An Evaluation Method of Brittleness Characteristics of Shale Based on the Unloading Experiment
Shale reservoir has an initial unloading effect during the natural uplift and erosion process, which causes the shale brittleness to change, affecting the design of the fracturing scheme. To consider this, the axial compression loading and confining pressure unloading experiment of shale is carried...
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MDPI AG
2019-05-01
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| Series: | Energies |
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| Online Access: | https://www.mdpi.com/1996-1073/12/9/1779 |
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| author | Xiaogui Zhou Haiming Liu Yintong Guo Lei Wang Zhenkun Hou Peng Deng |
| author_facet | Xiaogui Zhou Haiming Liu Yintong Guo Lei Wang Zhenkun Hou Peng Deng |
| author_sort | Xiaogui Zhou |
| collection | DOAJ |
| description | Shale reservoir has an initial unloading effect during the natural uplift and erosion process, which causes the shale brittleness to change, affecting the design of the fracturing scheme. To consider this, the axial compression loading and confining pressure unloading experiment of shale is carried out, and then the influence of unloading rate on the mechanical parameters, failure characteristics, and the brittleness of rock are analyzed. What is more, a new evaluation method of brittleness characteristics that take the unloading effect into consideration is proposed. The conclusions are as follows: (1) The unloading rate has a weakening effect on the mechanical parameters, such as the destructive confining pressure and the residual strength of the samples. (2) The failure characteristics of shale specimens are a single shear failure in an oblique section under low unloading rate, and multiple shear zones accompanied with bedding fracture under high unloading rate. (3) The brittleness of shale samples is well verified by the brittleness index <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>B</mi> <mrow> <mi>d</mi> <mn>1</mn> </mrow> </msub> </mrow> </semantics> </math> </inline-formula> and <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>B</mi> <mrow> <mi>d</mi> <mn>2</mn> </mrow> </msub> </mrow> </semantics> </math> </inline-formula> during the loading path; nevertheless, it has shortage at the unloading path. This paper proposes a new brittleness evaluation method which can consider the influence of the different unloading rates and unloading points. Furthermore, there is a nice characterization between the brittleness damage and this method. |
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| institution | Directory Open Access Journal |
| issn | 1996-1073 |
| language | English |
| last_indexed | 2024-04-11T22:03:43Z |
| publishDate | 2019-05-01 |
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| series | Energies |
| spelling | doaj.art-f6ae52f0d67b48cca3f66d8201fabb6e2022-12-22T04:00:49ZengMDPI AGEnergies1996-10732019-05-01129177910.3390/en12091779en12091779An Evaluation Method of Brittleness Characteristics of Shale Based on the Unloading ExperimentXiaogui Zhou0Haiming Liu1Yintong Guo2Lei Wang3Zhenkun Hou4Peng Deng5Yunnan Key Laboratory of Disaster Reduction in Civil Engineering, Faculty of Civil Engineering and Mechanics, Kunming University of Science and Technology, Kunming 650504, ChinaYunnan Key Laboratory of Disaster Reduction in Civil Engineering, Faculty of Civil Engineering and Mechanics, Kunming University of Science and Technology, Kunming 650504, ChinaState Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, ChinaState Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, ChinaGuangzhou Institute of Building Science Co., Ltd., Guangzhou 510440, ChinaState Key Laboratory for Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, ChinaShale reservoir has an initial unloading effect during the natural uplift and erosion process, which causes the shale brittleness to change, affecting the design of the fracturing scheme. To consider this, the axial compression loading and confining pressure unloading experiment of shale is carried out, and then the influence of unloading rate on the mechanical parameters, failure characteristics, and the brittleness of rock are analyzed. What is more, a new evaluation method of brittleness characteristics that take the unloading effect into consideration is proposed. The conclusions are as follows: (1) The unloading rate has a weakening effect on the mechanical parameters, such as the destructive confining pressure and the residual strength of the samples. (2) The failure characteristics of shale specimens are a single shear failure in an oblique section under low unloading rate, and multiple shear zones accompanied with bedding fracture under high unloading rate. (3) The brittleness of shale samples is well verified by the brittleness index <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>B</mi> <mrow> <mi>d</mi> <mn>1</mn> </mrow> </msub> </mrow> </semantics> </math> </inline-formula> and <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>B</mi> <mrow> <mi>d</mi> <mn>2</mn> </mrow> </msub> </mrow> </semantics> </math> </inline-formula> during the loading path; nevertheless, it has shortage at the unloading path. This paper proposes a new brittleness evaluation method which can consider the influence of the different unloading rates and unloading points. Furthermore, there is a nice characterization between the brittleness damage and this method.https://www.mdpi.com/1996-1073/12/9/1779shaleunloading ratebrittleness evaluationfailure characteristicsmechanical parameters |
| spellingShingle | Xiaogui Zhou Haiming Liu Yintong Guo Lei Wang Zhenkun Hou Peng Deng An Evaluation Method of Brittleness Characteristics of Shale Based on the Unloading Experiment Energies shale unloading rate brittleness evaluation failure characteristics mechanical parameters |
| title | An Evaluation Method of Brittleness Characteristics of Shale Based on the Unloading Experiment |
| title_full | An Evaluation Method of Brittleness Characteristics of Shale Based on the Unloading Experiment |
| title_fullStr | An Evaluation Method of Brittleness Characteristics of Shale Based on the Unloading Experiment |
| title_full_unstemmed | An Evaluation Method of Brittleness Characteristics of Shale Based on the Unloading Experiment |
| title_short | An Evaluation Method of Brittleness Characteristics of Shale Based on the Unloading Experiment |
| title_sort | evaluation method of brittleness characteristics of shale based on the unloading experiment |
| topic | shale unloading rate brittleness evaluation failure characteristics mechanical parameters |
| url | https://www.mdpi.com/1996-1073/12/9/1779 |
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