Diagenetic processes, such as dissolution and precipitation, occur naturally and on various timescales in clastic and carbonate rocks. Diagenesis starts as early as during deposition in the marine realm, and continues throughout the burial history of the rocks and/or any potential exhumation. Understanding diagenesis is particularly relevant for oil and gas reservoirs and for CO2 injection processes in carbonate formations. For both CO2 storage and CO2-EOR, injecting into carbonates or carbonate cemented siliciclastics will initiate dissolution/precipitation reactions, with unknown but potentially serious consequences. In this study, we propose to take advantage of Nature’s experiment with diagenesis over geological timescales as an analogue for long-term behavior of CO2 injection. The first step in this project will be to constrain the diagenetic history of Miocene carbonates from the Marion Plateau (offshore Northeastern Australia), a case example where dolomitized limestones are preserved at multiple stage of the diagenetic process.
The diagenetic study will use the numerous cores and samples available from the Marion Plateau, and advanced techniques such as clumped isotopes, coupled cathodoluminescence microscope and EDX and x-ray CT imagery at scales from the meter to the micron. Once this first step is achieved, the second step of the project will be to focus on simulations of flow at the pore-scale to study the interactions between hydrodynamic and geochemical processes in diagenesis, as the way in which these processes alter pore structure in carbonates and sandstones is poorly understood. Reactive transport models will be applied to try to emulate the diagenetic fabrics observed in cores from the Marion Plateau, and thus constrain potential rates and kinetics of diagenetic processes. The Marion Plateau is a perfect case study because diagenetic processes are dominated by a simple fluid flow model: seawater circulation within the platform. The overall goal of this original approach will be to better predict the effects of injecting large volumes of CO2 or brines into carbonate reservoirs, and has impact on improving oil recovery in mature basins and on effective CCS operation in carbonate plays such as the chalk in the North Sea.