Injecting carbon dioxide into shale reservoirs should accomplish two critical results: storing an unwanted greenhouse gas safely underground and improving the flow of oil and gas for better recovery. Unfortunately, current use of CO2 injections in reservoirs has not met the expected levels of sequestration or recovery predicted in lab experiments.
Dr. Maria Barrufet determined that models of CO2 behavior in a shale reservoir are inaccurate because most current research only focuses on the gas’ ability to move through shale rock. She believes a realistic forecast includes the interaction of CO2 with other factors present inside a shale reservoir, namely reservoir fluids, inorganic and organic materials, and high temperatures and pressures.
Through lab experiments, Barrufet found the slow fluid flow properties of the organic mineral kerogen acted as a barrier to initial injections of carbon dioxide. Her work revealed that injection pressures had to be maintained at a high level to force kerogen to absorb greenhouse gas. Barrufet applied extended soak times, keeping the pressures high for long periods of time, and recorded the results. She found CO2 eventually moved through the kerogen and beyond, reaching previously untouched areas of the shale samples. Duplicated in a reservoir, the results mean initial theories about CO2 injections for recovery and storage benefits were not wrong, simply misapplied.
“It is a fine, delicate balance,” said Barrufet. “Injections are critical to recovery and storage, but work best if applied with an understanding of the complexities within the reservoir.”