PRELIMINARY RESULTS OF DISSOLVED METHANE SAMPLING IN THE FOOTPRINT OF TEXAS SHALE PLAYS

Many constituents typically associated with oil and gas production, such as methane and higher-order hydrocarbons, exist naturally in shallow groundwater. Recent studies of aquifers in the footprint of several gas plays across the US have shown that (1) dissolved thermogenic methane may or may not be present in the shallow subsurface and (2) shallow thermogenic methane could be naturally occurring and emplaced through mostly vertical migration over geologic time and is not necessarily a consequence of gas production from a gas play. A team of researchers at The University of Texas at Austin Bureau of Economic Geology is currently conducting a large sampling campaign across the state of Texas to characterize shallow methane in fresh-water aquifers overlying shale plays and other tight formations. A total of ~700 samples has been taken so far in the Barnett, Eagle Ford, Haynesville shale areas as well as in the Delaware Basin of West Texas. The sampling for dissolved gas, often a delicate endeavor, is carefully performed. Analytical results suggest that dissolved methane is not widespread in shallow groundwater and that, when present at concentration greater than 10 mg/L, it is often of thermogenic origin according to the isotopic signature and to the presence of other light hydrocarbons.