu Wen Xu
Keyword(s):  
Numerical Analysis ◽  
Mechanical Response ◽  
Progressive Failure ◽  
Process Analysis ◽  
Failure Process ◽  
Water Inrush ◽  
Surrounding Rock ◽  
Factors Affecting ◽  
Rock Failure Process ◽  
Tunnel Instability

Fault is one of the most important factors affecting tunnel instability. As a significant and casual construction of Jinping II hydropower station, when the drain tunnel is excavated at depth of 1600 m, rockbursts and water inrush induced by several huge faults and zone of fracture have restricted the development of the whole construction. In this paper, a progressive failure progress numerical analysis code-RFPA (abbreviated from Rock Failure Process Analysis) is applied to investigate the influence of faults on tunnel instability and damaged zones. Numerical simulation is performed to analyze the stress distribution and wreck regions of the tunnel, and the results are consistent with the phenomena obtained from field observation. Moreover, the effects of fault characteristics and positions on the construction mechanical response are studied in details. Some distribution rules of surrounding rock stress of deep-buried tunnel are summarized to provide the reasonable references to TBM excavation and post-support of the drain tunnel, as well as the design and construction of similar engineering in future.

Numerical Simulation on Failure Patterns of Rock Discs and Rings Subject to Diametral Line Loads

2004 ◽  
Vol 261-263 ◽  
pp. 1517-1522 ◽  
Author(s):  
Wan Cheng Zhu ◽  
K.T. Chau ◽  
Chun An Tang
Keyword(s):  
Tensile Strength ◽  
Standardized Test ◽  
Process Analysis ◽  
Failure Process ◽  
Brazilian Test ◽  
Rock Failure ◽  
Numerical Code ◽  
Failure Patterns ◽  
Rock Failure Process ◽  
Indirect Tensile

Brazilian test is a standardized test for measuring indirect tensile strength of rock and concrete disc (or cylinder). Similar test called indirect tensile test has also been used for other geomaterials. Although splitting of the disc into two halves is the expected failure mode, other rupture modes had also been observed. More importantly, the splitting tensile strength of rock can vary significantly with the specimen geometry and loading condition. In this study, a numerical code called RFPA2D (abbreviated from Rock Failure Process Analysis) is used to simulate the failure process of disc and ring specimens subject to Brazilian test. The failure patterns and splitting tensile strengths of specimens with different size and loading-strip-width are simulated and compared with existing experimental results. In addition, two distinct failure patterns observed in ring tests have been simulated using RFPA2D and thus this verifies the applicability of RFPA2D in simulating rock failure process under static loads.

Influence of Oriented Perforation Design on Refracture Reorientation: Simulation and Experiment

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Minhui Qi ◽  
Mingzhong Li ◽  
Tiankui Guo ◽  
Chunting Liu ◽  
Song Gao ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Large Scale ◽  
Simulation Models ◽  
Fracture Initiation ◽  
Simulation Method ◽  
Induced Stress ◽  
Study Results ◽  
Simulation Results ◽  
Fracturing Experiments ◽  
The Impact

The oriented perforating is the essential technique to guide the refracture reorientation, but the influence of the oriented perforation design on the refracture steering radius is still unclear. In this paper, the factors influencing the refracture reorientation were studied by simulation models and experiments. The effects of initial fracture, well production, and perforations on the refracture initiation and propagation were analyzed. Three-dimensional finite element models were conducted to quantify the impact of perforation depth, density, and azimuth on the refracture. The large-scale three-axis hydraulic fracturing experiments guided by oriented perforations were also carried out to verify the fracture initiation position and propagation pattern of the simulation results. The research results showed that perforations change the near-wellbore induced stress distribution, thus changing the steering radius of the refracture. According to the simulation results, the oriented perforation design has a significant influence on the perforation guidance effect and refracture characteristics. Five hydraulic fracturing experiments proved the influence of perforating parameters on fracture initiation and morphology, which have a right consistency between the simulation results. This paper presents a numerical simulation method for evaluating the influence of the refracture reorientation characteristics under the consideration of multiple prerefracturing induced-stress and put forward the oriented perforation field design suggestions according to the study results.

The effect of stress on the primary permeability of rock cores—a facet of hydraulic fracturing

1981 ◽  
Vol 18 (2) ◽  
pp. 195-204 ◽  
Author(s):  
R. Heystee ◽  
J.-C. Roegiers
Keyword(s):  
Rock Mass ◽  
Hydraulic Fracturing ◽  
The State ◽  
Stress Conditions ◽  
Breakdown Pressure ◽  
Rock Types ◽  
State Of Stress ◽  
Pressurization Rate ◽  
Fluid Penetration ◽  
Fracturing Experiments

Recent laboratory hydraulic fracturing experiments have shown that fluid penetration into the rock mass adjacent to the borehole being pressurized has a significant influence on the magnitude of the breakdown pressure. One factor affecting the degree of penetration of the pressurizing fluid is the permeability of the rock mass, which in turn is a function of the state of stress present in the rock mass. To study this permeability–stress relationship, a radial permeameter was constructed and three rock types tested. Derived expressions show that during radially divergent and convergent flow in the permeameter, the state of stress in the rock specimen is tensile and compressive respectively. The radial permeameter test results show that the permeability of rock increases significantly under tensile stress conditions and reduces under compressive stress conditions. The results from this study were used to develop a conceptual model which explains the dependency of breakdown pressure levels on the pressurization rate.

Fracture Behavior and Water Migration in Heterogeneous and Porous Rocks

2005 ◽  
Vol 297-300 ◽  
pp. 2636-2641
Author(s):  
Lian Chong Li ◽  
Leslie George Tham ◽  
Tian Hong Yang ◽  
Xia Li
Keyword(s):  
Fluid Flow ◽  
Fracture Behavior ◽  
Rock Sample ◽  
Process Analysis ◽  
Failure Process ◽  
Compressive Loading ◽  
Porous Rocks ◽  
Rock Failure Process ◽  
Strength Character ◽  
Weak Zones

Based on the heterogeneous and porous characteristics of rock materials, a flow-stressdamage (FSD) model, implemented with the Rock Failure Process Analysis code (RFPA2D), is used to investigate the behavior of fluid flow and damage evolution, and their coupling action in rock sample that are subjected to both hydraulic and uniaxial compressive loading. A highly heterogeneous sample, containing grains, grain boundaries and weak zones, is employed in the numerical simulation. The simulation results provide a deep insight in the physical essence of the evolutionary nature of fracture phenomena as well as the fluid flow in heterogeneous materials, especially when they are highly stressed. The simulation result suggests that the nature of fluid flow and strength character in rocks strongly depends upon the heterogeneity of the rocks.

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