The extraction of natural gas from shale formations can offer a more sustainable fossil fuel option, but concerns have been raised about the methane emissions associated with this process. Researchers at Penn State have developed a new tool to estimate the methane emission potential of shale wells after they are no longer active. The study published in the journal Science of the Total Environment revealed that methane begins diffusing from the shale formation after well decommissioning, representing a significant source of emissions.
Shale formations have low permeability, making it difficult for gas to move through the rock. Operators use a process involving high-pressure pumping to open fractures in the shale and release the gas. However, only a fraction of the total natural gas resource is recovered through this method, leaving the rest trapped within the formation’s small pores. By analyzing shale samples and creating a mathematical model, the researchers were able to predict methane movement within the formation based on its pore structure.
This unified gas transport model integrates gas movement and shale structure to accurately estimate methane flux behavior. The team validated their model using experiments with Marcellus shale samples, demonstrating its effectiveness in predicting methane emissions potential. The tool provides industry professionals with a proactive way to calculate methane emissions flux based on sample information, helping them gauge potential leakage after well abandonment.
Methane emissions have a higher global warming potential than carbon dioxide, making mitigation efforts a top priority for the U.S. and its international partners. Long-term monitoring of methane emissions from abandoned shale gas wells is crucial to reducing overall emissions. The researchers found that as pressure within the reservoir decreases after well cessation, methane diffusion across the shale’s microporous system increases, leading to a continuous flow of methane towards the abandoned wellbore.
Regulatory requirements for proper plugging techniques and monitoring of abandoned wells are essential to prevent methane accumulation over time. Maintaining reservoir pressure even after a well stops producing could be an effective strategy to reduce methane emission potential from these wells. The study highlights the importance of understanding emissions potential post-well decommissioning, as diffusion emissions are comparable to those from flowback fluid during fracking operations.
In areas with a high concentration of shale gas wells like Pennsylvania, where over 20,000 wells have been drilled, mitigating methane emissions from abandoned wells is crucial. The U.S. and other countries have committed to reducing global methane emissions by 30% by 2030, underscoring the urgency of addressing this issue. By developing tools to estimate methane flux in shale formations, researchers are providing valuable insights for industry professionals to address methane leakage concerns and work towards a more sustainable energy future.
