Legacy Issues with Oil and Gas Development
As we've considered various aspects of oil and gas development there are inherently a variety of potential environmental risks to water resources, the landscape, and ecological habitat, which can be minimized with proper planning, engineering controls, and monitoring. Another consideration is the presence of historic conventional oil and gas wells in a given region and associated "legacy issues" such as methane emissions to the atmosphere or leakage of hydrocarbons and brine into aquifers or surface waters from existing operating wells or orphaned and abandoned wells. Orphaned and abandoned wells (OAWs) are wells drilled decades ago, are no longer active, but have no financially responsible party to properly plug and decommission the wells. The Pennsylvania Department of Environmental Protection (PaDEP) has oversight of these OAWs and researchers estimate upwards of 560,000 OAWs may exist in Pennsylvania alone! Costs to properly plug and decommission these wells may be $10,000 to $100,000 or more per well, so the costs to fix these legacy issues are staggering. In this section, we will cover methane emissions and potential water quality with OAWs.
Methane emissions: Legacy Oil and Gas Infrastructure
Sometimes the environmental costs associated with extractive industries are not apparent until many years later. When it comes to drilling, many states are impacted by OAW infrastructure that was neither documented when originally installed nor decommissioned/remediated when extraction ended. Pennsylvania, home to some of the largest and earliest oil fields, has an estimated 300,000 to 560,000 OAW oil and gas wells (per PaDEP), of which approximately 9,000 have known locations and the remaining vast majority have unknown locations. Part of the reason so many wells are ‘missing’ is because there were no regulations regarding oil and gas drilling until the 1950s – people didn’t have to report well locations. Because the oil was relatively shallow in Pennsylvania, it was pretty easy to extract. Landowners would drill in their backyards or on their farms, using the oil or gas to heat their homes until it ran out. Similarly, small companies would drill in an area until it ran dry, and then move on, or eventually go bankrupt. Since plugging wasn’t required in the early days of the oil and gas industry, most of these wells serve as conduits from shallow oil and gas fields to the surface. It’s been estimated that nearly 7% of Pennsylvania’s methane emissions are from these legacy wells (Kang et al., 2014, Direct Measurements of methane emissions from abandoned oil and gas wells in Pennsylvania, PNAS, v.111 n.51:18173–18177). In Pennsylvania, recent research suggests that conventional wells that are still operating have median fugitive methane emission of approximately 11% while more modern Marcellus shale gas wells have median fugitive emissions of 0.13% (Omara et al, 2016, Methane Emissions from Conventional and Unconventional Natural Gas Production Sites in the Marcellus Shale Basin, Environ Sci Technol. 2016 Feb 16;50(4):2099-107). As a whole, petroleum systems contribute to 33% of methane emissions in the United States as seen in the graphic below from the EPA's greenhouse gas emissions inventory. As we know methane is a potent greenhouse gas, therefore minimizing fugitive methane emissions is critical.
- Natural Gas and Petroleum Systems: 33%
- Enteric Fermentation: 22%
- Landfills: 20%
- Coal Mining: 9%
- Manure Management: 8%
- Other: 6%
Potential Water Resource Impacts from Legacy Wells
As wells age their casings or cement seals may deteriorate and lose integrity over time, assuming they were properly sealed in the first place. This condition can lead to oil, methane, or brine leakage into aquifers and surface waters, causing degradation of water quality. In fact, many old wells simply had their casings removed for the metal around the time of World War II in order to be used for building ships and other military needs. This means that it is even harder to locate these open boreholes because there is no metal that can be detected with magnetometers. The picture below shows an abandoned well surrounded by surface water with an oil sheen. Imagine the impact that several hundred thousand wells could have on water quality if they had some leakage.
Another hazard with the presence of OAWs is that they represent risks during shale energy development activities as they could possibly provide a vertical pathway for hydrocarbons or brine or perhaps even fracturing fluids. New regulations are being developed in Pennsylvania to minimize the risks of a "frac hit", where fractures could propagate into an existing operating conventional well or an OAW. These regulations would require conducting a survey to locate any wells within proximity to the shale well and to monitor pressure buildups in these wells if they were deemed to be a potential risk. While rare, there have been documented cases of methane migrating away from shale gas wells toward OAWs and causing groundwater and surface water impacts. The picture below shows a geyser of methane and groundwater flowing out of the ground from an OAW that was nearly a mile from the nearest shale gas well. Luckily it was in a relatively remote area and no one was injured, but it could have been a very dangerous situation.
It is clear that we must conduct oil and gas operations safely in order to protect human health and the environment. The existing legacy issues we have discussed here will be very costly to properly remediate, which is why it is important to develop these resources while keeping in mind the long-term impacts that could be passed on to future generations.