Information from research performed in a glass chip sandwiching an invisible two-nanometer diameter channel and sporting four injection ports can improve oil recovery estimations from shale reservoirs. Credit: Nancy Luedke/Texas A&M Engineering
While millions of barrels of oil are produced from shale reservoirs each day, a significant amount of petroleum is trapped in nanoscale pores amidst tight shale layering, and accurately estimating how much oil could be recovered from these areas is a major challenge. Current reservoir models are unable to predict oil behavior and recovery at such a small scale, which poses a problem for oil producers and their investors. Researchers at Texas A&M University have developed a new lab-on-a-chip platform with incredibly small 2 nm channels in order to observe the vapor-liquid phase transitions of oil in shale-like conditions, which can provide oil producers with new insights on the recovery of petroleum from unconventional shale reservoirs.
While labs-on-chips are commonly used in fields such as biomedicine and clinical diagnostics, they have rarely been used for petroleum research, and it took the Texas A&M team two years and several project stages to develop a suitable nanofluidics system for their objective. The lab-on-a-chip platforms were manufactured at the AggieFab Nanofabrication Facility and Microscopy and Imaging Center at Texas A&M. The team started with 50 nm diameter test channels before working down to the 2 nm diameter channels, which the researchers say makes their platform potentially the smallest nanopore-scale glass-topped lab-on-a-chip research platform to date. The nanochannels were characterized using atomic force microscopy and ultimately the researchers were able to capture direct images that aided observation studies of liquid to vapor to liquid transitions of oil on an unprecedented nanoscale.
The team was able to measure the differences in thermodynamic behavior between oil confined in the nanochannel and bulk or unconfined oil, as well as note significant differences between liquid-vapor phase transition pressure and vapor-liquid phase transition pressure. They found that nanopore behavior does influence oil production, which may explain discrepancies between estimated and actual oil recovery numbers seen in the petroleum industry, said corresponding author Hadi Nasrabadi. The experiments were performed at a pressure of 100 psi, but the researchers hope to eventually increase the levels to be more similar to actual reservoir conditions, which can range from 1,000 to 5,000 psi. They also hope to increase the experiment temperatures to more than 300°F (about 149°C). So far the researchers have managed to reach these parameters using 10 nm channel lab-on-chip platforms, but the 2 nm channel platform will need additional modifications to withstand these conditions, the researchers said. This research was funded by the Crisman Institute for Petroleum research and published in the American Chemical Society journal Langmuir.
In addition to petroleum research, the 2 nm channel lab-on-a-chip platform could also potentially be adapted to other research areas where similar nanoscale observations could yield new insights.
“At the 2-nm scale, even under normal pressure and temperature conditions, a nano-confined liquid can display properties similar to supercritical behavior,” said study co-author Debjyoti Banerjee. “And that has important implications for our understanding of supercritical fluids. Such insights could have deep implications for power production, space exploration and biotechnology applications. It’s truly remarkable.”