A probabilistic analysis of geological CO2 storage capacity changes associated with geochemical reactions

Abstract:

The total storage capacity of CO₂ in the subsurface is closely related to properties of the storage formation, particularly porosity and permeability, both of which may be altered due to geochemical reactions between formation rocks and subsurface fluids (including injected CO₂ and original fluid in place). The changes in porosity and permeability may affect the multiphase flow in the storage formation, and thus cause a considerable deviation from the CO₂ storage estimation if reactive transport was mis-represented or neglected at all in the numerical modeling and simulation. Such risk may be mitigated through simulating the multiphase flow coupled with reactive transport that is calibrated with site-specific data. While thermodynamic parameters (e.g., molecular weight, activation energy) are usually well-defined and provided in databases of most simulation packages, kinetic parameters (e.g., reactive surface area, reaction rate) have a wide range of uncertainty yet can only be modeled uniformly and constantly in spatial and temporal domain. For example, the heterogeneity and dynamic changing of reactive surface area of minerals are not described in any simulation package. Nevertheless, a stochastic approach regarding geochemical properties may provide a more unbiased interpretation of the reactive transport than the commonly used deterministic approach.

In this study, we investigate the evolution of storage capacity during and after CO₂ injection. In particular, we will evaluate the variation of porosity and permeability of the storage formation caused by geochemical reactions between fluids and rocks. The Morrow B sandstone at the Farnsworth Unit (FWU) enhanced oil recovery with CO₂ (CO₂-EOR) field in northern Texas was selected as a case study. Geochemical characteristics of the Morrow B sandstone will be studied in a stochastic approach conditioned by flow-through core experiment results. Simulation results are expected to provide a probabilistic analysis of CO₂ storage capacity at FWU with the geochemical process taken into consideration.