- Email: [email protected]
Integration Results of Soil CO2 Flux and Subsurface Gases in the Ressacada Pilot site, Southern Brazil
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 114 (2017) 3793 – 3804
13th International Conference on Greenhouse Gas Control Technologies, GHGT-13, 1418 November 2016, Lausanne, Switzerland
Integration results of soil CO2 flux and subsurface gases in the Ressacada Pilot site, Southern Brazil. Clarissa L. Meloa; Flávio S. Goudinhoa; Lia W. Bressana; Marcelo J. Constanta; Victor Hugo J. M. dos Santosa; Luiz Frederico Rodriguesa; Jessica P. Piresa; João Marcelo M. Ketzera; Andréa Cristina de C.A. Moreirab; Fátima do Rosáriob; Ana Paula S. Musseb. a
Pontifical Catholic University of Rio Grande do Sul – PUCRS – IPR – Institute of Petroleum and Natural Resources, Av. Bento Gonçalves, 4592, Porto Alegre - 90619-900, Brazil PETROBRAS – Petróleo Brasileiro S.A. – CENPES, Av. Horácio Macedo, 950, Rio de Janeiro – 21941915, Brazil
b
Abstract The first CO2 monitoring field lab at the Ressacada Farm, in the Southern region of Brazil, started in 2011 and until 2015 offered an excellent opportunity to run controlled CO 2 releases experiments in soil and shallow subsurface through vertical injection wells. This paper focus on the presentation and comparison of the results obtained at the last campaign realized at this site in August 2015. The results integrate a time-lapse monitoring experiment of CO2 migration in both saturated and unsaturated sand-rich sediments and soil, using soil CO2 flux measurements and subsurface gas analyses through CO2 concentrations (ppm) and carbon isotope ratios (δ 13C of CO2). The CO2 flux results in the studied area showed an increase in the flux values according to the increasing of injection rate and along the campaign are directed to the southwest portion of the area. However, even by injecting large amounts of CO2, fluxes are greatly reduced when it rains. The gas analysis also showed an increase in CO 2 concentrations according to the increasing of the injection rate mainly in the superficial levels of the monitoring wells (0.5m and 2m depth). The δ13C of CO2 found on the 3rd injection day showed the presence of CO2 injected and demonstrate that the sampling methodology with vacutainer vial was effective, since there is no atmospheric contamination. The correlation of isotopic analysis were consistent with the results of concentrations and CO2 fluxes and thus, it is clear that the CO2 breakthrough occurred from the 3rd day of injection, while were obtained the largest CO2 fluxes, the higher gas concentrations in the subsurface, as well as the industrial origin of δ 13C of CO2.
* Corresponding author. Tel.: +555133203689
E-mail address: [email protected]
© 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2017 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of GHGT-13. Peer-review under responsibility of the organizing committee of GHGT-13. Keywords: Monitoring, CO2, release, experiment;
1.
Introduction
Several CO2 controlled release experiments were performed at the Ressacada Farm in Florianópolis city, Southern region of Brazil (Figure 1), as a joint R&D project under the full sponsorship of PETROBRAS. The first CO2 monitoring field lab aimed to evaluate different monitoring tools with application purposes in geological carbon storage sites.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. 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 GHGT-13. doi:10.1016/j.egypro.2017.03.1510
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Clarissa L. Melo et al. / Energy Procedia 114 (2017) 3793 – 3804
Figure 1. Site location.
The first test was conducted in 2012 by a vertical well with the injection of CO2 occurring at a depth of 8 meters. As CO2 breakthrough occurred only after 13 days of injection the project team opted to use a shallower vertical well located in an area with geological conditions favoring a faster escape. Therefore, in 2013 it was held the second experiment, injecting around 32 Kg of CO2 continuously for 11 days in a vertical well with 3 meters depth and the results were much more satisfactory. The third experiment was realized in August 2015 during 12 days (1 background day, 10 injection days and 1 post-injection day) using the same vertical well built in 2013. In this campaign, with the methodologies and experimental techniques already established and a better knowledge of CO2 behavior in the studied area, it was injected a CO2 flow four times greater than in the first campaign. The tests started with flow rates of 150 g/hr, continuing with 300 g/h and reaching 400g/hr in the last 4 days of injection. During 10 days, it was injected four-cylinder totaling about 85 Kg of CO2. Measurements of soil CO2 emissions were done using two dynamic flow chambers covering 256 m2 of the studied area. The gas sampling was performed at 7 multi-level monitoring wells using a vacuum pump at 0.5m level and a peristaltic pump at 2, 4 and 6m depth (when detected groundwater). All these data were used to draw up contour maps enabling the characterization of CO 2 flux during the campaign and to demonstrate the presence of the injected CO2 in subsurface as well as prove their origin. The main goal of this paper is to present the comparison of soil CO2 flux measurements and subsurface gas analyses (CO2 concentrations and carbon isotope ratios). 2. Methods 2.1 Accumulation Chambers Soil CO2 emission, temperature and moisture were measured with two dynamic flow chambers, LI8100-A model (LI-COR) in a monitoring grid (Figure 2) with a total of 96 PVC collars covering 256 m2 of the study area. This grid was divided into two sides (A and B), each one with 48 collars with not regular distances between the collars: near the injection well the collars had intervals of 1 meter distance and away from the injection well 2 meters distance intervals. The CO2 concentration in the chamber was measured each second, taking an average reading time of 2 minutes per collar. Measurements were taken prior, during and after CO2 injection.
Clarissa L. Melo et al. / Energy Procedia 114 (2017) 3793 – 3804
Figure 2. Accumulation chambers monitoring grid. Numbers and characters are collars positions.
2.2 Subsurface gas sampling The gas sampling was performed in multi-level monitoring wells at 0.5 m deep with a vacuum pump (Figure 3) and 10 ml syringes that were totally filled with gas. Immediately after sampled, the gas was transferred to Vacutainer® vials and analyzed at the labs of the Institute of Petroleum and Natural Resources (IPR -PUCRS) for Gas Chromatography (GC) and Isotope Ratio Mass Spectrometry (IRMS). Samples of soil gas were collected before, during and after CO 2 injection and samples of injected CO2 were collected directly from the cylinder. Sampling of three water levels located in the saturated zone (2m, 4m, 6m) were performed with a peristaltic pump and a 10 mL syringe, transferred to Vacutainer vials and stored at 4°C until analysis at IPR labs. The parameters analyzed were CO and CO 2 and isotopic ratios 13C CO2.
. Fig.1. Gas sampling at 0.5m depth with syringe and vacuum pump.
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3. Results 3.1 Soil CO2 Flux Monitoring During the background survey, soil CO2 fluxes ranged between 0-47 µmol/m2/s. with the largest CO2 streams distributed to the southwest portion of the studied area (Figure 4A). CO2 fluxes started to change only 3 days after the beginning of injection, when the injection rate was increased from 150 g/h to 300 g/h. Significant variations in soil CO2 fluxes were observed in the area, especially in the southwest portion, reaching 98-351 µmol/m2/s in the 26B collar (Figure 4B). Despite the heavy rain that fell on the 4th day of injection, the flux values continued to increase. From the 6th day of injection when the rate increased to 400g/h, higher fluxes were observed in some collars near the injection well (1B=244 μmol/m2/s; 7B=172 μmol/m2/s), in addition to those values already observed in the southwest portion of the area (Figure 4C). From the 7th day by the end of injection (10th day), there was a clear trend of CO2 migration to the southwest area following the groundwater flow and exiting the flux chambers monitoring grid. The highest values were found in collars 26B (510 μmol/m2/s) and 45B (235 μmol/m2/s), as shown in Figure 4D. The post-injection survey already shows the reduction of CO 2 fluxes across the monitoring grid (Figure 4E).
Fig 4. Soil CO2 flux measurements (μmol/m2/s ) during the 3rd campaign at Ressacada Farm: 4A. Background survey; 4B. Survey on 3rd injection day; 4C. Survey on 6th injection day; 4D. Survey on 10th injection day; 4E. Post-injection survey.
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3.2 Subsurface Gas Monitoring 3.2.1 CO2 Concentration Measurements The evaluation of chromatographic results for subsurface gases collected in 4 levels of monitoring wells took into consideration the CO2 concentrations inside the cylinders used for injection as a reference for comparison and evaluation of data. These concentrations do not have the same values of the certificates of analysis provided by the supplier (99.5%). This difference occurs because the cylinder and the sample vial (Vacutainer) not exhibit the same internal pressure. In the cylinder, CO 2 is at a greater pressure than in the bottle. When a given amount of gas is transferred to another flask the tendency is that the molecules redistribute themselves in a new volume. Therefore, when the CO2 sampled from the cylinder is transferred to Vacutainer occurs a pressure lowering and the same amount of CO2 molecules that previously occupies a very small space, begins to hold a larger space, although the flask volume is smaller relative to the cylinder size. The samples ranged between 31% and 59% because the volume sampled difference in the cylinder-opening act. The larger the volume of CO2 collected, the greater the internal pressure and consequently higher concentration. At the levels 2, 4 and 6 meters, groundwater was sampled for headspace gas analysis, however the results represent the CO2 total concentrations (dissolved and undissolved in water). This occurs because gas bubbles were sampled concomitantly to the water and there is no accurate knowledge of this gas fraction in each sample, which did not allow obtaining the actual concentrations of CO2 dissolved in water. The analysis results may be seen in the Table 1. Table 1. Results of gas samples analysis (CO2 concentrations - ppm). N.D. = not detected
CO2 Concentrations (ppm) Well PM1
PM2
PM3
PM3B
PM4
PM4B
Level (m)
Background
Injection 1 day
3 day
6 day
10 day
Postinjection
0,5
N.D.
89,741
32,875
140,628
248,833
262,126
2
6,415
8,577
7,780
7,883
258,000
12,652
4
6,444
3,749
841
4,049
N.D.
1,724
6
3,542
N.D.
2,763
10,313
4,478
2,794
0,5
13,321
64,116
378,218
597,394
403,347
356,270
2
182
1,815
8,541
7,519
6,138
9,145
4
4,495
873
1,811
6,898
12,663
808
6
1,796
1,922
2,368
7,003
13,127
5,809
0,5
32,325
23,079
103,534
510,553
443,660
162,040
2
14,364
5,923
5,887
9,736
20,648
14,697
4
3,818
1,764
2,279
10,204
8,025
6,173
6
8,614
5,029
1,913
3,774
7,334
3,864
0,5
9,528
8,318
27,904
28,209
25,561
22,779
2
14,613
2,418
4,717
6,174
17,241
2,381
4
1,659
2,104
3,028
2,128
4,568
5,656
st
rd
th
th
6
4,233
1,792
7,246
12,385
1,096
4,582
0,5
18,014
10,460
38,535
281,040
454,509
423,320
2
5,934
3,415
1,935
8,633
10,447
6,798
4
7,393
5,650
1,748
132
1,682
5,381
6
4,344
1,735
853
2,005
8,176
2,517
0,5
20,124
15,633
17,724
29,898
11,383
1,579
2
3,649
859
699
2,167
6,995
3,087
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PM5
4
7,249
4,104
7,238
3,508
4,287
2,611
6
1,663
508
3,002
3,188
3,249
4,226
0,5
30,150
58,801
400,125
380,880
N.D.
228,644
2
7,533
N.D.
205,809
218,462
58,988
41,272
4
4,435
3,132
6,171
10,476
3,017
4,618
6
6,762
1,499
4,910
2,069
3,023
4,881
On Figure 5 shows CO2 concentrations obtained by chromatographic analysis for the 4 levels of monitoring wells in the background, 1st and 3rd injection days. Background values are very low, between 180 and 14000 ppm in the deeper levels and higher (32000 ppm) at the 0.5m level. On the first day of injection, it was possible to observe a slight increase in CO 2 concentration in the 0.5m level at PMs 1, 2 and 5. On the 3rd day, when the injection rate increased to 300 g/h, concentrations also increased significantly in the surface level of PMs 2 and 5 (378,217 ppm to 400,125 ppm, respectively), but also increased in the 2m level of PM 5, reaching 205,808 ppm. The 6th day of injection was marked by higher concentrations of CO2 in the surface (0.5 m) during the campaign (Figure 6), especially in PM 2 (597,393 ppm), PM 3 (510,553 ppm) and PM 5 (380,879 ppm). In 2m deep, PM 5 also reached its maximum concentration (218,462 ppm) on this day. With the injection stop, the CO2 concentrations on PM 5 - level 2m immediately decreased and became even lower on the post-injection survey. However, in the most superficial level, concentrations remained high during the post-injection measurements, but still lower than those measured on the injection days.
Clarissa L. Melo et al. / Energy Procedia 114 (2017) 3793 – 3804
Figure. 5. CO2 concentration in gasometric analyses. 5A represent the background; 5B represent the 3rd day of injection; 5C represent the 6th day of injection; 5D represent the post-injection day.
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3.2.2
Carbon Isotopic Ratios
The 13C isotopic ratio of CO2 provide us the origem of contribuites sources and can be used like a natural tracer of CO2 injected. Therefore, the 13C/12C isotopic ratio of samplers was correlated with inorganic standard Vienna Pee Dee Belemnite (VPDB), in a IRMS equipment, the results will be discussed below. The isotopic ratio of CO2 injected, showed values between -21.8 ‰ to -2.4 ‰, indicating the origin of fossil fuels. The isotopic signature of CO2 in subsurface, during the background period, showed values between -7,2‰ to -12,5‰ (Figure 6A). On the 3rd injection day, the isotopic ratio showed values between -7,37‰ to -22,3‰ (PM5, level 2 m), Figure 6B. On the 6th day of injection, the isotopic signatures of nearly all the PMs in the level of 0.5m, with the exception of PMs 3b and 4b, showed the presence of CO2 from fossil fuels, Figure 6C. The isotopic monitoring presented similar values on the post-injection, Figure 6D. All the results can be viewed on Table 2. Table 2. Isotopic signatures δ13C of CO2 (‰) obtained in samples from wells monitoring.
δ13C of CO2 (‰) Well PM1
PM2
PM3
PM3B
PM4
PM4B
PM5
Level (m)
Background
Injection 1 day
3 day
6 day
10 day
Postinjection
0.5 m
-11.50
-11.84
-10.80
-18.76
-21.12
-21.22
2m
-12.13
-12.22
-13.02
-13.29
-13.22
-13.90
4m
-11.28
-10.59
-11.37
-11.01
-11.96
-15.99
6m
-10.61
-8.30
-10.18
-9.68
-9.82
-11.43
0.5 m
-10.05
-16.66
-21.77
-22.26
-22.17
-21.84
2m
-12.50
-12.71
-12.96
-13.42
-12.75
-12.44
4m
-9.33
-9.29
-10.94
-11.19
-11.25
-9.27
6m
-7.43
-6.94
-10.26
-10.43
-10.52
-10.48
0.5 m
-10.48
-10.93
-18.42
-21.79
-22.17
-22.01
2m
-12.21
-12.31
-12.57
-12.91
-12.95
-12.89
4m
-9.97
-8.62
-10.12
-10.08
-11.51
-8.86
st
rd
th
th
6m
-9.25
-6.90
-9.07
-10.23
-9.93
-9.64
0.5 m
-9.60
-9.21
-9.12
-10.22
-14.92
-15.61
2m
-10.79
-11.42
-11.00
-11.56
-10.84
-10.72
4m
-9.83
-11.53
-9.27
-10.23
-9.17
-11.08
6m
-7.22
-8.95
-7.77
-6.94
-8.44
-8.55
0.5 m
-8.26
-8.36
-13.77
-21.55
-21.89
-21.70
2m
-9.99
-9.29
-10.93
-10.56
-10.79
-9.10
4m
-8.44
-7.36
-9.71
-11.08
-9.88
-9.18
6m
-7.31
-6.51
-7.37
-8.41
-8.80
-8.35
0.5 m
-8.86
-8.77
-8.53
-8.41
-9.76
-9.31
2m
-10.63
-8.90
-10.90
-10.55
-10.76
-8.76
4m
-9.08
-10.85
-9.99
-10.02
-10.29
-9.50
6m
-9.32
-10.47
-9.35
-9.75
-9.42
-7.20
0.5 m
-9.52
-15.27
-21.41
-22.00
-21.99
-21.76
2m
-10.63
-12.75
-22.30
-21.74
-22.12
-22.92
4m
-9.28
-8.91
-12.45
-15.03
-18.11
-9.20
6m
-7.98
-7.60
-9.42
-14.01
-14.27
-9.03
Figura 6. Isotopic ratio values. 6A represent the background; 6B represent the 3rd day of injection; 6C represent the 6th day of injection; 6D represent the post-injection day.
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4.
Integration results
In the following maps, the δ13C isotopic signature of CO2 obtained from IRMS, was represented by isovalue lines while CO2 concentrations are shown by color scale, Figure 7. The results of CO2 concentration showed an increase, starting from the 1st day of injection to post-injection, the majority of monitoring wells at depth of 0.5m. Concomitantly, the δ13C of CO 2 becomes more depleted in these wells in relation to the background (Figure 101) similar to values obtained in the CO2 samples injected (δ13C CO2 ≈ -22 ‰).
Clarissa L. Melo et al. / Energy Procedia 114 (2017) 3793 – 3804
Figure 7. Correlation of CO2 concentration x isotopic ratio. 7A represent the background; 7B represent the 3rd day of injection; 7C represent the 6th day of injection; 7D represent the post-injection day.
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5.
Conclusion After assessing the CO2 flow results in the study area was concluded that flow values increase when the injection rate increase. The same behavior is seen in the results of the analysis of CO2 concentration. The correlation of isotopic analysis were consistent with the results of concentrations and flow of CO2 and thus, it can be said that the CO2 breakthrough occurred from the 3rd day of injection, when the highest CO2 fluxes were obtained. The correlation between the concentration of CO2 and isotopic ratios, were able to demonstrate an integrated CO2 injected behavior throughout the campaign.
References [1] PETER, A. et al. Investigation of the geochemical impact of CO2 on shallow groundwater: design and implementation of a CO2 injection test in Northeast Germany. Environmental Earth Sciences, v. 67, n. 2, p. 335–349, 4 maio 2012. [2] Strunk Jr W, White EB. The elements of style. 3rd ed. New York: Macmillan; 1979.
ScienceDirect Energy Procedia 114 (2017) 3793 – 3804
13th International Conference on Greenhouse Gas Control Technologies, GHGT-13, 1418 November 2016, Lausanne, Switzerland
Integration results of soil CO2 flux and subsurface gases in the Ressacada Pilot site, Southern Brazil. Clarissa L. Meloa; Flávio S. Goudinhoa; Lia W. Bressana; Marcelo J. Constanta; Victor Hugo J. M. dos Santosa; Luiz Frederico Rodriguesa; Jessica P. Piresa; João Marcelo M. Ketzera; Andréa Cristina de C.A. Moreirab; Fátima do Rosáriob; Ana Paula S. Musseb. a
Pontifical Catholic University of Rio Grande do Sul – PUCRS – IPR – Institute of Petroleum and Natural Resources, Av. Bento Gonçalves, 4592, Porto Alegre - 90619-900, Brazil PETROBRAS – Petróleo Brasileiro S.A. – CENPES, Av. Horácio Macedo, 950, Rio de Janeiro – 21941915, Brazil
b
Abstract The first CO2 monitoring field lab at the Ressacada Farm, in the Southern region of Brazil, started in 2011 and until 2015 offered an excellent opportunity to run controlled CO 2 releases experiments in soil and shallow subsurface through vertical injection wells. This paper focus on the presentation and comparison of the results obtained at the last campaign realized at this site in August 2015. The results integrate a time-lapse monitoring experiment of CO2 migration in both saturated and unsaturated sand-rich sediments and soil, using soil CO2 flux measurements and subsurface gas analyses through CO2 concentrations (ppm) and carbon isotope ratios (δ 13C of CO2). The CO2 flux results in the studied area showed an increase in the flux values according to the increasing of injection rate and along the campaign are directed to the southwest portion of the area. However, even by injecting large amounts of CO2, fluxes are greatly reduced when it rains. The gas analysis also showed an increase in CO 2 concentrations according to the increasing of the injection rate mainly in the superficial levels of the monitoring wells (0.5m and 2m depth). The δ13C of CO2 found on the 3rd injection day showed the presence of CO2 injected and demonstrate that the sampling methodology with vacutainer vial was effective, since there is no atmospheric contamination. The correlation of isotopic analysis were consistent with the results of concentrations and CO2 fluxes and thus, it is clear that the CO2 breakthrough occurred from the 3rd day of injection, while were obtained the largest CO2 fluxes, the higher gas concentrations in the subsurface, as well as the industrial origin of δ 13C of CO2.
* Corresponding author. Tel.: +555133203689
E-mail address: [email protected]
© 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2017 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of GHGT-13. Peer-review under responsibility of the organizing committee of GHGT-13. Keywords: Monitoring, CO2, release, experiment;
1.
Introduction
Several CO2 controlled release experiments were performed at the Ressacada Farm in Florianópolis city, Southern region of Brazil (Figure 1), as a joint R&D project under the full sponsorship of PETROBRAS. The first CO2 monitoring field lab aimed to evaluate different monitoring tools with application purposes in geological carbon storage sites.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. 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 GHGT-13. doi:10.1016/j.egypro.2017.03.1510
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Clarissa L. Melo et al. / Energy Procedia 114 (2017) 3793 – 3804
Figure 1. Site location.
The first test was conducted in 2012 by a vertical well with the injection of CO2 occurring at a depth of 8 meters. As CO2 breakthrough occurred only after 13 days of injection the project team opted to use a shallower vertical well located in an area with geological conditions favoring a faster escape. Therefore, in 2013 it was held the second experiment, injecting around 32 Kg of CO2 continuously for 11 days in a vertical well with 3 meters depth and the results were much more satisfactory. The third experiment was realized in August 2015 during 12 days (1 background day, 10 injection days and 1 post-injection day) using the same vertical well built in 2013. In this campaign, with the methodologies and experimental techniques already established and a better knowledge of CO2 behavior in the studied area, it was injected a CO2 flow four times greater than in the first campaign. The tests started with flow rates of 150 g/hr, continuing with 300 g/h and reaching 400g/hr in the last 4 days of injection. During 10 days, it was injected four-cylinder totaling about 85 Kg of CO2. Measurements of soil CO2 emissions were done using two dynamic flow chambers covering 256 m2 of the studied area. The gas sampling was performed at 7 multi-level monitoring wells using a vacuum pump at 0.5m level and a peristaltic pump at 2, 4 and 6m depth (when detected groundwater). All these data were used to draw up contour maps enabling the characterization of CO 2 flux during the campaign and to demonstrate the presence of the injected CO2 in subsurface as well as prove their origin. The main goal of this paper is to present the comparison of soil CO2 flux measurements and subsurface gas analyses (CO2 concentrations and carbon isotope ratios). 2. Methods 2.1 Accumulation Chambers Soil CO2 emission, temperature and moisture were measured with two dynamic flow chambers, LI8100-A model (LI-COR) in a monitoring grid (Figure 2) with a total of 96 PVC collars covering 256 m2 of the study area. This grid was divided into two sides (A and B), each one with 48 collars with not regular distances between the collars: near the injection well the collars had intervals of 1 meter distance and away from the injection well 2 meters distance intervals. The CO2 concentration in the chamber was measured each second, taking an average reading time of 2 minutes per collar. Measurements were taken prior, during and after CO2 injection.
Clarissa L. Melo et al. / Energy Procedia 114 (2017) 3793 – 3804
Figure 2. Accumulation chambers monitoring grid. Numbers and characters are collars positions.
2.2 Subsurface gas sampling The gas sampling was performed in multi-level monitoring wells at 0.5 m deep with a vacuum pump (Figure 3) and 10 ml syringes that were totally filled with gas. Immediately after sampled, the gas was transferred to Vacutainer® vials and analyzed at the labs of the Institute of Petroleum and Natural Resources (IPR -PUCRS) for Gas Chromatography (GC) and Isotope Ratio Mass Spectrometry (IRMS). Samples of soil gas were collected before, during and after CO 2 injection and samples of injected CO2 were collected directly from the cylinder. Sampling of three water levels located in the saturated zone (2m, 4m, 6m) were performed with a peristaltic pump and a 10 mL syringe, transferred to Vacutainer vials and stored at 4°C until analysis at IPR labs. The parameters analyzed were CO and CO 2 and isotopic ratios 13C CO2.
. Fig.1. Gas sampling at 0.5m depth with syringe and vacuum pump.
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3. Results 3.1 Soil CO2 Flux Monitoring During the background survey, soil CO2 fluxes ranged between 0-47 µmol/m2/s. with the largest CO2 streams distributed to the southwest portion of the studied area (Figure 4A). CO2 fluxes started to change only 3 days after the beginning of injection, when the injection rate was increased from 150 g/h to 300 g/h. Significant variations in soil CO2 fluxes were observed in the area, especially in the southwest portion, reaching 98-351 µmol/m2/s in the 26B collar (Figure 4B). Despite the heavy rain that fell on the 4th day of injection, the flux values continued to increase. From the 6th day of injection when the rate increased to 400g/h, higher fluxes were observed in some collars near the injection well (1B=244 μmol/m2/s; 7B=172 μmol/m2/s), in addition to those values already observed in the southwest portion of the area (Figure 4C). From the 7th day by the end of injection (10th day), there was a clear trend of CO2 migration to the southwest area following the groundwater flow and exiting the flux chambers monitoring grid. The highest values were found in collars 26B (510 μmol/m2/s) and 45B (235 μmol/m2/s), as shown in Figure 4D. The post-injection survey already shows the reduction of CO 2 fluxes across the monitoring grid (Figure 4E).
Fig 4. Soil CO2 flux measurements (μmol/m2/s ) during the 3rd campaign at Ressacada Farm: 4A. Background survey; 4B. Survey on 3rd injection day; 4C. Survey on 6th injection day; 4D. Survey on 10th injection day; 4E. Post-injection survey.
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3.2 Subsurface Gas Monitoring 3.2.1 CO2 Concentration Measurements The evaluation of chromatographic results for subsurface gases collected in 4 levels of monitoring wells took into consideration the CO2 concentrations inside the cylinders used for injection as a reference for comparison and evaluation of data. These concentrations do not have the same values of the certificates of analysis provided by the supplier (99.5%). This difference occurs because the cylinder and the sample vial (Vacutainer) not exhibit the same internal pressure. In the cylinder, CO 2 is at a greater pressure than in the bottle. When a given amount of gas is transferred to another flask the tendency is that the molecules redistribute themselves in a new volume. Therefore, when the CO2 sampled from the cylinder is transferred to Vacutainer occurs a pressure lowering and the same amount of CO2 molecules that previously occupies a very small space, begins to hold a larger space, although the flask volume is smaller relative to the cylinder size. The samples ranged between 31% and 59% because the volume sampled difference in the cylinder-opening act. The larger the volume of CO2 collected, the greater the internal pressure and consequently higher concentration. At the levels 2, 4 and 6 meters, groundwater was sampled for headspace gas analysis, however the results represent the CO2 total concentrations (dissolved and undissolved in water). This occurs because gas bubbles were sampled concomitantly to the water and there is no accurate knowledge of this gas fraction in each sample, which did not allow obtaining the actual concentrations of CO2 dissolved in water. The analysis results may be seen in the Table 1. Table 1. Results of gas samples analysis (CO2 concentrations - ppm). N.D. = not detected
CO2 Concentrations (ppm) Well PM1
PM2
PM3
PM3B
PM4
PM4B
Level (m)
Background
Injection 1 day
3 day
6 day
10 day
Postinjection
0,5
N.D.
89,741
32,875
140,628
248,833
262,126
2
6,415
8,577
7,780
7,883
258,000
12,652
4
6,444
3,749
841
4,049
N.D.
1,724
6
3,542
N.D.
2,763
10,313
4,478
2,794
0,5
13,321
64,116
378,218
597,394
403,347
356,270
2
182
1,815
8,541
7,519
6,138
9,145
4
4,495
873
1,811
6,898
12,663
808
6
1,796
1,922
2,368
7,003
13,127
5,809
0,5
32,325
23,079
103,534
510,553
443,660
162,040
2
14,364
5,923
5,887
9,736
20,648
14,697
4
3,818
1,764
2,279
10,204
8,025
6,173
6
8,614
5,029
1,913
3,774
7,334
3,864
0,5
9,528
8,318
27,904
28,209
25,561
22,779
2
14,613
2,418
4,717
6,174
17,241
2,381
4
1,659
2,104
3,028
2,128
4,568
5,656
st
rd
th
th
6
4,233
1,792
7,246
12,385
1,096
4,582
0,5
18,014
10,460
38,535
281,040
454,509
423,320
2
5,934
3,415
1,935
8,633
10,447
6,798
4
7,393
5,650
1,748
132
1,682
5,381
6
4,344
1,735
853
2,005
8,176
2,517
0,5
20,124
15,633
17,724
29,898
11,383
1,579
2
3,649
859
699
2,167
6,995
3,087
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PM5
4
7,249
4,104
7,238
3,508
4,287
2,611
6
1,663
508
3,002
3,188
3,249
4,226
0,5
30,150
58,801
400,125
380,880
N.D.
228,644
2
7,533
N.D.
205,809
218,462
58,988
41,272
4
4,435
3,132
6,171
10,476
3,017
4,618
6
6,762
1,499
4,910
2,069
3,023
4,881
On Figure 5 shows CO2 concentrations obtained by chromatographic analysis for the 4 levels of monitoring wells in the background, 1st and 3rd injection days. Background values are very low, between 180 and 14000 ppm in the deeper levels and higher (32000 ppm) at the 0.5m level. On the first day of injection, it was possible to observe a slight increase in CO 2 concentration in the 0.5m level at PMs 1, 2 and 5. On the 3rd day, when the injection rate increased to 300 g/h, concentrations also increased significantly in the surface level of PMs 2 and 5 (378,217 ppm to 400,125 ppm, respectively), but also increased in the 2m level of PM 5, reaching 205,808 ppm. The 6th day of injection was marked by higher concentrations of CO2 in the surface (0.5 m) during the campaign (Figure 6), especially in PM 2 (597,393 ppm), PM 3 (510,553 ppm) and PM 5 (380,879 ppm). In 2m deep, PM 5 also reached its maximum concentration (218,462 ppm) on this day. With the injection stop, the CO2 concentrations on PM 5 - level 2m immediately decreased and became even lower on the post-injection survey. However, in the most superficial level, concentrations remained high during the post-injection measurements, but still lower than those measured on the injection days.
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Figure. 5. CO2 concentration in gasometric analyses. 5A represent the background; 5B represent the 3rd day of injection; 5C represent the 6th day of injection; 5D represent the post-injection day.
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3.2.2
Carbon Isotopic Ratios
The 13C isotopic ratio of CO2 provide us the origem of contribuites sources and can be used like a natural tracer of CO2 injected. Therefore, the 13C/12C isotopic ratio of samplers was correlated with inorganic standard Vienna Pee Dee Belemnite (VPDB), in a IRMS equipment, the results will be discussed below. The isotopic ratio of CO2 injected, showed values between -21.8 ‰ to -2.4 ‰, indicating the origin of fossil fuels. The isotopic signature of CO2 in subsurface, during the background period, showed values between -7,2‰ to -12,5‰ (Figure 6A). On the 3rd injection day, the isotopic ratio showed values between -7,37‰ to -22,3‰ (PM5, level 2 m), Figure 6B. On the 6th day of injection, the isotopic signatures of nearly all the PMs in the level of 0.5m, with the exception of PMs 3b and 4b, showed the presence of CO2 from fossil fuels, Figure 6C. The isotopic monitoring presented similar values on the post-injection, Figure 6D. All the results can be viewed on Table 2. Table 2. Isotopic signatures δ13C of CO2 (‰) obtained in samples from wells monitoring.
δ13C of CO2 (‰) Well PM1
PM2
PM3
PM3B
PM4
PM4B
PM5
Level (m)
Background
Injection 1 day
3 day
6 day
10 day
Postinjection
0.5 m
-11.50
-11.84
-10.80
-18.76
-21.12
-21.22
2m
-12.13
-12.22
-13.02
-13.29
-13.22
-13.90
4m
-11.28
-10.59
-11.37
-11.01
-11.96
-15.99
6m
-10.61
-8.30
-10.18
-9.68
-9.82
-11.43
0.5 m
-10.05
-16.66
-21.77
-22.26
-22.17
-21.84
2m
-12.50
-12.71
-12.96
-13.42
-12.75
-12.44
4m
-9.33
-9.29
-10.94
-11.19
-11.25
-9.27
6m
-7.43
-6.94
-10.26
-10.43
-10.52
-10.48
0.5 m
-10.48
-10.93
-18.42
-21.79
-22.17
-22.01
2m
-12.21
-12.31
-12.57
-12.91
-12.95
-12.89
4m
-9.97
-8.62
-10.12
-10.08
-11.51
-8.86
st
rd
th
th
6m
-9.25
-6.90
-9.07
-10.23
-9.93
-9.64
0.5 m
-9.60
-9.21
-9.12
-10.22
-14.92
-15.61
2m
-10.79
-11.42
-11.00
-11.56
-10.84
-10.72
4m
-9.83
-11.53
-9.27
-10.23
-9.17
-11.08
6m
-7.22
-8.95
-7.77
-6.94
-8.44
-8.55
0.5 m
-8.26
-8.36
-13.77
-21.55
-21.89
-21.70
2m
-9.99
-9.29
-10.93
-10.56
-10.79
-9.10
4m
-8.44
-7.36
-9.71
-11.08
-9.88
-9.18
6m
-7.31
-6.51
-7.37
-8.41
-8.80
-8.35
0.5 m
-8.86
-8.77
-8.53
-8.41
-9.76
-9.31
2m
-10.63
-8.90
-10.90
-10.55
-10.76
-8.76
4m
-9.08
-10.85
-9.99
-10.02
-10.29
-9.50
6m
-9.32
-10.47
-9.35
-9.75
-9.42
-7.20
0.5 m
-9.52
-15.27
-21.41
-22.00
-21.99
-21.76
2m
-10.63
-12.75
-22.30
-21.74
-22.12
-22.92
4m
-9.28
-8.91
-12.45
-15.03
-18.11
-9.20
6m
-7.98
-7.60
-9.42
-14.01
-14.27
-9.03
Figura 6. Isotopic ratio values. 6A represent the background; 6B represent the 3rd day of injection; 6C represent the 6th day of injection; 6D represent the post-injection day.
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4.
Integration results
In the following maps, the δ13C isotopic signature of CO2 obtained from IRMS, was represented by isovalue lines while CO2 concentrations are shown by color scale, Figure 7. The results of CO2 concentration showed an increase, starting from the 1st day of injection to post-injection, the majority of monitoring wells at depth of 0.5m. Concomitantly, the δ13C of CO 2 becomes more depleted in these wells in relation to the background (Figure 101) similar to values obtained in the CO2 samples injected (δ13C CO2 ≈ -22 ‰).
Clarissa L. Melo et al. / Energy Procedia 114 (2017) 3793 – 3804
Figure 7. Correlation of CO2 concentration x isotopic ratio. 7A represent the background; 7B represent the 3rd day of injection; 7C represent the 6th day of injection; 7D represent the post-injection day.
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5.
Conclusion After assessing the CO2 flow results in the study area was concluded that flow values increase when the injection rate increase. The same behavior is seen in the results of the analysis of CO2 concentration. The correlation of isotopic analysis were consistent with the results of concentrations and flow of CO2 and thus, it can be said that the CO2 breakthrough occurred from the 3rd day of injection, when the highest CO2 fluxes were obtained. The correlation between the concentration of CO2 and isotopic ratios, were able to demonstrate an integrated CO2 injected behavior throughout the campaign.
References [1] PETER, A. et al. Investigation of the geochemical impact of CO2 on shallow groundwater: design and implementation of a CO2 injection test in Northeast Germany. Environmental Earth Sciences, v. 67, n. 2, p. 335–349, 4 maio 2012. [2] Strunk Jr W, White EB. The elements of style. 3rd ed. New York: Macmillan; 1979.