Source Rock: The Organic Factory, Facts and Modelling

Abstract

E&P of fossil fuels requires understanding, assessing and predicting source rock attributes. These attributes include occurrence, organic-richness, organo-facies, type, kinetic parameters, impact on the nature of generated fluids, stratigraphic and lateral distribution, architecture at the regional and local scale, and lithology. These attributes are essential for conventional petroleum system exploration, specifically for populating 3D basin models, and they are mandatory for optimal exploitation of unconventional plays such as Shale plays (Shale oil/gas, underground kerogen shale retorting) and Coal Seams (Coal Bed Methane, Underground Coal Gasification). Accumulation of organic matter in sediment relies on an organic factory which is controlled by three main factors (Huc, 2013): 1) A sufficient primary production of biomass, which is controlled in the marine domain by the availability of nutrients (e.g. riverine input, coastal upwelling, transient eddies). In the continental domain, water budget and climate are the main drivers. 2) The level of alteration (a) during the sinking journey of organic detritus through the water column, from the production site to the sediment floor, thanks to the ballast effect provided by associated mineral grains (e.g. fecal pellets, aggregates), and (b) then eventually, as organomineral flocs, during their transfer along the Benthic Boundary Layer, following the water energy gradient toward the delivery site where organic remains are finally buried. 3) The condition of fossilization within the sediment, where organics are subjected to degradation by foraging biological communities during early burial and even on a longer time term by the deep-biosphere microbes. At this stage the impact of Redox reactions, following a decreasing energy yield sequence (e.g. O2, SO4--, and CO2 reduction) dependent on the concentration of available electron acceptors and linked to sedimentation rate, is instrumental.

AAPG Datapages/Search and Discovery Article #90337 ©2019 AAPG Middle East Region GTW, Regional Variations in Charge Systems and the Impact on Hydrocarbon Fluid Properties in Exploration, Dubai, UAE, February 11-13, 2019