Petrophysical study of faults in sandstone using petrographic image analysis and X-ray computerized tomography

Petrographic image analysis (PIA) and X-ray computerized tomography (CT) provide local determinations of porosity in sandstone. We have investigated small faults called deformation bands in porous sandstones using these techniques. Because the petrophysical properties of the fault rock vary at a small scale (mm scale), the ability of PIA and CT to determine porosity in small volumes of rock and to map porosity distribution in two and three dimensions is crucial. This information is used to recognize the processes involved in fault development and the different kinds of microstructures associated with dilatancy and compaction. The petrophysical study of fault rock in sandstone permits one to make predictions of the hydraulic properties of a fault and thereby evaluate the sealing or fluid transmitting characteristics of faulted reservoirs and aquifers. The results of this study indicate that faulting in sandstone alters the original porosity and permeability of the host rock: the porosity is reduced by an order of magnitude and the permeability is reduced by one to more than seven orders of magnitude for faults associated with compaction.     

Comparison of the effective pressure law for permeability and resistivity formation factor in Chelmsford granite

Permeability, resistivity formation factor, and pore volume change were simultaneously measured on samples of Chelmsford granite subjected to confining pressure and pore pressure cycles. Using a technique described in a previous paper, the tangent coefficients of the effective pressure law for permeability _k and for formation factor _F were determined. _k and _F did not differ significantly from one another. They showed a strong stress history dependence as has already been observed for _k in several crystalline rocks. According to the definition of the effective pressure law used here, two physical properties with identical 's must be related through a one-to-one functional relationship. Hence, the observation above suggests that such a relationship may be empirically found between permeability and formation factor. Indeed, analysis of the data revealed that, to a good approximation, permeability was inversely proportional to the formation factor. The same relation has previously been observed in other crystalline rocks. This relationship was included in a recent version of the so-called equivalent channel model. Using this model, the specific surface area of the cracksA _c/V_S, the standard deviation of the distribution of asperities heightsh and the hydraulic radiusm _o were evaluated. The following values were respectively found: 850 cm^–1, 0.008 m and 0.14 m. The specific surface area of the cracks was independently estimated on micrographs of polished sections using a standard quantitative stereology method. The result was in good agreement with the values estimated from the transport properties data.     

长江下游上河口段北岸无凝聚性砂岸的变形破坏规律

长江下游上河口段北岸,属南通市城港口范围,岸线在平面上是反“S” 型,大部分处于凹岸的顶冲区,尽管江岸的演变受诸如河型,迳流、潮汐、科氏力等主要因素的影响,但其变形破坏规律恰受以细粉砂层为主体的这一江岸介质条件的制约。文中分析了发生于近数十年来江岸的各种变形破坏形式和规律。对是否存在砂体的渗透变形问题,据水位观测,室内渗透变形试验和现场调查所得,亦作了较详细的分析。     

Numerical modeling of scour and deposition around permeable cylindrical structures

Flow past wall-mounted cylindrical structures is commonly encountered in natural rivers where piers of bridge crossings or vegetation stalks are common within channels.In the current study,the influence of cylindrical structures on flow/bathymetric alterations for three different permeabilities is explored via two-dimensional numerical modeling.In model construction processes,the structure permeability is varied with the surface void ratio along the perimeter of the cylinder,i.e.the density of emergent and submerged solid elements is used to delineate the cylinder boundaries.The validation of this model is guaranteed through careful comparison with experimental data obtained for similar hydrodynamic conditions and cylinder properties.The validated model then is applied to investigate flow properties and scour and deposition patterns with structure permeabilities of 0.0,0.38,and 0.62.Simulated results show that a permeable structure has less impeding effects on flow than a solid cylinder.The wake velocity reduction decreases 38% with a 63% increase in the structure permeability due to increasing intensity of the bleeding flow through surface voids,causing less flow contraction and diversion,lower turbulent kinetic energy,and lower lee-side scour around the permeable structure and less deposition downstream under live-bed conditions.     

马关某渣库场区水文地质特征分析

马关县地处云贵高原南部,区内岩溶地貌发育,以峰林、岩溶洼地、谷地为主。为探讨拟建项目场区的水文地质特征,初步认识拟建工程建筑物与地下水之间的相互影响程度。对研究区开展全面的水文地质条件调查,并进行水文地质钻探、抽水试验、注水试验、包气带饱和渗透等现场试验工作。结合前人研究成果,综合得出研究区内地下水类型主要为松散岩类孔隙水、碎屑岩裂隙水和碳酸盐岩类岩溶裂隙水;区内地下水动态及补、径、排条件稳定,对工程建筑物的稳定性影响较小;出露地层的渗透性为弱-中等,且包气带具有一定厚度,渗透性低,整体防污性能较好。     

周期振荡法在低渗透测量中的应用研究

周期振荡法是一种新兴的多孔介质渗透率测量方法，具有测量周期短、稳定性好、精度高等优点。然而，由于缺乏对周期振荡法的系统研究，该方法未能在低渗透测量领域得到推广应用。采用数值模拟方法，分别研究了不同孔隙率、渗透率对周期振荡法气压测量结果的影响，以及不同形式周期波在周期振荡法渗透率测量中的适用性。结果表明：无论是孔隙率，还是渗透率都会影响气体压力传递过程；周期振荡法渗透率测量时可以不需要初始气压平衡过程，一定时间后测量结果几乎不受初始气压状态影响；与正弦波相比，方波对下游气体压力响应的影响更明显，而且方波、三角波和锯齿波具有容易加载的特点，建议采用方波取代正弦波进行周期振荡法试验。研究成果对指导周期振荡法试验和解决低渗透测量难题有一定帮助。     

酸污染原状黄土渗透微观特征演变规律试验研究

研究污染黄土的渗透特性能够为污染场地的治理提供经济高效的方案措施。以蒸馏水作为渗液，采用GDS三轴渗透仪通过室内试验研究了盐酸、硝酸和硫酸侵蚀黄土的渗透特性变化规律，并从微观结构的变化进行机制分析。试验结果表明：相同固结应力条件下，不同类型污染土的渗透系数均随酸液浓度的增大而降低；随着酸液浓度增大，污染土骨架连接方式由点?点接触向点?面接触、面?面接触转变，土体内部大孔隙消散、小孔隙增多使得有效渗流孔隙减少，导致污染土渗透系数降低；相同试验条件下不同类型污染土渗透性能变化规律为：硫酸<硝酸<盐酸<水，即酸液增强了黄土防渗及防污性能。研究结果以期为黄土地区的工程活动和防污治理提供有效参考。     

露天采煤矿区土地的复垦：土壤透水性实验

露天采煤矿区土地的复垦：土壤透水性实验党志，万国江（中国科学院地球化学研究所，贵阳５５０００２）关键词露天采煤矿区，复垦，土壤透水性实验煤矿区土地复垦常用的方法是在矿渣表面覆盖一层约５～４０ｃｍ厚的土壤，种草植树以恢复植被。但在一些化学风化强烈的地区...     

Scales of rock permeability

Permeability is a transport property which is currently measured in Darcy units. Although this unit is very convenient for most purposes, its use prevents from recognizing that permeability has units of length squared. Physically, the square root of permeability can thus be seen as a characteristic length or a characteristic pore size. At the laboratory scale, the identification of this characteristic length is a good example of how experimental measurements and theoretical modelling can be integrated. Three distinct identifications are of current use, relying on three different techniques: image analysis of thin sections, mercury porosimetry and nitrogen adsorption. In each case, one or several theoretical models allow us to derive permeability from the experimental data (equivalent channel models, statistical models, effective media models, percolation and network models). Permeability varies with pressure and temperature and this is a decisive point for any extrapolation to crustal conditions. As far as pressure is concerned, most of the effect is due to cracks and a model which does not incorporate this fact will miss its goal. Temperature induced modifications can be the result of several processes: thermal cracking (due to thermal expansion mismatch and anisotropy, or to fluid pressure build up), and pressure solution are the two main ones. Experimental data on pressure and temperature effects are difficult to obtain but they are urgently needed. Finally, an important issue is: up to which point are these small scale data and models relevant when considering formations at the oil reservoir scale, or at the crust scale? At larger scales the identification of the characteristic scale is also a major goal which is examined.