Characteristic Trends in the Evolution of Reservoir Water Composition During O2 Storage - Hong P. Vu, Ralf R. Haese

CHARACTERISTIC TRENDS IN THE EVOLUTION OF RESERVOIR WATER COMPOSITION DURING CO2 STORAGE
Hong P. Vu, Ralf R. Haese

Site-specific characterisation, the prediction of CO2 plume migration and changes in physical-chemical conditions over time are important elements during the exploration and appraisal of prospective CO2 storage reservoirs. The formation water composition and lithologies can vary significantly between and within reservoirs. Consequently, the evolution of the formation water composition as a reflection of reactions between minerals and CO2-enriched water will vary as well. For example, the presence of minor carbonate content will buffer the acidity of water and the dissolution of potassium feldspar leads to a characteristic enrichment in dissolved potassium.

This project will compile relevant properties from national and international reservoirs with highly variable lithologies, formation water compositions, temperatures and rock/water-ratios (porosity), which are currently assessed for their CO2 storage prospectivity. The data will be used to determine the evolution of fluid-rock reactions and the respective formation water composition over time through reaction path modelling. We expect to identify characteristic trends and water quality indicators for particular reservoir conditions. The latter could be used for the development of monitoring plans. Our studies will also estimate the capacity to permanently immobilise CO2 through mineral (carbonate) precipitation.

The targeted CO2 storage reservoir in the Gippsland Basin is the Latrobe Group, which will be used as a case study to determine variations in the evolution of formation water within one reservoir. The Latrobe Group sandstone is a relatively homogenous high-porosity / high-permeability reservoir rock, which makes it highly suitable for CO2 storage. However, intraformational baffles in the form of coals, shales and carbonate (ankerite/siderite) cemented zones are found within and greensands at the top of the Latrobe Group. The reactivity of those lithologies are poorly understood and will be determined in support of CarbonNet’s assessments of CO2 reservoirs the Gippsland Basin.