Improving Quality with Water Based QC for Dissolved Gas Analysis in Water

Topics in Shale Gas
Oral Presentation

Prepared by

Contact Information: mark.bruce@testamericainc.com; 330-966-7267


ABSTRACT

Predrill background studies to support hydraulic fracturing activities in the various shale plays are a common risk management strategy. Ground water analysis for methane and other light hydrocarbon gases is a critical component of these studies. The Marcellus Shale Coalition identified lab to lab variability as a critical shortcoming with dissolved hydrocarbon gas analysis services. The most common reference method RSK-175 utilizes gas phase calibration standards, but does not include water based QC samples. Regular use of water based laboratory control samples (LCS) allows the laboratory to monitor the performance of the entire sample preparation process.

Systematic sample preparation process issues can occur that gas phase calibrations and LCSs do not catch. Most frequently this leads to a low bias in the field sample results. Eurofins TestAmerica has been using a water based certified reference material from LGC to monitor LCS recovery for methane, ethane, ethene and propane. These water based LCSs allow a lab to demonstrate consistent performance of the entire preparation and analysis process. Alternatively, low recoveries of the water based LCS analytes highlight process issues. For example, these issues could include losses during transfer steps from the field container to an autosampler vial, leaking “gas tight” syringes, too short headspace equilibration time or insufficient mixing of sample and headspace.

Control charts from several laboratories over several months show process upsets and when process control was regained. During the same periods gas phase based QC didn’t always show that process issues existed. The use of water based LCSs ensures more consistent data quality to the end users.