Experimental Study of Confinement Effect on Phase Behavior of Hydrocarbons in Nano-Slit Channels Using Nanofluidic Devices

A great amount of hydrocarbon pore volume in unconventional petroleum reservoirs is distributed in pores of very small sizes, ranging from a nanometer to 100 nm pores. In such a small pore size, fluid–rock interactions play a dominant role in determining the phase behavior of hydrocarbons, which can lead to significant deviations in phase behavior, and significant errors in reserves estimation and reservoir simulations regularly performed by conventional simulators. In our research, we investigated the fluid flow and behavior of hydrocarbon liquids when confined in nano-sized pores. For this end, we employed state-of-the-art technology called lab-on-a-chip technology to mimic shale rock media in a nanofluidic chip. This novel method gives us the ability to directly visualize hydrocarbon liquid inside nano-sized pores and measure fluid properties. Using nanofluidic chips as a nano-scale PVT cell, we have been able to monitor the fluid phase behavior in nano-channels, and measure the bubble point temperature and its changes under confinement effect in pore sizes of 4 nm, 10 nm, 50 nm, and 100 nm. We have performed experiments for pure components of hexane, heptane, and octane, as well as binary mixtures of hydrocarbons (pentane/hexane, pentane/heptane) and a ternary mixture (pentane/hexane/heptane). We have also been able to measure the dynamic contact angle of hydrocarbons when confined in nanopores. The results of our study show that at pore sizes of 10 nm and 4 nm, the confinement has a significate effect on alteration of hydrocarbon phase behavior by increasing the bubble point temperature. On the other hand, the quantity of such effects on bubble point temperature is almost negligible at pore sizes of 50 nm and 100 nm. As reasoning for this phenomenon, at small pores confinement effect is significant in the form of molecule–pore interactions, which leads to a significant effect on bubble point temperature. However, the molecule–wall interactions that lead to alteration of the phase behavior of hydrocarbons do not have a significant influence on the phase behavior compared to the common molecule–molecule interactions at larger pores, leading to bubble point temperatures close to those of bulk media