煤-气-水耦合作用下低阶烟煤力学损伤及渗透率演化机制研究

发布时间：2018-04-14 20:31

  本文选题：低阶煤 + 内在水分　； 参考：《中国矿业大学》2017年博士论文

【摘要】：目前针对中高阶煤的理论研究和勘探开发已较为成熟,尽管我国的低煤阶煤层气储量也相当可观,但是目前仍处于科研攻关阶段。低阶煤具有不同于中高阶煤的物化性质和孔裂隙构成等特征,并显现出高含水率的特点,从而导致低阶煤在煤岩力学性质及固气相互作用等方面与中高阶煤存在较大差异。以园子沟井田低煤阶储层2#煤层(Ro,max=0.65%)为研究背景,针对2#煤层的高内在水分含量和“高压力、低含量”的瓦斯赋存特征,综合运用岩石力学、损伤力学、渗流力学和吸附科学等理论方法,开展了煤、气、水共存条件下,水分对煤的吸附与解吸特性、力学损伤特征和渗透率演化规律的影响研究,进而分析内在水分对抽采过程中瓦斯运移的影响。主要获得以下结论:1)低阶煤具有含量较多的羟基等含氧官能团以及较为发达的微孔孔隙,使得园子沟低阶煤的持水能力明显高于中高阶煤的,最高内在水分含量为9.91%;水分对低阶煤吸附能力的弱化影响显著,Langmuir体积从干燥状态的39.97cm3/g以68.7%幅度降低至含水率6.90%时的12.51cm3/g,这与低阶煤的强持水特性有关;相比传统的线性式,负指数式能更好地描述湿煤吸附量与含水率的关系。低阶煤的扩散系数与含水率表现出增减交替的变化趋势,这与气态水在煤孔隙内集聚后对瓦斯扩散的阻碍,以及瓦斯吸附量降低的综合作用有关。2)黏聚力降低是导致型煤和原煤遇水后强度弱化的主因;在常规三轴压缩试验中,不含瓦斯时,型煤和原煤的强度分别表现为指数式以及近似线性的降低趋势;原煤的黏聚力为3.49~7.93MPa,是型煤的大约6倍,并且水分对两种煤的内摩擦角影响不明显,而黏聚力均表现出显著降低的趋势。气-水共存时,煤吸附气体和水分造成了煤表面能的降低,导致煤的强度弱化;当瓦斯压力不变时,水分增加导致瓦斯吸附作用对煤强度的弱化影响逐渐减弱,因此随含水率增加,煤强度仍在降低,而瓦斯对煤强度的软化系数表现出增大趋势。3)构建了基于Drucker-Prager强度准则并服从Weibull函数分布的含瓦斯煤岩细观统计损伤模型。该模型可较好的反演含水瓦斯煤的应力应变关系,并反映出水分和瓦斯气体诱发并促进煤体损伤发展的特征。水分比瓦斯气体对声发射活动的抑制作用更显著,相比干燥煤样,不含瓦斯时饱水煤样的AE计数和能量累计值分别降低了14.32倍和23.42倍;并且随着含水率增加,煤岩的破坏呈现出由突然破裂型向稳定破裂型转变,脆性减弱而塑性破坏特征增强的趋势。4)煤基质吸附瓦斯气体和内在水分的膨胀变形效应,和有效应力共同影响着渗透率的动态演化。静水压条件等围压时,当内在水分含量较高时,煤的渗透率表现出随瓦斯压力增加而逐渐增大趋势,这是由于煤吸附瓦斯的膨胀变形效应因水分的吸附作用而变弱,此时有效应力起控制作用。全应力应变过程中,煤岩声发射活动和损伤变量与渗透率演化整体上表现出一致性,压密和弹性阶段,声发射平静,损伤变量基本为0,渗透率降低了数倍;峰后阶段,声发射密集,干、湿煤的渗透率骤增约2~3个数量级;损伤变量迅速增加,并趋近于1。5)构建了基于单轴应变假设,表征弹性阶段内煤岩渗透率演化并考虑水分影响的SD渗透率改进模型。利用该模型计算得到低阶煤吸附瓦斯的极限膨胀变形量与含水率符合负指数关系;结合煤的吸附参数、变形参数及渗透参数与含水率的关系,SD改进模型可较好的反演静水压下渗透率数据变化规律,并且能反映出不同内在水分含量条件下煤岩渗透率动态演化特征。全应力应变过程中,结合细观统计损伤模型和SD改进模型,并引入损伤变量和渗透率骤增系数,构建了应力扰动作用下考虑水分影响的渗透率模型。6)基于煤的“双孔-单渗”弹性介质特性,结合扩散方程、渗流方程和SD渗透率改进模型以及煤体变形方程,构建了煤、气、水耦合作用下的煤层瓦斯运移模型。COMSOL软件解算结果表明,初始瓦斯含量相同时,煤的吸附能力和初始渗透率对抽采过程中瓦斯运移以及煤层相对瓦斯含量的影响最大。因此,对于原位低煤阶储层,初始渗透率一定时,内在水分含量较高导致煤吸附能力较低、游离气含量比例增大而瓦斯压力也较大,对于煤层瓦斯抽采具有一定的积极作用。
[Abstract]:At present, according to the theoretical research and the exploration and development of high rank coal has been mature, although the low rank coal gas reserves in China are also considerable, but it is still in the research stage. The low rank coal has physical and chemical properties and pore fracture in high rank structure characteristics, and shows the characteristics of high moisture content the resulting low rank coal in the coal and rock mechanics and solid gas interaction with high rank differences. In the garden Gou mine low rank coal reservoirs in 2# coal seam (Ro, max=0.65%) as the research background, according to the 2# coal seam in high water content and high pressure gas occurrence characteristics low content, comprehensive use of rock mechanics, damage mechanics, seepage mechanics and adsorption science theories and methods to carry out coal, gas and water under the condition of coexistence, adsorption and desorption characteristics of coal with water, affecting the mechanical damage characteristics and permeability evolution law The research, then analyze the effect of internal water drainage in the process of gas migration. The main conclusions are as follows: 1) the low rank coal has higher content of hydroxyl functional groups containing oxygen and micro pore is more developed, so that the water holding capacity of garden ditch of low rank coal was significantly higher than that in high rank coal, high inherent moisture content 9.91%; water weakening of low rank coal adsorption capacity significantly affect the volume of Langmuir from the dry state at 68.7% 39.97cm3/g to reduce the moisture content is 6.90% 12.51cm3/g, and the low rank coal with strong water holding characteristics; compared to the traditional linear, negative exponential can better describe the relationship between adsorption quantity and wet coal moisture diffusion coefficient and moisture content. The low rank coal rate showed a trend or alternate, the obstacles of the gas diffusion and the water vapor concentration in coal pores, comprehensive cooperation and reduce the volume of a gas adsorption .2) is a major cause of cohesion decreases the strength weakening of coal and raw water; in conventional triaxial compression tests of the three, without gas, coal and raw strength respectively for the performance index and the approximate linear decrease trend; cohesion of coal is 3.49~7.93MPa, is about 6 times higher than coal, and the water of the two coal internal friction angle and cohesion effect is not obvious, showed significant decreasing trend. The coexistence of gas and water, coal gas and water adsorption resulted in the decrease of coal surface energy, resulting in the weakening of the strength of coal; when the gas pressure is constant, the increase of moisture leads to weakening of gas adsorption on coal the strength of the effect gradually weakened, so with the increase of water content, coal strength is still lower, and the gas of coal strength softening coefficient showed increasing trend of.3) Drucker-Prager was constructed based on strength criterion and obey the distribution function of Weibull containing gas The coal rock meso statistical damage model. The model of coal gas water inversion shows the relationship between stress and strain, and reflect the characteristics of water and gas induced damage of coal and promote development. More significant inhibition of water gas ratio on the acoustic emission activities, compared to dry coal samples, AE count and energy the gas containing water saturated coal samples of the cumulative values were decreased by 14.32 times and 23.42 times; and with the increase of water content of coal and rock damage by showing a sudden rupture to stable fracture transformation, brittle weakened and plastic damage characteristics of increased.4) expansion deformation of coal matrix adsorption gas and moisture the effective stress and affect the dynamic evolution of permeability. The hydrostatic pressure conditions of confining pressure, when high inherent moisture content, the permeability of coal showed a gradually increasing trend with the increase of gas pressure, which is due to The swelling deformation effect of gas adsorption of coal by adsorption of water becomes weak, the effective stress control. The complete stress-strain process, coal rock acoustic emission and damage variable and permeability evolution integralaffections consistency, compression and elastic stage, AE quiet, as the basic damage variable 0, the permeability decreased by several times; after peak phase, the acoustic emission intensity, dry, wet coal permeability increased about 2~3 orders of magnitude; the damage variable is increasing rapidly, and close to 1.5) was constructed based on the assumption of uniaxial strain, improved SD permeability characterization in elastic phase permeability evolution and considering effects of moisture model. The calculated ultimate low rank coal gas adsorption using the model of swelling deformation and moisture content accords with negative exponential relationship; combined with the coal adsorption parameters, deformation parameters and permeability parameters and water content, improved SD model can better anti Do the static permeability change rule data under pressure, and can reflect the dynamic evolution characteristics of coal permeability of different inherent moisture conditions. The complete stress-strain process, combined with the meso statistical damage model and improved SD model, and the damage variable and the permeability coefficient increased, constructed.6 permeability model under the action of force disturbance considering the effects of moisture) of coal "double - and single permeability" elastic medium characteristics based on the combination of the diffusion equation, flow equation and SD equation model and improved permeability deformation of coal, coal gas, construction, water coupling for coal layer gas migration model.COMSOL software calculation results show that the initial gas content of the same and the influence of coal adsorption capacity and initial permeability on the recovery process of gas migration and coal seam gas content. Therefore, for in situ low rank coal reservoir, the initial permeability of a timing, internal Higher moisture content leads to lower adsorption capacity of coal, higher free gas content and higher gas pressure, which plays a positive role in coal seam gas drainage.

【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TD712
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本文编号：1750898