An application of exploratory factor analysis in the deconvolution of heavy oil biodegradation, charging and mixing history in southeastern Mexico

Abstract

Forty-seven heavy oil samples of three genetic types and similar maturity levels (early oil window) reflect that oils in the southeastern Mexico Basin have experienced complex oil biodegradation, charging and mixing processes. Strong oil fingerprinting signatures from the non- to slightly biodegraded, later charged oils discourage effective determination of biodegradation levels using the existing biodegradation scales. The later charges are recognized by accumulation of n-alkanes, peak/hump ratios and abundant diamondoids. Bicyclic sesquiterpanes show systematic changes caused by biodegradation, whereas very similar hopane and sterane distribution patterns indicate no obvious microbial alteration of hopanes and steranes. Distributions of 2–5 ring aromatic hydrocarbons display regular trends caused by biodegradation, based on which a biodegradation parameter was derived. It shows a higher resolution than an adapted Manco score (Larter et al., 2012). Biodegradation parameters were also derived based on systematic changes in NSO compound distributions. However, deconvolution of oil biodegradation, charging and mixing history is not achievable from a univariate or bivariate perspective. Hence, a multivariate method, exploratory factor analysis (EFA) was applied, incorporating biodegradation ratios and concentrations of compounds chiefly from the fresh charges. The EFA results categorize the studied oils into three broad biodegradation level ranges along with different amounts of the later fresh charge. Our study highlights that chemometric methods might be used to unravel complex oil biodegradation, charging and mixing history of petroleum systems worldwide.