Chemically
enhanced oil recovery (cEOR) is an expensive endeavor
that yields modest levels of oil recovery. In order to make it economically
viable, an improved understanding of the process is needed. For example,
knowledge of the types of compounds in crude oil that are strongly
bound to reservoir surfaces would facilitate the design of more efficient
cEOR formulations. In this research study, the fractionation step
of the previously published distillation, precipitation, and fractionation
mass spectrometry (MS) method was utilized to determine the types
of compounds in crude oil that are strongly or weakly bound to kaolinite,
a prevalent clay mineral found in many oil reservoirs. The results
obtained using high-resolution MS experiments revealed that the average
molecular weight and the number of aromatic rings were similar for
both the strongly and weakly bound compounds. On the other hand, hydrocarbons
with no heteroatoms were ∼2.5 times more abundant in the strongly
bound compounds than in the nonbound compounds, while heteroatom-containing
compounds were more abundant in the nonbound compounds. An analogous
binding study performed on a model compound mixture corroborated the
above findings that nonpolar compounds prefer to bind to kaolinite
than polar compounds. These results suggest that more valuable oil
components (nonpolar hydrocarbons) remain in the reservoirs after
water flooding, and therefore, cEOR efforts with the appropriate formulation
could increase the economic feasibility of the process. The method
described herein should also be applicable for the characterization
of compounds that bind strongly to different types of mineral surfaces,
and the role of temperature, salinity, and pH is studied.