Decarbonization of the mining industry on the basis of closing the energy generation, on the basis of cogeneration of coal mine methane, and on the internal consumption of the mine is a promising direction in ensuring sustainable development. Known problems of deep underground mining do not allow for realizing the potential of man-made gas reservoirs due to the deterioration of the conditions of development of reserves of georesources. The aim of the work was to improve recommendations for the substantiation of drilling parameters for undermined drainage boreholes for increasing methane production from unconventional coal-gas collectors. The authors’ approach innovation lies in the possibility of using the established patterns of better natural stability of undermined boreholes to optimize them as spatial orientation parameters in an existing drilling passport for the improvement of methane extraction productivity. For this purpose, smoothing (LOESS) of the experimental data of two similar types of wells was used; then deterministic interpolation methods in combination with a three-dimensional representation of the response function in “gnuplot” were used. As a result, it was found that the increase in the inclination angle from 40° to 60° leads to a significant transformation of the model of the studied process, accompanied by a decline in the dynamics of methane emission and a decrease in the distance of the productive work zone of this type of well from 13 to 5 m before the roof landing, which then is replaced by a sharp increase in the productive work zone up to 35 m ahead of the longwall face. This allows under specific conditions for recommending increasing the productivity of methane capex from technogenic disturbed coal-gas reservoir replacement of wells with a smaller angle of rise to the transition to a more frequent grid of clusters from wells #4.

/pdf/substantiation-of-drilling-parameters-for-undermined-3v9dvwxk.pdf

Substantiation of Drilling Parameters for Undermined Drainage Boreholes for Increasing Methane Production from Unconventional Coal-Gas Collectors

Overburden isolated grout injection (OIGI) can well reduce surface subsidence, waste emission, and coal resource waste while preserving the ecological integrity of mining areas, thereby becoming the development direction of green coal mining in the future. However, its influence law and control mechanism on methane emission under coal seam mining remain unclear. In light of this, data including methane emission and surface subsidence during the mining of the 22301 working face in Tunlan Mine was collected by on-site measurements through online methane extraction monitoring systems, leveling instruments, and electronic total stations. The collected data and geological information were subject to numerical simulation and theoretical analysis to explore the methane emission law and its controlling factors after OIGI. The results demonstrate the following: (1) The total methane emission decreases by 46% after the implementation of OIGI, primarily due to reduced methane emission from the adjacent seams into the mining coal seam. (2) After OIGI, the vertical stress on the coal and rock strata in goaf rises, while the stress on the surrounding coal pillars decreases; the stress in the whole stope tends to be distributed more uniformly. (3) A relationship between the overburden stress and permeability was established, which reveals that stress plays a major role in controlling methane emission from adjacent seams into the goaf. After OIGI, the rising stress on the overburden above the goaf reduces the porosity and permeability, narrowing methane migration pathways, consequently reducing the volume of methane emission from surrounding seams into the coal seam. Stress redistribution after mining gives rise to methane rivers and low-permeability walls around the goaf, the volumes of which decrease as the grouting pressure rises. Methane rivers are where methane accumulates, and pre-drainage boreholes from adjacent seams should be directed towards these methane rivers to achieve enhanced methane extraction. The conclusions of this study provide theoretical support for efficient methane extraction under OIGI mining. 

Influence law and control mechanism of overburden isolated grout injection on methane emission in the working face

Isolated overburden grout injection technology mining and grouting parameters discussion and optimization

Water–sand mixture inrush generally poses a significant threat to the safe operation of the quarry of coal mines. Therefore, proactive management initiatives are essential to enhance the impact resulting from mining operations. A novel approach involving grouting into the unconsolidated sand aquifer and the weathered zone was initially executed in the 1010-1 panel of the Wugou coal mine in Anhui Province, China. Considering the hydrogeological conditions of the study area, over 70 thousand tons of cement and fly ash were injected through 42 boreholes. Sampling, laboratory tests, similar materials model simulations, and numerical simulations of the trending and dipping profiles were all employed to elucidate the evolution and characteristics during the progression of the No. 10 coal seam. The outcomes illustrated that the grouting execution had transformed the structure of the porous media, weakened the watery media, and intensified the mechanical strength of the No. 4 aquifer and the weathering zone. This transformation proved beneficial in reducing the heights of the caving zone and water-conductive fracture zone, leaving more coal–rock pillars for safety. Twenty-seven underground detection drill holes and whole-space 3D resistivity exploration were adopted to verify its transformed property of low water content. During the mining process, the height of the caving zone at 19.70 m was measured through inter-hole parallel electrical detection. The pressure of hydraulic supports in the grouted area did not exceed the rated working pressure during mining. All of these findings highlight the significant impact of grouting in this study area. The successive safe mining of the 1010-1 panel demonstrates that grouting can be used to prevent water–sand mixture inrush during mining operations. 

A New Technique of Grouting to Prevent Water–Sand Mixture Inrush inside the Mine Panel—A Case Study

Investigations into the cementation properties and microstructural evolution of coal-derived solid waste-cellulose ether composite grout

The slurry diffusion radius is an important parameter in grouting engineering. In some cases, injection into partial overburden is needed in grouting engineering, and it is thus critical to control the slurry diffusion so as to reduce unnecessary grout take. In an effort to solve such issues in longwall overburden grouting, we proposed the addition of cement as a means of modifying fly ash slurry in order to reduce grout diffusion and grout take. The characteristics of the modified slurry were determined under different water-ash ratios and cement-blending ratios. The cement-blending ratio was found to have a small effect on the density of the slurry but a significant effect on the slurry’s precipitation rate and viscosity. The slurry diffusion experimental system was established to study the diffusion radius and consolidation. Results for both the fly ash slurry and the modified slurry revealed a circular diffusion pattern centered around the grouting borehole. The diffusion radius of the modified slurry made with 10% cement was 19.4% lower than that of the fly ash slurry, but its solidification thickness appeared to increase. The modified slurry diffusion had a two-stage effect: a “stability control stage” and a “consolidation control stage.” In the consolidation control stage, the diffusion radius of the modified slurry was smaller than that of the fly ash slurry, and this stage was the key to control the diffusion radius of the slurry. Field trials were conducted based on the results of the study, and grout take was reduced effectively. This research provides a theoretical basis for slurry diffusion radius control in longwall grouting.

Experimental Study on the Diffusion Radius of Modified Slurry Used in Longwall Overburden Isolated Grouting

Surface subsidence in coal mine areas can cause serious geological hazards. After a coal seam is mined, the overlying rock layers fracture, collapse, and expand; the fractured and bulking rock masses are then continuously compacted under the action of overburden load, which eventually leads to surface subsidence. Overburden isolated grout filling via surface boreholes, and high-pressure grouting to mining-induced fissures under the hard rock layer, uses the grouting pressure to compact the lower fractured and bulking rock masses in advance, replacing the subsidence void and effectively controlling the surface subsidence. The characteristics of rock mass collapse, bulking, and compaction associated with mining and grouting are the key to the design of grouting parameters and surface subsidence control. In this paper, a theoretical model of the rock masses’ compactness during grouting injection is proposed, which determines the compaction of rock masses under the action of grouting filling. An experimental study was conducted to reproduce the grouting pressure evolution and the rock masses compaction in response to grout filling. The results indicated that the rock mass compaction was small in the no-pressure stage, and that the low-pressure and pressure-boost stages were key to generating the compaction effect of the grout filling. It was found that compaction grouting substantially increased the filled volume by transforming the fractured and bulking space of the rock masses into a filled space. Using engineering measurement data, the rock masses compaction law for grouting is verified. This paper provides a theoretical basis for the design of overburden grouting parameters and the evaluation of subsidence control effectiveness.

/pdf/compaction-response-of-mining-induced-rock-masses-to-1ubdfqch.pdf

Compaction Response of Mining-Induced Rock Masses to Longwall Overburden Isolated Grouting

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Experimental Study on the Diffusion Radius of Modified Slurry Used in Longwall Overburden Isolated Grouting

Compaction Response of Mining-Induced Rock Masses to Longwall Overburden Isolated Grouting