The Marcellus Shale and Natural Gas
Some layers of rock underlying New York State contain large quantities of natural gas (methane), including the Marcellus shale and the Utica shale. Shale is rock formed from sediments consisting of very small, clay-like particles; it is essentially mud turned into stone. The natural gas is found in pores in the shale that are so small that the gas is essentially trapped. Because gas within the shale does not flow quickly on its own, conventional well drilling techniques are not commercially viable. To recover this gas reserve, the shale rock must be fractured. A relatively new combination of drilling technologies and approaches - called horizontal hydraulic fracturing (or hydrofracking) - allows gas to be recovered from shale. As a result, new wells are now being drilled in the Marcellus shale in Pennsylvania and other neighboring states.
Developing a shale gas well begins with drilling a vertical hole, similar to most wells we frequently think of, such as water wells. Horizontal drilling techniques are then used to extend the vertical well sideways. This creates a well that bores through the horizontal shale layer for a greater distance than would be possible with a vertical well alone. Hydraulic fracturing, a common technique used in constructing or reviving natural gas, geothermal and water wells, is then used to initiate, or “stimulate,” the recovery of natural gas from the shale. During the fracturing process water, sand, and a mixture of chemical additives are forced down the well under high pressure causing many paper-thin fractures to form or expand in the rock. The sand acts to hold these fractures open so that trapped gas may begin to move toward the well.
For a diagram of this process go to
For an interactive tutorial on shale gas drilling and development go to
Another more detailed introduction of Marcellus shale is provided by the Paleontological Research Institute at
One of the keys features of shale gas development using horizontal drilling techniques is the establishment of multiple wells on a single pad. Multiple wells can be drilled that extend horizontally in different directions. The New York State revised draft Supplemental Generic Environmental Impact Statement (rdSGEIS) suggests that one well pad (with multiple horizontal wells) would be allowed for every 640 acres (one per square mile). Another feature of shale gas development is the relatively short lifespan of a single well, and the subsequent need for additional well development in order to maintain high levels of gas production. Individual wells produce a majority of their recoverable gas within the first few years. Natural gas production then tends to decline rapidly. As additional wells are drilled to replace older ones, the overall number of wells and well pads increases. Given the potential density of wells, and the possibility of a large overall number of wells over time, there is concern not only about the impact of individual wells, but also about the cumulative impacts of development across a region and through time. Many activities associated with shale gas development, including road, pipeline, and well pad construction, water withdrawals and waste water disposal, could potentially impact water resources.
It has been estimated that the Marcellus shale contains significant amounts of natural gas (greater than 100 trillion cubic feet). To put this in perspective, yearly U.S. natural gas consumption is between 20 and 30 trillion cubic feet. So, it is likely that interest in developing this resource will remain high for the foreseeable future. At the same time, there is a critical need for greater understanding and assessment of the impacts this development may have on the environment, on public infrastructure, and on local communities, regions, and economies. The New York State Water Resources Institute is working to identify these potential impacts within the context of regional water resources, and management and regulatory policies. It is unclear whether development will proceed in NY and, if so, what it will ultimately look like, and how it will be regulated. From the experience of other states, however, it is clear that education and planning can lead to more successful outcomes in the face of development.
The environmental impact statement issued by the New York State Department of Environmental Conservation can be viewed at
A brief analysis of the implications of multi-well drilling patterns can be viewed at
Runoff From Wellpads
Drilling Impacts on Groundwater
Spills and Leaks at the Surface
Wastewater management trends in PA (link)
Lessons for NY from EPA Pavilion Study (link)
Regional, collective impacts on water resources (link)
Testing Drinking Water (link)
On-going study of drinking water in New York by Cornell University Soil & Water Lab (link)
Understanding Isotopes (link)
Framework for Assessing Water Resource Impacts (link)
Marcellus thickness, depth (link)
Marcellus extent in NY (link)
Marcellus in Susquehanna Basin (link)
Marcellus in Delaware Basin (link)
NY and Chesapeake Bay (link)
References for understanding shale gas impacts (link)