XRF Determination of Elemental Composition of King County Clearfork Silty Clay Loam Following Exposure to Methane Seepage.

Gases from hydrocarbon reservoirs diffuse through subsurface soils and reach the surface through microseeps and macroseeps.  Of those that reach surface soils, methane is the most abundant.  In an effort to determine the presence of such seepage through indirect means, ED-XRF fluorescence spectroscopy is employed in this study to determine the effects on bulk soil elemental composition following a period of exposure to methane.  Magnetic susceptibility was also measured.  We observed a significant direct disparity in total ppm Ca, Al, Fe, Co, Ni.  Indirectly, organic atomic composition (total C, H, O, N) was also very disparate between control and experimental samples.  We were able to determine that what we likely observed was a difference in oxidation/reduction conditions, as well as other far more subtle reactions.  The experimental samples were limited in exposure to oxygen due to methane seepage and therefore experienced little change in the aforementioned elemental compositions, whereas the control soil underwent oxidation and exhibited a dramatic increase in indirectly measured C, H, O and N, along with a proportional decrease in potentially ferromagnetic atoms.  This was supported by the magnetic susceptibility measurements, which decreased far more for the oxidized samples than for those exposed to methane.