The Correlations of the Unconventional Reservoirs Properties and the Huff-n-Puff Gas EOR Potential Performance

Cyclic (huff-n-puff) gas injection as a method of increasing oil recovery from unconventional reservoirs with low permeability has shown sufficiently positive results to justify its implementation in a number of fields. Nonetheless, not all of such injection results in encouraging results. Some field implementations of huff-n-puff results in marginal oil recovery increase from that of primary production case. The characteristics of an unconventional reservoir may have something to do with the appropriate choice of injection gas for use in that reservoir. For instance, a reservoir with oil that is low in heavy components (C7+) from molar fraction standpoint might not a proper candidate for a huff-n-puff field gas injection. In other words, for such type of injection gas to perform well in increasing oil recovery, the in situ oil should have a certain level of C7+ molar fraction. This study aims at finding out what types of gas are the proper choices for huff-n-puff injection gases in unconventional reservoirs with specific characteristics. In a sense, it can be considered as an attempt to create a kind of screening criteria related to the injection gas suitable for huff-n-puff EOR in such an unconventional reservoir. In achieving that, a number of models which are based on real field data of a number of producing oil fields in continental United States are used in numerical simulations. The analysis on the results provided insights on the proper injection gas selections as tabulated in this writing.