Visualization of Carbon Dioxide Enhanced Oil Recovery by Diffusion in Fractured Chalk

Abstract

This work demonstrates that diffusion may be a viable oil-recovery mechanism in fractured reservoirs during injection of carbon dioxide (CO 2 ) for enhanced oil recovery, depending on the CO 2 distribution within the fracture network and distance between fractures. High oil recovery was observed during miscible, supercritical CO 2 injection (R F ¼ 86% original oil in place) in the laboratory with a fractured chalk core plug with a large permeability contrast. Dynamic 3D fluid saturations from computed-tomography (CT) imaging made it possible to study the local oil displacement in the vicinity of the fracture, and to calculate an effective diffusion coefficient with analytical methods. The obtained diffusion coefficient varies between 0.83 and 1.2 Â10 À9 m 2 =s, depending on the method used for calculation. A numerical sensitivity analysis, with a validated numerical model that reproduced the experiments, showed that the rate of oil production during CO 2 injection declined exponentially with increasing diffusion lengths from the CO 2 -filled fracture and oil-filled matrix. In a numerical upscaling effort, with the experimentally achieved diffusion coefficient, oilrecovery rates and local flow were studied in an inverted five-spot pattern in a heavily fractured carbonate reservoir.

Mobility control during CO2 EOR in fractured carbonates using foam: Laboratory evaluation and numerical simulations

“…In contrast, oil recovery from fractured systems was identified by: 1) a rapid breakthrough of CO2 before 0.05PV injected, where most of the oil was produced after CO2-breakthrough, 2) a low production rate from the onset of CO2 injection, 3) a long tail production and 4) no differential pressure across the core length, which indicated recovery by diffusion. This corroborates previous results in chalk (Eide et al, 2015b;Fernø et al, 2015).…”

Flow visualization of CO2 in tight shale formations at reservoir conditions

“…10.1002/2015GL065100 and the reported coefficient agrees reasonably well to other CO 2 -decane diffusion coefficient ranging between 0.83 and 5.05 · 10 À9 m 2 /s [Eide et al, 2015;Renner, 1988;Tenga et al, 2014;Trivedi and Babadagli, 2006], although the literature did not use the same temperature and pressure conditions and the rock type as studied in this work. The measured 11 CO 2 intensity profiles deviate from equation (1) over time as the boundary condition is violated, as expected, when the CO 2 reach the outer end of the core.…”

Methods for Enhancing Recovery of Heavy Crude Oil

“…The oil transportability in the small pores improves, then the CO 2 can extract oil from the unconventional core samples by diffusion. The result proves that by injecting this gas, it is able to recover up to 99% of oil samples in 24 hours under reservoir condition exposure, and it summarizes that the CO 2 could be injected to highly fractured tight reservoirs through fractures to recover oil [35,36].…”