scholarly journals Experimental Study on Hydraulic Fracturing of High Asphalt Concrete Core Rock-Fill Dam

2019 ◽  
Vol 9 (11) ◽  
pp. 2285 ◽  
Author(s):  
Zhengxing Wang ◽  
Jutao Hao ◽  
Jian Yang ◽  
Yan Cao ◽  
Xiulin Li ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Asphalt Concrete ◽  
Water Pressure ◽  
Concrete Core ◽  
Mix Proportion ◽  
Local Shear ◽  
Test Result ◽  
Rule Out ◽  
Shear Dilatancy

In this paper, we experiment on the hydraulic fracturing of asphalt concrete with a voids content higher than 3%, which has arisen from the possible local shear dilatancy of Quxue asphalt’s core wall of concrete core dam, the highest one of the sort constructed in the world. The model test has shown that under the sole water pressure 0.13 MPa—relevant to the pressure where the dilatancy could appear at core wall of Quxue dam—the asphalt concrete with a voids content of 3.5% underwent hydraulic fracturing. Furthermore, the asphalt concrete with a voids content of 3.0% was tested for nearly 500 h and no sign of hydraulic fracturing was found, which again confirmed the threshold requirement for a 3% voids content to the impervious asphalt concrete to the hydraulic fracture concern. According to the analysis of the test result, the theory of fracture mechanics could be applied to the hydraulic fracture of asphalt concrete with a voids content between 3.4~4.0%, which behaved during hydraulic fracturing like a quasi-brittle material, similar to concrete. Because the hydraulic fracturing could occur in the shear dilatant asphalt concrete, a proper mix proportion of asphalt concrete to a project with adverse stress state should be carefully designed to rule out the possibility of shear dilatancy.

The Study of Fractured Rock Mass Instability of the Law Based on the Hydraulic Fracturing

2012 ◽  
Vol 496 ◽  
pp. 538-541
Author(s):  
Zhi Qiang Kang ◽  
Wein Jie Li ◽  
Yu Bo Jia
Keyword(s):  
Rock Mass ◽  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Fractured Rock ◽  
Water Pressure ◽  
Overburden Rock ◽  
Fractured Rock Mass ◽  
Water Seepage ◽  
Vertical Loading ◽  
The Law

Fractured rock mass, Hydraulic fracture, RFPA2D-Flow, Instability of the law. Abstract. Based on the theory of fluid-solid coupling, Studying on the effect of permeability about damage and stress, Analysis of influence factors what hydraulic fracturing process, fracture propagation pattern, and influencing factors including shape and magnitude of inlet hole, stress conditions, and specimen strength were investigated. Application of rock failure process analysis software coupled seepage-stress F-RFPA2D, numerical simulated rock water pressure to cause crack rupture instability process, research the fracture law of the rock on water pressure and vertical loading. Combine similar physical experiment model, contrast analysis of two broken results and stress-strain curve, reveals instability mechanical behavior of rock hydraulic fracture process. Obtain deep mining in the process of mine water seepage and water extrude, overburden rock crack up, expand, water seepage, water extrude, instability rupture process rules.

scholarly journals Hydraulic Fracture Propagation and Permeability Evolution in the Composite Thin Coal Seam

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Shenglong Liu ◽  
Bingxiang Huang ◽  
Weiyong Lu ◽  
Haoze Li ◽  
Ding Li ◽  
...  
Keyword(s):  
Coal Seam ◽  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Water Pressure ◽  
Fracture Propagation ◽  
Injection Pressure ◽  
Unstable Fracture ◽  
Permeability Evolution ◽  
Thin Coal Seam ◽  
Hf Propagation

Hydraulic fracturing can improve the permeability of composite thin coal seam. Recently, characterizing hydraulic fracture (HF) propagation inside the coal seam and evaluating the permeability enhancement with HF extension remain challenging and crucial. In this work, based on the geological characteristics of the coal seam in a coal mine of the southwest China, the RFPA2D-Flow software is employed to simulate the HF propagation and its permeability-increasing effect in the composite thin coal seam, and a couple of outcomes were obtained. (1) Continuous propagation of the hydraulic microcrack-band is the prominent characteristic of HF propagation. With the increment of the injection-water pressure, HF generation in the composite thin coal seam can be divided into three stages: stress accumulation, stable fracture propagation, and unstable fracture propagation. (2) The hydraulic microcrack-band propagates continuously driven by the fluid-injection pressure. The microcrack-band not only cracks the coal seam but also fractures the gangue sandwiched between the coal seams. (3) The permeability in the composite thin coal seam increases significantly with the propagation of hydraulic microcrack-band. The permeability increases by 1~2 magnitudes after hydraulic fracturing. This study provides references to the field applications of hydraulic fracturing in the composite thin coal seam, such as optimizing hydraulic fracturing parameters, improving gas drainage, and safe-efficient mining.

A case study of hydraulic fracturing using finite element methods

1999 ◽  
Vol 36 (5) ◽  
pp. 861-875 ◽  
Author(s):  
Axel KL Ng ◽  
John C Small
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Water Pressure ◽  
Numerical Procedure ◽  
Tensile Fracture ◽  
Rock Fill ◽  
The Core ◽  
Element Method

Hydraulic fracturing can occur in the clay core of an earth and rock-fill dam if the vertical effective stress in the core is reduced to levels that are small enough to allow a tensile fracture to occur. This situation may arise if the total stress in the core is reduced by the "arching effect" where the core settles relative to the rock-fill shoulders of the dam. Water pressure increases in the core which occur on first impounding of water will reduce effective stresses further, and if they reach low enough values, a fracture will occur. The design of earth dams to resist hydraulic fracture is therefore of great importance (especially those dams with thin vertical or near-vertical central cores), as there have been several dam failures in the past that have been attributed to hydraulic fracture. This paper presents a method of predicting hydraulic fracture in the core of earth and rock-fill dams by using a numerical procedure based on the finite element method. The finite element procedure makes use of special joint elements that allow fluid flow and fracture to be modeled and is an advance over previous methods in that it allows the complete history of pore-pressure development in the core of a dam to be simulated. A study of the behaviour of the Hyttejuvet Dam, which was thought to have failed due to hydraulic fracturing, is also carried out, and the results of the analysis suggest that the failure of the dam was probably due to hydraulic fracturing that occurred during first filling of the reservoir. The fractures predicted occur at about the location that the actual fracture was thought to have been located. Key words: hydraulic fracture, earth and rock-fill dams, finite element method.

scholarly journals A Theoretical Model for Hydraulic Fracturing through Two Symmetric Radial Perforations Emanating from A Borehole

2019 ◽  
Vol 2019 ◽  
pp. 1-21 ◽  
Author(s):  
Shibin Tang ◽  
Zhuo Dong ◽  
Dong Duan ◽  
Yingchun Li
Keyword(s):  
Theoretical Model ◽  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Water Pressure ◽  
Fracture Initiation ◽  
Mixed Mode Fracture ◽  
Anisotropy Coefficient ◽  
Stress Criterion ◽  
Stress Anisotropy ◽  
Critical Initiation

The production enhancement of oil, gas, or geothermal reservoirs through hydraulic fracturing requires an in-depth study on the fracture initiation and propagation from the borehole. According to the linear elastic fracture mechanics, a theoretical model is developed to calculate the stress intensity factors of two symmetric radial cracks emanating from a pressurized borehole. The maximum tangential stress criterion under the mix-mode condition is developed to investigate the hydraulic fracture initiation. The critical water pressure and critical initiation angle predicted by the theoretical model match closely the experimental results reported in the literature. The influence of the stress anisotropy coefficient, the perforation angle and length, the borehole radius, the ratio between the water pressures in the fracture and the borehole, and Biot’s coefficient are investigated. Moreover, the effects of the injected high water pressure (i.e., larger than the critical water pressure) on the fracture initiation angle are studied to further understand the characteristics of hydraulic fracture initiation. The results indicate that the perforation angle and length, the borehole radius, and the stress anisotropy coefficient have a relatively strong influence on the critical water pressure and critical initiation angle. During high-pressure water injection, the fracture initiation angle decreases as the ratio between the water pressure in the fracture and the borehole and Biot’s ratio increase. The theoretical model provides a comprehensive understanding of the fracture twist, the mixed-mode fracture propagation feature, and the hydraulic fracturing optimization.

scholarly journals Experimental and Numerical Investigation on Basic Law of Dense Linear Multihole Directional Hydraulic Fracturing

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-19
Author(s):  
Xin Zhang ◽  
Yuqi Zhang
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Large Scale ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
In Situ Stress ◽  
Hydraulic Fractures ◽  
Directional Hydraulic Fracturing ◽  
Basic Law

Using the dense linear multihole to control the directional hydraulic fracturing is a significant technical method to realize roof control in mining engineering. By combining the large-scale true triaxial directional hydraulic fracturing experiment with the discrete element numerical simulation experiment, the basic law of dense linear holes controlling directional hydraulic fracturing was studied. The results show the following: (1) Using the dense linear holes to control directional hydraulic fracturing can effectively form directional hydraulic fractures extending along the borehole line. (2) The hydraulic fracturing simulation program is very suitable for studying the basic law of directional hydraulic fracturing. (3) The reason why the hydraulic fracture can be controlled and oriented is that firstly, due to the mutual compression between the dense holes, the maximum effective tangential tensile stress appears on the connecting line of the drilling hole, where the hydraulic fracture is easy to be initiated. Secondly, due to the effect of pore water pressure, the disturbed stress zone appears at the tip of the hydraulic fracture, and the stress concentration zone overlaps with each other to form the stress guiding strip, which controls the propagation and formation of directional hydraulic fractures. (4) The angle between the drilling line and the direction of the maximum principal stress, the in situ stress, and the hole spacing has significant effects on the directional hydraulic fracturing effect. The smaller the angle, the difference of the in situ stress, and the hole spacing, the better the directional hydraulic fracturing effect. (5) The directional effect of synchronous hydraulic fracturing is better than that of sequential hydraulic fracturing. (6) According to the multihole linear codirectional hydraulic fracturing experiments, five typical directional hydraulic fracture propagation modes are summarized.

scholarly journals Numerical simulation of the laws of fracture propagation of multi-hole linear co-directional hydraulic fracturing

2021 ◽  
pp. 014459872198899
Author(s):  
Weiyong Lu ◽  
Changchun He
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Minimum Principle ◽  
Fracture Propagation ◽  
Axial Direction ◽  
Rock Breaking ◽  
Hydraulic Fractures ◽  
Directional Hydraulic Fracturing ◽  
Fracture Intersection ◽  
Expansion Stage

Directional rupture is one of the most important and most common problems related to rock breaking. The goal of directional rock breaking can be effectively achieved via multi-hole linear co-directional hydraulic fracturing. In this paper, the XSite software was utilized to verify the experimental results of multi-hole linear co-directional hydraulic fracturing., and its basic law is studied. The results indicate that the process of multi-hole linear co-directional hydraulic fracturing can be divided into four stages: water injection boost, hydraulic fracture initiation, and the unstable and stable propagation of hydraulic fracture. The stable expansion stage lasts longer and produces more microcracks than the unstable expansion stage. Due to the existence of the borehole-sealing device, the three-dimensional hydraulic fracture first initiates and expands along the axial direction in the bare borehole section, then extends along the axial direction in the non-bare hole section and finally expands along the axial direction in the rock mass without the borehole. The network formed by hydraulic fracture in rock is not a pure plane, but rather a curved spatial surface. The curved spatial surface passes through both the centre of the borehole and the axial direction relative to the borehole. Due to the boundary effect, the curved spatial surface goes toward the plane in which the maximum principal stress occurs. The local ground stress field is changed due to the initiation and propagation of hydraulic fractures. The propagation direction of the fractures between the fracturing boreholes will be deflected. A fracture propagation pressure that is greater than the minimum principle stress and a tension field that is induced in the leading edge of the fracture end, will aid to fracture intersection; as a result, the possibility of connecting the boreholes will increase.

scholarly journals A numerical investigation on the performance of hydraulic fracturing in naturally fractured gas reservoirs based on stimulated rock volume

2020 ◽  
Vol 10 (8) ◽  
pp. 3333-3345
Author(s):  
Ali Al-Rubaie ◽  
Hisham Khaled Ben Mahmud
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Natural Fracture ◽  
Shear Stresses ◽  
Individual Element ◽  
Natural Fractures ◽  
Gas Reservoirs ◽  
Stimulated Reservoir Volume ◽  
Reservoir Volume ◽  
Naturally Fractured

Abstract All reservoirs are fractured to some degree. Depending on the density, dimension, orientation and the cementation of natural fractures and the location where the hydraulic fracturing is done, preexisting natural fractures can impact hydraulic fracture propagation and the associated flow capacity. Understanding the interactions between hydraulic fracture and natural fractures is crucial in estimating fracture complexity, stimulated reservoir volume, drained reservoir volume and completion efficiency. However, because of the presence of natural fractures with diffuse penetration and different orientations, the operation is complicated in naturally fractured gas reservoirs. For this purpose, two numerical methods are proposed for simulating the hydraulic fracture in a naturally fractured gas reservoir. However, what hydraulic fracture looks like in the subsurface, especially in unconventional reservoirs, remain elusive, and many times, field observations contradict our common beliefs. In this study, the hydraulic fracture model is considered in terms of the state of tensions, on the interaction between the hydraulic fracture and the natural fracture (45°), and the effect of length and height of hydraulic fracture developed and how to distribute induced stress around the well. In order to determine the direction in which the hydraulic fracture is formed strikethrough, the finite difference method and the individual element for numerical solution are used and simulated. The results indicate that the optimum hydraulic fracture time was when the hydraulic fracture is able to connect natural fractures with large streams and connected to the well, and there is a fundamental difference between the tensile and shear opening. The analysis indicates that the growing hydraulic fracture, the tensile and shear stresses applied to the natural fracture.

Performance of five D-dimer assays for the exclusion of symptomatic distal leg vein thrombosis

2012 ◽  
Vol 107 (02) ◽  
pp. 369-378 ◽  
Author(s):  
Jan Schwonberg ◽  
Carola Hecking ◽  
Marc Schindewolf ◽  
Dimitrios Zgouras ◽  
Susanne Lehmeyer ◽  
...  
Keyword(s):  
High Sensitivity ◽  
Diagnostic Value ◽  
Vein Thrombosis ◽  
Clinical Probability ◽  
Wells Score ◽  
Deep Vein ◽  
Test Result ◽  
D Dimer ◽  
Rule Out ◽  
Compression Ultrasonography

SummaryThe diagnostic value of D-dimer (DD) in the exclusion of proximal deep-vein thrombosis (DVT) is well-established but is less well-known in the exclusion of distal (infrapopliteal) DVT. Therefore, we evaluated the diagnostic abilities of five DD assays (Vidas-DD, Liatest-DD, HemosIL-DD, HemosIL-DDHS, Innovance-DD) for excluding symptomatic proximal and distal leg DVT. A total of 243 outpatients whose symptoms were suggestive of DVT received complete compression ultrasonography (cCUS) of the symptomatic leg(s). The clinical probability of DVT (PTP) was assessed by Wells score. Thirty-eight proximal and 31 distal DVTs (17 tibial/fibular DVTs, 14 muscle DVTs) were diagnosed by cCUS. Although all assays showed high sensitivity for proximal DVT (range 97–100%), the sensitivity was poor for distal DVT (range 78–93%). None of the assays were individually able to rule out all DVTs as a stand-alone test (negative predictive value [NPV] 91–96%). However, a negative DD test result combined with a low PTP exhibited a NPV of 100% for all DVTs (including proximal, tibial/fibular, and muscle DVTs) with the HemosIL-DDHS and Innovance-DD. All proximal and tibial/fibular DVTs, but not all muscle DVTs, could be ruled out with this strategy using the Liatest-DD and Vidas-DD. The HemosIL-DD could not exclude distal leg DVT, even in combination with a low PTP. The combination of a negative DD with a low PTP showed a specificity of 32–35% for all DVTs. In conclusion, our study shows that when used in conjunction with a low PTP some DD assays are useful tools for the exclusion of distal leg DVT.

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