This composite view shows injection and production wells and the surrounding monitoring wells. (Image courtesy of SEQEnergy)

Global warming is a difficult problem with which to contend. If fossil fuels are going to continue to be part of the global energy mix, even for a few decades, which seems likely, a better way must be found to deal with carbon dioxide (CO2).

The need to deal with CO2 led to the formation of the SEQ Project, which began in 2005 with the objective of identifying and developing new methods to reduce, eliminate, or permanently store CO2 emissions from fossil fuel combustion with minimal potential disruption to the world energy economy.

The project team tasked with this objective is determined to contribute meaningfully to improving the present carbon capture and sequestration (CCS) model by eliminating as much of the conventionally proposed CCS cycle and reducing as much CCS logistics as possible.

This team was formed by a unique set of nuclear and conventional power industry professionals along with professionals from oil and gas engineering, chemistry, physics, and business, many of whom had previously and successfully worked together.

Working toward the goal
During the four-and-half-year life of the SEQ Project, the team has investigated — and in some cases designed — alternative combustion processes, gas capture mechanisms, gas sequestration mechanisms, gas storage, production and transport processes, and methods of converting CO2 post-combustion into a solid, widely usable, and saleable product.

After investigating various combustion alternatives, the team concluded that natural gas, even in conventional power cycles, contributes so much less CO2 per unit of energy produced compared to coal (about one-third) that an objective should be set to address obvious inefficiencies in the natural gas distribution system to enable greater and more efficient use of this resource.

Unlike the electrical power industry, which is moving rapidly toward distributed storage with batteries, flywheels, and capacitors, natural gas lacks a distributed storage alternative. Distributed gas storage would have great potential value to distributors and end users.

A drawback of natural gas is that it suffers from the same peak demand loads as electricity. For electricity, distributed storage is available; now gas storage with SEQ storage will enable far more efficient pipeline use and will enable commercial users— particularly peak users such as gas turbine power plants— to obtain significantly lower cost gas and to potentially operate at higher levels of efficiency.

Natural gas transport
Today, natural gas is shipped in tankers such as LNG carriers. LNG is a cryogenically liquefied natural gas. But many gas fields are too remote for pipelines and too small for massively capital- intensive LNG facilities.

For gas storage, methane hydrates offer about one-third of the packing density by unit volume of LNG, but since hydrate formation and hydrate facilities would cost less than one-third that of LNG, these factors offset each other. Moreover, these types of hydrate facilities are far less complicated and can be mobilized to zones where LNG is not practical. Another plus is that methane gas stored in hydrates is stable. It will not explode so long as it remains a solid.

A newly developed modular, scalable methane hydrate system has been designed for distributed natural gas storage as well as for offshore gathering and transportation. The system is projected to deliver efficiency gains and fuel cost savings of 15% to 20% to gas turbine power plant operators for a projected sub-two year payback.

Top thinkers on CCS describe a cycle where the CO2 is captured by means of chilled ammonia or amine processes. The captured CO2 is then assumed to be compressed and is shipped over pipelines that would have to be constructed to remote geologic zones where the CO2 could be injected either to induce increased oil production or to become permanently trapped in a geological structure at a molecular level.

The team examined all phases of these CCS processes in detail and concluded that while these proposed means for capture are costly, they are well developed, fall within potentially acceptable cost boundaries, and are sponsored by large and capable companies.

A CO2 disposal transportation system would rival or markedly exceed the scale of the natural gas distribution system in the US, yet little consideration has apparently been given to the true cost or logistics of this type of system. Both the cost and the logistics of constructing and operating such a transport system would be imposing, even in a healthy, debt-free economy.

Bulk compressed gas storage of CO2
The SEQ team developed a large-scale, non-excavated geologic storage system that could safely and verifiably store large volumes of CO2 or other compressed gases for interim or long periods of time. The system is designed to be located where the storage is needed — for instance, near a power plant CO2 source. For CO2 sequestration, this approach would eliminate the transportation requirement or serve as a needed buffer in a long-distance transport system.

This underground storage system concept addresses all of the key issues for handling CO2: monitoring, auditing, reparability, barrier protection, and safe replicable storage.

Storing CO2
For bulk storage, the SEQ reservoir is not excavated. Instead, it uses natural porosity and employs conventional oil and gas drilling tools and methods. Proven barrier materials are injected into the perimeter of a drilled and artificially fractured porous formation to create a reservoir that is securely isolated and repairable for leaks. Other underground storage models require strict pre-geologic settings (salt or cavern) or rely on depleted gas fields, which are notorious for leakage. Based upon others’ data, SEQ reservoirs can be constructed in an estimated 75% of the US and the world, are leak-proof, and yet are projected to cost no more than conventional high-cycle capacity storage.

Natural gas storage is a large business in Europe and Asia today. There is a projected 90 Tcf of new storage required in the next 10 to 15 years in Europe alone. It is doubtful that conventional methods will be able to meet this need.

Clearly, there is another set of potential applications of SEQ underground nonexcavated storage technology, including natural gas storage or LNG storage at the delivery seaport.

But the most efficient form of widely usable bulk energy storage is compressed air energy storage (CAES) because pumped hydro is not location-flexible and most good sites are already in use. CAES particularly fits widespread wind generation.

In 2008, the SEQ team began to re-examine carbon dioxide storage from a new perspective. From the outset the team believed that the most elegant means of dealing with the CO2 is to convert it to a useful material. Other R&D teams have had similar notions. Some have proposed models where CO2 is made into a carbonate. But another alternative solution may be at hand.

The team believes that it has developed an ultimate means of converting CO2 into a non-toxic solid for permanent storage or reuse. There are many more potential, valuable applications for this solid material: concrete reinforcement, improved soil tilth, and metal reinforcement. Much work remains, and the concepts are highly confidential at present, but the team is hopeful that it will fulfill the highest goal set before it — an elegant, minimally disruptive, and economically acceptable means of reducing the carbon impact of fossil fuel combustion.