In unconventional shale plays both sides of the hydrocarbon systems - source and reservoir - are joined together in one shale unit. Many workflows established in exploration of conventional hydrocarbon systems, are focused on one side only, reservoir or source rock units. Therefore new workflows are needed for the comprehensive assessment of shale systems - as source, trap and seal altogether - for a better understanding and enhanced evaluation of unconventional shale plays. OPTICAL KEROGEN ANALYSIS is a new workflow, focused on the needs of unconventional shale play analysis, based on optical methods to analyse both sides of the system: the source rock potential by high resolution studies of kerogen composition and maturation and the reservoir potential by the analysis of kerogen microporosity estimated from kerogen preservation, indicating the gas storage capacity of the shales. Beside the optical analysis some basic chemical analysis is included in this workflow: TOC and optional CNS analysis.
Kerogen composition quantifies the components of the total kerogen according to schemes developed for palynofacies analysis. The palynologically defined organic matter groups get transfered to standard kerogen types, leading to the detailed quantification of each kerogen type seperately. This enhances significantly the resolution and reliability of kerogen analysis, compared to bulk-rock geochemical methods like Rock Eval pyrolysis. Kerogen preservation indicates the level of generated hydrocarbons due to the increasing degradation of organic matter during hydrocarbon generation. On the other hand, of particular interest for unconventional shale plays, preservation is a key parameter for the estimation of kerogen microporosity and therefore for the storage capacity of shale plays, because most of the secondary generated gas is trapped there. Optical analysis of maturation is based on vitrinite reflectance and palynomorph colour indices. For vitrinite reflectance a new digital analysis workflow is used based on high resolution digital images of vitrinite. This strongly enhances both, resolution and reliabiltiy of VR analysis, especially for fine-grained rocks with dispersed organic matter like shales. Cross-calibration of both methods improves the confidence level of maturation data, leading to enhanced palaeothermal models of basin and hydrocarbon system development. Data from OPTICAL KEROGEN ANALYSIS can get implemented directly into organofacies based hydrocarbom system modeling.
OPTICAL KEROGEN ANALYSIS is tested at organic rich shales from potential unconventional shale plays in different geological settings and stratigraphical ages: from the Carboniferous in Germany, the lower Palaeozoic of northern and eastern Europe and the lower Jurassic of southern Germany.