No abstract

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.