Storage considerations in CCS

In previous blog posts, we reviewed the basics of how CO₂ can be captured ahead of compression, transportation, and ultimately storage; these included both pre  and post combustion capture methods from large plants with high CO₂ emissions such as power plants or refineries.

Types of storage sites

After capture, the CO₂ must be stored safely and securely. There are two key types of storage sites including depleted oil and gas reservoirs and deep saline formations.

Depleted oil and gas reservoirs are ideal because their geology is well known and are proven traps of liquids and gases. Alternatively deep saline formations exist in most regions of the world and appear to have a very large capacity for CO₂ storage.

A third and largely unproven storage option are coal seams (that can’t be mined); in this process the injected CO₂ adsorbs to the surface of the coal and in the process releases previously absorbed methane gas, which can then be produced and recovered.

Large volumes in small but deep reservoirs

One benefit of using deeper depleted oil and gas or saline reservoirs for storage is that when CO₂ is injected into these deeper reservoirs at higher pressure and temperatures, it  typically becomes supercritical in situ allowing very large volumes of CO₂ emissions to be securely stored in comparatively small geological formations.

CCS projects and participants

There are many CCS storage projects occurring globally, a good summary of the ongoing projects and industry participants can be found here. Another good high level and online reference on carbon storage can be found here.

Carbon workflow

Each geological CO₂ storage project will most likely be conducted in the following key phases within an industry standard carbon workflow or process:

1. Site assessment and detailed characterization involving geological characterization, reservoir simulation, and well engineering.
2. Site design and construction including CO₂ injection, monitoring, and production facilities.
3. Repository monitoring to reconcile observed and predicted behavior and support site risk management through operations and closure.
4. Site decommissioning including closure and post-closure activities for field facilities and transfer of site management.

Regulatory frameworks for storage

Carbon storage will also require new policy and regulatory frameworks to ensure storage risks are managed in a consistent way; the regulatory framework presented in the recent SPE paper Guidelines for a Regulatory Framework to Accommodate Geological Storage of CO₂ in Alberta is a good example and reference.

Summary

In response to the challenges of CCS, we are seeing growing interest and industry leadership in international forums, global collaborative research efforts, and support of organizations dedicated to addressing CO₂ issues; we are also seeing the emergence of both proven and new carbon technologies and services that will better enable CCS projects on a large scale.

Kambiz.