The energy mix required to satisfy global needs will include fossil hydrocarbons for some time to come. Therefore, estimating existing reserves, i.e., the quantity of liquid organic compounds present in natural porous media, remains crucially important. These free compounds represent the fraction of oil potentially recoverable and the easiest to extract. The adsorption phenomena within sedimentary organic matter (OM) significantly affect both this proportion and the composition and retention mechanism of oils in source rocks.
In order to optimize the characterization of this phenomenon, an analytical methodology was developed to estimate the total amount of free vs adsorbed compounds. It is based on a specific method of the Rock-Eval®a technology, widely used to estimate the type and thermal maturity of OM(1) using pyrolysis. The idea is to record the global surface area under each thermal peak parameters Sh0 and Sh1) measured during vaporization by an FIDb between 100 and 350°C. These values are first obtained from a whole rock sample, to estimate the total free and adsorbed liquids, and then from the corresponding OM isolated from the mineral matrixc, which corresponds only to the adsorbed oils. The free liquid hydrocarbon fraction is finally calculated as the difference between these last two values (figure).
In oil exploration, this methodology could be used to identify potential producible free liquid zones most suitable for successful development. Making modifications to Rock-Eval®d operating conditions and detectors, the proposed methodology could be applied to new research topics such as the characterization of OM from soil, organic-rich rocks and recent sediments, as well as oils and lubricants.
a - Physico-chemical apparatus used to quantify the organic carbon content of rocks.
b - Flame Ionization Detector.
c - Using non-oxidizing acid treatments.
d - Analysis temperature and conditions during pyrolysis and oxidation phases.
(1) M.-F. Romero-Sarmiento, 2019, AAPG Bulletin
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