Enhanced oil recovery (EOR) has been using CO₂ since the 1970s to increase recovery of oil. It makes the oil easier flowing by reducing its effective viscosity and can also help 'push out' the oil that has been left by primary and secondary production methods. Currently, more CO₂ is left or stored in the oil bearing formation than by any other type of carbon storage.

In Saskatchewan, Canada, the Weyburn oil field is extending its life through EOR. The field uses CO₂ imported from the US via pipeline and has stored approximately 17 MT of CO₂ to date.

Dr Steve Whittaker

The Petroleum Technology Research Centre (PTRC) in Regina, Saskatchewan has been conducting research in how the CO₂ can be monitored working with the operator of the field, Cenovus. The future role of EOR in large-scale storage is the subject of debate in the research community as currently CO₂ is costly to obtain and EOR fields are typically regulated under conventional oil and gas production regimes instead of CCS regulation.

Dr Steve Whittaker has been coordinating the research in the Weyburn project for several years and is well placed to comment on EOR’s future with respect to CCS. I have asked Steve a few questions about the role of EOR within the world of CCS.

Q1: EOR is by far the most important geological storage mechanism at the present by volume. Do you think it will continue to increase in importance?

CO₂-EOR will almost certainly increase in relative importance as far as contributing to the amount of CO₂ stored geologically.  The effectiveness of the method to recover oil in depleting reservoirs provides the economic driver to initiate new projects, and currently most large-scale capture projects in North America are associated with probable CO₂-EOR operations.

In addition, the effectiveness of CO₂ flooding is being tested in a wider range of reservoir conditions including in heavier oil reservoirs and in thinner beds.  As the CO₂ delivery infrastructure expands, this method can be deployed economically in smaller and more marginal fields.

Q2: How does EOR inform other methods of storage?

CO₂-EOR sites provide natural laboratories for studying a wide-range of aspects involving geological storage associated with industrial-scale quantities of CO₂ injection.  The geological characteristics of reservoirs undergoing CO₂-EOR are generally well understood and learnings around determining and maintaining appropriate injection pressures relative to sealing thresholds can be transferred to other storage scenarios.  Reservoir fluids may be sampled periodically to monitor changes associated with fluid-rock interaction to improve reactive transport modelling, and the oil fields provide opportunities to test monitoring methods that are applicable to saline aquifer disposal.  The development of well completion technologies associated with CO₂ originated within the sphere of EOR activities.

Q3: What do you see as some of the issues in transitioning a EOR field to dedicated CO₂ storage?

Policy, regulations and the price of carbon are currently the biggest uncertainties regarding what will ultimately move an EOR field to a dedicated CO₂ storage site.  Storage sites will likely require more rigorous monitoring than exists for current EOR sites and operators may need to initiate additional surveillance methods than typically performed to satisfy regulatory obligations.  Depending on carbon price, operators may try to maximize CO₂ injection during operations to gain extra credits which alters the general philosophy of the CO₂-EOR procedure.  Injection of CO₂ may continue past economic oil production but without continued fluid extraction may relatively quickly reach threshold pressures.

Q4: EOR has been focussed largely in the Permian Basin, Southeastern US and Canada. Do you see scope in other areas both in North America and further afield?

The suitability for CO₂-EOR exists in reservoirs globally, so there is considerable scope for deploying this technology in across a much broader geographic distribution than is found currently.   North America has benefited from a relatively inexpensive and accessible source of CO₂ from natural CO₂ reservoirs.   As more anthropogenic sources of CO₂ are captured and become available, more regions will employ CO₂-EOR including other areas of North America and in off-shore reservoirs.

Thanks for your time, Steve. For anyone wanting to find out more about the Weyburn-Midale CO₂ Project, please visit the PTRC website. If you have any questions for Steve, please pose them by leaving a comment on this blog.