ALBERT

Description: 〈span〉〈div〉ABSTRACT〈/div〉Free and sorbed low-to-medium molecular weight thermovaporized hydrocarbons (〈C〈sub〉20〈/sub〉) are the main organic compounds released at the temperature range corresponding to the Rock-Eval〈sup〉®〈/sup〉 Shale Play〈sup〉TM〈/sup〉〈span〉Sh〈/span〉〈span〉0〈/span〉 parameter (100°C–200°C), whereas medium and high molecular weight thermovaporized compounds (〈 C〈sub〉30〈/sub〉) are the predominant components that are thermal released in the temperature range corresponding to the Shale Play 〈span〉Sh1〈/span〉 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 (〈span〉Sh0〈/span〉 and 〈span〉Sh1〈/span〉) 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 (〈span〉HC〈/span〉〈sub〉〈span〉Total,rock〈/span〉〈/sub〉) is mainly considered as the total amount of free liquid hydrocarbons (〈span〉HC〈/span〉〈sub〉〈span〉Free〈/span〉〈/sub〉) and sorbed liquid hydrocarbons (〈span〉HC〈/span〉〈sub〉〈span〉Sorbed,OM〈/span〉〈/sub〉) still contained in the investigated rock sample.The hydrocarbon content obtained from OM concentrates, however, only reflects the sorbed liquid hydrocarbons.In these equations, 〈span〉TOC〈/span〉〈sub〉〈span〉rock〈/span〉〈/sub〉 is the total organic carbon of the rock sample; 〈span〉TOC〈/span〉〈sub〉〈span〉OM〈/span〉〈/sub〉 corresponds to the 〈span〉TOC〈/span〉 content of the OM concentrate sample; 〈span〉Mass〈/span〉〈sub〉〈span〉rock〈/span〉〈/sub〉 is the initial mass of the rock sample; 〈span〉Mass〈/span〉〈sub〉〈span〉OM〈/span〉〈/sub〉 is the initial mass of the OM concentrate sample; 〈span〉FIDsignal〈/span〉〈sub〉〈span〉rock〈/span〉〈/sub〉〈sup〉〈span〉Sh0+Sh1〈/span〉〈/sup〉 is the flame ionization detection (FID) signal that corresponds to the global surface area under each thermal peak (〈span〉Sh0〈/span〉 and 〈span〉Sh1〈/span〉) generated by the Rock-Eval FID; 〈span〉FIDsignal〈/span〉〈sub〉〈span〉OM〈/span〉〈/sub〉〈sup〉〈span〉Sh0+Sh1〈/span〉〈/sup〉 corresponds to the global surface area under each thermal peak (〈span〉Sh0〈/span〉 and 〈span〉Sh1〈/span〉) 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 (〈span〉HC〈/span〉〈sub〉〈span〉Free〈/span〉〈/sub〉 = 〈span〉HC〈/span〉〈sub〉〈span〉Total,rock〈/span〉〈/sub〉 − 〈span〉HC〈/span〉〈sub〉〈span〉Sorbed,OM〈/span〉〈/sub〉). 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 〈span〉FreeHC〈/span〉〈sup〉〈span〉Sh0〈/span〉〈/sup〉 and 〈span〉FreeHC〈/span〉〈sup〉〈span〉Sh0〈/span〉〈/sup〉〈sup〉+〈/sup〉〈sup〉〈span〉Sh1〈/span〉〈/sup〉 could be used to identify potential producible free liquid hydrocarbons intervals in early exploration campaigns.〈/span〉