Informatics Publishing Limited

Lei Wang ¹, Haiying Song ², Weishu Liu ³

Affiliations
1 Financial Research Department, Shanghai National Accounting Institute, Shanghai 200030, CN
2 Ingdo International Trading Group, Shanghai 200030, CN
3 School of Information Management and Engineering, Zhejiang University of Finance and Economics, Hangzhou 310018, Zhejiang, CN

Abstract

Open access (OA) publishing which eliminates various restrictions on access has greatly changed the landscape of scientific publishing. OA publishing is now widely acknowledged to accelerate the knowledge production and dissemination. Accompanying the changing global research landscape, the volume of OA publications has also risen rapidly over the past decade.

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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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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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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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Lei Wang ¹, Yao Wei ¹, Yongyi Ren ²

Affiliations
1 College of Architecture and Civil Engineering, Xi'an University of Science and Technology, Xi'an 710054, CN
2 Economic and Technical Research Institute, Shandong Electric Power Company State Grid, Jinan 250 000, CN

Abstract

In view of the problems such as spray layer peeling-off, reduced anchoring force and serious floor heave in the weakly cemented soft rock roadway in the west region, we took samples from the sandy mudstone formation in the main haulage roadway of Luxin Coal Mine in Inner Mongolia and performed triaxial compression tests at different confining pressure in the lab. The test data show that the post-peak strain behaviour of the mudstone is obviously softened and there exists residual deformation, thus the tri-linear strain-softening model is more suitable for analysis. We made fish corrections to the bi-linear strain-softening model in FLAC to achieve the numerical application of the model. The verification model shows that the tri-linear strain-softening model better describes the deformation features of mudstone. We analyzed the construction stability of the mudstone roadway and conducted evaluation based on the softening index. The results show that due to the increasing softening degree and softening depth of the mudstone roadway, the shotcreting support system has no obvious effect in controlling the deformation of the surrounding rock, and that the bolt axial force first increases and later decreases, losing its retaining effect.

Keywords

Weakly Cemented Mudstone, Triaxial Compression, Strain Softening, Degree Of Softening, Numerical Simulation.

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