PENNSYLVANIA LEGACY WELL INTEGRITY AND EMISSIONS STUDY

Oil and gas development in Pennsylvania has been ongoing for over 150 years, with the most recent phase of exploration and production activities targeting shale gas plays, including the prolific Marcellus and Utica shales. Much of the contemporary dialog relating to oil and gas development and environmental protection has been directed toward operating well integrity, with little research focusing on the final stage of an oil or gas well’s life, which involves proper well plugging. Materials and techniques historically used for well plugging are inadequate by today’s standards. Additionally, because oil and gas development had been taking place for nearly a century prior to permitting requirements enacted in 1955, an estimated 200,000 or more abandoned wells are yet to be accounted for in the state.

It is important to note that the legacy well overprint poses substantial development challenges for the shale gas industry in certain parts of the state where the penetration depths of older wells may render them vulnerable to the transmission of pressures and fluids originating at nearby shale wells undergoing hydraulic fracturing, i.e., hydraulic fracturing communication. In such cases, the adjacent abandoned well may serve as a conduit to shallower intervals of the subsurface. Development challenges are compounded in areas of natural gas extraction that coincide with deep underground coal mining.

To better understand hydraulic fracturing communication risk factors and evaluate other characteristics of the legacy well population in the state, a recent field assessment has been implemented in Pennsylvania. As part of this assessment, Department of Environmental Protection (DEP) representatives have analyzed and evaluated the integrity of a random, representative selection of abandoned, orphan, and plugged conventional wells in historical development areas. Some of the study locations intersect with current or prospective areas of shale gas development. It is anticipated that the results of this study will make it possible to better quantify the agency’s plugging liability, allow DEP to explore different funding models to address the state's legacy well problem, and inform regulatory program activities considerate of environmental risk.