Page 315 - Enhanced Oil Recovery in Shale and Tight Reservoirs

288 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 10.4 Surfactant phase saturation for 300 nD and 0.1 porosity at 20 days.

et al., 2001). This was confirmed by an experimental and theoretical study
by Koo and Kleinstreuer (2003). Thus, the continuum theory is still appli-
cable to fluid flow through nanopores in shale matrix in a practical sense.
From the above discussion, the imbibition velocity in the low-
permeability rock should be one-412nd of that in the high-permeability
rock. In other words, the oil recovery factor (RF) in the low-permeability
rock should be close to that (45.2%) in the high-permeability rock by
412 138 ¼ 56,856 days, since the RF in the high-permeability rock is
45.2% by 138 days of imbibition. However, the simulation data shows that
the RF is only 26.8% by more than 2 million days. Why? There must exist
other forces in addition to capillary force and viscous force, and/or other rea-
sons. We now discuss the possible causes as follows.
First, Eq. (10.1) describes the wetting phase (water) imbibition into an air
capillary tube. The resistance of air is neglected; water “freely” imbibes into
the capillary tube of air. In the water-oil system, the oil resistance must be
considered. In addition, water and oil are slightly compressible. For water