【作者】 赵东；

【导师】 赵阳升； 冯增朝；

【作者基本信息】 太原理工大学 ， 采矿工程， 2012， 博士

【摘要】 煤层气的高效和安全开采,既可以防治矿井瓦斯灾害的发生,又可以提高能源的利用效率。针对采用过热水或过热水蒸气,加热煤层开采煤层气的施工方案和工艺,本文进行了较小煤试样的细观渗流试验研究、不同温度和水压作用下大尺寸煤试样对瓦斯的吸附解吸试验研究、毛细管中水和甲烷的运移机理研究以及相应的数值模拟研究。对既定方案所涉及到的水-热耦合作用下煤体瓦斯的吸附解吸机理,进行了较系统的研究,主要得到以下结论：1)成功研制用于固体—气、液二相流体渗流的细观试验装置,可以进行煤在显微CT观测下的吸附甲烷和高压注水试验,及其相应的观测和分析。通过对2mmx2.5mmx10mm的煤试样进行CT观测后得出,煤试样吸附甲烷后,相同区域、相同阂值的孔隙率下降约3%,但是随着吸附压力的进一步增加,孔隙率下降的趋势不明显。煤试样在高压注水后,相同区域、相同阈值的孔隙率下降约4%,但是随着注水压力的进一步增加,孔隙率下降的趋势不明显,并且卸载水压后,孔隙率仍会呈现微量的降低。2)采用自主研制的吸附—注水—解吸成套试验系统,进行了原位取芯得到的含瓦斯煤样在高压注水后的恒温(20℃)解吸特性试验,结果表明：含瓦斯煤样未注水时的自然解吸规律,与实际矿井的瓦斯涌出规律相近。水对含瓦斯煤样的解吸能力影响较大,等吸附平衡压力的水压注入含瓦斯煤样中,其解吸量只有自然解吸时的50%～70%,得到终态解吸率随注水压力变化的函数关系式。不同注水压力的解吸试验中,得到解吸率随时间变化的函数关系式,其影响因素主要是文中所定义的解吸时间效应临界值t0,注水压力越高,t0值越大。结合煤试样的孔隙分布规律,计算得出煤在不同水压作用下,水能够进入到煤中的临界孔隙尺度,此值越小,解吸率越低,推导得出煤体瓦斯解吸率与吸附平衡瓦斯压力和煤的孔隙分布相关的函数关系式。3)通过含瓦斯煤样在高压注水后的升温(30～110℃)解吸特性试验得出,注水后的煤样,瓦斯的解吸能力随着温度的上升逐渐增强,一旦达到或超过水的沸点后,解吸会发生突变。升温至90℃时,含瓦斯煤样在8MPa压力注水后的解吸率,要高于未注水自然解吸时的解吸率。得到解吸率随温度变化的函数关系式,与流体活性及表面吸附势有关。4)通过高压注水后煤样的恒温吸附瓦斯特性试验得出,相同初始吸附压力下,煤样的吸附速率随含水率的增加有不同程度的降低；相同时间内的吸附量,亦随含水率的增加而减少。得到终态吸附量和含水率之间,呈现一定的相关性。5)通过煤样的高温(30～270℃)吸附—解吸特性试验得出,定容吸附实验中吸附量的下降速率随温度的升高逐渐降低,吸附平衡压力的上升速率随温度的升高逐渐增大；而定压吸附实验中吸附量的下降速率始终随温度的升高而逐渐增大。得到在实验温度(30～270℃)、气体压力(≤7MPa)的范围内,煤对甲烷的吸附始终是第一类吸附,并且在恒温条件到达一定压力时,会出现吸附极限。得到单分子层吸附模型中的吸附参数a、b均随温度的升高呈现负指数规律的衰减,微观上表现为煤表面可吸附气体的吸附位活性随着温度的升高逐渐降低。6)以单一毛细一端封闭一端开口的煤壁毛细管为研究对象,得到水进入到煤中孔隙的孔径临界关系式,其作用机理：一是卸载水压之后,封闭管内的气体会推动毛细管中的水柱向外运动,因此,此时的管内气体压力会大于水柱产生的毛细管力；二是在管内的毛细管水柱不完全排出的前提下,会达到一个气液的平衡。并且得到温度作用下水—气流动的相变规律的不等关系式,说明了水的相变点是一个临界点,低于此值仍然是二相流的状态,而一旦高于此值,就转变为一相流,即可以对此进行单相甲烷气体流动的渗流解吸特性研究。7)建立了温度作用下煤中甲烷—水的耦合流动数学模型,此模型由含瓦斯煤样注水后的温度作用方程、气—水各自流动的运动方程以及连续性方程组成。8)通过对不同尺度、不同孔隙率下的微观孔隙级煤试样进行的数值试验,得出：相同的初始外界水压力下,试样的内部气体压力越大,水渗流的区域越小,水压/气压=2时的渗流区域大约是无气体压力时的2/3。对于薄板模型,恒温条件下,相同孔隙率模型的渗流速率与所选择的试样的尺度有关；相同尺度模型的渗流速率与模型孔隙率的大小有关。对于立方模型,渗流速率与试样尺度的关系不大。9)数值试验中,随着温度的上升,气体逐渐侵占原先水渗流的孔隙单元,而且温度到达一定值后,气体几乎会全部占据所有孔隙单元,并且水压/气压=10时所需要的温度值大约在240-270℃之间,而水压/气压=5时所需要的温度值只有120～150℃左右。拟合得出,气体渗流区域百分比随温度变化,呈现良好的线性相关性；对于薄板模型,线性相关性与孔隙率的大小和模型的尺度有关；对于立方模型,线性相关性不仅与孔隙率的大小和模型的尺度有关,而且还与升温前的渗流状态有关。更多还原

【Abstract】 The high efficiency exploitation and utilization methods of coalbed methane, not only the mine gas disasters were decreased but also energy utilized efficiencies were improved.For the industry project and technology of coalbed methane exploitation, superheating water or vapour was adopted to inject into coal seam afterwards so many fractures were shaped. The paper was stated theoretical study, meso-permeation of two phase fluid mechanics experiments, macro-large scale coal samples in laboratory on different temperature and water pressure of methane adsorption or desorption experiments, and micro-small scale coal specimen corresponding with laboratory ones in numerical studies. Finally, the adsorption or desorption law of coalbed methane influenced by coupling of water and temperature was studied systematically for the probable technology. And the results showed that: 1) The meso two phase fluid permeation testing machine of coal-gas-water was also successful manufactured. And the viewings of coal adsorbed methane and high pressure water injection experiments under micro CT were observing. It is presented for the coal specimen of2mm×2.5mm×10mm and showed that once coal specimen adsorbed methane, the porosity was decreased about3%at the same zone and the tendency was not obvious followed by gas pressure increased. Once after water injection, the porosity was also decreased about4%at the same zone. If external water unloaded, the porosity was still decreased.2) The adsorption-water injection-desorption testing machine was manufactured by own for room temperature (20℃) desorption characteristics experiments of high pressure water injection after adsorption methane using direct cylinder raw coal sample, the results presented that:the natural desorption law of experimental coal sample is the same as actual coal mine. Desorption percentages (PD) in different water injection conditions are obeyed one time effect formula, the value is determined by critical value of desorption time effect t0, the law is more water pressure, larger the value. Desorption characteristics of methane bearing coal sample are mostly influenced by water, PD are only50～70%times to natural at equality water pressure with gas pressure. Followed by water injection pressure increased, final PD is relative with water pressure. Combining porous distribution law of coal samples, the critical pore size-scale of water into coal sample was calculated in different water pressure. The smaller is critical value, the lower is PD. And PD of coal sample is related with equilibrium adsorption methane pressure and porous distribution law of coal.3) For the temperature raised (30～110℃) desorption characteristic experiments of coal sample in high pressure water injection after adsorbed methane, the results presented that:desorption capacity of methane bearing coal sample after water injection is improved as a function of temperature rose. Desorption will reach saltation once up to or exceed boiling point of water. And the PD in90℃after water injection is still larger than natural PD. There is a function relationship between PD and temperature; they are related with liquid activity and surface adsorption potential.4) For the methane adsorption experiments of water bearing coal sample and the results presented that:the methane adsorption capacity will decreased after block coal sample adsorbed water. It is existed functional relationship between adsorption capacity and moisture rate.5) For the high temperature (30～270℃) desorption characteristic experiments of methane bearing coal sample, the results presented that:the decreasing velocity of adsorption in fixed volume experiments is decreased with temperature rose; increasing velocity of equilibrium adsorption gas pressure is increased with temperature rose. The decreasing velocity of adsorption in fixed pressure experiments is increased with temperature rose. In experimental temperature (30～270℃) and gas pressure (<7MPa), the adsorption is still the first one of coal adsorb methane and would be reach maximum value once up to definite gas pressure at the constant temperature. It is defined the single molecular adsorption model. The adsorption parameter a and b in single molecular adsorption is decreased in minus exponential law as a function of temperature. The actual mechanism is adsorption activity at the surface of coal is decreased with temperature rose.6) In theoretical studies, coal base single capillary pipe which one side sealing the other opening is adopted as research object and pore size critical formula of water injecting into coal is deduced. There are two conditions in actual use:the first is after water pressure unloaded, the gas in pipe is move out so gas pressure was more than capillary force due to water; the second is there is a new equilibrium between gas and liquid if water still exists in capillary pipe. The inequality of phase change law coupling of liquid and gas influenced by temperature is deduced. It is presented that the phase change point of water is a critical one, there was two phase fluid state which less than it and become single phase state once more than it. In that case gas and liquid fluid has become gas fluid, and could be used as permeation and desorption features.7) The temperature and coupling fluid mathematical model of methane-water in coal has been deduced. It is composed of methane bearing coal sample equation as a function of temperature after water injection, kinematics and continuity equations of single gas and water.8) The corresponding numerical studies of micro porous coal specimen in different size-scale and porosity were preceded, and the results presented that:at the same initial external water pressure, the more inner gas pressure of specimen, the smaller seepage zone of water. The zone of water divide gas equal2is about2/3times of no gas. The seepage velocity is related with specimen size-scale for sheet model of same porosity at constant temperature, seepage velocity is related with model porosity of same size-scale. But the seepage velocity is not related with specimen size-scale for cube model.9) Porous units of former water become gas followed by temperature rose, and once up to definite value, all of the units are full of gas. Water pressure divide gas equal10will at240～270℃for all gas units, but only120～150℃with water divide gas equal5. Beyond results simulation, percentage of gas seepage area is displayed good linear correlation as a function of temperature. The linear correlation is related with porosity and size-scale for sheet model. And the correlation is not only related with porosity and size-scale, but also seepage condition before warming up for cube model.更多还原