2016 NGWA Groundwater Summit

Laser Sensing for Monitoring Headspace Methane

Monday, April 25, 2016: 2:40 p.m.
Confluence Ballroom C (The Westin Denver Downtown)
Daniel Soeder , South Dakota School of Mines & Technology

The migration of methane gas in groundwater is a concern for many domestic well users, especially in areas of natural gas development.  Commercial gas sensors for monitoring methane in groundwater wells typically utilize electrochemical devices.  Laser sensing has proven to be a more reliable and accurate technology for detecting methane and other gases in air.  A tuned laser produces light at wavelengths equal to the spectral absorption bands of the gas in question.  The presence of the gas in the path of the laser beam attenuates the light as a function of concentration, which is then measured with a photocell.  Laser gas detectors are solid state devices that only require the introduction of the gas sample into the laser beam path.  Laboratory tests with a commercial unit had an accurate detection range from 10 ppm methane to the lower explosive limit of 5%.

Although these sensors perform well in a laboratory environment, deploying them in the field for environmental monitoring is challenging.  Along with power supply and data storage issues, the major problem is moisture condensation in the sensor, which can create data inconsistencies.  Field deployment of the laser sensor for continuous monitoring of methane in the headspace of a groundwater well required the use of a commercial gas drying method to remove humidity.  Low power requirements were critical.  As configured, the field-deployable device collects an air sample from the well headspace, pumps it through a drying system, and then into the laser sensor to measure methane concentration.  Ambient temperature and pressure are also measured before discharging the gas.  The entire unit is contained within a medium-size utility box, and field sampling requires only the insertion of a 5 mm (1/4 inch) collection tube into the monitoring well headspace.  Field tests are ongoing in support of a patent application.

Daniel Soeder, South Dakota School of Mines & Technology
Dan Soeder is the new Energy Resources Initiative director at South Dakota School of Mines & Technology in Rapid City. He was previously a research scientist at the U.S. Department of Energy (DOE) National Energy Technology Laboratory in Morgantown, West Virginia, from 2009 to 2017, where his focus was on gas shale. He came to DOE with 18 years of experience as a hydrologist with the U.S. Geological Survey in the Mid-Atlantic region and on the Yucca Mountain Project. Prior to that, he spent a decade performing production research on tight sandstone and shale at the Gas Technology Institute in Chicago, and two years as a DOE contractor on the Eastern Gas Shales Project, where he recovered and characterized shale drill core. He holds BS and MS degrees in geology from Cleveland State University and Bowling Green State University in Ohio.