Prediction of loess soil-water characteristic curve by mercury intrusion porosimetry

Mercury intrusion porosimetry(MIP)is a simple and fast way to obtain the pore distribution of soil and can be used to estimate the soil-water characteristic curve(SWCC).In previous studies,soil was assumed to be a perfect wettability material,and the contact angle(CA)of the soil-water interface was taken as zero in the SWCC prediction method.However,the CA has proved to be much greater than zero even for hydrophilic soils according to some soil wettability experiments,and it has a significant effect on predicting the SWCC.In this research,a method for predicting the SWCC by MIP,which takes the CA as a fitting coefficient,is proposed.The pore size distribution curves are measured by MIP,and the SWCCs of two loess soils are measured by pressure plate and filter paper tests.When the CA is taken as70°and 50°for the wetting and drying process,respectively,the SWCCs predicted by the pore size distribution curves agree well with the measured SWCCs.The predicted suction range of the proposed method is 0-105 k Pa.The consistency of the results suggests that utilizing the MIP test to predict the SWCC with a proper CA is effective for loess.

Determining the soil-water retention curve using mercury intrusion porosimetry test in consideration of soil volume change

It is well-known that a close link exists between soil-water retention curve(SWRC)and pore size distribution(PSD).Theoretically,mercury intrusion porosimetry(MIP)test simulates a soil drying path and the test results can be used to deduce the SWRC(termed SWRCMIP).However,SWRCMIP does not include the effect of volume change,compared with the conventional SWRC that is directly determined by suction measurement or suction control techniques.For deformable soils,there is a significant difference between conventional SWRC and SWRCMIP.In this study,drying test was carried out on a reconstituted silty soil,and the volume change,suction,and PSD were measured on samples with different water contents.The change in the deduced SWRCMIP and its relationship with the conventional SWRC were analyzed.The results showed that the volume change of soil is the main reason accounting for the difference between conventional SWRC and SWRCMIP.Based on the test results,a transformation model was then proposed for conventional SWRC and SWRCMIP,for which the soil state with no volume change is taken as a reference.Comparison between the experimental and predicted SWRCs showed that the proposed model can well consider the influence of soil volume change on its water retention property.

Comparison of the Pore Structure of Ultralow-Permeability Reservoirs Between the East and West Subsags of the Lishui Sag Using Constant-Rate Mercury Injection

In this study, the differences in reservoir parameters, such as pore radius, throat radius, and pore-throat ratio, between the east and west subsags of the Lishui Sag are analyzed by using data obtained from a constant-rate mercury injection experiment. Furthermore, the quality of the reservoirs in the two subsags is systematically evaluated. Results show that the throat radius of the Lishui west subsag is larger than that of the east subsag, and this parameter has a positive correlation with reservoir quality. However, the pore-throat ratio of the east subsag is larger than that of the west subsag, which has an inverse relationship with reservoir quality. The main reasons for this reservoir difference can be attributed to sedimentation and diagenesis. The sedimentary facies types of the Lishui east subsag are the fan delta, shore lake, shallow lake, and shore shallow lake;their sandstone composition maturity is low;the clay mineral content is high;and the rock has undergone strong diagenesis. Therefore, the physical conditions of the reservoir are poor. However, the sandstones in the Lishui west subsag have weak cementation and compaction, mainly with an intergranular pore structure type, which leads to good connectivity between pores. Therefore, the storage performance and seepage capacity of the Lishui west subsag are better than those of the east subsag;the west subsag is the main area of oil and gas accumulation, as confirmed in the process of exploration and development.

Influence of Dry Density on Soil-Water Retention Curve of Unsaturated Soils and Its Mechanism Based on Mercury Intrusion Porosimetry

The soil-water retention curve(SWRC)can be used to evaluate the ability of unsaturated soils to attract water at various water contents and suctions. In this study, drying SWRCs for a kind of sandy soil were obtained in the laboratory by using self-modified SWRC apparatus. In addition, the porosity and the pore size distribution of the samples were investigated by a mercury porosimetry test in order to analyze the effect of dry density. Results showed that the soil-water retention of the soil specimens was strongly dependent on the dry density. Under zero suction, soil specimens with a higher dry density exhibited lower initial volumetric water content. The higher the dry density of soil, the more slowly the volumetric water content decreased with the increase of suction. There was a general and consistent trend for a soil specimen to possess a larger air-entry value and residual suction, while smaller slope of SWRC when it had a higher density. This was probably attributed to the presence of smaller interconnected pores in the soil specimen with a higher dry density. The proportion of large diameter pores decreased in comparison to pores with small diameters in the soil tested. The measured total pore volume of the soil specimen, which had a larger dry density, was lower than that of the relatively loose specimens.

Research on pore microstructure features for dredger fill based on mercury intrusion method

The material composition and microstructure have a comprehensive influence on geological engineering properties of dredger fill.The porosity of the dredger fill is an important characteristic of microscopic structure.Taken dredger fill from Binhai New Area in Tianjin as research object,the distribution trend of pore is obtained by granularmetric analysis,mineral composition analysis and mercury intrusion method.By discussing the variation regulation of dredger fill in two different kinds of processing methods,certain theoretical basis is provided for evaluating the engineering geological properties of dredger fill.It can be concluded from the test results that after drainage treatment,the porosity decreased and the structure unit changed from the relatively loose state to aggregate state.In certain depth range,the consolidation effect of dredger fill with drainage treatment is better than that without drainage treatment.

硼砂-硅酸钠碱激发矿渣砂浆干缩和微观特性试验研究

碱激发材料(AAMs)具有高强、低碳等优点,但是其相较于水泥基材料较大的干燥收缩率限制了其应用和推广。该文设计了一种复合激发剂,开展了硼砂-硅酸钠碱激发矿渣(AAS)砂浆的干缩和微观特性试验研究。采用压汞法(MIP)、X射线衍射(XRD)、扫描电子显微镜(SEM)和傅里叶变换红外光谱(FTIR)对样品进行测试和表征,分析了复合激发剂减缩机理。试验结果表明,硼砂-硅酸钠复合激发剂有效降低了AAS砂浆的干缩;XRD结果显示AAS砂浆中存在钠硼解石相(NaCaB_(5)O_(6)(OH)_(6)(H_(2)O)_(5));FTIR分析表明,最优硼砂比例下(20%),AAS砂浆的Si—O—T(T代表Si、Al或B)谱带明显增强,通过MIP分析得到AAS砂浆的中孔(<50nm)数量减少,这有助于缓解收缩应力,降低砂浆的干缩率。该研究结果可以为AAMs的减缩和应用提供参考依据,激发学生在建筑领域的碳减排思维,提升解决关键问题的能力。

干湿循环与盐溶液作用下红黏土-膨润土混合土体变与渗透特性

针对红黏土-膨润土混合土材料在干湿循环作用及复杂化学环境下的性能演化问题,开展了盐溶液入渗作用下红黏土-膨润土混合土的干湿循环试验研究,分析了干湿循环次数、膨润土掺入比、盐溶液浓度对压实混合土材料体变特征与渗透特性的影响,并结合压汞试验揭示了试样收缩变形与渗透系数变化的微观机制。结果表明:随着干湿循环次数的增加,压实红黏土-膨润土混合土试样累计收缩变形逐渐增大,收缩趋势随入渗盐溶液浓度的增加而增大;干湿循环过程中试样渗透系数呈先增大后减少的趋势,且随着盐溶液浓度增加而逐渐降低;增大混合土中膨润土掺量可以提高试样化学相容性,减少胀缩变形并减小渗透系数。压汞试验表明,盐溶液入渗及干湿循环作用导致土体孔隙“双峰”分布特征减弱,土体中的大孔数量及孔径减小,小孔略有增多;随着入渗的盐溶液浓度增加,小孔变化不明显,而土体总孔隙率及大孔数量减小,进而导致土体收缩变形增大、渗透系数减小。

深层砂岩储层孔隙结构特征及影响因素——以银额盆地拐子湖凹陷为例

以银额盆地拐子湖凹陷巴音戈壁组深层砂岩为研究对象,在探究储层基本特征的基础上,采用恒速压汞法区分孔隙与喉道,定量地表征孔喉特征参数;通过扫描电子显微镜和铸体薄片,定性地表征孔喉形态特征,分析微观孔隙的结构差异;结合孔喉分形维数划分孔隙类型,探讨影响储层孔隙发育的主要因素。研究结果表明,该区储层岩石类型以长石岩屑砂岩为主,成分成熟度较低,平均孔隙度为10.8%,平均渗透率为1.17 mD,属于低孔低渗型储层。储集空间类型主要为原生粒间孔、溶蚀孔和微裂缝,孔隙半径平均值为195μm,喉道半径平均值为3.5μm,储层的孔隙结构类型分为微孔小喉型、小孔小喉型和大孔粗喉型。研究区储层孔喉比总体上较大,良好的孔喉配置关系是影响储层物性的重要因素,影响孔隙发育的主控因素则是早期成岩作用、有机酸溶蚀和烃类充注的综合作用。经过相对较弱的压实作用和胶结作用改造后,原始碎屑为后期溶蚀提供了物质和空间基础,储层顶部和底部巨厚的富有机质泥岩提供了有机酸溶蚀和烃类充注的物源。

水下自护混凝土与钢筋握裹力试验研究

随着水下自护混凝土技术的推广和应用,其关键工艺参数水下保护剂浓度对水下自护钢筋混凝土结构性能的影响成为关注的热点。基于水下自护技术,在常用工作浓度范围内,对水下自护混凝土的素混凝土力学性能、混凝土与钢筋握裹力、微观孔隙结构开展了试验研究。试验结果表明:在不同水下保护剂浓度下,水下自护素混凝土抗压强度水陆强度比均超过80%;混凝土与钢筋握裹力水陆强度比约在40%~65%,水下保护剂浓度越高,混凝土与钢筋握裹力水陆强度比越低;混凝土基质区域孔隙率和混凝土与钢筋握裹力存在负相关关系;水下保护剂能够有效提升水下自护混凝土的力学性能,但水下保护剂浓度的提升会对混凝土与钢筋握裹力强度造成不利影响。因此,合理选择水下保护剂浓度并增加钢筋用量是提升水下自护钢筋混凝土工程的可靠性的重要举措。

单、双孔隙结构非饱和黏土孔隙分布变化规律试验研究

由于孔隙分布曲线的复杂性,在非饱和过程中黏土的孔隙结构变化规律尚不明晰,这导致基于孔隙分布模型计算土-水特征曲线存在较大的误差。针对这一问题,基于干缩试验与压汞试验,对单孔与双孔结构重塑黏土在脱湿过程中孔隙分布曲线的变化规律进行了定量分析。研究表明:在脱湿过程中孔隙分布曲线存在平移、缩放等变换。构建了t分布和双t分布函数,提取了孔隙分布曲线的自由度、峰值、峰值对应的孔隙直径作为特征参数来表征孔隙分布变化规律,发现了特征参数和土样孔隙比之间存在较好的线性关系。基于试验结果,建立了含水率-孔隙比-孔隙分布曲线关系,提出了一个考虑孔隙结构变化的重塑黏土土-水特征曲线计算框架。最后,与试验测得的土-水特征曲线进行比较,验证了所提出的计算方法的准确性。

基于低温液氮浸溶处理的淮南矿区松软中阶煤孔隙特征

为了研究低温液氮浸溶处理对淮南矿区中阶煤孔隙结构及其分形特征影响,采用不同液氮浸溶时间处理煤样,通过压汞法和液氮吸附法对煤体的孔隙结构加以测定,结合分形理论从多角度分析不同浸溶时间下煤体孔隙的发育规律及其尺度特征。结果表明:随着液氮浸溶时间的增加,煤体总孔容由198.089×10^(-3) cm^(3)/g上升至371.553×10^(-3) cm^(3)/g,总比表面积则由4.984m^(2)/g下降至4.496 m^(2)/g,效果显著;煤体吸附孔减小,渗流孔增加,吸附孔的孔隙连通性增加形成更大级别的孔隙,逐渐向渗流孔转变;渗流孔分形维数和吸附孔分形维数与液氮浸溶时间呈现负线性相关,液氮浸溶对于渗流孔分形维数比对吸附孔分形维数的影响程度更为显著;渗流孔分形维数和吸附孔分形维数随着液氮浸溶时间的增大逐渐降低,表明了煤体内部孔隙随着液氮浸溶时间的增大结构复杂程度降低,孔隙之间的贯通性增强,煤体孔隙度和渗透性的增加;综合分形维数随着煤体平均孔径和总孔体积的增加而减小,随着总比表面积的增加而增加,随着液氮浸溶时间的增加,煤体综合分形维数下降,煤体的吸附能力有所减弱,渗流能力有所增强,有助于提升淮南矿区低渗煤层煤层气抽采效果。

复合调理对淤泥机械压滤脱水特性的影响机理分析

机械压滤脱水是广泛应用的河湖淤泥脱水工艺,淤泥调理方式是影响机械压滤脱水效率的关键因素之一,采用聚丙烯酰胺(PAM)为代表的絮凝剂调理以及絮凝剂与无机调理剂联用的复合调理是2种典型的淤泥调理措施。复合调理近年来发展迅速,研究絮凝剂单一调理与复合调理对机械脱水效率的影响、探索作用机理,对淤泥机械压滤脱水的工艺优化具有重要意义。以官田湖底泥为试验对象,对比PAM、新型低碱性淤泥改性剂(LAC)的淤泥调理、脱水效果,分析PAM及PAM+LAC复合调理淤泥脱水工艺参数,利用压汞试验与扫描电镜(SEM)揭示复合调理对脱水泥饼结构影响。结果表明,调理药剂的促进作用主要在过滤脱水阶段最显著;LAC具有替代和强化PAM调理效果的作用,改善了泥饼卸料性能;加入LAC有助于维持泥饼骨架结构和增大泥饼孔隙,增加的孔隙以开口孔隙为主。

Fractal analysis of small-micro pores and estimation of permeability of loess using mercury intrusion porosimetry

Many popular models have been proposed to study the fractal properties of the pores of porous materials based on mercury intrusion porosimetry(MIP).However,most of these models do not directly apply to the small-micro pores of loess,which have a significant impact on the throat pores and tunnels for fluid flow.Therefore,in this study we used a combination of techniques,including routine physical examination,MIP analysis,and scanning electron microscope(SEM)image analysis,to study these small-micro pores and their saturated water permeability properties.The techniques were used to determine whether the fractal dimensions of six MIP fractal models could be used to evaluate the microstructure types and permeability properties of loess.The results showed that the Neimark model is suitable for analysis of small-micro pores.When applied to saturated water permeability,the results from this model satisfied the correlation significance test and were consistent with those from SEM analysis.A high clay content and density cause an increase in the number of small-micro pores,leading to more roughness and heterogeneity of the pore structure,and an increase in the fractal dimensions.This process further leads to a decrease in the content of macro-meso pores and saturated water permeability.Furthermore,we propose new parameters:the*Ellipse and its area ratios(*EAR).These parameters,coupled with 2D-SEM and 3D-MIP fractal dimensions,can effectively and quantitatively be used to evaluate the types of loess microstructures(from typeⅠto typeⅢ)and the saturated water permeability(magnitude from 1×10^(-4)cm/s to 1×10^(-5)cm/s).

陶瓷抛光废料制备UHPC的耐久性能试验研究

为探究陶瓷抛光废料(CPW)对超高性能混凝土(UHPC)耐久性能的影响,采用CPW分别取代部分水泥、粉煤灰和硅灰制备UHPC,主要研究了CPW对UHPC孔隙结构、力学性能、体积稳定性、抗氯离子渗透性能以及抗硫酸盐侵蚀性能的影响。结果表明,随着CPW分别取代水泥、粉煤灰、硅灰量的增加,UHPC的孔隙率增大,导致UHPC的抗氯离子渗透性能下降。CPW取代粉煤灰会增大UHPC的自收缩,而取代水泥和硅灰会减小UHPC的自收缩。CPW取代水泥会降低UHPC的抗压强度,但对硫酸盐侵蚀后UHPC的抗蚀系数和抗压强度有所提升;当CPW取代20%(质量分数)的水泥时,硫酸盐侵蚀90 d的UHPC的抗压强度达到最高。

掺有成孔碎渣的再生骨料混凝土的抗压及抗氯盐侵蚀性能

公路桥梁冲孔灌注桩施工会产生大量成孔碎渣,将其就近应用于公路桥梁的混凝土构件不失为一种有效对策。结合再生粗骨料的循环利用,同时考虑到沿海地区混凝土结构受氯盐侵蚀影响较大,文中采用成孔碎渣和再生粗骨料分别取代天然砂和天然粗骨料,制备了掺有成孔碎渣的再生骨料混凝土,开展了该类混凝土共计96个试件的抗压和抗氯盐侵蚀试验(48个抗压试件采用Φ150、高300 mm圆柱体,48个抗氯盐侵蚀试件采用Φ100、高50 mm圆柱体),以及成孔碎渣、河砂和砂浆各自的压汞测试,研究了成孔碎渣取代率(0、50%、70%、100%)和再生粗骨料取代率(0、50%、70%、100%)对该类混凝土抗压性能和抗氯盐侵蚀性能的影响。试验结果表明:该类混凝土的抗压强度总体上随着成孔碎渣取代率和再生粗骨料取代率的增加逐渐降低,且二者所引发的降幅大体相当;与再生粗骨料相比,成孔碎渣对该类混凝土弹性模量和峰值应变的影响相对有限;该类混凝土的氯离子迁移系数随成孔碎渣取代率和再生粗骨料取代率的增加总体上都逐渐增大,但成孔碎渣的影响明显低于再生粗骨料;随着成孔碎渣取代率的增加,该类混凝土的孔隙率总体呈现出先快后慢逐渐增大的趋势。实际工程中同时采用成孔碎渣和再生粗骨料时,建议二者的最大取代率都以50%为限。

低–中阶煤压汞实验可靠性分析与压缩性校正

低−中阶煤煤质软、在高压条件下煤基质压缩效应明显,应用压汞实验能否得到可靠的孔隙结构存在争议。选取4种低−中阶煤样品,通过对比不同粒度样品的进汞曲线、压汞前后的宏观与显微特征,建立高压段进汞量的校正方法,研究了压汞实验对低−中阶煤中孔隙测试结果的可靠性。结果表明:(1)柱状样品能保留更多的原生裂隙,有效避免低压阶段的粒间孔与麻皮效应,更适用于低−中阶煤的压汞测试;(2)宏观与微观尺度下均未发现汞在高压下对煤基质与孔隙的破坏作用,压汞孔容偏高主要是煤基质压缩效应的结果,压缩性校正后压汞测孔隙率与氦气测孔隙率基本一致,6~100 nm的孔容校正后与低温N2吸附结果的差值降低了29.87%~55.49%,表明压汞实验可以应用于低−中阶煤中孔隙结构的测定;(3)针对高压阶段的煤基质压缩效应,建立了压缩性累积校正方法,对大于20 MPa高压段数据进行校正后,进汞量降低了0.0170~0.0323 mL/g,纳米孔隙与低温N2吸附实验结果更为接近;(4)低−中阶煤中孔隙的孔容主要源于大孔,褐煤与长焰煤孔隙发育差异显著,褐煤压汞孔容为0.1687 cm^(3)/g,长焰煤压汞孔容介于0.0272~0.0720 cm^(3)/g,孔隙特别发育的样品,植物组织胞腔孔是孔容的主要来源。

一种基于压汞-吸附法的不规则泥页岩样品孔隙度测定方法

针对泥页岩样品孔隙度测定中柱塞样制备难度大,低孔、低渗样品测定结果误差大等问题,采用压汞-吸附法对泥页岩块状样品、粉末状样品分别开展高压压汞、低温N_(2)、CO_(2)吸附实验,通过Washburn方程、BJH模型及DR模型分析,获取岩样总孔容,与压汞实验所测岩样密度相乘,即可求取不规则泥页岩样品的孔隙度。实验结果表明,压汞-吸附法对于孔隙发育程度不一的白云质泥岩、页岩、粉砂岩等多种岩性均具有较好的适用性,且与氦气法、煤油法具有可比性及一致性,可以作为多种岩性孔隙度测定的统一实验方法。

新疆油页岩升温过程中孔隙结构演化特征

孔隙结构是油页岩描述的重要特征,直接影响页岩油气的储存和运移。因此,研究孔隙结构演化对指导油页岩原位开采具有重要意义。本文以新疆巴里坤油页岩为研究对象,利用热重(TG)、低温氮气吸附(LTNA)与压汞(MIP)等试验,结合LTNA-MIP联合精确表征方法,揭示巴里坤油页岩热解失质量规律及升温过程中孔隙发育特征,并对孔隙结构演化过程和机理进行研究。结果表明:新疆油页岩热重可分为低温缓慢失质量阶段(20~360℃)、中温快速失质量阶段(360~500℃)和高温缓慢失质量阶段(500~600℃),由于该油页岩具有低挥发分、高含油率、高灰分的特点,中、高温阶段是主要的失质量阶段;巴里坤油页岩内部孔隙类型复杂,升温过程中,微、小孔由狭缝形演变为导管状,中、大孔始终以墨水瓶状为主。墨水瓶状孔隙在300~400℃和500~600℃这2个温度区间集中发育,有效孔隙则在400~500℃大量发育。低温段以原生大孔为主,在自由水蒸汽压、矿物热膨胀和沥青质软化共同影响下,孔隙结构变化较小;中温段有机质集中热解,产生扩孔效应,单位孔隙体积大幅增加,孔隙类型以中孔为主;高温段黏土矿物失水、石英相变产生膨胀压力,大孔、中孔进一步扩展。

陆相混积型页岩储集层孔隙结构特征及其控制因素

陆相混合沉积岩岩性复杂,储集层物性差异大,其孔隙结构及其主控因素,是揭示陆相混积型页岩储集层物性的关键。通过岩石薄片、铸体薄片、扫描电镜、高压压汞、恒速压汞、X射线衍射等,识别了吉木萨尔凹陷二叠系芦草沟组页岩储集层岩性,分析了不同岩性的孔隙结构特征及其与成岩作用的关系。芦草沟组页岩储集层主要发育泥晶白云岩、粉砂质砂屑白云岩、石灰质粉砂岩、石灰质泥岩、粉砂质凝灰岩和石灰质凝灰岩6种岩性。粉砂质砂屑白云岩、石灰质粉砂岩和粉砂质凝灰岩压实程度中等,溶蚀孔发育,孔喉半径大,孔隙连通性及孔喉分选好,储集层物性好;石灰质凝灰岩压实作用中等,主要以方解石、自生石英及方沸石胶结为主,储集层物性中等;泥晶白云岩和石灰质泥岩成分单一,压实作用较强,溶蚀作用弱,孔喉半径小,物性差。

DLH油田低渗砂岩孔隙分形定量表征方法研究

针对常规表征方法难以精确表征低渗砂岩储层孔隙空间分布复杂性和不规则性的问题,提出了适用于低渗砂岩储层的分形维数计算方法,实现了低渗砂岩储层孔隙特征的定量表征。基于不同分形维数计算方法差异性的分析,优选采用MIFA方法求解低渗砂岩储层的分形维数(在2.042~2.324),相关性最佳;确定了排驱压力、平均孔喉半径、变异系数以及均值系数作为储层孔喉分布复杂程度和非均质程度的综合表征参数;基于恒速压汞分形维数的求解,发现低渗砂岩储层非均质程度呈中小孔喉大于微小孔喉,喉道分布大于孔隙分布的特点;低渗砂岩储层的分形维数与启动压力梯度和应力敏感性损害率的实验结果均存在一定的相互关系,分形维数越大,孔喉分布的非均质性越强,启动压力梯度越大且应力敏感性的损害程度也将加剧。低渗砂岩储层分形维数的计算可用于室内实验结果的定性预测和判断,也可作为油藏工程中应用相渗曲线时的重要判别标准。