Use of Trace Element Analysis in Oils; "Detailed Trace Element Analysis of Saudi Arabian Crude Oils: Steps Towards Geochemical Production Allocation”

Trace element analysis of crude oil goes through several steps before using instruments to determine concentrations of major trace and ultra-trace elements. Instruments include the ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometer) for higher abundance elements and QQQ-ICP-MS (Triple Quadrupole ICP-Mass Spectrometer) for lower abundance elements. With techniques developed at the University of Houston ICP lab, precise trace element fingerprints of up to 57 elements may be determined. Several trace elements and their ratios can act as proxies for redox conditions, e.g., vanadium, nickel, molybdenum, and uranium. In this study, I present inorganic and organic analyses of Saudi Arabian crude oils to establish element and peak/height ratio fingerprints, respectively of each oil and results of mixing tests to attempt to allocate proportions of end-members from mixtures. I examined aspects of geochemical data collected on Saudi Arabian oils to provide interpretations regarding source rocks and oil fingerprints and to assist in validating a technique for production allocation. For allocation tests, oils were analyzed and multielement fingerprints were established for each oil. These fingerprinted oils were then mixed in known proportions. The oils were sampled and analyzed in replicate to establish elemental fingerprints. The commingled oil was then allocated proportionally using a computer program (ALLO_TRACE) developed at the University of Houston. We performed a similar test using organic geochemical fingerprints of each oil through previously developed software by (Schlumberger). In this technique, end-member mixed oil peak height ratios are used to determine proportions. Inorganic and organic methods appear to provide similar allocation results. Trace element un- mixing reached target allocations within ~5% accuracy for end-members proportions. The advantages of geochemical allocation technology over similar tools such as Production Logging Tools (PLTs) would be significant, especially regarding reduction in costs, mitigating chances of downhole tool failures with PLTs, and low-cost production monitoring. The geochemical allocation will have the added benefits of not only better crude oil characterization, but also understanding changes in commingled production oil compositions and the nature of subsurface drainage or connectivity with unconventional reservoirs. Fingerprints would provide benefit in oil-oil and oil-source rock correlations for risk analysis of exploration prospects and plays.