Novel diamondoid-based maturity models using naturally occurring petroleum fluids

Diamondoids have been extensively used in petroleum geochemistry for thermal maturity assessment of hydrocarbon fluids and the source rocks from which they are derived. Both diamondoid concentrations and diamondoid indices have been proposed as maturity indicators, but no relationships have been shown to be universally applicable across multiple petroleum systems and source rock types. Here, we present a new quantitative maturity calibration for fluids from marine source rocks, based on diamondoids data from oils and gas condensates produced across a well-constrained maturity gradient of 0.5% to 1.5% vitrinite reflectance equivalent (VRE) in a combination of conventional and unconventional plays.We systematically examine the relationships between diamondoid compositions and VRE as estimated from source rock measurements and basin models and observe distinct maturity ranges for generation and destruction of diamondoids of increasing carbon numbers. Notably, the absolute concentrations of ethyl-substituted adamantane isomers display the strongest and most consistent maturity relationships across all petroleum systems included in our data set.Four new diamondoid maturity models are proposed, of which the most promising is based on the relative abundances of adamantane and its suspected precursor, perhydrotriquinacene. We call this parameter the adamantane index and find that it displays an excellent relationship to VRE in our data set (adjusted coefficient of determination of 0.87) that is superior to the performance of all previously established diamondoid indices.Collectively, our work represents a major advance in understanding the evolution of diamondoid distributions in naturally occurring hydrocarbon fluids and enables better quantitative maturity estimation using an integrated diamondoid workflow for exploration and production geochemistry applications.