兴隆坪隧道施工通风流场及天然气瓦斯分布规律研究

以成都至贵阳高铁兴隆坪天然气高瓦斯隧道压入式通风设计为案例,运用离散化的数学方法模拟、分析流体流动和热交换理论,对隧道开挖进行了通风数值模拟,研究通风状态下瓦斯的分布及运动规律,并对比研究压入式通风不同时间段洞内不同位置的天然气瓦斯浓度、压力、逸散速度的变化情况,数值模拟分析表明:在压入式通风条件下,隧道内还存在部分区域瓦斯浓度值偏高的情况。为防止瓦斯积聚并为使整个隧道瓦斯浓度值保持在允许范围内,在施工过程中需增设通风竖井并配合局扇作为补充措施,以确保施工安全。

Theory and practice of integrated coal production and gas extraction

The integrated extraction of coal and gas combines coal mining with gas capture. Taking into account the gas deposition and flow conditions in the Chinese coal basins, this paper describes the status of the theory and key technologies of this integrated extraction system, and presents its application and practice in the Shaqu, Zhongxing, Fenghuangshan and Pingmei mines. Areas for further improvements in future studies are discussed, focusing in particular on the fundamentals of the extraction system to make it greener, more scientific, and more advanced in both the exploitation and utilization of coal and the gas in coal.

Technology of gas drainage and utilization in Huaibei mining area

With the characteristics of coal seam geology and gas occurrence,a'ground-underground' integrated gas drainage method was formed,which can relieve gaspressure and increase permeability by mining the protection seams in conditional regions.After coal seam gas drainage,high gas outburst seam was converted to low gas safetyseam.In the coal face mining process,safety and high efficient coal mining were realizedby the measure of gas-suction over mining.In addition to the drainage gas for civil gasand gas power generation,the Huaibei Mining Group has actively carried out research onthe utilization technology of methane drainage by ventilation.On the one hand,it can saveprecious energy;on the other hand,it can protect the environment for people's survival.In2007,the amount of coal mine gas drainage was 120 hm3;the rate of coal mine gasdrainage was 44%.Compared with the year 2002,the amount of coal mine gas drainageincreased by two times.Meanwhile,the utilization rate of gas increased rapidly.

Coal and gas outburst mechanism of the “Three Soft” coal seam in western Henan

Based on the particularities of gas outbursts,i.e.,low gas bearing capacity and low gas pressure in the "Three Soft" coal seam in western Henan,we applied the theories of plate tectonics and regional structural evolution to investigate the mechanism of this seam and its impact on the coal seam gas formation.Our investigation revealed that coal and gas outbursts are distributed in a strip in a NW direction,with a number of high-penetration mines scattered towards the south side and low-gas mines largely located on the north side.We analyzed the statistics of 38 gas explosions and the rock-coal sturdiness number coefficient f of 167 sampling sites in the region and found the gas outburst mechanism that features a "low indicator outburst phenomenon".The mechanism is characterized by structural coal as its core,a low gas bearing capacity,low gas pressure and sturdiness coefficient f mostly less than 0.3.Our research results provide a theoretical foundation for effective control of gas disasters.

Gas pipeline explosion resistance technology

Based on the features and requirements of gas drainage system, an optimized explosion resistance technology is done after a comprehensive analysis and research about the triple IR （Infrared Ray） flame detection technology, explosion resistance valve technology and explosion resistance control technology. An intelligent PLC （Programmable Logic Controller） resistance control system is designed which can cut offthe gas branch quickly and accurately, and the controller have automatic pressure maintaining function, valve rotation limit function, remote and local control interlock function. The reliability and rationality of explosion resistance technology is verified by gas pipeline explosion propagation and resistance simulation test. Overall response time of explosion resistance system is less than 100ms, and the spread of fire in gas pipeline can be prevented effectively.

Pulsating hydraulic fracturing technology in low permeability coal seams

Based on the difficult situation of gas drainage in a single coal bed of high gas content and low perme- ability, we investigate the technology of pulsating hydraulic pressure relief, the process of crank plunger movement and the mechanism of pulsating pressure formation using theoretical research, mathematical modeling and field testing. We analyze the effect of pulsating pressure on the formation and growth of fractures in coal by using the pulsating hydraulic theory in hydraulics. The research results show that the amplitude of fluctuating pressure tends to increase in the case where the exit is blocked, caused by pulsating pressure reflection and frictional resistance superposition, and it contributes to the growth of fractures in coal. The crack initiation pressure of pulsating hydraulic fracturing is 8 MPa, which is half than that of normal hydraulic fracturing; the pulsating hydraulic fracturing influence radius reaches 8 m. The total amount of gas extraction is increased by 3.6 times, and reaches 50 LJmin at the highest point. The extraction flow increases greatly, and is 4 times larger than that of drilling without fracturing and 1.2 times larger than that of normal hydraulic fracturing. The technology provides a technical measure for gas drainage of high gas content and low permeability in the single coal bed.

Physical characteristics of high-rank coal reservoirs in different coal-body structures and the mechanism of coalbed methane production

The physical characteristics of coal reservoirs are important for evaluating the potential for gas desorption, diffusion, and seepage during coalbed methane （CBM） production, and influence the performance of CBM wells. Based on data from mercury injection experiments, low-temperature liquid nitrogen adsorption, isothermal adsorption, initial velocity tests of methane diffusion, and gas natural desorption data from a CBM field, herein the physical characteristics of reservoirs of high-rank coals with different coal-body structures are described, including porosity, adsorption/desorption, diffusion, and seepage. Geometric models are constructed for these reservoirs. The modes of diffusion are discussed and a comprehensive diffusion-seepage model is constructed. The following conclusions were obtained. First, the pore distribution of tectonically deformed coal is different from that of normal coal. Compared to normal coal, all types of pore, including micropores （〈10 nm）, transitional pores （10-100 nm）, mesopores （100-1000 nm）, and macropores （〉1000 nm）, are more abundant in tectonically deformed coal, especially mesopores and macropores. The increase in pore abundance is greater with increasing tectonic deformation of coal; in addition, the pore connectivity is altered. These are the key factors causing differences in other reservoir physical characteristics, such as adsorption/desorption and diffusion in coals with different coal-body structures. Second, normal and cataclastic coals mainly contain micropores. The lack of macropores and its bad connectivity limit gas desorption and diffusion during the early stage of CBM production. However, the good connectivity of micropores is favorable for gas desorption and diffusion in later gas production stage. Thus, because of the slow decline in the rate of gas desorption, long-term gas production can easily be obtained from these reservoirs. Third, under natural conditions the adsorption/desorption properties of granulated and mylonitized coal are good, and the diffusion ability is also enhanced. However, for in situ reservoir conditions, the high dependence of reservoir permeability on stress results in a weak seepage of gas; thus, desorption and diffusion is limited. Fourth, during gas production, the pore range in which transitional diffusion takes place always increases, but that for Fick diffusion decreases. This is a reason for the reduction in diffusion capacity, in which micropores and transitional pores are the primary factors limiting gas diffusion. Finally, the proposed comprehensive model of CBM production under in situ reservoir conditions elucidates the key factors limiting gas production, which is helpful for selection of reservoir stimulation methods.