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Radioactivity in wastes generated from shale gas exploration and production – North-Eastern Poland
Journal of Environmental Radioactivity 175-176 (2017) 34e38
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Radioactivity in wastes generated from shale gas exploration and production e North-Eastern Poland Paweł Jodłowski a, Jan Macuda b, Jakub Nowak a, *, Chau Nguyen Dinh c w, Poland AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Al. Mickiewicza 30, 30-059 Krako w, Poland AGH University of Science and Technology, Faculty of Drilling, Oil and Gas, Al. Mickiewicza 30, 30-059 Krako c w, Poland AGH University of Science and Technology, Faculty of Geology, Geophysics and Environmental Protection, Al. Mickiewicza 30, 30-059 Krako a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 December 2016 Received in revised form 29 March 2017 Accepted 10 April 2017
In the present study, the K-40, U-238, Ra-226, Pb-210, Ra-228 and Th-228 activity concentrations were measured in 64 samples of wastes generated from shale gas exploration in North-Eastern Poland. The measured samples consist of drill cuttings, solid phase of waste drilling muds, fracking fluids, return fracking fluids and waste proppants. The measured activity concentrations in solid samples vary in a wide range from 116 to around 1100 Bq/kg for K-40, from 14 to 393 Bq/kg for U-238, from 15 to 415 Bq/kg for Ra-226, from 12 to 391 Bq/kg for Pb-210, from a few Bq/kg to 516 Bq/kg for Ra-228 and from a few Bq/ kg to 515 Bq/kg for Th-228. Excluding the waste proppants, the measured activity concentrations in solid samples oscillate around their worldwide average values in soil. In the case of the waste proppants, the activity concentrations of radionuclides from uranium and thorium decay series are significantly elevated and equal to several hundreds of Bq/kg but it is connected with the mineralogical composition of proppants. The significant enhancement of Ra-226 and Ra-228 activity concentrations after fracking process was observed in the case of return fracking fluids, but the radium isotopes content in these fluids is comparable with that in waste waters from copper and coal mines in Poland. © 2017 Elsevier Ltd. All rights reserved.
Keywords: Shale gas Hydraulic fracturing Radioactivity NORM Wastes Poland
1. Introduction Shale gas exploration and production, involving the extensive application of well-stimulation techniques (hydraulic fracturing) in horizontal wellbore sections to release gas from rock formations, poses a potential threat to the environment. The hydraulic fracturing process requires the use of very large amounts of water and chemicals necessary for the preparation of fracking fluids and other technological fluids used for borehole drilling (Javadpour, 2009; Karacan et al., 2011; Shabani et al., 2014). Consequently, in the course of this process, a large amount of waste in the form of return fluids and small amounts of proppants are generated. In addition, during the wellbore drilling, wastes are generated in the form of waste drilling fluid and drill cuttings (hard scales). The threat posed by shale gas exploration and production includes soil degradation, local pollution of the ground surface by fuels and technological liquids, contamination of surface water and groundwater, resulting from uncontrolled discharges of wastewater to them (Macuda,
* Corresponding author. E-mail address: jakub.nowak@fis.agh.edu.pl (J. Nowak). http://dx.doi.org/10.1016/j.jenvrad.2017.04.006 0265-931X/© 2017 Elsevier Ltd. All rights reserved.
2010). Beside the above-mentioned hazards to the environment and humans, others may be attributable to the radiation hazard associated with radioactivity from natural radionuclides, widely occurring in the rocks of shale gas deposits and other formations. These radionuclides derive from natural radioactive decay series, mainly from two series: the uranium decay series (the primary radionuclide is U-238) and thorium decay series (the parent radionuclide is Th-232) and potassium K-40. From a radiation protection point of view, the most important radionuclides are radium Ra-226 (the half-live is T1/2 ¼ 1600 years), radon Rn-222 (T1/2 ¼ 3.8 days), lead Pb-210 (T1/2 ¼ 22.2 years) and polonium Po-210 (T1/2 ¼ 138.4 days) from the uranium series; from the thorium series, in turn, the most important radionuclides are Ra228 (T1/2 ¼ 5.75 years), thorium Th-228 (T1/2 ¼ 1.91 years), Ra224 (T1/2 ¼ 3.6 day) and Rn-220 (T1/2 ¼ 56 s). The third major source of radiation is the radioactive isotope of potassium, K-40, with a natural abundance of 0.0119%. Potassium occurs in significant quantities in the Earth's crust (about 2.5%). In the gas and oil mining industry, the radiation hazard associated with NORM mainly results from the migration of U-238 and Th-232 decay
P. Jodłowski et al. / Journal of Environmental Radioactivity 175-176 (2017) 34e38
products along with a mixture of oil, gas and water extracted from a wellbore. These products (mainly radium isotopes: Ra-226 and Ra228) accumulate in sludge and hard scales. The average concentrations of radium isotopes in sludge and hard scales vary in a wide range from 100 Bq/kg to 15,000 kBq/kg. In general, radium concentrations are lower in sludge than in hard scales. The opposite applies to Pb-210, for which the concentration is relatively low in hard scales, but in the case of sludge the Pb-210 activity concentration may reach even 1000 kBq/kg and more (UNSCEAR, 2000; IAEA, 2003; UNSCEAR, 2008; OGP, 2008). In the literature, there are few papers dealing with the problem of NORM in shale gas exploration and production. For example, the U.S. Geological Survey conducted a study of the activity concentrations of Ra-226 and Ra-228 in waters co-produced with oil and gas from Marcellus Shale. Radium concentrations vary in a range of 1.3 Bq/L to 590 Bq/L for Ra-226 and of 0.08 Bq/L to 44 Bq/L for Ra228 (Rowan et al., 2011). In turn, the study carried out for radioactivity in samples taken from four reservoirs of fracking fluids located at the Barnett deposit, show that concentrations of natural radionuclides in analysed samples do not exceed 204 Bq/kg for K40, 89 Bq/kg for Ra-226 and 26 Bq/kg for Ra-228 (Rich and Crosby, 2013). In order to assess radioactive contamination of wastes resulting from shale gas, measurements of the natural radionuclides (K-40, U-238, Ra-226, Pb-210, Ra-228, Th-228) activity concentrations in wastes samples were performed. The samples of solid phase of
35
waste drilling muds, drill cuttings, fracking fluids, return fracking fluids and waste proppants were collected from selected drilling sk Pomerania, rigs located in North-Eastern Poland (i.e. from Gdan across Mazovia to Lublin Region) in two of the most prospective basins of the Baltic Basin and Lublin Trough (Fig. 1). In this paper, the authors only provide information about the types of samples and assign sample codes due to information confidentiality. 2. Sampling and methods Samples for analysis were taken from selected drilling rigs from August 2012 until June 2014. 64 samples consisting of fracking fluids, return fracking fluids, solid phase of waste drilling muds, waste proppants (these being proppants which flowed back from boreholes together with return fracking fluids after hydraulic fracturing) and drill cuttings were collected. Fluids were drawn directly from the sampling site to glass containers with a volume of 1 L, in turn, solid samples were packed into plastic bags. Samples of fracking fluid were collected before the injection into wellbores, in contrast to other types of samples collected after the processes of drilling and hydraulic fracturing. Samples of return fracking fluids were collected after the set of shale shakers, desanders and centrifuges which separate solid phase from return fracking fluids. After the transport to the laboratory, samples were sealed into beakers. There were two types of beakers used: the aluminium cylindrical beaker of the volume of 121 mL (used for solid samples)
Fig. 1. Location of the most prospective shale basin in Poland (modified from San Leon Energy, 2013).
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and glass cylindrical beaker with the volume of 210 mL (for liquid samples). In order to obtain radioactive equilibrium in the samples between Ra-226 and its progenies Rn-222, Pb-214 and Bi-214, measurements were performed after at least 21 days from sample sealing. Samples were measured by gamma-spectrometer with an HPGe detector with relative efficiency of 42% and resolution of 1.9 keV for 1332 keV line (Canberra GX4020). Spectra were collected for 10e50 h and it depended on the activity of the study samples to guarantee the relative uncertainty of the gamma count rate lower than 3%. As standard samples, reference materials RG produced by the International Atomic Energy Agency (IAEA) were used. A detailed description of the methodology was presented by Jodłowski and Kalita (2010). K-40 was quantified using its 1461 keV emission, U-238 via its granddaughter Pa-234m 1001 keV emission line and Pb-210 via its 46.5 keV emission. Ra-226 was determined via its granddaughters Pb-214 (352 keV) and Bi-214 (609 keV, 1120 keV and 1764 keV) emissions. Ra-228 was assayed via the emissions of its daughter Ac228 (911 keV, 967 keV) and Th-228 via the emissions of its granddaughter Tl-208 (583 keV, 2614 keV). The self-attenuation correction in Pb-210 measurements accounting the difference of density of the samples and standard ones was introduced follow the transmission method proposed by Cutshall, together with the recently proposed modification (Cutshall et al., 1983; Jodłowski, 2016). 3. Results and discussion The measured activity concentration of natural radionuclides (at the sampling time) in samples taken from selected shale gas drilling rigs in North-Eastern Poland are presented in Table 1. The activity concentrations of natural radionuclides in solid samples vary over a wide range up to 1100 Bq/kg for K-40 (with one exception ZPW-1), up to 415 Bq/kg for U-238, Ra-226 and Pb-210 and up to 516 Bq/kg for Ra-228 and Th-228. Generally, measured activity concentrations vary around their worldwide average values in soil. The only exception are samples of waste proppants in which the activity concentrations of radionuclides from uranium and thorium decay series are significantly elevated and can reach even 516 Bq/kg for Ra-228. By comparison, according to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 2008) the worldwide average activity concentrations of K-40, Ra-226 and Th-232 in soil are 412 Bq/kg, 32 Bq/kg and 45 Bq/ kg respectively, while the average concentrations of these elements in the Earth's crust are equal to around 750, 50 and 50 Bq/kg respectively. These concentrations in the Earth's Crust strongly depend on geology and they vary in a wide range from a few Bq/kg to 2000 Bq/kg for K-40, to 150 Bq/kg for Ra-226 and to several hundreds of Bq/kg for Th-232. The average activity concentrations of K-40, Ra-226 and Ra-228 in drill cuttings are 815 Bq/kg, 62 Bq/kg and 37 Bq/kg respectively, while their concentrations in solid phase of waste drilling muds are equal to 966 Bq/kg, 25 Bq/kg and 20 Bq/kg respectively. For one sample of solid phase of waste drilling muds (ZPW-1), the very high activity concentration of K-40 (3590 Bq/kg) was observed. This fact is related to the chemical composition of drilling mud. Drilling mud with high concentration of potassium chloride was used in this case during the drilling of boreholes. The waste proppants are the only material for which elevated radioactivity was observed. The average activity concentrations of K-40, Ra-226 and Ra-228 in waste proppants are 183 Bq/kg, 278 Bq/ kg and 340 Bq/kg respectively. Samples of waste proppants from Baltic Basin are characterised by the high activity concentration of Ra-226 and Ra-228 (up to 415 Bq/kg and 516 Bq/kg respectively). In
case of Lublin Trough, the activity concentration of Ra-226 and Ra228 in the waste proppant PRZ-5 amounts to 216 Bq/kg and 246 Bq/ kg respectively, while the waste proppant PRZ-4 shows very low radioactivity. In the authors’ opinion, the elevated radioactivity in waste proppants is not related to hydraulic fracturing but to the mineralogical composition of proppants. The following arguments support the above statement: - The waste proppant is the proppant surplus which doesn't penetrate the fractures, it has contact only with fracking fluids; - Adsorption is the only process that may lead to an increase in radioactivity of proppants. It is strongly driven by chemical and physical properties of adsorbed compounds and adsorbents. Thus, it is impossible to obtain an equilibrium in the uranium and thorium decay series in samples of waste proppant, as a results of adsorption, but such equilibrium was observed. In order to prove the above statement, the proppant sample with the highest concentration of radionuclides (PRZ-2) was remeasured. The sample was washed in 9M solution of HNO3 at 90 C to remove from the proppant surface all adsorbed substances before the measurement. Obtained results of radionuclides activity concentrations in the proppant sample are the same as previous one within measurement uncertainty. In all studied solid samples (OSW, ZPW, PRZ) the activity concentrations of radionuclides from uranium decay series (U-238, Ra226 and Pb-210) are equal and similarly for Ra-228 and Th-228 in thorium decay series. In other words, in the studied samples there is radioactive equilibrium between U-238 and daughters, and between Ra-228 and daughters. For the fracking fluids average activity concentrations of K-40 is 75 Bq/L (median 5 Bq/L). However, nearly half of the samples contain potassium (K-40) at concentrations below the detection limit (5 Bq/L), while the activity concentrations of U-238, Ra-226, Pb-210, Ra-228 and Th-228 in all samples are below the detection limit in all samples. In return fracking fluids the average activity concentration of K40, Ra-226 and Ra-228 are equal to 66 Bq/L, 42 Bq/L and 20 Bq/L respectively, while the activity concentrations of U-238, Pb-210 and Th-228 are below the detection limit. It means that there is no radioactive equilibrium between U-238 and Ra-226 (uranium series) and between Ra-228 and Th-228 (thorium series). In comparison, the average concentrations of Ra-226, Ra-228 in return fracking fluids with the concentrations in fracking fluids (collected before the wellbore injection) shows significant radioactivity enhancement after the fracking process. The absence of Th-228 in return fracking fluids is related to the fact that thorium (leached from host rocks) forms low soluble and high adsorbed compounds in contrast to radium (Langmuir, 1997; Siegel and Bryan, 2004; Nguyen et al., 2011). The average activity concentrations of Ra-226 and Ra-228 in return fracking fluids are at the level of their highest concentrations observed in groundwater in Poland. The radium activity concentration in Polish groundwater varies in a wide range from a few mBq/L to 65 Bq/L for Ra-226 and from 10 mBq/L to around 14 Bq/L for Ra-228 (Nguyen et al., 2012; Nowak et al., 2012). In case of waste waters generated by the mining industry, the radium concentration is usually higher than in groundwater. For example, the radium content in mine water from the Upper Silesia coal mines in Poland vary from 0.18 to 21 Bq/L (Chałupnik et al., 2001), while in mine water from copper mines in the vicinity of town Lubin in SW Poland, the radium activity concentrations vary in a broad range from 30 mBq/L to about 100 Bq/L e the median is 1.1 Bq/L (Nguyen et al., 2008). Generally, the content of Ra-226 and Ra-228 in return fracking fluids is at the level of the radium concentrations observed
P. Jodłowski et al. / Journal of Environmental Radioactivity 175-176 (2017) 34e38
37
Table 1 The activity concentrations of natural radionuclides (K-40, U-238, Ra-226, Pb-210, Ra-228 and Th-228) in samples of wastes from selected shale gas drilling rigs (The activity concentrations are given at the moment of sampling). Rig number
Sample ID
Activity concentration K-40
U-238
Ra-226
1092 ± 30 446 ± 15 816 ± 24 794 ± 24 816 ± 25 897 ± 28
<35 <35 <35 36 ± 27 87 ± 24 61 ± 27
30 29 43 44 70 75
918 ± 30 739 ± 22 446e1092 815/816
99 ± 35 70 ± 24 35e99 57/49
120 ± 4 85 ± 3 29e120 62/57
<35 <35 <35 46 ± 15 <35
15 18 29 29 21
38 ± 22 <35 35e46 37/35
44 ± 2 19 ± 1 15e44 25/21
28 ± 15 54 ± 13 15e54 30/28
26 ± 1 19 ± 2 13e31 20/19
24 ± 1 16 ± 2 13e26 18/17
137 ± 20 <5 <5
<30 <30 <30
<2 <2 <2
<5 <5 <5
<2 <2 <2
<2 <2 <2
<5 499 ± 20 5e499 75/5
<30 <30 <30 <30
<2 <2 <2 <2
<5 <5 <5 <5
<2 <2 <2 <2
<2 <2 <2 <2
333 ± 13 62 ± 14 56 ± 11 <10 17 ± 8 17 ± 8 13 ± 6 18 ± 8
<30 <30 <30 <30 <30 <30 <30 <30
<2 43 ± 2 51 ± 2 4±2 28 ± 1 37 ± 2 41 ± 2 41 ± 2
<5 <5 <5 <5 <5 <5 <5 <5
<2 28 ± 1 31 ± 2 4±1 24 ± 1 30 ± 1 35 ± 2 36 ± 2
<2 <2 <2 <2 <2 <2 <2 <2
<10 16 ± 5 99 ± 10 79 ± 12 545 ± 20 5e545 66/27
<30 <30 <30 <30 <30 <30 <30
38 ± 2 53 ± 2 52 ± 2 66 ± 2 50 ± 2 2e70 42/43
<5 <5 <5 <5 <5 <5 <5
18 ± 2 28 ± 1 22 ± 1 33 ± 2 24 ± 1 2 < 5 36 20/19
<2 <2 <2 <2 <2 <2 <2
272 ± 12 182 ± 9 191 ± 8
389 ± 70 364 ± 53 393 ± 51
334 ± 10 408 ± 12 415 ± 13
319 ± 20 391 ± 30 372 ± 20
417 ± 13 514 ± 17 516 ± 16
418 ± 13 504 ± 17 515 ± 16
116 ± 5 152 ± 10 116e272 183/182
14 ± 12 186 ± 31 14e393 271/364
15 ± 1 216 ± 10 15e415 278/334
12 ± 4 223 ± 13 12e391 263/319
8±2 246 ± 12 8e516 340/417
5±2 245 ± 12 5e515 337/418
[Bq/kg]; [Bq/L] Drill cuttingsbe8 samples Baltic Basin 1 OSW-1 OSW-2 2 OSW-3 4 OSW-4 OSW-5 7 OSW-6 Lublin Trough 3 OSW-7 5 OSW-8 range average/medianc
Solid phase of waste drilling mudsbe7 samples Baltic Basin 1 ZPW-1 3590 ± 110 2 ZPW-2 289 ± 10 4 ZPW-3 881 ± 26 ZPW-4 726 ± 22 7 ZPW-5 344 ± 11 Lublin Trough 3 ZPW-6 506 ± 18 5 ZPW-7 423 ± 13 range 289e3590 average/medianc 966/506 Fracking fluidsde14 samples Baltic Basin 1 P-1 2 P-2 7 P-3 Lublin Trough 3 P-4 5 P-5 range average/medianc Return fracking fluidsd,ee30 samples Baltic Basin 1 PZ-1 PZ-2 PZ-3 2 PZ-4 7 PZ-5 PZ-6 PZ-7 PZ-8 Lublin Trough 3 PZ-9 PZ-10 5 PZ-11 PZ-12 PZ-13 range c average/median Waste proppantsb,fe5 samples Baltic Basin 1 PRZ-1 2 PRZ-2 PRZ-3 Lublin Trough 3 PRZ-4 5 PRZ-5 range average/medianc a b c d e f
Pb-210
Ra-228
Th-228
a
± ± ± ± ± ±
± ± ± ± ±
1 1 2 2 2 4
1 1 1 1 1
43 30 49 49 97 53
± ± ± ± ± ±
5 15 12 6 9 12
143 ± 12 87 ± 10 30e143 69/51
23 18 36 38 15
± ± ± ± ±
15 11 8 5 11
35 22 40 31 40 47
± ± ± ± ± ±
2 1 2 2 2 2
43 ± 2 36 ± 2 22e47 37/38
17 16 13 31 20
± ± ± ± ±
1 1 1 2 1
33 19 41 33 41 47
± ± ± ± ± ±
2 1 2 2 2 2
43 ± 2 35 ± 2 19e47 37/38
17 15 13 26 18
± ± ± ± ±
1 1 1 2 1
[Bq/kg] for drill cutting, solid phase of waste drilling muds and waste proppants, [Bq/L] for fracking fluid and return fracking fluids. In the table, all results were presented. For results below the detection limit, the value of detection limit was used to calculate the average and median value of the radionuclides activity concentrations. In the table, selected results were presented; the results for other samples are similar; the average and median value were calculated for all results. Return fracking fluids were collected after the set of shale shakers, desanders and centrifuges which separate solid phase from fluids. It is proppants which flowed back from a borehole together with return fracking fluids after hydraulic fracturing.
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in waste waters from coal and copper mines located in Poland. 4. Conclusions Generally, the activity concentrations of K-40, U-238, Pb-210, Ra-226 and Th-228 in solid samples are at the level of their worldwide average concentrations in soil and in the Earth's crust. In analysed solid samples, radioactive equilibrium occurs between U238 and daughters, and between Ra-228 and daughters. Only waste proppants show elevated radioactivity. The activity concentrations of Ra-226 and Ra-228 in waste proppants are several times higher than their concentration in typical environmental samples (e.g. in soil). The average activity concentrations of Ra-226 and Ra-228 in return fluids are at the level of the radium concentrations in mine waters from coal and copper mines in Poland and at the level of the highest Ra-226 and Ra-228 activity concentrations observed in Polish groundwater. The significant enhancement of radium activity concentrations after the fracking process was observed in the case of return fracking fluids. The study shows that radiation hazard from the solid wastes generated from shale gas exploration in Poland is negligible. Regarding the fluid wastes, the radiation hazard is commensurable with that associated with copper and coal exploration. Acknowledgements This work was funded by the Polish Ministry of Environment (project no. 117/GDOS/DON/2012) and the Polish Ministry of Science and Higher Education (grant no. 11.220.01). The authors would like to thank prof. Krzysztof Bahranowski and Adam Gaweł for their help. References Chałupnik, S., Michalik, B., Wysocka, M., Skubacz, K., Mielnikow, A., 2001. Contamination of settling ponds and rivers as a result of discharge of radiumbearing waters from Polish coal mines. J. Environ. Radioact. 54 (1), 85e98. Cutshall, N.H., Larsen, I.L., Olsen, C.R., 1983. Direct analysis of Pb-210 in sediment samples: a self-absorption corrections. Nucl. Instrum. Methods Phys. Res. 206, 309e312. IAEA, 2003. Radiation Protection and the Management of Radioactive Waste in the Oil and Gas Industry. Safety Reports Series No. 34. International Atomic Energy
Agency, Vienna. Jodłowski, P., Kalita, S.J., 2010. Gamma-ray spectrometry laboratory for highprecision measurements of radionuclide concentrations in environmental samples. Nukleonika 55, 143e148. Jodłowski, P., 2016. A revision factor to the Cutshall self-attenuation correction in 210Pb gamma-spectrometry measurements. Appl. Radiat. Isotopes 109, 566e569. Javadpour, F., 2009. Nanopores and apparent permeability of gas flow in mudrocks (shales and siltstone). J. Can. Petroleum Technol. 48 (8), 16e21. € Ruiz, F.A., Cote , M., Phipps, S., 2011. Coal mine methane: a review of Karacan, C.O., capture and utilization practices with benefits to mining safety and to greenhouse gas reduction. Int. J. Coal Geol. 86, 121e156. Langmuir, D., 1997. Aqueous Environmental Chemistry. Prentice Hall, Upper Saddle River, New Jersey. Macuda, J., 2010. Environmental aspects of unconventional gas production. Przegla˛ d Geol. 58 (3), 266e270. Nguyen, D.C., Jodłowski, P., Kalita, S.J., Olko, P., Chrusciel, E., Maksymowicz, A., rski, M., Bilski, P., Budzianowski, M., 2008. Natural radiation and its Waligo hazard in copper ore mines in Poland. Acta Geophys. 56 (2), 505e517. ski, M., Jodłowski, P., Nowak, J., Ro za _ n ski, K., Sleziak, Nguyen, D.C., Dulin M., Wachniew, P., 2011. Natural radioactivity in groundwater e a review. Isotopes Environ. Health Stud. 47 (4), 415e437. Nguyen, D.C., Rajchel, L., Nowak, J., Jodłowski, J., 2012. Radium isotopes in the Polish Outer Carpathian mineral waters of various chemical composition. J. Environ. Radioact. 112, 38e44. Nowak, J., Chau, N.D., Rajchel, L., 2012. Natural radioactive nuclides in the thermal waters of the Polish Inner Carpathians. Geol. Carpathica 63 (4), 343e351. OGP, 2008. Guidelines for the Management of Naturally Occurring Radioactive Material (NORM) in the Oil & Gas Industry. Report No. 412. International Association of Oil & Gas Producers. Rich, A.L., Crosby, E.C., 2013. Analysis of reserve pit sludge from unconventional natural gas hydraulic fracturing and drilling operations for the presence of technologically enhanced naturally occurring radioactive material (tenorm). New Solutions 23 (1), 117e135. Rowan, E.L., Engle, M.A., Kirby, C.S., Kraemer, T.F., 2011. Radium Content of Oil- and Gas-Field Produced Waters in the Northern Appalachian Basin (USA): Summary and Discussion of Data. Scientific Investigations Report 2011e5135. U.S. Geological Survey. http://pubs.usgs.gov/sir/2011/5135/pdf/sir2011-5135.pdf. San Leon Energy, 2013. Corporate Presentation Q1 2013. http://www. sanleonenergy.com/media/446612/sle_corp_presentation_q1_2013_25_2_13_ final2.pdf. Shabani, K.S., Ardejani, F.D., Badii, K., Olya, M.E., 2014. Acid mine drainage treatment by perlite nanomineral, batch and continuous systems. Archives Min. Sci. 59 (1), 107e122. Siegel, M.D., Bryan, C.R., 2004. Environmental geochemistry of radioactive contamination. In: Lollar, B.S. (Ed.), Treatise on Geochemistry. Elsevier, Oxford, pp. 205e262. UNSCEAR, 2000. Sources and Effects of Ionizing Radiation. Report to the General Assembly, with Scientific Annexes. United Nations Scientific Committee on the Effects of Atomic Radiation. http://www.unscear.org. UNSCEAR, 2008. Sources and Effects of Ionizing Radiation. Report to the General Assembly, with Scientific Annexes. United Nations Scientific Committee on the Effects of Atomic Radiation. http://www.unscear.org.
Contents lists available at ScienceDirect
Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Radioactivity in wastes generated from shale gas exploration and production e North-Eastern Poland Paweł Jodłowski a, Jan Macuda b, Jakub Nowak a, *, Chau Nguyen Dinh c w, Poland AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Al. Mickiewicza 30, 30-059 Krako w, Poland AGH University of Science and Technology, Faculty of Drilling, Oil and Gas, Al. Mickiewicza 30, 30-059 Krako c w, Poland AGH University of Science and Technology, Faculty of Geology, Geophysics and Environmental Protection, Al. Mickiewicza 30, 30-059 Krako a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 December 2016 Received in revised form 29 March 2017 Accepted 10 April 2017
In the present study, the K-40, U-238, Ra-226, Pb-210, Ra-228 and Th-228 activity concentrations were measured in 64 samples of wastes generated from shale gas exploration in North-Eastern Poland. The measured samples consist of drill cuttings, solid phase of waste drilling muds, fracking fluids, return fracking fluids and waste proppants. The measured activity concentrations in solid samples vary in a wide range from 116 to around 1100 Bq/kg for K-40, from 14 to 393 Bq/kg for U-238, from 15 to 415 Bq/kg for Ra-226, from 12 to 391 Bq/kg for Pb-210, from a few Bq/kg to 516 Bq/kg for Ra-228 and from a few Bq/ kg to 515 Bq/kg for Th-228. Excluding the waste proppants, the measured activity concentrations in solid samples oscillate around their worldwide average values in soil. In the case of the waste proppants, the activity concentrations of radionuclides from uranium and thorium decay series are significantly elevated and equal to several hundreds of Bq/kg but it is connected with the mineralogical composition of proppants. The significant enhancement of Ra-226 and Ra-228 activity concentrations after fracking process was observed in the case of return fracking fluids, but the radium isotopes content in these fluids is comparable with that in waste waters from copper and coal mines in Poland. © 2017 Elsevier Ltd. All rights reserved.
Keywords: Shale gas Hydraulic fracturing Radioactivity NORM Wastes Poland
1. Introduction Shale gas exploration and production, involving the extensive application of well-stimulation techniques (hydraulic fracturing) in horizontal wellbore sections to release gas from rock formations, poses a potential threat to the environment. The hydraulic fracturing process requires the use of very large amounts of water and chemicals necessary for the preparation of fracking fluids and other technological fluids used for borehole drilling (Javadpour, 2009; Karacan et al., 2011; Shabani et al., 2014). Consequently, in the course of this process, a large amount of waste in the form of return fluids and small amounts of proppants are generated. In addition, during the wellbore drilling, wastes are generated in the form of waste drilling fluid and drill cuttings (hard scales). The threat posed by shale gas exploration and production includes soil degradation, local pollution of the ground surface by fuels and technological liquids, contamination of surface water and groundwater, resulting from uncontrolled discharges of wastewater to them (Macuda,
* Corresponding author. E-mail address: jakub.nowak@fis.agh.edu.pl (J. Nowak). http://dx.doi.org/10.1016/j.jenvrad.2017.04.006 0265-931X/© 2017 Elsevier Ltd. All rights reserved.
2010). Beside the above-mentioned hazards to the environment and humans, others may be attributable to the radiation hazard associated with radioactivity from natural radionuclides, widely occurring in the rocks of shale gas deposits and other formations. These radionuclides derive from natural radioactive decay series, mainly from two series: the uranium decay series (the primary radionuclide is U-238) and thorium decay series (the parent radionuclide is Th-232) and potassium K-40. From a radiation protection point of view, the most important radionuclides are radium Ra-226 (the half-live is T1/2 ¼ 1600 years), radon Rn-222 (T1/2 ¼ 3.8 days), lead Pb-210 (T1/2 ¼ 22.2 years) and polonium Po-210 (T1/2 ¼ 138.4 days) from the uranium series; from the thorium series, in turn, the most important radionuclides are Ra228 (T1/2 ¼ 5.75 years), thorium Th-228 (T1/2 ¼ 1.91 years), Ra224 (T1/2 ¼ 3.6 day) and Rn-220 (T1/2 ¼ 56 s). The third major source of radiation is the radioactive isotope of potassium, K-40, with a natural abundance of 0.0119%. Potassium occurs in significant quantities in the Earth's crust (about 2.5%). In the gas and oil mining industry, the radiation hazard associated with NORM mainly results from the migration of U-238 and Th-232 decay
P. Jodłowski et al. / Journal of Environmental Radioactivity 175-176 (2017) 34e38
products along with a mixture of oil, gas and water extracted from a wellbore. These products (mainly radium isotopes: Ra-226 and Ra228) accumulate in sludge and hard scales. The average concentrations of radium isotopes in sludge and hard scales vary in a wide range from 100 Bq/kg to 15,000 kBq/kg. In general, radium concentrations are lower in sludge than in hard scales. The opposite applies to Pb-210, for which the concentration is relatively low in hard scales, but in the case of sludge the Pb-210 activity concentration may reach even 1000 kBq/kg and more (UNSCEAR, 2000; IAEA, 2003; UNSCEAR, 2008; OGP, 2008). In the literature, there are few papers dealing with the problem of NORM in shale gas exploration and production. For example, the U.S. Geological Survey conducted a study of the activity concentrations of Ra-226 and Ra-228 in waters co-produced with oil and gas from Marcellus Shale. Radium concentrations vary in a range of 1.3 Bq/L to 590 Bq/L for Ra-226 and of 0.08 Bq/L to 44 Bq/L for Ra228 (Rowan et al., 2011). In turn, the study carried out for radioactivity in samples taken from four reservoirs of fracking fluids located at the Barnett deposit, show that concentrations of natural radionuclides in analysed samples do not exceed 204 Bq/kg for K40, 89 Bq/kg for Ra-226 and 26 Bq/kg for Ra-228 (Rich and Crosby, 2013). In order to assess radioactive contamination of wastes resulting from shale gas, measurements of the natural radionuclides (K-40, U-238, Ra-226, Pb-210, Ra-228, Th-228) activity concentrations in wastes samples were performed. The samples of solid phase of
35
waste drilling muds, drill cuttings, fracking fluids, return fracking fluids and waste proppants were collected from selected drilling sk Pomerania, rigs located in North-Eastern Poland (i.e. from Gdan across Mazovia to Lublin Region) in two of the most prospective basins of the Baltic Basin and Lublin Trough (Fig. 1). In this paper, the authors only provide information about the types of samples and assign sample codes due to information confidentiality. 2. Sampling and methods Samples for analysis were taken from selected drilling rigs from August 2012 until June 2014. 64 samples consisting of fracking fluids, return fracking fluids, solid phase of waste drilling muds, waste proppants (these being proppants which flowed back from boreholes together with return fracking fluids after hydraulic fracturing) and drill cuttings were collected. Fluids were drawn directly from the sampling site to glass containers with a volume of 1 L, in turn, solid samples were packed into plastic bags. Samples of fracking fluid were collected before the injection into wellbores, in contrast to other types of samples collected after the processes of drilling and hydraulic fracturing. Samples of return fracking fluids were collected after the set of shale shakers, desanders and centrifuges which separate solid phase from return fracking fluids. After the transport to the laboratory, samples were sealed into beakers. There were two types of beakers used: the aluminium cylindrical beaker of the volume of 121 mL (used for solid samples)
Fig. 1. Location of the most prospective shale basin in Poland (modified from San Leon Energy, 2013).
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and glass cylindrical beaker with the volume of 210 mL (for liquid samples). In order to obtain radioactive equilibrium in the samples between Ra-226 and its progenies Rn-222, Pb-214 and Bi-214, measurements were performed after at least 21 days from sample sealing. Samples were measured by gamma-spectrometer with an HPGe detector with relative efficiency of 42% and resolution of 1.9 keV for 1332 keV line (Canberra GX4020). Spectra were collected for 10e50 h and it depended on the activity of the study samples to guarantee the relative uncertainty of the gamma count rate lower than 3%. As standard samples, reference materials RG produced by the International Atomic Energy Agency (IAEA) were used. A detailed description of the methodology was presented by Jodłowski and Kalita (2010). K-40 was quantified using its 1461 keV emission, U-238 via its granddaughter Pa-234m 1001 keV emission line and Pb-210 via its 46.5 keV emission. Ra-226 was determined via its granddaughters Pb-214 (352 keV) and Bi-214 (609 keV, 1120 keV and 1764 keV) emissions. Ra-228 was assayed via the emissions of its daughter Ac228 (911 keV, 967 keV) and Th-228 via the emissions of its granddaughter Tl-208 (583 keV, 2614 keV). The self-attenuation correction in Pb-210 measurements accounting the difference of density of the samples and standard ones was introduced follow the transmission method proposed by Cutshall, together with the recently proposed modification (Cutshall et al., 1983; Jodłowski, 2016). 3. Results and discussion The measured activity concentration of natural radionuclides (at the sampling time) in samples taken from selected shale gas drilling rigs in North-Eastern Poland are presented in Table 1. The activity concentrations of natural radionuclides in solid samples vary over a wide range up to 1100 Bq/kg for K-40 (with one exception ZPW-1), up to 415 Bq/kg for U-238, Ra-226 and Pb-210 and up to 516 Bq/kg for Ra-228 and Th-228. Generally, measured activity concentrations vary around their worldwide average values in soil. The only exception are samples of waste proppants in which the activity concentrations of radionuclides from uranium and thorium decay series are significantly elevated and can reach even 516 Bq/kg for Ra-228. By comparison, according to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 2008) the worldwide average activity concentrations of K-40, Ra-226 and Th-232 in soil are 412 Bq/kg, 32 Bq/kg and 45 Bq/ kg respectively, while the average concentrations of these elements in the Earth's crust are equal to around 750, 50 and 50 Bq/kg respectively. These concentrations in the Earth's Crust strongly depend on geology and they vary in a wide range from a few Bq/kg to 2000 Bq/kg for K-40, to 150 Bq/kg for Ra-226 and to several hundreds of Bq/kg for Th-232. The average activity concentrations of K-40, Ra-226 and Ra-228 in drill cuttings are 815 Bq/kg, 62 Bq/kg and 37 Bq/kg respectively, while their concentrations in solid phase of waste drilling muds are equal to 966 Bq/kg, 25 Bq/kg and 20 Bq/kg respectively. For one sample of solid phase of waste drilling muds (ZPW-1), the very high activity concentration of K-40 (3590 Bq/kg) was observed. This fact is related to the chemical composition of drilling mud. Drilling mud with high concentration of potassium chloride was used in this case during the drilling of boreholes. The waste proppants are the only material for which elevated radioactivity was observed. The average activity concentrations of K-40, Ra-226 and Ra-228 in waste proppants are 183 Bq/kg, 278 Bq/ kg and 340 Bq/kg respectively. Samples of waste proppants from Baltic Basin are characterised by the high activity concentration of Ra-226 and Ra-228 (up to 415 Bq/kg and 516 Bq/kg respectively). In
case of Lublin Trough, the activity concentration of Ra-226 and Ra228 in the waste proppant PRZ-5 amounts to 216 Bq/kg and 246 Bq/ kg respectively, while the waste proppant PRZ-4 shows very low radioactivity. In the authors’ opinion, the elevated radioactivity in waste proppants is not related to hydraulic fracturing but to the mineralogical composition of proppants. The following arguments support the above statement: - The waste proppant is the proppant surplus which doesn't penetrate the fractures, it has contact only with fracking fluids; - Adsorption is the only process that may lead to an increase in radioactivity of proppants. It is strongly driven by chemical and physical properties of adsorbed compounds and adsorbents. Thus, it is impossible to obtain an equilibrium in the uranium and thorium decay series in samples of waste proppant, as a results of adsorption, but such equilibrium was observed. In order to prove the above statement, the proppant sample with the highest concentration of radionuclides (PRZ-2) was remeasured. The sample was washed in 9M solution of HNO3 at 90 C to remove from the proppant surface all adsorbed substances before the measurement. Obtained results of radionuclides activity concentrations in the proppant sample are the same as previous one within measurement uncertainty. In all studied solid samples (OSW, ZPW, PRZ) the activity concentrations of radionuclides from uranium decay series (U-238, Ra226 and Pb-210) are equal and similarly for Ra-228 and Th-228 in thorium decay series. In other words, in the studied samples there is radioactive equilibrium between U-238 and daughters, and between Ra-228 and daughters. For the fracking fluids average activity concentrations of K-40 is 75 Bq/L (median 5 Bq/L). However, nearly half of the samples contain potassium (K-40) at concentrations below the detection limit (5 Bq/L), while the activity concentrations of U-238, Ra-226, Pb-210, Ra-228 and Th-228 in all samples are below the detection limit in all samples. In return fracking fluids the average activity concentration of K40, Ra-226 and Ra-228 are equal to 66 Bq/L, 42 Bq/L and 20 Bq/L respectively, while the activity concentrations of U-238, Pb-210 and Th-228 are below the detection limit. It means that there is no radioactive equilibrium between U-238 and Ra-226 (uranium series) and between Ra-228 and Th-228 (thorium series). In comparison, the average concentrations of Ra-226, Ra-228 in return fracking fluids with the concentrations in fracking fluids (collected before the wellbore injection) shows significant radioactivity enhancement after the fracking process. The absence of Th-228 in return fracking fluids is related to the fact that thorium (leached from host rocks) forms low soluble and high adsorbed compounds in contrast to radium (Langmuir, 1997; Siegel and Bryan, 2004; Nguyen et al., 2011). The average activity concentrations of Ra-226 and Ra-228 in return fracking fluids are at the level of their highest concentrations observed in groundwater in Poland. The radium activity concentration in Polish groundwater varies in a wide range from a few mBq/L to 65 Bq/L for Ra-226 and from 10 mBq/L to around 14 Bq/L for Ra-228 (Nguyen et al., 2012; Nowak et al., 2012). In case of waste waters generated by the mining industry, the radium concentration is usually higher than in groundwater. For example, the radium content in mine water from the Upper Silesia coal mines in Poland vary from 0.18 to 21 Bq/L (Chałupnik et al., 2001), while in mine water from copper mines in the vicinity of town Lubin in SW Poland, the radium activity concentrations vary in a broad range from 30 mBq/L to about 100 Bq/L e the median is 1.1 Bq/L (Nguyen et al., 2008). Generally, the content of Ra-226 and Ra-228 in return fracking fluids is at the level of the radium concentrations observed
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37
Table 1 The activity concentrations of natural radionuclides (K-40, U-238, Ra-226, Pb-210, Ra-228 and Th-228) in samples of wastes from selected shale gas drilling rigs (The activity concentrations are given at the moment of sampling). Rig number
Sample ID
Activity concentration K-40
U-238
Ra-226
1092 ± 30 446 ± 15 816 ± 24 794 ± 24 816 ± 25 897 ± 28
<35 <35 <35 36 ± 27 87 ± 24 61 ± 27
30 29 43 44 70 75
918 ± 30 739 ± 22 446e1092 815/816
99 ± 35 70 ± 24 35e99 57/49
120 ± 4 85 ± 3 29e120 62/57
<35 <35 <35 46 ± 15 <35
15 18 29 29 21
38 ± 22 <35 35e46 37/35
44 ± 2 19 ± 1 15e44 25/21
28 ± 15 54 ± 13 15e54 30/28
26 ± 1 19 ± 2 13e31 20/19
24 ± 1 16 ± 2 13e26 18/17
137 ± 20 <5 <5
<30 <30 <30
<2 <2 <2
<5 <5 <5
<2 <2 <2
<2 <2 <2
<5 499 ± 20 5e499 75/5
<30 <30 <30 <30
<2 <2 <2 <2
<5 <5 <5 <5
<2 <2 <2 <2
<2 <2 <2 <2
333 ± 13 62 ± 14 56 ± 11 <10 17 ± 8 17 ± 8 13 ± 6 18 ± 8
<30 <30 <30 <30 <30 <30 <30 <30
<2 43 ± 2 51 ± 2 4±2 28 ± 1 37 ± 2 41 ± 2 41 ± 2
<5 <5 <5 <5 <5 <5 <5 <5
<2 28 ± 1 31 ± 2 4±1 24 ± 1 30 ± 1 35 ± 2 36 ± 2
<2 <2 <2 <2 <2 <2 <2 <2
<10 16 ± 5 99 ± 10 79 ± 12 545 ± 20 5e545 66/27
<30 <30 <30 <30 <30 <30 <30
38 ± 2 53 ± 2 52 ± 2 66 ± 2 50 ± 2 2e70 42/43
<5 <5 <5 <5 <5 <5 <5
18 ± 2 28 ± 1 22 ± 1 33 ± 2 24 ± 1 2 < 5 36 20/19
<2 <2 <2 <2 <2 <2 <2
272 ± 12 182 ± 9 191 ± 8
389 ± 70 364 ± 53 393 ± 51
334 ± 10 408 ± 12 415 ± 13
319 ± 20 391 ± 30 372 ± 20
417 ± 13 514 ± 17 516 ± 16
418 ± 13 504 ± 17 515 ± 16
116 ± 5 152 ± 10 116e272 183/182
14 ± 12 186 ± 31 14e393 271/364
15 ± 1 216 ± 10 15e415 278/334
12 ± 4 223 ± 13 12e391 263/319
8±2 246 ± 12 8e516 340/417
5±2 245 ± 12 5e515 337/418
[Bq/kg]; [Bq/L] Drill cuttingsbe8 samples Baltic Basin 1 OSW-1 OSW-2 2 OSW-3 4 OSW-4 OSW-5 7 OSW-6 Lublin Trough 3 OSW-7 5 OSW-8 range average/medianc
Solid phase of waste drilling mudsbe7 samples Baltic Basin 1 ZPW-1 3590 ± 110 2 ZPW-2 289 ± 10 4 ZPW-3 881 ± 26 ZPW-4 726 ± 22 7 ZPW-5 344 ± 11 Lublin Trough 3 ZPW-6 506 ± 18 5 ZPW-7 423 ± 13 range 289e3590 average/medianc 966/506 Fracking fluidsde14 samples Baltic Basin 1 P-1 2 P-2 7 P-3 Lublin Trough 3 P-4 5 P-5 range average/medianc Return fracking fluidsd,ee30 samples Baltic Basin 1 PZ-1 PZ-2 PZ-3 2 PZ-4 7 PZ-5 PZ-6 PZ-7 PZ-8 Lublin Trough 3 PZ-9 PZ-10 5 PZ-11 PZ-12 PZ-13 range c average/median Waste proppantsb,fe5 samples Baltic Basin 1 PRZ-1 2 PRZ-2 PRZ-3 Lublin Trough 3 PRZ-4 5 PRZ-5 range average/medianc a b c d e f
Pb-210
Ra-228
Th-228
a
± ± ± ± ± ±
± ± ± ± ±
1 1 2 2 2 4
1 1 1 1 1
43 30 49 49 97 53
± ± ± ± ± ±
5 15 12 6 9 12
143 ± 12 87 ± 10 30e143 69/51
23 18 36 38 15
± ± ± ± ±
15 11 8 5 11
35 22 40 31 40 47
± ± ± ± ± ±
2 1 2 2 2 2
43 ± 2 36 ± 2 22e47 37/38
17 16 13 31 20
± ± ± ± ±
1 1 1 2 1
33 19 41 33 41 47
± ± ± ± ± ±
2 1 2 2 2 2
43 ± 2 35 ± 2 19e47 37/38
17 15 13 26 18
± ± ± ± ±
1 1 1 2 1
[Bq/kg] for drill cutting, solid phase of waste drilling muds and waste proppants, [Bq/L] for fracking fluid and return fracking fluids. In the table, all results were presented. For results below the detection limit, the value of detection limit was used to calculate the average and median value of the radionuclides activity concentrations. In the table, selected results were presented; the results for other samples are similar; the average and median value were calculated for all results. Return fracking fluids were collected after the set of shale shakers, desanders and centrifuges which separate solid phase from fluids. It is proppants which flowed back from a borehole together with return fracking fluids after hydraulic fracturing.
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in waste waters from coal and copper mines located in Poland. 4. Conclusions Generally, the activity concentrations of K-40, U-238, Pb-210, Ra-226 and Th-228 in solid samples are at the level of their worldwide average concentrations in soil and in the Earth's crust. In analysed solid samples, radioactive equilibrium occurs between U238 and daughters, and between Ra-228 and daughters. Only waste proppants show elevated radioactivity. The activity concentrations of Ra-226 and Ra-228 in waste proppants are several times higher than their concentration in typical environmental samples (e.g. in soil). The average activity concentrations of Ra-226 and Ra-228 in return fluids are at the level of the radium concentrations in mine waters from coal and copper mines in Poland and at the level of the highest Ra-226 and Ra-228 activity concentrations observed in Polish groundwater. The significant enhancement of radium activity concentrations after the fracking process was observed in the case of return fracking fluids. The study shows that radiation hazard from the solid wastes generated from shale gas exploration in Poland is negligible. Regarding the fluid wastes, the radiation hazard is commensurable with that associated with copper and coal exploration. Acknowledgements This work was funded by the Polish Ministry of Environment (project no. 117/GDOS/DON/2012) and the Polish Ministry of Science and Higher Education (grant no. 11.220.01). The authors would like to thank prof. Krzysztof Bahranowski and Adam Gaweł for their help. References Chałupnik, S., Michalik, B., Wysocka, M., Skubacz, K., Mielnikow, A., 2001. Contamination of settling ponds and rivers as a result of discharge of radiumbearing waters from Polish coal mines. J. Environ. Radioact. 54 (1), 85e98. Cutshall, N.H., Larsen, I.L., Olsen, C.R., 1983. Direct analysis of Pb-210 in sediment samples: a self-absorption corrections. Nucl. Instrum. Methods Phys. Res. 206, 309e312. IAEA, 2003. Radiation Protection and the Management of Radioactive Waste in the Oil and Gas Industry. Safety Reports Series No. 34. International Atomic Energy
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