INTEGRATED ORGANIC MATURATION

High-resolution Organic Maturation based on Vitrinite Reflectance and Palynomorph Colour Indices for maximum accessibility and reliability of maturation data

Benefits for HC Exploration

• digital image based VR analysis enables measurements of small vitrinite grains down to pixel-size (<10μm) without any side effects
• strongly improved interpretation of mixed VR data sets by identification of degraded and recycled vitrinite vs. in-situ vitrinite populations
• better identification of real vitrinite vs. vitrinite-like particles by image analysis
• VR analysis is limited by availability of vitrinite, which is not available before middle Silurian times and rare towards distal marine basin settings
• palynomorph colour indices are good alternatives for analysis of organic maturation and hydrocarbon generation levels, when vitrinite is absent
• combination VR / palynomorph colours minimizes uncertainty of maturation analysis by maximum application to different geological settings and reliability by data cross-check from both methods

Overview

Vitrinite Reflectance – Principles

Vitrinite Reflectance – New Method

Vitrinite Reflectance – Limitations

Palynomorph Colour Indices

Add Ons for integrated source rock analysis

Optical Kerogen Analysis – integrated analysis of kerogen composition and preservation for enhanced evaluation of hydrocarbon potential
Core Logging and Thin Section Analysis – texture and composition of source rocks (organic rich shales)
SEM ANALYSIS – high-resolution analysis of microporosity (kerogen and rock-matrix), rock texture and mineral/kerogen distribution and quantification
Clay Mineralogy and Carbonate Quantification – information on petromechanical properties and quantification of swellable vs. non-swellable clay minerals

Vitrinite reflectance (VR) is the classical method in organic maturation, providing detailed maturation data. All organic matter shows reflectance of light, but only VR is calibrated for the recalculation of exact palaeotemperatures and therefore for precise organic maturation data. VR was developed for coal analysis and is classically done using a photometer, analysing the reflectance of a measuring field (> 100μm), depending on the aperture of the photometer.

Classical VR works well for large vitrinite clasts, typical for coals, but is problematic for small vitrinite particles, typical for dispersed kerogen of hydrocarbon source rocks. Reflectance of the measuring field represents a mix of different materials with different reflectance (vitrinite, other organic & inorganic particles, mounting residue), giving a mixed reflectance value.

Limited accuracy and reliability for small vitrinite particles in HC source rocks by mixed reflectance values from classical photometer-based VR analysis.

New VR method is based on recalculating VR from of digital images of vitrinite particles. High-resolution digital images (b/w) of vitrinite particles taken from reflected-light microscopy.

Different grey levels of b/w images represent different reflectance levels, which are re-calculated to real VR by specific image analysis software. High-resolution reflectance analysis of single vitrinite grains down to pixel-size (<10 μm) without any negative side effects (mixed values).

Better identification of in-situ, recycled and degraded vitrinite particles in mixed vitrinite assemblages and separation of real vitrinite from vitrinite-like particles.

Vitrinite is widely distributed from terrestrial to marine environments, with some limitations by facies types and stratigraphy of studied systems.

Vitrinite is available (but still very limited)  from the late Silurian, thus VR analysis not applicable in early Palaeozoic hydrocarbon systems (Cambrian to Silurian). Vitrinite – woody material from higher land plants – is common in terrestrial to marine environments, but rare to absent in distal marine basin environments.

Alternative methods needed when vitrinite is not available (due to facies, preservation or stratigraphical limitation), like palynomorph colour indices, using marine palynomorphs (acritarchs, dinocysts) or cryptospores (for early Palaeozoic terrestrial system)..

Palynomorph colour analysis based on spore colour index (SCI) or thermal alteration index (TAI) used as alternative, when vitrinite is not available (due to facies, preservation or stratigraphical limitation).

SCI/TAI developed for spores and pollen, but can be applied to marine palynomorphs (acritarchs dinocysts) equally. SCI/TAI enables maturation analysis in a wide range of geological settings – terrestrial to deep marine. SCI/TAI provides easy-access, first estimates of organic maturation levels. SCI/TAI for independent cross-check of vitrinite reflectance data sets to provide maximum accessibility and reliability of organic maturation data.