Assessments regularly change based on our understanding of geology, as well as advances in technology.
As more is learned about the geology of a given formation, both from USGS research and from industry activity, a clearer picture of the potential recoverable oil and gas resources can be created.
In some cases, industry activity can show that a rock formation that was previous thought to have significant quantities of oil and gas does not. In other cases, advances in research techniques and tools can show a rock formation is more likely to have the conditions necessary to produce oil and gas.
A major source of changes in USGS assessments was the advent of production from continuous resource accumulations, such as shale and other “tight” or impermeable formations.
Learn more: USGS Energy Assessments