Effect of Confinement on Bubble Point Temperature Shift of Hydrocarbon Mixtures: Experimental Investigation Using Nanofluidic Devices

Abstract

Abstract 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 commercial simulators. In our research, we investigated the fluid phase 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 measure the bubble point temperature and its changes under confinement effect in pore sizes of 10 nm, 50 nm and 100 nm. We have performed experiments for binary mixtures of hydrocarbons (pentane/hexane, pentane/heptane) and a ternary hydrocarbon mixture (pentane/hexane/heptane). The results of our study shows that at 10 nm pores, 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 a conclusion, confinement effect is significant in form of molecule-pore interactions, which leads to a significant effect on bubble point temperature. Furthermore, molecule–wall interactions that lead to alteration of phase behavior of hydrocarbons do not have a significant influence on the common molecule–molecule interactions at pore size of 50 nm and 100 nm, leading to bubble point temperatures close to those of bulk media.