Egs-ploration organic petrology

Whole rock analysis is the preferred method for vitrinite reflectance analysis. This allows the experienced analyst to separate primary from recycled vitrinite. Hydrocarbon migration indications, in the form of matrix bitumen stain, wisps or globules, are preserved. This approach gives a better indication of organic carbon content.

Vitrinite reflectance on isolated kerogen is faster to analyze than whole rock. However, it is more difficult to distinguish primary from recycled particles. Determinations are less well constrained as populations often include both primary and recycled vitrinite. Matrix indications for hydrocarbon migration are lost. It is more difficult to polish. This is more costly than whole rock analysis, as kerogen isolation must be performed

Vitrinite reflectance on whole rock is performed in combination with visual kerogen analysis. This is recommended as the best approach for rigorously constrained thermal maturation data from reflectance, spore coloration index /thermal alteration index and liptinite fluorescence. It is also an excellent analysis for detailed source rock evaluation from kerogen distributions. This analysis is the most cost effective and comprehensive analysis offered.

Vitrinite reflectance on vitrinite phytoclasts from an isolated kerogen is performed in combination with visual kerogen analysis. This yields fairly well constrained VRo, TAI/SCI data. Disadvantages include difficulty in distinguishing primary and recycled particles in reflected light; matrix indications of migration and lamination are lost; vitrinite can be altered during digestion; often difficult to get a good polish when multiple samples are mounted in one block.

In samples devoid of vitrinite and in high maturity shale, bitumen reflectance is calibrated to vitrinite reflectance. Graptolite and chitinozoan reflectance are also used in samples older than Devonian/Silurian age.

Individual coal macerals are identified, counted and separated into the three main maceral groups: Vitrinite; Liptinite; Inertinite. This analysis is done using a point-counting stage. 500 points are counted to yield quantitative data.

Visual kerogen analysis. This ‘Types’ the kerogen assemblages into Type-I (oil-prone) Type II (mixed oil/gas-prone), Type III (gas-prone) and Type IV (inert/overmature/unreactive). Marine-derived organic matter can be distinguished from terrestrially-derived material. Thermal maturation indications are assessed from spore coloration and thermal alteration indices in conjunction with liptinite fluorescence.

Thermal alteration and spore color indices are very good proxies for temperature change. Spores are highly sensitive to thermal change and alter color with increased thermal stress. Our standard chart is a hybrid between 3 established scales that evolved from Humble, CoreLab and Munsell. This analysis is performed on isolated kerogen strewn on slides. Kerogen isolation adds to analysis costs and turnaround time. It is more cost effective when performed with visual kerogen analysis.

This is a laboratory preparation. Acid digestion dissolves the mineral matrix leaving organic matter particles, which are purified and concentrated. Residues can be dried and used for pyrolysis or optical analysis. Longer turnaround times are typical, as digestion is a fairly time consuming process. Automation, however, has increased through-put and yields ‘clean’ reproducible kerogen that is considered one of the best-quality preparations available to industry at the present time.

Automated and hand polishing techniques are used depending on the nature of the material submitted for analysis. This attention to detail for every sample produces the best polished surfaces possible going forward into analysis.