Project highlights technique’s potential to kill two birds with one stone.

The U.S. Department of Energy (DOE) and its Southwest Regional Partnership (SWP) recently began injecting carbon dioxide (CO2) into a large coalbed, while simultaneously recovering valuable natural gas.

The SWP plans to inject up to 35,000 tons of CO2 in a 6-month demonstration at the San Juan Basin near Navajo City, N.M. Unlike other enhanced coalbed methane recovery projects, this demonstration will develop ways to maximize permanent storage of the injected CO2, a process called geologic carbon sequestration.

Many coalbeds in the United States are saturated with natural gas (methane), but the gas is difficult to produce because methane chemically binds to coal. However, CO2 shares this same tendency to bind to coal. Injecting CO2 into the coalbed essentially displaces the methane and makes the gas easier to produce. This process is called enhanced coalbed methane recovery.

The San Juan Basin was selected for the project because it is considered one of the top-ranked basins worldwide for coalbed methane recovery, and, thus, also is a prime candidate for value-added CO2 sequestration. Its advantages include favorable geology, high methane content, available CO2 from nearby power plants, low capital and operating costs, and well-developed natural gas and CO2 pipelines. The San Juan basin contains coals that are exceptionally permeable, at least compared to other regional coalbeds. Due to the tendency of coal to swell when in contact with CO2, high initial coal permeability is required to maintain effective CO2 injection rates (high injectivity) over time. DOE has established high injectivity as a sequestration program goal for large-scale, low-cost CO2 sequestration in coal.

The injection site consists of three coalbed methane-producing wells, and a centrally located injection well. The coals, which occur at depths of approximately 3,000 feet, are about 75 feet thick,  and are split among three seams over a 175-foot interval. This area of the San Juan coalbed fairway previously had undergone significant coalbed methane production.

In addition to the CO2 injection, the SWP intends to make use of the project’s produced water. Coalbed methane production typically results in a great deal of produced water. The SWP plans to take some of this produced water, desalinate it, and use it to irrigate nearby riparian areas stressed by prolonged drought. Resulting vegetation growth should induce additional CO2 uptake, another form of carbon sequestration.

DOE’s Regional Carbon Sequestration Partnership Program, managed by the Office of Fossil Energy’s National Energy Technology Laboratory (NETL), includes seven partnering regions established to determine the best approaches for capturing and permanently storing CO2, a greenhouse gas that contributes to global climate change. The partnerships are made up of state agencies, universities, private companies and nonprofit organizations that form the core of a nationwide network helping to establish the most suitable technologies, regulation and infrastructure needs for carbon sequestration. The partnerships include more than 350 organizations, spanning 42 states, three Indian nations and four Canadian provinces.

The SWP is led by the New Mexico Institute of Mining and Technology, and includes the states of Colorado, Oklahoma, New Mexico, Utah, and portions of Arizona, Kansas, Texas and Wyoming. The partnership currently is conducting five field tests – three geologic and two terrestrial – all at various stages of planning and execution. Each is designed to validate the most promising carbon sequestration technologies and infrastructure concepts.