Identifying the source(s) and composition of alleged stray gas can be challenging. It may be due to the site operations, a natural condition, or a combination of both. It may be non-threatening. Or it could pose a significant risk.
Biogenic methane is quite common. And it could be the source of your alleged stray gas. But when human health and safety is at risk, you must have the defensible data to know for sure. On the positive side, that knowledge will help you decide when you need to assess or halt operations and when you can proceed safely.
To develop defensible conclusions regarding methane source(s), successful protocols involve:
- Using a variety of methods, including Summa cannisters and laboratory-proprietary apparatus, to collect samples.
- Applying specialized and tiered analytical methane differentiation techniques to test the gas samples.
Carefully interpreting the data using multiple lines of evidence and the principles that include the following:
- Thermogenic methane is produced by thermal cracking of heavier hydrocarbons and some of the more volatile heavier hydrocarbons like butane, pentane and hexane are often present. However, the absence of these heavier hydrocarbons is not proof that the methane is biogenic.
- Biogenic methane (typically almost 100% pure) is produced by low temperature biological processes and butane, pentane and hexane are usually absent from its pure form.
- Hydrocarbon species testing are not 100% conclusive in most cases. To increase certainty, we always also look at the stable isotope ratios for carbon and hydrogen in the methane.
- Individual isotope testing results are cross-plotted and typically fall into one of three methane genesis regions. However, some samples may plot in inconclusive areas between regions. This can occur due to mixing of methane from different sources or other factors and requires expert interpretation.
Differentiating biogenic from thermogenic methane helps you pinpoint the origin/potential source(s) and plan your path forward.
With the right protocol, you can determine your risk(s), define the origin and identify potential sources of stray gas, and delineate the extent of any migration/stray gas plumes. You can then implement measures to ensure public health and safety; evaluate natural background gas concentrations in the area; conduct periodic monitoring to define trends and confirm a remedy; and proactively understand and address any contributing factors that may affect migration pathways; and seal/remediate any root causes, if necessary.
At Apex, we can help. Contact us to learn more.
Tom Fort, Principal Scientist