Page 113 - Enhanced Oil Recovery in Shale and Tight Reservoirs

100 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 4.22 Total hydrocarbon recovery factors versus injected BOE volume from
different operation schemes.

in the core-scale, ethane provides the highest recovery; the RFs from
methanol and IPA are similar and close to that from no huff-n-puff; the
RF from methane is the lowest. Part of the reasons for the lowest recovery
can be better explained from the individual RFs later. Similar results are
obtained when the total hydrocarbon recovery factors are plotted again
the BOE volumes injected (Fig. 4.22).
The RF for an individual component follows the above equation except
that “total hydrocarbon moles” is replaced by “total component i moles.”
Component i can be methane, butane, heptane, or decane. The component
moles in the oil and gas phases are added together. The RFs of individual
components are shown in Fig. 4.23. It can be seen that methane performs
almost as well as ethane to recover condensate components (butane,
heptane, and decane), but RF of methane is the lowest. The lowest recovery
is because the RF definition excludes the remaining methane. Part of the
remaining methane may be from the injected methane. But the RFs of
other components do not have their own components injected and thus
no exclusion is in their RF calculation. Apparently, this definition of RF
is not perfect. But the earlier definition in the preceding section seems to
have the effect. The objective to inject a gas or solvent is to recover
condensate components. We need to pay attention to those recoveries
when evaluating the recovery performance. Also note that methane