Micro-environments in Shale

Abstract

Isolated micro-environments may develop in shale or at interfaces to other lithologies. The isolation from the bulk matrix creates an environment in which specific hydrogeochemical conditions may develop due to organic-inorganic interactions. It is the conversion of labile organic matter during early diagenesis or during the early oil window in small natural reactors with or without the buffer potential of the bulk rock which leads to processes different from those at a bulk scale. During both early diagenesis and early oil window acidic and corrosive hydrogeochemical conditions develop due to the release of low molecular weight organic acids (e.g., acetic acid) or carbon dioxide, and lead to dissolution of labile minerals, but also to precipitation of solid solutions at equilibrium. In the talk two selected topics will be presented in form of a slide show with pictures presenting features on a nanometre scale. First, early diagenetic micro-environments for the formation of nano-sized titania polymorphs will be visualized. Second, the formation of stylolitic micro-environments at the interfaces to carbonates will be introduced which is controlled by the organic matter content and its conversion. The talk shall introduce micro-environments in shale, and their significance for geochemical processes apart from the bulk scale.