松辽盆地南部海坨子地区超低渗透储层特征与形成因素

通过详细的岩心观察和描述,同时结合铸体薄片、扫描电镜、X-射线衍射、压汞、核磁共振以及物性等资料的研究,认为海坨子地区扶余油层为末端扇中部亚相沉积,储层岩石类型主要为岩屑长石砂岩和长石岩屑砂岩,孔喉结构为小孔隙、细喉或微细喉型,束缚水饱和度高,渗流能力差,属于超低渗透储层。沉积作用和成岩作用是扶余油层超低渗透储层形成的关键。末端扇沉积控制了扶余油层原始沉积物的粒度、碎屑成分以及填隙物成分和含量,使得储层初始孔渗性较差,同时强烈的机械压实作用导致扶余油层原生粒间孔隙体积直线下降,而胶结作用,尤其碳酸盐连晶状基底胶结几乎完全封堵了孔喉,喉道内伊利石等粘土矿物的搭桥生长,也使孔喉变得越来越曲折、狭窄,储层渗流能力因此遭受严重破坏。此外,末端扇储层中大量非渗透性隔夹层导致的强非均质性也是超低渗透储层形成的一个因素。溶蚀作用对扶余油层渗透性的改善有限,但成岩微裂缝和构造裂缝的发育对海坨子地区超低渗透油藏的开发起着至关重要的作用。     

Conditions for instabilities in collapsible solids including volume implosion and compaction banding

We review conditions for material instabilities in porous solids induced by a bifurcation of solution into non-unique strain rate fields. Bifurcation modes considered include jumps in the strain rate tensor of ranks one and higher representing deformation band and diffuse instability modes, respectively. Eigenmodes (e-modes) are extracted for each type of instability to fully characterize various frameworks of deformation in collapsible solids. For diffuse instability these e-modes are determined from a homogeneous system of linear equations emanating from the condition of zero jump in the stress rate tensor, which in turn demands that the tangent constitutive tensor be singular for the existence of nontrivial solutions. For isotropic materials we describe two types of singularity of the constitutive tensor: (a) singularity of the constitutive matrix in principal axes, and (b) singularity of spin. Accordingly, we derive the e-modes for each type of singularity. We utilize the singularity of the constitutive matrix in principal axes as a precursor to volume implosion in collapsible solids such as loose sands undergoing liquefaction instability and high-porosity rocks undergoing cataclastic flow. Finally, we compare conditions and e-modes for volume implosion and compaction banding, two similar failure modes ubiquitous in granular soils and rocks.Supported by U.S. Department of Energy, Grant DE-FG02-03ER15454, and U.S. National Science Foundation, Grants CMS-0201317 and CMS-0324674.     

Compaction bands and induced permeability reduction in Tuffeau de Maastricht calcarenite

The mechanical behavior and permeability of the Tuffeau de Maastricht calcarenite were studied. Compactions bands were found to form in the “transitional” regime between brittle faulting and cataclastic flow. In order to predict the formation of compaction bands, bifurcation analysis was applied on a model developed by Lade and Kim. The numerical results proved to be in good agreement with the experimental ones where the localization point was identified to be the onset of shear-enhanced compaction (a threshold in differential stress after which significant reduction of porosity is induced). Before the onset of shear-enhanced compaction, permeability was primarily controlled by the effective mean stress, independent of the deviatoric stresses. With the onset of shear-enhanced compaction, however, coupling of the deviatoric and hydrostatic stresses induced considerable permeability and porosity reduction.     

兰州高坪湿陷性黄土地基处理方法分析

根据兰州地区3处大厚度高坪黄土的天然密度、含水量、土粒比重等物理性质指标沿深度变化的统计规律,分析了计算值-天然孔隙比随这些指标的变化规律,得出黄土天然孔隙比简化的计算公式。藉此分析强夯法、挤密桩法等地基处理方法的合理设计参数:对于强夯法,平均夯沉量可以作为初步设计参数和质量检测指标;对于挤密桩法,确定了加固深度和处理后的孔隙比,即可确定桩间距和桩径的比值。     

增大击实功的击实试验研究

压实度是路基填筑时控制路基强度和稳定性的关键指标。通过室内试验研究了击实功对路基压实度的影响。结果表明,增大击实功,路基土的最大干密度和7d无侧限抗压强度都有显著提高,抗压强度最大增幅达到50％左右。因此增加路基土的密实度,可以明显地提高路基土的强度,延长路基的使用寿命。     

Feedback mechanisms in chemo-mechanical multi-scale modeling of soil and sediment compaction

Geomaterials respond to some environmental circumstances through generation of a series of feedback mechanisms of damage, deformation, erosion, and chemical processes or reactions: e.g. osmosis, dissolution and precipitation, mineral transformations. These mechanisms are coupled at different scales. Several natural geomechanical processes, as sediment compaction, rock weathering or landsliding appear to include such sequences of mechanisms. A multi-physics model of sediment compaction is examined from the point of view of feedbacks and feedforwards for the phenomena involved at micro- and meso-scale. Two types of feedback are identified: constitutive feedbacks and boundary condition feedbacks. A numerical sensitivity study points out which feedbacks and feedforwards are strong and which are weak.     

废旧轮胎胶粉-黏土混合土的击实性能

废旧轮胎橡胶颗粒用于填埋场衬垫材料改性,有望提高衬垫系统的有效性。击实性能是衬垫设计和施工的基础,但目前缺乏针对性研究,击实机理不够明确。开展废旧轮胎胶粉-黏土混合土的击实试验研究,探讨橡胶颗粒粒径、掺入比等因素对混合土击实性能的影响规律和压实机制。研究表明,当橡胶掺入比从0增大到25%时,胶粉-高岭土的最优含水率增大,胶粉-红黏土的最优含水率减小,变化在2.4%范围内; 混合土的最大干密度从1.65gcm-3减小至约1.40gcm-3; 试验选用的橡胶颗粒粒径对最优含水率和最大干密度差异不显著。在击实过程中橡胶颗粒回弹和橡胶颗粒比表面积变化两种效应下,最优含水率随橡胶掺入比的增加表现出减小(大颗粒时)、不变和增加(小颗粒时)的变化规律,并与基质土的性质密切相关。给出了初步设计时改性黏土含水率和干密度的控制方法,能够基本满足规范中对压实黏土的含水率和压实度的要求,且其渗透系数小于1.010-7cms-1。     

On changes in porosity and volume during burial of argillaceous sediments

The porosity and hence volume of argillaceous sediments is determined by: (1) the magnitude of the effective stress acting within the sediment; (2) the previous stress history of the sediment; and (3) at shallow depths of burial, by features such as the mineralogy and the nature of the depositional environment. Stress paths and the critical state diagrams for a number of clays are used to investigate the range of porosities possible in argillaceous sediments as the effective stresses increase. It is found that all porosity/effective stress curves converge at large stresses. The change in porosity is strongly dependent on the mean effective stress but largely independent of the deviatoric stress, and thus is largely independent of the nature of the stress field acting on the basin (compressional, extensional etc.). Because of the dependence of porosity on the mean effective stress, no simple relationship exists between porosity and depth of burial but in the absence of overpressured pore fluids and assuming the sediment is not overconsolidated, it is possible to contour the porosity/effective stress diagram in terms of burial depths. These data should assist in recalculating stratigraphic thicknesses for basin reconstruction and stratigraphic correlation studies.     

砂砾岩储集体成岩差异性分析 ——以玛北斜坡带三叠系百口泉组为例

凭借着高产油气流,玛湖凹陷北斜坡带百口泉组砂砾岩储层成为近年来颇受储层沉积学家们关注的热点区域。层段内砂砾岩储层储集物性表现出明显的差异性,其控制机理一直尚未明确。本文按照流体成因差异,将层段内岩石相划分为4 种类型：牵引流成因的砂砾岩相、含砾砂岩相、砂岩相,以及重力流成因的砂砾岩相。在不断埋深过程中,重力流砂砾岩相的压实进程远远早于且明显强于牵引流砂砾岩相。而随后持续深埋过程中,重力流砂砾岩相孔隙度不再明显降低,渗透率却呈现明显增加,表明重力流砂砾岩相内的微裂缝开始发育。上述压实效应的差异造成了在储集空间上,牵引流砂砾岩相以原生粒间孔为主要类型,而重力流砂砾岩相则以粒内溶孔和微裂缝为主要类型。最终在宏观储集物性上,牵引流砂砾岩相储集性能明显优于重力流砂砾岩相,成为研究层段内有效的储集体。     

Structural controls on mechanical compaction within sandstones: An example from the Apsheron Peninsula,Azerbaijan

Mechanical compaction of sand-rich reservoirs usually occurs during shallow burial and involves the rearrangement of framework grains and the ductile deformation of soft lithoclasts. The reservoir quality (porosity and permeability) of some Neogene sandstones of the South Caspian Basin has, however, been dramatically reduced by mechanical compaction involving extensive grain-fracturing (i.e. porosity collapse). These sandstones were probably susceptible to pervasive grain-fracturing because they were buried rapidly and experienced compressional deformation prior to reaching 80 °C. Consequently, they did not undergo quartz cementation and were therefore exposed to high stresses while they were extremely weak. Grain-size and structural position are also important controls on the distribution of grain fracturing in the onshore analogue in the Apsheron Peninsula. Microstructural analysis confirms that susceptibility to distributed grain-fracturing increases with increasing grain-size. Structural position has also an important impact on the distribution of porosity collapse. In particular, sandstones within the hinges of folded sections have undergone much more extensive grain-fracturing than within the surrounding area; the increased stresses in this structural position have enhanced distributed grain-fracturing and subsequent deformation band development.