Yangsheng Zhao

Experiments on mechanical properties of salt rocks under cyclic loading

The primary purpose of underground gas storages is to provide gas for seasonal consumptions or strategic reserve. The periodical operations of gas injection and extraction lead to cyclic loading on the walls and surrounding rocks of gas storages. To investigate the mechanical behaviors of different host rocks in bedded salt deposit, laboratory experiments were conducted on the samples of rock salt, thenardite, glauberite and gypsum. The mechanical properties of rock samples under monotonic and cyclic loadings were studied. Testing results show that, under monotonic loading, the uniaxial compressive stress (UCS) of glauberite is the largest (17.3 MPa), while that of rock salt is the smallest (14.0 MPa). The UCSs of thenardite and gypsum are 16.3 and 14.6 MPa, respectively. The maximum strain at the peak strength of rock salt (halite) is much greater than those of the other three rocks. The elastic moduli of halite, thenardite, glauberite and gypsum are 3.0, 4.2, 5.1 and 6.8 GPa, respectively. Under cyclic loading, the peak strengths of the rock specimens are deteriorated except for rock salt. The peak strengths of thenardite, glauberite and gypsum decrease by 33.7%, 19.1% and 35.5%, respectively; and the strains of the three rocks at the peak strengths are almost the same. However, the strain of rock salt at the peak strength increases by 1.98%, twice more than that under monotonic loading. Under monotonic loading, deformation of the tested rock salt, thenardite and glauberite shows in an elastoplastic style. However, it changes to a ductile style under cyclic loading. Brittle deformation and failure are only observed for gypsum. The results should be helpful for engineering design and operation of gas storage in bedded salt deposit.

Problems of Evolving Porous Media and Dissolved Glauberite Micro-scopic Analysis by Micro-Computed Tomography: Evolving Porous Media (1)

In this study, the evolution phenomena and mechanism of porous media were analyzed according to the driving factors, i.e., external force, heat, seepage, coupled chemical reaction and seepage, coupled chemical reaction and heat flow, and live porous media. According to the evolution mechanism, the evolution can be categorized as natural evolution, artificial evolution, and natural–artificial evolution. Taking the dissolution of glauberite ore as the example, the detailed evolution characteristics and behavior were investigated. The evolution characteristics of pores and the residual porous skeleton were investigated using micro-computed tomography. The results indicate that (1) The variation of the dissolution thickness of glauberite with time follows a power function. (2) The total void ratio of the residual porous media remains almost the same and is typically in a range of 20–22 %. The diffusion coefficient of the residual porous skeleton is

Effect of Temperature on Deformation of Triaxially Stressed Anthracite

0.013 \,\hbox {cm}^{2}/\hbox {h}

Effect of strain rate on the mechanical properties of salt rock

0.013cm2/h. (3) In the process of glauberite dissolution, three zones are formed from the interface to the outside: a crystallization completion zone, a crystalline transition zone, and a development zone of dissolution and crystallization. The crystallization completion zone is formed after 15 h dissolution. The thickness of the crystallization transition zone and development zone of dissolution and crystallization is approximately 0.5–1.0 mm.

Triaxial compression system for rock testing under high temperature and high pressure

Moisture and thermal are the key factors for influencing methane desorption during CBM exploitation. Using high-pressure water injection technology into coalbed, new fractures and pathways are formed to transport methane. A phenomenon of water-inhibiting gas flow existed. This study is focused on various water pressures impacted on gas-adsorbed coal samples, and then the desorption capacity could be revealed under different conditions. And the results are shown that methane desorption capacity was decreased with the increase in water pressure at room temperature and the downtrend would be steady until water pressure was large enough. Heating could promote gas desorption capacity effectively, with the increasing of water injection pressures, and the promotion of thermal on desorption became more obvious. These results are expected to provide a clearer understanding of theoretical efficiency of heat water or steam injection into coalbed, and they can provide some theoretical and experimental guidance on CBM production and methane control.

Numerical simulation of the top coal caving process using the discrete element method

Coal is a particular organic rock that is sensitive to temperature and pressure. The physical–mechanical behaviors of coal bed as influenced by the coupling of temperature and pressure are different from those under conventional testing conditions in engineering applications such as underground coal gasification (UCG) and coal-bed methane heat-injection extraction (CMHE). Coal-bed deformation is related to channel formation, distribution and propagation in UCG, and affects the formation of hightemperature vapor channels in CMHE significantly. Therefore, the investigation of thermal deformation coupling with temperature and pressure is of great significance in the analysis of the channel and roof stability and surface subsidence in UCG, and the formation of heat flow channels in CMHE. In the last decades, extensive laboratory research has been performed on rock samples exposed to high temperatures to investigate temperature influence on physical, thermal and mechanical properties. Wong and Brace (1979) measured thermal expansion of six rocks involving granite, diabase, marble, limestone, dunite and quartzite and found that thermal expansion of six rock samples was typically irreversible after heating above room temperature and the coefficient of thermal expansion of a rock is usually much higher than the average coefficients for the minerals in the rock at temperature of 2–38 C and confining pressure up to 600 MPa. Heard (1980), Heard and Page (1982) studied the coefficient of linear thermal expansion of Climax Stock quartz monzonite, Westerly and Stripa granites and concluded that the coefficient of linear thermal expansion for these rocks was neither constant with nor a simple function of temperature or pressure at effective pressures of 0, 13.8 and 27.6 MPa and temperature up to 300 C. Heuze (1983) reviewed linear thermal expansion coefficient variation with temperature for numerous granites and concluded that a sharp increase in expansion before the as bs transition and great decrease occurred beyond the transition temperature. Lin (2002) measured the permanent strain of thermal expansion on Inada granite which increased almost exponentially. Dwivedi et al. (2008) studied coefficient of linear thermal expansion of India granite at temperature up to 200 C and room pressure. The conclusion is clear that thermal expansion of rock is nonlinear. In addition, thermal deformation of some sedimentary rocks such as sandstone and claystone was also measured and had the similar evolution characteristics & Zijun Feng fzj3893811@126.com