On-line recovery system coupled to a Rock-Eval® device: An analytical methodology for characterization of liquid and solid samples
Résumé
The Rock-Eval® device has been widely used to identify the type and the thermal maturity of sedimentary organic matter, as well as for quantifying the total organic carbon content. Traditionally, it is a screening tool to estimate the petroleum generation potential of source rocks using standardized parameters. More recently, a new Rock-Eval® method (Shale Play™) was proposed for the investigation of the hydrocarbon content of liquid-rich tight rock samples. In this study, we describe a dual vacuum and on-line system that was developed to recover most compounds that are thermally released during a Rock-Eval® Shale Play™ analysis. Thermally vaporized products are divided so that half is analyzed by the Rock-Eval® flame ionization detector (FID) while the other portion is cryogenically trapped in the on-line recovery system. The trapped products can then be transferred via a vacuum line system into a sample vial for subsequent molecular and/or isotopic composition analyses. The recovery vacuum line volumes were calibrated using known quantities of gas (CH4 and CO2). Sample transfer without isotopic fractionation was demonstrated for CO2 evolved from Rock-Eval® preparation of pure carbonate standards (siderite, magnesite and azurite). Recovery efficiencies were first measured on C8-C16 n-alkane standards and then on produced oil samples. Results indicate a high quantitative recovery and an accurate mass balance of most compounds released during the Shale Play™ Sh0 thermovaporization step (100–200 °C). Thermally vaporized compounds released at higher temperatures Sh1 (200–350 °C) are recovered at lower efficiencies, but are still suitable for subsequent characterization. The coupled Rock-Eval® and recovery system could have applications beyond petroleum geochemistry.
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