laboratory experiments on forming the chemical composition of flowback brine from hydraulic fracturing with energized fluid

Available online at www.sciencedirect.com ScienceDirect Procedia Earth and Planetary Science 17 (2017) 582 – 585 15th Water-Rock Interaction International Symposium, WRI-15 Laboratory experiments on forming the chemical composition of flowback brine from hydraulic fracturing with energized fluid Krzysztof Labusa,1, Piotr Kaszab; Marian Tureka; Piotr Dydoa Agata Jakóbik-Kolona, Klaudia Wilkb, Grzegorz Leśniakb a Silesian University of Technology, Akademicka St., Gliwice 44- 100, Poland Oil and Gas Institute –National Research Institute, 25A Lubicz St 31-503 Kraków, Poland b Abstract After the completion of hydraulic fracturing, some part of injected fluids mixed with the formation brines - so called flowback brine, migrate back through the well to the surface Our autoclave experiments were aimed to reproduce and evaluate the chemical composition of the flowback brine derived from CO2-energized fluid fracturing of shale gas of the Baltic province (Poland).Results show the flowback composition is controlled mainly by the interactions between fracturing fluids and original pore water, and to a lesser extent with the reservoir rock © 2017 2017The TheAuthors Authors Published by Elsevier Published by Elsevier B.V.B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the organizing committee of WRI-15 Peer-review under responsibility of the organizing committee of WRI-15 Keywords:hydraulc fracturing, flowback chemical composition, energized fluid Introduction Hydraulic fracturing consists of a controlled propagation of fractures in the hydrocarbon reservoir formations, through the injection of high volume of specially crafted fluids, under high pressure The resulting fractures remain open by introducing proppant into their space, allowing the injected fluid to return – as so called flowback brine (and then recycling the return fluid), and to increase oil or gas inflow into the well Fracturing is necessary for the production of hydrocarbons from previously inaccessible formations of low permeability1 When the fracturing * Corresponding author Tel.: +48-32-2372942; fax: +48-32-2372290 E-mail address: krzysztof.labus@polsl.pl 1878-5220 © 2017 The Authors Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the organizing committee of WRI-15 doi:10.1016/j.proeps.2016.12.149 Krzysztof Labus et al / Procedia Earth and Planetary Science 17 (2017) 582 – 585 fluids are water-based, the phenomenon of permeability damage may occur, caused by swelling of clay minerals or other physical and chemical interactions occurring in the fractured formation Minimizing these unfavorable effects is possible thanks to the substituting of water by gas Fracturing fluids prepared in such a manner are called energized fluids2 The chemistry of the flowback brine is the result of interaction between relevant fracturing fluids and reservoir rock Our experiments allow us to evaluate the composition of the flowback fluid, estimate its impact on the environment and to select the appropriate recycling technology Materials and methods The experiments determining the impact of CO2-based energized fracturing fluid on the rock samples were conducted to obtain simulated fluids, of chemical composition as close as possible to the flowback brine from fracturing unconventional formations The autoclave used (PARR, USA), made of Hastelloy, was equipped with a needle valve for receiving liquid samples, a valve for injection of gas, thermocouple, and an electronic pressure transducer Additionally a tube with particulate filter, reaching the bottom of the reactor, was attached to the sampling valve Rock samples representing shale gas formations of the Baltic province were placed in the autoclave, pressure vessel and piping were flushed with CO2 gas, and next the fracturing fluid was injected Fracturing fluid contained 50% vol carbon dioxide, initially at supercritical state, and water solution of: foaming agent, polymers, clay swelling inhibitor, scaling inhibitor and biocide Representative mineral composition of rock samples, as determined by x-ray diffraction analysis were as follows: quartz - 33%, chlorite - 7%, albite - 6%, calcite - 5%, pyrite - 2%, and muscovite - 47% The autoclave was placed in a heating mantle on a shaker table The reaction was carried out for 20 days at simulated reservoir conditions of 80±2°C, and an initial pressure of about 250 bar Liquid samples were collected for analyses at equal time intervals, each time reducing the pressure by 10 bar and maintaining the temperature constant The procedure used allowed for an approximate simulation of the slow filtration of liquid - the flowback brine, associated with a decrease in pressure after the fracturing process Changes in pressure and temperature during the experiment are shown in Fig.1 Concentrations of major ions, microelements and pH values were determined in the collected samples Fig 1.Pressure and temperature during the experiment Results The results of analysis of reaction fluid – the flowback brine, as expected, showed a significant increase in the concentrations of all the analytes in comparison to fluid before the reaction 3.The increase in the concentrations of 583 584 Krzysztof Labus et al / Procedia Earth and Planetary Science 17 (2017) 582 – 585 major ions was the highest in the case of sulphate, the highest increase in microelements was recorded for iron (Tab 1) During the experiment, initially in the first 2-3 days, we observed a sharp increase in the concentration of major ions, and next the concentrations remained close to stabilization (Fig 2) This phenomenon is probably associated with the release of pore water, which composition significantly different from the original fracturing fluid The phenomenon of dissolution of halite as the main source of flowback mineralization should be excluded, given the low value of the Cl /Br index (Fig 2), as it was also reported for Marcellus shale flowback brine4 Our waters plot to the high-Br side of the seawater evaporation path, indicating that halite dissolution is not the major source of Cl The flowback composition suggests that they also can be mixtures of bittern brine5 with more dilute water A slow, steady increase in the concentration of sulfate was also observed, which can be associated with the oxidation of sulphide by the fracturing fluid (wherein the aqueous base was prepared at ambient conditions) and/or caused by the dissolution of epsomite, as the growth of magnesium and sulfate concentration is highly correlated in the flowback waters Variations in the chemical composition of the fluid are also the result of the reaction with the rock matrix (mainly carbonates and silicates - as evidenced by a stable increase in the concentration of silicon (Fig.3) and to a lesser extent of the interaction between the test liquid and the material of the autoclave The latter phenomenon has been considered in identification of the background concentration of metal cations in the laboratory simulated flowback brine On the basis of experiments carried out for the blank (the composition of fracturing fluid, placed for days in the autoclave without rock sample inside, was analyzed) It was shown that the reaction of fracturing fluid with the alloy of the autoclave may be responsible for the participation of some metals in the resulting solution This share amounted to, for example: 30% - in the case of total iron and 25% -in the case of cobalt (Fig 3) Table 1.Multiplicity of concentration of selected major ions and microelements in the reaction liquid [-] Cl- SO42- HCO3- Ca2+ Na+ K+ Mg2+ Li+ Multiplicity of concentration 15 11 12 69 Microelement Al Ba Co Si Fe Ti B Sr Multiplicity of concentration 17 16 158 63 39 Ion Fig Chlorides concentrations and Cl//B ratio, during the experiment 585 Krzysztof Labus et al / Procedia Earth and Planetary Science 17 (2017) 582 – 585 0,25 35 30 0,2 Si mg/L Co mg/L 25 0,15 0,1 20 15 10 0,05 0 10 Days 15 20 10 15 20 Days Fig Cobalt and Silicon concentrations during the experiment (red square indicates the concentration resulting from the reaction with the autoclave) The pH remained close to neutrality in the flowback brine, however a slight decrease in the second half or the experiment was observed – Tab.2 This might be attributed to the dissolution of pyrite, which leads to the generation small loads of sulfuric acid and lowering of pH, as reported also in6 Table pH in the reaction liquid Day pH 13 17 6.95 7.05 6.70 6.60 Conclusions The chemical composition of the flowback brine is the result of interactions between fracturing fluids, pore water and the reservoir rock The increase in the concentrations of major ions and microelements was the highest for sulfate, and for iron, respectively The initial sharp increase in the concentrations of analytes, followed by their stabilization is probably associated with the release of original brine from the fractured pores of the sample Low values of the Cl /Br index not support the halite dissolution as a source of the flowback salinity The chemical composition of the fluids is also modified by the reaction with the rock matrix It was also found, that for a proper assessment of the simulated flowback brine formation it is necessary to determine the background resulting from the interaction of the test medium with the material of the autoclave Acknowledgements The research leading to these results, performed within the ENFLUID Project, has received funding from the Polish-Norwegian Research Programme operated by the National Centre for Research and Development under the Norwegian Financial Mechanism 2009-2014 in the frame of Project Contract No Pol-Nor/196923/49/2013 References Economides MJ, Nolte KG (eds.) 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Treatise on Geochemistry 2014, 2nd ed vol 7: 472-515 Oxford: Elsevier Dobrzyński D, Wolicka D, Poszytek A, Borkowski A “All quiet at the bottom”, that is about the need to undertake multidisciplinary research of interactions in the fracturing fluids – gas-containing shale – groundwater system (in Polish, English summary) Biul PIG 2013; 456: 113-118  ... background concentration of metal cations in the laboratory simulated flowback brine On the basis of experiments carried out for the blank (the composition of fracturing fluid, placed for days in the. .. energized fracturing fluid on the rock samples were conducted to obtain simulated fluids, of chemical composition as close as possible to the flowback brine from fracturing unconventional formations The. .. Variations in the chemical composition of the fluid are also the result of the reaction with the rock matrix (mainly carbonates and silicates - as evidenced by a stable increase in the concentration