The Hole Sealing Technology of Solid-Liquid Materials with Three Pluggings and Two Injections for Gas Extraction Hole in the Coal Mine.

The sealing quality of the gas extraction holes determines the extracted gas concentration. Based on this, the paper reveals the basic principle of hole sealing by analyzing the gas leakage mechanism of the borehole. The hole sealing technology of solid-liquid materials with three pluggings and two injections for the gas extraction hole is proposed, and the hole sealing device and material are developed. Through testing the granularity distribution of the solid material, as well as the surface tension and contact angle of the slurry, the hole sealing material that can meet the requirements of accessible, sticky, and anti-deformation is selected. The sealing material enters microcracks and bonds coal rock more easily. First, the solid material is injected for hole sealing. Second, the liquid material can be injected repeatedly to maintain a high concentration for holes with poor sealing and gas concentration attenuation in the late stage of gas extraction. Field tests show that the gas concentration of solid material is 1.3 times that of the conventional material after 30 days of sealing. The liquid material injected after the concentration decline enables the gas extraction concentration to be recovered at 85%.

Culture medium optimization for producing biomethane by coal anaerobic digestion.

The culture medium in biogas field have been used in coalbed gas bioengineering (CBGB). However, there is a huge difference between the substrate of biogas fermentation and coal. It is necessary to study and optimize the culture medium in the anaerobic digestion (AD) system with coal as substrate. In this study, the single factor test and response surface curve analysis are used to clarify the essential components in the culture medium and the optimal content of these chemicals. The influence of a single component on microbial community structure and major metabolic pathways in AD system are discussed. Under the optimal conditions, SEM observation show that the coal surface sediment is significantly reduced after AD process. The results of GC-MS show that there is no significant difference in the composition and content of organic compounds in the liquid phase before and after the optimization; the microbial community structure and gene function did not weaken with the decrease of culture medium addition, but formed a more targeted and stable microbial community.

Low-Yield Genesis of Coalbed Methane Stripper Wells in China and Key Technologies for Increasing Gas Production.

For the problem where numerous coalbed methane (CBM) stripper wells exist in China, this paper analyzes the genesis of the stripper wells from the aspects of geological conditions and development technologies combined with the CBM development of some typical blocks. A series of key secondary stimulation technologies for CBM stripper wells are put forward, including low-damage fracturing fluid for preventing reservoir damages, proppants with multigraded sizes for supporting multilevel fractures, large-scale fracture network stimulation (FNS) for improving reservoir permeability, and coal measure gas development for increasing the exploitable resources within a single well scope, as well as coordinated stimulation of parent-child wells for the overall production improvement of low-yield blocks. Also, it is pointed out that all types of stripper wells could adopt the low-damage fracturing fluid and multigraded proppant and optimize the drainage schedule to inhibit reservoir damage and promote the maintenance of fracture conductivity. For resource-controlled stripper wells, large-scale FNS of coal seams, coal measure gas development, and coordinated stimulation of parent-child wells could be adopted according to the differences in resource abundance and coal seam distribution. For the stripper wells controlled by the coal structure and ground stress, FNS of the surrounding rock could be conducted to construct stable and efficient channels for CBM migration. In addition, by conducting large-scale FNS, the stimulation effect of fracturing-controlled stripper wells improves, while after unblocking and reopening the existing reservoir fractures of the drainage-controlled stripper wells, an optimized drainage schedule could be adopted to prevent reservoir damages and promote the maintenance of fracture conductivity.

Geochemical controls on the enrichment of fluoride in the mine water of the Shendong mining area, China.

Underground coal mining produces large amounts of mine water annually in the Shendong mining area of China. Due to the severe scarcity of water resources, mine water is extensively used for productive, domestic, and ecological demands. However, mine water exhibits high fluoride levels. For water-use security, reduction of fluoride exposure and environmental protection, knowledge of sources and geochemical controls of fluoride enrichment in mine water is required. The results showed that F- concentrations of mine waters vary from 0.05 to 11.65 mg/L, with a mean value of 1.96 mg/L, and 51% of the mine waters contain F- concentrations exceeding the Chinese drinking water standard (1 mg/L). The overall mine water quality is influenced by cation exchange, mineral dissolution, pyrite oxidation, silicate weathering and so on. The high-fluoride mine waters are all associated with Na-type, with a remarkable cation composition feature of higher Na+ and lower Ca2+ and Mg2+ concentrations. Overall, the high-fluoride mine waters are well-matched with the water environment with higher pH, TDS, and EC levels. PCA reveals that the geochemical controls on the enrichment of F- in mine waters include dissolution of fluoride-bearing minerals and F--OH- ion exchange; the former process is mainly caused by the decrease in Ca2+ concentrations resulting from Na + -Ca2+ cation exchange and mineral precipitation, and the latter process benefits from a highly alkaline water environment, facilitating the substitution of OH- in the mine water for F- within or absorbed on the minerals. Evaporation also controls F- enrichment in local areas.

Effects of orthokeratology lenses and frame glasses on anisometropia in primary and middle school students with low myopia in one eye / 中国学校卫生

Objective@#To investigate the effects of orthokeratology lenses and frame glasses on anisometropia in children with low myopia in one eye.@*Methods@#Between January 2017 and January 2018, 120 children of primary and secondary school age with myopic anisometropia low myopia in one eye presenting to the Second People s Hospital of Yunnan Province were selected as research objects,with average refractive error of(-1.00,-2.50)D in one eye and(-0.50,0.50)D in another eye. Participants were divided into an experimental group and a control group (60 cases per group), according to a random number grouping method. The control group were given frame glasses, while the experimental group were given orthokeratology lenses. A prospective study was conducted to compare and analyze the lengths of the posterior eye axis (AL) and spherical equivalent (SE), measured at different time intervals between the two groups.@*Results@#There were some initial differences in AL and SE between the two groups before the experiment began; however, this difference was not statistically significant (P>0.05). After 12 months, participants myopic eyes given the orthokeratology lenses had shorter AL[(24.91±0.11)mm] compared to the control group[(25.02±0.09)mm],participants health eyes had longer AL[(24.58±0.24)mm] compared to the control group[(24.20±0.13)mm]. One month after the subjects stopped wearing plastic mirrors,participants myopic eyes had higher SE[(-2.22±0.78)D] compared to the control group[(-2.64±0.21)D],and had lower that in the control group[(-0.96±0.84)(-0.37±0.54)D](t=4.02，-4.58，P<0.05).@*Conclusion@#In children with low myopia in one eye, compared with wearers of frame glasses, wearing corneal shape lenses can effectively restrain AL extend and control the progression of eye myopia. At the same time, wearing corneal shape lenses can promote contralateral healthy eye axial extension and an increase in diopter, reduce the anisometropia value, solve the problems of a binocular visual axis development imbalance, and promote coordinated eye development.

Characteristics of Dust in Coal Mines in Central North China and Its Research Significance.

The identification of the dust characteristics in coal mine working faces is essential for preventing coal dust explosion and occupational diseases. In this paper, dust samples from the coal mines in southern Shanxi province and Henan province, central North China, were selected as the research objects. The results show that the dust contains primarily organic matter, as well as considerable amounts of minerals. The chemical composition of dust at the working faces is the most complex. According to the proportion of PM10, the dust composition can be divided into three types: symmetrical, fine-dominated, and coarse-dominated. The wettability of dust increases with the increase of the oxygen-carbon ratio on its surface, increase of ash content, decrease of fixed carbon content, and decrease of particle size. In addition, the great variety of harmful elements in dust, some with a high content, can harm the human body. An explosion index is proposed to evaluate the likeliness tendency of coal dust explosion based on several key affecting factors. The surfactant (0.05% AN solution) adopted in this paper can significantly increase the wettability of coal dust and inhibit the generation of dust greatly, showing good ability in preventing coal dust explosion and occupational diseases.

The diversity of hydrogen-producing bacteria and methanogens within an in situ coal seam.

BACKGROUND: Biogenic and biogenic-thermogenic coalbed methane (CBM) are important energy reserves for unconventional natural gas. Thus, to investigate biogenic gas formation mechanisms, a series of fresh coal samples from several representative areas of China were analyzed to detect hydrogen-producing bacteria and methanogens in an in situ coal seam. Complete microbial DNA sequences were extracted from enrichment cultures grown on coal using the Miseq high-throughput sequencing technique to study the diversity of microbial communities. The species present and differences between the dominant hydrogen-producing bacteria and methanogens in the coal seam are then considered based on environmental factors. RESULTS: Sequences in the Archaea domain were classified into four phyla and included members from Euryarchaeota, Thaumarchaeota, Woesearchaeota, and Pacearchaeota. The Bacteria domain included members of the phyla: Firmicutes, Proteobacteria, Bacteroidetes, Actinobacteria, Acidobacteria, Verrucomicrobia, Planctomycetes, Chloroflexi, and Nitrospirae. The hydrogen-producing bacteria was dominated by the genera: Clostridium, Enterobacter, Klebsiella, Citrobacter, and Bacillus; the methanogens included the genera: Methanorix, Methanosarcina, Methanoculleus, Methanobrevibacter, Methanobacterium, Methanofollis, and Methanomassiliicoccus. CONCLUSION: Traces of hydrogen-producing bacteria and methanogens were detected in both biogenic and non-biogenic CBM areas. The diversity and abundance of bacteria in the biogenic CBM areas are relatively higher than in the areas without biogenic CBM. The community structure and distribution characteristics depend on coal rank, trace metal elements, temperature, depth and groundwater dynamic conditions. Biogenic gas was mainly composed of hydrogen and methane, the difference and diversity were caused by microbe-specific fermentation of substrates; as well as by the environmental conditions. This discovery is a significant contribution to extreme microbiology, and thus lays the foundation for research on biogenic CBM.