Experimental study of the effects of a multistage pore-throat structure on the seepage characteristics of sandstones in the Beibuwan Basin:Insights into the flooding mode

To investigate the relationship between grain sizes, seepage capacity, and oil-displacement efficiency in the Liushagang Formation of the Beibuwan Basin, this study identifies the multistage pore-throat structure as a crucial factor through a comparison of oil displacement in microscopic pore-throat experiments. The two-phase flow evaluation method based on the Li-Horne model is utilized to effectively characterize and quantify the seepage characteristics of different reservoirs, closely relating them to the distribution of microscopic pores and throats. It is observed that conglomerate sandstones at different stages exhibit significant heterogeneity and noticeable differences in seepage capacity, highlighting the crucial role played by certain large pore throats in determining seepage capacity and oil displacement efficiency. Furthermore, it was found that the displacement effects of conglomeratic sandstones with strong heterogeneity were inferior to those of conventional homogeneous sandstone, as evidenced by multiple displacement experiments conducted on core samples with varying granularities and flooding systems. Subsequently, core-based experiments on associated gas flooding after water flooding were conducted to address the challenge of achieving satisfactory results in a single displacement mode for reservoirs with significant heterogeneity. The results indicate that the oil recovery rates for associated gas flooding after water flooding increased by 7.3%-16.4% compared with water flooding alone at a gas-oil ratio of approximately 7000 m^(3)/m^(3). Therefore, considering the advantages of gas flooding in terms of seepage capacity, oil exchange ratio, and the potential for two-phase production, gas flooding is recommended as an energy supplement mode for homogeneous reservoirs in the presence of sufficient gas source and appropriate tectonic angle. On the other hand, associated gas flooding after water flooding is suggested to achieve a more favorable development effect compared to a single mode of energy supplementation for strongly heterogeneous sandstone reservoirs.

Effect of particle gradation on pore structure and seepage law of solution in weathered crust elution-deposited rare earth ores

Both CT and Avizo software were used to explore the effect of particle gradation on the evolution characteristics of pore structure and seepage paths in weathered crust elution-deposited rare earth ores during leaching.The results showed that the pore areas in four kinds of ore samples before leaching were mainly concentrated in 10^(4)–10^(7)μm^(2),whose pore quantities accounted for 96.89%,94.94%,90.48%,and 89.45%,respectively,while the corresponding pore volume only accounted for 30.74%,14.55%,7.58%,and 2.84%of the total pore volume.With the decrease of fractal dimension,the average pore throat length increased,but pore throat quantities,the average pore throat radius and coordination number decreased.Compared with that before leaching,the change degree of pore structure during leaching increased with the fractal dimension decreasing.For example,the reduction rate of the average coordination number of ore samples was 14.36%,21.30%,28.00%,and 32.90%,respectively.Seepage simulation results indicated that seepage paths were uniformly distributed before leaching while the streamline density and seepage velocity increased with the fractal dimension decreasing.Besides,the phenomenon of the streamline interruption gradually reduced during leaching while preferential seepage got more obvious with the decrease of the fractal dimension.

Effect of seepage-induced erosion on soil macropore structure

Internal erosion is one of the important factors causing geological disasters.The microstructure of soil can change with seepage erosion,resulting in changes in the hydraulic and mechanical properties of the soil.The evolution of seepage erosion is investigated with X-ray computed tomography(CT)in this study.The change in macropore structure characteristics during the seepage erosion test is quantified and the influence of seepage erosion on soil deformation is analyzed.Moreover,a pore network model(PNM)is established for the specimens and the evolution of the connected pore size characteristics is assessed.The results show that the macropore structure is significantly affected by seepage erosion,especially in terms of the porosity and pore geometry characteristics.The changes in macropore structure characteristics are most obvious in the lower part of the specimen.The influence of seepage erosion on the pore size distribution(PSD)and soil deformation is heterogeneous and closely dependent on the spatial location of the soil.Moreover,seepage erosion enhances macropore connectivity and has a directional impact on macropore orientation.These findings can provide a reference for the theoretical modeling and numerical simulation of the seepage erosion and improve the understanding of the seepage erosion evolution in engineering practice.

Controlling Effects of Tight Reservoir Micropore Structures on Seepage Ability: A Case Study of the Upper Paleozoic of the Eastern Ordos Basin, China

In this study, the types of micropores in a reservoir are analyzed using casting thin section(CTS) observation and scanning electron microscopy(SEM) experiments. The high-pressure mercury injection(HPMI) and constant-rate mercury injection(CRMI) experiments are performed to study the micropore structure of the reservoir. Nuclear magnetic resonance(NMR), gas-water relative seepage, and gas-water two-phase displacement studies are performed to examine the seepage ability and parameters of the reservoir, and further analyses are done to confirm the controlling effects of reservoir micropore structures on seepage ability. The experimental results show that Benxi, Taiyuan, Shanxi, and Shihezi formations in the study area are typical ultra-low porosity and ultra-low permeability reservoirs. Owing to compaction and later diagenetic transformation, they contain few primary pores. Secondary pores are the main pore types of reservoirs in the study area. Six main types of secondary pores are: intergranular dissolved pores, intragranular dissolved pores, lithic dissolved pores, intercrystalline dissolved pores, micropores, and microfracture. The results show that reservoirs with small pore-throat radius, medium displacement pressure, and large differences in pore-throat structures are present in the study area. The four types of micropore structures observed are: lower displacement pressure and fine pores with medium-fine throats, low displacement pressure and fine micropores with fine throats, medium displacement pressure and micropores with micro-fine throats, and high displacement pressure and micropores with micro throats. The micropore structure is complex, and the reservoir seepage ability is poor in the study areas. The movable fluid saturation, range of the gas-water two-phase seepage zone, and displacement types are the three parameters that well represent the reservoir seepage ability. According to the characteristic parameters of microscopic pore structure and seepage characteristics, the reservoirs in the study area are classified into four types(Ⅰ–Ⅳ), and types Ⅰ, Ⅱ, and Ⅲ are the main types observed. From type Ⅰ to type Ⅳ, the displacement pressure increases, and the movable fluid saturation and gas-water two-phase seepage zone decrease, and the displacement type changes from the reticulation-uniform displacement to dendritic and snake like.

Analysis of the Microstructure and Macroscopic Fluid-Dynamics Behavior of Soft Soil after Seepage Consolidation

The purpose is to study the microstructure and macroscopic fluid-dynamic behavior of soft soil after it has been subjected to a seepage consolidation procedure.First,the microscopic pore structure of soft clay is quantitatively studied by a scanning electron microscope technique.Second,the average contact area rate of soil particles is obtained employing statistical analysis applied to microscopic images of soft soil,and the macroscopic porosity of soft clay is determined through an indoor geotechnical test.Finally,mathematical relationships are introduced by fitting the results of the test.The results show that the unmodified empirical equation for the permeability coefficient of coarse-grained soil produces large errors in calculations related to cohesive soils.By contrast,the permeability coefficient calculated by the empirical equation modified by the average contact area ratio theory is in good agreement with the measured average value of the indoor test.

Synthesis and Structure of anti-Configuration Complex [Cu(tssb)_2]·2[(H_3O)Cl]·4H_2O

The title complex [Cu(tssb)2]2[(H3O)Cl]4H2O (C18H34Cl2CuN2O14S2) (tssb = tau- rine salicylaldehyde Schiff base) has been synthesized by the reaction of taurine salicylaldehyde Schiff base (tssb) and copper acetate in water-ethanol. Its single-crystal structure was determined by X-ray diffraction method. The crystal structure belongs to triclinic, space group P1 with a = 0.7407(1), b = 1.3329(3), c = 1.5736(3) nm, ?= 103.800(4), ?= 95.030(4), ?= 104.416(4)? Mr = 701.06, V = 1.4433(5) nm3, Z = 2, Dc = 1.613 g/cm3, = 1.153 mm-1 and F(000) = 726. The compound is an infinitely expanding three-dimensional network connected with hydrogen bonds. The Cu(Ⅱ) atom is coordinated by two nitrogen and two oxygen atoms to form a distorted planar coordination compound which adopts anti-configuration because two sulfonic acid groups are posi- tioned diagonally on a plane.

Research on the Seepage Safety Monitoring Indexes of the High Core Rockfill Dam

The study on developing the reasonable safety monitoring indexes plays a most importantly role in the health monitoring of high core rockfill dams. However, researches on this topic are relatively scarce both at home and abroad. In this paper, the characteristics and failure modes of seepage in high core rockfill dam are analyzed firstly. Then, a safety monitoring index based on seepage quantity, which reflects the overall seepage behavior, is developed, using the real-time monitoring data and its safety monitoring model. Moreover, another safety monitoring index based on seepage gradient, reflecting the local seepage behavior, is proposed, combining the spatial layout of osmo- meters and local failure mechanisms of core wall. Additionally, one more safety monitoring index based on permeability coefficient, which considers the overall and local seepage behaviors, is developed, on the basis of establishing the finite element analysis model and real-time seepage coefficient inversion analysis model of high core rockfill dam. A case study on these indexes of Nuozhadu high core rockfill dam is developed, which improves the reliability of seepage safety evaluation of the dam.

Pore structure characteristics of the relative water-resisting layer on the top of the Ordovician in Longgu Coal Mine

In order to study the permeability and water-resisting ability of the strata on the top of the Ordovician in Longgu Coal Mine, this paper tested the permeability and porosity of the strata, investigated the fracture and pore structure features of the strata, and identified the main channels which govern the permeability and water-resisting ability of the strata. The permeability of the upper, central and lower strata shows as 2.0504 × 10^-3-2.782762× 10^-3, 4.1092 × 10^-3 -7.3387 × 10^-3 and 2.0891 ×10^-3-3.2705 × 10-3 μm^2, respectively, and porosity of that is 0.6786-0.9197%, 0.3109-0.3951% and 0.9829-1.8655%, respectively. The results indicate that： （I） the main channels of the relative water-resisting layer are the pore throats with a diameter more than 6 μm; （2） the major proportion of pore throats in the vertical flow channel and the permeability first increases and then sharply decreases; （3） the fractures occurring from the top to 20 m in depth of the strata were filled and there occurred almost no fracture under the depth of 40 m; and （4） the ratio of turning point of the main flow channel in the strata on top of Ordovician can be used to confirm the thickness of filled water-resisting lavers.

The Role of Fracture Structure in Leachate Pollution at Landfills:A Case Study of a Landfill in Chongqing City

This paper studies a landfill where there are three faults running through. As serious pollution has occurred to the geological environment, the landfill is to be closed up and renovated. The paper aims to explore the role of fracture structure in leachate pollution at the landfill. The research was carried out in several stages. First, mathematical models of the pre-renovation landfill with three faults running through and the landfill after renovation were established. And then, the boundary conditions and parameters of the two mathematical models were determined. The groundwater level of the landfills was simulated in order to modify the two mathematical models. As a result, a feasible mathematical model was achieved. Based on this model, a comparison was made of the COD concentration variations in the inside leachate and outside leachate between the two landfills. Accordingly, the impacts of the fracture structure on the pollution of leachate at the landfills could be identified. The study results show that while faults contribute to the migration of ieachate, they also serve as a confluence of leachate, thus further deteriorating the environment. The COD concentrations of the inside leachate and the outside leachate of the pre-renovation landfill are respectively 800 mg/L and 220 mg/L higher than those of the post-renovation landfill. Therefore, measures must be taken to handle the ieachate seepage in areas where there are faults as well as the neighboring areas so as to get the environmental pollution under control.

Study on Seepage Control in Complicated Hydrogeological Conditions on the Right Bank of JinPing-I Hydropower Station

With consideration of the special hydrogeological conditions and layout characteristics of the hydraulic structures, the seepage control measures of dam abutment and underground powerhouse on the right bank of JinPing-I hydropower station is drawn up. Based on the three dimensional finite element analysis of seepage control with dry area virtual flow constant mesh analysis method, the rationality of the seepage control measures of dam abutment and underground powerhouse has been verified and the key factors affecting the effect of seepage have been compared. In combination with the curtain of dam abutment, the curtain of underground powerhouse is reasonable. The results showed that the steel liner of penstock after the curtain is necessary.

鄂尔多斯盆地长7_(3)亚段储层微观孔隙结构和固液作用力

针对鄂尔多斯盆地长7_(3)亚段页岩储层孔隙结构和固液作用力问题,首先,通过聚焦离子束电子显微镜、计算机断层扫描技术和原子力显微镜对纯页岩储层样品开展研究;其次,结合Avizo软件建立页岩多尺度三维重构模型,定量分析页岩孔隙结构特征;最后,提出页岩储层固液相互作用黏附力测试方法,测定原油与孔隙壁面之间的黏附力。研究结果表明:长7_(3)储层发育有粒间孔、粒内孔和有机质孔隙,有机质孔隙形状主要有条状、弯月状和椭圆状;在微米尺度下,可以清晰看到层理缝;在纳米尺度下,不同页岩结构的样品孔隙结构特征无明显差异,孔喉形态多为片状和条状;有机质与原油之间的黏附力最大,长英质与原油之间的黏附力次之,层理面与原油之间的黏附力最小,3种平均黏附力分别为0.098、0.063和0.041μN,长7_(3)页岩储层中壁面原油启动难度较大,这从力学角度解释了该区为原位转化重点区域的原因。

盾构隧道进出洞施工渗漏诱发结构倒塌试验研究

为明确隧道进出洞施工时因渗漏而诱发的结构倒塌发展过程,设计并开展缩尺模型试验。根据相似关系设计模型试验,制作模型土体与模型盾构隧道。参考实际进出洞施工渗漏事故案例,触发模型盾构隧道渗漏,在模型箱内重现隧道结构倒塌的全过程,并观测事故发展过程中的地层响应、隧道外部土压力变化、隧道倒塌发展过程。通过分析隧道进出洞施工中不同位置发生渗漏后结构的倒塌响应,对比不同位置渗漏对隧道进出洞施工致灾发展过程的影响。试验研究发现:1)隧道进出洞施工发生渗漏后,外部土体由于渗流侵蚀产生不稳定土洞,土洞经历了形成—失稳—再现的循环过程;2)隧道结构倒塌是由不稳定土洞失稳坠落冲击隧道结构导致的;3)隧道顶部和腰部2种不同位置渗漏后外部土体侵蚀发展的本质相同,但是不同渗漏位置产生的土洞形状有明显差异,导致最终隧道倒塌位置有所差异。

天然气水合物微观测试技术与应用进展

天然气水合物作为一种重要的战略资源,其在沉积物中的动态聚散过程非常复杂,涉及的许多科学问题需要从微观层面来解答。微观测试技术可以在毫米、微米甚至纳米尺度上获取研究对象的状态、演化等特征信息,是天然气水合物基础研究的重要手段。本文系统回顾了基于X射线计算机层析扫描(X-CT)、X射线衍射(XRD)、固体核磁共振(NMR)、低场核磁共振(LFNMR)、拉曼光谱(RM)、扫描电子显微镜(SEM)和高压差示扫描量热(HPDSC)等技术建立的天然气水合物微观测试技术体系;重点介绍了各项技术的特点及进展,以及相关微观测试技术在含水合物沉积物微观结构量化表征、微观渗流特征等方面的应用成果与最新进展;提出了天然气水合物微观测试技术与应用的研究方向与趋势,旨在为天然气水合物的深入研究提供更多思路。

多元结构地基对防渗墙渗透溶蚀演化规律的影响

深厚覆盖层地基渗透性能和厚度变化会影响坝基渗流场的分布,进而改变坝基防渗墙溶蚀演化进程。为研究多元结构地基变化对防渗墙渗透溶蚀的影响机制,结合流体力学、化学动力学理论和对流-扩散方程,提出覆盖层地基混凝土防渗墙渗透溶蚀耦合分析模型,研究强透水层、弱透水层和第三透水层厚度及渗透系数对防渗墙中钙离子浓度、孔隙率和渗流特性的影响。结果表明:随服役年份增长,防渗墙钙离子浓度表现为先快速增长至峰值,随后不断下降的趋势,孔隙率和渗透系数呈指数型增长变化规律,大坝总渗透流量不断增大;各影响因素中,弱透水层渗透系数对防渗墙钙离子浓度、孔隙率和大坝总渗流量的影响最大,其次为强透水层厚度及其渗透系数;各工况下混凝土防渗墙使用年限为38.46~44.00年。研究成果可为深厚覆盖层多元结构地基上的土石坝工程的长效服役性能评估提供理论依据。

基于改进QSGS-LBM法的各向异性重构土体的渗流模拟

为解决传统四参数随机生长(quartet structure generation set, QSGS)方法重构模型与真实土体情况不符的缺陷,提出一种改进的QSGS方法,在综合考虑各向异性、孔隙率、土体颗粒大小情况下构建各向异性多孔介质模型.采用两点自相关函数法验证模型的有效性,并结合格子玻尔兹曼方法自编Matlab程序来模拟细观渗流过程.实验发现,各向同性模型和土体CT切片的两点相关系数最大差值是各向异性模型的2.5倍以上,且流体粒子在孔道中线处的渗流速度最大,达到0.03,在孔壁处渗流速度接近于0.结果表明,各向异性模型在孔隙结构和空间分布上更接近真实土体情况,流体在渗流后期出现大孔隙优先流现象和指进现象.

基于格子Boltzmann方法的地埋管管群换热的模拟研究

土壤结构和地下水通常会影响地埋管换热器的传热,本文将利用随机四参数生成法建立双分布函数格子Boltzmann模型,对有渗流条件下地埋管管群换热器与饱和土壤多孔介质的换热情况进行了模拟,分析了影响埋管外土壤平均温度的主要因素。研究表明,土壤热传导特性主要受土壤孔隙度、地下水渗流速度和土壤骨架导热系数k s的影响。本文的研究结论对考虑土壤渗流的地下换热器的设计具有一定的指导意义。

关中盆地新近系蓝田-灞河组热储层物性及渗流特征研究

关中盆地地热资源丰富,开发利用地热能有助于调整能源结构、降低雾霾及改善环境。新近系蓝田-灞河组是目前地热开采的主要热储层,明确储层物性及渗流机理对地热资源的高效规模开发利用及回灌具有重要意义。通过钻井岩心及测井资料,结合压汞、铸体薄片、核磁共振等相关测试手段,对渭河盆地新近系主要层位蓝田-灞河组的物性特征、孔隙结构特征、渗流特征进行了详细分析。研究结果表明:①基于地热井及钻孔测井资料,西安凹陷蓝田-灞河组孔隙度为20%~25%,渗透率为100~200 mD,固市凹陷孔隙度为10%~20%,渗透率为1~100 mD,西安凹陷物性条件优于固市凹陷,在平面上孔渗均表现为由盆地边缘向盆地中部增大的趋势。②蓝田-灞河组孔隙以原生粒间孔、粒间残余孔隙为主,局部见少量微裂缝发育,见少量长石溶孔。孔喉分布比较均匀,主要介于10~16μm之间,渗透率贡献值高。出水量大,单位厚度砂岩单位涌水量高,富水性及渗流特征好。③蓝田-灞河组砂岩储层类型属于Ⅱ类储集层,综合评价为高孔隙度渗透层,是最有利的地热开发层段。

含瓦斯煤岩构造界面剪切-渗流耦合试验方法及教学设计实践

富含瓦斯的煤系断层/裂缝等地质构造界面结构在自然界煤岩体中广泛存在,含瓦斯煤岩构造界面剪切渗流耦合作用机制与煤系构造区域瓦斯动力灾害密切相关。基于此,该文介绍了含瓦斯煤岩构造界面剪切渗流耦合系统试验方法,重点分析了煤岩试样滑动界面的剪切力学特征,以及界面物理结构特征演化和高度表征方法。结果表明:煤岩界面剪切力学响应由煤层构造界面凸体承担,界面凸体强度越高峰值剪切强度越大,同时黏滑应力降增大但相应黏滑事件频率降低;其他条件一定时,增大法向应力使得煤岩构造界面剪切强度增大,能够积累更多的应变能,在剪切过程内黏滑次数更少,但是在达到阈值破裂失稳时会产生更大的应力降,释放更多能量。该研究成果可对探究含瓦斯煤岩界面剪切力学特性以及阐明含瓦斯煤岩构造界面动力失稳诱发灾害提供理论指导;同时该文将科研成果反哺教学,基于“试验系统—试验方法—结果分析—物理表征”相结合的方法,把科研理论和现场技术难题相结合,为产学研融合以及科研-教学协同提升提供相应的探索。

基于计算机断层扫描的浆砌石真实三维孔隙网络模型及其渗流数值模拟

为研究浆砌石渗流规律,以广东省某已运行30余年的浆砌石拱坝典型芯样为例,基于计算机断层扫描(CT)技术构建了浆砌石真实三维孔隙网络模型,并对不同孔隙结构和水压差下浆砌石的渗流特性进行模拟。结果表明,高流速的渗流路径沿着大孔隙所在位置集中,流线更加顺直平滑,而其周围的小孔隙内渗流路径则较为分散;大孔隙中流速和流量更大,大流速会冲蚀浆砌石结构从而促进联通孔隙向着微裂隙转变,小孔隙向着大孔隙转变;随着水头差增大,浆砌石最大流速和最大流量均逐渐增大,且孔隙结构越发育,增大幅度越大。

考虑间断级配影响的土石混合体水力侵蚀分异机理

近年来,堆积体滑坡频发,已成为西南地区最典型的滑坡类型。研究表明,超过50%的库区堆积体滑坡诱因为水力侵蚀,因此降雨、岸坡侵蚀、波浪掏蚀成为库区滑坡灾害防治重点关注的问题。同时,土石混合体自身的间断级配会对其水力特性造成明显影响,进而导致水力侵蚀作用下堆积体内部的颗粒运移规律具有独特性。采用自主研发的土石混合体渗透侵蚀试验装置,模拟土石混合体内部细观侵蚀过程,阐明其侵蚀分异机理,揭示间断级配的影响。结果表明:土石混合体侵蚀过程主要分为快速侵蚀、侵蚀减缓、稳定渗流3个阶段,超过60%的侵蚀在快速侵蚀阶段完成;与良好级配试样相比,间断级配试样的侵蚀量更大,初始侵蚀更剧烈,快速侵蚀阶段更短暂;间断级配对土石混合体水力侵蚀分异的影响同样明显,细颗粒缺失结构的细颗粒尺寸单一,不易堵塞渗流通道,渗透系数高于良好级配试样,且最大渗透系数与最终渗透系数差异较小;中颗粒缺失结构因大量细颗粒下沉堵塞渗流通道导致渗透系数明显低于良好级配试样;粗颗粒缺失结构内部块石承载骨架结构差,孔隙大,易引发大块石局部破坏,渗透系数高于良好级配试样。