Skip to main content Skip to secondary navigation

Quantifying multiple source rock contributions to petroleum fluids: bias in using compound ratios and neglecting the gas fraction

Main content start

Compound ratios mix in non-linear fashion for endmembers like black oil vs. gas condensate. Correlations and allocations of endmember contributions apply only to the molecular-weight range of analysed compounds. In this study, biomarker concentrations for four pairs of endmember fluids with GLRs from 100 to 50,000 scf/bbl were mathematically combined to yield four series of binary mixtures in 5% increments. The purpose was to evaluate reliability of chemometric analyses to assign genetic affinities and to deconvolute the relative contributions of endmembers to each mixture. Hierarchical cluster analysis (HCA) of biomarker ratios shows that mixtures having major contributions of gas condensate cluster with those dominated by input from the oil-prone endmember, resulting in incorrect genetic classifications. Mixture deconvolution by alternating least squares regression of ratios (ALS-R) can seriously underestimate the contribution of the gas condensate or higher GLR oil source, as can ALS of concentrations on a whole-liquid basis (ALS-C WL). A biased view of the contributions from source rocks to mixtures hinders understanding of petroleum systems and distorts expectations of fluid phase and bulk properties. However, ALS of compound concentrations on a whole-fluid basis (ALS-C WF) correctly assigns the relative contributions of endmembers because it includes the gas fraction (C1-C5) and the liquids (C6+).

Graph

Related People