A Large scale X-Ray micro-tomography dataset of steady-state multiphase flow
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This dataset contains raw and segmented X-Ray micro-tomography images from steady-state drainage and imbibition flow experiments in two distinct Bentheimer sandstones. The dataset is presented and utilised in the paper 'Representative elementary volumes, hysteresis and heterogeneity in multiphase flow from the pore to continuum scale' available at: https://eartharxiv.org/2aejr/. Full details of the experimental setup, procedure and imaging analysis can be found in the paper and supporting information. The experiments consist of steady-state co-injection core floods with micro-CT imaging and simulatenous pressure measurments, performed on two Bentheimer sandstone cores. These cores have a diameter of 12.35mm (cored with a 12.7mm,1/2"drill bit), and length 73.2mm and 64.7mm, with core-averged porosities of 0.203 and 0.223 respectively. The shallow-marine Bentheimer sandstone typically consists of around 95% quartz with minor feldspar and clay and has a well-sorted grain size distribution. The first core is relatively homogeneous, whilst the second has oblique, low porosity layers orientated approximately 60 degrees to the flow direction. Brine (3.5wt.%KI) and decane (99.9%pure, Sigma-Aldrich) are used as wetting and non-wetting phases respectively, with an interfacial tension of appromxiately 51.16 mN/m (for the pure DI water - decanesystem). The outcrop Bentheimer is strongly water-wetting. The experiments are performed with a confining pressure of 4.5MPa, and pore-pressure of 1.5MPa. Scans are performed with a Zeiss Versa 510 X-Ray microscope with a flat panel detector and various microscope objectives. Firstly, a full-core dry scan is obtained, at a resolution of 6 microns. The core is then saturated with high salinity brine (30wt.%KI), and a full core scan obtained for differential imaging purposes. The working fluid brine (3.5wt.%KI) is then pumped through the core, fully displacing the high-salinity brine, and the absolute permeability is measured. Following this, decane and brine are co-injected into the core at constant total flow rate (0.1 ml/min) varying the fractional flow in a drainage and imbibition process. At each fractional flow, once the differential pressure has stabilised a full-core scan is taken followed by zoom-in, region of interest scans. For the 'full core' scans, 11 and 10 individual scans are taken at increasingvertical locations in each core, to cover a total volume after processing of 1950 x 1950 x 10800 voxels (11.7mm x 11.7mm x 64.8mm) and 1900 x 1900 x 9550 voxels (11.4mm x 11.4mm x 57.3mm) respectively. Approximately 5mm is lost from the images near the inlet and outlet of the core due to noise from the end-pieces and the cone angle of the X-Ray beam. There is significant overlap between each scan to allow registration and merging of the full image. Each individual scan image is normalised to pre-selected references to obtain consistent grey-scale values throughout the core, registered with the first scan, and then merged to create a single image of the core. These are the 'raw' scans available in this data set. After each full-core scan, a selection of zoom-in, region of interest scans are performed to facilitate the interfacial curvature measurements in the paper. A 4x microscope objective lens is used to aquire each image, with the detector position varied to achieve a 3.5 micron resolution and 2 micron resolution image, each containing 1000 cubed voxels. These are the raw, ROI scans available in the dataset. The segmented images are also available in the data set for the full core and region of interest scans. The segmented images show the connected and disconnected oil for the full core scans (binary images with 1 being the oil), and grain, water and total oil for the region of the interest images. Alongside this, the segmented porosity map is also available, which was generated through segmentation of the differential image (high salinity and dry raw images). Details of the differential segmentation and watershed segmented used for the fluid phases can be found in the paper. The full core images herein have been divided into 50 equal subvolumes to faciliate downloading and utilising the dataset with small CPU and RAM requirements. The full, merged images can be found on the UKCCSRC data repository. All resolution data is contained within the file name: full_core means 6um, 3_45 means 3.45 microns, 3_5 means 3.5 microns and 2_00 means 2 microns. Absolute voxel sizes in the images may differ but can be changed in settings to match the given scan resolutions mentioned previously. Also contained in the file names are the oil fractional flow and flood process. DraFo05 refers to a drainage step with a fractional flow of oil of 0.05. ImbFo5 refers to a imbibition step with a fractional flow of oil of 0.5.
本数据集包含两种不同本特海姆砂岩（Bentheimer sandstone）在稳态驱替与自吸流动实验中获取的原始及分割后的X射线显微断层扫描（X-Ray micro-tomography）图像。本数据集依托并应用于论文《从孔隙到连续介质尺度的多相流代表性体元、滞后效应与非均质性》，论文链接为：https://eartharxiv.org/2aejr/。实验设置、流程及成像分析的完整细节可参阅该论文及其辅助材料。 本实验针对两块本特海姆砂岩岩心开展，采用稳态共注岩心驱替方案，同步采集显微CT（micro-CT）图像与压力数据。两块岩心直径均为12.35mm（采用12.7mm（1/2英寸）钻头钻取），长度分别为73.2mm与64.7mm，岩心平均孔隙度分别为0.203与0.223。本特海姆砂岩属于浅海相沉积，通常含约95%的石英，辅以少量长石与黏土，且粒度分选良好。第一块岩心相对均质，而第二块岩心存在与流动方向呈约60°夹角的倾斜低孔隙度层理。 实验分别采用3.5wt.%碘化钾盐水与99.9%纯度的正癸烷（Sigma-Aldrich出品）作为润湿相与非润湿相，二者的界面张力约为51.16 mN/m（对应纯去离子水-正癸烷体系）。该露头本特海姆砂岩具有强水湿特性。实验采用4.5MPa围压与1.5MPa孔隙压力开展。扫描使用蔡司Versa 510 X射线显微镜（Zeiss Versa 510 X-Ray microscope），配备平板探测器与多款显微物镜。 首先以6微米的分辨率完成岩心全干式扫描。随后将岩心饱和于高盐度盐水（30wt.%KI）中，并为差分成像需求完成一次全岩心扫描。之后将实验用盐水（3.5wt.%KI）泵入岩心，完全驱替出高盐度盐水，并测定岩心绝对渗透率。此后以恒定总流速（0.1 ml/min）向岩心共注入正癸烷与盐水，通过改变分流比完成驱替与自吸流程。在每个分流比条件下，待压差稳定后先完成一次全岩心扫描，随后进行感兴趣区域（region of interest，ROI）放大扫描。 针对全岩心扫描，两块岩心分别沿垂直方向递增位置采集11次与10次独立扫描，处理后总体素体积分别为1950×1950×10800（11.7mm×11.7mm×64.8mm）与1900×1900×9550（11.4mm×11.4mm×57.3mm）。由于岩心两端接头产生的噪声以及X射线束的锥角效应，岩心进出口附近的图像会损失约5mm的有效区域。各次扫描之间存在显著重叠，以便于后续配准与拼接为完整图像。每幅独立扫描图像均通过预选定的参考图像进行归一化处理，以保证全岩心范围内灰度值一致；随后与首次扫描图像配准并拼接为单幅完整岩心图像。本数据集提供的“原始扫描图像”即为此类处理后的结果。每次全岩心扫描完成后，还会采集若干次感兴趣区域放大扫描，以支撑论文中的界面曲率测量工作。 扫描采用4倍显微物镜，通过调整探测器位置分别获取3.5微米与2微米分辨率的图像，单幅图像包含1000×1000×1000体素。本数据集提供的原始感兴趣区域扫描图像即为此类数据。本数据集同时提供全岩心与感兴趣区域扫描的分割图像。全岩心分割图像为二值图，其中像素值1代表连通与非连通的油相；感兴趣区域分割图像则分别标注了颗粒、水相与总油相。此外，数据集还包含通过差分图像（高盐度扫描与干式扫描图像）分割得到的孔隙度分布图。流体相的差分分割与分水岭分割（watershed segmentation）细节可参阅该论文。 为便于低CPU与内存需求下的下载与使用，本文提供的全岩心图像已被均分为50个子体积块。完整拼接图像可于英国碳捕获与储存研究中心（UKCCSRC）数据仓库获取。文件名中包含所有分辨率信息：full_core代表6微米分辨率，3_45代表3.45微米，3_5代表3.5微米，2_00代表2微米。图像中的绝对体素尺寸可能存在差异，但可通过设置调整以匹配前文提及的扫描分辨率。文件名中还包含油相分流比与驱替过程信息：DraFo05代表油相分流比为0.05的驱替步骤，ImbFo5代表油相分流比为0.5的自吸步骤。
