气体运移导致煤体结构变形演化特征研究——以注入氦气为例

气体运移引起煤体变形是研究煤层气抽采、预防瓦斯突出与温室气体的地质封存的核心问题。一般认为,有效应力变化是控制岩土类材料骨架变形的关键因素。但大量测试结果表明,煤的渗透率与有效应力(或者孔隙压力)表现出非线性关系。为此,应实时观测在静孔隙压力与三轴应力状态下氦气流动导致原煤变形演化全过程。在静孔隙压力状态下煤体积经历从收缩到回弹过程。注气压力越大,煤的收缩与回弹量越大,且收缩量总是大于回弹量。在三轴应力状态下注气初期煤样迅速膨胀。随着注气达到平衡状态,煤变形过程与约束条件表现出紧密相关性,即在应力约束下煤的膨胀率相比注气初期明显减缓;在位移约束下煤由膨胀转向收缩。上述试验结果表明,仅有孔隙压力作用下,煤基质与裂隙之间孔隙压力差可以压缩煤体,随着气体扩散的进行,可恢复煤的部分压缩变形量。在三轴应力状态下,煤的总体变形是裂隙与基质两者变形共同作用的结果。在应力约束下煤基质与裂隙可以自由膨胀。而煤体在位移约束下,因气体扩散导致煤基质膨胀只能挤压裂隙。根据上述实测结果探讨注气导致煤骨架变形演化机制,为深入理解煤裂隙与基质相互作用对煤渗透率演化提供试验依据。     

低温氮吸附法判识构造煤的实验研究

煤体结构是煤与瓦斯突出防治和煤与瓦斯共采的重要地质因素之一。为了区分煤体结构在地应力作用下的破坏程度,采集了淮北矿业股份有限公司桃园煤矿8283采煤工作面煤样,基于自相似原理和实验室内对煤样的加压模拟实验,通过煤基质纳米级孔隙在低温氮吸附-解吸曲线上的响应对比分析,建立了低温氮吸附法判识煤体结构的方法,并对淮北矿业股份有限公司桃园煤矿10号煤层内1026和1035工作面煤体宏观结构及微观孔隙发育特征进行了对比研究。结果表明,煤体微观孔隙结构变化与构造煤发育程度密切相关;随着煤体破坏程度的提高,在吸附-解吸曲线上表现为吸附量明显增大,纳米级孔隙的比表面积和比孔容明显增加,平均孔径略有增加;构造煤解吸曲线上有明显的陡降点,而原生结构煤的解吸曲线不具有这个特征。     

煤储层物性对甲烷碳同位素分馏的影响

煤层气作为一种吸附气,在储层中解吸扩散运移时甲烷碳同位素发生分馏。笔者通过采集山西晋城和新疆昌吉不同演化程度的煤样进行解吸试验,系统记录整个解吸过程中甲烷碳同位素组成的变化情况,研究了储层物性对甲烷碳同位素分馏的影响。结果表明：对于基质致密的煤样,解吸气体的δ13C1随时间增加逐渐变重,其变化的速率具有先快后慢的阶段性特点。对于基质疏松的煤样,解吸气体的δ13C1随时间增加先轻后重,这是由于取芯操作及煤样解吸过程中的基质收缩变形破坏了煤体原生结构,从而对正常的同位素分馏效应产生了影响。随着成熟度的增高,煤中微孔丰度增加,气体解吸扩散过程中受的限制增强,同位素分馏效果更显著。压裂裂缝的存在影响了煤层甲烷碳同位素的分馏效果,使得试采过程中井口气样δ13C1的变化规律不明显。     

煤岩强度离散性及三轴压缩试验研究

简述了煤的强度离散性原因。采用超声脉冲穿透法测量煤样波速并进行岩石力学试验,回归分析得出了煤岩试件声速与其力学参数之间的关系式,为尽可能避免因煤样离散性而带来的盲目试验提供了一条技术途径。采用MTS815岩石伺服试验系统进行了煤样三轴压缩试验。结果表明,与花岗岩等高强度岩石不同,由于煤的孔隙裂隙发育在围压作用下孔隙裂隙被压密闭合,煤的弹性模量随围压增大而增大,但并非线性关系;煤的轴向破坏应力及残余强度均随围压增大而增大。研究结论对于在破碎煤体中掘进的巷道的锚固机理研究有重要指导意义。     

受载原煤中瓦斯的扩散规律

为研究受载原煤中瓦斯的扩散规律,以原煤煤样为实验对象,利用自主研发的含瓦斯煤热流固耦合实验系统,在恒温的三轴加载条件下,进行了加载-吸附-解吸-再加载直至煤样破坏过程中的瓦斯解吸实验。研究结果表明,受载原煤的解吸量随时间变化规律符合颗粒煤瓦斯解吸的数学模型;在恒温恒围压下,随轴压的增大,受载原煤瓦斯的解吸量呈下降趋势;当轴压大于峰值强度后,瓦斯解吸量随轴压迅速增大;受载原煤煤样压密、线弹性阶段瓦斯解吸-运移速度随应力增大而线性减小;当煤样处于屈服阶段和峰值破坏阶段瓦斯解吸-运移速度随应力增大呈指数式增长。研究成果对瓦斯抽采,瓦斯突出机理研究有一定的理论价值。      

五轮山矿区可采煤层地质特征及含气性

贵州省五轮山矿区的含煤地层为龙潭组,钻孔煤心化验资料和瓦斯解吸数据、煤样压汞试验表明,可采煤层显微煤岩类型以微镜惰煤为主,煤化作用符合深成变质作用的一般规律,煤体原生结构煤占优势。主煤层孔隙结构特征的孔容和孔表面积差异较大,因此可采煤层含气较高,解吸能力相对较弱。     

构造煤中煤层气扩散-渗流特征及其机理

煤层气产出一般要经过解吸、扩散和渗流三个阶段,而煤层气在变形较强的构造煤中的扩散过程不同于在原生结构煤或变形较弱的煤体中的扩散。外界压力的变化只是构造煤吸附与解吸整个过程的一种外在因素,构造煤的变形和结构变化以及吸附势场的转换才是构造煤吸附与解吸的内在因素,是导致解吸过程不可逆性的根本原因。当构造煤体与CH4等多元气体间的吸附平衡状态遭到破坏时,变形较强的构造煤在降压后会产生解吸滞后现象;而变形较弱的煤,分子结构中的气体会很快解吸,第一阶段是气体解吸作用,第二阶段是游离气体从微孔向较大孔隙扩散的过程,气体扩散速率主要由第二阶段决定。构造煤气体扩散机理主要是由孔隙形状、大小、连通性和多元气体性质和状态所决定的。韧性变形煤的微孔隙比较发达,所以韧性变形煤以Knudsen扩散为主,脆性变形煤的中、大孔隙所占比例较大,而且脆性变形煤的孔隙之间具有很好的连通性,所以脆性变形煤以Fick型扩散为主,脆-韧性变形煤以及接近脆-韧性变形煤的脆性变形煤和韧性变形煤均以过渡型扩散为主。在试井渗透率比较中,一定变形程度的脆性变形煤>韧性变形煤,脆性变形煤中以过渡孔为主,其余为微孔,测不出亚微孔和极微孔,脆性变形还增加了各孔隙之间的相互连通性。韧性变形煤中过渡孔比表面积所占比例下降,微孔和亚微孔增高,扩散主要发生在微孔和过渡孔中,所以韧性变形煤的试井渗透率低于脆性变形煤的试井渗透率。     

煤体吸附膨胀变形模型理论研究

为了深入探讨煤体吸附瓦斯发生膨胀变形效应的力学行为,基于煤-气吸附界面的表面自由能变化等于煤体弹性能的变化基本假设,从理论上推导了煤体吸附膨胀模型中吸附膨胀变形表达式和吸附膨胀应力表达式,模型中各参数的物理意义明确。通过已有的试验数据分别从低气体压、中气体压和高气体压3个角度对吸附变形模型的适用性和正确性进行了验证。模拟结果表明,模型预测数据与已有的试验数据吻合度较高,能够很好地描述不同气体在不同压力条件下的煤体吸附膨胀差异性,拟合精度均较高;在综合考虑吸附膨胀应力和气体压力对煤体吸附膨胀变形影响前提下,忽略吸附气体体积Va对煤体吸附膨胀变形的影响。     

受载含瓦斯原煤解吸规律实验研究

依托自行研发的含瓦斯煤热–流–固–力耦合吸附/解吸实验系统,测定了不同围压和孔隙压力组合条件下,煤样加载破坏过程中不同加载阶段的瓦斯解吸量,并对实验数据进行了拟合,分析了轴压、围压和孔隙压力对含瓦斯原煤解吸规律的影响。结果表明:在煤样整个加载破坏过程中,受载原煤瓦斯解吸量呈现先减小后增加的“V”型变化趋势,且最小出现在屈服强度阶段,最大出现在脆性破坏阶段;受载原煤瓦斯解吸量随围压的增大而减小,随吸附平衡压力的增大而增大。      

水-力耦合下煤岩力学特性及损伤本构模型研究

为探究水分对煤岩力学特性的影响,利用含瓦斯煤热-流-固耦合三轴伺服渗流试验装置,开展不同含水率下原煤三轴压缩试验研究。基于弹性损伤力学,推导表征不同含水率下煤岩整体损伤的损伤变量,建立水-力耦合作用下煤岩分段损伤本构模型,得到煤岩的变形随含水率的变化规律。结果表明:(1)不同含水率下煤岩的变形规律基本一致,破坏过程可分为峰前应力阶段、峰后应力阶段和残余阶段;(2)随着含水率增大,煤岩受水分作用峰值应力降低,泊松比增大,弹性模量均呈线性单调减小,煤岩脆性逐渐减小;(3)所建立的损伤本构模型可以较好地表征不同含水率下全应力-应变过程中的变形特征,适用于分析不同含水率下煤体三轴压缩应力应变问题;(4)损伤修正系数q和损伤本构系数n共同决定了损伤本构模型的曲线形状,q反映了煤岩残余变形的特征,n反映了应力-应变曲线的峰后不同的软化程度。     

An improved permeability model of coal for coalbed methane recovery and CO2 geosequestration

An alternative approach is proposed to develop an improved permeability model for coalbed methane (CBM) and CO₂-enhanced CBM (ECBM) recovery, and CO₂ geosequestration in coal. This approach integrates the textural and mechanical properties to describe the anisotropy of gas permeability in coal reservoirs. The model accounts for the stress dependent deformation using a stress–strain correlation, which allows determination of directional permeability for coals. The stress–strain correlation was developed by combining mechanical strain with sorption-induced strain for any given direction. The mechanical strain of coal is described by the general thermo-poro-elastic constitutive equations for solid materials under isothermal conditions and the sorption-induced strain is approximated by treating the swelling/shrinkage of coal matrix equivalent to the thermal contraction/expansion of materials. With directional strains, the permeability of coal in any given direction can be modeled based on the theory of rock hydraulics. In this study, the proposed model was tested with both literature data and experiments. The experiments were carried out using a specially designed true tri-axial stress coal permeameter (TTSCP). The results show that the proposed model provides better predictions for the literature data compared with other conventional coal permeability models. The model also gives reasonable agreement between the predicted and measured stress–strains and directional permeabilities under laboratory conditions.     

空化水射流热效应影响煤体渗透率试验研究

对空化水射流空泡溃灭瞬间和空化噪声声场作用产生的热效应进行了分析,得到了热效应作用下的煤体渗透率表达式,并开展了不同空化条件(泵压、空化腔围压)下的煤体温度和瓦斯渗流试验。结果表明:空化腔围压一定时,温度随泵压的增大而升高;而泵压一定时,温度随空化腔围压的增大而减小。当热应力大于平均有效应力时,煤体热膨胀出现微变形,产生的张应力使裂隙变宽、数量增多;热效应使得游离瓦斯内能增加,分子自由程大大缩短,同时吸附瓦斯解吸使得煤基质发生收缩效应,导致微孔隙及微裂隙结构产生膨胀变形,从而影响煤体渗透率。试验得到渗透率随温度升高呈指数规律增大,与理论得到的渗透率表达式描述的规律相符。     

华北南部构造煤纳米级孔隙结构演化特征及作用机理

构造煤是在构造应力作用下,煤体发生变形或破坏的一类煤,在世界主要产煤国家皆有分布。构造变形不同程度的改变着煤的大分子结构和化学成分,而且也影响到构造煤的纳米级孔隙结构(<10 0 nm ) ,它是煤层气的主要吸附空间。通过构造煤显微组分和镜质组油浸最大反射率的测定,采用液氮吸附法对不同变质变形环境、不同变形系列构造煤的纳米级孔隙分类、孔隙结构特征进行了深入系统的研究,并结合高分辨透射电子显微镜和X射线衍射对大分子结构和孔隙结构的分析,结果表明:不同类型构造煤纳米级孔径结构自然分类,可将孔径结构划分为过渡孔(15～10 0 nm )、微孔(5～15 nm )、亚微孔(2 .5～5 nm )和极微孔(<2 .5 nm ) 4类。低煤级变形变质环境中随着构造变形的增强,不同类型构造煤过渡孔孔容明显降低,微孔及其下孔径段孔容明显增多,可见亚微孔和极微孔,过渡孔的比表面积大幅度降低,而亚微孔的却增加得较快。从脆韧性变形煤至韧性变形煤,总孔体积、累积比表面积、N2 吸附量随着构造变形的增强,这些结构参数均迅速增加,但中值半径进一步下降。非均质结构煤孔隙参数与弱脆性变形煤相当。中、高煤级变形变质环境形成的各种类型构造煤与低煤级变质变形环境相比,孔隙参数的变化基本一致。但不同类型构造煤的变化又有所区别     

Study on frost heaving characteristics of sandstone under different freezing conditions北大核心CSCD

At present,artificial freezing method has become one of the effective methods for coal mine shaft to pass through water-rich soft rock strata,which can stop the movement of groundwater and limit the deformation of surrounding rock. In order to study the frost heaving characteristics of sandstone under different freezing conditions,frost heaving tests of saturated and dry Cretaceous red sandstone samples under different freezing rates （10 ℃·h-1,5 ℃·h-1,2 ℃·h-1,1 ℃·h-1）and different confining pressures（5 MPa,10 MPa,15 MPa,20 MPa,25 MPa）were carried out by using GCTS（Geotechnical Consulting & Testing Systems）servo-controlled low temperature and high pressure triaxial rock testing system. In this paper,based on the existing theory of physical and mechanical properties of frozen soil,we studied the frost heaving law of sandstone under different freezing conditions and explored the frost heaving mechanism. The result shows that in the process of cooling,the dry rock sample always produce cold shrinkage deformation,while the saturated rock sample first produce cold shrinkage deformation,then produce frost deformation,and finally the deformation tends to be stable. The deformation of saturated rock samples is much larger than that of dry rock samples. The larger the stress level of rock samples at the same temperature is,the smaller the frost deformation is,which shows a linear negative correlation,mainly because the high confining pressure limits the volume expansion of the water phase in the pore inside the rock samples when it becomes ice. The frost deformation of rock samples is mainly affected by confining pressure and water content,while the frost heaving rate is mainly affected by cooling rate. Under this test condition,the higher the cooling rate of sandstone is,the higher the frost heaving rate is,and the relationship between them is approximately linear. For saturated rock samples,the confining pressure reduces the rock frost heaving by limiting the expansion during the phase transformation of ice water,and the temperature affects the rock frost heaving by affecting the freezing rate of pore water and the thermal expansion and cold contraction of rock skeleton. For dry rock samples,the deformation is mainly due to the volume contraction of rock mineral particles caused by thermal expansion and cold contraction effect,and the greater the temperature change,the greater the deformation. Based on the experimental results and theoretical analysis method,a calculation formula of rock frost heaving considering the influence of confining pressure was established. By calculating the frost heave of sandstone samples under different confining pressures,it is found that the calculated values are in good agreement with the experimental results. Moreover,according to the calculation formula of frost heaving,the influence factors of rock frost heaving during freezing can be divided into two categories：internal cause and external cause. The internal cause includes porosity,saturation,volume modulus of ice and rock skeleton,and the external cause includes temperature and confining pressure. For saturated rock,the frost heaving is mainly affected by factors such as confining pressure,temperature and porosity. When the saturation,porosity and freezing rate are low,the rock may only produce shrinkage deformation,because these indicators determine whether the rock produces frost heave or freeze shrinkage. The mechanism of rock frost heaving is very complicated due to the interaction and restriction between the internal and external factors and the dynamic changes of rock micro-structure and mechanical properties during the process of frost heaving. The research results can provide theoretical reference for freezing construction scheme design of deep coal seam mine construction,and also provide a theoretical basis for the study of physical and mechanical properties and engineering application of soft rock in frozen soil area. © 2022 Science Press (China).     

含瓦斯煤孔隙率和有效应力影响因素试验研究

以孔隙率基本定义和力学平衡原理为出发点,充分考虑由煤层瓦斯的吸附膨胀和解吸收缩、温度效应的热胀冷缩和煤体骨架受孔隙瓦斯压力的压缩共同引起的本体变形,建立了在压缩条件下(扩容前)的含瓦斯煤孔隙率动态演化模型和以吸附热力学参数及瓦斯压力表达的有效应力方程,并分别根据现场实测孔隙率数据和含瓦斯煤三轴应力试验数据,对所建立的理论模型进行了验证。结果表明,理论计算值与实测资料和试验结论一致性较好,理论模型拟合精度较好,误差不大,所得结论对煤层气开采和矿井瓦斯灾害防治具有一定的指导意义。     

韩城矿区构造煤纳米级孔隙结构的分形特征

构造变形可以引起煤纳米级孔隙结构的变化,变形机制的不同对孔隙结构的影响程度也不同。煤的孔隙非均质性极强,传统实验方法难以准确地描述孔隙结构的复杂性,而分形理论提供了描述这一复杂性的量化方法。基于渭北煤田韩城矿区不同类型构造煤的低温氮吸附实验,采用分形FHH方法,定量表征了构造变形对煤纳米级孔隙结构的影响程度。结果表明:韧性变形煤比脆性变形煤的孔隙分形维数高,孔隙结构复杂,非均质性增强,导致毛细凝聚效应增强,吸附滞后突出;构造煤分形维数随着平均孔径的降低和中孔含量的升高而增大,说明构造变形程度越大,平均孔径越小,孔隙结构越复杂。研究认为,分形维数定量反映了煤构造变形的强弱,可以指示煤中纳米级孔隙结构的变形程度。      

Current Research Status and Prospect of Tectonically Deformed Coal

A number of studies have shown that development areas of weak deformation brittle series of tectonically deformed coal are often the favorable areas for coalbed methane development, and the distribution area of the mylonitic coal of ductile deformation is a danger zone of mine gas outburst. Therefore, faced with solving the key scientific issues and technical problems of the coal bed methane exploration and development and gas outburst prediction and evaluation, more and more attention has been paid to the research on tectonically deformed coal. This paper first systematically elaborated the main research progress on the concept and classification of tectonically deformed coals, their deformation characteristics, and the pore fissure structure and chemical structure. Then, it pointed out that there was a lack of research on the ductile deformation mechanism of coal, and this key scientific problem needs further research in the future. It seemed that the structural and geochemical process of chemical elements migration and accumulation during coal deformation was a new field which is worth exploring. Through refining stress sensitive elements, their distribution and evolution patterns in different stress-strain environments and different types of tectonically deformed coals might be revealed, and then they could become a predictive index which indicates the significance of distribution of tectonically deformed coals and gas outburst prediction. It was thought that geophysical response characteristics and research of detection theory and interpretation method of different types of tectonically deformed coal and gas enrichment area should be an important development direction in the future.     

脆性变形序列构造煤纳米孔隙和粗糙度的原子力显微镜研究

煤孔隙结构是煤层气勘探开发与煤矿安全研究中的关键问题之一。构造煤相比于原生结构煤非均质性强,是煤储层研究中的热点和难点。采用原子力显微镜,结合NanoScope Analysis和Gwyddion分析软件,对脆性变形序列构造煤的孔隙结构和表面粗糙度特征进行研究。结果表明:构造作用整体上促进了脆性变形煤孔隙的发育,但不同脆性变形构造煤受构造作用影响的程度存在明显差异。根据煤受构造作用影响的程度,脆性变形煤孔隙结构演化可划分为强弱2个阶段:弱脆性变形阶段(原生结构煤—碎裂煤—片状煤—碎斑煤)构造作用对煤体的孔隙结构影响较小,平均孔数量缓慢增长,平均孔径缓慢减小,该阶段构造作用主要促进了100~200 nm大孔的发育;强脆性变形阶段(碎斑煤—碎粒煤—薄片煤)构造作用对煤体孔隙结构产生了显著影响,平均孔数量迅速增长,平均孔径迅速减小,这一阶段构造作用主要促进了10~50 nm介孔和50~100 nm大孔的发育。这表明脆性变形构造煤孔隙结构并非简单的线性演变。不同脆性变形煤的算术平均粗糙度和均方根粗糙度参数分别为3.00~6.05 nm和3.94~7.62 nm,其中,弱脆性变形阶段粗糙度整体较高且无明显变化,而强脆性变形阶段粗糙度迅速降低。通过AFM剖面分析,建立了煤表面孔隙形态的数学模型。基于该模型的算术平均粗糙度模拟结果表明,大孔是煤表面粗糙度的主要贡献者,构造作用主要通过影响煤中的孔隙结构,进而影响煤的表面粗糙度。