Geochemical evaluation of flowback brine from Marcellus gas wells ...

L.O. Haluszczak et al. / Applied Geochemistry xxx (2012) xxx–xxx 5of brine from oil wells; the remaining 26 of the Dresel samples arefrom gas wells. There are 17 hydrofractured Marcellus wells fromthe DEP BOGM well data.6Halite dissolutionA4. Results5Fig. 1 illustrates the Cl content of flowback water from eighthorizontal Marcellus wells from Hayes (2009), plus Well B ofBlauch et al. (2009). Flowback waters from these wells of the GTIseries show a major increase in Cl as later flowback waters are returnedfrom the well over the 14 days of the flowback period(Fig. 1), though one sample drops to lower values at 14 days. Thelater concentrations in others are many times the seawater concentrationof 19,000 mg/L. The median Cl content in the eight samplesincreases from 82 mg/L in the injected water to 98,000 mg/L inthe 14-day flowback. A further increase is observed for the fourwells sampled at 90 days. Other significant constituents showingincreased concentration in later flowback water are Na, Ca, Mg,Br, Ba, Sr, Fe, Mn, K and total dissolved solids (TDS) (Table 1), aswell as Ra (Rowan et al., 2011). Many minor elements, includingB and Li are also enriched. The pH remains near neutrality in theflowback.Sulfate decreases in the flowback, probably because SO 4 is verylow in the in situ brine. The low SO 4 allows high contents of alkalineearth elements (Ca, Sr, Ba, Ra). Alkali elements (Na, K, Li) andhalides (Cl, Br) are generally greatly enriched.The data from Blauch et al. (2009) also show greatly increasedconcentrations of Cl and other constituents as flowback progressesafter hydraulic fracturing. Blauch et al. (2009) show astrong correlation of increased Ca with Cl for well A.Hayes (2009) reports low concentrations of Cl, TDS and otherconstituents in the injected water at most of the wells, in the rangeof local surface and shallow ground waters. For a few, the injectedwater evidently consisted partly of flowback water from previouswells, based on elevated Cl, Ca, Ba and other elements. Both the injectedwaters and the flowback have pH in the range 6–8, indicatingthat dissolution of rock minerals by an acidic solution does notexplain the increased cation concentrations. Low contents of Cl andSO 4 as well as near-neutral pH in the injected water indicate thatHCl and H 2 SO 4 were not components of the injection fluid, and thatacid attack by the injected water does not explain the high concentrationsof cations in the flowback water.A map of the Cl content of flowback was examined. Basedmainly on the Dresel data, an area of low Cl in water from oil wellsappears to exist in part of NW PA, but other regions seem to havegenerally high Cl and TDS in both conventional gas well and Marcellusflowback brines.Carpenter (1978) and others (Stoessel and Moore, 1983; Dresel,1985; Steuber et al., 1998; Kharaka et al., 1987; Connelly et al.,1990; Gupta et al., 2011) used a plot of Br vs. Cl to examine therelationship of brines to evaporated seawater (Fig. 4). Evaporationof seawater leads to enrichment in both Cl and Br during initialevaporation and precipitation of calcite and gypsum, but when haliteprecipitates, the halite contains much lower Br than the associatedbrine, leading to a nearly horizontal trend for the residualbrine on the graph. Because of this effect, brines with high Br/Cl resultfrom evaporation of seawater past the point of halite precipitation.These highly evaporated brines may then be diluted byfresh water, sea water, other brines or injected water to producebrines plotting at Br values greater than the seawater evaporationcurve. In contrast, later dissolution of the low-Br halite would leadto lower Br/Cl in the brine.The Cl–Br plot was used by Dresel (1985) and Dresel and Rose(2010) to show that the conventional brines in Pennsylvania werederived from highly evaporated seawater that had been diluted43SWFresh waterdilutionSeawaterdilution0 1 2 3 4with fresh water or seawater (Fig. 4). A contribution from halitedissolution is possible, though probably minor.Plotting the Marcellus flowback waters on this graph indicatesthat they also can be explained as mixtures of highly evaporatedbrine with more dilute water (Fig. 4). Using the seawater and freshwatermixing lines Dresel (1985) presented in the original figure,both the conventional brine and the flowback waters plot in positionsthat indicate dilution of an original brine with freshwater,seawater or injected fracturing fluid.The Marcellus waters plot to the high-Br side (low Cl/Br) of theseawater evaporation path, indicating that halite dissolution is notthe major source of Cl , as was proposed by Blauch et al. (2009).The halite observed in Marcellus cores by these workers may haveprecipitated by evaporation from pore fluid on removal of the corefrom the well, but except for one sample, halite dissolution cannothave been a major process in the formation of the Marcellus brines.Gupta et al. (2011) show that highly evaporated seawater canbe diluted and then dissolve appreciable halite but still remain belowthe seawater evaporation curve. They show that in the Albertabasin, brines plotting below the curve are mixtures of four processes:seawater evaporation, dilution by fresh water, dilution byseawater and halite dissolution. Thus, halite dissolution can be acontributing process for waters plotting below the seawater evaporationcurve, but must be subordinate to the evaporation effects.Based on the results of the Cl–Br plot, the Marcellus flowbackwater is considered to have developed analogously to the conventionalbrines, by evaporation of seawater into the halite stage, andthen dilution to the present composition. Most of the samples fallnear dilution curves for the Composition A postulated by Dreseland Rose (2010) to have been the parent evaporated seawaterbrine, as shown in Fig. 4. Some scatter to lower Br could be interpretedas halite dissolution.Graphs of both Ca and Mg vs. Br show clear similarities betweenthe conventional brines and the flowback waters (Fig. 5). Calciumand Mg show a positive linear relation with Br, which is relativelyconservative during evaporation and dilution. The flowback waterscontain markedly higher Ca than any evaporated seawater, andmarkedly lower Mg. This pattern was also found for the conventionalbrines (Dresel, 1985), indicating a common process of originfor the conventional and Marcellus brines. Dresel (1985) showedthat this pattern could be explained by conversion of calcite todolomite during the early history of the evaporated brine, and thatthe evaporated seawater contained sufficient Mg to account for theexcess Ca by dolomitization of calcite.GTIBOGMDreselSW EvapHaliteFig. 4. Plot of Log Cl vs. Log Br, showing seawater (SW) evaporation path andcomposition of flowback brines and production water from oil and gas wells.Dashed lines indicate dilution paths. Seawater evaporation line from McCaffreyet al. (1987).Please cite this article in press as: Haluszczak, L.O., et al. Geochemical evaluation of flowback brine from Marcellus gas wells in Pennsylvania, USA. Appl.Geochem. (2012), http://dx.doi.org/10.1016/j.apgeochem.2012.10.002

L.O. Haluszczak et al. / Applied Geochemistry xxx (2012) xxx–xxx 7The U concentrations in the brines are low (Table 3). The lowconcentrations, despite relatively high U in the Marcellus blackshale, are evidently due to the reducing nature of the pore water,and the resulting very low solubility of U. However, Ra and itsdaughters diffuse out of their host and into the SO 4 -poor brine.The drinking water limit for Ba is 2 mg/L (US EPA, 2011b). Concentrationsof Ba in the late stage flowback are commonly thousandsof mg/L. Barium is another potentially toxic constituent inthe Marcellus brines, along with Br and other solutes.Because of the low porosity of the Marcellus shale, the source ofthe brine deserves consideration. Logs of Marcellus holes indicatelow porosity and low conductance of any water phase (Engelder, pers.comm., 2012). However, conductance of pore water inferred fromdrill logs may not be reliable (Kharaka, pers. comm., 2012). The brineclearly is derived from the zone of completion and fracturing in andadjacent to the Marcellus. It seems possible that brine is derived froma combination of pore space in the Marcellus plus fractures in theMarcellus and fractures and porosity in the adjacent formations.5. Conclusions1. Flowback water from later stage flowback from Marcellus wellscontains very high concentrations of TDS, Cl, Br, Na, Ca, Sr, Ba,Ra and other elements. The levels of TDS, Cl and some otherconstituents can be 5–10 times the concentration in seawater.2. Late stage flowback did not originate by dissolution of rock mineralsby acidified injected water, because the injected water forthe GTI wells has near-neutral pH and low levels of Cl and SO 4 .3. The chemistry of the later flowback water is similar to brinesproduced from conventional oil and gas wells tapping permeablehost formations ranging in age from Ordovician to Devonian.4. The Cl–Br relations indicate that the late flowback waters developedfrom a highly saline brine evaporated from seawater intothe stage of halite precipitation, and then diluted and mixedwith seawater, fresh water and injected fluids.5. The late stage flowback contains concentrations of Ra 226 ,Ra 228 ,Ba and other constituents far higher than drinking water limits.Improper disposal of the flowback can lead to unsafe levels ofthese and other constituents in water, biota and sediment fromwells and streams.6. The high salinity and toxicity of these waters must be a key criterionin the technology for disposal of both the flowbackwaters and the continuing outflow of production waters.AcknowledgementsWe are grateful to Christine Regalla, PSU PhD candidate whosepatience and ingenuity is much appreciated and to Juliane Haggerty,PSU Graduate student, for her assistance. Assistance from severalpersons at the Pennsylvania Department of EnvironmentalProtection was essential in this study: Ron Schwartz, Assistant RegionalDirector (Southwest), Kareen Milcic, Permitting Manager inWater Management (Southwest), John Harper, PA DCNR Geologist,and James Fuller, PA Buereau of Oil and Gas Management. Dr. CarlKirby of Bucknell University was very helpful in providing theHayes (2009) report and a tabular summary of the data from thisreport. We are indebted to two reviewers for valuable commentsand suggestions.ReferencesBlauch, M.E., Myers, R.R., Moore, T.R., Lipinski, B.A., Houston, N.A., 2009. MarcellusShale Post-Frac Flowback Waters- Where is All the Salt Coming From and Whatare the Implications? Society of Petroleum Engineers, Eastern RegionalMeeting: Charleston, WV, September 23–25, 2009. Paper SPE 125740.Carpenter, A.B., 1978. Origin and chemical evolution of brines in sedimentarybasins. Oklahoma Geol. Surv. Circular 79, 60–77.Collins, A.G., 1975. 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