POTENTIAL WATER-QUALITY RISKS FROM ORPHANED WELLS IN PRINCIPAL AND SECONDARY AQUIFERS OF THE UNITED STATES

Over the history of oil and gas production in the United States, millions of wells have been drilled for exploration and extraction of resources. Hundreds of thousands of wells are no longer in active production and are currently under orphaned status, with no responsible party recognized for ownership or liable for plugging. Orphaned wells pose potential threats to water resources, most notably by providing pathways for contaminants such as hydrocarbons and brines from deeper formations to migrate to water-supply aquifers. Local geologic controls and the failure of well infrastructure can contribute to well integrity loss and the transport of contaminants within and between aquifer systems. Here, we investigate the potential risk to drinking-water resources posed by orphaned wells at the national level. We use geospatial and statistical methods to evaluate three sets of risk factors in principal and secondary aquifer systems across the United States, including: 1) factors related to the characteristics and density of orphaned wells; 2) factors that can influence the loss of well integrity; and 3) factors related to groundwater withdrawals and who is using water resources in the event of water-quality disturbances. Approximately 64,000 of the 117,672 orphaned wells identified to date fall within a principal aquifer system, while the remainder fall within a secondary aquifer system. Many of these orphaned wells have co-occurring factors that increase the risk of degradation and use of groundwater resources. This work represents the first comprehensive look at the nexus between orphaned wells and groundwater resources on a national scale with applicability to oil and gas wells of all types.