【作者】 吴迪；

【导师】 孙可明；

【作者基本信息】 辽宁工程技术大学 ， 工程力学， 2013， 博士

【摘要】 针对我国煤矿开采过程中由于煤层赋存条件和开采技术等因素制约而导致的大量残煤及煤层气资源滞留井下的现实和缓解温室气体CO2的减排压力,结合残煤受开采扰动影响引起应力场变化和残煤内部形成由块状散体和实体组成的复杂结构,对CO2注入残留煤层过程中渗流、扩散、吸附、驱替置换CH4影响显著的特点,并考虑了温度对于CH4/CO2吸附解吸的影响,本文采用实验研究、理论分析和数值模拟相结合的方法,开展了CO2注入残留煤层非等温渗流实验、CH4和CO2单组分气体及CH4/CO2二元混合气的非等温吸附解吸实验、CO2驱替置换CH4实验以及煤层注入CO2驱替CH4的数值模拟研究,在考虑热力作用下残留煤层注入CO2驱替CH4的机理和规律方面取得了如下研究成果：(1)根据CH4和CO2的非等温渗流实验,揭示了CH4和CO2的渗透性随孔隙压力、煤样体积应力和温度的变化规律,即CH4和CO2的渗透性随孔隙压力变化符合正指数变化规律,随体积应力变化符合负指数变化规律,温度越高,CH4和CO2的渗透性越小,并得出CH4和CO2气体在煤中的渗流规律为非达西渗流。相同渗流条件下,煤样中CO2的渗透能力要高于CH4渗透能力1个量级。(2)根据CH4的非等温吸附解吸实验,进一步验证了块状型煤等温条件下吸附和解吸是可逆的、吸附量与压力之间符合Langmuir方程和解吸实验出现滞后现象等吸附解吸特征；在不同温度条件下,吸附和解吸规律变化具有分区性,在10℃-30℃区间,温度越高,吸附量下降梯度越大,吸附平衡时10℃的吸附量约为30℃吸附量的4-5倍；在30℃-50℃区间,温度变化对于吸附量和解吸量的变化幅度影响较小。利用Langmuir方程拟合出CH4气体在不同温度条件下的吸附解吸方程。(3)根据CH4/CO2混合气的非等温吸附实验,揭示了混合气吸附量和解吸量随压力、温度及组分配比的变化规律。在同一温度条件下,混合气吸附量随压力的变化规律符合Langmuir方程,混合气中CO2浓度越大,混合气的吸附量越大,CO2的吸附能力明显大于CH4,吸附平衡时CO2的最大吸附量约为CH4最大吸附量的2倍,相同条件下型煤试件吸附实验所得的吸附量小于煤粉的吸附量。CO2的吸附率和CH4的解吸率与煤对不同组分气体的分离因子有关,CO2相对于CH4的分离因子越大,CO2的吸附率和CH4的解吸率越高。在30℃-60℃C区间,温度对于混合气的吸附量影响较小,同一组分混合气吸附平衡时在40℃吸附量出现最大值。(4)根据CO2驱替CH4实验,揭示了煤样体积应力、孔隙压力和温度对于CH4驱替量的影响规律。在相同温度条件下,CO2相对于CH4分离因子越大的煤,注入CO2孔隙压力越大、注入时间越长、煤层体积应力越小,驱替效果越明显；在20℃-50℃区间,相同条件下CH4的驱替量变化趋势为V20℃>V40℃>V30℃>V50℃因此可以得出20℃是CH4的合理驱替温度。(5)建立了热力条件下残留煤层注入CO2驱替CH4的渗流、扩散、吸附、解吸的力学模型,并进行了数值模拟计算,模拟结果表明：注入的CO2气体是通过减少煤层CH4的分压和CH4/CO2之间竞争吸附双重作用来提高CH4的抽采率,残留煤层注入CO2可以促进煤层中CH4的解吸,进而提高煤层CH4的采收率和达到CO2地下封存的目的；同时环境温度的变化,也会对CH4的解吸量产生影响,温度越高,CH4越容易解吸,模拟结果与实验一致。更多还原

【Abstract】 According to the reality of large amount of residual coal and coal bed methane resources abandoned underground caused by the occurrence conditions in coal seams and the mining technology restrictions during the mining process and alleviating the pressure of the CO2emissions, combining with that the changed stress field induced by disturbance of mining residual coal and the complex construction composed of granular material in bulk and solid formed in residual coal have a obvious influence on seepage, diffusion, adsorption and CH4displacement-replacement during injecting CO2into coal seams, and considering temperature influence on CH4/CO2. adsorption-desorption, this paper carried out the non-isothermal seepage experiment of CO2, CH4/CO2single component and binary mixture non-isothermal adsorption experiment, CH4displacement-replacement experiment with CO2and its numerical simulation in coal seams during CO2injected with the combination method of theoretical analysis, experiment research and numerical simulation, the results on the displacement mechanism and migration law of CH4by injecting CO2into residual coal under coupled thermo-mechanical condition are as follows:(1) The CO2and CH4non-isothermal seepage experiment reveals the change rule of CH4/CO2permeability with pore pressure, coal sample volume stress and temperature, namely gas permeability satisfied the positive exponent change rule with the pore pressure change, satisfied the negative exponent change rule with the volume stress, the higher temperature the lower permeability of CO2and CH4, and the seepage rule of CO2and CH4in coal belongs to non-Darcy seepage, the permeability of CO2in coal is ten times larger than that of CH4in the same conditions.(2) The CH4non-isothermal adsorption-desorption experiment verified the adsorption desorption characteristics that in isothermal condition, adsorption and desorption on block briquette is reversible, the adsorption quantity and pressure satisfied the Langmuir equation and lag phenomenon appeared in desorption experiments; in different temperature conditions, adsorption and desorption change rule has regionality. Between10℃to30℃, the higher temperature, the more adsorption quantity gradient declined, adsorption quantity at10℃is4-5times larger than that at30℃when adsorption was balance; Between30℃to50℃, temperature change has little influence on adsorption quantity and desorption quantity. Fitted the CH4adsorption-desorption equation with Langmuir equation in different temperature conditions.(3) CH4/CO2non-isothermal adsorption experiment revealed the change rule of gas mixture adsorption quantity and desorption quantity with the change of pressure, temperature and the component proportion. In the same temperature conditions, gas mixture adsorption quantity change rule with pressure satisfied Langmuir equation, the more CO2concentration in gas mixture, the more CO2quantity, the adsorption ability to CO2is obviously more than that to CH4in gas mixture, the max CO2adsorption quantity is two times than CH4when adsorption is balance. In the same conditions, the adsorption quantity got from the experiment on briquette sample was less than that on coal powder. CO2adsorption rate and CH4desorption rate are concerned with the separation factor of different gas components to coal, the larger CO2separation factor relative to CH4, the more CO2adsorption rate and CH4desorption rate would be. Between30℃to60℃, temperature has less influence on gas mixture adsorption, the max adsorption quantity appeared at40℃in gas mixture with the same component.(4) Gas displacement experiment revealed the CH4displacement quantity influence rule with coal sample volume stress, pore pressure and temperature. In the same temperature conditions, the coal with more separation factor on CO2relative to CH4, the larger injecting CO2pore pressure, the longer injecting time and the less volume stress in coal seams, the better displacement effect; Between20℃-50℃, the displacement quantity change tendency is V20℃> V40℃> V30℃> V50℃under the same conditions, so20℃is the rational displacement temperature.(5) Established the diffusion, seepage, adsorption and desorption mathematical model of CH4displacement by injecting CO2in residual coal under thermo-mechanical condition, and simulated numerically, the results show that:CO2injected improved the CH4extraction rate through the double effects of declining CH4pressure in coal seams and competitive adsorption between CH4and CO2, and then improved the CH4recovery efficiency and realized the purpose of CO2underground storage; Meanwhile, the surrounding temperature change could also influence CH4desorption quantity, the higher temperature, the easier CH4desorbed, the simulation results above is consistent with the experiment.更多还原