循环加卸载作用下砂岩孔隙度与渗透率演化规律试验研究

研究砂岩在多次循环荷载作用下孔隙度及渗透率随荷载的变化规律,利用致密岩石惰性气体渗透率测试系统对砂岩进行了5次循环加卸载试验。试验结果表明:砂岩的孔隙度和渗透率随围压的增大而减小,循环加卸载过程中,砂岩的孔隙度、渗透率在加载阶段与卸载阶段的变化曲线均是不重合的。围压加载阶段孔隙度和渗透率随围压的变化关系均呈指数关系,在围压卸载阶段孔隙度与渗透率随围压变化均呈幂函数关系。砂岩在低围压条件下渗透率随围压变化的程度较大,在高围压条件下渗透率变化程度较小。加载阶段砂岩渗透率变化程度在第1次循环期间较大,从第2次循环开始由于岩样一定程度的压密渗透率随围压变化越来越小,而卸载阶段5次循环过程中渗透率随围压的减小而增大,但是循环次数增加过程中,渗透率的恢复程度相对于第一次循环越来越小。     

砂岩渗透性能微观图像分形分析

砂岩渗透性能一般都通过实验室或野外试验测试确定。本文基于岩石微观空隙分形特点．确立了岩石渗透率与分形维数的定量关系,实现了直接利用岩芯电镜扫描微观图像分形技术测定岩石宏观渗透性能的目标。为了精确统计SEM图像中不规则孔的面积、周长、半径、个数等参数,解决获取切片孔喉分形维数这一难题,应用Imagepro plus专业图像软件处理扫描电镜切片图像。将岩石渗透率理论值与实验室渗透率测定结果对比,结果表明：宏观渗透率与微观分形参数D的理论关系式成立,具有工程应用推广价值。     

Evolution of poroelastic properties and permeability in damaged sandstone

This paper is devoted to experimental investigation of mechanical behavior, poroelastic properties and permeability in saturated sandstone. The emphasis is to study the evolution of Biot’s coefficients and permeability with the growth of microcracks. Basic mechanical responses are first investigated through triaxial compression tests, showing nonlinear stress–strain relations, volumetric dilatancy, pressure sensitivity, elastic modulus degradation and induced anisotropy. Original tests are then performed for the determination of Biot’s coefficients in the axial and radial directions at different levels of stress. It is shown that the evolution of Biot’s coefficient is clearly anisotropic in nature due to the oriented closure of initial microcracks and growth of induced microcracks. The rock permeability in axial direction is also measured for different values of stress; it decreases in the first stage with the closure of microcracks and then progressively increases due to the opening of induced microcracks. However, the permeability significantly increases only when the coalescence of microcracks occurs.     

Effects of effective stress and temperature on permeability of sandstone from CO_2-plume geothermal reservoir

Rock is generally complex and heterogeneous,therefore the heterogeneity effects of effective stress and temperature on permeability should be taken into account.In this study,two-part Hooke's model(TPHM) is introduced to understand the influences of effective stress and temperature on permeability of soft and hard parts(two parts) of rock based on coupling thermo-hydro-mechanical tests.Under a fixed temperature level(25 ℃.35 ℃.50 ℃.65 ℃.80 ℃.90 ℃ and 95 ℃).the tests were carried out in a conventional triaxial system whereas the confining pressure was remained at 50 MPa.and the pore pressure was increased to the specified levels step by step.i.e.8 MPa,18 MPa.28 MPa.38 MPa.41 MPa,44 MPa.46 MPa and 48 MPa.The temperature-dependent relationships for two parts permeabilities are proposed on the basis of the initial test results.We point out that temperature of 65 ℃-90 ℃ is the threshold for the development of CO_2-plume geothermal(CPC) reservoir sandstone cracking under low effective stress(2-9 MPa) based on the relationship between temperature and soft part permeability.Furthermore,we discuss the effect of temperature on the two parts in the rock.The results indicate that as the temperature increases from 25 ℃ to 65 ℃.the flow channel in the hard part has a stronger response to temperature than that in the soft part at a fixed effective stress level,which is opposite to the situation of effective stress.Considering that natural rock is generally heterogeneous with non-uniform pore structure,we suggest a physical interpretation of the phenomenon that before the thermal cracking threshold the two parts have different responses to temperature.     

A geometrical fractal model for the porosity and permeability of hydraulic cement pastes

This study reports on a geometric model which capably represents various aspects of the porosity of hardened cement pastes. It is composed of two interconnected fractal units. The experimental data for model development and appraisal is obtained from the cumulative curve of mercury intrusion porosimetry on pastes of Type I Portland Cement (water/cement: 0.3–0.7; curing ages: 1–56 d). The fractal character of the porosity was recorded to 2–3 orders of magnitude of the pore size, between about 2 nm and 1 μm. On a par with the fractal dimension, the predictions of the model are in agreement with the experimental data even with regard to the fraction of the voids and the range and distribution of pore size. Finally the model has been used to calculate fluid permeability coefficients which are in accord with the experimental values.     

低强度脉冲超声激发的声微流增强藻酸钙凝胶支架材料的孔隙率和通透性研究

低强度脉冲超声(LIPUS)激发的声微流场所产生的剪切应力可作用于细胞膜表面,从而显著增强细胞膜的通透性。构建了三维藻酸钙凝胶支架培养系统,来模拟有利于细胞生长的营养供给和新陈代谢体内微环境;基于扫描电子显微镜、体内荧光图像和激光共聚焦图像观测技术,对LIPUS增强三维藻酸钙凝胶支架材料的孔隙率和通透性的作用机制和参数相关性进行了系统的研究。结果表明,三维藻酸钙凝胶支架材料的孔隙率和通透性可随着LIPUS的驱动声压的升高而显著增强。此外,通过对三维支架材料内的细胞增殖情况分析,发现在适当的LIPUS驱动声压(如P-=0.055 MPa)下,HeLa细胞在LIPUS作用下的三维藻酸钙凝胶支架材料中可获得更高的增殖率。     

Elastic wave velocities and permeability evolution during compaction of Bleurswiller sandstone

Field observations and laboratory experiments have recently documented the formation of compaction bands in porous sandstones [Mollema and Antonellini, Tectonophysics 1996;267:209–28; Olsson and Holcomb, Geophys Res Lett 2000;27:3537–40; Bésuelle, J Geophys Res 2001;106:13435–42; Klein et al., Phys Chem Earth 2001;26:21–5]. It has been observed experimentally [Wong et al., J Geophys Res 2001;28:2521–4; Baud et al., J Geophys Res 2003, submitted; Fortin et al., 2003, Abstract EGS-AGU Nice] that under axisymmetric compression, compaction bands develop sub-perpendicular to the main compressive stress which is predicted theoretically in the framework of strain localization theory [Bésuelle, J Geophys Res 2001;106:13435–42; Issen and Rudnicki, J Geophys Res 2000;105:21529–36]. Volumetric strain, fluid transport and elastic properties are intimately coupled to one another, for they all depend on a few intrinsic parameters such as the porosity, the crack density, and the matrix and fluid elastic properties. On the one hand, Scott et al. [Rock Mech Min Sci Geomech 1993;30:763–9] showed that elastic wave velocities were clearly affected during the deformation of porous sandstones. On the other hand, Zhu and Wong [J Geophys Res 1997;102:3027–41] showed that the relation between the evolution of permeability and volumetric strain during compaction of sandstones was not straightforward. In this study, we present for the first time the simultaneous evolution of volumetric strain, elastic wave velocities and permeability for a set of deformation experiments of Bleurswiller sandstone. We show that, although very coherent to one another, those three sets are not systematically correlated. Indeed, inelastic compaction, whether it is distributed or localized, is accompanied by a drastic decrease of elastic wave velocities due to grain crushing, a decrease of permeability and porosity due to pore collapse. Using simple statistical physics concepts based on the study of Kachanov [Adv Appl Mech 1993;30:259–445] and Guéguen and Dienes [Math Geol 1989;21:1–13], we try to understand and address the issue of coupling/decoupling between volumetric strain (mainly sensitive to equant porosity variations), elastic properties (mainly sensitive to crack density) and permeability (theoretically sensitive to both) during the formation of compaction bands. Finally, we show that the mineral composition of a sandstone is a key parameter controlling the effective pressure at which the onset of pore collapse P^* takes place.     

渗流-应力-流变耦合作用下破碎带砂岩渗透演化规律试验研究

膝状挠曲破碎带是一些水电站坝基的主要工程地质问题。破碎带岩性为完整性较差的软弱砂岩,直接关系到坝基的变形和稳定。基于破碎带砂岩组织结构疏松、含水率较高、物理力学性能较差等特点,对渗流-应力耦合作用下流变过程中的岩石渗透特性进行测试。分析应力-应变过程中的渗透规律,研究流变过程中渗透系数演化规律,探讨渗透性演化破坏机制。得到轴向、环向和体积变形对渗透系数的影响及围压和孔隙压力对渗透特性的影响规律。结果表明:初始加载导致渗透系数快速减小,并随着非线性变形增加降低程度逐步趋缓;且环向变形比轴向变形更能灵敏地反映渗透系数演化规律;岩样非均质性引起孔隙度略有不同,加载作用导致渗透系数随时间变化存在部分波动,但整体呈线性降低;稳态流变阶段渗透系数恢复至平缓下降,说明波动对渗透系数的整体演化无显著影响,且围压增加导致渗透系数降低。     

不同粒度砂岩力学和渗透特性试验研究

为探讨砂岩粒度对力学行为和渗透特性的影响,利用MTS815 Flex Test GT岩石力学试验系统,对取自同一工程的粗粒砂岩、中粒砂岩和细粒砂岩进行常规三轴试验和三轴压缩全过程渗透试验。研究表明:随着粒度减小,砂岩抗压强度及抗剪强度参数c和φ均增大;渗透水压作用下砂岩强度降低5.15%~24.66%。渗透率变化规律与变形变化特征呈阶段对应:线弹性阶段砂岩内部孔隙被压密,渗透率降低;弹塑性阶段渗透率先是缓慢增加然后急剧上升,在峰后达到最大值;峰后继续破坏阶段渗透率又呈逐渐降低特征。相同粒度砂岩的渗透性随围压增加而降低,且不同围压下渗透率可拟合成线性函数;相同围压下不同粒度砂岩渗透率整体特征表现为:粗粒砂岩渗透率K约为中粒砂岩的105倍,中粒砂岩渗透率K约为细粒砂岩的10倍。     

不同掺和料透水混凝土透水系数与孔隙率的关系探讨

研究了不同掺量粉煤灰、矿粉、钢渣粉对透水混凝土透水系数和孔隙率的影响规律及它们之间的关系,对比了同条件下7d、28d混凝土的透水系数。试验结果表明:W/B=(0.2-0.32)条件下,加入掺和料后,透水混凝土的透水系数与孔隙率均有不同程度的降低。同等条件下透水系数与孔隙率不呈线性关系,但有很好的相关性,通过曲线拟合得到了不同掺和料对应的关系式。28d透水系数与7d透水系数相近,但28d透水系数略有降低。     

Cyclic loading tests on sandstone and limestone shale aggregates used in unbound forest roads

This study examined the performance of two aggregates subjected to cyclic loading in a large-scale test rig. The two aggregates examined were: (i) a sandstone from Co. Cork, Ireland and (ii) a limestone shale from Co. Limerick, Ireland. The aggregates were classified and their engineering properties established and compared. Various depths of the aggregates, overlaying a 1-m-deep formation layer, were compacted and subjected to a cyclic loading regime of incrementally increasing pressures of 500, 750 and 1000 kPa. Each aggregate was tested for up to 150,000 load applications. The resilient pressures, resilient surface deflections and permanent deformations were measured. The sandstone performed well in a dry state but poorly when wetted up. The shale behaved poorly but the addition of a wet mix macadam (WWM) layer greatly improved its performance.     

Experimental measurement of permeability evolution in sandstone during hydrostatic compaction and triaxial deformation

Bulletin of Engineering Geology and the Environment - The permeability of sandstone during hydrostatic compaction and triaxial deformation was measured using a rock triaxial servo-controlled...     

Fabric,porosity and water permeability of calcarenites from Apulia (SE Italy) used as building and ornamental stone

The purpose of the study was to determine the properties influencing the performance of Apulian calcarenites as past and present building and ornamental stone. A comparison of qualitative fabric observations in petrographic thin sections and quantitative measurements of physical properties, including porosity, pore size distribution and permeability, is discussed. The results suggest that the mercury intrusion porosimetry data and qualitative fabric analysis related to pore size distribution are the most critical observations regarding the potential for the stone to take in and hold water and hence to weather. Electronic Publication     

不同饱和度砂岩渗透率、孔隙度随应力变化规律研究

 制备含水饱和度为0%～70%的砂岩岩样,利用低渗透岩石气体渗透测试装置,对不同含水饱和度的砂岩岩样进行气渗试验,测量其在不同围压和渗压下的渗透率以及对应围压下的孔隙度,分析和讨论不同含水饱和度低渗透砂岩渗透率、孔隙度与应力三者之间的关系。得到以下结论：含水饱和度低于50%的低渗透砂岩,其气测渗透率随孔隙压力的增大而减小,含水饱和度高于50%的低渗透砂岩,其气测渗透率的变化规律相反;气测渗透率与孔隙压力符合指数函数关系;随着含水饱和度的增大,气测渗透率对孔隙压力变化的敏感性减少,且气测渗透率对孔隙压力变化的敏感性随着孔隙压力的增大而增大;绝对渗透率、孔隙度与围压均呈指数函数关系;随着含水饱和度的增大,绝对渗透率对围压变化的敏感性增大,对孔隙度变化的敏感性减小,且绝对渗透率和孔隙度对围压变化的敏感性均是随着围压增大而减小;低渗透砂岩的孔隙度与其绝对渗透率的变化成正相关,孔隙度的少量降低即能引起其绝对渗透率的大幅度下降;绝对渗透率与孔隙度成指数函数关系;随着含水饱和度增大,绝对渗透率对孔隙度变化的敏感性增强,且随着孔隙度的增大,绝对渗透率对孔隙度变化的敏感性也逐渐增强。     

周期性渗透压作用下红砂岩渗透特性试验研究

水库运行期水位的周期性变化使软岩岸坡防洪限制水位以下的岩体长期处在周期性变化渗透压作用的环境中,这种周期性变化的渗透作用对软岩的渗透特性将产生很大的影响。以三峡库区红砂岩为研究对象,利用自主研发的"具有模拟库水位周期性变化环境下水压变化条件的渗透仪"对红砂岩进行周期性渗透试验,探讨防洪限制水位以下的红砂岩在周期性渗透压作用下的渗透特性变化规律。试验结果表明,随着周期性渗透压的变化,红砂岩的渗水量在第一个渗透周期增长最快,而后逐渐减小;随着周期性渗透压的变化,红砂岩的渗透速度和渗透系数也呈周期性变化;不同岩样的累计渗水量、渗透速度和渗透系数的变化存在一定的差异,但经过4个渗透周期之后,红砂岩的累积渗水量、渗透速度和渗透系数随压力的变化范围稳定,且变化趋势一致。研究结果说明,三峡水库岸坡防洪限制水位以下的红砂岩在水库运行期经历4次周期性水位变化之后,渗透特性逐渐趋于稳定。     

Microcracks development and porosity evolution in sandstone,Sichuan basin,China: an experimental approach

Bulletin of Engineering Geology and the Environment - The process of fault rupture is closely related to the weakening of fault rock. The weakening process of fault rock from Sichuan basin was...     

拉曼光谱地学应用及在页岩孔隙研究中的新进展

拉曼光谱仪在地学中主要用于分析矿物、流体包裹体及生物化石等的结构及组分。用于流体包裹体测试时能直接获得其成分及含量,还可进一步了解成岩过程中流体包裹体所在地层的温度及压力等参数。因此,拉曼光谱可提供研究流体性质、沉积环境及成藏期次所需的重要依据。利用拉曼光谱可进一步认识烃类在纳米级孔隙中的充填及成熟情况,为估算页岩气原始地质储量提供有力证据,目前对有机纳米孔隙所捕集的烃类进行定量分析仍有待进一步研究。     

多期次应力变化对砂岩渗透率和孔隙结构影响的

The variations of reservoir stress caused by the multi-stage and discontinuous nature of the process in the CO₂ geological storage, leading to the change of permeability and pore structure of the rock, have a direct impact on CO₂ injection and storage. Through laboratory experiments, variations in the permeability of sandstone in the Liujiagou formation of the Ordos CCS (CO₂ capture and storage) demonstration project are analyzed under cyclic variations in injection pressure and confining pressure and multi-stage loading and unloading. In addition, the variations in the micro-pore structure are analyzed based on micro-pore structure tests. The main conclusions are as follows: (1) Both the confining pressure and the injection pressure have a significant effect on the permeability of the reservoir rock. And the influence degree can reach 30% and 80%, respectively. The relative permeability changes with pressure, and it between the loading and unloading stages is higher at low pressures than at high pressures. (2) Mathematical models of permeability as a function of confining pressure and injection pressure are constructed. The mathematical models representing different cyclical processes are quite different. (3) The effects of the interval between the experiments on permeability changes are different for different pressure modes. The rock permeability can recover better under the injection pressure variation than confining pressure variation. (4) The variations during multiple stress cycles have a significant effect on the micropore structure. The increase in micropores with mesopores at small widths and the decrease of macropores result in a decrease in the permeability of the rock samples.     

高温三轴应力作用下油页岩的渗透特征各向异性演化规律实验研究

油页岩各向异性渗透率影响热解油气和对流加热流体在油页岩岩层中的运移速度和范围。因此,研究高温下油页岩渗透率的各向异性特征对于原位注热开采油页岩具有重要意义。采用实时高温三轴稳态法渗透测试系统研究了不同温度不同层理方向的油页岩的渗透率的演化规律。研究表明,垂直层理方向的渗透率在20℃～450℃在10^-20 m²之下,超出了稳态法渗透测试系统测试范围,处于超低渗阶段;当温度超过450℃之后,渗透率处于2.5×10^-19～1.17×10^-17 m²范围,450℃称之为垂直层理渗透率演化的阈值温度。平行层理的渗透率在20℃～400℃范围,都处于较低渗透率阶段,为2.3×10^-19～2.9×10^-18 m²,当温度高于400℃,平行层理方向的渗透率急剧增加,量级在10^-16～10^-15范围,因此400℃被称为平行层理渗透率演化的阈值温度。然后利用高温三轴瞬态法渗透测试系统,测得了...     

滑溜水在页岩纳米级孔隙的表观渗透率分形模型

为研究页岩基质孔隙表观渗透率,借助分形统计方法描述页岩孔隙复杂形态,构建页岩基质纳米级孔隙的表观渗透率模型,探讨分形参数、工程参数、流体性质与毛管力效应等因素对表观渗透率的影响。结果表明,流体性质的变化对滑溜水在页岩纳米尺度孔隙中的流动形成附加阻力,毛管力效应形成驱动力,温度与孔隙度同时影响流体性质与毛管力效应。流体性质的变化与毛管力效应同时影响表观渗透率,毛管力效应变化所带来的影响大于流体性质变化所带来的影响。研究结果对滑溜水的返排与气井生产的稳定性与长效性具有理论指导意义。