Caprock Systems for CO₂ Geological Storage

Publication Overview

The study involved a detailed literature review of recent and ongoing research in this topic, with engineering judgement drawn from the findings. The study focussed on caprocks in the context of CO₂ storage in deep saline formations, although depleted hydrocarbon fields were also considered, in the context of the associated wide body of available knowledge. Particular issues considered by the study included:

• Caprock characteristics for site selection purposes;
• Geomechanical, geochemical and other relevant processes, and their coupling into predictive performance models;
• Potential leakage pathways and mechanisms, including faults, fractures and by diffusion;
• Discussion of the time frames and rates of leakage for the various mechanisms and caprock systems;
• Best practices for caprock assessment including data collection and modelling methodologies.

Publication Summary

The seal potential of a caprock system may be defined as the capacity, geometry and integrity of the caprock. Seal capacity refers to the maximum CO₂ column height that can be retained in the underlying reservoir, before pressure exerted by buoyancy exceeds capillary entry pressure, thus allowing CO₂ to migrate through the caprock. Seal geometry refers to the thickness and lateral extent of the caprock. Seal integrity refers to caprock geomechanical properties, in the context of ambient stress fields that may be modified by CO₂ injection and any associated abstraction of reservoir fluids.