QUANTIFYING METHANE EMISSIONS FROM ORPHANED OIL AND GAS WELLS: A SUBTYPE-BASED SAMPLING STRATEGY IN KENTUCKY

The Bipartisan Infrastructure Law provided funding to plug orphaned oil and gas wells (OOGWs) in the United States. The legislation also recommended measuring methane emissions from OOGWs. Working with the Kentucky Division of Oil and Gas, the Kentucky Geological Survey is heading up a program to measure methane emissions from OOGWs. As there are more than 14,000 known OOGWs in Kentucky and 650 planned pluggings in the initial phase of funding, it is not feasible to measure every well. To systemically estimate emissions, we defined a smaller sample subset based on well subtypes for measurement. Well subtypes are based on the age of the producing geologic formation and type of hydrocarbons produced. More broadly, well subtypes are representative of the larger orphaned well population in Kentucky across the Appalachian Basin, Illinois Basin, and Cincinnati Arch geologic provinces. For OOGWs in the initial phase of plugging we defined 13 subtypes, most of which formerly produced oil. From there inferential statistics can be used to target wells most likely to be high methane emitters. Working with the Well Done Foundation, we measured methane emissions on 40 OOGWs that are part of an initial package of 50 measurements. Estimated methane emissions equal the product of the average flow rate of the well into a Ventbuster flow meter and gas composition from a sample collected at the end of the test. The flow meter may be connected to a chamber or directly to the wellhead and flow tests last from 12 to 30 hours. Early results show a large range of emissions magnitudes from 6.073*10^-4 to 16167 mg/hour. Well subtypes in which gas is the primary hydrocarbon phase account for more than 90% of the total emissions even though they make up 18% of the OOGWs measured to date.