ABSTRACT

Free and sorbed low-to-medium molecular weight thermovaporized hydrocarbons (<C20) are the main organic compounds released at the temperature range corresponding to the Rock-Eval® Shale PlayTMSh0 parameter (100°C–200°C), whereas medium and high molecular weight thermovaporized compounds (< C30) are the predominant components that are thermal released in the temperature range corresponding to the Shale Play Sh1 parameter (200°C–350°C). Now, an analytical methodology is proposed here to predict the quantity of free versus sorbed hydrocarbons still present in any liquid-rich sedimentary rock. The method compares shale play parameters (Sh0 and Sh1) obtained from both whole-rock samples and their corresponding organic matter (OM) concentrates isolated by standard nonoxidizing acid treatments and drying procedures. The hydrocarbon content obtained from whole rock (HCTotal,rock) is mainly considered as the total amount of free liquid hydrocarbons (HCFree) and sorbed liquid hydrocarbons (HCSorbed,OM) still contained in the investigated rock sample. 
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The hydrocarbon content obtained from OM concentrates, however, only reflects the sorbed liquid hydrocarbons. 
formula

In these equations, TOCrock is the total organic carbon of the rock sample; TOCOM corresponds to the TOC content of the OM concentrate sample; Massrock is the initial mass of the rock sample; MassOM is the initial mass of the OM concentrate sample; FIDsignalrockSh0+Sh1 is the flame ionization detection (FID) signal that corresponds to the global surface area under each thermal peak (Sh0 and Sh1) generated by the Rock-Eval FID; FIDsignalOMSh0+Sh1 corresponds to the global surface area under each thermal peak (Sh0 and Sh1) measured by the Rock-Eval FID between 100°C and 350°C after the themovaporization of the OM concentrate sample. Free liquid hydrocarbons are finally calculated as the difference between these last two values (HCFree = HCTotal,rockHCSorbed,OM). This paper illustrates the application of this methodology on rock samples derived from the Vaca Muerta Formation (Argentina). Along the selected vertical profile, the lower rock interval contains approximately 60% of sorbed liquid hydrocarbons, whereas the upper sample contains more than 90% free liquid hydrocarbons. The parameters FreeHCSh0 and FreeHCSh0+Sh1 could be used to identify potential producible free liquid hydrocarbons intervals in early exploration campaigns.

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