EVALUATION OF SOLID PHASE EXTRACTION TECHNIQUES FOR AROMATIC AND SATURATE COMPOUNDS IN TYPE II-S OILS

Isomer ratios from saturate and aromatic hydrocarbons are commonly used in geochemical characterization to assess maturity, lithology, depositional environment, migration, and secondary alteration in oil samples. These input parameters are needed for basin modeling and sweet-spot mapping, which can significantly affect the planning of the next drill location. However, whole oils can be difficult to analyze by gas chromatography-mass spectrometry (GCMS) due to the complexity of long-chained hydrocarbons and coelution issues. Therefore, meticulous separation of aromatic and saturate fractions is needed prior to analysis with a GCMS.

The scientific literature records the use of a wide variety of separation techniques. Traditional liquid column chromatography techniques yield quality separations of both saturates and aromatics, however, the labor-intensive method requires using large quantities of hazardous solvents. Solid-phase extraction (SPE) techniques however allow for serial separations using minor quantities of solvents. There are numerous SPE cartridges available for these types of separations whose simplicity in preparation make them ideal alternatives to the more labor-intensive column methods. Presented is a column separation study covering the use of 7 different SPE cartridges (using SiOH, Si, Fl, Ag-ion, AgNO₃, Al-N, and C18) compared to traditional liquid column chromatography (using activated silica) to test the quality of separations of the aromatic and saturate fraction from whole oil. Four sulfur-rich oils generated from Type II-S kerogen are utilized that differ in maturity from early oil, to peak, then late and finally condensate maturity. Specific saturate biomarkers (hopanes, terpanes, and steranes), aromatic biomarkers (triaromatic steroids), and aromatic compounds (dibenzothiophenes and phenanthrenes) are analyzed using GCMS techniques to discern differences in peak resolution, isomer ratios, and how they influence the maturity calculated for the oil samples. Results from this study suggest the use of SPE compared to standard column chromatography can increase the efficiency of whole oil separations used to determine maturity to expedite hydrocarbon exploration.