Results from baseline and

Transcription

1 SHale gas Exploration and Exploitation induced Risks Results from baseline and post-frac monitoring Nelly Montcoudiol Second Annual Meeting Blackpool - June 5-7, 2017 This project has received funding from the European Union s Horizon 2020 research and innovation programme under grant agreement No

2 Data collection in the field Continuous data Site visits GW levels Alkalinity P atm, T air Samples for lab analyses / QA Ions Metals Dissolved gases Isotopes Physico-chemical parameters Set up for groundwater sampling at well GW3 2 P abs, T GW & Spec. Cond.

3 Groundwater levels Correction for barometric effects GW level variations Recharge 3

4 Correction of groundwater levels for barometric effect Distinction open vs closed wells P abs (head) = P w (WL) + P atm Closed wells (GW2) Pressure (level) changes measured in the well reflects pressure (level) l) changes in the aquifer Open wells (GW1, GW3 & GW4) Imbalance between pressure (level) in the well and pressure (level) l) in the unconfined aquifer Confined P atm Unconfined Confined P atm WL Unconfined P abs P abs with delay P abs P abs with delay 4

5 Correction of groundwater levels for barometric effect Distinction open vs closed wells Closed well (GW2) t ~ 0 (1h30 by correlation analysis with Tsoft; Van Camp & Vauterin 2005) P atm P abs α 1 Graphical method from Gonthier (2007): α = 0.16 elastic aquifer FFT filter (widthband 0.01 cpd) P abs (head) = P w (WL) + P atm GW2 Earth tides 1 cpd 2 cpd 1 cpd 2cpd Min 18:00 00:30/12:30 22:15 11:00/23:00 Max 06:00 06:30/18:30 10:15 5:00/17:00 5

6 Correction of groundwater levels for barometric effect Distinction open vs closed wells Open wells (GW1, GW3 & GW4) Variable t P atm P abs α 1 P abs (head) = P w (WL) + P atm t = 4-9h t = 7-22h t =1014h 10-14h BETCO (Rasmussen & Crawford 1997; Toll & Rasmussen 2007) Correlation analysis with Tsoft: lag time between Patm and Pabs GW1 GW3 GW4 Lag time 3h45 16h30 7h45 6

7 Groundwater levels Wysin-2H Wysin-3H 7

8 Water stable isotopes (δ 18 O and δ 2 H) 8

9 Recharge model 9

10 Recharge model Sensitivity analysis Reference model: 189 mm (1 year-period) Parameter sensitivity Parameter Parameter variation Recharge Sensitivity Crop type / growth length Between seasons Wheat Pasture Wood Corn Rye grass Bare soil Dead vegetation (1 month) Live vegetation (2 months) 189 mm 165 mm 123 mm mm 122 mm 189 mm 189 mm 187 mm Soil type Silt loam to loamy sand mm -- Depth of surface soil layer Runoff 5 cm 10 cm 15 cm 0% 10% 20% 30% 184 mm 189 mm 187 mm 241 mm 215 mm 189 mm 163 mm Max. plant height Max. rooting depth --

11 Recharge model Crop type / growth length Runoff 11

12 Recharge model Composite model Applied at catchment scale / accounts for variable soil occupation 25% wheat 25% rye grass 20% wood 15% pasture 15% corn Dry spring Some recharge Wet summer Limited recharge Wet autumn Recharge Feb. Mar. Apr. May Jun. Jul. Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Rain (mm) Recharge (mm) Recharge (%)

13 Recharge model 13

14 Recharge model Sensitivity of composite model Wood and pasture fixed (20 and 15% resp.) Wheat: 15 35% Corn: 5 20% Rye grass: 15 40% 14

15 Groundwater quality Physico-chemical parameters Groundwater chemistry 15

16 Physico-chemical parameters: temperature Baseline Post-frac GW C 8.14 C GW C 8.10 C GW C 8.07 C GW C 7.89 C 16

17 Physico-chemical parameters: spec. conductivity Baseline Post-frac GW1 478 µs/cm 479 µs/cm GW4 468 µs/cm 471 µs/cm GW2 459 µs/cm 451 µs/cm GW3 448 µs/cm 442 µs/cm 17

18 Physico-chemical parameters: dissolved O 2 18

19 Physico-chemical parameters: redox 19

20 Physico-chemical parameters: ph 20

21 Groundwater chemistry Major ions Groundwater Ca-HCO 3 Manganese > 50 µg/l Traces of As, Ba, F - & Sr Frac fluid Na-HCO 3? Flowback fluid Na-Cl Rich in metals: Ba, Br, Li, Mn and Sr focus of postfrac monitoring Ca meq/l Mg Na SO 4 Cl HCO meq/l meq/l Scale 1:200 21

22 Groundwater chemistry Temporal variability during baseline <0.1 Max / 3 rd quartile / median / 1 st quartile / min (4 site visits) PGI baseline (range and average of 3 drilled boreholes) 22

23 Groundwater chemistry: post-frac monitoring 23

24 Groundwater chemistry: other parameters Dissolved gases Results from commercial lab below detection limits (40 µg/l) Additional tests with other labs: different sampling method (no contact with atmosphere) BGS Isotech lab. BGS & BGR (June visit) Other isotopic data (on-going) Sulphate isotopes: δ 34 S Carbon isotopes: δ 13 C DIC BGS Well CH 4 (µg/l) CO 2 (mg/l) Ethane (µg/l) GW1 512± ±0.5 <2 GW ± ± NA GW3 60.8± ±1.0 NA GW4 8.2± ±0.9 NA GW4 (dup.) 9.9± ±0.8 NA Isotech Well CH 4 (µg/l) Ethane (µg/l) Propane (µg/l) GW1 5.3±0.3 <0.2 <0.3 GW1a GW2 85±0 62±0 8.5± ± ±0 0.38±0.02 < <0.3 GW1b GW3 8.2±0.4 79±4 0.56±0.03 < ±0.02 <0.3 GW1c GW4 8.4±0.4 12± ±0.04 < ±0.03 <0.3 GW4 (dup.) 12±0.6 <0.2 <0.3 24

25 Conclusions & perspectives p Typical Quaternary aquifer Semi-confined to confined, with limited variations of groundwater levels => heterogeneities Recharge mainly occurring in Autumn (2016 data) Similar chemistry: Ca-HCO 3 water type, with limited temporal variability Signature of flowback fluid completely different No short-term impacts on GW resources from the exploration well / hydraulic fracturing Statistics for robust conclusions Groundwater model Aquifer behaviour Scenarios of impact 25

26 Reference list Allen, R. G., L. S. Pereira, D. Raes & M. Smith, Crop evapotranspiration - Guidelines for computing crop water requirements - FAO Irrigation and drainage paper 56. Food and Agriculture Organisation. Rome URL: Gonthier, G. J., A graphical method for estimation of barometric efficiency from continuous data-concepts and application to a site in the Piedmont, Air Force Plant 6, Marietta, Georgia. Scientific Investigation Report U.S. Geological Survey. Reston, Virginia, USA. 29 p. URL: gov/sir/2007/5111/pdf/sir pdf. IAEA, RCWIP (Regionalized Cluster-Based Water Isotope Prediction) Model gridded precipitation δ 18 Oδ 2 H δ 18 O and δ 2 H isoscape data. International Atomic Energy Agency. Vienna, Austria. From accessed April IAEA/WMO, Global Network of Isotopes in Precipitation. The GNIP Database. From Rasmussen, T. C. & L. A. Crawford, Identifying and removing barometric pressure effects in confined and unconfined aquifers. Ground Water. 35(3): DOI: /j tb00111.x. Toll, N. J. & T. C. Rasmussen, Removal of barometric pressure effects and Earth tides from observed water levels. Ground Water. 45(1): DOI: /j x. Van Camp, M. & P. Vauterin, Tsoft: graphical and interactive software for the analysis of time series and Earth tides. Computers & Geosciences. 31(5): DOI: /j.cageo

27 Correction of groundwater levels for barometric effect 27

28 Groundwater levels 28

29 Temperature 29