Seminars and Events at the Center
Daniel J. Soeder
Hydrologist,
USGS MD-DE-DC WSC
Thursday, April 23, 2009 at 11:00 - Noon
Water resources and natural gas production from the Marcellus Shale
Abstract
The Devonian-age Marcellus Shale in the Appalachian Basin has recently become a "hot" target for natural gas drilling, with potentially recoverable reserves of 363 trillion cubic feet. For many years, eastern gas shales were considered to be a marginal hydrocarbon resource, but higher prices for natural gas and new drilling technology have made the Marcellus Shale economically competitive. Drilling of the Marcellus Shale has occurred recently in Pennsylvania and West Virginia, and significant acreage has been leased in New York, Ohio and western Maryland.
Production of shale gas presents a number of technical and economic challenges. Permeability of these fine-grained rocks is usually very low, so in order to produce an economical amount of gas, high-permeability flowpaths must be created into the formation. This is achieved by drilling a borehole horizontally for long distances through the shale, and by hydraulic fracturing (hydrofracturing), which uses pressurized water to create fractures into the rock from the wellbore. Combining the two techniques allows many permeable pathways to penetrate an enormous volume of rock, producing commercial quantities of gas. Horizontal drilling requires large volumes of water to make drilling mud, the circulating fluid that lubricates and cools the drill bit, and returns drill cuttings to the surface. Hydrofracturing uses even larger volumes of water, up to 4 million gallons per well, to create the fractures needed to produce natural gas. This fluid must be recovered from the well after the fracturing is completed to allow the gas to flow. Disposal of the recovered hydrofracturing fluid can be problematic, because it is often contaminated with proprietary chemicals used to enhance the fracturing process, and with formation fluids from the shale, which may include brines, heavy metals, organics and radionuclides.
The main water-resource concerns of gas shale drilling include 1) the potential impacts on local water resources from supplying the large volumes of water needed for drilling and hydrofracturing, 2) potential degradation of small watersheds and headwater streams from erosion caused by the numerous heavy vehicles used to transport water, supplies and equipment into remote drill sites on unimproved rural roads, and 3) options for the disposal of large quantities of potentially contaminated drilling mud and recovered hydrofracturing fluid.
