ABSTRACT

Source and Fate of Hydraulic Fracturing Water in the Barnett Shale: A Historical Perspective JEAN-PHILIPPE NICOT, BRIDGET R. SCANLON, ROBERT C. REEDY, AND RUTH A. COSTLEY

1.1 INTRODUCTION

Hydraulic fracturing (HF) has become a hotly debated topic, particularly in regard to the volume of water used and the potential for aquifer contamination. (1, 2) Although HF and horizontal drilling has been practiced for decades, the combination of the two resulted in the exponential increase in gas production from <1% of U.S. gas production in the early 2000s to 40% in 2012 (3) (9.6 Tcf; 9.6 × 1012 standard cubic feet; 272 Gm3). With expansion of HF into more water-scarce regions in the western U.S. and potential expansion into semiarid regions globally, understanding the volume of water required for HF is particularly important. Even in more humid settings, water availability can be an issue during droughts. Previous studies estimated HF water use for Texas [2011: 81.5 thousand AF (kAF), 100.2 million m3 (Mm3), including shales and tight formations,

SI section] and in Colorado (2011: 15 kAF/yr, 18.5 Mm3/yr). (4, 5) An estimated 13.2 kAF (16.3 Mm3) was used for HF in Oklahoma in 2011. (6) Although these water-use estimates represent a small fraction of water used in each state (~0.1% in Colorado, ~0.5% in Texas, and <0.5% in Oklahoma), the volumes may be significant locally, depending on competition with other sectors. Additional water-use estimates are available for the Marcellus Shale, totaling 32 kAF (39 Mm3) consumed between June 2008 and the end of 2012 in the Susquehanna River Basin, mostly in 2011-2012 (15-20 kAF/yr; 18-25 Mm3/yr) (7) and 23.5 kAF (29 Mm3) within the 2008-2012 period in the Upper Ohio River Basin, mostly in 2011-2012 (8.4 kAF/yr; 10.4 Mm3/yr). (8) Water demand in the Bakken area is estimated to be ~22 kAF/yr (~27 Mm3/yr). (9, 10)

Understanding the source of the water used for HF is important to assess the impact on water resources. To date, much of the water used has been fresh water from surface water or groundwater sources. Plays in more humid regions generally rely on surface water, whereas limited surface water availability in more semiarid regions may result in more groundwater use. The Marcellus Shale play uses predominantly surface water controlled by different river basins, e.g., the Susquehanna and Delaware basins. (11) In contrast, the Eagle Ford play lies mostly in a semiarid region and relies heavily on groundwater from the Carrizo-Wilcox aquifer because of limited surface water availability. (4)

The amount of HF water that fl ows back to the surface, commingled with water from the formation (produced water), termed fl owback-produced (FP) water (see SI), is important because it controls the absolute volume that can be reused or recycled or the volume that must be disposed. (12, 13) Reuse is generally understood as requiring little treatment, whereas recycling suggests more involved treatment. (12) Shale formations (Marcellus (14) and Eagle Ford (15)) traditionally have been described as having small volumes of FP water.