Correlations between Crude Oil Composition and Produced Water Quality: A Multivariate Analysis Approach

A matrix of 18 synthetic produced water samples was analyzed by partial least-squares (PLS) regression modeling. This has been done to investigate the correlation between crude oil properties and water solubility and affinity of the dissolved hydrocarbons for air/water interface which is referred to as produced water quality. The synthetic produced water samples were prepared with nine crude oils and two aqueous phases in the presence and absence of divalent cations (Ca2+, Mg2+). The total organic carbon content and dynamic surface tension was determined for the samples. The findings of the PLS modeling are summarized as follows: produced water quality was not correlated to the amount (wt %) of aromatics, resins, and asphaltenes in the crude oils but with the amount (wt 96) of heteroatoms present in the different fractions. The water solubility and affinity for air/water interfaces of the crude oil hydrocarbons was promoted by oxygen-containing compounds and reduced by nitrogen- and sulfur-containing compounds. Heteroatom-containing molecules of similar class originating from aromatic, resin, and asphaltene fractions of crude oils contributed to different degrees of water solubility and affinity for adsorption at air water interfaces. This can be related to the differences in the molecular structures of the compounds. Furthermore, the presence of divalent cations showed more influence on the quality of produced water samples of crude oils with high total acid number and nitrogen content.