Extraction is a process of separating absorbed compounds from the rock matrix by repeatedly flushing the sample (continuous extraction) with an appropriate solvent. In Soxhlet extraction, the powdered samples are extracted with dichloromethane, a polar solvent very effective at extracting and dissolving oils. The soluble organic matter can then be analyzed by a variety of techniques, including gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), and stable carbon isotopic composition to compare source rocks and relate them to recovered oils.
Thermal extraction replicates the results of Soxhlet extraction of rock samples by continuous heating of a sample. While solvent extraction can lead to loss by evaporation of the light ends, the thermal extractor functions as a closed system, performing subsequent analysis by gas chromatography and gas chromatography-mass spectrometryof the thermally-extracted compounds. The data obtained, including the lighter compounds, can be used for oil-source characterization and correlation.