Recent scientific evidence suggests that estimates of the volume of methane released from hydraulically fractured wells across the United States have been underestimated, , . There may be more negative effects on local air quality, public health, and global climate change impacts than previously understood.
There are several causes of methane emissions from hydraulically fractured wells. They include:
- Intentionally venting natural gas
- Leaks and uncontrolled releases due to faulty well construction or deterioration of well cement or casing
- Neglectful or improper well closure (when a well is orphaned)
- Other mechanical failures or human errors
Methane emissions can occur during all phases of drilling, production, and closing a well. When a well is drilled, some brine from the targeted rock formation and oil or natural gas may flow to the surface. A release of fluid and gas also occurs after the initial injection of hydraulic fracturing fluid. Specialized equipment can be used to capture this natural gas; however, it is not standard industry practice. Most often natural gas would simply be released, known as venting. When conditions make it uneconomical to capture natural gas or the area lacks pipeline infrastructure to transport natural gas, excess natural gas may be vented or burned and released into the air through flaring, which converts methane to carbon dioxide.
If a well is improperly constructed, cracks or holes in cement and casing can allow large volumes of natural gas to escape. Even in properly constructed well, cement and casing can erode over the lifetime of a well, releasing natural gas if undetected and unrepaired. If a well is not properly closed and sealed at the end of its lifetime, natural gas can escape from the open wellbore. Other accidental releases can occur during production as the result of human error, mechanical issues, or problems in transport, .
Regulations to protect public health in communities with active oil and gas operations rely on accurately monitoring and estimating methane emissions from hydraulically fractured wells. Methane emissions must also be factored into any calculation of greenhouse gas emissions to better understand total emissions of the hydraulic fracturing industry. Inaccurate estimates could hinder U.S. efforts to reduce methane emissions to mitigate climate change and protect public health locally.