Zengchao Feng

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

Isothermal methane adsorption experiments at different temperature stages using the monolayer adsorption principle

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

Multi-scale characteristics of coal structure by x-ray computed tomography (x-ray CT), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP)

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.

Distribution law of temperature changes during methane adsorption and desorption in coal using infrared thermography technology

The fracture-pore double porosity medium is one of the most common media in nature, for example, rock mass in strata. Fracture has a more significant effect on fluid flow than a pore in a fracture-pore double porosity medium. Hence, the fracture effect on percolation should be considered when studying the percolation phenomenon in porous media. In this paper, based on the fractal distribution law, three-dimensional (3D) fracture surfaces, and two-dimensional (2D) fracture traces in rock mass, the locations of fracture surfaces or traces are determined using a random function of uniform distribution. Pores are superimposed to build a fractal fracture-pore double medium. Numerical experiments were performed to show percolation phenomena in the fracture-pore double medium. The percolation threshold can be determined from three independent variables (porosity n, fracture fractal dimension D, and initial value of fracture number N0). Once any two are determined, the percolation probability exists at a critical point with the remaining parameter changing. When the initial value of the fracture number is greater than zero, the percolation threshold in the fracture-pore medium is much smaller than that in a pore medium. When the fracture number equals zero, the fracture-pore medium degenerates to a pore medium, and both percolation thresholds are the same.

Anisotropy Characteristics of Stress Relaxation in Coal: An Improved Fractional Derivative Constitutive Model

Isothermal methane adsorption methods are widely used in CBM and shale gas reservoirs; it is related to gas content. Adsorption volume is not only an important parameter for evaluating the characteristics of coal but can also provide a basis for adsorption capacity calculations. Thus, apparent and absolute adsorption volumes were introduced in this study and calculations of adsorption volume were modified, while differences between the two former variables were compared and analyzed and fitted formulas between adsorption parameter and temperature were established. Results show that differences between apparent and absolute adsorption volumes become much more significant as temperature rises; the adsorption ability of coal conforms to a close relationship with specific surface area (SA). And the Langmuir parameter a which represented the saturated adsorption capacity is increased slowly with temperature rises because of the increase in SA, and Langmuir parameter b which represented the saturated adsorption pressure is sharply decreased with temperature rises. The adsorption properties of lumpy coal are also discussed in this paper; they are good for preventing gas contents in in-situ CBM reservoirs.

An improved hardening-damage creep model of lean coal: a theoretical and experimental study

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.

Experimental Study of the Characteristic Changes of Coal Resistivity during the Gas Adsorption/Desorption Process

It is of great benefit to study the material and structural heterogeneity of coal for better understanding the coalbed methane (CBM) storage and enrichment. In this paper, multi-scale X-ray computed tomography (CT), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) at multi scales were conducted to thoroughly study the material distribution, heterogeneity, pore development, porosity and permeability of coal. It is suitable and reasonable to divide the testing samples into three structural categories by average density and heterogeneity degree, and the meso structure in the three categories accords with the morphology on SEM images. The pore size distribution and pore development of each subsample cannot be correspondingly related to their respective structure category or morphology due to different observation scales, while the macro pore size development, accumulated macro pore volume and macro pores porosity accord with the meso structure category and morphology information by CT and SEM at the same scale very well. Given the effect of macro pores on permeability and the contribution of micro pores to CBM storage capacity, reservoirs with developed micro pores and macro pores may be the most suitable coal reservoir for CBM exploitation.It is of great benefit to study the material and structural heterogeneity of coal for better understanding the coalbed methane (CBM) storage and enrichment. In this paper, multi-scale X-ray computed tomography (CT), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) at multi scales were conducted to thoroughly study the material distribution, heterogeneity, pore development, porosity and permeability of coal. It is suitable and reasonable to divide the testing samples into three structural categories by average density and heterogeneity degree, and the meso structure in the three categories accords with the morphology on SEM images. The pore size distribution and pore development of each subsample cannot be correspondingly related to their respective structure category or morphology due to different observation scales, while the macro pore size development, accumulated macro pore volume and macro pores porosity accord with the meso structure category and morphology information by C...

Variation law of adsorption heat of methane and coal with inhomogeneous potential well

Gas adsorption and desorption is a thermodynamic process that takes place within coal as temperature changes and that is related to methane (CH4) storage. As infrared thermographic technology has been applied in this context to measure surface temperature changes, the aim of this research was to further elucidate the distribution law underlying this process as well as the thermal effects induced by heat adsorption and desorption in coal. Specimens of two different coal ranks were used in this study, and the surface temperature changes seen in the latter were detected. A contour line map was then drawn on the basis of initial results enabling a distribution law of temperature changes for samples. The results show that different regions of coal sample surfaces exhibit different heating rates during the adsorption process, but they all depends on gas storage capacity to a certain extent. It proposes a correlation coefficient that expresses the relationship between temperature change and gas adsorption capacity that could also be used to evaluate the feasibility of coalbed CH4 extraction in the field. And finally, this study is deduced a method to reveal the actual adsorption capacity of coal or CH4 reservoirs in in situ coal seams.Gas adsorption and desorption is a thermodynamic process that takes place within coal as temperature changes and that is related to methane (CH4) storage. As infrared thermographic technology has been applied in this context to measure surface temperature changes, the aim of this research was to further elucidate the distribution law underlying this process as well as the thermal effects induced by heat adsorption and desorption in coal. Specimens of two different coal ranks were used in this study, and the surface temperature changes seen in the latter were detected. A contour line map was then drawn on the basis of initial results enabling a distribution law of temperature changes for samples. The results show that different regions of coal sample surfaces exhibit different heating rates during the adsorption process, but they all depends on gas storage capacity to a certain extent. It proposes a correlation coefficient that expresses the relationship between temperature change and gas adsorption capaci...