RUI: Investigating Natural Seepage of Light Alkanes from Oil and Natural Gas Deposits

Loyola Marymount University, Los Angeles CA

Investigators

Abstract

Because of the importance of hydrocarbons in various facets of atmospheric chemistry, determining where the hydrocarbons come from (sources) and the various pathways by which they are removed from the atmosphere (sinks) is of considerable importance. The total source strength for a particular hydrocarbon over a finite time period (usually a year) can be determined for geographical areas of various sizes - for individual cities, regions, countries, and the planet. One potentially underreported source of methane that has recently attracted attention is geologic emissions, including thermogenically derived seepage. Natural seepage is categorized as macroseepage, which involves outgassing from large vents, or microseepage, which is not visible. Although macroseepage is estimated to be a larger source of methane, microseepage has recently been estimated to be a relatively significant methane source (between 10 and 25 Tg annually). However, this estimation is rough, as the majority of microseepage studies have focused on sites in Europe and a handful of western states. The studies have found a wide range in microseepage fluxes that depend on a variety of factors including season, coastal influence, and a wide variety of geological factors such as soil type, depth of deposit, and proximity of nearby faults. This project will lead to a better understanding of the regional, national, and global budgets of methane and six light alkanes (ethane, propane, n-butane, i-butane, n-pentane, and i-pentane). Specifically, the contribution of oil and natural gas emissions via natural seepage will be quantified using flux chamber measurements for the seven gases. The work on this project is well suited to undergraduates. The students who help build the methane analytical system will learn a great deal about gas chromatography to supplement their knowledge gained in an Instrumental Analysis course. Students that work on the data collection will gain an insight into Atmospheric Chemistry field work and learn how to analyze samples using highly specialized analytical systems. This work will also allow students to learn some aspects of Atmospheric Chemistry, a subject that they are not currently taught at LMU. Students will also work on data analysis, which will include identifying, integrating, and quantifying chromatography peaks and calculating flux rates of different light alkanes. Students will also be fully involved in the dissemination of data including presentations at conferences and writing journal articles.