LEE HUNT GEOPHYSICIST, CARBON ALPHA, LHUNT@CARBONALPHA.COM
All aspects of a CCS project are tied back to risk management;
value in the geosciences, including seismic, are directly related to their role in reducing project risk.
Much of the world is looking to carbon capture and storage (CCS) to reduce anthropogenic carbon dioxide (CO2) emissions. The number of carbon storage projects under development has exploded – with over 200 currently proposed projects worldwide (Hauber, 2023). Geoscientists engaged in subsurface work on these projects are interested in providing the most value possible to these projects. But where is that value added? Is it in the early stages of the work, prior to a project being approved for development, or is it at a later stage when the project has passed through its final investment decision (FID)? There is a strong argument to be made that geoscientific and engineering value should be maximized after FID. This is when most of the capital is spent, including tremendous investment in development drilling, logging, coring, well testing, and in measurement, monitoring and verification (MMV) – particularly time-lapse seismic. Should most benefits not occur where the largest amount of capital is expended? Unfortunately, this is not a logical necessity and the highest expenditures do not always equate to the highest value.
We present an argument that geoscientists are uniquely positioned to bring profound value to CCS projects in the early stages through foundational geological and geophysical work.
Stages of CCS – when and where the value is added
CCS projects have reasonably well agreed upon stages (CSA, 2022, NETL, 2017), which are shown in Figure 1. These stages include Screen and Select, Characterize, Develop, Operate, and Closure. The FID point follows Characterization and precedes the actual project development. Project investment is very small to nil in the Screen and Select stage, which is conducted largely as a desktop exercise involving public data. Still, Screen and Select involves an important winnowing of projects and sites that are easily found to be inappropriate for the permanent storage of CO2. At the recent 2023 CSEG/CEGA/CWLS GeoConvention, there were several presentations that involved work within the Screen and Select stage including that of Sweet et al., (2023) and Cooper et al., (2023).
The Characterize stage involves a heavier investment in capital, for it is here that it must be determined to a very high degree of certainty whether the site truly has the capacity, and injectivity and seal integrity to safely and economically store CO2. These investments include seismic data, drilling, logging, coring, and testing of appraisal wells. While such new information has a cost, it can result in avoiding hazards like faults, identifying reservoir quality changes, or picking one site over another based on specific information that could not have been determined from public data. Determining the correct level of capital to invest in the Characterize stage is somewhat of a business conundrum, for on one hand informational certainty is required to confidently make the FID decision, and on the other hand business leaders are typically reluctant to expose capital on projects that they are uncertain will go ahead. Publications on the Characterization stage are more difficult to find for current projects in this stage due to their confidential status.
The capital being spent on geosciences after FID, during the Develop, Operate and Close stages, is generally one to two orders of magnitude higher than the investment prior to FID. During these stages injector wells are drilled, permanent microseismic monitoring arrays may be placed, the CO2 is captured, transportation infrastructure is built, and MMV activities such as baseline and repeat seismic surveys are conducted. Additional monitoring investments can include ongoing geochemical groundwater studies, downhole well temperature, pressure and geochemical observation, and satellite monitoring. In some projects the baseline and repeat seismic elements account for up to one half of the entire MMV capital.
Given this tremendous cost disparity, it is natural to conclude that value from geosciences mostly comes after FID, and value certainly does come from these stages. But where large amounts of capital are spent may also be where capital is inefficiently utilized. If this is indeed where the vast majority – ten times or more – of the capital is spent, then it is reasonable to conclude that this is where skilled geoscientists may be tasked with finding ways to improve their programs. It is therefore not difficult to predict that geoscientific literature will soon be rife with articles on new ways to perform MMV that are more efficient and effective than the older ones. These advances – when they happen – will be valuable.
And yet we shall argue that there is potentially more value to be added before FID.
Figure 1. The stages of a CCS project. Early-stage CCS are all the activities prior to FID.
CCS is a risk focused business
Every aspect of CCS project development fits under the umbrella of risk management, and this risk-centricity supports our argument that the early stages of the project are where geoscientists can add tremendous value. Despite the risk focus, CCS projects are significantly less risky than conventional oil and gas projects. However, in CCS only an infinitesimal amount of risk is tolerated. In many ways CCS risk management is more like that of construction or process engineering than oil and gas. This type of approach may be familiar to engineers; however, geoscientists may find it quite foreign. Let us examine these ideas of risk management further.
CCS projects are, ideally, much deeper than most oil and gas plays for a host of reasons including:
The need for the CO2 to be in a supercritical state, which occurs at specific pressures and temperatures.
For greater density and efficient storage
To reduce the mobility of the CO2
Risk reduction: In general, the greatest chance of a release of CO2 from storage would be through a wellbore that penetrates the storage complex (Health and Safety Laboratory, 2008, Bourne, 2010). Therefore, projects are often placed below producing zones or away from them.
While the greater depth of an idealized CCS project is a compelling difference from oil and gas exploration, that is not a reason for the risk focus of this endeavor, it is more of an outcome of it. The CCS approach to risk is largely driven by the effects of these projects on both the public trust and on the carbon credit economy. There are three key elements to this:
The public and environmental wellbeing are of great concern to the project. The storage of CO2 is critical in the management or minimization of the man-made elements of climate change.
Liability for the project may be handed over to governments in some jurisdictions, such as the Government of Alberta (GOA). Providing assurance of the containment of the CO2 – and a lack of risk thereof – is critically important. CO2 is being stored in perpetuity. We are injecting the gas into the ground, and we need to be very certain that it stays there.
There is a commercial risk that is tied up with CCS. The carbon credit market depends on storage projects working reliably.
Stated another way, instead of pulling critical minerals or petroleum from the geosphere we are injecting CO2, which is considered hazardous, into the ground, for forever. We need to be absolutely sure that there is very little risk this gas will ever escape.
It is for these reasons that risk management could be argued as being central to – or to underly – all project stages for CCS (NETL, 2017). The concerns being managed include the elements we most often associate with risk such as: health, safety, and the environment. But in CCS and other geologic storage projects, risk management extends to the performance of the storage system. System performance itself covers a wide variety of elements, including the reliability of the equipment, the capacity and injectivity of the reservoir, and the safety and safe operating parameters of the storage complex. And so it is that the geostatic models of the storage system, as well as the MMV plans, that are created and updated by all CCS practitioners fall under the auspices of risk management (CSA, 2017).
The concern over risk follows the full life cycle of a CCS project. This includes, in some regions of the world, an eventual hand-off of the project and its liabilities to the public after the Closure stage. The liabilities therefore span decades, and even longer.
We stated earlier that geoscientific capital expenditures are one to two orders of magnitude higher after FID than before. Much of these costs are in the service of the risk management and MMV activities we just described.
Concept of the bowtie
So how does the risk centricity of CCS support the argument that there is tremendous value to be added from geosciences before FID? The value is written in a tool known as a risk bowtie (Figure 2). A risk bowtie is an element of the risk management process, and is a visual model used for evaluating hazards. The elements of a risk bowtie are the following (ISO, 2018):
threats or causes of the hazard,
preventions to each threat,
the hazard itself- called the event or top event,
the mitigations that may occur after the event has occurred, and
the potential consequences of the event.
The preventions will prove to be very important in our value argument. Each of these can be considered as an independent layer that, in aggregate, acts to make the chance of the event happening very low. The mathematical background describing how the preventative layers result in very low levels of risk is part of a method called Layers of Protective Analysis (LOPA) (Markowski and Kotynia, 2011). A similar analysis can be done for the mitigations and their effect on the chance of a consequence coming to pass after an event occurs. LOPA methods can be used to create qualitative-quantitative risk estimates for hazards associated with storage complexes. These risk estimates can help inform the correct level of investment in MMV activities and even assess the value of information of each activity.
Figure 2. Conceptual risk bowtie, adapted after Markowski and Kotynia (2011). The arrows indicate causality.
Value message written in the bowtie: the preventions and mitigations
The conceptual bowtie may seem too opaque to make our value argument; a more detailed example is required. In Figure 3 the conceptual bowtie is used to consider a key hazard – the escape of CO2 from the storage complex. This illustration bears some similarity to a bowtie produced for the same event from the Quest project (de Groot, 2015), though it is not identical. Only the elements of the bowtie necessary for this discussion are filled in. Let us go through this figure more exhaustively:
The key hazard or top event is the escape of CO2 above the ultimate seal.
Everything on the left side of the top event precedes the event, and everything on the right-hand side follows the event.
The Threats (leftmost) are the possible causes of the event. In the case of an escape of CO2, this includes processes like the migration of CO2 along a legacy wellbore, escape through the rock matrix of the storage complex, migration along a fault, escape because the injection pressure re-activates a fault, or escape of CO2 because the injection pressure opens a fracture.
Just to the right of the threats are the layers of prevention, which are shaded in light blue and dark blue. These are safeguards that could prevent a threat from leading to an actual event. The light blue elements are called passive safeguards, and they are inherent to the site. The dark blue elements are active safeguards, which require action by the project team. Typically, there is both a MMV and a mitigation element to active safeguards. MMV might find and diagnose the threat, and mitigation might act to stop or minimize the threat.
Just right of the top event are the recovery and /or mitigation layers. These are similar to the preventions on the left side of the top event in that they are either passive or active. The difference between these safeguards and the ones on the left-hand side of the bowtie is that the event has already occurred. These safeguards now have to do with what consequences may occur as a result. The passive safeguards (light blue) are inherent to the site and are geologic in nature, while the active ones (dark blue) require an action by the project team and have both MMV and mitigation elements to them. Similar to the active and passive prevention safeguards on the left side of the bowtie, the active recovery and mitigation elements use MMV to diagnose the issue – which is now an event – and employ mitigations to minimize or stop the effects of the event.
Furthest on the right in Figure 3 are the consequences, which are the resultant damage that could occur should the event proceed through the safeguards.
Populating a risk bowtie requires a deep understanding of the carbon storage site – the kind of understanding that follows the Characterization stage. Figure 4 is a geological model of the site that the risk bowtie in Figure 3 was created for. It represents important elements of the geologic setting and is used to help populate the bowtie. This is a Basal Cambrian Sand (BCS) type of storage complex, with the storage reservoir sitting directly on top of the Precambrian granitoid basement, which acts as the bottom seal. A series of baffles, shale seals and an ultimate seal (a salt) overlay the reservoir. All these strata form the storage complex. Above the complex are a series of auxiliary storage reservoirs, aquitards (shales), and eventually the groundwater and the surface.
Figure 3. Generalized risk bow-tie considering a top event of CO2 escaping above the top seal.
Figure 4. Storage complex model. The storage complex includes the entire section from the base seal to the top of the ultimate seal. This model helps to inform the risk bowtie layers of prevention and mitigation.
With this model in mind, we can dissect the risk bowtie. For example, let’s examine the “Migration along a matrix pathway” threat. This threat simply means that the CO2 migrates through all the overlaying strata and escapes the entire storage complex. The prevention safeguard layers are critical to our value argument, and they include:
The first baffle, which the CO2 would have to migrate through.
The 1st and 2nd seals, which are thick shale sections in the model in Figure 4.
The ultimate seal, which is a salt.
Capillary trapping mechanisms throughout the complex.
The point to note here is that all this prevention is a result of the inherent geology of the site. One of the goals of the Characterization stage is to assure with a high level of certainty that sufficient preventative geologic strata exist at the site to stop the escape of CO2. Examples of assurance to mitigate this threat might include an active grid of seismic to be certain that no large-scale faults breach the entire seal section, that the salt is not leached from parts of the site, that core analysis has been acquired to demonstrate that the seals are impermeable to a pressurized column of CO2, or that seismic and well control proves that the shale and salt seals are indeed deposited over the entire site. Geoscience takes on a similar role even once the CO2 has escaped the storage complex. The passive recovery elements include layers like aquitards and auxiliary storage formations, the existence of which can only be assessed by geoscientific data.
A similar theme is seen for each of the threats that are filled in for Figure 3. Let us look at one more threat from the risk bowtie of Figure 3 – the “Induced stress reactivates a fault” threat. This threat arises because the injection pressures become high enough that a pre-existing fault reactivates and CO2 escapes the storage complex through this fault. The passive safeguards for this threat are once more geologic. One of the first passive safeguards is to avoid injecting near a fault. The only way to mindfully stay away from a fault is to know where it is. Aeromagnetic data may identify some faults, but seismic is likely necessary to image these threats to the required level of confidence. Another of the safeguards is termed “geomechanics” and refers to having acquired a sufficient understanding of the geomechanics of the site to set appropriate limits on the injection pressure. This understanding may require data from log, core, seismic, and cyclic diagnostic fracture injection testing (DFIT) and full injection testing prior to FID. Unless sufficient geomechanical data already exists for a site, this data will have to be acquired – perhaps from appraisal drilling and testing. Another safeguard is the salt section re-sealing the re-activated fault. As in the other threats, the geology of the site itself is the prevention, and we can only know that the site has these properties through extensive geoscientific Characterization.
Readers are encouraged to go through the other threats that have been filled in for Figure 3 and consider the associated geologic preventions and how a project team could be assured that they exist and are effective for a site.
Geosciences value: an ounce of prevention is better than a pound of cure
We have spent very little time discussing the active safeguards and recovery elements. These are comprised of MMV activities like repeat seismic surveys, which might image the errant CO2, or mitigations such as shutting in an injector well once the CO2 has escaped. Imaging escaped CO2 is an important capability to have, and is critical to MMV, but it is in response to a hazardous event having occurred. Shutting in or remediating an injection well because of escaping CO2 would also be in response to a hazard, which is not ideal. The MMV activities and the mitigations are in aggregate quite expensive. They occur, largely, after FID, where most of the capital is spent.
Our value argument is the following: prevention is better than mitigation. It is better to – through careful Characterization – choose sites that have extensive and sufficient passive geologic safeguards such that these threats can never happen, or are at least highly unlikely to occur. Better site characterization using seismic and appraisal drilling leads to optimal site selection at FID, reducing costly mitigations later in a project.
Where does the Characterization activity sit in the risk bowtie? These activities – the geoscientific assurance investments – are the passive safeguard layers that sit on the left-hand side of the bowtie. They are part of the process of prevention. Figure 5 reinforces this point by illustrating the stages of CCS project development from the perspective of the risk bowtie. The salient addition is that the risk management activities prior to FID are concerned with prevention and most (but not all) the activities after FID are concerned with recovery or mitigation of an event. We argue that prevention is more cost effective than mitigation, and that prevention is about geoscientific work in the early stages of a project.
Figure 5. Stages of a CCS project with activities and references to the risk bowtie for CO2 migration event.
Tying it all together
The risk bowtie tells the story of value for a CCS project event. Geoscientific and engineering actions for preventing adverse events as well as diagnosing and recovering for them are both justified and assigned value through this risk management tool. We had stated earlier that CCS is risk-centric, and this is an example of how all activities can be tied to and justified by risk assessment. For some geoscientists, this may seem strange, though it is more a reframing than a wholesale change of principle – the actions carried out could be justified with numerous other centers of thought. Lastly, although the growing field of CCS will almost certainly see a tremendous level of innovation in the coming years, foundational storage complex characterization will always be an important part of effective project management. After all, assurance of the right geology is the first, best way to avoid expensive problems in projects.
The author wishes to thank his colleagues at Carbon Alpha, particularly Eric Street, Graham Hack, Anne Halladay and Bob Bryden.
Lee Hunt is a professional geophysicist with three decades of experience working virtually every play in the WCSB and many other basins. He has drilled over 400 horizontal and vertical wells, using 2D and 3D seismic, and has experience with the oldest, most primitive techniques as well as the newest, most advanced ones. And he has catalogued the value of these experiences in some 50 conference presentations and journal publications. Lee was appointed as the 2012 CSEG Distinguished Lecturer, a national lecture tour where he spoke about AVO analysis, fracture and hazard detection and the economic value of processing and interpretive techniques. In 2020, he was chosen as the 2020 CSEG Symposium Honoree, the ninth such honoree in the history of the society. Lee and his co-authors won Excellence of Oral Presentation for the 1997 SEPM Convention, the 2000 CSEG Convention Best Paper Award, the 2008 CSEG Convention Best Geophysical Abstract, the 2008 CSEG Best Technical Luncheon Talk, the 2010 CSEG Convention Best Geophysical Oral Presentation, the Best Exploration Paper at VII INGPET in 2011, Honorable Mention for Best Paper in The Leading Edge in 2011, and Best Paper in the CSEG Recorder in 2011. He was a participant in the creation of the CSEG MLA, APEGA’s Q.I. Practice Standard, as well as APEGA’s Guideline for the Ethical Use of Geophysical Data. He was also one of the principal designers of the first CSEG Value of Geophysics with Case Histories course.
Lee currently works as Principal, Geophysics for Carbon Alpha, a Carbon Capture and Sequestration company. On the personal side, Lee Hunt is an Ironman Triathlete, an enthusiastic sport rock climber and an author. His published works of fiction include the novels Dynamicist, Herald, Knight in Retrograde, Last Worst Hopes, and Bed of Rose and Thorns. Lee is also a contributing journalist for Big-Media.ca when time allows.