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Risk assessment of CO2 storage

World-wide plans to store vast quantities of CO2 under ground is emerging. Hence, risk management for CO2 containment is a key issue.

The efficiency and safety of the CO2 storage depends on expert assessment of several risks.

In this article, our experts highlight just a handful of the risks that must be assessed as part of an investor’s due diligence process.

Risks of CO2 leakage in legacy wells

The choice of storage location usually includes legacy wells for substrate information. In turn, legacy wells present a risk for the safe containment of CO2. It’s well known that many – perhaps even most – P&A’d wells are leaking gas and oil to the surface.

Another legacy well problem is that over time, reactions between CO2 and cement can alter cement characteristics. Also, CO2 is likely to cause corrosion of casings, possibly generating new conduits.

Wells are usually plugged and abandoned with the aim of preventing hydrocarbons leaking out of reservoirs. The plugs are set to seal hydrocarbons according to oil and gas standards at the time of P&A. So, it’s not surprising that when evaluated today, their integrity for CCS purposes is uncertain – the lack of documentation and low-quality log data simply adds to the challenge.

CO2 invasion of reservoirs with hydrocarbons and aquifers for industrial and human consumption

CO2 is stored in reservoirs next to oil and gas fields because of the convenience of existing infrastructure and geological well and seismic data.

The control of CO2 migration requires good geomodels with reliable lithology, porosity, permeability, pressures, and barriers to flow. While monitoring CO2 plume migration allows us to control these situations, it won’t prevent build up of the CO2 columns and over-pressure.

In general, there is a strategic choice of whether to store CO2 in a trap (similar to an oil and gas accumulation) or allow it to percolate a saline aquifer. In the latter case, risk of top seal failure is less, compared to accumulation of a CO2 column that builds over-pressure.

When focusing on CO2 invasion, there’s also the potentially catastrophic risk of it infiltrating water resources. This makes water unusable for irrigation, industrial and human consumption. Ultimately, CO2 leakage into the atmosphere is a total failure of a project and lethal to public health. For this reason, many countries have prohibited storing of CO2 onshore.

Containment of CO2

Long term containment of CO2 requires a full review.

Geomechanical review and analysis with respect to:

  • Maximum and minimum horizontal stress
  • Faulting, tectonic history, regional tectonic forces
  • Lithological barriers and formation strength/integrity
  • Potential for building a CO2 column inducing over-pressure

Economic risk – judicial questions

Most countries have regulations and targets in place to reduce CO2 emissions, which means transport of CO2 across borders may create complex hurdles.

Judicial questions on how to treat CO2 as ‘waste’ need to be understood and a strategy agreed among all parties before transportation.

The lack of a robust legislative global framework presents considerable economic risk. Most CO2 emission capture and storage projects are driven by authorities to meet emission reduction targets, and so when CO2 is shipped across borders, the question arises – who will take responsibility and credit for meeting CO2 emission goals?

International standards

There is an international standard (ISO 27914), which describes the procedures for screening, qualifying and certifying CO2 storage. It’s a comprehensive set of guidelines and requirements, that must be satisfied as a prerequisite for issuing a certificate of operations.

Each phase of CO2 storage, from screening to selection, characterisation and qualification, is subject to a certificate being issued. This is the framework that AGR’s highly experienced team of experts in CCS use as the basis for their work with clients across the world.

For more information on our risk evaluation work in CCS, please contact us.

Ole-rygg Ole B. Rygg, PhD
Group Managing Director Wells at ABL Group
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