Storing carbon dioxide (CO2) emissions produced by a wide variety of industries keeps this greenhouse gas out of the atmosphere.
The injection and storage of CO2 has been working safely and effectively for 45 years. In fact, With abundant underground storage resources at our disposal, storage remains the easiest and most logical CO2 mitigation solution.
There are many similar geological systems throughout the world that are capable of retaining centuries’ worth of CO2 captured from industrial processes. Although geologic storage of gases occurs naturally and has been used safely by industry for many decades, it remains a challenge to describe this process to the public.
Fortunately, there are many locations globally that have formations with these characteristics; most are in vast geological features called sedimentary basins. Almost all oil and gas production is associated with sedimentary basins, and the types of geologic formations that trap oil and gas (and also naturally occurring CO2) are similar to those that make good CO2 storage reservoirs.
HOW DOES GEOLOGICAL STORAGE OF CO2 WORK?
Geological storage involves injecting CO2 captured from industrial processes into rock formations deep underground, thereby permanently removing it from the atmosphere.
Typically, the following geologic characteristics are associated with effective storage sites:
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rock formations have enough millimetre-sized voids, or pores, to provide the capacity to store the CO2
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pores in the rock are sufficiently connected, a feature called permeability, to accept the amount of CO2 at the rate it is injected, allowing the CO2 to move and spread out within the formation
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an extensive cap rock or barrier at the top of the formation to contain the CO2 permanently.
Figure 1: Storage Overview
Storage formations are typically of two types, Saline formations providing a saltdome that can be washed out to create a cavity or depleted Oil and Gas Reservoirs.
CO2 can be stored and later piped to wells for the use of CO2 in enhanced oil recovery.
The storage overview figure shows the different types of storage options available.
1. Deep saline formations refer to any saline waterbearing formation (the water can range from slightly brackish to many times the concentration of seawater, but is usually non-potable). The saline formation is sealed by a caprock for permanent storage.
2. Depleted oil or gas fields that are no longer economic for oil or gas production, but have established trapping and storage characteristics.
3. EOR, which involves injecting CO2 to increase oil production from mature oil fields.
FACT SHEET GEOLOGICAL STORAGE OF CO2
HOW IS CO2 INJECTED UNDERGROUND AND WHY DOES IT STAY THERE?
Once captured, the CO2 is compressed into a fluid almost as dense as water and pumped down through a well into a porous geological formation. The pores in underground formations are initially filled with a fluid – either oil, gas, or salty water. Whilst a majority of existing CCS facilities utilise storage associated with EOR, future deployment of CCS will increasingly require storage in deep saline aquifers, which have wider geographical distribution and larger theoretical storage resources in comparison to oil and gas reservoirs. Because injected CO2 is slightly more buoyant than the salty water that co-exists within the storage formation, a portion of the CO2 will migrate to the top of the formation and become structurally trapped beneath the impermeable cap rock that acts as a seal. In most natural systems, there are numerous barriers between the reservoir and the surface.
Some of the trapped CO2 will slowly start to dissolve into the saline water and become trapped indefinitely (called solution trapping); another portion may become trapped in tiny pore spaces (referred to as residual trapping). The ultimate trapping process involves dissolved CO2 reacting with the reservoir rocks to form a new mineral. This process, called mineral trapping, may be relatively quick or very slow, but it effectively locks the CO2 into a solid mineral permanently.
HOW MUCH CO2 CAN BE STORED UNDERGROUND?
Many people assume that one of the biggest challenges impeding the acceleration of CCS facilities is limited underground CO2 storage resources.
The reality is, there is more underground storage resource than is actually needed to meet climate targets.
In fact, a large proportion of the world’s key CO2 storage locations have now been vigorously assessed and almost every high-emitting nation has demonstrated substantial underground storage resources. As an example, there is between 2,000 and 20,000 billion tonnes of storage resources in North America alone. Countries including China, Canada, Norway, Australia, US and the UK all boast significant storage availability, and other countries such as Japan, India, Brazil and South Africa have also proven their storage capability.
Facts and images originate from the Global CCS Institute. please visit www.GlobalCCSInstitute.com to learn more.
Helium Extraction
Helium is mined along with natural gas, using a drill rig to drill wells deep into the earth’s crust. A drill rig must penetrate a layer called the Cap Rock to reach a natural gas reserve. Once located, the natural gas and Helium rise and fill the rig, which are then led through a series of piping systems that transport the natural gas and crude Helium to a refining plant.
Most crude Helium tapped from natural gas reserves is only around 50% pure, so other gases must be separated through a scrubbing process. There is a significant amount of Nitrogen in crude Helium, as well as methane gases that must be removed. Cryogenic separation units compress the crude Helium, cooling the gases at subzero temperatures until they are liquified. Once liquified, the Nitrogen and methane gases are drained.
After this cooling process, heat and Oxygen are added to remove any Hydrogen left over. When Hydrogen and Oxygen molecules meet, they create water. The gases undertake an additional cooling process, in which the Hydrogen and Oxygen are drained from the mixture. Once Helium has gone through each of these steps, tiny particles are added to complete additional purification until the Helium reaches 99.99% purity.
The two most important sources of helium in the United States are the Hugoton-Panhandle field complex, which is located in Texas, Oklahoma, and Kansas, and ExxonMobil's LaBarge field, which is located in the Riley Ridge area of southwestern Wyoming. Most production from the Hugoton-Panhandle complex is connected to or could be connected to the BLM helium pipeline and Cliffside storage facility near Amarillo, Texas. Approximately 2.8 billion scf (78 million scm) of helium was produced from this area in 1996, 2.2 billion scf (61 million scm) of which was sold and 0.6 billion scf (17 million scm) of which was stored in the Bush Dome reservoir. ExxonMobil's Shute Creek processing plant produces approximately 1.0 billion scf (28 million scm) from the LaBarge field, with the remaining 0.2 billion scf (5.5 million scm) coming from other facilities in Colorado and Utah.