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Carbon Energy Delivers Innovations in Underground Coal Gasification

By Morné Engelbrecht
Managing Director and CEO, Carbon Energy Limited

After decades on the fringes of world energy production, advancements in underground coal gasification (UCG) are proving the process can deliver high-quality syngas on a commercial scale with limited impact on the surrounding environment, at a lower cost than current coal-to-gas production in Australia.

Carbon Energy Limited, based in Australia, has built on many years of work by that country’s leading research organization, the Commonwealth Scientific and Industrial Research Organisation (CSIRO), to further develop and demonstrate a UCG technology that has satisfied stringent technical and environmental assessments by a panel of government-appointed independent scientists. Decommissioning and rehabilitation processes have also been assessed by the state environmental protection authority.

Today UCG is poised to become a valuable option to help meet future domestic and global energy demand because it offers an environmentally responsible and economically attractive means of extracting energy from otherwise unmineable coal.


One of the stumbling blocks that has held UCG back from becoming a fully commercial industry has been the inability to extract a consistent-quality syngas required for continuous feed into the selected downstream industrial process (whether for fuel or fertilizer production, electricity generation, or other uses that require syngas as a raw feedstock).

UCG requires ignition (heating of the underground coal seam to high temperatures between 1200 and 1600°C) to initiate the gasification process, and the subsequent injection of an oxidant (e.g., air or oxygen and steam) to maintain the syngas production. Traditional UCG approaches have employed a “batch process” using vertical wells and requiring manual intervention and reignition approximately every 30 days. This causes fluctuations in temperature and syngas quality.

Carbon Energy’s process, developed over more than 16 years of research and in-field trials, has been proven to address this issue by using a unique design that provides continuous automated gasification in a panel of coal to produce a high-quality syngas for up to 10 years (see Figure 1). This innovation, called the Controlled Retraction Injection Point (CRIP), was extremely important in achieving the consistently high-quality syngas that was produced continuously over many months during Carbon Energy’s demonstration at Bloodwood Creek in Queensland.

FIGURE 1. Carbon Energy’s approach to UCG

FIGURE 1. Carbon Energy’s approach to UCG

With horizontal in-seam injection and production wells, and an oxidant injection point that retracts as the coal face is gasified, the gasification process is maintained at a consistent temperature, which in turn produces consistent quality syngas. Moreover, a significant proportion of the potentially contaminating by-products produced with the syngas are destroyed in the path of the gasification face, contributing to the now-proven environmental credentials of the technology.


Global primary energy demand is expected to rise 37% by 2040, according to the International Energy Agency’s “World Energy Outlook 2014”.1 With the world’s hunger for energy growing, unlocking new energy sources that are commercially sustainable and are amenable to carbon capture techniques is a priority. Coal is predicted to remain a significant source of energy for the world given its widespread availability and low cost. UCG is a technology that is able to maximize the energy extracted from coal, while ensuring a small environmental impact and footprint.

Carbon Energy’s technology has improved on previous UCG methods and been shown to extract 60 times more energy than coalbed methane extraction on the same area of coal. It is also able to produce syngas from coal seams previously considered too deep and uneconomical for traditional coal extraction technologies. Carbon Energy’s recently completed demonstration at Bloodwood Creek was operated at depths of more than 200 meters below the surface; however, operation at far greater depths is also possible and commercially viable.

Rigorous scientific assessments and independent review have shown that potential environmental issues around waste and impacts on groundwater have also been overcome. With site selection methodology developed by CSIRO, refined engineering design to geothermal standards, and demonstrated operating protocols, it has been demonstrated that environmental impacts are kept to a minimum. With the physical footprint of the UCG operations contained to 50 hectares of land while recovering a significant volume of energy, good relationships are maintained with landholders. Together with the proven environmental credentials, this should assist Carbon Energy to achieve a social license to operate its unique technology.


Carbon Energy’s proposed Blue Gum Gas Project neighbors the existing demonstration site in the Surat Basin at Bloodwood Creek, about 200 km west of Brisbane, Queensland, Australia. Once government approvals are received, Carbon Energy will build and operate a commercial-scale UCG plant that will produce syngas which will be processed above ground to deliver pipeline-quality synthetic natural gas (SNG). The plant will produce 25 PJ of natural gas per annum, which is approximately 0.687 billion Nm3/yr natural gas equivalent, suitable for use by existing connected homes and domestic industries. SNG production is expected to commence within three years of the start of construction.

Carbon Energy’s proposed commercial Blue Gum Gas project will be located near the existing demonstration site.

Carbon Energy’s proposed commercial Blue Gum Gas project will be located near the existing demonstration site.

Carbon Energy’s focus on developing SNG over power or ammonia production has been driven by commercial demand. The domestic natural gas market on the east coast of Australia will see a significant increase in natural gas prices as the export of coal seam gas commences. East coast manufacturers are eager to find a low-cost natural gas feedstock. The Blue Gum Gas Project will be located near existing infrastructure enabling ready transport of natural gas to customers.

Carbon Energy operated a demonstration (pilot) project at Bloodwood Creek in Queensland from 2008 to 2012 in order to fine-tune the application of their unique technology, and to collect necessary data to submit to the state government for approval to operate the technology in Queensland. Although most of the syngas over the demonstration period was flared, the syngas was used to power generators, with power used on site and also exported to the local electricity grid.

The pilot-scale demonstration project involved operating two underground gasifiers. The “panels” of coal where the gasifiers operated were constructed at a depth of about 200 meters, are 500 meters long, and 30 meters wide, with an average thickness of 8–9 meters. A panel of this size has sufficient coal to produce syngas continuously for five years. However, as proof of concept of the technology was achieved after almost two years of continuous production of high-quality syngas from the second gasifier, further expenditure on the pilot was unwarranted and the demonstration project was decommissioned.

The commercial-scale project will simply replicate the panel module at the scale required for the project. In the case of the proposed Blue Gum Gas Project, around 40 of these panels will be required to generate 25 PJ of syngas per annum.

Environmental Review

An Independent Scientific Panel (ISP) was appointed by the Queensland government in 2009 to review and report on the pilot projects being conducted in the state at that time, focusing on the technical and environmental aspects of UCG technology. Technology developers were required to prepare a comprehensive report on their pilot projects and submit these reports to the ISP for review.

The final peer-reviewed ISP report on the pilot projects was released in July 2013. The government gave in-principle support to the ISP’s conclusions that the capability to commission and operate a UCG gasifier had been demonstrated, and that “the technology could, in principle, be operated in a manner that is socially acceptable and environmentally safe when compared to a wide range of other existing resource-using activities”. However, the government required that the technology developers demonstrate successful decommissioning prior to any approval being granted for a commercial-scale project.

Essentially, this meant that Carbon Energy needed to provide evidence that gasification had ceased at the pilot project site and that any of the relevant environmental values affected by the underground coal gasification process (excluding surface facilities and landform, which would be addressed under normal processes) could be restored to a condition agreed to with the Department of Environment and Heritage Protection (DEHP). There was a particular focus on groundwater quality, which could potentially be impacted adversely by UCG by-products.

Carbon Energy’s UCG pilot site

Carbon Energy’s UCG pilot site

To meet the government’s requirement, Carbon Energy prepared a comprehensive Decommissioning Report and Rehabilitation Plan and submitted these documents on 29 August 2014 and 1 October 2014, respectively. Preparation of these documents involved a full site investigation by an independent Suitably Qualified Person for contaminated land assessment (as authorized under the Environmental Protection Act 1994), which in turn involved a drilling program for collection and laboratory analysis of decommissioned gasifier cavity water and core samples, core samples from new near-cavity boreholes, and baseline core samples. Analysis of the data from these new wells was in addition to analysis of results from the ongoing monitoring of groundwater quality from 24 monitoring wells surrounding the gasifier cavity and located in the target coal seam and overlying and underlying rock formations.

The Queensland DEHP has advised Carbon Energy that its expert consultants have completed the review of Carbon Energy’s Decommissioning Report and Rehabilitation Plan. This review will be referred to the Department of Natural Resources and Mines (DNRM), which is the lead agency in the matter of UCG policy, for a government decision on commercialization of the technology in Queensland.

Decommissioning Plan

  • The Decommissioning Plan was required to include:
  • Evidence that gasification had ceased
  • Quantification of any contaminant load
  • Delineation of the zone of impact of any contamination
  • Evidence that any contaminants were not increasing or moving outside of the lower-pressure zone maintained by Carbon Energy around the gasifier cavities.

The process data clearly showed that gasification stopped within 48 hours of initiating the shutdown procedure (see Figure 2). This was evidenced by changes in the composition of vented gas, which quickly returned to high percentages of natural methane gas with a sharp decline in the concentrations of hydrogen and carbon dioxide, and declining syngas flow rate and temperature.

FIGURE 2. Carbon Energy’s pilot-scale demonstration

FIGURE 2. Carbon Energy’s pilot-scale demonstration

Once gasification stops, it cannot start again naturally, due to the absence of oxygen 200 meters underground beneath a tightly sealed formation, with the UCG panel surrounded by groundwater.

The results of the groundwater quality investigation showed that:

  • The majority of remaining UCG by-product was within the cavity.
  • More than 90% of by-products were eliminated by steam venting during the shutdown procedure.
  • Concentrations of remaining by-products are decreasing.

Both during operation and after decommissioning, pressure in the gasifier is maintained at a level below the regional groundwater pressure so that groundwater continuously flows toward and into the gasifier cavity. The pressure is controlled by Carbon Energy from the surface. This approach successfully contains UCG by-products within the small area of low pressure.

Environmental testing was completed to ensure that the pilot operations had been concluded safely.

Environmental testing was completed to ensure that the pilot operations had been concluded safely.

Rehabilitation Plan

As previously indicated, the purpose of the Rehabilitation Plan was to demonstrate Carbon Energy’s ability to restore the relevant environmental values of the site, those essentially being groundwater quality. Given the baseline quality of the groundwater (which is not fit for human consumption), the applicable environmental values for the Bloodwood Creek site were identified as stock watering and human health.

Based on the results of the site investigation, a risk assessment and highly conservative fate and transport modeling based on the applicable environmental values, it was concluded that the current groundwater conditions within the cavity do not pose harm to human health or the environment.

The independent Suitably Qualified Person under the Environ-mental Protection Act 1994 signed off on the Rehabilitation Plan, which concluded that:

  • The low levels of remaining by-products will rapidly and naturally reduce to baseline levels.
  • No environmental receptors are likely to be impacted.
  • No active remediation is required.

Parameters have been proposed for a range of chemicals against which groundwater analysis will be assessed on a regular basis and reported to the government. Monthly reporting of groundwater results from the groundwater monitoring network will also continue.


Carbon Energy has demonstrated its technology is a significant advance in UCG, in producing consistently high-quality syngas that can support commercially viable downstream use. More than 100 years since the first suggestion of gasifying coal underground, Carbon Energy’s approach is an attractive, environmentally responsible, and economically viable means of utilizing the energy potential of coal considered too deep for viable conventional mining.


  1. International Energy Agency. (2014, 12 November). World energy outlook 2014, press release, www.worldenergyoutlook.org/

For more information, please email askus@carbonenergy.com.au


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Underground Coal Gasification: An Overview of an Emerging Coal Conversion Technology

By Cliff Mallett
Chairman,A Underground Coal Gasification Association
Technical Director, Carbon Energy Limited

Fossil fuels undeniably remain the world’s principal source of energy. They have underpinned the growth of industry and standards of living for the last 300 years. However, finding ways to continue to utilize fossil fuels in a low-carbon and otherwise environmentally-friendly manner is a global priority.

Underground coal gasification (UCG) is one approach to energy production that may allow for emissions and other environmental impacts to be effectively managed. Decarbonization could be achieved by gasifying coal and reforming the syngas product to hydrogen (H2, a clean energy carrier) and safely store the carbon dioxide (CO2).

UCG demonstration rig

UCG demonstration rig

Coal gasification has been carried out for centuries. During the 19th and early 20th centuries numerous towns had their own gas works, responsible for making coal gas (i.e., syngas) from mined coal. The gas was piped to homes and industry. Coal gas, or town gas, is now referred to as syngas and is a mixture of energy gases such as H2, carbon monoxide (CO), as well as methane (CH4).

The development of carrying out gasification underground, UCG, can be attributed to researchers and innovators from around the world. The earliest recorded idea of producing energy by gasifying coal underground came from Sir William Siemens in the late 1800s.1 Working with his brothers, a coal gasifier was invented, which Siemens suggested be placed underground.

The subsequent major step in the development of UCG was in 1910 when patents were granted to an American engineer for UCG methods that closely resemble modern approaches. Then, in 1912, a British chemist, Sir William Ramsay, proposed gasifying coal underground as a way to avoid emissions from burning coal, which were resulting in air quality issues in cities at the time. He believed that this coal-derived syngas would be the fuel of the future.

Ramsay began preparations to trial UCG, but the outbreak of World War I derailed his plans. Interest in UCG was rekindled in the 1930s with the USSR conducting extensive experiments. However, the program was scaled back in the 1960s when the USSR discovered huge natural gas and oil reserves. More recently, momentum has grown yet again as countries including China, the U.S., Canada, Argentina, and Chile have commenced UCG projects.


Most coal-derived energy is obtained when the contained carbon reacts with oxygen (O2), yielding CO2 and releasing energy in the form of heat. If excess O2 is present, combustion occurs with nearly all the carbon converted to CO2. When coal is gasified in an O2-deficient environment, some coal is converted to heat and CO2 and this heat drives the conversion of the remaining coal to syngas. Syngas generated from UCG contains about 80% of the energy that was in the original coal.

To gasify coal underground, O2 or air is pumped down a borehole into a coal seam, the coal is gasified in a cavity created by the conversion of coal to syngas, and the sygnas is extracted through a different (i.e., production) borehole. A number of underground gasifier designs have been demonstrated, the latest being from Australia-based Carbon Energy. In a demonstration project its technology provided consistently high-energy syngas over 20 months and demonstrated the same could be achieved from a single panel of coal for up to 10 years (see article on page 61 for further details).


The primary reason to gasify coal underground is the low cost of energy production. Estimates from UCG companies on the cost of producing UCG syngas range from US$1–3/GJ depending on the coal deposit and on whether air or oxygen is used as the oxidant.2,3 Additional UCG benefits include:

  • It is applicable to very large, deep resources that can consist of low-quality coal not suited for conventional mining (normally conventional mining occurs above 1000 m). The estimated amount of usable coal at such depths could equal or exceed all current mineable coal resources and be a game changer for global energy supply.
  • The energy is produced as syngas, which is readily cleaned using existing processes and transported via pipelines.
  • Multiple uses exist for syngas, such as a fuel for power station gas engines to produce electricity, or chemical feedstock for the production of fertilizers, diesel and gasoline, and methanol derivatives such as olefins and plastics. Syngas can also be readily processed into natural gas.
  • Compared to coalbed methane extraction from the same coal seam, UCG generates over 60 times more energy.
  • UCG offers a small environmental footprint with little surface impact and minimal waste generation.
  • The health and safety issues associated with people working underground can be avoided.
One important benefit of UCG is the small footprint.

One important benefit of UCG is the small footprint.


Early 20th-century UCG trials resulted in significant lessons learned that allowed researchers and technology providers to improve the efficiency and environmental credentials of UCG. One of the major concerns related to UCG has been the ability to avoid affecting groundwater quality. Modern UCG technologies have evolved to ensure destruction of potential contaminants as part of the gasification and decommissioning processes, as well as managing operating pressures to protect groundwater.

A particular observation that evolved from early trials and subsequent research was the “Clean Cavern” concept. This is the process whereby the gasifier is self-cleaned via the steam produced during operation and following decommissioning (during decommissioning while the ground retains heat steam continues to be generated). Another important practice is ensuring that the pressure of the gas in the gasifier is always kept below that of the groundwater surrounding the gasifier cavity. Thus, groundwater is continuously flowing into the gasifier and liquids which could potentially contain chemicals will not be pushed out into the surrounding strata (see Figure 1). The pressure is controlled by the operator using pressure valves at the surface.

FIGURE 1. Operating UCG with a pressure lower than the surrounding area draws groundwater toward the gasifier.

FIGURE 1. Operating UCG with a pressure lower than the surrounding area draws groundwater toward the gasifier.

In addition, the high temperature in the cavity during gasification destroys many of the potentially contaminating organic by-products produced during the process. When operation of a gasifier is stopped, the groundwater pressure in the cavity is reduced to near atmospheric pressure (much lower than the surrounding pressure) to increase the volume of groundwater flowing into the cavity, which increases steam production. A significant percentage of remaining by-products are carried to the surface as vapor via the production well and combusted. This overall approach to UCG has now been successfully implemented at sites in the U.S., Spain, Australia, and South Africa.

Another historic concern related to UCG has been the ability to understand and predict ground subsidence. The UCG process creates a cavity similar to those found at conventional underground coal mines. These cavities are well understood thanks to conventional mining, and thus their behavior can be predicted accurately with modern 3D computer models. Similar to conventional underground coal mining, ground subsidence is predicted before UCG operations commence; if surface subsidence is predicted to significantly affect current or future land use or infrastructure, UCG will not proceed at that particular site.

One of the most rigorous long-term environmental evaluations of UCG pilot sites was carried out by the Queensland Government in Australia from 2008 to 2014. An Independent Scientific Panel appointed by the state government reviewed four years of UCG Pilot Project operations and concluded in the “Independent Scientific Panel Report on the Underground Coal Gasification Pilot Trials” (June 2013) that UCG “could be conducted in a manner that is socially acceptable and environmentally safe when compared to a wide range of resource using activities”.

Decommissioning and rehabilitation of an underground UCG gasifier cavity had not been attempted in the Queensland trials at the time of the ISP evaluations, but in late 2014, independent experts advised the government that Carbon Energy had successfully decommissioned its gasifier, and steam cleaning of the cavity resulted in the cavity posing no environmental or health risks. Groundwater quality will rapidly and naturally be restored to pre-project conditions and no active remediation is required.


Industrial processes require specific, controlled conditions for optimal and safe operation and UCG is no exception. The conditions required for operation of the underground gasifer are established through exploration, prior to construction or operation of a UCG panel. For example, proper UCG site selection is critical—several hydrogeological conditions must be satisfied before proceeding with construction.

First, the coal seam being gasified must be overlain by impermeable strata. The buoyancy of the gas forces it to move upward; thus, the gas will be lost unless the coal seam is capped by strata through which the gas cannot pass, such as shale or clay beds. Second, as coal seams always have some permeability and gas is able to move laterally through coal, the groundwater in the surrounding coal seam must be at a higher pressure than the pressure in the gasifier to prevent the flow of gas away from the gasifier cavity. These primary criteria are illustrated in Figure 2. Other characteristics also must exist at a suitable UCG site—for example adequate groundwater pressure for gasification to occur, coal seams of adequate thickness to maintain gasification temperatures, and appropriate separation from overlying and underlying water-bearing formations.

FIGURE 2. Primary criteria required for a suitable UCG site.

FIGURE 2. Primary criteria required for a suitable UCG site.

Field tests and digital modeling facilitate the development of hydrological models that can be used to predict risks to water supplies. Just as with subsidence modeling, if harmful effects are predicted in the exploration stage, UCG will not proceed.

Similar to other resource production industries, UCG requires appropriate pre-development exploration and investigations to ensure that hydrogeological conditions suit the technology being applied.


Until recently, there have been few new developments in UCG. A commercial UCG plant has been running for many years in Uzbekistan; however detailed information on the operation or output of that plant has not been made public. Developed countries with accessible resources have chosen to access shallower coal deposits using traditional mining methods. Additionally, projects based on traditional approaches to UCG have struggled to produce a consistent, high-quality syngas.

Looking at almost a hundred historical UCG sites worldwide,5 the main difficulties can be categorized as follows:

  • Insufficient knowledge of the site geology
  • Inability to drill boreholes with necessary precision
  • Operating with inappropriate gasification parameters
  • Lack of understanding of the impact of the gasification process on the surrounds of the underground cavity.

More recently, however, there have been major technological innovations which have addressed the issues encountered in previous UCG projects (see Table 2).


These advances facilitate proper site investigation, UCG design performance modeling, and identification of issues with respect to product gas or environmental impacts which demand specification or exclude the site as a UCG prospect. In addition, UCG operators now have access to real-time control of underground processes. This allows interpretation of changes in UCG performance and the design of appropriate responses.

The UCG ignition panel is used to carefully control the process underground.

The UCG ignition panel is used to carefully control the process underground.

Since 2000, long-term UCG pilots in Australia, China, and South Africa utilizing the technologies shown in Table 2 have successfully demonstrated that deep UCG can be low cost and environmentally benign. Results from these trials continue to demonstrate that UCG’s major challenges have been resolved and has led China to incorporate this technology into its Five-Year Plan process for resources and energy.

Recent progress and innovation have made it possible that UCG will be an important technology in the future energy mix. However, progress in nontechnical areas must be made with respect to the interrelated areas of government regulation, community understanding and engagement, and project financing.

Given that the production cost of UCG syngas can be significantly lower than that for production of energy by other means, and its demonstrated environmental credentials, UCG presents an opportunity for high-potential growth investors looking for approaches to generate low-emissions power, synthetic natural gas and other fuels, and chemicals from coal.


Energy demands continue to grow globally, particularly in emerging economies in Asia and Africa. At the same time, there is pressure to minimize the cost and maximize the availability of energy supplies as well as the social imperative to reduce the environmental impact associated with energy.

The adaption and application of new petroleum and mining techniques have demonstrated that consistent supplies of high-quality syngas can be safely produced in commercial-scale UCG projects. Further progress and innovation in the field of UCG has been seen recently and several new commercial UCG projects are nearing commencement. Once the first commercial project is successfully established, I believe there will be an avalanche of follow-on projects, and the industry will become a valuable contributor to global energy production.

The syngas created underground is collected and processed above ground.

The syngas created underground is collected and processed above ground.

A. Dr. Cliff Mallett served as Chairman of the Underground Coal Gasification Association from 2013 to 2015. His tenure at that position concluded near the time of article preparation. Dr. Mallett is also Technical Director at Carbon Energy. Thus, some of the technical innovation discussed in the article is based on his direct involvement with Carbon Energy.


  1. Klimenko, A.Y. (2009). Early ideas in underground coal gasification and their evolution. Energies, 2(2), www.mdpi.com/1996-1073/2/2/456
  2. Carbon Energy. (2012, 26 June). Carbon Energy UCG syngas – low cost source of natural gas. ASX/Media Announcement, www.carbonenergy.com.au/IRM/Company/ShowPage.aspx/PDFs/1561-83497961/LowCostSourceofNaturalGas
  3. Pricewaterhouse Coopers. (2008, May). Industry review and an assessment of the potential of UCG and UCG value added products, www.lincenergy.com/data/media_news_articles/relatedreport-02.pdf
  4. Moran, C., da Costa, J., & Cuff, C. (2013, June). Independent Scientific Panel report on underground coal gasification pilot trials, Independent Scientific Panel to the Queensland Government, www.fraw.org.uk/files/extreme/derm_2013.pdf
  5. UCG Association. (2015). Worldwide UCG projects and developments, www.ucgassociation.org/index.php/ucg-technology/worldwide-ucg-projects-developments (accessed April 2015)

The author can be reached at Cliff@carbonenergy.com.au


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