MARCELLUS SHALE GAS DEVELOPMENT IN PENNSYLVANIA (Invited Presentation)

As home of the modern Marcellus shale gas play, Pennsylvania has seen significant permitting, drilling, and completion activities over the past eight years. Although discovered in Washington County, southwestern Pennsylvania by the vertically drilled Renz No. 1 in late 2004, Marcellus exploration and development has since spread throughout the western and northern regions of the state, such that by the end of 2011, 1,700+ Marcellus shale gas-producing wells were reported to have been completed, with several thousand more permitted and/or in the process of being drilled. About three-fourths of these have been drilled horizontally and completed using large-volume hydraulic fracturing (fracing) methods, which can involve as many as 20 to 30 frac stages and utilize an average of 4.0 mgal water per well. Although Marcellus wells have been completed in 34 counties across Pennsylvania, two particular hubs of Marcellus development exist: southwestern and northeastern Pennsylvania. These regions exhibit unique geology, production, and legacy issues, all of which have impacted the manner and extent to which the Marcellus shale play has been developed in these areas. In the southwest, the organic-rich shale is relatively thin (about 20-100 ft), and is being produced through the completion of both horizontal and vertical wells (horizontal/vertical ratio=1.2). Here, the average measured well depth is 9,300 ft, average shale gas production is 670 Mcfd, and well stimulations require about 2.6 mgal water per well. In the northeast, the Marcellus shale is thicker (generally 100-250 ft or more), and most wells are completed horizontally (horizontal/vertical ratio=3.7). In this region, the average measured well depth is 10,900 ft, average production is 2.7 Mmcfd, and fracing typically requires 3.7 mgal water per well. Over the past few years, a noticeable shift has occurred with respect to how the petroleum industry manages and ultimately disposes wastewaters from shale gas operations. From 2009 to 2010, 74% of these waters were sent to either industrial or municipal treatment plants, 4% were disposed in injection wells, and 22% were reused on well sites. In 2011, however, water reuse at Marcellus well sites more than doubled (56%), with 16% disposed in injection wells and only 25% sent to industrial treatment plants.