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Mine gas drainage is an important work in high gas outburst coal mines. How to improve the gas drainage concentration and drainage volume has always been the direction of exploration by coal mine technicians. In this paper, the experiment and field test of displacing CH4 with liquid CO2 were carried out. In the process of low temperature liquid CO2 phase transformation, a low stress and high permeability pressure relief area is formed in the coal and rock mass, so as to accelerate the free state of primary gas in coal and realize the intensified gas extraction of low-permeability coal seams. The results show that CH4 concentration and displacement efficiency in the displacement flow decrease at a greater rate and then stabilize; the cumulative CH4 displacement volume increases rapidly and stabilizes after reaching the critical time; the average concentration of gas drainage from single hole increases from 27.2% to 53.2%, and the gas drainage purity increases 2.3 times from 0.018 m3/min to 0.041 m3/min. The technology is simple to operate, does not produce high temperature and open flame, has the advantages of economy, safety, high efficiency and so on, it can be popularized and applied in gas mines. [ABSTRACT FROM AUTHOR]

This paper investigated the effects of gas pressure, in-situ stress, and coal strength on coal and gas outbursts (CGO) based on the laboratory CGO experimental data. Based on the hypothesis of the comprehensive of CGO, the single-factor control variable method was used to analyze and evaluate the relative outburst intensity, the characteristics of outburst holes, the distribution of pulverized coal, the drops of outburst gas pressure, and the pulverized coal density under different outbursts experimental condition. The improved CGO energy equation and instability criterion are proposed as a direction to study the occurrence of CGO as an energy evolution direction. Furthermore, the results shows that the initial outburst gas pressure was 0.45 MPa during the experimental conditions of in-situ stress was 5 MPa, and the coal strength was 0.24 MPa. The gas pressure is directly proportional to the relative outburst intensity, while the in-situ stress and coal strength are inversely proportional to the relative outburst intensity. After the CGO occurred, the outburst coal always show spallation and pulverization characteristics. The results highlight that the gas pressure plays a key role in pulverizing and throwing out the pulverized coal, and the in-situ stress mainly plays a role in destroying the coal, and the coal strength plays a resistance role during the CGO occurs. It is also found that pulverized coal particles size less than 0.28 mm can be used to represent the distribution pattern of the total weight of outburst pulverized coal particles in the different outburst interval. These results clearly illustrate that using effective methods to control gas pressure, in-situ stress, and coal strength has an important role in preventing and controlling CGO on coal mining sites. [ABSTRACT FROM AUTHOR]

The objective of this paper is to identify the outburst danger of coal from the perspective of adsorption capacity, nitrogen adsorption experiments had been performed on six different coal samples. With cubic spline interpolation method, the amount of nitrogen adsorbed in the coal at p/p0 = 0.001, 0.01, 0.50, and 0.99 were obtained. The results show that the outburst coal has more micropores than that of non-outburst coal. When the relative pressure p/p0 is 0.001 and 0.50, six coal samples have significant differences in adsorption capacity. Using the adsorption amount of these two points as the quantitative indexes, six coal samples were classified into two types by iterative self-organizing analysis technique (ISODATA). Compared with the results of traditional classification, the results obtained by the new classification method in this paper are consistent with that. The iterative self-organizing analysis technique can be as a method to identify the risk of coal and gas outburst. The cluster center in the classification process can be dynamically optimized. The data obtained in the experiment are limited, and some experiments were needed to continuously optimize the cluster center to make it keep within a little range. This method has a deep understanding of the structure and the quantity of coal pores. It not only has an important significance for studying the mechanism of coal and gas outburst, but also makes the identification of coal and gas outburst easier. [ABSTRACT FROM AUTHOR]

Coal and gas outbursts classification has become more important than before due to the serious threat to the safety of coal production, in this paper, we proposed a novel combination model consists of feature decomposition and reconstruction, feature selection and feature extraction for classification of coal and gas outbursts. First, EMD is used to decompose the coal and gas outbursts index features into a number of different IMFS; Second, in order to find out the relevance of IMFS with regard to the features, a wrapper algorithm Boruta with the RF classifier is employed, and the IMFS which has high relevance with the feature are selected to form a new index feature, then the new obtained features construct new influencing factors that affect coal and gas outbursts; Furtherly, in order to eliminate the redundancy between the new generated features and the uncorrelation between the index features and outbursts, the LDA is used to extract the features with class differentiation. Finally, the SVM classifiers based on the optimal parameters by Bayesian optimisation algorithm is employed to evaluate the proposed feature extraction scheme. Experimental results show that the proposed comprehensive model can achieve significant performance in terms of classification accuracy and feature size compared to existing methods for coal and gas outbursts classification. [ABSTRACT FROM AUTHOR]

The section of appropriate prediction index is of great importance for coal and gas outburst prediction. The quantity of gas emission is a key factor directly relating to the outburst risk of tunneling working face in the coal roadways. Therefore, accurately predicting the quantity of gas emission is necessary and critical to prevent and control outbursts. In this paper, using the sphere diffusion equation of coal particle gas and radial unsteady flow equations of coal seam gas to analysis gas flow of fallen coal and coal wall, and a dynamic prediction model of gas emission is established including key factors, research shows that: (1) in tunneling working face, the change rule of gas emission of the new model, in which mechanical state, physical properties of coal seam, roadway tunneling parameters, and gas adsorption parameters are considered, is the same as that of the conventional index, which indicates the feasibility of the new model; (2) The new model shows that the gas emission is positively correlated with the gas pressure, driving speed and permeability coefficient of coal seam, and negatively correlated with the uniaxial compressive strength of coal mass; (3) By comparing the old prediction model of gas emission, the predicted value of the new model is closer to the measured value, fluctuating within a smaller range, and has a higher accuracy after taking the gas emission of coal particle into account. In addition, the multiple characteristics of the coal body in front of the working face are comprehensively considered. The research results offer practical significance for improving gas prevention and control of tunneling working face. [ABSTRACT FROM AUTHOR]

Underground coal seam gas drainage is an effective method to lower the risk of coal and gas outburst disaster. However, it is difficult to drainage gas in the low-permeability coal seam, especially low-permeability thick coal seam with a tectonic coal sub-layer. Due to the special structure of this coal seam, many conventional technologies are inefficient. In this paper, to stimulate the coal seam gas drainage, we proposed a hydraulic flushing cavitation technology. Theory analysis, numerical simulation and field tests ware carried out to study the stress relief and permeability increase after adopting this technology. The results indicated that a large hole was formed in the coal seam, which enlarged the scope of stress relief and plastic damaged, and the coal seam permeability and gas drainage efficiency increased significantly. [ABSTRACT FROM AUTHOR]

Gas outburst can result in great loss of life and property during tunnel construction. Gas outburst in tunnels in non-coal formation is often more harmful than that in coal-bearing formation. In order to take effective countermeasures to prevent the occurrence of gas outburst during tunnel construction, it is essential to assess the risk of gas outburst before tunnel construction. This paper attempts to establish an assessment system for evaluating the risk of gas outburst in tunnels in non-coal formation in the survey phase of tunnelling based on the attribute mathematical theory. Based on the principle of relevance and operability, eight factors that influence the gas outburst in non-coal formation are selected as the attribute evaluation indices. Attribute measure functions are constructed to calculate the single index attribute measures for evaluation indices. The fuzzy Analytic Hierarchy Process is used to determine weights of evaluation indices. A confidence criterion is applied to recognize the risk grade of the evaluation object. The proposed attribute evaluation system is applied to assess the gas outburst risk in a tunnel in the survey phase. The evaluation results show good agreement with the practical situation of gas, verifying the applicability of this attribute assessment system. [ABSTRACT FROM AUTHOR]

Gas drainage for the single and low gas permeability coal seam is the key technical problem hampering efficient coal mine gas drainage and without which mining safely cannot be realised in China. To solve this problem, this paper presents an engineering method for enhanced coalbed methane recovery based on high-pressure hydraulic flush from floor tunnels. The first step is to evaluate when the likelihood of coal and gas outburst reaches dangerous levels according to coal seam parameters (including coal seam gas contents, gas pressure, permeability and geological conditions). With these parameters in place, the second step is to determine and optimise borehole parameters, such as the effective influencing radius of hydraulic flush, hydraulic flush space between drills and borehole number to make sure that the coal seam stress is fully released and permeability is dramatically increased. What is also included in this step is the employment of a high-pressure hydraulic flush of coal from boreholes drilled from tunnels developed in the floor of the coal seam. Parameters of water pressure, water flow rate and the volume of coal flushed out are selected based on on-site testing and numerical modelling. Finally, numerical modelling and onsite testing are employed to validate the effects of enhanced coalbed methane recovery, which is whether or not coal and gas outburst danger is eliminated according to the national standards of China. The results show that the technology could improve the permeability of a coal seam and that the gas seepage coefficient was increased by about 10.50 times, the pre-gas drainage ratio was up to 35.5–70.4% and the borehole gas drainage experienced a process of increase-steady-decrease, which delayed 15–20 days of the attenuation time. [ABSTRACT FROM PUBLISHER]

Coal mine methane (CMM) drainage is an effective method to curb the occurrence of coal and gas outburst and gas explosion, to reduce the amount of greenhouse gas emission, and to make full use of the clean energy(methane). Sealing in-seam horizontal boreholes plays a vital role in CMM drainage. Reasonable sealing length is an important factor to achieve high extraction efficiency and reduce the cost of construction. To determine the minimum reasonable sealing length of drainage boreholes, the radius of the fracture zone was obtained based on the ideal elastoplastic model, and this radius was taken as the minimum sealing length. The influencing factors of the minimum sealing length were analyzed and engineering verification test was taken in Zhongmacun mine in Henan province, China. The research results show that the minimum reasonable sealing length should be longer for a larger radius of the coal roadway and the coal seam with a deeper buried depth, while the minimum reasonable sealing length can be shortened with the increase of uniaxial compressive strength and the supporting stress of the coal roadway. The 11.07 m of sealing length calculated by theories was basically consistent with the 12 m of sealing length verified by the method of drilling cuttings. The reasonableness of sealing length (12 m) was verified by the test results of methane concentration and flux within 40 days. All those outcomes can provide references for other mines to determine the minimum reasonable sealing length of in-seam boreholes for CMM drainage. [ABSTRACT FROM AUTHOR]

We present a very high-resolution bathy-morphological map of the offshore sector around the Scoglio d’Affrica islet (northern Tyrrhenian Sea, Italy). The study area covers a sector of 45 km2, between 3 and 85 m depth. Its central part, i.e. the apex of the Ridge, is characterised by a flat or gently sloping seafloor, where three mud volcanoes, and 250 pockmarks are recognised. Differently, the western and eastern Ridge flanks are steeper and characterised by 60 quasi-rectilinear escarpments and small ridges, more than 20 morphological highs, and elongated channels occasionally floored by bedforms. The seafloor shallower than 40 m is covered by Posidonia oceanica, forming compact and continuous or fragmented meadows intermingled with sandy patches. The main map represents the bathy-morphological setting of the area, which is largely affected by fluid seepage, providing insights for habitat mapping and preliminary marine geohazard assessment due to the violent gas outburst from mud volcanoes. [ABSTRACT FROM AUTHOR]

As the depth of coal mining is gradually increased in China, the intensity of related coal and gas outbursts will become ever-greater. Accurate forecasting of coal and gas outburst is the key to preventing and controlling such incidents. This study uses gray relational analysis (GRA) to identify the four main geological and environmental indicators of coal and gas outburst risk based on the characteristics of the factors influencing coal and gas outburst and their relationships with outburst strength. A Fuzzy SPA (F-SPA) model was constructed using set pair analysis and the coupled weighting method, and coal and gas outburst intensity level was predicted for 25 locations in coal mine No. 8 in the Pingdingshan mining area using the F-SPA model and applying a confidence criterion. The forecast results were compared with those derived using three other methods as well as against actual outbursts that have occurred at those locations. The results of this comparison show that the method proposed in this study has a forecast accuracy of up to 96%. The reliability of the prediction model is verified by error analysis. This case study demonstrates the reliability of the proposed method and provides a new tool for the prevention and control of coal and gas outburst hazards. [ABSTRACT FROM AUTHOR]

Hydraulic cavity has been demonstrated to be an efficient gas extraction technology in the single, soft, and low-permeability coal seam in China. However, the permeability evolution around hydraulic cavity has not been fully understood due to the lack of the permeability model in the post-peak stage, which leads to a great challenge for the gas extraction simulation and thus the borehole design. Therefore, we developed a fully coupled dual-porosity gas extraction model that considers the effects of coal damage on the permeability evolution. Based on this model, we analyzed the permeability evolution and the gas migration characteristics around the hydraulic cavity and designed a hydraulic cavity scheme for the Shijiazhuang coalmine. The field application results prove that our simulation results are correct. [ABSTRACT FROM AUTHOR]