Alberta contains significant bitumen resource volumes in heterogeneous carbonate formations. Recovery of this bitumen requires reduction of oil viscosity, coupled with drainage of low viscosity oil to high permeability production pathways. Oil viscosity reduction is most commonly accomplished through heat, via steam injection into the reservoir. While steam leads to fast drainage of oil from high permeable secondary porosity, access to the matrix is more difficult. Imbibition of water (steam condensate) can potentially lead to some access to the rock matrix, but wettability is still not well-defined in these systems. This work considers the results of several core flooding studies whereby solvent is used to recover bypassed oil in the carbonate pore matrix.
Solvent soaking tests are presented, validating the potential for solvent processes to mobilize bitumen at low and intermediate temperatures. Subsequently the results are provided for full diameter carbonate cores, which were first exposed to steam, and then were circulated in steam/solvent and solvent with varying temperatures. A process is described, whereby a heated reservoir is contacted by solvent while it cools. The combination of initial heat (elevated mass transfer) and subsequent cooling (elevated solvent solubility) leads to significant incremental oil production beyond that of steam alone. The application of solvent as a post-steam recovery process has considerable potential for increasing oil recovery by accessing previous bypassed oil within the carbonate matrix.