Comparison of co-located laser and metal oxide continuous monitoring systems

Abstract

Accurate measurement of methane (CH4) concentrations on oil and gas sites is essential for accurate estimates of methane emission rates via inversion algorithms. Different types of continuous monitoring sensors are offered as commercial solutions, with varying accuracy. In this paper we compare data from co-located Metal Oxide (MOx) and Laser Spectroscopy (LS) sensors on a midstream oil and gas site, with the goal of quantifying the differences in raw concentration measurements between the two technologies. We first analyze the impact of meteorological variables on the difference between MOx and LS concentrations measurements taken at the same time and location, finding that temperatures from 30 to 70 degrees Fahrenheit and higher humidity contribute to larger concentration differences on average. Further, analysis of enhanced methane concentrations (likely from emissions on the site) recorded by both sets of sensors reveals that the LS sensors consistently record larger methane concentrations during these periods. This difference means that when using concentration measurements from both sensor technologies in inversion algorithms to estimate emission rates, using MOx sensor data would likely lead to underestimating emission rates, although we did not test this explicitly in this report.