1、 1 原文 Control and prevention of gas outbursts in coal mines, RiosaOlloniego coalfield, Spain Mara B. Daz Aguado C. Gonzlez NiciezaAbstract Underground coal mines have always had to control the presence of different gases in the mining environment. Among these gases, methane is the most important one
2、, since it is inherent to coal. Despite of the technical developments in recent decades, methane hazards have not yet been fully avoided. This is partly due to the increasing depths of modern mines, where methane emissions are higher, and also to other mining-related circumstances, such as the incre
3、ase in production rates and its consequences: difficulties in controlling the increasing methane levels, increasing mechanization, the use of explosives and not paying close attention to methane control systems. The main purposes of this paper are to establish site measurements using some critical p
4、arameters that are not part of the standard mining-control methods for risk assessment and to analyze the gas behavior of subvertical coal seams in deep mines in order to prevent gas incidents from occurring. The ultimate goal is the improvement in mining conditions and therefore in safety condition
5、s. For this purpose, two different mines were instrumented for mine control and monitoring. Both mines belong to the RiosaOlloniego coalfield, in the Asturias Central Basin, Spain and the areas instrumented are mined via subhorizontal sublevels at an actual depth of around 1000 m under the overburde
6、n of Mount Lusorio. During this research, a property favoring gas outbursts was site measured for the first time in an outburst-prone coal (8th Coalbed), gas pressure and its variations, which contributed to complete the data available from previous characterizations and to set some guidelines for a
7、ssessing the potential outburst-prone areas. A gas-measurement-tube set has been designed for measuring gas pressure as well as its variation over time as a result of nearby workings and to calculate permeability. The paper establishes the effect of overlapping of works, but it also shows the effica
8、cy of two preventive measures to be applied: high pressure water infusion and the exploitation of a protective coal seam (7th Coalbed), that must be mined preferably two complete sublevels before commencing the advance in the outburst-prone coalbed. Both measures constitute an improvement in the min
9、ing sequence and therefore in safety, and should be completed with a systematic measurement to control the risk: gas pressure in the 8th Coalbed in the area of influence of other workings, to establish the most suitable moment to renew the advance. Further researches could focus on ascertaining the
10、2 permeability, not only in mined areas but also in areas of the mine that are still not affected by mining work and on tuning more finely the ranges of influence of overstress time and overlap distance of the workings of the 7th Coalbed in the 8th Coalbed. 1. Introduction Coalbed and coal mine meth
11、ane research is thriving due to the fact that power generation from coal mine methane will continue to be a growing industry over the coming years in certain countries. For instance, China, where 790 Mm3 of CH4 were drained off in 1999 (Huang, 2000), has 30 Tm3 of estimated CBM potential in the deve
12、loped mining areas (Zhu, 2000). The estimate by Tyler et al. (1992) of the in-place gas in the United States is about 19 Tm3, while Germanys total estimated coalbed methane resources are 3 Tm3, very similar to Polish or English resources (World Coal Institute, 1998). This increase in the CBM commerc
13、e has opened up new lines of research and has allowed the scientific community to increase its knowledge of some of the propertiesof coal and of methane gas, above all with respect to the properties that determine gas flow, which until now had not been sufficiently analyzed. Some of these parameters
14、 are the same ones that affect the occurrence of coal mining hazards, as methane has the potential to become a source of different fatal or non-fatal disastrous events. 2. Description of the Asturian Central basin and of the 8th Coalbed The 8th Coalbed of the RiosaOlloniego unit, located in the Sout
15、hwest of the Asturian Central Coal Basin (the largest coal basin in the Cantabrian Mountains, IGME, 1985), has CBM potential of about 4.81 Gm3. This is around 19.8% of the estimated resources of the Asturian Central Basin and 12.8 % of the total assessed CBM resources in Spain (Zapatero et al., 2004
16、). 3.84 Gm3 of the CBM potential of the 8th Coalbed belongs to San Nicols and Montsacro: 1.08 Gm3 to San Nicols area and 2.76Gm3 to Riosa, down to the 800m level (IGME, 2002). The minable coalbeds of this unit are concentrated in Westphalian continental sediments (Surez-Ruiz and Jimnez, 2004). The R
17、iosaOlloniego geological unit consists of three seams series: Esperanza, with a total thickness of 350 m, contains 36 coalbeds with a cumulative coal thickness of 3.5 to 6.5 m； Pudingas, which is 700 m thick, has 35 coalbeds with a thickness of 57m； whereas the Canales series, the most important one
18、, I 800 m thick, with 812 coalbeds that sum up to 1215 m thick. This series, which contains the 8th Coalbed, the coalbed of interest in this study, has a total thickness of 10.26mat SanNicols and 15.13matMontsacro (Pends et al., 2004). Fig. 1 shows the geological map of the two coal mines, whereas F
19、ig. 2represents a front view of both mines and the location of the instrumented areas. In this particular study, the 8th Coalbed is situated at a depth of between 993 and 1017 m, in an area of low seismi intensity. Instantaneous outbursts pose a hazard to safe, productive extraction of coal in both
20、mines. The mechanisms of gas outbursts are still unresolved but include the effect of stress, gas content and properties of the coal. Other factors such as geological features, mining methods, bord and pillar 3 workings or increase in rate of advance may combine to exacerbate the problem (Beamish an
21、d Crosdale, 1998). Some of the main properties of the 8th Coalbed favoring gas outbursts (Creedy and Garner, 2001； Daz Aguado, 2004) had been previously studied by the mining company, in their internal reports M.B. Daz Aguado, C. Gonzlez Nicieza / International Journal of Coal Geology 69 (2007) 2532
22、66 255 Fig. 1. Geological map. as well as in the different research studies cited in Section 1: the geological structure of the basin, the stress state of the coalbed and its surrounding wall rock and some properties of both coal-bearing strata and the coalbed itself. The next paragraphs summarize t
23、he state of the research when this project started. Many researchers have studied relationships between coal outbursts and geological factors. Cao et al. (2001), found that, in the four mining districts analyzed, outbursts occurred within tectonically altered zones surrounding reverse faults； this c
24、ould help to delimit outburst-prone zones. In the 8th Coalbed, some minor outbursts in the past could be related to faults or changes in coal seam thickness. Hence, general geological inspections are carried out systematically, as well as daily monitoring of any possible anomalies. But, in any case, some other outbursts could be related neither to local nor general faults.
