Spontaneous imbibition is a capillary‐driven phenomenon in which a wetting fluid displaces a nonwetting fluid from voids without any increase in external pressure. This study compared forward predictions of early‐time displacement of air by water within Mode I fractures in 14 low‐porosity rock cores using a new fractal model with those based on an established parallel plate model. Spontaneous imbibition was measured using dynamic neutron radiography, along with independent determinations of equilibrium contact angle, fracture aperture width, and fracture surface fractal dimension, D_s. The predicted uptake curves generally agreed with the experimental data. However, both models overpredicted the height of the wetting front at any given time. This overprediction may be due to lateral losses of wetting fluid to the matrix by spontaneous imbibition through fracture surfaces. The predictions of the fractal model were consistently closer to the observed values than those of the parallel plate model, and for the best cases, their upper and lower confidence intervals bounded the data points. In 12 out of 14 cases, the RMSD for the fractal model was less than that for the parallel plate model. A paired t test indicated that, on average, the RMSD for the fractal model was significantly lower than that for the parallel plate model. This statistically improved prediction can be attributed to the retardation of predicted uptake achieved through the introduction of a fracture surface roughness parameter (i.e., D_s) in the fractal model.

中文翻译：

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非饱和岩石裂缝中水的早期自发吸收的正演预测

自发吸收是一种毛细管驱动的现象，在这种现象中，润湿液将非润湿液从孔隙中置换出来，而外部压力没有任何增加。这项研究使用新的分形模型和基于已建立的平行板模型的模型，比较了14个低孔隙度岩心在模式I裂缝中水在空气中早期置换的前瞻性预测。使用动态中子射线照相术测量自发吸收，并独立确定平衡接触角，裂缝孔径宽度和裂缝表面分形维数D _s。。预测的吸收曲线通常与实验数据一致。但是，这两个模型在任何给定时间都过度预测了润湿前沿的高度。这种过度预测可能是由于通过裂缝表面自发吸收而使润湿液向基体的侧向损失所致。分形模型的预测始终比平行板模型的预测值更接近实测值，在最佳情况下，其上下置信区间限制了数据点。在14例中的12例中，分形模型的RMSD小于平行板模型的RMSD。一对t试验表明，平均而言，分形模型的RMSD明显低于平行板模型的RMSD。这种统计上改进的预测可以归因于通过在分形模型中引入裂缝表面粗糙度参数（即D _s）而实现的预测吸收的延迟。