ASSESSING THE OCCURRENCE AND SOURCES OF NATURAL GASES IN GROUNDWATER FROM THE SOUTHERN HIGH PLAINS, WEST TEXAS

The Ogallala Aquifer is the largest source of fresh water used both in agriculture and urban activities in the Southern High Plains (SHP) of West Texas. Due to its declining water-table levels and limited availability in the outer regions of the SHP, brackish groundwater from the deeper Dockum Aquifer is becoming a viable option for a future freshwater source after desalination. Recent development of unconventional hydrocarbon resources (oil and gas) such as shale deposits has been raising concerns across the U.S. regarding environmental impacts of hydraulic fracturing (fracking), including potential contamination of shallow groundwater by stray gases, saline formation waters, and fracturing chemicals. However, sound scientific hydrogeological field studies are lacking on the effects of both conventional and unconventional oil and gas exploration on the quality of groundwater from the Ogallala and Dockum Aquifers in West Texas. Such information is critical for the stakeholders (public, oil-gas companies, and local-state governments) to manage and mitigate potential negative environmental impacts of shale energy development.

We have initiated a study of hydrological monitoring and analysis of groundwater from these aquifers, using an extensive network of domestic and public wells on the SHP. Our preliminary results shows that while the Ogallala Aquifer remains essentially methane free, the Dockum Aquifer contains appreciable levels of methane, and minor levels of ethane, propane, and butane in certain areas. Groundwater wells containing elevated levels of natural gases appear to be correlated with the proximity of petroleum exploration activities. Carbon and hydrogen isotope analysis of the methane from the Dockum Aquifer also suggest that elevated levels of natural gases in the wells from the proximity of petroleum fields are thermogenic in origin. Natural gases from other wells of the Dockum Formation are more methane-dominated and may have more complex sources and history. A more comprehensive monitoring and analysis of hydrologic and geochemical parameters could help identify likely sources (natural vs. anthropogenic) and history of stray gases and other possible environmental contaminants in groundwater in the SHP.