Investigation of Rate and Method Dependency in Relative Permeability

帝国理工学院的研究人员已经发现，局部毛细血管压力的空间异质性是速率依赖性的主要贡献者。假设当流速降低时，将达到压力梯度阈值，低于该压力梯度阈值，流动特性将变得依赖于流速。这表示相对于粘性驱动流动力显著的毛细力的出现。阈值本身将针对岩石;特别是非均质性的强度（例如孔隙进入压力的分布）、空间结构（即层、溶洞等）以及异质性相对于流动的方向（平行、垂直、倾斜、随机）。来自X射线成像的饱和度变化将提供关于毛细管不均匀性的信息，然后可以数字化参数化。结合样品的岩相学、压汞毛细管压力测量和2D模拟，可以预测排液过程的速率依赖性，类似于烃类圈闭填充过程。这项工作将扩大到渗吸过程，以研究水驱油机制。为了研究塞尺度数据（cm）和模拟网格块尺度数据（~m）之间的差异，建议实验室设置（入口、出口和周长）对岩石施加的边界影响测量本身。影响的严重程度可能取决于岩石中所见的异质性的水平和类型。已经观察到，对于主要流动路径在限制套筒上变窄的层状岩石，相对渗透率随着流速的降低而降低[1，2]。所提出的方法将是创建一个数值模型的岩石核心，并使用该模型来消除实验边界对结果的影响，从而提取一组更合适的流动特性，从实验室文物。

Researchers at Imperial College have identified that spatial heterogeneity in local capillary pressure is a major contributor to rate dependency. It is postulated that when flow rates are reduced, a pressure gradient threshold will be reached below which the flow properties will become rate dependent. This represents the emergence of capillary forces that are significant relative to the viscous driven flow forces. The threshold itself will be specific to the rock; particularly the strength of the heterogeneity (e.g. distribution of pore entry pressures), the spatial structure (i.e. layers, vugs, etc.) and orientation of the heterogeneity with respect to flow (parallel, perpendicular, oblique, random). Saturation variability from X-ray imaging will provide information about capillary heterogeneity which could then be parameterised digitally. Together with petrography of the sample, mercury injection capillary pressure measurements and 2D simulation, a prediction of rate dependency can be made for drainage processes, akin to the hydrocarbon trap filling process. This work will be expanded to imbibition processes to investigate water displacing oil mechanisms. To investigate the discrepancy between plug scale data (cm) and simulation grid block scale data (~m's) it is suggested that the boundaries imposed on the rock by the laboratory setup (inlet, outlet and circumference) effect the measurements themselves. The severity of the effect may depend on the level and type of heterogeneity seen in the rock. It has been observed that for a layered rock where dominant flow paths pinch out on the confinement sleeve, relative permeability decreases with decreasing flow rate [1, 2]. The approach proposed will be to create a numerical model of the rock core and use the model to remove the effects that the experimental boundaries have on the result, and thus extract a more appropriate set of flow properties free from laboratory artefacts.