--> A Quick Analytical Approach to Estimate Both Free Versus Sorbed Hydrocarbon Contents in Organic-Rich Source Rocks

AAPG ACE 2018

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A Quick Analytical Approach to Estimate Both Free Versus Sorbed Hydrocarbon Contents in Organic-Rich Source Rocks

Abstract

It has been recently demonstrated that free and sorbed low-to-medium molecular weight aliphatic and aromatic hydrocarbons (20) are the main organic compounds released at the temperature range corresponding to the Rock-Eval Shale Play Sh0 parameter (100-200°C) whereas medium and high-molecular weight hydrocarbons (C10–C30 aromatics and saturates) are predominant components thermally released in the temperature range corresponding to the Rock-Eval Shale Play Sh1 parameter (200-350°C; Romero-Sarmiento et al., 2016). Now, we propose in this study, a quick analytical methodology to obtain a better estimation of the quantity of free versus sorbed hydrocarbons still present in any organic-rich sedimentary rock. The method is based on a comparative approach between Rock-Eval Shale Play parameters (Sh0 & Sh1) obtained from whole rock samples (initial state) and their corresponding organic matter (OM) concentrates isolated by standard non-oxidizing acid treatments and drying procedures (Patent pending 17/59447).

In this way, the hydrocarbon content index (HCcont = Sh0+ Sh1) obtained from whole rock is mainly considered as the total amount of free and sorbed hydrocarbons still contained in the investigated sample whereas the hydrocarbon content index (HCcont) obtained from OM concentrates only reflects the sorbed hydrocarbons. Free hydrocarbons are finally calculated by the difference of these two last values.

The proposed analytical workflow was tested on samples derived from a borehole LJE-1010 drilled in the Jurassic Vaca Muerta Formation (lower Vaca Muerta member, Neuquén Basin – Argentina). Along this vertical profile, we demonstrated here, that the most deep rock interval (3112 m) is mainly dominated by ~60% of sorbed hydrocarbons approximately whereas the shallower sample (3094 m) contains over ~90% of free hydrocarbons. These data could be quickly used to identify potential producible free hydrocarbons intervals in early exploration campaigns. It should be also noted that this methodology can be applied to all kind of sedimentary rock samples containing well-preserved hydrocarbons and in particular to unconventional shale play samples.