Organic petrology is the microscopic examination of source rock samples and the most reliable method to determine source rock maturity and kerogen type. It provides information on the type and degree of hydrocarbon generation and basic information on the depositional environment.
Weatherford Laboratories provides a full suite of organic petrology services, including vitrinite, bitumen and zooclast reflectance, maturation estimates based on spore coloration and liptinite fluorescence colors, and kerogen descriptions based on both semi-quantitative and point count methods.
Vitrinite reflectance, carried out on polished sample mounts, requires an experienced eye to identify representative vitrinite particles suitable for measuring.
Samples are mounted and polished according to ASTM and ISO standards. Vitrinite reflectance is carried out under reflected white light. Semi-quantitative kerogen descriptions provide approximate percentages of oil-prone and gas-prone components. Samples are also examined under UV light for liptinite fluorescence colors to obtain a maturity estimate. Examination of kerogen strew slides under transmitted light provides a Thermal Alteration Index (TAI) based on spore coloration.
Weatherford Laboratories employs a global group of certified petrologists with a wealth of experience in both coal and dispersed organic matter petrology.
In addition to vitrinite reflectance, Weatherford Laboratories also provides reflectance measurements of bitumen/pyrobitumen and zooclasts (i.e., graptolites and chitinozoa). An equivalent vitrinite reflectance value is calculated using known conversions, which is particularly useful in pre-Devonian sediments where vitrinite is absent.
Complete Organic Petrology
All Weatherford Laboratories organic petrology reports are accompanied by color photomicrographs showing examples of measured vitrinite particles, bitumen lenses, zooclasts, spore coloration, liptinite fluorescence, etc. A picture is worth a thousand words!
In addition to semi-quantitative kerogen descriptions, we can also supply a very detailed description based on over 500 point counts, covering 43 separate components.
Samples can be prepared either as whole rock mounts or kerogen concentrates according to the client's requirements.
- Microscopic examination of samples can identify the presence of lignite additives or caved material that can produce 'false positives' in pyrolysis data.
- VR data from samples on either side of an unconformity can be used to help determine the amount of overburden removal. This is especially useful for basin modelling.
- Assess extent of the effect of thermal anomalies such as igneous intrusions.
- Determine the true kerogen type of a source rock in high mature samples. Inferences of source rock type from pyrolysis data alone in such samples are typically unreliable.
- Vitrinite reflectance suppression can pose a problem in highly liptinitic or oil-saturated samples. The reflectance suppression effect can be observed and corrected to provide the true vitrinite reflectance value.