Assessment of Unconventional Energy Potential of Methane Released from Active and Abandoned Mines

Science Center Objects

Large underground coal mines, especially longwall mines, disturb an extensive layer of strata overlying and underlying the mined coal seam due to induced stresses and due to collapse of the coal-bearing strata into the void left from mined coal. This volume of strata disturbed by mining is termed as the gas emission zone, which often contains other gassy coal seams of non-economic value, thin conventional gas reservoirs and also gassy shales, which are neither mined nor degasified prior to mining, but release their gas into this zone during and after mining with varying rates.

In an active mine, the gas emission zone, and thus its volume, continuously increase in the direction of mining and as new panels are developed in the same district. The exact nature of the gas emission zone is almost unknown and is dependent on the geology and mining conditions. The gas emission zone liberates and accumulates significant amounts of coal mine methane as a by-product of active mining, and is also the main source and reservoir for abandoned mine methane after mines are closed.

Objectives

This project has started in FY 2018 with the goal of constructing the building blocks of a methodology needed to be able to reliably predict methane emissions and emission potentials from active and abandoned mines in coal mining basins in the United States. The ultimate goal will be to produce a national assessment for energy potential from these resources, which currently does not exist, using advanced geologic, engineering and mapping techniques.

The primary goals of the project are to:

  1. Identify and develop the geologic framework for an active and an abandoned coal mine
  2. Gather and utilize available geologic and site-specific data
  3. Develop a draft assessment methodology to predict methane emissions from the sites by taking into account geologic, hydrologic, engineering, and operational factors
  4. Form the basis of establishing a reliable probabilistic assessment methodology and the beginning of a comprehensive inventory of emissions from coal mines for additional energy production
  5. Seek collaboration with other USGS Science Centers and outside entities

Relevance and Impact

This topic is a new addition to the portfolio of the USGS Energy Resources Program (ERP) in terms of exploring additional energy resources for the nation. Potential national and international collaborators and direct beneficiaries of this project for its scientific and assessment products are coal and gas companies, universities and research establishments, EPA, U.S. Department of Energy (DOE), U.S. Energy Information Administration (EIA), National Institute for Occupational Safety and Health (NIOSH), MSHA, and State Geological Surveys, as well as United Nations Economic Commission for Europe (UNECE), Commonwealth Scientific and Industrial Research Organization (CSIRO), International Energy Agency (IEA), European Union (EU) Commission, and other international organizations in coal-producing countries where active and abandoned mines are located and that are interested in preventing release of CMM and AMM due to their greenhouse gas potential.

This project has the potential for helping coal companies, and the coal mining industry in general in the United States and potentially elsewhere. Coal mine methane and abandoned mine methane capture and use can add significant value, besides safety, to mining operations through harnessing the value of a natural resource, which otherwise is wasted, by delivering economic returns through energy sales or cost savings. This, in return, helps coal companies in their efforts to improve safety, productivity and profit. Furthermore, the development of local coal mine methane and abandoned mine methane resources may result in the availability of a potentially low-cost supply of gas that could be used to help attract new industry to a region. Equally important, from a socio-economic point of view, this project and its potential outcomes may help converting lost mining and mining-related jobs in coal communities by creating new and closely related work opportunities for their economic viability.

Useful Links

Methane Control and Prediction Software

Coal Mine Methane Review Paper

US EPA’s Coal Mine Methane Cash Flow Model

UNECE Coal Mine Methane

Key Findings and Accomplishments

Coal mine and abandoned mine methane resource assessments require knowledge of geology, panel layout, production wells, ventilation fans, and availability of different data types and data sources. Initial efforts concentrated on building a comparative methodology for assessing coal mine methane and abandoned mine methane potential and production from longwall panels based on varying data availability. The aim was to estimate and compare the results to estimate methane availability and gas production potential from longwall panels. The methodologies were applied on two adjacent panels of a longwall mine located in the northern Appalachian Basin. This approach may serve as a technical roadmap for evaluating coal mine and abandoned mine methane potential and shows how different data could be gathered to support this purpose.

Initial results were presented at 35th TSOP Annual Meeting in Beijing, China, that was held August 17-21, 2018.