Carbon and hydrogen isotopes of neo-pentane for biodegraded natural gas correlation

Abstract

In severely biodegraded gases, every common C1-C5 hydrocarbon (methane, ethane, propane, iso-butane, n-butane, iso-pentane, n-pentane) and CO2 have been altered, negating the power of carbon and hydrogen isotopic compositions as correlation tools. Here, we show that neo-pentane (2,2-dimethylpropane) is recalcitrant, having an extreme resistance to biodegradation. In a gas biodegradation series with a common source from the Carnarvon Basin, Western Australia, the carbon and hydrogen isotopic compositions of neo-pentane provide the sole means by which a severely biodegraded gas can be correlated with a moderately biodegraded gas and a non-biodegraded gas. As such, the sterically hindered structure involving 2,2-dimethyl hydrocarbons can be exploited in gas (and oil) correlation studies. Crown