Generation of cutting heat and simulation of core tube wall temperature during coring in primary structure coal seam.

When the drilling core method is used to determine the coalbed gas content, the cutting heat generated by the core bit cutting coal will increase the core tube temperature, and the excessively high core tube temperature will have an heating effect on the coal core, which will accelerate the coal core gas desorption rate and increase the gas loss amount. The generation of cutting heat of core bit and the measurement of core tube temperature are the basis for grasping the gas desorption law of coal core and projecting the amount of gas loss. Firstly, the self-developed core tube temperature measurement device was used to conduct on-site core temperature measurement experiments at different cutting speeds.

Gas displacement characteristics during the water wetting process of gas-bearing coal and microscopic influence mechanism.

Gas and dust posed a threat to the safe working environment of miners. The key to the effectiveness of coal seam water injection in controlling gas and dust was the wetting of the coal body by water. The gas displacement characteristics were crucial for evaluating the wetting effect of coal.

Desorption Characteristics of CH-CH Mixed Gas in Heavy Hydrocarbon-Rich Coal Seams.

The gas desorption characteristics of coal are closely related to the gas content of the coal seam. The gas in heavy hydrocarbon-rich coal seams contains CH and CH heavy hydrocarbons. However, most current research on the gas desorption characteristics of coal seams focuses on CH analysis, ignoring the influence of the CH heavy hydrocarbon gas.

Anisotropic Damage Mechanism of Coal Seam Water Injection with Multiphase Coupling.

After coal seam water injection, coal mechanical properties will change with brittleness weakening and plasticity enhancement. Aiming at the problem of coal damage caused by the coal seam water injection process, based on nonlinear pore elasticity theory and continuum damage theory, a nonlinear pore elastic damage model considering anisotropic characteristics is proposed to calculate and analyze the gas-liquid-solid multiphase coupling effect with the fully coupled finite element method during the coal seam water injection process. The research results indicate that the wetting radius of calculated results by the model agrees well with the in situ test results, and the relative errors are less than 10%.

Study on the Effect of Pore Structure on Desorption Hysteresis of Deep Coking Coal under High-Temperature and High-Pressure Conditions.

Pore space is the main desorption space for methane in coal; to study the effect of changes in pore structure on the desorption hysteresis effect of methane in coal under high-temperature and high-pressure conditions, the coking coal from Pingdingshan Twelve Mine was taken as the research object, and the isothermal adsorption and desorption curves were obtained and quantitatively analyzed at different temperatures and pressures by the help of isothermal adsorption and desorption experiments, combined with the pressed mercury experiments and the low-temperature liquid nitrogen adsorption experiments to test the pore structure of the coal samples before and after the adsorption and desorption tests. The pore structure of coal samples before and after the adsorption and desorption tests was tested by combining the mercury pressure test and the low-temperature liquid nitrogen adsorption test, and the influence of the change in the pore structure of coal samples after the high-temperature and high-pressure adsorption and desorption tests on the hysteresis effect of methane desorption was studied. The results showed that under the same pressure, the pore volume of coal samples increased with the increase in temperature, the pore-specific surface area showed a tendency to decrease, and the fractal dimension could well characterize the relationship between the pore structure and the pore surface of coal, in which the fractal dimension of the pores in the large pore size section gradually increased with the increase of temperature, and the fractal dimension in the small pore size section gradually decreased; there was a good correlation between the pore structure of the coal samples after the high-temperature and high-pressure adsorption and desorption tests and the hysteresis coefficient of desorption.

Experimental Study on Coal and Gas Outburst Risk under Different Water Content Rates in Strong Outburst Coal Seams.

To investigate the alleviation potency of coal seam water infusion on coal and gas outburst, this paper focuses on the Qidong coal mine outburst coal seam, where outburst accidents have occurred many times, and obtains the impact of water content on outburst prediction parameters by studying the features of outburst parameters and gas desorption law under different water content rates. How water content affects outburst was also researched through the use of a self-made outburst simulation test system, and the relationship between water content and outburst intensity and critical gas pressure was studied. It can be concluded that with the rise of water content, the initial velocity of gas diffusion, the gas desorption index of drilling cuttings, and the adsorption constant decrease, but the firmness coefficient () increase, and these indicators are exponentially related to the water content.

Study on Adsorption Characteristics of Deep Coking Coal Based on Molecular Simulation and Experiments.

To study the effect of high temperature and high pressure on the adsorption characteristics of coking coal, Liulin coking coal and Pingdingshan coking coal were selected as the research objects, and isotherm adsorption curves at different temperatures and pressures were obtained by combining isotherm adsorption experiments and molecular dynamics methods. The effect of high temperature and high pressure on the adsorption characteristics of coking coal was analyzed, and an isothermal adsorption model suitable for high-temperature and high-pressure conditions was studied. The results show that the adsorption characteristics of deep coking coal can be well characterized by the molecular dynamics method.

Research on Factors and Influencing Correlation of Coal Core Temperature during Coring.

The core-tube method is a common method to measure the coal seam gas content (CSGC). However, cutting heat and friction heat will be generated in the core-tube coring process, which will increase the coal core temperature and the coal core gas loss, thus resulting in a large error in the determination of the gas content. The accuracy of the gas content determination is closely related to the temperature variation of coal core during core-taking.

Volume Recovery Method for Non-Seal Gas Pressure Measurement Technology: A Comparative Study.

Coal seam gas pressure is one of the basic parameters for coalbed methane resource exploitation and coal mine gas disaster prevention. However, the present coal seam gas pressure measurement technology requires harsh field measurement conditions and a long testing period. In this study, a novel non-seal gas pressure measurement technology is proposed, and this technology is mainly aimed at three different changes before and after the collection of coal samples and realizes the real gas pressure measurement through the compensation of gas leakage, in situ volume recovery of the coal core, and reservoir temperature simulation.

Temperature of the Core Tube Wall during Coring in Coal Seam: Experiment and Modeling.

Temperature is the primary factor affecting the law of coal gas desorption. When the core method is used to measure the coal seam gas content (CSGC), the temperature of the coal core sample (CCS) will increase because the heat generated by the core bit cutting and rubbing the coal is transferred to the CCS through the core tube. To solve the above problems, the temperature of the core tube wall during coring at core depths of 10, 20, and 30 m was measured by a self-designed temperature measuring device.

Measurement and Modeling of Spontaneous Capillary Imbibition in Coal.

Coal is a typical dual-porosity medium. The implementation process of water invasion technology in coal is actually a process of spontaneous imbibition of external water. To obtain a model of spontaneous capillary imbibition in coal, the spontaneous imbibition of water in coal samples with different production loads is conducted experimentally.

Experiment and Modeling of Permeability under Different Impact Loads in a Structural Anisotropic Coal Body.

A mount of bedding and cleat in a coal body causes that the mechanical property and gas permeability are anisotropic in a coal seam, partly. To reveal the permeability change law of the impacted coal, a self-developed vertical split Hopkinson pressure bar (SHPB) device is used to carry out the dynamic impact mechanical property tests of coal samples in three different coring directions under five impact loads and then the permeability of the impacted coal samples is measured by a permeability measuring instrument under different gas pressures. Finally, a calculation model for the anisotropic coal permeability is established to analyze the permeability distribution law in any direction with different angles to the bedding plane.

Physical Simulation of Temperature and Pressure Evolvement in Coal by Different Refrigeration Modes for Freezing Coring.

Reduction of gas desorption capacity by cooling coal samples seems a feasible way to improve the accuracy of gas in place estimation. To find an efficient refrigeration mode for the freezing coring technology, the freezing tests for coal containing gas (at 0, 1.09, and 2.

Freezing method for rock cross-cut coal uncovering I: Mechanical properties of a frozen coal seam for preventing outburst.

A comprehensive technology is proposed to realize fast and safe rock cross-cut coal uncovering (RCCCU) based on artificial freezing engineering method. This comprehensive technology includes four steps, namely, drilling a borehole, wetting the coal body by water injection, gas drainage and freezing the coal seam by liquid nitrogen injection. In this paper, the compressive strength, tensile strength and shear strength of frozen coal specimens are tested to obtain the mechanical parameters of the specimen.