Considering capillary force, viscous force, and gravity and buoyancy effects due to the oil–water density difference during the imbibition process, a new mathematical model for core-scale spontaneous imbibition considering gravity and buoyancy is established. The imbibition rates with and without gravity and buoyancy in high-, low-, and ultralow-interfacial tension (IFT) solutions are compared. The study shows that oil buoyancy can accelerate the imbibition rate, and with increasing core permeability and decreasing IFT, the differences in imbibition rate with and without gravity and buoyancy become more significant. At a high IFT of dozens of mN/m, the gravity and buoyancy effects are nonsignificant and can be ignored, but at a low IFT such as at 0.355 mN/m and a core permeability above 1 mD, gravity and buoyancy must be considered in spontaneous imbibition simulations. In low-IFT solutions, the critical inverse Bond number when gravity and buoyancy must be considered is approximately 1 × 10⁻².

中文翻译：

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致密油藏低界面张力自吸的重力和浮力效应数学模型

考虑渗吸过程中油水密度差引起的毛细管力、粘性力、重力和浮力效应，建立了考虑重力和浮力的岩心尺度自吸新数学模型。比较了在高、低和超低界面张力 (IFT) 解决方案中有和没有重力和浮力的情况下的吸入率。研究表明，石油浮力可以加快渗吸速率，随着岩心渗透率的增加和IFT的减小，有无重力和浮力的渗吸速率差异变得更加显着。在几十 mN/m 的高 IFT 下，重力和浮力效应不显着，可以忽略，但在低 IFT 时，例如 0.355 mN/m 和高于 1 mD 的岩心渗透率，在自吸模拟中必须考虑重力和浮力。在低 IFT 解决方案中，必须考虑重力和浮力时的临界反键数约为 1 × 10^－2．