Informatics Publishing Limited

Tongtao Wang ¹, Chunhe Yang ¹, Xiangzhen Yan ², Hongling Ma ¹, Xilin Shi ¹, J. J. K. Daemen ³

Affiliations
1 State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, Hubei, CN
2 College of Pipeline and Civil Engineering, China University of Petroleum, Qingdao 266555, CN
3 Mackay School of Earth Sciences and Engineering, University of Nevada, Reno 89557, Nevada, US

Abstract

An equivalent permeability model (EPM) is presented to calculate the equivalent permeability of non-salt layers, which makes the sealing evaluation of bedded salt cavern natural gas storage by numerical simulation easy and sufficient. In the numerical simulations, the effects of non-salt layer property parameters, i.e. horizontal permeability, vertical permeability and dip angle on the sealing of bedded salt cavern natural gas storage can be expressed by a single parameter, the equivalent permeability. We have studied the influence of non-salt dip angle, permeability anisotropy, permeability, buried depth, gas pressure, etc. on the time that it takes for the natural gas to migrate to the ground surface through the non-salt layer formation. The examples show that the EPM is precise and correct, and can meet the actual engineering demands, which includes fewer parameters, and it is implemented easily in numerical simulations. The time needed for natural gas to migrate to the surface is proportional to the increase in anisotropy of permeability and buried depth, but inversely proportional to the increase of non-salt layer dip angle, permeability and internal pressure. The permeability and the dip angle of non-salt layers are the key factors to be considered when analysing the sealing of bedded salt cavern natural gas storage.

Keywords

Numerical Simulation, Permeability Anisotropy, Salt Cavern, Sealing.

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Feng Xu ¹, Chunhe Yang ¹, Yintong Guo ¹, Tongtao Wang ¹, Lei Wang ¹, Ping Zhang ²

Affiliations
1 State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, Hubei, CN
2 State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, CN

Abstract

To understand the effect of confining pressure on the mechanical properties of thermally treated coarse sandstone, uniaxial and triaxial compression tests were conducted for six groups of thermally treated sandstone from Xujiahe Formation in southwestern China under confining pressures of 0-40 MPa. The test results indicate that 600°C is a critical threshold of the thermal damage of sandstone by SEM and mechanical tests. When temperature is below 600°C, few micro cracks are observed by SEM. Peak strength, elastic modulus, cohesion and internal friction angle remain constant or increase with increasing temperature and all these values decrease when temperature is above or equal to 600°C under different confining pressures. Under the uniaxial and low confining pressure (≤ 5 MPa), the failure mode shows single or multiple splitting planes and it is easier to generate complex cracks with increasing temperature. Under high confining pressure (10-40 MPa), the failure mode shows a simple shear plane after treatment at different temperatures, i.e. 25-1000°C. The results may provide guidance for rock engineering design after high temperature exposure.

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Yanqiang Du ¹, Chunhe Yang ¹, Chao Zhang ², Shangwei Wu ¹

Affiliations
1 State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing-400044, CN
2 State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan-430071, CN

Abstract

Located in northwestern China, Qijiagou tailings pond is examined in this study. Since tailings pond is the fillings of tailings, physical properties of material in tailings pond are determined utilizing in-situ testing and laboratory experimentation. Geo-Slope software is employed to establish a simplified two-dimension model of the tailings pond and to analyze the seepage flow field. Static stability is evaluated with the limit equilibrium method while the equivalent linear method is applied to determine time-history response of the system. Calculated results reveal the dry beach length is reduced from 200 m to 90 m and the phreatic line rises by 2-3 m in the design flood. Partial liquefaction occurs in the zone from water edge to the water reservoir tip while maximum liquefaction depth is approximately 15 m under water level. The safety factor of tailings pond varies with seismic time process and the minimum safety factor is 1.5.

Keywords

Tailings Pond, Safety Assessment, Stability, Dynamic Response, Liquefaction.

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Shuai Heng ¹, Chunhe Yang ², Lei Wang ², J. J. K. Daemen ³

Affiliations
1 School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo, Henan Province - 454000, CN
2 State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, Hubei - 430071, CN
3 Machay School of Earth Sciences and Engineering, University of Nevada, Reno, NV, US

Abstract

To realize the control on geometry of fracture network and improve the individual well production of shale gas reservoirs, hydraulic fracturing simulation tests of shale outcrops for horizontal well were carried out. This was based on an established true triaxial hydraulic fracturing simulation test system, to analyse the propagation and formation of a complex fracture network. The results show that the typical severe fluctuation of pump pressure during extension, is an obvious feature of hydraulic fracturing by Stimulated Reservoir Volume (SRV). Due to the large size and abundant natural fractures in shale specimens, the acoustic emission (AE) energy is weak during propagation of hydraulic fractures. However, fracture propagation can still be effectively determined to some extent, although relatively few AE events are detected. Hydraulic fractures from horizontal well initiate approximately along the maximal in situ stress. But the fractures gradually deviate from the orientation when extending. Branching, re-orientation or penetrating bedding planes and then interconnecting with natural fractures or weak beddings are the main mechanisms of the formation of complicated fracture networks.

Keywords

Fracture Propagation, Fracture Network, Hydraulic Fracturing, Shale, Stimulated Reservoir Volume.

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Zhenkun Hou ¹, Marte Gutierrez ², Anming Wang ¹, Abdulhadi Almrabat ², Chunhe Yang ³

Affiliations
1 College of Geosciences and Engineering, North China University of Water Resources and Electric Power, Zhengzhou 450045, CN
2 Department of Civil and Environment Engineering, Colorado School of Mines, Golden 80401, US
3 State Key Laboratory for Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, CN

Abstract

The mechanical characteristics of Longmaxi Formation shale with different degrees of fracturing-fluid saturation were characterized by applying triaxial compression tests at a confining pressure of 50 MPa. The test samples were collected from fresh outcrop shale in Dayou, Chongqing, China and the shale brittleness was evaluated based on brittleness-drop coefficient, stress decrease coefficient and softening modulus. The weakening of related rock parameters of shale specimens being immersed in fracturing-fluid for different time periods was studied and discussed. The degree of deterioration of the peak strengths, elastic and softening moduli and brittleness were significant and varied exponentially when the samples were soaked in fracturing-fluid. The samples were found to fail by shear on the whole accompanied by varying degrees of bedding plane cracking. With increase of sample immersion time, the number of shear failure surfaces changes from one to two and finally to more than three. The length and number of cracks parallel to bedding planes increased gradually, however, no cracks were formed perpendicular to the bedding plane even when the shale was soaked for a long time. The weakening of the brittleness and mechanical parameters with sample fracturing-fluid saturation are mainly related to change of stress state at the crack tips caused by hydration swelling, the dissolution caused by alkaline fracturing-fluid and the formation of liquid film on the surface of shale particles, all of which are the results of mechanical–physical–chemical coupling.

Keywords

Brittleness Evaluation Index, Hydration Swelling, Immersion Time, Longmaxi Formation Shale, Triaxial Compression, Weakening Mechanism.

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Feng Xu ¹, Zongling Yan ¹, Lei Wang ², Yintong Guo ², Chunhe Yang ²

Affiliations
1 National and Local Joint Engineering Laboratory for Road Engineering and Technology in Mountainous Areas, Chongqing, CN
2 State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, CN

Abstract

To understand the effect of the drilling fluid on hardness characteristics of tight sandstone, indentation hardness tests were conducted on tight sandstone which were soaked in a water- or oil-based drilling fluid at different temperatures and time. The results of the study indicate that: (1) the hardness of tight sandstone decreased rapidly after being soaked in the water-based or oil-based drilling fluid and it decreased by 22.9% and 10.1% respectively after two hours; (2) with the increase in soaking time, the hardness remained almost constant when soaked in the oil-based drilling fluid. However, the reduction in hardness reached 33.1% after soaking in the water-based drilling fluid for 15 days; (3) there was little change in the hardness with the increase in temperature in the oil-based drilling fluid, but in the water-based drilling fluid, the hardness decreased at a temperature above 50°C; (4) high temperature would cause mineral expansion and hydration, resulting in hardness reduction with increase in soaking time in the water-based drilling fluid which would lead to the softening of the tight sandstone’s surface structure.

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