# Experimental Study of the Shear Characteristics of Fault Filled with Different Types of Gouge in Underground Gas Storage

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## Abstract

**:**

## 1. Introduction

## 2. Fault Rock Shear Experiment

#### 2.1. Experimental Scheme Design

#### 2.2. Experimental Sample Preparation

#### 2.2.1. Preparation of Fault Plane

#### 2.2.2. Fault Gouge Configuration

#### 2.3. Experimental Steps

## 3. Analysis of Experimental Results

#### 3.1. Effect of Different Normal Stresses on Shear Properties

#### 3.2. Effects of Different Clay Mineral Contents on the Shear Properties of Fault Rocks

#### 3.3. Analysis of Fractal Dimension of Fault Surface Roughness

_{hc}represents the height value set of the method, ${N}_{i,j}$ represents the number of boxes needed at the Grid

_{i,j}grid; $N(\delta )$ represents the number of boxes required to cover the entire fault plane; D is the fractal dimension of the fault surface roughness; ${\delta}_{i}$ is the size and length of the cube box unit;

## 4. Conclusions

- (1)
- High-precision engraving machines and high-precision 3D scanners are used to reproduce shear and tension faults, ensuring the comparability of faults. Fault rocks with different properties of fault gouge are closer to the properties of real fault zones.
- (2)
- Under the same experimental conditions, the shear strength of the shear-type fault surface model is higher than that of the tensile-type fault surface model, which means that the tensile-type fault zone is more likely to slip and activate during the injection and production process of the gas reservoir. Compared with the influence of clay mineral content in fault gouges, the roughness of the fault plane has a greater influence on the shear strength of fault rocks.
- (3)
- Within the same type of fault surface, the higher the clay mineral content in the fault gouge, the greater the shear strength of the fault rock.
- (4)
- Under the same fault model and normal stress conditions, fault gouge has no obvious influence rule on the roughness of the shear fault surface; under the same fault model and fault gouge conditions, the greater the normal stress, the smaller the roughness of the shear fault surface.
- (5)
- Due to the limitations of the experimental equipment, the fault plane was set to a horizontal state, which differs somewhat from the actual fault plane. However, by converting the stress state and dip angle of the actual fault plane, a similar method can be used. When the fault dip angle is small and the stress on the ground is the same, the roughness of the contact surface after activation is relatively small. Therefore, in the construction and operation stages of gas storage tanks, it is necessary to focus on faults with small dip angles and tensile-type faults as much as possible.

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 3.**Initial fault plane ((

**a**) is the upper surface of the shear fault model, (

**b**) is the lower surface of the shear fault model, (

**c**) is the upper surface of the tensile fault model, (

**d**) is the lower surface of the tensile fault model).

**Figure 9.**The completed direct shear experiment sample. (

**a**) is shear type experimental sample; (

**b**) is a tensile type experimental sample.

**Figure 11.**The shear stress–shear displacement curves for shear fault surface filled with 3 types of fault gouge ((

**a**) is No. 1 fault gouge, (

**b**) is No. 2 fault gouge, and (

**c**) is No. 3 fault gouge).

**Figure 12.**The shear stress–shear displacement curves of the tensile fault surface filled with three types of fault gouge ((

**a**) is No. 1 fault gouge, (

**b**) is No. 2 fault gouge, (

**c**) is No. 3 fault gouge).

**Figure 13.**The linear fitting relationship between the shear strength and the normal stress of the fault rocks with three types of fault gouge ((

**a**) is No. 1 fault gouge, (

**b**) is No. 2 fault gouge, (

**c**) is No. 3 fault gouge) and shear fault plane.

**Figure 14.**The linear fitting relationship between the shear strength and the normal stress of the fault rocks with three types of fault gouge ((

**a**) is No. 1 fault gouge, (

**b**) is No. 2 fault gouge, (

**c**) is No. 3 fault gouge) and the tensile fault plane.

**Figure 15.**Effect of fault gouge type on cohesion and friction angle. (

**a**) is the relationship between cohesion and fault gouge type; (

**b**) is the relationship between friction angle and fault gouge type.

**Figure 16.**Schematic diagram of mesh division (Modified from Wu et al. [22]).

**Figure 17.**(

**a**) The relationship between the fractal dimension of the shear fault and the type of fault gouge (

**b**) The relationship between the fractal dimension of the tension fault and the type of fault gouge (

**c**) The relationship between the fractal dimension of the shear fault and the normal stress (

**d**) The relationship between the fractal dimension of the tension fault and the normal stress.

Fault Gouge Type | Mass Ratio | Clay Mineral Content (%) |
---|---|---|

NO. 1 | Kaolin/Coarse particles/Montmorillonite/illite/Water/Hydroxypropyl Methyl Cellulose = 30:20:37.5:12.5:60:2 | 49.4 |

NO. 2 | Kaolin/Coarse particles/Montmorillonite/illite/Water/Hydroxypropyl Methyl Cellulose = 30:30:30:10:60:2 | 43.2 |

NO. 3 | Kaolin/Coarse particles/Montmorillonite/illite/Water/Hydroxypropyl Methyl Cellulose = 30:40:22.5:7.5:60:2 | 37 |

Fault Model | Experiment Number | Fault Gouge Type | Normal Stress (MPa) |
---|---|---|---|

Shear fault model | JQ-1 | NO. 1 | 2 |

JQ-2 | 4 | ||

JQ-3 | 6 | ||

JQ-4 | 8 | ||

JQ-5 | NO. 2 | 2 | |

JQ-6 | 4 | ||

JQ-7 | 6 | ||

JQ-8 | 8 | ||

JQ-9 | NO. 3 | 2 | |

JQ-10 | 4 | ||

JQ-11 | 6 | ||

JQ-12 | 8 |

Fault Model | Parameter | Normal | Tangential |
---|---|---|---|

Shear fault model | Displacement velocity | 0.1 KN/s | 1 mm/min |

Force/Displacement Target | 15 KN | 10 mm | |

Tension fault model | Displacement velocity | 1 mm/min | \ |

displacement target | 10 mm | \ |

**Table 4.**Cohesion and friction angle obtained from the direct shear tests of two types of fault rocks filled by different types of fault gouge.

Fault Model | Group Number | Cohesion (MPa) | Friction Angle (°) | Clay Mineral Content (%) |
---|---|---|---|---|

Shear fault model | Group 1 | 1.15 | 41.6 | 49.4 |

Group 2 | 1.79 | 38.4 | 43.2 | |

Group 3 | 1.61 | 37.3 | 37.0 | |

Tension fault model | Group 4 | 0.83 | 25.2 | 49.4 |

Group 5 | 0.68 | 29.4 | 43.2 | |

Group 6 | 0.31 | 26.1 | 37.0 |

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## Share and Cite

**MDPI and ACS Style**

Ding, G.; Liu, H.; Xia, D.; Wang, D.; Huang, F.; Guo, H.; Xie, L.; Guo, Y.; Wu, M.; Mao, H. Experimental Study of the Shear Characteristics of Fault Filled with Different Types of Gouge in Underground Gas Storage. *Energies* **2023**, *16*, 3119.
https://doi.org/10.3390/en16073119

**AMA Style**

Ding G, Liu H, Xia D, Wang D, Huang F, Guo H, Xie L, Guo Y, Wu M, Mao H. Experimental Study of the Shear Characteristics of Fault Filled with Different Types of Gouge in Underground Gas Storage. *Energies*. 2023; 16(7):3119.
https://doi.org/10.3390/en16073119

**Chicago/Turabian Style**

Ding, Guosheng, Hejuan Liu, Debin Xia, Duocai Wang, Famu Huang, Haitao Guo, Lihuan Xie, Yintong Guo, Mingyang Wu, and Haijun Mao. 2023. "Experimental Study of the Shear Characteristics of Fault Filled with Different Types of Gouge in Underground Gas Storage" *Energies* 16, no. 7: 3119.
https://doi.org/10.3390/en16073119