Starkey Citizens for a Clean & Healthy Environment
Geochemical Evaluation of Fowback Brine from Marcellus Gas Wells in Pennsylvania

With accelerated production of natural gas from shales using hydraulic fracturing of wells diverted along the bedding, there is a growing concern over the composition and fate of water thatflows back up the wells (Soeder and Kappel, 2009; Gregory et al.,2011; Howarth et al., 2011). Typically, many million litres of normal surface or ground water plus sand and chemical additives are injected and pressurized into an individual well to accomplish fracturing (‘‘fracking’’) and release of gas from shales. Typically about 25% of this volume flows back to the surface on release of pressure. These waters commonly have very high concentrations of some inorganic solutes, and the potential for return of the organic additives. Safe disposal and handling of these waters can be improved by understanding their origin and characteristics.

Flowback waters are commonly considered to be fluids thatflow out of a well within the first 2 weeks after stimulation by fracturing, whereas production waters are the remaining fluid thatflows from the well after the initial 2-week period. Flowback is driven by release of the pressure and rock deformation induced by the fracturing process. In this paper, flowback waters are extended to include any aqueous fluid that flows from a well up to 90 days after hydraulic fracturing in order to encompass a series of samples over90 days.

Strictly speaking,a ‘‘brine’’is water with more than 35,000 mg/L total dissolved solids (Kharaka and Hanor, 2004). The term ‘‘Mar-cellus brine’’ will be used for brines emerging from wells penetrating the Marcellus Formation, but does not necessarily indicate that the waters had been hosted mainly in the low-porosity Marcellus,as discussed later.

After hydraulic fracturing in the Marcellus and some other gas-producing shales, the concentration of dissolved salts in flowback and production waters increases dramatically with time (Blauchet al., 2009; Rowan et al., 2011; Haluszczak, 2011; Pritz and Kirby,2010;Fig. 1;Table 1).

The purpose of this paper is to document the increase in solute concentrations, and to provide evidence for the origin of these highly saline flowback waters. The main existing hypothesis is that the increased concentration of salts in flowback waters is due to dissolution of constituents from the shale by the water injected during hydraulic fracturing (Blauch et al., 2009). However, an alter-native origin of the high salinity is release of in situ brines (formation water) similar to those that Poth (1962), Dresel (1985)and Dresel and Rose (2010)found were produced from most oil and natural gas wells in Pennsylvania.
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