Using natural CO2 reservoir to constrain geochemical models for CO2 geological sequestration

Abstract

Numerical modeling of geochemical transport processes is necessary to investigate long-term CO2 storage in deep saline formations, because aluminosilicate mineral alteration is very slow under ambient deep-formation conditions and is not amenable to experimental study. Geochemical transport modeling can solve many problems and answer questions related to CO2 geological sequestration. The numerical modeling provides valuable insights regarding the physical and chemical consequences of CO2 injection in the subsurface environment. However, the reliability and applicability of the models need to be tested and validated if they are applied for CO2 geological sequestration. Issues on model validations are important if CO2 injection technologies are to be implemented safely, efficiently, and predictably. Validation of geochemical transport models could be different from conventional model validation methods for groundwater flow and solute transport. For the short-term behaviors, the models can be validated using laboratory and field experiments. For the long-term mineral alteration and CO2 sequestration, the natural analogue using high-pressure CO2 reservoirs could be a best way to validate the model. In this paper, a natural CO2 reservoir in southern Songliao Basin of China, which is past accumulations of CO2 in geological formation associated with magmatic or volcanic activity, was selected. Although the length of CO2 exposure and hence the rates of reaction for the natural system is not known in detail, we have shown that it is indeed possible to use observation data of mineral alteration in the natural CO2 reservoir to constrain thermodynamic and kinetic data of minerals used in the model, and to confine conditions of temperature, pressure, salinity, and primary mineral composition.