Assessing Emissions from Active and Abandoned Coal Mines

Science Center Objects

Gas emission zone liberates and accumulates significant amounts of coal mine methane as a by-product of active mining. In most active mines, coal mine methane is controlled by wellbores, called gob gas ventholes. Despite the presence of these wellbores, it is not possible to capture all of the methane generated within the gas emission zone. As a consequence, a large amount of gas migrates into the mine and is exhausted to the atmosphere with ventilation air. Eventually, part of the gas generated during mining stays in the emission zone, and with additional emissions, becomes abandoned mine methane after the panels are sealed or the mines are abandoned completely. Abandoned mines that are sealed properly may become gas reservoirs from which methane can be extracted and utilized by available technologies. Capturing and utilizing coal mine and abandoned mine methane can alleviate the harmful effects of methane emissions to the atmosphere and can provide an energy resource through use of the recovered gas.

A technical barrier to economical utilization of coal mine and abandoned mine methane is the uncertainty about how much methane may be available in the gas emission zone as a resource during mining, as well as after the panels are sealed and the mine is abandoned. Another difficulty is estimating how much of the potential methane resource can be produced from gob gas ventholes converted to capture abandoned mine methane. Coal mine and abandoned mine methane resource assessments and overcoming these difficulties require knowledge of geology, panel layout, production wells, ventilation fans, and availability of different data types and data sources. A reliable assessment methodology for gas emission zone and to quantify coal mine methane and abandoned mine methane emissions and their resource potential does not currently exist.

Objectives

The objective of this task is to develop a monitoring strategy, or a data evaluation strategy for the existing data, and a draft assessment methodology to predict methane emissions from the sites by taking into account geologic, hydrologic, engineering, and operational factors.

Methodology

This task involves selecting a coal mine and developing a geologic framework for defining the gas emission zone to quantify emission sources and their contribution to coal mine methane and abandoned mine methane. Available geologic and site-specific data will be gathered from USGS, U.S. Environmental Protection Agency (EPA), State Geological Surveys, and Mine Safety and Health Administration (MSHA) databases. Based on mine and geological characteristics, the characteristic size of the emission zone for each coal mining basin will be defined. By using software tools and the coal resource maps, the emission sources within the gas emission zones will be defined and quantified for their contribution to coal mine and abandoned mine methane potentials.

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

Two assessment methodologies that might be used depending on the availability of data were developed following a 5-tier approach:

  1. Define gas emission zone
  2. Estimate gas in place within different intervals of the gas emission zone
  3. Estimate how of the estimated gas in place is removed from different intervals during mining
  4. Estimate the amount of gas available for abandoned mine methane recovery
  5. Estimate productivity of abandoned mine methane wells.

The first assessment method is based on geostatistics and, relied on an extensive geological data set, measured shaft gas emissions, and gob gas venthole production data. The second method is based on a probabilistic method, and relied on a minimal amount of geologic data, predicted emission, wellbore recoveries, and displayed uncertainty as probabilistic distributions. The aim was to estimate and compare the results to estimate CMM and AMM availability and gas production potential from longwall panels.