To elucidate the imbibition behavior of water in complex temperature and stress environments, spontaneous imbibition experiments were conducted on unsaturated matrix sandstones at different vertical temperature gradients by neutron radiography technology. Additionally, corresponding dynamic models of water imbibition in porous media were established. The research results reveal the phased characteristics of sandstone spontaneous imbibition and the influence of vertical temperature gradient on the evolution of wetting front. Specifically, the initial development speed of the wetting front increases with an increase in the vertical temperature gradient, indicating a direct relationship. However, the growth rate of the wetting front gradually slows down with increasing time, eventually reaching a saturated state. Model validation demonstrates that the traditional Washburn's law is still valid in isothermal conditions without temperature gradient (G=0). Further analysis indicates that the imbibition rate has a direct correlation with linear thermal expansion coefficient (α) and viscosity temperature coefficient (β) across various vertical temperature gradients, and an inverse correlation with surface tension temperature coefficient (γ). Furthermore, when the values of α, β, and γ fall below 0.001, their impact on the imbibition rate becomes negligible. The sensitivity of the imbibition rate to parameters γ, β, and α decreases in that order, with γ being the most sensitive, followed by β, and α being the least sensitive. Moreover, the relative importance of α, β, and γ dictates their specific influence on the imbibition rate, and a synergistic effect exists among these parameters, which collectively influence the water absorption behavior of sandstone.

中文翻译：

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不同垂直温度梯度下不饱和砂岩的自发吸吸：中子射线照相实验与动力学模型


为阐明水在复杂温度和应力环境下的吸吸行为，采用中子射线照相技术对不同垂直温度梯度的非饱和基质砂岩进行了自发吸吸实验。此外，还建立了多孔介质中水渗吸的相应动力学模型。研究结果揭示了砂岩自渗的阶段性特征以及垂直温度梯度对润湿前沿演变的影响。具体来说，润湿前沿的初始发展速度随着垂直温度梯度的增加而增加，表明存在直接关系。然而，润湿前沿的生长速度随着时间的增加而逐渐减慢，最终达到饱和状态。模型验证表明，传统的 Washburn 定律在没有温度梯度 （G=0） 的等温条件下仍然有效。进一步分析表明，在各种垂直温度梯度上，吸吸速率与线性热膨胀系数 （α） 和粘度温度系数 （β） 呈直接相关，与表面张力温度系数 （γ） 呈负相关。此外，当 α、β 和 γ 的值低于 0.001 时，它们对吸水率的影响变得可以忽略不计。渗吸速率对参数 γ、 β 和 α 的敏感性按此顺序降低，γ 最敏感，其次是 β，α 是最不敏感的。此外，α、β 和 γ 的相对重要性决定了它们对吸水速率的特定影响，并且这些参数之间存在协同效应，它们共同影响砂岩的吸水行为。