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因素。假定当流量降低时，将达到一个压力梯度阈值，低于该阈值，流动特性将与速率相关。这表明毛细力的出现，相对于粘性驱动的流动力是重要的。阈值本身将是特定于岩石的；特别是非均质性的强度（如孔隙进入压力的分布）、空间结构（如层、洞等）和非均质性与流动的方向（平行、垂直、倾斜、随机）。x射线成像的饱和度变异性将提供毛细管非均质性的信息，然后可以数字化参数化。结合样品的岩石学、压汞毛细管压力测量和二维模拟，可以对排水过程（类似于油气圈闭充填过程）的速率依赖性进行预测。这项工作将扩展到吸胀过程，以研究水驱油机制。为了研究塞子尺度数据（cm）与模拟网格块尺度数据（~m）之间的差异，认为实验室设置在岩石上的边界（入口、出口和周长）本身影响了测量结果。这种影响的严重程度可能取决于岩石中所见的非均质性的水平和类型。已经观察到，对于主导流道在约束套筒上掐出的层状岩石，相对渗透率随着流量的减小而降低[1,2]。提出的方法是创建岩心的数值模型，并使用该模型去除实验边界对结果的影响，从而从实验室人工制品中提取出一组更合适的流动特性。

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.