Improved Accuracy of Dissolved Hydrocarbon Gas Analysis in Water

Oral Presentation

Prepared by M. Bruce
TestAmerica, 4101 Shuffel St NW, North Canton, Ohio, 44720, United States


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. No fully validated USEPA methods are available yet. ASTM recently released D8028 to address many of the limitations of the previous analytical options. Other organizations are also considering development of improved methods. LGC is developing water based reference materials that can be used as external proficiency test samples, analysis batch QC samples and calibration standards. Thus, impartially demonstrating method performance in the near future will be more easily accomplished.

Initially TestAmerica developed its own dissolved gas analyte in water reference materials to evaluate the accuracy of its laboratory processes. Analytical process differences between handling of water samples and gas phase based standards can introduce a low bias. These biases arise from analyte losses and non-equilibrium conditions. Use of water based reference materials facilitates evaluation of each step in the analytical process. Switching to water phase calibration standards can significantly improve the accuracy of the final results, but regulatory acceptance for this practice is limited at present. The stability of water based standards has been studied in several different storage scenarios and ranges from minutes to several months. Internal and external proficiency test samples demonstrate that routinely meeting the 70-130% recovery window requested by many lab clients is possible.