高煤阶煤孔隙结构及分形特征

高煤阶煤与中低煤阶煤在孔隙结构特征方面存在明显差异,分形理论为定量描述高煤阶煤储层孔隙特征提供了有效手段。基于扫描电镜、压汞实验和孔渗测试,以华北地区最大镜质体反射率(Ro,max)在19%~295%之间的9个煤样为研究对象,采用分段回归的方法对各样品进行不同孔径段分形维数计算,并讨论了孔隙结构分形维数与孔隙体积百分比、Ro,max、孔隙度和渗透率的关系。结果表明,高煤阶煤微小孔发育,半封闭孔含量较高,孔隙连通性一般,且孔隙结构具有明显的分段分形特征,同一煤样的超大孔(孔隙半径r＞5 μm)、大孔(05 μm＜r＜5 μm)、中孔(005 μm＜r＜05 μm)和微小孔(r＜005 μm)的分形维数依次减小;各煤样超大孔、大孔、中孔分形维数均随Ro,max增加而增加,随对应孔隙体积百分比增加而减小;孔隙度或渗透率与超大孔、大孔和中孔、微小孔分形维数分别呈二次相关、线性正相关、负相关;各分形区间分形维数分布的偏度和峰度与孔隙度或渗透率分别呈高度正相关和负相关,这为高煤阶煤孔隙度、渗透率提供了理想的线性方程(y=ax+b)预测模型。     

川中大安寨段灰岩裂缝分形特征及孔隙结构模型

通过对川中大安寨段介壳灰岩中裂缝进行非常规自相似特征分析,探讨了裂缝及储层岩石孔隙结构的分形特征,认为岩石中的裂缝和孔隙都是复杂的分形体,运用实际资料证实了这种分形体的长程相关性,定量计算出分形维数,该维数可以作为定量评价单井裂缝发育程度的重要参数,以此为基础,提出了新的孔隙结构模型－阶梯状孔隙结构模型。     

页岩微纳米孔隙结构分形特征研究

页岩气作为非常规气,是一种重要能源。页岩的孔隙结构特征是衡量与评价页岩储层存储能力与可压裂性的重要参数。选取威远海相页岩（1#）、龙马溪海相页岩（2#）、瑶曲凝灰岩（4#）以及瑶曲陆相页岩（5#,6#）,进行压汞实验、氮气吸附性实验以及核磁共振实验。利用分形理论,表征孔隙结构的非均质性,揭示分形维数和孔隙结构之间的关系。结果表明:孔隙在0.1~100 μm范围采用压汞实验,陆相页岩样品得到的分形维数要比海相页岩样品大;孔隙在2~200 nm范围采用氮气吸附实验,海相页岩的分形维数比陆相页岩大;相比之下,孔隙在10 nm~10 μm范围采用核磁共振实验得到的焦石坝海相页岩与陆相页岩的分形维数大小比较接近。尤其是本文统计的氮气吸附实验样本中,焦石坝海相页岩的分形维数最大,即焦石坝海相页岩的微孔结构最为发育,非均质性最强。因此分形维数可作为一种用于评价页岩孔隙非均质性与储存压裂效果的重要参数。     

储层砂岩孔隙分形性质的研究

根据统计特征体测量分形维数的测试原理，用砂岩断面的扫描电镜图片半自动分析方法，对砂岩孔隙的分形维数和分形孔隙度进行了测试，得到了储层砂岩隙的分形性质与砂岩的成分结构及作岩作用的关系，文章还对分形范围，分形维数，分形孔隙度及分形孔隙度与总孔隙度之比值作了评述。     

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。      

阳泉新景矿高煤级煤的孔隙结构分形特征

分形理论是宏观上定量评价储层非均质性的有效手段。以阳泉新景矿高煤级煤样品压汞数据为基础,建立分形几何模型,定量描述了孔隙结构。实验结果表明：样品孔隙以纳米孔为主,孔径、比表面积及孔容也集中分布在纳米孔段。煤样孔径65 nm以上的孔隙具有显著的分形特征,分维值分布范围为2.89~2.99,体积增量呈现阶段式的变化,孔隙结构复杂;孔径65 nm以下孔隙几乎无分形特征,比表面积增量与孔径在对数坐标中呈线性关系;基于分形特征及分子运动规律,将储层孔隙以孔径65 nm为界划分为扩散孔和渗透孔2个大类6个小类。分维值与体积孔隙中值半径、总孔隙体积呈负相关,与孔径65 nm以上的孔隙体积、比表面积呈正相关,与孔隙度无相关性。分形分维值对储层结构具有较全面的表征能力,可以作为综合指标在煤储层孔隙研究中加以应用。     

应用分形理论研究煤孔隙结构

通过对淮南、淮北两个研究区内各煤矿不同煤级煤样进行的压汞法孔隙测量结果的分析，表明用分形维数可以表示煤的孔隙结构特征，而且煤孔隙体积分形维数随着变变质程度的增高而减小，渗透性随煤级的增加而减弱。     

基于热力学模型的煤孔隙结构分形表征

煤的孔隙结构复杂,难以用传统的欧氏几何理论描述其复杂性,而分形理论可定量表征孔隙结构的复杂程度。通过对渭北煤田韩城矿区10个煤样进行的压汞实验,采用热力学分形模型,获得了煤的渗流孔的分形维数,定量表征了煤的孔隙特征,并探讨了分形维数与渗透率的关系。研究表明：对于同等变质程度的煤来说,煤中吸附孔越多,孔隙分形维数越大;煤孔隙分形维数与渗透性呈负相关关系。由此可见,煤的渗流孔分形维数可作为煤储层渗透性评价的定量指标之一。     

基于分形理论的致密砂岩渗透率预测模型

渗透率是决定致密砂岩储层渗流能力并最终决定产能的关键因素。【目的】由于致密砂岩储层孔隙结构复杂、非均质性强,其渗透率变化范围大,预测困难,亟需开发适用于致密砂岩的渗透率预测模型。【方法】以塔里木盆地库车坳陷KS2气藏白垩系巴什基奇克组致密砂岩为研究对象,综合物性测试、薄片鉴定、扫描电镜成像分析、高压压汞技术、核磁共振技术及分形理论,对致密砂岩孔隙结构进行定性、定量表征。【结果】基于分形理论,充分考虑孔隙结构非均质性对渗透率的影响,提出了两个新的、基于分形理论的致密砂岩渗透率预测模型。【结论】与r_apex渗透率预测模型相比,r₂₀分形模型、SDR₍(>40))分形模型的渗透率预测精度分别提升了42%与20%。     

海相、海陆过渡相页岩矿物组成对页岩孔隙分形特征的影响

贵州地区海相和海陆过渡相富有机质页岩普遍发育,但页岩矿物组成差异大,页岩孔隙结构复杂,为定量研究矿物组成对页岩孔隙结构的影响,以低温氮气吸附和X衍射实验为基础,利用FHH模型计算孔隙分形维数并研究矿物组成对其影响。结果表明,海相页岩的分形维数D1为2.322～2.756,D2为2.756～2.914;海陆过渡相页岩的D1为2.538～2.814,D2为2.751～2.922,说明海相和海陆过渡相页岩的孔隙结构较复杂,海陆过渡相页岩的储集性较好,而海相页岩的储集性能变化较大,影响因素复杂。海相页岩孔隙的D2与有机质丰度呈"先正后负"的关系,与黏土矿物含量、石英含量呈"先负后正"的关系,与黄铁矿含量呈正相关;D1的影响因素复杂,与矿物组成不具有明显的相关性。海陆过渡相页岩孔隙分形维数与有机质丰度、黏土矿物含量、黄铁矿含量呈正相关关系,与石英含量呈负相关。有机质丰度和黏土矿物含量是影响页岩孔隙结构的最主要的因素。     

饱水过程中松散土体渗透性变化研究

针对三峡库区广泛存在的紫红色岩(土)的工程地质特征,考虑库区水位的变化,以黄腊石滑坡群的石榴树包滑坡表层原状松散土体为研究对象,设计一定流速条件下的饱水试验,探索在流动的水溶液饱和条件下紫红色松散土体渗透性随时间的变化规律,并分析变化原因。研究发现:饱水过程中,紫红色松散土体的渗透性有很强的时间效应,随着饱水时间的积累,渗透系数呈现显著的线性增大后减小并最终趋于稳定的规律。对比饱水前后土样微观结构以及化学成分分析结果,发现水流对松散土体颗粒的物理运移以及水对土体的化学溶蚀作用、水土之间的离子交换吸附作用影响土体的结构,从而影响了紫红色土体的渗透性。     

泥石流源区砾石土分形特征及其与渗透系数关系试验研究

以取自泥石流易发区的182个砾石土土样为基础,进行室内颗分试验,通过分形理论计算各土样的分维值,经计算发现,泥石流源区砾石土以一重分形为主,一重分形的土样占样本总数的88.46%,一重分形土样的分维值介于2.250～2.798之间;以此数据为基础配置土样,通过自制、可控的常水头试验装置进行渗透试验。试验结果表明,渗透系数k与分维值D之间有极显著的相关性,且在干密度为1.8 g/cm3时相关性最好。通过多元回归分析发现,不同密度条件下,k与D之间均有较好的幂函数关系;相同的分维值条件下土样的渗透系数随密度的增大呈减小的趋势,分维值在2.450～2.600之间时,样本的干密度 与渗透系数k之间的幂函数关系较为明显。试验结果可以为泥石流启动的临界雨量研究提供理论基础,提高已有预报模型的普适性及精度。     

A study on the permeability and flow behavior of surfactant foam in unconsolidated media

Foaming injected gas is a useful and promising technique for achieving mobility control in porous media. The foam flow is influenced by the foam ability, stability, bubble size and the grain size of the porous media. In this study, the effects of two surfactants, their concentrations, foam quality (gas content) and the additive on the foam ability and stability are evaluated. The results show that the better ability and stability of foam can be obtained through regulating the parameters mentioned above. The permeability test indicates that the foam possesses a lower flow rate than the surfactant solution. Not only that, the conductivity discrepancy among three sands is also reduced when foam is present. The primary mechanism for foam flow in different type of unconsolidated sand is Jamin effect which depends on the foam ability and stability. Experimental determination of the foam distribution and morphology in heterogeneous pores, via two-dimension sand plate by means of stereoscopic microscope is carried out to explain the effect of foam size–bubble size relationship on Jamin effect. The results show that when the bubbles are adequately stable, the flow behavior (transfiguration and fracture) of foam is determined by the relationship between the foam size and the pore size. The resistances arising from transfiguration and fracture lead to different foam conductivity in three sands. The more decrease of discrepancy between medium and fine sand is caused by the fact that transfiguration is able to generate more resistance than fracture.     

Mesoscale experimental study on chemical composition,pore size distribution,and permeability of tailings

To study the seepage characteristics of tailing sand, an indoor sand column test was performed with three kinds of tailing sand obtained from Henan and Shaanxi provinces, China. River sand, quartz sand, and glass beads were also employed for comparison. Using the nuclear magnetic resonance, the researchers studied pore size distribution and permeability under different hydraulic gradients. The chemical composition and particle morphology were analyzed by energy-dispersive spectrometry and X-ray diffraction. The results were as follows. (1) The three kinds of tailings sand are small in diameter, mainly in the range from 0.15 to 0.5 mm. Their diameter distribution is more concentrated than river sand. The surface of tailing sand is rough. As for chemical composition, tailing sand contains many kinds of metal elements. (2) With hydraulic gradient increasing, the micropores in the tailings samples become fewer, the larger pores grow in number, and the peak of the pore size distribution changes to the left; blocking is more obvious. (3) The small pores gradually decrease during the test. Under the influence of groundwater pressure, the smaller gravel could migrate and block tiny pores. The structure of particle arrangement becomes denser. Therefore, it would prevent the seepage liquid from passing through the medium. The permeability coefficient K decreases.     

非饱和黏土质砂的渗气规律试验研究

为了探讨非饱和黏土质砂的渗气规律,对常规三轴仪进行了改造,使其能够进行非饱和土渗气性量测,改进后的渗气装置具有构造简单、制样方便、试样均匀性好、加载系统稳定、可用量测的气压力梯度范围较大、提高了量测精度等优点,并解决了量测空气体积困难的问题和渗气试验气体从刚性壁和试样边缘流出的问题。使用该套仪器研究了不同干密度和不同含水率条件下气体流速与渗透系数随压力梯度变化的规律,分析了气体流速、渗气系数同含水率和干密度之间的依存关系,建立了渗气系数与含水率和干密度之间的函数关系。研究结果表明：试样在所研究的含水率、干密度范围,非饱和黏土质砂中气体流动可用达西定律描述。     

Analysis of a new surface-sampling technique for unconsolidated sand populations

A new surface-sampling technique for unconsolidated sands on aeolian dunes is introduced and analyzed in terms of an elementary mathematical model. The sampling bias inherent to the technique is modeled using a simple geometric argument. This shows that samples drawn from 2D slices of a 3D population are naturally biased toward larger sand grains, with the n^th moment of the surface (2D) distribution proportional to the (n+1)^th moment of the bulk (3D) distribution. Laboratory tests of the sampling technique allow an empirical relation for the sampling bias to be determined, and comparison shows the model and empirical relations to be in close agreement for the particular population distributions considered. Possible corrections to the model, as suggested by the empirical analysis, are also discussed.     

粗粒土压实特性及颗粒破碎分形特征试验研究

对多个级配不同含水率的粗粒土进行击实试验,研究粗粒土的压实特性和颗粒破碎分形特征。结果表明,粗粒土最大干密度随级配中粗粒含量的增大而增大,当粗粒含量P5=70%时,最大干密度出现最大值;当P5＞70%时,最大干密度又随粗粒含量的增大而减小,粗粒土击实破碎后的粒径分布具有良好的分形特性,破碎分形维数为2.279 0～2.892 2,均大于击实前粗粒土粒度分形维数;相同级配条件下,粗粒土破碎分形维数随含水率的增大而增大,且粗粒含量P5＞50%时,增幅显著;粗粒土破碎分形维数D与破碎率Bg存在良好的线性关系,且击实前后粗粒土粒度分形维数差值能客观表征颗粒破碎的程度;粗粒含量和含水率是影响颗粒破碎率的两个重要因素,但相对于含水率而言,粗粒含量对破碎率的影响更加显著。     

A probabilistic permeability model and the pore size density function

Mathematical interpretation of the pore size disribution (PSD) data as measured by mercury intrusion porosimetry was revealed in detail. The PSD data were commonly presented as cumulative intruded volume per gram of specimen versus pore size. In this paper, however, they were expressed in a dimensionless term for convenient mathematical operations. The pore size density function was deduced from the PSD data using the finite difference approximation and curve-fitting technique. For the prediction of permeability, first the published correlations between permeability and pore geometry were critically reviewed. A probabilistic permeability model based on the pore size density function was then developed, which can be thought of as a generalization of Childs and Collis-George's model. Predictions of permeability of the compacted soils studied using the developed model were very good for a wide range of permeabilities.     

松散承压含水层渗透系数变化规律与估算模型研究

我国华北隐伏型煤田的煤系普遍被第四系松散层覆盖,其中的松散承压含水层在煤矿生产中常带来矿井突水、地表沉降、井筒变形破坏等水文地质灾害,造成巨大经济损失和人员伤亡。渗透系数是反映松散承压含水层土体介质渗透能力的重要参数,其数值的合理估算,对该类煤矿水文地质灾害的防治具有重要指导意义。目前,华北隐伏型煤田松散承压含水层渗透系数往往仅通过现场抽水试验确定,基于地质勘探钻孔信息与数据估算松散承压含水层渗透系数的模型研究较少。通过收集淮北煤田祁东煤矿松散承压含水层已有抽水试验的钻孔信息与数据,选取承压含水层厚度、泥层砂层比、最厚砂层占比、有效应力与底砾层厚比作为影响指标,分别与渗透系数进行相关性分析。最终确定底砾层厚比、有效应力、泥层砂层比为关键影响指标,并分析其对渗透系数的影响规律。结果表明,松散承压含水层渗透系数随底砾层厚比的增加而增大,随有效应力和泥层砂层比的增加而减小。在此基础上,采用多元线性回归分析,提出了基于底砾层厚比、有效应力、泥层砂层比的渗透系数估算模型。并将该估算模型应用于淮北煤田祁南、朱仙庄、青东煤矿松散承压含水层的渗透系数估算,结果显示估算结果与试验值一致。     

南京粉细砂空间孔隙结构表征单元体确定

确定统一的表征单元体(REV)尺寸是研究土体细观孔隙结构时首先需要解决的问题。使用6.5μm分辨率同步辐射显微CT扫描南京粉细砂试样,从土样三维重构模型的5个代表性部位提取5组立方体孔隙REV,对每个REV采用最大球算法分析,建立孔隙网络模型,从中提取孔隙率、单位体积孔隙数、孔隙平均体积、孔隙最小体积、孔隙最大半径、孔隙最小半径、孔隙平均半径、孔隙截面积平均形状因子等8个孔隙结构参数,建立其与REV尺寸间的相关性。利用假设检验T检验和F检验,最终确定样品孔隙结构参数的统一REV边长尺寸为400像素,即2.60mm。该方法可用于砂土、粉土等颗粒土体细观孔隙结构分析。