Natural Gas Plays in the Marcellus Shale: Challenges and Potential Opportunities

Figure 1 features locations of shale basins across the U.S. that bear natural gas. There are many reasons to pursue the development of natural gas. First, the supply of natural gas in the U.S. is very reliable, and the delivery system is less subject to interruption compared to imported fossil fuel. Second, the high energy content of natural gas (about 30 kJ/m3 [1000 Btu/ft3]) and a well-developed infrastructure make it easy to use natural gas in a number of applications. Finally, natural gas is efficient and clean burning, emitting approximately half the CO2 when compared with burning coal along with lower levels of sulfur dioxide (SOx), nitrogen oxide (NOx), carbon monoxide (CO), and mercury (Hg). In the trend toward a sustainable green economy, this potentially vast energy resource, with lower carbon emissions than coal or oil, is already a bridge fuel as the U.S. develops more sustainable and renewable fuel options. The U.S. has abundant natural gas resources within the Barnett Shale, Haynesville/Bossier Shale, Antrim Shale, Fayetteville Shale, New Albany Shale, and Marcellus Shale. Technically recoverable natural gas from these shales is more than 1,744 trillion cubic feet (Tcf) (50 km3), which includes 211 Tcf of proven reserves (1). At the annual production rate of about 19.3 Tcf, there is enough natural gas to supply the U.S. for the next 90 years with some estimates extending the supply to 116 years. The total number of natural gas and condensate wells in the U.S. rose 5.7% in 2008 to a record 478,562 with some of the produced natural gas lost via flaring (2). However, available data on flaring of natural gas is incomplete and inconsistent. This article is focused on the Marcellus Shale because it is the most expansive shale gas in play in the U.S. The Marcellus Shale, which is Devonian age (416-359.2 My), belongs to a group of black, organic-rich shales that are common constituents of sedimentary deposits. In shale deposition, the clay-sized grains tend to lie flat as the sediments accumulate. Pressurized compaction results in flat sheet-like deposits with thin laminar bedding that lithifies into thinly layered shale rock. Natural gas is formed as the organic materials in these deposits degrade anaerobically. The Marcellus Shale gas is mostly thermogenic, with enough heat and pressure to produce primarily dry natural gas. Covering an area of 240,000 km2 (95,000 mi2), it underlies a large portion of Pennsylvania, east of West Virginia, and parts of New York, Ohio, and Maryland (Figure 1). Recent production data suggest that recoverable reserves from Marcellus Shale could be as large as 489 Tcf (3, 4). Natural gas extraction in the Marcellus Shale is currently an expensive endeavor. A typical horizontal drilled well, using multistage fracturing techniques, costs roughly $3-5 million to complete. The large amount of water used, and management of the wastewater are also very costly factors. Nevertheless, Marcellus Shale extraction is expected to usher jobs creation and other economic opportunities. A large demand for laborers at the gas fields and support businesses, such as drilling contractors, hydraulic fracturing companies, and