Carbon sequestration is the process of capturing and storage of atmospheric carbon dioxide. The objective of any carbon sequestration project is to store CO2 safely for hundreds or thousands of years with a goal of mitigating global climate change. Based on literature, coupled geochemistry with fluid flow is essential for modelling of CCS mechanisms such as multiphase flow, solute transport, mineral dissolution, and precipitation. Geochemical modelling has an important role in understanding these processes, in the short term there will be some dissolution due to CO2 injection to the reservoir and in the long-term, mineralization of CO2 could potentially occur. This mineralization may then subsequently have a large effect on the storage volume and storage development plan.

In numerical dynamic modelling there are always simplifications made to reduce the simulation runtime, however, for coupled geochemistry, oversimplification may cause incorrect results. The question which this paper is going to answer is how much simplification is required in the coupled geochemistry dynamic flow modelling of CCS.

To answer the question, a sector model from an aquifer with one CO2 injection well is extracted and coupled geochemistry with compositional simulation modelling is performed. The model included CO2 solubility and geochemistry with three minerals (‘Anorthite’, ‘Calcite’ and ‘Kaolinite’) and their respective geochemical reactions. Then the same model is simplified by decreasing the number of minerals and reactions to only ‘Calcite’ and one reaction. In the model with three minerals ‘Anorthite’ is dissolved whereas ‘Kaolinite’ is precipitated throughout the simulation and ‘Calcite’ initially is dissolved and then precipitated. In the model with one mineral there is a very small amount of ‘Calcite’ dissolution. The results showed that the amount of mineralization in the model with three reactions is about 10% of the injected CO2 after 1,000 years from the start of injection while in the simplified one-mineral model is almost zero.

The results of this study prove that oversimplifying the geochemistry potentially can cause the model to miss some of the active geochemistry processes, leading to erroneous results in the simulation. The simplification should be based on the lab mineralogy data (the amount of each mineral in the core) and the static ageing experiments. However, it is proposed at least 3-5 minerals to be considered in the model even though the small amount of each mineral could have a large secondary affect on the reactions from another mineral.

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