In a groundbreaking study, a research team that included a Johns Hopkins engineer compiled and analyzed an unprecedented amount of regulatory data that describe the integrity of oil and gas wells in multiple states. The study results, published in the Proceedings of the National Academy of Sciences, provides valuable insights for industry operators and regulatory agencies seeking to prevent well leakage and ensure the success of carbon storage, oil and gas production, natural gas storage, and hydrogen storage operations.
"The study focuses on oil and gas well integrity, specifically on onshore oil and gas wells. This is relevant, for example, to evaluating the environmental risks related to unconventional oil and gas development," said Harihar Rajaram, an environmental health and engineering professor at Johns Hopkins University's Whiting School of Engineering, a co-author on the study led by researchers at U.S. Department of Energy's National Energy Technology Laboratory. "To understand the environmental risks of leaking oil and gas wells, it is important to first estimate what fraction of oil and gas wells have experienced integrity issues."
Oil and gas wells are designed to fully contain (via a series of nested steel pipes with cement in between) any fluids they are pumping up from oil and gas reservoirs. However, due to stresses underground, cement may crack or separate from the adjacent steel casing, causing integrity issues, and, in some cases, leakage.
While more than 900,000 oil and gas wells are currently active in U.S., accurate estimates of the percentage of these wells that have experienced integrity issues during their lifetime have been limited by data availability. Although most states require some form of well integrity testing—for example, using a pressure gauge to monitor the buildup of gases outside the production casing—these data are not made publicly available in readily accessible digital databases.
In the new study, researchers address this issue by using advanced computational techniques to gather and extract data from more than 470,000 regulatory records describing the results of well integrity tests performed in Colorado, New Mexico, and Pennsylvania on more than 100,000 wells before 2018. The data extracted from these records represent the largest and most complete record yet assembled to review the integrity of U.S. oil and gas wells.
The team focused on estimating the percentage of oil and gas wells that have exhibited pressures and flows indicative of an integrity issue. Testing records from Pennsylvania showed that 14.1% of wells tested prior to 2018 have potentially experienced an integrity issue. Data from different hydrocarbon-producing regions within Colorado and New Mexico revealed that wells experienced integrity issues with a wider range of frequencies (0.3%-26.5%) than previously reported, which highlights the need to better understand regional trends and variations across different oil and gas fields in well integrity. Directional wells were more likely to exhibit integrity issues than vertical wells in Colorado and Pennsylvania. Most wells with integrity issues experienced leakage internal to the well system that did not escape into groundwater. Testing around wells for indicators of gas leakage into groundwater is not a widespread practice, but 3.0% of Colorado wells tested and 0.1% of New Mexico wells tested exhibited characteristics that made them susceptible to leakage outside the well.
"It is important to note that an integrity issue does not imply that fluids have leaked outside an oil and gas well and created a risk for groundwater contamination," Rajaram said. "In Colorado, for instance, most of the wells at risk for groundwater contamination are older vertical wells that were built with short surface casings that do not protect deeper groundwater aquifers that were later designated as water resources. Wells with high surface casing pressures can be identified and remediated to prevent integrity issues. "
The researchers say that study findings demonstrate the value of statewide well testing programs. They also highlight the challenges of interpreting disparate inter-jurisdictional well testing data and suggest the need for a comprehensive standardized well testing protocol. The researchers recommended the adoption of a comprehensive, standardized testing protocol [to] ensure the compatibility of testing results from different jurisdictions, enable the establishment of a uniform criteria for identifying well integrity issues, and ease the compilation of test results.
"Monitoring oil and gas well integrity based on surface casing pressure or casing vent flow measurements is relatively cheap and helps to identify problematic wells early and remediate them," Rajaram said. "Making data from these monitoring efforts openly available and readily accessible really helps: It adds a level of transparency to inform all stakeholders about potential contamination risks, and helps to flag wells with potentially compromised integrity and remediate them before any leakage occurs."
The team also recommends that future research should continue to aggregate and analyze this type of data, to better inform stakeholder decision making.