The effect of fluid saturation in an anisotropic multi-scale equant porosity model

It is recognised that exchange of fluid between fractures and the rock matrix can have a strong impact on a rock's anisotropic elastic properties. A recent theoretical advance considers the effect of the scale length of the fractures. We show that under certain circumstances, this model can be simplified. The simplified model matches laboratory data. A prediction of the model is that frequency-dependent effects are important for fluid substitution in the anisotropic case.     

Impacts « multi-échelle » d'un échange (Mg,Ca)–Pb et ses conséquences sur l'augmentation de la perméabilité d'une bentonite

The article addresses the structural effects of solutions of lead nitrate on a suspended or compacted bentonite. A permeability increase is observed on compacted clay. Investigating the composition of output solution, using X-Rays Diffusion at Small Angles and Scanning Electron Microscopy, this permeability increase is explained from structural variations at nanometric (reduction of particle size) and micrometric scales (microfissuration of aggregates). To cite this article: N. Jozja et al., C. R. Geoscience 335 (2003).     

天祝-永登地区大地电磁资料的一维各向异性反演

对分布在甘肃天祝、永登一带的10个大地电磁测点资料进行了一维各向异性介质反演研究，并与二维对称各向异性介质反演结果进行了对比。结果表明在大多数情况下一维各向异性反演有可能揭示出地壳介质电导率各向异性结构的主要特征；同时利用某些平均阻抗和特征阻抗的一维各向同性介质反演亦可获得较为可信的电性分层界面。反演所获得之介质电导率可能为各主方向电导率主值的某种平均。     

岩石孔隙结构的地震信号特征

岩石孔隙结构是控制砂岩和碳酸盐岩的地震波速度和渗透率的重要参数之一。如果两种类似的岩石其孔隙度一定,而渗透率不同,那么它们的声波速度相差2km/s,而渗透率两者则可能相差近6个数量级,即从0.01mD到20mO。在本文中我们总结了由一个广义孔隙弹性理论简化的一个双参数弹性速度模型，以描述孔隙结构对弹性波的影响。由于矿物和储层的流体是给定的,我们用孔隙度和骨架的柔性(挠性)因子来确定速度模型,这个模型可以用于地震反演和储层表征,已改善孔隙度和储量的计算骨架柔性因子可用于岩石结构(PST)类型的定量分类,并可以利用叠前、叠后的两种地震资料将其与孔隙的连通性和渗透率联系起来。本项研究同时也有助于说明为什么振幅与偏移距(AVO)分析用于流体检测在某些情况下失败。这是由于孔隙结构对地震波的影响能够掩盖所有流体效应，特别是在碳酸岩中。     

利用流动单元计算高含水油田渗透率

油田进入高含水期,储层参数发生了变化。用传统的解释方法计算渗透率很难达到理想的精度。作者提出利用储层流体流动单元流动带指标反算渗透率的方法,并应用于辽河油田欢26断块高含水油田储层评价中,取得了良好的应用效果。     

The Interstitial Environment of Sandy Beaches

Abstract. The interstitial system of sandy beaches is lacunar and has its dimensions defined by the sand granulometry. It can be described by features such as pore size, porosity, permeability, and water content. The most important process occurring in this system, water filtration, is driven by inputs of freshwater from groundwater discharge, and inputs of seawater by tides, wave run-up, and subtidal wave pumping. Reflective beaches have seawater input effected mainly by waves; they filter large water volumes with short residence times. Dissipative beaches display the opposite patterns, slowly filtering small volumes input by tides. Flow patterns and their effects on interstitial climate are described. The water table of the beach moves in response to groundwater discharge, tides, and waves and influences erosion/accretion processes on the beach face: a high water table promotes erosion. A series of moisture zones can be recognised from the dry surface sand at upper tide levels, to permanently saturated sand below the low tide water table, namely: a stratum of dry sand, a stratum of retention, a stratum of resurgence, and stratum of saturation. Interstitial chemistry is briefly described in terms of salinity changes, organic loads, oxygen content, and nutrient cycling. It is concluded that the interstitial environment of sandy beaches spans a continuum between physically and chemically controlled extremes: the former condition occurs on coarse sand reflective beaches, which experience low organic inputs and high filtration rates of large water volumes — resulting in powerful hydrodynamic forces; the latter occurs on dissipative beaches of fine sand, which are subject to high organic inputs and low filtration volumes — resulting in stagnation and steep vertical chemical gradients. Many intermediate situations occur and these are more favourable to interstitial life than either of the extremes.     

The influence of particle morphology on microbially induced CaCO3 clogging in granular media

Abstract

Sporosarcina pasteurii (ATCC 11859) is a nitrogen-circulating bacterium capable of precipitating calcium carbonate given a calcium source and urea. This microbially induced carbonate precipitation (MICP) is able to infill inter-granular porosity and act as a biological clogging agent, thus having a wide potential application in strengthening coastal foundations, preventing erosion by seas and rivers and in reducing sand liquefaction potential in coastal areas. A successful MICP application requires the understanding of the primary parameters that influence the microbially mediated process to achieve its engineering goals, such as injection scheme, chemical concentrations, retention times, and injection rates. However, the granular morphology has generally been oversimplified to ideal shape without enough consideration in previous studies. The following explores the critical micro-scale influence of particle morphology on mechanisms of microbially induced clogging. Spherical, non-spherical and angular particles were used as granular aggregates in permeating column experiments with the resulting permeability and calcium carbonate content of the treated aggregates examined. Microscopic examination (SEM) defines the features of the distribution of microbially precipitated calcium carbonate and the forms of clogging. The results show: (1) given a fixed duration of treatment, the calcium carbonate content for the spherical particle aggregate is significantly higher than that for near-spherical and angular particle aggregates; (2) for identical durations of treatment, the maximum permeability reduction occurs for angular particles (rather than for spherical particles with the highest carbonate content). This suggests that the microscopic distribution of calcium carbonate is significantly influenced by particle morphology, exerting a critical control in the effectiveness of clogging. SEM images indicate that the microbial calcium carbonate precipitates encapsulate the spherical particles as a near-uniform shell and occlude the pore space only by increasing the shell thickness. In contrast, the near-spherical and angular particles are only partially coated by a calcium carbonate film with scattered crystals of vaterite and calcite further clogging the void space. The polyhedral nature of the non-spherical particles tends to result in a slot-shaped pore structure which critically defines the hydraulic conductivity of the ensemble medium. As the microbial vaterite and calcite continue to accumulate on the particle surface, these slot-shaped pore structures become increasingly more tortuous – resulting in a noticeable reduction of permeability at a lower calcium carbonate content.     

微生物胶结砂岩型铀矿砂的抗渗性能试验研究

地浸采铀产生的污染物通过渗透迁移作用威胁地下水资源,已成为制约地浸采铀技术发展的瓶颈,而微生物胶结技术能有效地降低砂岩铀矿的渗透性,是目前抑制污染物向采区周围地下水迁移的有效方法。因此,选用巴氏芽孢杆菌,分析其耐酸性;利用自行研制的砂岩型铀矿砂渗透系数试验装置,测得不同胶结液浓度、不同菌液与胶结液体积比以及不同注浆轮次条件下砂岩型铀矿砂的渗透系数,确定其最优的参数配比;采用扫描电镜（scanning election microscopy,简称 SEM）和X射线衍射光谱（X-ray diffraction,简称 XRD）等设备,表征微生物胶结前后铀矿砂的矿物成分及其微观结构,研究其微生物胶结抗渗机制。研究结果表明：巴氏芽孢杆菌在 pH = 4 时仍具有较好的繁殖能力和脲酶活性,能适应铀矿砂的酸性环境;在一定范围内增大胶结液浓度、菌液与胶结液的体积比可以促进碳酸钙的生成,最佳的胶结液浓度为 1 mol/L、菌液与胶结液体积比为1:3、注浆轮次为7时,注浆后铀矿砂的减渗率达到 95.33%;胶结后铀矿砂的渗透系数随注浆轮次的增加而降低,经过11轮注浆后铀矿砂的减渗率高达99.75%,渗透系数下降到 2.8×10⁻⁵ cm/s;沉积的碳酸钙晶型主要为方解石,方解石堵塞铀矿砂粒间孔隙,并将矿砂颗粒胶结成整体,是铀矿砂渗透系数降低的主要原因。微生物诱导碳酸钙沉淀胶结铀矿砂的抗渗机制为控制和减少地下水污染提供重要的理论指导。     

动渗耦合作用下软黏土渗透系数演化机制分析

针对天津地区滨海软黏土,开展了一系列动渗耦合三轴试验,系统分析了长期循环作用下软黏土渗透系数的变化规律。结合扫描电镜（SEM）和压汞试验（MIP）对不同变形阶段软黏土的微观结构特征进行分析,阐述了渗透系数的演化规律及机制。研究表明：在动渗耦合作用下,软黏土渗透系数呈现三阶段变化特征;渗透系数随渗流力呈现先增大后减小的变化规律,随动应力和频率呈现先减小后增大的特征。微观试验表明,渗透系数的演化是微结构孔隙大小、形态、分布特征渐进调整的宏观体现：加载初期,颗粒间的架空超大孔隙（孔隙直径D>2.5 μm）大幅压缩,孔隙形态变化不大,渗透系数呈线性衰减;加载中期,大颗粒破碎生成的小颗粒密布填充于大颗粒间,生成大量“密小而曲折”的小孔隙（0.05 μm<D<0.1 μm）,渗透系数呈现缓慢下降;加载末期,结构致密稳定,渗透系数基本不变。对于非稳定变形,颗粒团（聚）体间重新生成“条带”状孔隙,渗透系数反弹增大。该研究成果可为流固耦合分析中渗透系数的确定提供理论依据。     

新疆库拜煤田铁列克矿区地应力分布及其对煤层气开发的影响

地应力、煤储层渗透率和煤储层压力等是影响煤层气开发的重要因素。通过分析新疆库拜煤田铁列克矿区注入/压降试井及原地应力测试数据,结合铁列克矿区煤层气井日产气量分析,研究了新疆库拜煤田铁列克矿区地应力变化规律及其对煤层气开发的影响,分析了铁西矿区和铁东矿区煤储层地应力特征及其对煤储层物性的影响。结果表明:(1)地应力状态在垂向上发生变化,埋深处于550~650 m、650~850 m和850~1 200 m时,地应力状态类型依次为σ_H>σ_v>σ_h、σ_H≈σ_v>σ_h和σ_v>σ_H>σ_h;(2)埋深850 m处既是垂直主应力和最大水平主应力的转换点也是渗透率趋势变化点,指示了地应力对渗透率的控制作用;(3)渗透率和煤储层压力与地应力分别呈负相关和正相关关系;(4)地应力对产能的负效应大于地应力对产能的正效应,使典型日产气量随着地应力的增大而减小;(5)铁西矿区和铁东矿区中部煤储层碎粒煤较发育、吸附孔体积和含气量均较大,是煤层气开发的有利区带。研究成果可为库拜煤田下一步煤层气开发提供理论指导。