低流速高含水油水两相流超声传感器持水率测量特性（英文）

国内陆上处于中晚期开采的低孔低渗油藏已进入高含水生产状态,其井筒内油水两相流分散相(油滴)局部流速及浓度呈严重的非均匀流动剖面特性,致使油井持水率检测难度很大。本文采用脉冲透射式的超声传感器对低流速高含水油水两相流持水率进行测量。首先,使用多物理场耦合有限元法计算超声场灵敏度分布,对超声传感器激励频率进行了优化。通过计算不同持油率下声压级衰减率,对超声传感器直径的适用性进行了考察。在此基础上,研究了油滴直径及分布对超声传感器声场分布特性的影响。为验证优化后的超声传感器测量特性,搭建了低流速高含水垂直上升油水两相流流动环试验装置,并获取了超声传感器持水率输出响应特性。结果发现超声传感器对水包油段塞流(DOS/W)的测量分辨率较差,但对水包油泡状流(DO/W)和水包油细小泡状流(VFD O/W)具有较好的分辨率。研究表明脉冲透射式超声法对低流速高含水油水两相流持水率测量存在潜在的应用价值。     

水平井生产测井组合仪模拟井测量数据分析与模型建立

由于水平油水两相流局部流速及局部相含率沿管径方向存在复杂分布,致使其流量及相含率测量非常困难.本文利用伞集流涡轮流量计、电导传感器、过流式电容传感器构成的生产测井组合仪,在水平油水两相流模拟井中开展了动态实验,分析了流动特性及管子角度倾斜对涡轮流量计及含水率传感器响应特性的影响.根据电容及电导传感器在不同总流量及含水率范围的响应分辨特性,分别采用变系数漂移模型及统计模型预测分相流量,发现变系数漂移模型能够自适应调整模型中的流型参数,且对油水两相分相流量具有较高预测精度.     

水平井产出剖面解释模型及图版

水平井中因重力分异普遍存在层流,且流型受井斜角度影响变得复杂,致使常规生产测井仪器不完全适用于水平井,资料解释难度大大增加.首先简要介绍了国外新型水平井测量仪器及解释方法所取得的进展;其次,重点阐述了我们通过理论研究和实验模拟初步得出的水平井产出剖面解释模型和实验解释图版,该模型以滑脱速度模型为核心,采用改进后的井下刻度技术和最优化方法进行了校正.最后,通过利用我们制作的水平井产出剖面解释软件对X井进行了解释,经实践证明,该方法应用效果良好.     

油水饱和泥质砂岩流动电位的频散特性

油水饱和泥质砂岩中流动电位的研究对于揭示含油储层震电勘探和动电测井的机理有着重要的意义.本文首先从岩石孔隙的微观结构出发,构造了描述水润湿条件下油水饱和泥质砂岩储层的毛管模型.在模型中依据油水流动遵守的Navier-Stokes方程和电化学传质动力学理论,建立了描述油水饱和泥质砂岩流动电位的数学方程,并数学模拟了岩石储渗参数对流动电位频散特性的影响规律.研究结果表明:储层孔隙内流体受到的粘滞力与惯性力控制着水相和油相的流动,从而决定了流动电位的频散特性.随着孔隙度的增大,油水两相各自的有效渗透率均增大;而含水饱和度的升高使得水相有效渗透率增大,油相有效渗透率减小.在水润湿条件下,流动电位耦合系数随含水饱和度升高而增大,随束缚水饱和度的升高而减小.另外,流动电位相对耦合系数也随含水饱和度的升高而增大,但无频散现象.     

低流速高含水条件下油水两相流产出剖面测井方法（英文）

为了获得低流速高含水条件下油井内油水两相流产出剖面,本文提出了一种由场聚焦弧形对壁式电导传感器(ATCS)与插入式相关流量计(CFM)构成的组合测井方法,并通过实验对其测量特性进行了验证。采用场聚焦弧形对壁式电导传感器测量分相持率,插入式相关流量计实现混合流速的测量,通过建立基于流型的漂移模型对分相表观速度进行了预测。研究结果表明,场聚焦弧形对壁式电导传感器对持水率有很好的分辨率,且基于传感器信号及非线性时间序列分析方法可以实现流型的准确识别。插入式相关流量计由于插入体的流型调控作用,增强了上下游信号的相关性,简化了相关速度与混合流速的关系。基于漂移模型可实现不同流型分相表观速度的高精度预测。     

一种利用共振声谱法检测气液两相介质中气体含量的新方法

根据共振声谱原理,建立了气液两相介质中圆柱共振腔共振声谱的实验测量系统,研究了共振腔体中不同含量的气体对共振声谱的幅度和共振频率的影响.实验结果表明：共振幅度和共振频率随着气体流量的增加都呈指数衰减变化趋势,但共振幅度比共振频率的衰减速度快,都可反映气体流量的变化.另外,在理论上,推导了均匀流体模型气液两相介质中的圆柱共振腔的共振频率计算公式,并模拟计算了共振频率和气体含量的变化规律曲线.理论研究结果表明,随着持气率的增加,共振频率减小;当持气率较小时,共振频率衰减较快.这一结论已经被本文实验测量结果所验证.理论和实验研究表明,利用共振声谱法可以检测气液混相介质中气体含量,它为发展生产井中气液两相流分相含量检测方法提供一种可能的途径.     

岩石孔喉道中表面粗糙度对油水两相流动的影响

岩石孔喉道中表面粗糙性是影响油水两相流动的重要因素之一.本文利用格子波尔兹曼数值模拟方法模拟了在光滑和粗糙孔喉道中的水驱油的流动特性,通过比较亲水和亲油的孔喉道模型中的含水饱和度、油水相对渗透率的变化,分析粗糙度对于流动特性的影响.结果表示:1)无论是亲水性还是亲油性模型,孔喉道表面的粗糙性对于油水流动都起阻碍作用;2)由于孔喉道表面粗糙元间空隙的存在,一部分油被圈闭于空隙中,不能实现完全驱替;3)水驱油的过程中,亲水性的孔喉道的含水饱和度和油水相对渗透率均高于亲油性孔喉道;4)在亲水性孔喉道中,粗糙性对含水饱和度和油水相对渗透率的影响更为明显,亲油性孔喉道次之;5)亲油性孔喉道的粗糙性增加到一定的程度后,它对流动的阻碍作用不再随着粗糙性的增加而逐渐增强.     

超低渗透砂岩油藏微观渗流特征及驱油效率的影响因素

通过鄂尔多斯盆地超低渗透砂岩油藏油水相对渗透率测定和微观模型驱替实验,探讨超低渗透砂岩油藏微观渗流特征及驱油效率的影响因素.研究结果表明,超低渗透砂岩油藏储层相对渗透率曲线特征表现为:束缚水饱和度高,残余油饱和度高,驱油效率低,油水两相共渗区范围窄.随含水饱和度增加,油相相对渗透率急剧下降,水相相对渗透率上升缓慢,无因次采油指数和油井产量大幅度下降.超低渗透砂岩油藏微观驱替特征表现为:最终驱油效率低,随注入倍数增加,采收率和含水率增高.注入倍数为1~2 PV过程中采收率与含水率增加幅度较大;注入倍数在3~4 PV时,采收率和含水率增加幅度趋于平缓.超低渗透砂岩油藏影响驱油效率的因素可以分为反映油藏固有特征的内在因素和反映驱替条件的外在因素.     

气水两相裂缝型介质孔隙流体微观分布模式及其声学响应特性

关于声波速度与流体饱和度的关系已开展了大量实验工作,声波速度随饱和度的变化规律与孔隙流体在孔隙尺度范围分布的不均匀性有关,从理论上采用等效流体模型来定量表征通常存在着较大偏差。从弹性波动理论出发,以纵波震源作为激发震源项,采用时间域二阶和空间域八阶的交错网格有限差分方法对气水两相裂缝型介质的声波波场进行了数值模拟。通过计算不同孔隙流体分布模式下和不同饱和度情况下岩样的声波速度,分析了岩样在不同孔隙流体分布模式下声波速度随饱和度的变化规律,并对物理实验得出的声波速度随饱和度变化的规律从孔隙流体微观分布角度给出了合理解释。数值计算方法简单且精度高,对地震数据解释以及烃类开采过程中监测孔隙流体结构和组分变化有一定的指导作用。     

地形对颗粒驱动重力流影响的模拟实验研究

颗粒驱动重力流由悬浮在流体中的颗粒提供驱动力并侵入到环境流体之中,交换流体实验研究是理解此类流体运动本质的主要手段之一。将颗粒驱动重力流与自然火山碎屑密度流的流体参数进行正确配比,能够理解火山碎屑密度流的流动和堆积过程的本质。本文介绍了火山碎屑密度流及其物理模拟实验研究,并对其物理本质(颗粒驱动重力流)的箱子模型进行推导。通过在实验水箱中模拟不同的地形变化,对颗粒驱动重力流在遇到地形变化时的运动特征和颗粒堆积特征进行研究。本论文设定了两种地形障碍对颗粒驱动重力流的影响模式:横亘的限定高度障碍物和侧向部分遮挡障碍物。横亘障碍物对流体底界形成整体阻挡;侧向部分遮挡障碍物在垂直方向上对流体侧界形成阻挡,对流体底界形成部分阻挡。通过记录流体遇到障碍物时的现象,获取流体前锋速度,测定颗粒堆积密度,评估横亘障碍物高度(小于或等于流体前锋高度),侧向遮挡程度对成分/颗粒驱动重力流流动特征和堆积特征的影响为:(1)成分重力流在通过有限高度横亘阻挡时,不同高度障碍物对流体的运动状态产生的影响体现为流体重新回到"惯性—浮力相"的距离长短和前锋减速特征不同。当障碍物高度分别相当于流体前锋高度的～1/3、～2/3和～1/1时,流体重回"惯性—浮力相"所需的距离为障碍物高度的35.1～38.6倍、12.0～18.1倍和2.1～4.3倍,三者不呈现线性关系;在通过上述高度横亘阻挡之后,流体前锋速度按照t~(5/6),t~(3/4)和t~(2/3)衰减。(2)颗粒驱动重力流体通过相当于其前锋高度的1/3、2/3和1/1横亘障碍物之后,无量纲化流体前锋运动特征的L/T斜率分别为～2/9、～1/9和～1/16。不同位置、相同高度的横亘阻挡对流体前锋减速模式产生相同的影响;流体前锋在通过较高障碍物之后的减速更加明显。h_b~(6.9)h_b~(7.2)h_b~(15)(3)与通过较高障碍物相比,当颗粒实验流体通过较低障碍物时,其堆积曲线下降较缓慢。当流体通过高度分别为流体前锋高度的～1/3、～2/3和～1/1的障碍物之后,堆积曲线呈现出、和的变化特征。与距离较近的障碍物相比,距离较远的障碍物对颗粒驱动重力流通过障碍物之后颗粒堆积的影响更大。(4)侧向遮挡对成分重力流体流动状态的影响具有滞后性。阻挡比例越小,这种滞后性越明显。当盐水流体通过占水箱宽度1/4挡板之后,其前锋位置的变化特征为t~(0.771),通过占水箱宽度1/2挡板之后为t~(0.700),通过占水箱宽度3/4挡板之后为t~(0.623),未呈现线性关系。(5)不同程度侧向遮挡对颗粒驱动流体前锋运动特征、沉积特征和堆积结果的影响表现出复杂性:在颗粒驱动重力流体通过侧向遮挡之后的最初一段距离内,流体前锋速度没有较大的改变。随着挡板宽度的增加,经过挡板之后的实验流体将会更快地进入减速阶段。与较宽挡板相比,颗粒驱动重力流在通过较窄挡板之后的堆积曲线下降较平缓。在经过相同宽度的挡板之后,初始约化重力大的流体,在经过挡板之后堆积曲线下降的越平缓。与参考实验流体相比,通过1/4遮挡的流体前锋速度与参考实验流体相当,并在后期超越参考实验流体,在遮挡位置之后的堆积物总量也大于参考实验流体;通过1/2遮挡的流体前锋速度在无量纲时间T100内明显下降,在T100之后加速超过参考实验流体,最终堆积总量小于参考实验流体;通过3/4遮挡的颗粒驱动重力流前锋速度和堆积结果都有显著下降。利用流体力学相似性原理,对实验流体的各项参数进行无量纲分析并与天然火山碎屑密度流进行对比。本论文的研究内容能够代表低密度火山碎屑流的物理特征,并适用于以下两种地质情况:(1)火山碎屑密度流翻越(破)火口缘的运动和堆积特征;(2)火山碎屑密度流通过曲折山谷的运动和堆积特征。根据本文实验的启示,对长白山天池火山八卦庙期火山碎屑流在火山口缘内外分布特征进行初步探讨;对1991年日本云仙岳火山碎屑流造成的人员伤亡原因进行初步探讨。本文的研究细化了火山碎屑密度流在遇到不同形态障碍物时的流态变化,为火山灾害评估提供更详细的解决方案;在实验过程中所摸索出来的一些经验和实验技术,为实验火山学的进一步发展提供经验。     

Topographic forcing of flow partition and flow structures at river bifurcations

This paper presents the predicted flow dynamics from the application of a Reynolds‐averaged Navier–Stokes model to a series of bifurcation geometries with morphologies measured during previous flume experiments. The topography of the bifurcations consists of either plane or bedform‐dominated beds which may or may not possess discordance between the two bifurcation distributaries. Numerical predictions are compared with experimental results to assess the ability of the numerical model to reproduce the division of flow into the bifurcation distributaries. The hydrodynamic model predicts: (1) diverting fluxes in the upstream channel which direct water into the distributaries; (2) super‐elevation of the free surface induced at the bifurcation edge by pressure differences; and (3) counter‐rotating secondary circulation cells which develop upstream of the apex of the bifurcation and move into the downstream channels, with water converging at the surface and diverging at the bed. When bedforms are not present, weak transversal fluxes characterize the upstream channel for almost its entire length, associated with clearly distinguishable secondary circulation cells, although these may be under‐estimated by the turbulence model used in the solution. In the bedform dominated case, the same hydrodynamic conditions were not observed, with the bifurcation influence restricted and depth scale secondary circulation cells not forming. The results also demonstrate the dominant effect bed discordance has upon flow division between the two distributaries. Finally, results indicate that in bedform dominated rivers. Consequently, we suggest that sand‐bed river bifurcations are more likely to have an influence that extends much further upstream and have a greater impact upon water distribution. This may contribute to observed morphological differences between sand‐bedded and gravel‐bedded braided river networks. Copyright © 2012 John Wiley & Sons, Ltd.     

Texas environmental flow standards and the hydrology-based environmental flow regime methodology

Abstract

In 2007, the Texas legislature created a program to identify environmental flow standards statewide through the coordinated efforts of scientific and stakeholder groups and rulemaking by the Texas Commission on Environmental Quality. To aid in this task, a Hydrology-based Environmental Flow Regime (HEFR) method was developed that combines a suite of user-customizable hydrologic statistics with an implementation framework. Following the concepts of the Natural Flow Paradigm, the methodology includes the separation of a long-term hydrograph into key flow components (e.g. subsistence, base, high-flow pulse and overbank) defined by the Texas Instream Flow Program. Seasonal, annual and inter-annual flow component statistics were then coupled with biology, water quality and geomorphology overlays, where available, and with implementation rules applied to example large-scale water supply projects to support development of environmental flow standards for use in water rights permit conditions. The HEFR methodology and resulting flow recommendations are compared to two contemporary in-stream flow studies and adopted environmental flow standards. Subsistence flows were fairly similar. Baseflows were in a similar range, but fewer than three seasonal levels have sometimes been specified in in-stream flow studies. Episodic events are quite different in terms of magnitude, frequency, duration and applicable number.

Editor D. Koutsoyiannis; Guest editor M. Acreman

Citation Opdyke, D.R., Oborny, E.L., Vaugh, S.K., and Mayes, K.B., 2014. Texas environmental flow standards and the hydrology-based environmental flow regime methodology. Hydrological Sciences Journal, 59 (3–4), 820–830.     

The development of new analytic elements for transient flow and multiaquifer flow

We deal in this paper with an ongoing development of the analytic element method. We present in outline new analytic line elements that are suitable to model general flow fields, i.e., flow fields that possess a continuously varying areal inflow or outflow. These elements are constructed specifically to model the leakage through leaky layers that separate aquifers in leaky systems and to model transient effects. The leakage or release from storage underneath linear features is modeled precisely by the new elements; the singularity in leakage is matched exactly by the approximate solution. Applications are given for a problem involving leakage and for a case of transient flow. We note that the analytic elements can be used also to reproduce the effect of continuously varying aquifer properties, e.g., the hydraulic conductivity or the elevation of the base of the aquifer. In the latter case, the elements would reproduce the rotation of the flow field caused by the variation in properties, rather than the divergence as for the case of leakage.     

Textural analysis and flow mechanism of the Donzurubo subaqueous pyroclastic flow deposits

The Donzurubo subaqueous pyroclastic flow deposits deposited in subaqueous environments maintaining high temperatures (about 500°C). Each flow unit of these pyroclastic flow deposits shows some characteristic size distributions in its stratigraphic column. The concentration of pumice at the top clearly defines the top facies of a flow unit. Median diameter (Md Ø) and the averages of the largest ten essential dense debris increase gradually starting from both the top and the bottom of the flow unit. The maximum points of Md Ø and the averages of the largest ten essential dense debris are usually found in the middle zone of each flow unit, but the Md Ø maximum points are generally in a lower position than the averages. Mechanical analyses show that the deposits consist of polymodal populations. They show, on the whole, an asymmetrical distribution, which is mainly due to the absence of the coarser fractions of the main population. The size distribution characteristics and the C-M pattern of the deposits suggest that these subaqueous pyroclastic flow deposits were not originated by homogeneously suspended turbulent flows but by incandescent turbulent flows with layered suspension.     

Modeling axisymmetric flow and transport

Unmodified versions of common computer programs such as MODFLOW, MT3DMS, and SEAWAT that use Cartesian geometry can accurately simulate axially symmetric ground water flow and solute transport. Axisymmetric flow and transport are simulated by adjusting several input parameters to account for the increase in flow area with radial distance from the injection or extraction well. Logarithmic weighting of interblock transmissivity, a standard option in MODFLOW, can be used for axisymmetric models to represent the linear change in hydraulic conductance within a single finite-difference cell. Results from three test problems (ground water extraction, an aquifer push-pull test, and upconing of saline water into an extraction well) show good agreement with analytical solutions or with results from other numerical models designed specifically to simulate the axisymmetric geometry. Axisymmetric models are not commonly used but can offer an efficient alternative to full three-dimensional models, provided the assumption of axial symmetry can be justified. For the upconing problem, the axisymmetric model was more than 1000 times faster than an equivalent three-dimensional model. Computational gains with the axisymmetric models may be useful for quickly determining appropriate levels of grid resolution for three-dimensional models and for estimating aquifer parameters from field tests.     

A residual flow procedure and application for free surface flow in porous media

A finite element procedure based on the extension of the saturated flow domain into the partially saturated zone above the free surface is proposed. The finite element equations are derived by using a pseudo variational principle which results into a residual or correction load vector. The steady or transient free surface is corrected by using the residual load in an iterative scheme. The proposed procedure uses only one (initial) mesh and does not require modification of the mesh during iterations. It is compared (qualitatively) with other procedures such as variable mesh and variational inequalities. The procedure provides satisfactory comparisons with a number of closed-form solutions and laboratory test results; two applications involving the latter are described in the paper.     

Effect of saltating sediment on flow resistance and bed roughness in overland flow

The acceleration of saltating grains by overland flow causes momentum to be transferred from the flow to the grains, thereby increasing flow resistance and bed roughness. To assess the impact of saltating sediment on overland flow hydraulics, velocity profiles in transitional and turbulent flows on a fixed sand-covered bed were measured using hot-film anemometry. Five discharges were studied. At each discharge, three flows were measured: one free of sediment, one with a relatively low sediment load, and one with a relatively high sediment load. In these flows from 83 to 90 per cent of the sediment was travelling by saltation. As a result, in the sediment-laden flows the near-bed velocities were smaller and the velocity profiles steeper than those in the equivalent sediment-free flows. Sediment loads ranged up to 87·0 per cent of transport capacity and accounted for as much as 20·8 per cent of flow resistance (measured by the friction factor) and 89·7 per cent of bed roughness (measured by the ratio of the roughness length to median grain diameter). It is concluded that saltating sediment has a considerable impact on overland flow hydraulics, at least on fixed granular beds. Saltation is likely to have a relatively smaller effect on overland flow on natural hillslopes and agricultural fields where form and wave resistance dominate. Still, saltation is generally of greater significance in overland flow than in river flow, and for this reason its effect on overland flow hydraulics is deserving of further study. © 1998 John Wiley & Sons, Ltd.     

Approaches to the simulation of unconfined flow and perched groundwater flow in MODFLOW

Various approaches have been proposed to manage the nonlinearities associated with the unconfined flow equation and to simulate perched groundwater conditions using the MODFLOW family of codes. The approaches comprise a variety of numerical techniques to prevent dry cells from becoming inactive and to achieve a stable solution focused on formulations of the unconfined, partially-saturated, groundwater flow equation. Keeping dry cells active avoids a discontinuous head solution which in turn improves the effectiveness of parameter estimation software that relies on continuous derivatives. Most approaches implement an upstream weighting of intercell conductance and Newton-Raphson linearization to obtain robust convergence. In this study, several published approaches were implemented in a stepwise manner into MODFLOW for comparative analysis. First, a comparative analysis of the methods is presented using synthetic examples that create convergence issues or difficulty in handling perched conditions with the more common dry-cell simulation capabilities of MODFLOW. Next, a field-scale three-dimensional simulation is presented to examine the stability and performance of the discussed approaches in larger, practical, simulation settings.     

Resistance to flow in rough supercritical sheet flow

Shallow water depths on steep slopes of as much as fifty per cent can be measured easily by weighing a light flume and the water it contains. Because water accelerates along the flume, a good approximation of the steady state depth is obtained when the recording balance is fixed to its bottom end. From the unit discharge and the depth, and not from measurements of the surface velocity, the Darcy-Weisbach friction coefficient can be calculated. The present results show that this friction coefficient is larger in thin sheet flows than that calculated from the equation for rough turbulent flow. This latter could fit at a Reynolds Number of 50,000. When the regime is laminar (Re < 2,440) the Darcy-Weisbach friction coefficient always exceeds the theoretical value of 96/Re. The great relative depth of standing and travelling waves could account for this discrepancy together with turbulence and wake formation around bottom grains. Herein it is assumed that a regime can prevail where a laminar superlayer glides over a turbulent sublayer in the vicinity of bottom grains, because the ratio of the surface velocity to the mean velocity can greatly exceed 1.5, especially on steep slopes. Until photographs of the streamlines are taken, no statement about flow regimes in supercritical sheet flow can be made.     

Coupled groundwater flow and transport: 1. Verification of variable density flow and transport models

This work examines variable density flow and corresponding solute transport in groundwater systems. Fluid dynamics of salty solutions with significant density variations are of increasing interest in many problems of subsurface hydrology. The mathematical model comprises a set of non-linear, coupled, partial differential equations to be solved for pressure/hydraulic head and mass fraction/concentration of the solute component. The governing equations and underlying assumptions are developed and discussed. The equation of solute mass conservation is formulated in terms of mass fraction and mass concentration. Different levels of the approximation of density variations in the mass balance equations are used for convection problems (e.g. the Boussinesq approximation and its extension, fully density approximation). The impact of these simplifications is studied by use of numerical modelling.Numerical models for nonlinear problems, such as density-driven convection, must be carefully verified in a particular series of tests. Standard benchmarks for proving variable density flow models are the Henry, Elder, and salt dome (HYDROCOIN level 1 case 5) problems. We studied these benchmarks using two finite element simulators - ROCKFLOW, which was developed at the Institute of Fluid Mechanics and Computer Applications in Civil Engineering and FEFLOW, which was developed at the Institute for Water Resources Planning and Systems Research Ltd. Although both simulators are based on the Galerkin finite element method, they differ in many approximation details such as temporal discretization (Crank-Nicolson vs predictor-corrector schemes), spatial discretization (triangular and quadrilateral elements), finite element basis functions (linear, bilinear, biquadratic), iteration schemes (Newton, Picard) and solvers (direct, iterative). The numerical analysis illustrates discretization effects and defects arising from the different levels of the density of approximation. We contribute new results for the salt dome problem, for which inconsistent findings exist in literature. Applications of the verified numerical models to more complex problems, such as thermohaline and three-dimensional convection systems, will be presented in the second part of this paper.