(335b) Phase Dependent Carbon Dioxide Recovery from Nanopores of Shale Matrix: An Experimental Investigation

Enhanced oil recovery (EOR) in unconventional reservoirs is an extremely promising method to increase
oil recovery beyond that of hydraulic fracturing. This research studies the ability of carbon dioxide (CO2)
to increase oil recovery from nanopores of unconventional oil reservoirs. The research focuses on the
impact of CO2 phase on its ability to extrude through the matrix of the shale and studies this flow
behavior.

Initially, experiments were conducted to investigate the interaction of CO2 with crude oil. Crude oil was
obtained from Western Desert of Egypt. The interaction experiments were conducted using nano-
composite membranes with a mesh size varying from 10 nm to 100 nm. Following this, coreflooding
experiments were conducted using outcrop shale cores. These experiments were conducted under
different pressure and temperature conditions to ensure that the CO2 was in gaseous, liquid, and
supercritical phase. Finally, a mathematical study was conducted using the experimental results to
determine the type of flow regime occurring in all pore sizes of the shale core.

When testing the interaction between the crude oil and the CO2 using nano composite membranes, it
was found that the CO2 managed to force a volume of the oil through the nano sized membranes. With
time however, the pores in the membranes began to become plugged which resulted in cessation of
flow completely. The membranes were then analyzed, and it was found that the oil has a considerable
volume of paraffinic wax and asphaltene. The coreflooding experiments showed that the CO2 will
extrude into the shale samples when a high enough pressure is reached. The propagation occurred at a
very low rate however, reaching a maximum of 1 cm every 14.3 hours. If the pressure is increased
significantly, the core fractures. Based on the coreflooding results, the flow regime in the core plug was
studied. Based on the pore size distribution, it was found that for pores less than 30 nm, the dominant
flow regime was Knudsen diffusion, whereas between 100 and 31 nm, the flow regime was transition
flow, and finally, any pore size greater than 100 nm could be modeled using Darcy flow, with gas
slippage correction.

This research shows that supercritical CO2 can propagate into the matrix of unconventional reservoirs,
including the nanopores. The flow regime of the CO2 was a function of its phase and the size of the
pores. The research also shows that in nanoscale, supercritical CO2 will follow Knudsen diffusion into the
cores. This can help improve the application of CO2 EOR in unconventional reservoirs.