Sample Types and Typical Analyses

Whole Rock

A portion of the rock is removed, pulverized, and put into a Rock Eval instrument for pyrolysis. The Rock Eval heats up the rock sample to crack the hydrocarbons in the rock, simulating hydrocarbon generation, and resulting data (S1, S2, Tmax, e.g.) tell the geochemist something about sample contamination, source type and hydrocarbon potential (i.e., oil-prone, gas-prone, or mixed), and maturity. These data are stored in the RockEval table in GWIS. This is also the preferred method for screening large sections of a well, to focus in on the potential source horizons. Total Organic Carbon content (TOC) may be obtained from a separate TOC analysis, typically on a LECO instrument. There is also a TOC table in GWIS for Leco-derived values, or TOC values obtained from other sources.

Once the horizons of interest are identified, the geochemist will typically request further analyses on these. A portion of the rock will be pulverized and extracted with organic solvents. The material extracted is suspended in solvent (is a liquid), so then can be subjected to any analyses that are typically performed on an oil sample. This extractable, soluble organic material is called bitumen, and is made up of saturate, aromatic, asphaltene, and other compounds (NSO's or resins). (Refer to 'oil' section to see what further analyses can be performed on extracts.)

An extracted portion of the rock may be prepared for kerogen analysis. Kerogen is the insoluble organic component of a potential source rock. The rock would be treated with acids to dissolve away rock material, leaving only the organic matter. The remaining organic material would undergo visual kerogen analysis, where the matter is prepared and subjected to microscopic examination. The different bits of organic matter and their proportions are visually described. Information related to visual kerogen description goes into the Visual Kerogen table in GWIS. Vitrinite is one kind of organic particle contained in organic-rich rocks. Measuring the reflectance of vitrinite in oil via microscopic techniques is a way geochemists estimate rock maturity.

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