For NETL engineer Eilis Rosenbaum and her colleagues, Pennsylvania serves as ground zero to develop reliable, cost-effective technologies needed to permanently plug abandoned or orphaned oil and gas wells that emit methane, a potent greenhouse gas.

Pennsylvania is the birthplace of the modern U.S. oil industry, which began in 1859 when Edwin Drake drilled the first commercial oil well in northwest Pennsylvania.

“Part of that legacy is an estimated 200,000 old, unplugged and ownerless oil and gas wells that exist today in the state,” Rosenbaum said. “We are starting in Pennsylvania to address this source of greenhouse gas, which also pollutes streams and water supplies, because we have a working relationship with the state Department of Environmental Protection (DEP). But what we accomplish in Pennsylvania has implications that can benefit the entire country.”   

The state DEP has issued a letter in support of ongoing research by Rosenbaum and her colleagues (NETL’s Richard Spaulding, Igor Haljasmaa, Justin Mackey, Phillip McElroy, James Fazio and Dustin Crandall, and the University of Pittsburgh’s John Brigham and Carlos Garcia Verdugo) to identify and test affordable materials to permanently plug these hazards.

Their work could provide a blueprint and processes to plug leaking wells across the nation, which, according to the U.S. Environmental Protection Agency, has more than 2.1 million unplugged, abandoned wells.

Plugging old wells that emit methane and carbon dioxide, another greenhouse gas, is a significant component of the Biden Administration’s plan to address climate change. It is also a major initiative of the Bipartisan Infrastructure Law. The federal legislation includes $4.7 billion for orphaned well site plugging, remediation and restoration activities.

Cement has been a key material for plugging wells and will continue to be used in the producing zone, the geologic interval in the wellbore where hydrocarbons are extracted. “We are exploring the use of other materials to plug other intervals or spaces in the wellbore,” Rosenbaum said.

These novel, non-cement materials offer significant advantages because they are less expensive and avoid the larger environmental footprint of plugging with cement. Kilns used to manufacture cement are major emitters of carbon dioxide.

NETL researchers are focusing on using bentonite, a natural clay, in plugging operations. Their investigations employ laboratory experiments and computational fluid dynamics, which simulate the flow of fluids (liquid or gas), to quantify how water-to-bentonite mixing ratios impact the stability of gel spacers between cemented layers.

The team has prepared several recommendations for new procedures and Pennsylvania code updates to plug oil and gas wells. For instance, the NETL recommendations call for increasing the concentration of bentonite from 4% to 8% in gel layers to prevent fluids from migrating to the surface or groundwater.

Salt in brines destabilizes bentonite gels; however, NETL researchers have found that brine should not impact bentonite plugs unless it is thoroughly mixed with bentonite. NETL researchers are preparing to publish a report identifying the amount of salt that would destabilize the gel to provide guidance on mix water requirements.

“In Pennsylvania, wells that are not properly plugged accounted for more than a third of confirmed stray gas migration incidents, emitting methane into the atmosphere, drinking water supplies, homes and other structures,” Rosenbaum said. “It’s important that we get this right and work with the Pennsylvania DEP and other stakeholders to modify our materials and methods to increase plugging effectiveness.”

NETL is a DOE national laboratory that drives innovation and delivers technological solutions for an environmentally sustainable and prosperous energy future. By leveraging its world-class talent and research facilities, NETL is ensuring affordable, abundant and reliable energy that drives a robust economy and national security, while developing technologies to manage carbon across the full life cycle, enabling environmental sustainability for all Americans.