A Method for High Precision Determination of up to 57 Trace and Ultra-Trace Elements in Crude Oils Using Triple Quad-Icp-Ms with Applications in Exploration, Production Allocation, and Refining

An effective method to accurately and precisely analyze multiple elements in crude oils using high temperature and pressure digestions in a single reaction chamber (SRC) microwave, the ICP-OES and QQQ-ICP-MS analytical instruments was developed. The best of the SRC microwave-assisted acid digestions was shown to be acceptable for 19 analytes using a certified organometallic standard, with average recoveries of 93%-113%. The method developed was used to test a natural crude oil reference material (NIST 8505) for quantifying 57 elements. Our result for vanadium (the only element recommended for NIST 8505) concentration, 390±0.4 µg/g, agrees well with the published value 390±10 µg/g. The number of quantified analytes for NIST 8505 was extended to 52 elements (RSDs≤15.6%) with most RSDs<5%. The analytical method was also used to develop a geochemical technique of production allocation by analyzing the concentrations of specific elements in five end-member crude oils and a manually mixed crude oil of the end members in precisely controlled proportions. The obtained concentrations of the commingled and end-member oils were input into a program developed called “ALLO-TRACE” to calculate the contributing fractions of the end-member oils to the commingled oil using multiple analyte-based linear equations. Accuracies and uncertainties in terms of RSDs of most calculations are within 4% and 3%, respectively. The method was also used for geochemical fingerprinting of 20 crude oil samples thought to be derived from the Monterey Formation source rock/reservoir in the Santa Maria Basin. Three distinct fingerprints were derived from three wells where the oils were sampled. We also conducted whole-oil GC analyses on a subset for these crudes. The results indicate that the crude oils may be similar to subzones from within the Monterey Formation similar to extractable organic matter (EOM) from an onshore core of the Monterey Formation previously studied. The Monterey Formation was deposited under disoxic to reducing deep marine basinal conditions in the Miocene Period (16-6 Ma). These basins were associated with basins formed during pull-apart or transtensional wrench-faulted tectonic activity. It was bathyal depths (ocean environment 200-4000 m) of this basin during accumulation. Transitional-marine organic matter accumulated during the transtensional basin formation.