Laboratory core flooding of formation water, N₂ and CO₂

Project Summary

When it comes to underground CO₂ storage there are a number of factors related to the candidate storage medium which needs to be thoroughly investigated before the commencement of the CO₂ injection, including: storage capacity, containment integrity, injectivity, the behaviour of the CO₂ plume and how it would evolve.

ANLEC R&D commissioned research to assess innovative ways to evaluate these uncertainties.

This project examined the concept of using N₂ as a surrogate for CO₂ in trial subsurface injections to characterise a storage resource. The technique would make regulatory compliance much simpler.

Methodology:

• Two sets of four conventional unsteady state core-flood experiments were conducted, one set using CO₂-water and the other using CO₂-N₂-water fluid systems.
• Three x-ray imaged core-flood experiments conducted using the CO₂-N₂-water system.
• Core-flood numerical simulations performed investigating the effect of a number of possible core-scale heterogeneities on the results of the core-flood experiments.

Dispersion coefficients were measured for the N₂-CO₂ system under reservoir conditions.

Key conclusions are:

• The levels of residually trapped N₂ during an N₂ trial injection may be an overestimation of that which may be achieved during a subsequent CO₂ storage process.
• Buoyancy forces during N2 injection can reveal vertical pathways for subsequently injected CO₂ and therefore gain a better site characterisation.
• Sensitivity to capillary pressure and heterogeneity appears to be determined by core properties rather than by invading fluid. Therefore, N₂ trial injection provides an inexpensive and low-risk way of understanding the heterogeneity structure of a reservoir, which is a critical unknown for CO₂
• The concept of site characterisation using the injection of an inert gas such as N₂ may deliver valuable information to any CO₂ geo-sequestration site.