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Geochemistry of Trace Elements as a Tool for Geochemical Production Allocation: Case Study of Crude Oils From the Arabian Basin


Geochemical production allocation has been shown to provide an effective tool for reservoir development. Hence, crude-oil commingling together with reservoir connectivity or compartmentalization can be inferred from crude-oil fingerprinting. Most geochemical production allocation analytical techniques are focused on a gas-chromatographic approach to examine saturate and aromatic hydrocarbon compounds. Inorganic geochemistry, specifically trace element analyses, remains an underexplored and underutilized tool. In this study, we present new techniques to prepare and analyze crude-oil and results of comingling experiments, together with the evidence that inorganic geochemistry can further enhance conventional production allocation approaches and mitigate expense.

A collection of crude-oil from the Arabian Basin has been analyzed using a two instrument approach (Casey et al., 2016, Wang et al., 2017). Geochemical techniques include analysis of an SRC (single-reaction chamber) microwave digested samples by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma Triple-Quadrupole Mass Spectrometry (ICP-MS-QQQ) for major, trace, and ultra-trace elemental composition of crude-oils. Additionally, Gas Chromatography-Flame Ionization Detector (GC-FID) was used for gasoline range hydrocarbons together with overall normal alkanes distribution. Results suggest that the oils can be divided into three groups (A, B, C families), two of which represent end-members, whereas the third group can be considered as a mixture of the two members. The evidence is presented using spider diagrams of more than 50 elements. Moreover, heptane star diagrams further support our interpretation, for instance, 3,3 dimethyl pentane together with 2,2 dimethyl pentene ratio compared to the rest of heptane isomers help to separate the three oil families.

Elemental techniques developed can generate > 50 precise elemental abundances and > 3000 elemental ratios. We have conducted commingling experiments with end member compositions to test a deconvolution routine that allows accurate percentage allocations for the commingled oil to end member compositions. We suggest that these routines could be applied to conventional pipeline commingling and stratified reservoir commingling allocation at considerably lower expense than utilization of PLT logging techniques.