Tracing Migration through Mudstone Top Seals: a Case Study from the Vienna Basin

Abstract

Summary Seal rock characterization became increasingly relevant in a geological storage context in recent years, as the suitability of proven hydrocarbon traps is not yet well understood for alternative pore fluids such as H2 or CO2. Structures which do not contain hydrocarbons as an indirect proof of their integrity may nevertheless be potential storage sites. Furthermore, the exploration of new hydrocarbon prospects still requires an understanding of all petroleum systems elements including the quality distribution of regional and local seal rocks such as mudstones. This work introduces a comprehensive seal rock investigation workflow including multiple petrophysical and image-based porosimetry techniques to capture and compare multiscale (nm to mm) porosity characteristics. Furthermore, geochemical evidence (based on Fluid Inclusion Chemostratigraphy and Rock-Eval pyrolysis) of hydrocarbon migration into and diffusion through a working Middle Miocene (Badenian) top seal in the Vienna Basin is presented. The main aims of this contribution are i) to highlight the capabilities of different state-of-the-art characterization techniques to visualize multi-scale changes in cap rock properties as a result of depositional variations, and ii) to present a new geochemical tool to prove migration and/or diffusion through low-permeable top seals.