Experimental Study on Capillary Imbibition of Shale Oil in Nanochannels

Shale oil has been receiving more and more attention, because of its promising contribution to energy development and utilization. Capillary imbibition in shale nanopores widely exists in the storage and recovery of shale oil. Despite the ubiquitous nature, shale oil imbibition in nanoconfined space and the effect of nanopore walls on flow are still unclear. Here, we report an experimental study of shale oil capillary imbibition in single nanochannels with heights ranging from 34 nm to 100 nm. Nanofluidic chips with silicon dioxide surface were designed and fabricated, and a shale oil sample from the Shengli Oil field was adopted and characterized. It was found that, during the imbibition process, the meniscus position exhibited a square root relation with time, which was consistent with the trend predicted by the Lucas–Washburn equation. However, the observed imbibition process was slower than the theoretical prediction, up to 60% slower for imbibition in 34 nm channels, and the deviation increased as the channel height decreased. The height dependence of the deviation was investigated and the interfacial layer model was proposed to quantitatively dissect the dominant mechanism. Our results showed that, because of the strong intermolecular force between surface and liquid, shale oil formed an interfacial layer of two to three layers of molecules on the channel walls, which significantly increased flow resistance in the nanochannels. The effects of dynamic contact angle, surface wettability, and trapped gas were also discussed. Our research investigates natural shale oil imbibition in single nanochannels and quantitatively analyzes the deviation of the nanoconfined flow from the theoretical flow process, which provides novel insights for shale oil exploration and recovery.