Coal Seam Gas Extraction by Integrated Drillings and Punchings from the Floor Roadway considering Hydraulic-Mechanical Coupling Effect

Owing to the exhaustion of shallow coal resources, deep mining has been occupied in coal mines. Deep buried coal seams are featured by the great ground stress, high gas pressure, and low permeability, which boost the risk of gas disasters and thus dramatically threaten the security about coal mines. Coal seam gas pressure and gas content can be decreased by gas extraction, which is the primary measure to prevent and control mine gas disasters. The coal mass is simplified into a continuous medium with dual structure of pores and fractures and single permeability. In consideration of the combined effects of gas slippage and two-phase flow, a hydraulic-mechanical coupling model for gas migration in coals is proposed. This model involves the equations of gas sorption and diffusion, gas and water seepage, coal deformation, and evolution of porosity and permeability. Based on these, the procedure of gas extraction through the floor roadway combined with hydraulic punching and ordinary drainage holes was simulated, and the gas extraction results were used to evaluate the outburst danger of roadway excavation and to verify the engineering practice. Results show that gas extraction can reduce coal seam gas pressure and slow down the rate of gas release, and the established hydraulic-mechanical coupling model can accurately reveal the law of gas extraction by drilling and punching boreholes. After adopting the gas extraction technology of drilling and hydraulic punching from the floor roadway, the remaining gas pressure and gas content are reduced to lower than 0.5 MPa and 5.68 m3/t, respectively. The achievements set a theoretical foundation to the application of drilling and punching integrated technology to enhance gas extraction.

Research and application of coal and gas outburst early warning system based on gas geological features

The geological structure of coal mines has always been a dangerous object of attention in coal mine outburst prevention work. In order to realize coal mine safety information management and early warning of gas disasters, comprehensive use of gas geological theory, coal mine disaster warning theory, computer information technology and other analysis methods, considering the influence of geological structure, coal seam occurrence parameters, and gas parameters, an early warning indicator system for identifying the risk of coal and gas outbursts reflecting the geological characteristics of gas has been constructed. The coal and gas outburst risk identification and early warning system is constructed using the principle of multi-index step-by-step identification and extreme value determination, and it is applied on-site in the 3303 Measure Lane in the East Shaft Area of Sihe Mine. The research results show that the constructed early warning system can provide accurate early warning for the area (belt) affected by the geological structure by 10m, and can provide accurate early warning of coal and gas outbursts based on the outburst signs of gas geology such as the thickness of soft layers and changes in coal seam thickness. This technology provides effective support for coal mines to effectively prevent gas disasters and ensure coal mine production safety.

Design of an Automatic Detector for Gas Desorption of Coal Samples

Gas content measurement is a common technique in the prevention of coalmine gas disasters. During the measurement, the gas desorption amount of field coal samples needs to be obtained by an instrument working under the principle of gas collection by water displacement (GCWD). The instrument is poorly automated, and susceptible to the influence of subjective factors. To overcome these defects, this paper designs an automatic detector of gas desorption, aiming to realize automated detection. Firstly, the authors analyzed the gas desorption detection process, and clarified the contents and features of the information to be collected. On this basis, the hardware and software systems of the multi-data automatic detector were developed based on digital circuit design and multi-sensor detection. To further improve the measuring accuracy of gas desorption, the multi-range multi-stage mode was introduced to the automatic detector. Application results show that the proposed detector can automatedly collect and store gas desorption amount, ambient pressure, and temperature, greatly improve the degree of automation, and minimize the influence of subjective factors. The popularization of this detector will make gas desorption measurement more efficient and effective, laying a solid basis for the prevention of coalmine gas disasters.

Experimental Investigation of the Use of Expansive Materials to Increase Permeability in Coal Seams through Expansive Fracturing

Hydration reactions of expansive materials are typically very safe, easy to induce, and low in cost, while the crushing of such materials is typically free from noise, dust, vibration, and toxic gases. In the present study, to realize the application of expansive materials in the prevention of coal seam gas disasters, the microstructure, heat release rate, and expansive pressure of expansive materials were investigated for different degrees of hydration based on temperature and pressure measurements and using a scanning electron microscope (SEM); fracture characteristics were determined based on fracture tests of coal-like materials. The results show that the expansive material with +30% water has the lowest hydration temperature (100°C). The expansive pressure of the steel tube was found to reach 57 MPa, which is deemed suitable for application in coal seams. The strain and displacement of coal-like materials were found to increase with time, with four main cracks appearing. Based on these results, it is feasible that hydration reactions of expansive materials could increase both gas drainage and permeability in coal seams, thus reducing the risk of rock burst around boreholes in coal seams.

Experimental Study on the Permeability Evolution and Gas Flow Law of Post-Strength Soft Coal

Permeability is an essential indicator for predicting gas drainage yield and preventing mine gas disasters, which is significantly influenced by the stress paths and the integrity of coal. Conventional research on permeability mainly focused on the permeability evolution of initial undamaged or fractured (prefabricated fractures) coal under various stress paths; little attention has been paid to post-strength coal (stress-induced damage), especially for soft coal. To determine the permeability evolution and gas flow law of post-strength soft coal samples under various stress paths, we used the experimental method combined with the numerical method in this study. The results showed that when the confining pressure and axial pressure of post-strength soft coal samples were unloaded, the permeability increased by 1.25–1.32 times; when the coal samples were loaded into the secondary damage, the permeability first decreased and then increased. The simulation part in this study found that the development of the fracture of coal samples under triaxial compression was divided into four stages. Gas flow law of post-strength soft coal was significantly influenced by fracture locations, and the gas pressure and gas flow field near the fracture were disturbed.

Developing prescriptive environmental protection models from descriptive human accident behavior

Purpose – This study aims to examine human-made oil–gas disasters to illustrate how a prescriptive model could be developed. Resilience to human-made disasters, such as oil or gas spills, can be improved by using prescriptive models developed by analyzing past behavior. This type of study is useful for urban planning and monitoring, as there is a higher probability of human triggered disasters in densely populated areas. Design/methodology/approach – This study examined 10 years of more than 1,000 oil–gas disasters that were caused by humans in the upstate New York area to illustrate how a prescriptive model could be developed. Findings – A statistically significant predictive model was developed that indicated humans in certain industry categories were approximately six times more likely to have an oil–gas accident resulting in environmental pollution. Research limitations/implications – A prescriptive environmental protection model based on human accident behavior would generalize to all levels of government for policy planning, and it would be relevant to environmental protection groups in any region with a large population of humans using oil and gas (that covers most countries on earth). Originality/value – The empirical risk management literature was reviewed to identify factors related to environmental accident prediction with the goal of developing an explanatory model that would fit the oil–gas human accident data.