Abstract
Most of the industrialized countries have started to significantly reduce their greenhouse gases emissions. CO2 capture and geological storage processes entered an operational phase with the emergence of several pilot-sites where different technologies are tested. The major part of the total induced cost occurs during the capture, in the separation step, where CO2 is dissociated from other gas components. The gas mixture composition can vary considerably both qualitatively and quantitatively, based on the origin of CO2, the chosen process of capture and the concerned industrial sector. Indeed, in addition to CO2, several components can be present at various concentration levels, including O2, N2, SOx, H2S, NyOx, H2, CO, and Ar that are a concern to the energy industry. These impurities can have an impact on the chemical reactivity with water, reservoir or cap-rock forming minerals, and the materials constituting injection or monitoring wells installed in a repository site. Moreover, some impurities (SOx, H2S, NyOx, CO) are toxic for human health and the environment, even at low concentrations.
The role of these gas impurities on the geochemical behavior of the storage sites is presently not well documented (a few experimental results on the CO2-H2S mixture and some geochemical simulations on CO2-H2S/SO2). In 2006, two projects funded by the ANR, “Puits-CO2” and “Gaz Annexes”, have been initiated and were mainly focused on the experimental characterization of the impact of gas mixture on the reactivity of minerals and materials present within geological repositories. The Institut National Polytechnique de Lorraine (INPL) directed the second project, which finished in May 2011 and led to important experimental/modeling results on individual gases and even to first investigations on the water-gas mixture-rock system.
Based on the technical experience gained and the laboratory equipment acquired from these previous research efforts, it is appropriate to propose a new project to study the behavior of co-injected gases mixtures under storage conditions. In this investigation, our research team will focus efforts on numerical modeling of the water-gas-rock system. The main thrust of purpose of this proposal is to conduct geochemical simulations to model the long-term behavior of co-injected gases within CO2 storage sites. We will then focus on the:
- Impact of CO2 and co-injected gases on the minerals and reservoir geochemistry,
- Possible inferences on the environment in case of leak.
Besides, we recommend extending thermodynamic databases by acquiring essential experimental data, which will allow fitting and validating the appropriate equations of state for all these systems. A series of experiments achieved in realistic pressure and temperature conditions and investigating reservoir-rock and gas mixtures systems will enable us to compare results of numerical simulations with the results of experiments to validate the newly implemented codes. We will focus the research program on some impurities (SO2, NO, O2) and evaluate their influence on the reservoir-rocks (silicates + clay minerals) expected to provide specific reactivity (e.g. iron containing minerals). For such reservoir rocks, the learning acquired about the fate of impurities in reservoir will lead to some conclusions about the possible composition of unexpected leakages and their impacts on environment and health. Finally, integrating the results of the whole project, some first recommendations about the composition of injected CO2 stream will be formulated in order to minimize environmental risks.