| In the coal mine safety production,the gas disaster has been the most important enemy that threatens the safety of the underground mine.According to related statistics,since 1949,the gas disasters lead to catastrophic events that one hundred people were killed up to more than 20.Throughout the coal mine safety history since the founding of the People’s republic of China,there is an upward trend about gas disasters,serious and especially serious safety accidents induced by gas disasters.theory,technology and engineering about prevention and control of coal and gas outburst have been a hot topic in the field of national science and technology research.China has a large amount of coal resources,but its permeability is generally low.According to the statistics of the relevant departments,93.4% of the coal mine in China is a soft coal seam,the permeability coefficient is mostly less than 0.05 mD,so the possibility of gas accident in the process of production is very high.In recent years,with the popularity of "Draining Gas Before Coal Mining" thought and technology of mature gradually,at the same time to obtain two kinds of energy of coal and coal bed methane,new problems have emerged in the management of gas,that is looking for a method that high gas content,but the low permeability of the coal seam can not only expand the range of gas drainage,but also to improve the gas drainage rate.In Zhongliangshan mine area of Chongqing provience,high gas content,low permeability and low f value of coal seam,and the coal seam in close steeply inclined thin coal seam group,and all of this make the gas extraction difficult,technical requirements high.In this paper,taking Zhongliangshan south mine as the research obiect,the gas occurrence condition of coal seam and existing pumping scheme are deeply analysised,at the same time,In line with the principle of increasing gas extraction quantity,reducing the risk of gas outburst accident,rapid and efficient gas drainage theory,technology,equipment research and engineering application are developed,innovative achievements have been made in the technology,equipment and engineering application of hydraulic gas drainage,and this has also become the core research results of this paper.The new idea proposed in this paper is the dynamic effect with high pressure water(cavitation,vibration and shock etc.)induced by coal seam dynamic process stress and rock fracture development accelerate the increase in high gas coal seam crack development,increasing the permeability of coal seam,and creating favorable conditions for coal seam gas extraction;Combined with the practice of the gas disaster prevention and control in Zhongliangshan mine,carry out the high pressure water jet cutting and hydraulic fracturing in the near distance,steep and low permeability thin coal seam group dynamic effect and the gas disaster control technology research;Through theoretical analysis and numerical simulation two kinds of methods,deduce the effect mode of high pressure water jet separation technology,analyse the characteristics of solid,liquid and gas in coal underwater pressure coupling characteristics among solid,liquid,gas in the coal under the action of water pressure were analysed,and study the dynamic evolution law of stress field and crack field,In order to determine the gas migration dynamic effect of high pressure water jet,hydraulic fracturing and fragmentation in the coal seam and the relationship between dynamic permeability;Through studying the technology of on the low permeability of the coal seam in high pressure water jet separation and hydraulic fracturing relieving stress and improving permeability technology,so as to realize gas drainage,disaster prevention and control technologysuccessfully application in gas disaster prevention and control project of Zhongliangshan south mine.The main research results are as follows:(1)Directional mechanism of hydraulic fracturing is studied.Based on the determination of the basic parameters of coal in the south of ZhongLiangShan,analyse the pressure induced cracking mechanism of the high-pressure water to coal seam,reveal the dynamic effect of pressure relief and permeability of coal seam.Firstly define the importance of the fracture control design of the fracture in the hydraulic fracturing,and then on this basis,according to the two main steps of the drilling water injection fracturing(drilling,water injection),analyse the stress distribution of the surrounding rock mass after drilling,respectively,then according to the different positions of the water injection pressure holes arranged in the coal,clarify the crack initiation principle in the case of the thickness of coal seam and the deviation angle of the borehole.(2)High pressure water jet cutting anti-reflection principle research.By collecting the coal samples in Zhongliangshan south coal mine,determining its physical and mechanical properties,and combining with fluid mechanics and damage mechanics theory,analysis of the mineral in Zhongliangshan south by using the function principle which is improving the extraction efficiency by the high pressure water jet cut penetration method : under the effect of the high pressure water jet,coal will produce cracks,at the same time,it also will happen the tension compression deformation and the shear deformation.Making the coal produce damage and and causing the crack expansion occur which exist in coal originally,at the same time,the coal will produces new damage cracks,reduces the stress,which can not only improve the permeability coefficient of coal,but also increase the exposure area of coal.The adsorption desorption of gas on coal is favorable to the adsorption,becoming a free gas,and it is benefiting to improve the extraction efficiency of the coal bed gas.(3)High pressure water jet cutting of key parameters and gas extraction effect research.Based on the basic parameters determination of the mineral of Zhongliangshan south analysis reasonably of high pressure water jet cutting hydraulic parameters.According to Crow cutting theory,analyze the main factors indepth that affect the depth of water jet cutting,there are mainly two: first,hydraulic parameters(including jet pressure and nozzle diameter),and the second,cutting conditions(including nozzle traverse speed and repeated cutting times).Through theoretical analysis of the influencing factors of the effective drainage radius of gas pre drainage holes,determine the test method of effective extraction radius,and do the drainage radius test after high pressure water jet cutting in the North mine of Zhongliangshan,the results of field investigation show that: in the 25 MPa slot under pressure,the calculated pressure water jet cutting radius of up to 1.57 m,natural emission radius can reach 4.58 m,effective radius of gas drainage can reach 9.14 m,the gas limiting extraction time is about 10 months,and the results are basically consistent with the field investigation.(4)Field test research and engineering management innovation of hydraulic technology.Based on the analysis of the mechanism of high pressure water to coal seam,the hydraulic fracturing technology and the existing fracturing equipment in Zhongliangshan can be applied to the gas drainage of the low permeability outburst coal seam in Zhongliangshan.Fracturing results show that: the BRW31.5/200 emulsion pump in the pump pressure under the condition of 24~27Mpa,40min~70min fracturing range up to 15m~25m;The BZW-200/50 type emulsion pump in the pump pressure under the condition of 35~40Mpa,80min~100min fracturing range up to 70m~100m;pressure 35MPa~40MPa,80min~100,min under the condition of fracturing range up to 70 m ~100m.Hydraulic fracturing technology can be applied to the coal seam in Zhongliang Mount,and can achieve a better effect of pumping.After the directional hydraulic fracturing test,the distance between the end hole of the gas pre drainage hole is increased by one times,which significantly reduced the amount of drilling engineering,and the average single hole gas drainage volume increased by 925%;The average extraction concentration is increased by 80%,and it can be used for a long time.Every time in the process of fracturing,emulsion pump are in full load condition,each fracturing injection water little difference,the maximum fracturing radius of the South Mine reaches 70 m,and the minimum fracturing radius of the North Mine is only 10 m,the fracturing effect of the South Mine is more obvious than in the North mine.Through the comparison and analysis of the South and North mineralized fracturing test of regional geological conditions shows,South Mine test of regional geological conditions is relatively good,within the test area,the faults and fracture are less,and the coal seam can be extended along the guide slot,and the amount of water loss is less than that of the coal seam.Therefore,in the selection of fracturing area,should be preferred in the area of better geological conditions.Zhongliangshan existing fracturing equipment(BZW200/50 emulsion pump,KJR19 x 6S-63 MPa high pressure pipe,high pressure flow meter,etc.),the sealing process and other basic to meet the existing fracturing needs.Based on the determination of the basic parameters of coal in the south of Zhongliangshan,develop the technology of high pressure water jet cutting applicable to Zhongliangshan Mining Area.Field engineering application shows that the South mine 140NEC4-C5 extraction lane,high pressure water jet cutting hole accumulative smoking 4.41 times the original volume of gas sampling drilling,the average standard of the high pressure water jet cutting hole pumping mining scalar is 4.2 times the original drilling to reach the expected goal of drainage pure volume increased by 50%.In the rock cross-cut coal drilling of the North-70NEC3 and the South-20NWC0,after using high pressure water jet assisted rock cross cut coal uncovering,drilling quantity reduced more than 40%.Contrast the effect of hydraulic fracturing and the geological conditions of coal seam in the experimental area in South mine with in North mine,it proved that the poor geological conditions in the region,mainly to take high pressure water jet cutting for pressure relief and permeability increasing,for the future development of steep and close distance coal seam group hydraulic measures summed up the engineering experience.In accordance with the relevant state policies and norms of gas drainage,and Combining with the practical engineering experience of pumping and mining in Zhongliangshan mine for many years,this paersummaries and fully implements the gas drainage engineering management pattern,which is suitable for short distance thin seam group,that is,"close to the hole,tight sealing,comprehensive pumping,long-term pumping" Twelve word measures.(5)Technology and management guarantee mechanism of outburst prevention in gas outburst mineWe have established the early warning indicator system and early warning model of coal and gas outburst mine inZhongliang Mount,and havecustomized a series of professional software system,completed the construction of coal and gas outburst real-time diagnosis and early warning system in Zhongliang Mount and the establishment of the guarantee system of early warning system.Thus,we realized the automatic management of outburst prevention information,outburst disaster real-time monitoring,online analysis,intelligent warning,comprehensive management,LAN and prominent warning information for immediate release and real-time sharing,achieved the danger of coal and gas outburst intelligent early warning,decision support,and improved the safety of mine outburst prevention technology and management level. |
