UCG offers the potential to produce fuels and hydrocarbon feedstock from coal deposits which may otherwise be unrecoverable. By introducing a carefully controlled supply of air or oxygen through wells into a coal seam, the coal can be reacted in situ to produce mixtures of hydrogen, carbon monoxide, carbon dioxide, methane and other gases. These can be recovered to the surface through wells and used as fuel for power generation or as feedstock for the production of chemicals and other hydrocarbon products.

The UCG syngas is similar to syngas obtained from conventional surface coal gasification systems, but production is achieved at a much lower cost.

The initial two-year technical agreement with LLNL will address three broad areas of UCG technology:

• Carbon management to evaluate the feasibility of carbon dioxide storage underground;

• Environmental risk assessment and management; and

• Numerical modeling of the UCG processes to understand and history match pilot test results.

The technical objective based on BP’s in-house data is for LLNL to provide BP with expertise, model results, new capabilities and insights into the operation and environmental management of UCG. LLNL has been working with UCG technology development and field deployment for more than 30 years and will provide its experience and capabilities in advanced computation and modeling, engineering, environmental management, and carbon management (including carbon sequestration).

A number of countries, including the US, Former Soviet Union (FSU), China and Australia, have carries out UCG tests over the preceding decades. The FSU alone carried out more than 50 years of research on UCG, field tests and several commercial projects, including an electric power plant in Uzbekistan that is still in operation today.

According to LLNL, multiple commercial projects are in various stages of development in the US, Canada, South Africa, India, Australia, New Zealand, and China to produce power, liquid fuels, and synthetic natural gas.

In May, for example, construction began on China’s first industrial-pilot underground coal gasification (UCG) project in the Northern Inner Mongolia Autonomous Region. Seven ignition and production wells reached the coalbed 200 meters below ground by May 23 in the project's $112 million first phase. The project consists of underground drilling and ignition, aboveground coal-gasification power generation, and chemical production.

Several processes exist to initiate and control UCG reactions, including the Controlled Retraction Injection Point (CRIP) process [developed by LLNL] and Ergo Exergy’s proprietary εUCG process. These ignition processes create a syngas stream which is compositionally similar to surface-produced syngas. It can have higher CO₂ and hydrogen products due to a number of factors, including a higher than optimal rate of water flux into the UCG reactor and ash catalysis of water-gas shift. Because of the nature of in-situ conversion, UCG syngas is lower in sulfur, tar, particulates and mercury than conventional syngas and has very low ash content. Other components are similar and can be managed through conventional gas processing and clean up.

The economics of UCG appear extremely promising. The capital expenses of UCG plants appear to be substantially less than the equivalent plant fed by surface gasifiers because purchase of a gasifier is not required. Similarly, operating expenses are likely to be much lower because of the lack of coal mining, coal transportation, and significantly reduced ash management facilities. Even for configurations requiring a substantial environmental monitoring program and additional swing facilities, UCG plants retain many economic advantages.

—from “Best Practices in Underground Coal Gasification”

There are two primary, shorter-term environmental hazards associated with UCG: ground-water contamination and surface subsidence. Both of these, according to LLNL, appear avoidable through careful site selection and management.

Environmental risk assessment for UCG has unique aspects, requiring consideration of a complex array of changing conditions, including high cavity temperatures, steep thermal gradients, and stress fields obtained during and after the burn process. In the context of the site stratigraphy, structure and hydrogeology, risk models must evaluate the permeability changes from cavity development and collapse as well as the effects of changes in buoyancy, thermal and mechanical forces on the transport of organic and inorganic contaminants. Operational variables (e.g., temperature, feed gas composition) also impact the amount and nature of contaminants produced and groundwater flow directions. Furthermore, subsequent use of the cavity for CO₂ sequestration will impact the mobility of byproducts and will alter risk.

The longer-term issue is carbon management. LLNL suggests that because the UCG syngas reaches the surface at elevated pressure and high temperature, decarbonization may proceed at reduced—or in some cases, extremely low—cost. LLNL has begun to investigate both traditional and novel means of UCG decarbonization as part of an integrated energy and environmental strategy.

LLNL is carrying out a research program aimed at investigating the key processes and mechanisms of CO₂ storage risk. The lab has also signed a MOU with ErgoExergy to look for appropriate opportunities to conduct lab- and field-based investigations on this subject.

Ergo Exergy contributed to the initial work at Linc Energy’s Chinchilla project in Australia. (Earlier post.) Ergo Exergy technology is also being used in the first Underground Coal Gasification plant in Africa, which started operation in January 2007.

BP has experience and extensive activities managing and producing coal-bed methane and other gas resources, using technologies and expertise in seismic interpretation, directional drilling and fracturing techniques.

Resources:

• LLNL Capabilities in Underground Coal Gasification

• Best Practices in Underground Coal Gasification (LLNL)