CCP - FAQs - About CCS: Storage, Monitoring and Verification
Surely there are not geologic storage options in all parts of the world that want to produce energy? How could this work in practice?
Preliminary industry research shows a good correlation between the areas where emissions come from and the areas where geological storage options are most plentiful.
Large point sources of CO₂ are concentrated in proximity to major industrial and urban areas. Many such sources are within 300 km of areas that potentially hold formations suitable for geological storage. Critically many of these potential storage sites are far larger than their local point sources offering the opportunity for one site to serve as storage for numerous CO₂ point sources, which could be linked by a cost-effective pipeline transport network thus affording economies of scale.
What capacity will these storage options have? Is this a matter of years, decades, centuries? Isn’t this type of technology just as unsustainable as the burning of fossil fuels?
With the IPCC forecasting global storage capacity as likely to exceed 2000GtCO₂ (2,000,000 MM tonnes of carbon dioxide in common parlance) and global CO₂ emissions currently round 24GtCO₂ per year the total capacity would roughly be around 83 years given no global emissions cuts and 100% CO₂ storage.
Using a more conservative and realistic metric, the CO₂ capacity of the world’s hydrocarbon reservoirs is estimated to be around 800GtCO₂ which would allow approximately 34 years of storage at 100% utilization.
But why is it safe? What makes CO₂ stay down there? Isn’t this like the nuclear waste problem – for it to be safe it has to be managed for thousands of years? Who has heard of a company or government that has continued for that long?
There are multiple mechanisms by which CO₂ can be trapped for long periods of geological time, deep within the Earth. Depending on site-specific characteristics and the way in which CO₂ is injected, these mechanisms come into effect at different rates.
These mechanisms include:
Structural trapping, which means CO₂ gas is compressed into a liquid by increasing pressure deep under the surface of the earth, where it is stored within porous rocks and trapped by impermeable cap-rock above the layer of permeable rock.
Residual trapping, which occurs when the CO₂ fluid becomes stuck in the pore space within the rock and cannot move. Like a sponge that needs to be squeezed of air before it takes on water, these rocks trap and lock CO₂ within their pores.
Dissolution and Mineral Trapping, which is when CO₂ dissolves in the salty water present in geological formations. Since the CO₂ makes the saline water heavier, it naturally sinks to the bottom of the formation over time. Also when CO₂ dissolves in the saline water the resulting solution is a weak acid that reacts with minerals in the rock, forming new minerals and binding CO₂ to rocks permanently.
Potential leakage is a critical matter that is not taken lightly by the CCS industry. The CCP recognise that the possible environmental outcomes of a widespread CO₂ leak, including damage to life and property and the prospect of not fulfilling greenhouse gas mitigation directives.
This makes characterizing and choosing the geological storage site the
most critical part in mitigating the risk of CO₂ storage. But experiences
to date have shown that CO₂ storage sites can be operated and
monitored safely, and their performance monitored and verified.
But what are the main risks – what about faults in the underground structure? What about old and abandoned oil or gas wells if you are using depleted fields?
According to the IPCC report on CCS: “Observations from engineered and natural analogues as well as models suggest that the fraction retained in appropriately selected and managed geological reservoirs is very likely to exceed 99% over 100 years and is likely to exceed 99% over 1,000 years.”
The presence of faults need not deter development of CO₂ storage projects unless such faults are capable of transmitting fluids across formations. Faults naturally vary in their transmissivity through their vertical extent so migrating CO₂ rich fluids may be attenuated in shallower formations. Storage projects with faults capable of transmitting injected fluids into natural resources (e.g., drinking water, extractable oil and gas deposits) or the near surface environment or atmosphere should be avoided.
Wells are often cited as prone to leakage. More than 35 years of operating experience in CO₂ EOR in the US, however, indicates that standard hydrocarbon well construction is suitable to contain CO₂, even at pressures above original reservoir pressure. Portland cement has been shown in aggressive laboratory experiments to be susceptible to degradation. Recent well surveys (include logging and cement and casing sampling), however, have shown that well materials are still providing a boundary to fluid movement. Thus the well “system” performs better in the field than individual components of wells fare in the lab.
In practice in one of member company BP’s demonstration projects, one million tonnes of CO₂ from BP, Statoil and Sonatrach’s natural dry gas field has been stored in an underground geological formation at Krechba every year since 2004.
The system compresses and injects the CO₂ in wells 1,800 metres
deep into a lower level of the gas reservoir where the reservoir is filled
with water. Sophisticated monitoring equipment has not detected any leakage
of CO₂, and our other demonstration projects such as Statoil’s
Sleipner have shown the same results. It is clear that robust site selection
assures the safe, secure long-term storage of CO₂.
But what about during the operation and early years of sealing – can the engineers do anything to stop a leak?
Storage formations, by their natural characteristics, both chosen and then engineered to be highly secure and every feasible measure to ensure the well is properly sealed. One aspect of CO₂ to keep in mind, though, is that at supercritical stage, any potential leaks are gradual and can be quickly detected to prevent the escape of any further CO₂. In essence, CO₂, dispersed as it is in the pore spaces of the storage rock, is not a bubble of gas that can burst up to the surface. Therefore, once a leak is detected by the monitoring regime in place at any stage of the long-term storage process, there are many ways engineers can prevent further CO₂ leakage.
I have heard that CO₂ is poisonous and that it has killed people and animals in Africa when it has escaped from a lake reservoir? Won’t there be a risk of this happening? What would happen to nearby cities or communities if there was a leakage?
In general, CO₂ is about as dangerous as water. Everyone’s breath contains CO₂, and it is heavier than air. If you were to breathe in pure CO₂, you would drown in a few minutes.
As we have seen in Lake Nyos, Cameroon, in 1986, the release of a concentrated amount of CO₂ can be fatal. As a result of this natural disaster, more than 1,700 people were killed from what was believed to be a small volcanic eruption that occurred in the lakebed. There are alternative theories, but this widespread contamination was a result of a naturally gasified lake having its state provoked by an unpredictable natural occurrence. The particular geographic situation of Lake Nyos meant that gases could not escape and dissipate in open air as easily, as mountains and valleys worked to contain the denser-than-air CO₂ in the lake’s vicinity.
However, like water vapor, CO₂ dissipates rapidly in open air. CO₂ mixed with water becomes about as acidic as orange juice. If the CO₂ stream is defined as a waste, the operator of a storage site will have to comply with waste management requirements (which may be inappropriate for CO₂). Transport of CO₂ for injection into deep geological formations under the seabed has been clarified and is allowed under international treaties.
While the risk of leakage and contamination is minimal, our efforts are
focused on assuring safe storage along with long-term monitoring and site
evaluation that makes certain that we select the most suitable storage
sites and that the CO₂ injected there stays there. Lake Nyos
represents a natural CO₂ gasified lake erupting via natural
underground pressure, and the proposed storage sites for CO₂ are
thoroughly evaluated to assure this type of scenario is geologically prevented.
What is the real experience of doing CO₂ injection? Is it really practical or just an idea?
According to the IPCC: “With appropriate site selection informed by available subsurface information, a monitoring program to detect problems, a regulatory system, and the appropriate use of remediation methods to stop or control CO₂ releases if they arise, the local health, safety and environment risks of geological storage would be comparable to risks of current activities such as natural gas storage, EOR, and deep underground disposal of acid gas.”
One CCS technique, EOR, has been a reality in the petroleum industry for more than 30 years. Beginning in the early 1970s in Texas, the industry’s professionals have developed millions of hours of experience in understanding the geology behind CO₂ storage and the unique formation of each underground storage site.
Today, EOR is practiced around the world in countries including the US, Canada, Brazil, Turkey and Hungary. There are, in fact, more than 70 projects in the US alone—with an estimated 500 million tonnes of CO₂ currently in US oil fields in West Texas.
From a CO₂ transport perspective, the US already has an advanced operational infrastructure in place, including more than 2,500 km of CO₂ pipeline transporting more than 40 million tonnes of CO₂ per year from naturally occurring fields of CO₂ in states like Colorado to hundreds of miles away in Texas where it is used for Enhanced Oil Recovery. The US also is home to the world’s longest CO₂ pipeline - the Cortez pipeline which is over 800km long, going from West Texas to Colorado.
Demonstration projects have consistently shown there is little risk of
environmental contamination via leakage and that safe CO₂ storage
is a reality and not just a concept.
CO₂ will be highly pressurised when it is being injected. Isn’t this dangerous?
CO₂ will be injected at pressures similar to those present in the storage reservoir. Multiple decades of operations demonstrate that gas injection at high pressures is safe when appropriate controls are in place. Regulations are in place to prevent operators from injecting at pressures that would damage the confining (seal) zone.
Are there enough storage sites to really make the difference you claim? Where are principal storage sites located? Are some areas more naturally rich in storage capabilities than others?
The CO₂ capacity of the world’s hydrocarbon reservoirs is estimated
to be around 800GtCO₂ (800 gigatons of carbon dioxide). Estimates
of the capacity of saline formations vary greatly – between 100,000 MMtCO2
– 104,000 MM GtCO₂ - so more work must
be done to assess their technical potential. However the IPCC found that
global storage capacity is likely to exceed 2,000,000 MM tonnes CO₂.
With total CO₂ emissions currently around 24,000 MM CO₂ per year,
and the projected decreases meant to be implemented, this theoretically
provides a capacity for more than 100 years of storage (accounting for
the proportion of emissions that can be addressed by CCS).