Analysis of the main CO2 trapping mechanisms in the storage process in carbonate reservoirs

Abstract

In a recent attempt, in October 2018, the International Panel on Climate Change (IPCC) suggested a 1.5°C temperature increase limit to reduce the risk associated with long-lasting or irreversible changes, such as the loss of some ecosystems from uncontrolled global warming. In this sense, the Carbon Capture and Storage (CCS) processes are seen as a promising tool for meeting temperature targets. In Brazil, the Rio Bonito Formation in the Paraná Basin is being located close to the regions with the highest concentration of stationary emitting sources, have great potential for generating natural gas and CO2 storage. But for that, it is necessary to understand the various mechanisms involved firstly. The main mechanisms of CO2 trapping are structural/hydrodynamic, residual gas, solubility and mineral. The structural mechanism is related to the geometry of structural traps and sealed geological structures. The residual gas mechanism depends on the movement of CO2 and the aqueous phase through saturation hysteresis and capillary forces. Solubility trapping is a chemical trapping of CO2 as a soluble component brine. And finally, mineral trapping is a geochemical trapping of CO2 as a mineral phase, where CO2 is converted into carbonate minerals (like Calcite, Dolomite, Siderite). This research proposal aims to evaluate the CO2 storage capacity of the Rio Bonito Formation considering the dissolution of CO2 in water and CO2 mineralization. For this purpose, we will use the reactive flow available in the GEM compositional simulator. Reactive transport modeling is an important tool to study the destination and transport of injected CO2, the amount of CO2 dissolved in aquifers and trapped by carbonate minerals, and the variations of these trapping mechanisms over time. Mineral trapping of CO2, where the injected CO2 reacts with the minerals underground to form a stable solid carbonate phase, minimizes the risk of CO2 leakage significantly. Carbon mineralization is one CCS technology that can capture large quantities of CO2 and convert it into stable carbonate products that can be stored easily. Although the CO2 mineralization process was once thought to occur over hundreds of years, an Iceland-based pilot project has demonstrated that most of the injected CO2 into basaltic rock is mineralized in less than two years. If suitable cations (e.g., Ca2+ or Mg2+) are present in the vicinity of carbonate ion (CO32), insoluble calcite will form in any geological formation. This mechanism must also be studied because mineral dissolution and precipitation change the void volume of the porous medium. And porosity change may lead to permeability variations. Another relevant aspect to be studied is cap rock integrity, linked to the safety aspect of CO2 storage. The network of natural fractures, CO2 dissolution in water mechanisms, CO2 precipitation/dissolution and cap rock integrity processes will be evaluated in this research. To achieve the research objectives, a methodology will be developed to evaluate these mechanisms and to establish the coupling between different scales (nano, micro and macro). This will be done integrating molecular dynamics simulation results with compositional reservoir simulation. Initially, a synthetic model will be built using data from the literature on the main properties of the Rio Bonito Formation and/or correlations that allow estimating these properties. Subsequently, a more complete reservoir model can be employed using real data from this formation. This should measure the potential of the Rio Bonito Formation in the CO2 storage, through the joint action of these different mechanisms. (AU)