ANLEC Project : Raman Spectroscopy detecting CO 2, SOx and NOx in Precipice Sandstone

Transcription

1 ANLEC Project 19: Raman Spectroscopy detecting CO, SOx and NOx in Precipice Sandstone Milestone 1.: Experiments and geochemical simulations of coinjection of CO, SO and NO L.G. Turner 1, J.K. Pearce 1, Sue D. Golding 1, G.A. Myers, Q. Morgan 1 School of Earth Sciences, The University of Queensland, QLD, Australia WellDog Pty Ltd. l.turner@uq.edu.au (L.G. Turner); j.pearce@uq.edu.au (J.K. Pearce) Date of original submission: 1 th July 1 Date of revised version submission: 1

2 Acknowledgements The authors wish to acknowledge financial assistance provided through Australian National Low Emissions Coal Research and Development (ANLEC R&D). ANLEC R&D is supported by Australian Coal Association Low Emissions Technology Limited and the Australian Government through the Clean Energy Initiative. The authors would also like to acknowledge the extensive experimental assistance provided by Dr. Dean Biddle (UQ) and assistance provided by the UQ Centre for Microscopy and Microanalysis (CMM), Advanced Water Management Centre (AWMC), Earth Sciences Geochemistry Laboratory and the Land and Agriculture Centre. The authors also thank Grant Dawson for his assistance in numerous discussions during the preparation of this report, and Dirk Kirste (Simon Fraser University, BC, Canada) for his assistance during geochemical simulations.

3 Executive summary Project 19: Raman Spectroscopy detecting CO, SOx and NOx in Precipice Sandstone, is aimed at supporting CO storage projects in Australian sedimentary basins, specifically the CTSCo Surat CO storage demonstration project. The specific objectives in SubProject 1 include: 1. Understand the identities and concentrations of the aqueous dissociation species of CO, SOx, and NOx in Precipice Sandstone groundwater for the Surat CCS Project.. Validation of likely Precipice Sandstone groundwater desktop and model outcomes with waterrock equilibration batch reactor experiments and ex situ analyses at Surat conditions.. Understand the likely change in concentration of CO, SO X and NO X dissolution species arising from the test injection of a GHG Stream derived from a Wallooncoalfired Queensland Power Station (Millmerran).. Laboratory batch reactor (and geochemical modelling) validation of fate, and change in concentration, and identities of dissolution products in Precipice Sandstone reactions with ex situ sampling and analysis. Including NOxCO waterprecipice Sandstone core reactions, and SOxNOxCO waterrock reactions using a Wallooncoalfired Queensland Power Station simulated gas mixture. This report also accompanies Milestone Reports.1 and.. The Milestone 1. Report (Turner et al., 1) provided a desktop study of baseline groundwater composition of the Precipice Sandstone within close proximity to the West Wandoan 1 well (subproject 1.). Equilibration experiments with N and Precipice Sandstone core samples revealed significantly larger sulfate (SO ) concentrations than those reported in the desktop study (subproject 1.). Additional experiments with a CO /NO gas mix confirmed the presence of both nitrate (NO ) and nitrite (NO ) species (subproject 1.). The concentration of NO was significantly higher than NO, indicating the formation predominantly of dissociated HNO over HNO. This report discusses batch experiments of additional Precipice Sandstone core samples with CO /NO, CO /SO and CO /SO /NO gas mixtures. All experiments were performed at sequestration conditions relevant to the Surat Basin ( C and 1 MPa). Geochemical modelling results are also discussed. Dissolved NO and SO were the dominant dissociation species observed during CO /NO, CO /SO /NO and CO /SO experiments. Mineral dissolution and some minor mineral precipitation (predominantly in the form of Feoxides) was also observed on Precipice Sandstone. The reported concentrations of both NO and SO were greater than the projected limit of detection (LOD) for the DRRS tool (Myers et al., 1b). Geochemical modelling studies with Geochemist s Workbench

4 (GWB) were able to simulate elemental mobilisation reasonably well. However, the predicted concentration of NO and NH were consistently larger than those measured experimentally. The concentration of NO displayed a distinctive first order type decline during CO /NO and CO /SO /NO experiments. It was postulated that Fe, released into solution through the corrosion of Febearing minerals such as FeMgchlorite, enabled reduction of NO to Feoxides and N O or N gas. This is an important observation, since insitu Raman spectroscopy may detect very little NO in solution, whilst NO concentration would remain relatively high. Geochemical simulations for the reaction of Precipice Sandstone core samples were performed. The models predicted mineral dissolution and precipitation reasonably well, though were less able to predict the variation in concentration of NOx species, in particular NO. This is an important finding as the fate of N species is currently not well constrained in geochemical models in general. In the Evergreen Formation, some lower sections are calcite cemented or Feclay rich. CO or CO saturated fluid may interact with the lower sections of the Evergreen Formation to release Fe. If the tool DRRS is used on the Evergreen Formation or in the overlying Hutton Sandstone etc. for leakage detection, the concentration of NOx (and SOx) may be different through interaction with the more reactive rock packages (changing the necessary LOD). Therefore we suggest in future further experiments and geochemical models to determine the NOx and SOx products and concentrations for the Evergreen Formation (and potentially the Hutton Sandstone).

5 List of Figures Figure 1. Photographs of whole core sections and cubic subsample surface of Precipice Sandstone samples used during batch leaching experiments Figure. SEM images of WC191 before (a,b) and after (c) reaction with CO /NO Figure. WC191 offcuts and PEEK sample holder following reaction with CO /NO... 1 Figure. SEM images and EDS spectra of WC11 before (a) and after (bd) reaction with CO /SO at 1 MPa and 1 C Figure. SEM images of WC before (a,b) and after (c) reaction with CO /NO... 1 Figure. SEM images of WC before (a,b,d) and after (c,e) reaction with CO /SO /NO Figure. SEM images of WC11 before (a,b) and after (c) reaction with CO /SO /NO Figure. Incremental water chemistry of selected elements (a,b), dissolved nitrogen species (c) and bicarbonate (d) during reaction of WC191 with CO /NO.... Figure 9. Incremental water chemistry (a, b), dissolved sulfur species (c) and HCO concentration (d) during reaction of WC11 with CO /SO.... Figure 1. Calculated phase stability diagram of versus log fo (g) for reaction of WC11 with CO /SO at C and 1 bar.... Figure 11. NOx species evolution during reaction of WC with CO /NO.... Figure 1. NOx (a) and SOx (b) species evolution during blank reaction with CO /SO /NO and low salinity water with no rock core.... Figure 1. Incremental water chemistry of selected elements during reaction of WC with CO /SO /NO.... Figure 1. NOx (a) and SOx (b) species evolution during reaction of WC with first N then CO /SO /NO gas.... Figure 1. Incremental water chemistry of selected elements during reaction of WC11 with CO /SO /NO... 9 Figure 1. NOx (a) and SOx (b) species evolution during reaction of WC11 with first N then CO /SO /NO.... Figure 1. NO (left column) and Fe (right column) concentration changes over time during CO /NO (ab) and CO /SO /NO (cd) experiments Figure 1. NO evolution during (a) CO /NO and (b) CO /SO /NO experiments.... Figure 19. Influence of initial sample Fe content (as measured by whole rock digestion) on initial measured NO concentration (A)... Figure. SOx species evolution for CO /SO /NO experiments, (a) SO, (b) SO, (c) S O and (d) S....

6 Figure 1. Modelled (lines) and experimental values (icons) during experiments with different rock cores and (a) CO /NO, (b) CO /SO and (c) CO /SO /NO.... Figure. Geochemical simulation results (dashed lines) and experimental data (symbols) during reaction of WC11 with CO /NO... Figure. Geochemical simulation results (coloured lines) and experimental data (symbols) during reaction of WC11 with CO /SO... Figure. Geochemical simulation results (coloured lines) and experimental data (symbols) during reaction of WC191 with CO /NO... 1 Figure. Geochemical simulation results (coloured lines) and experimental data (symbols) during reaction of WC with CO /NO... Figure. Geochemical simulation results (coloured lines) and experimental data (symbols) during reaction of WC11 with CO /SO /NO... Figure. Geochemical simulation results (coloured lines) and experimental data (symbols) during reaction of WC with CO /SO /NO... Figure A1. Incremental water chemistry for WC11 reaction with CO /NO... 1

7 List of Tables Table 1. Expected SOx and NOx composition of CO stream at West Wandoan 1 site... 1 Table. Mineralogy (wt.%) of samples based upon semiquantitative XRD and SEM studies. WC11 has been previously reacted with CO /NO... 1 Table. Summary of experiments performed with CO gas mixtures Table. Summary of initial water composition and input conditions for GWB simulations Table. Kinetic parameters used in script files GWB modelling Table. Summary of initial, postn equilibration and end fluid composition (mg/l) and during batch leaching experiments.... Table. Summary of fitting parameters for NO reduction during CO /NO and CO /SO /NO experiments.... Table. Summary of mineral dissolution and new phases precipitated from GWB simulations.... Table 9: Summary of the initial (t = days) and maximum concentration of SOx and NOx dissociation species detected during blank and core sample experiments with CO /NO, CO /SO and CO /SO /NO....

8 Contents Acknowledgements... Executive summary... List of Figures... List of Tables... Contents... 1 Introduction... 1 Methodology Batch reactor experiments Core sampling Experimental procedure Analytical methods Geochemical modelling... 1 Results and discussion SEMEDS Water chemistry WC191 CO /NO..... WC11 CO /SO..... WC CO /NO..... CO /SO /NO blank reaction..... WC CO /SO /NO..... WC11 CO /SO /NO.... NOx species evolution Fe and NO..... Fe and NO..... Influence of O fugacity on NOx speciation...

9 . SOx species evolution.... GWB modelling WC11 CO /NO..... WC11 CO /SO..... WC191 CO /NO..... WC CO /NO WC11 CO /SO /NO..... WC CO /SO /NO.... SOx and NOx dissociation species concentrations... Conclusions and recommendations... References... Appendix... Appendix I. Geochemical modelling parameters... Appendix II. Incremental water chemistry for WC11 reaction with CO /NO

10 1 Introduction The separated CO stream from a post combustion capture (PCC) plant is expected to contain a proportion of nitrogen oxides (NOx) and sulfur oxides (SOx) impurities (Table 1). The accurate subsurface distribution and impact of low concentrations of impurities such as NOx/SOx and CO in groundwater will be a significant indicator of the extent of the subsurface GHG plume derived from coalfired power stations. Groundwater chemistry is known to vary both experimentally and in a field injection scenario during a relatively short period (Kirste et al., 1). Thus, in situ and rapid determination of CO /SOx/NOx dissociation products would be highly beneficial. WellDog have developed a Downhole Reservoir Raman Spectroscopy (DRRS) tool that has been used extensively to analyse dissolved methane insitu, and to a lesser extent, nitrogen and carbon dioxide in coal seam reservoirs. The Milestone.1 report provided a Desktop study of the expected dissociation species during sequestration of a CO /SO /NO (Myers et al., 1a). Thirteen target compounds were assessed, which were identified as important dissolution and dissociation products of SOx, NOx, and CO derived from the injection of GHG streams into groundwater. Unique Raman spectra for all but one dissociation product were identified, thereby highlighting the suitability of the DRRS tool for sequestration type scenarios. The Milestone 1. report provided a desktop study of baseline levels of SOx and NOx in solution via a thorough investigation of Precipice Groundwater composition in sites within close proximity to the West Wandoan 1 well (Turner et al., 1). The report also discussed the distribution of NOx dissociation species during experiments with CO /NO gas mixture, water (similar to the expected downhole composition) and Precipice Sandstone samples from the West Wandoan 1 well (drilled by CTSCo for a CO injection feasibility study in the Surat Basin). This report delivers results from additional experiments with CO /NO, CO /SO, and CO /SO /NO gas mixtures with Precipice Sandstone core samples of varying composition. Geochemical simulations using Geochemist s Workbench (GWB) software are also discussed. Table 1. Expected SOx and NOx composition of CO stream at West Wandoan 1 site based upon review of separated CO stream composition presented in Milestone 1. (Turner et al., 1). Gas NO SO 1 Composition (ppm) N.1 CO balance 1

11 Methodology.1 Batch reactor experiments.1.1 Core sampling Core samples for batch leaching experiments were cut from three different depths from the Precipice Sandstone core in the West Wandoan 1. The subsamples from each region consisted of a 1x1x1 mm cube and a sample offcut of variable dimensions to form a total sample mass of approximately 1 g. Whole core images indicating the regions from which subsamples were cut are shown in Figure 1. The samples are summarised as follows: WC11 and WC11 were sampled from a highly quartzose region ( m) adjacent to that used during a previous CO /NO experiment (Turner et al., 1). WC191 was sampled from a clay rich baffled region of the Precipice Sandstone at a lower depth interval ( m). WC and WC were sampled from an additional quartzose region at a lower depth interval ( m). The mineralogy of unreacted offcuts is shown in Table. Mineralogy was initially quantified by Xray diffraction (XRD). Since some reactive minerals are present in trace amounts not sufficiently large enough to be quantifiable by XRD (or QEMSCAN), SEMEDS was also performed. Further sample characterisation by SEMEDS revealed the presence of minerals in trace amounts that may contribute significantly to the observed water chemistry following batch reactions with CO /SOx/NOx. Trace minerals included Kfeldspar, illite/muscovite, ankerite, FeMgchlorite, calcite and sulfates such as arcanite (K SO ) and mirabillite (Na SO :1H O). WC11 WC m 11. m 1.1 m 1. m 111. m WC WC m WC Figure 1. Photographs of whole core sections and cubic subsample surface of Precipice Sandstone samples used during batch leaching experiments. Highly quartzose regions include WC11, WC11, WC and WC. WC191 was sampled from a clay rich baffled unit. 11

12 Table. Mineralogy (wt.%) of samples based upon semiquantitative XRD and SEM studies. WC11 has been previously reacted with CO /NO (labelled P11B in Milestone 1. report).approximate sampling depth is shown in brackets. (11 m) (11m) (11m) (1 m) (111 m) (111m) Mineral WC11 WC11 WC11 WC191 WC WC Chalcedony Kfeldspar Kaolinite Illite.1.1 Muscovite...1 Calcite.1.E Ankerite. FeMgChlorite Phlogopite.1 Arcanite.1 Mirabilite..1. Experimental procedure Batch experiments were performed using unstirred ml Parr reactors with custombuilt thermoplastic (PEEK) vessel liners, sample holders and a dip tube assembly. The experimental procedure has been used and described in a number of previous investigations (Farquhar et al., 1, Dawson et al., 1, Pearce et al., 1a, Pearce et al., 1b, Turner et al., 1) and summarised below: Core sample (1 mm cube and offcut) placed within PEEK holder in high pressure vessel containing 1 ml of fluid; The sample line was purged and pressurised with N to remove any residual oxygen and the pressure and temperature raised to 1 MPa and C to simulate downhole conditions in the Surat Basin; N was replaced with the reactive gases (CO /NO, or CO /SO or CO /SO /NO) and aliquots of fluid regularly sampled for the entire reaction period (up to days). The various analytical techniques employed in this study are discussed in Section.1.. A summary of the experiments performed is shown in Table. The composition of NO and SO in the CO /NO and CO /SO /NO gas mixtures were similar to the expected composition at the West Wandoan 1 site (Table 1). The following should be noted: Since no water samples were obtained at WW1 well, initial CO /NO experiments (WC11, WC and WC191) utilised an initial water composition of 1 ppm NaCl/1 ppm 1

13 NaHCO to maintain consistency with previous experiments while the groundwater of nearby sites was determined in a previous literature study (Turner et al., 1). Experiments with CO /SO /NO utilised lower salinity water expected to be more representative of the West Wandoan 1 site based on samples from nearby bores i.e. ppm NaCl/1 ppm NaHCO. A SO /CO experiment was performed to check expected SO product identities while waiting on delivery of the CO /SO /NO gas mixture. The concentration of SO in the WC11 experiment was approximately 1x higher than expected, as current amine based capture systems have limited tolerance to SO and generally require <1 ppm) (Pearce et al., 1a). It is noted that the higher concentration would cause more significant mineral dissolution, and provide an upper limit for SOx dissociation species. All core samples were initially reacted with N (at C and 1 MPa) for up to 1 days in order to assess waterrock interactions prior to the introduction of the reactive gas mixture. However the first reaction performed, WC11, had a separate N waterrock soak. Table. Summary of experiments performed with CO gas mixtures. All experiments were performed at C and 1 MPa. Sample Depth Fluid (ppm) Gas (ppm) Duration ICPOES Anions SEMEDS (m) NaCl NaHCO SO NO CO (days) Blank n/a 1 1 balance yes yes n/a WC balance yes yes yes WC balance 1 *1 yes yes yes WC balance 1 *1 yes yes yes WC balance * yes yes yes WC balance * yes yes yes WC balance * yes yes yes Blank n/a 1 1 balance yes yes n/a *1 Included days of equilibration with N * Included 1 days of equilibration with N..1. Analytical methods During the experiments fluid was incrementally sampled over the reaction period and analysed for: and conductivity via a TPS WP1 meter and probes (error of ±.1). Dissolved elemental concentration (Al, Ca, Fe, K, Mg, Mn, Na, S and Si) via a Varian Vista Pro ICPOES on sampled aliquots acidified to % HNO. Dissolved sulfur species (SO, SO, S O, S ) and Cl concentration via a compact Dionex ICS ion chromatograph with an AD absorbance (nm) and a DS heated 1

14 conductivity detector ( o C). Aliquots were preserved with a sulphide antioxidant buffer (SAOB) prior to analysis (KellerLehmann et al., ). Dissolved nitrogen species (NO, NO and NH ) via flow injection analysis (FIA).. Geochemical modelling Batch reactor experiments were modelled using Geochemist s Workbench (GWB) software. Kinetic models were constructed using the thermo.com.v.rco S.dat database. A CO fugacity of. bar was calculated based upon a solubility model for. mol/kg NaCl at C and 1 bar (Duan and Sun, ). The amount of either NO(g) or SO (g) added was guided by the experimentally measured concentration of SOx and NOx dissociation species. The aqueous species NH (aq), N (aq) and N were suppressed in the geochemical model in order to allow the formation of NO and NO observed experimentally. Additional basis parameters are listed in Table. The water composition after days of equilibration with N was used for WC11 and WC191, and after 1 days N equilibration for WC, WC11 and WC. The input water composition for WC11 was modified to match a previous experiment with N only, as reported in Milestone.1. The input mineralogy for all samples was based upon a combination of semiquantitative XRD, SEM EDS and water chemistry data from batch experiments (see Table ). Chalcedony was used a proxy to quartz in order to increase simulated SiO (aq) values to match experimental data. The use of chalcedony is consistent with previous modelling of the Precipice Sandstone (Dawson et al., 1, Farquhar et al., 1, Pearce et al., 1a, Haese et al., 1). This polymorph was also recently employed by Hutcheon et al. (1) to model CO storage in the Weyburn site. Kinetic modelling parameters are listed in Table and described in more in Appendix I. The initial mineral surface area values (A s ) in Table were altered in order to allow data fit with the experimentally measured values. Reactive surface areas were generally increased 1x for the clay minerals and 1x for carbonate and sulfate minerals, consistent with the work of Pearce et al. (1a) and following from White and Brantley (199). A number of GWB modelling studies with pure CO (Farquhar et al., 1, Dawson et al., 1) and CO /SO (Pearce et al., 1a, Pearce et al., 1b, Dawson et al., 1, Haese et al., 1, Haese et al., 1) have been published, though this is the first of its kind to investigate CO /NO and CO /SO /NO interactions. 1

15 Table. Summary of initial water composition and input conditions for GWB simulations. All values are in mg/kg, unless otherwise stated. NO(g) and SO (g) values represent the cutoff point for their respective addition according to experimentally measured NOx or SOx in solution. WC11 WC11 WC191 WC WC11 WC Parameter CO /NO CO /SO CO /NO CO /NO CO /SO /NO CO /SO /NO H O (kg) Al Ca Cl Fe HCO K Mg Na SiO (aq) SO NH (aq) CO (g) (fugacity) O (g) (log fugacity)... NO(g) (mmol) SO (g) (mmol) Measured Calculated EC (us/cm) Table. Kinetic parameters used in script files GWB modelling. Arcanite and mirabilite employed GWB inbuilt script functions. Mineral K (acid) E a(acid) n K (neut) E a(neut) A s 1 K (precip) (mol/cm /s) (kj/mol) (mol/cm /s) (kj/mol) (cm /g) (mol/cm /s) Chalcedony 1.E1. 1 K (diss) E1 Kfeldspar.1E E1. 1 K (diss) E1 Kaolinite.9E1.9..1E1. K (diss) /1 E1 Illite 1.91E1...91E 1. K (diss) E1 Muscovite 1.E1...E1. K (diss) E1 Calcite.1E E1. 1 K (diss) 1E1 Ankerite 1.9E..9 1.E1. 1 K (diss) /1e E1 Siderite 1.9E..9 1.E1. 1 K (diss) E1 FeMgChlorite 1.E E1 9. K (diss) E1 Hematite.E E19. 1 K (diss) 1E1 Arcanite 1.E1 1 Mirabilite 1.E1 1 Pyrite.E E9.9 1 K (diss) E1 1 Initial value subsequently modified T 1

16 Results and discussion.1 SEMEDS SEM images of unreacted core WC191 revealed minor KCa sulfate (Figure a) and more abundant quartz, kaolinite and muscovite. Muscovite appeared to show no significant morphological changes following reaction with CO /NO (Figure b,c). A brown precipitate was observed on the PEEK sample holder following reaction, possibly indicating the formation of Feoxides (Figure ). Similar observations were made following a CO /NO experiment with a clay rich Evergreen sample from the West Wandoan 1 well (Tanaka et al., 1a). However, these precipitates were not observed on the surface of WC191 during the post reaction SEM survey and may have been fine coatings in too low and abundance. Similar brown Feoxide coatings were observed elsewhere in CO /O /SO reactions of WW1 cores (Dawson et al., 1). SEM images of unreacted WC11 revealed a primary quartzose structure with minor rutile and chlorite (Figure a), and pore filling kaolinite. Fesulphide precipitation was observed following reaction in CO /SO, primarily in the regions concentration with high Fetype clays (Figure b, c). Feoxide precipitation of varying morphology was also observed (Figure d). WC and WC contained predominantly quartz and muscovite (Figure a), with lesser amounts of Kfeldspar, kaolinite, rutile and Tibearing oxyphologopite (Figure b). Oxyphologopite has also been previously observed in Hutton Sandstone and Evergreen Formation samples from the Chinchilla well (Farquhar et al., 1). No obvious alteration of kaolinite in WC (Figure b,c) and oxyphologopite in WC (Figure c) was observed following reaction with CO /NO and CO /SO /NO respectively. Minor Fesulphide coating of a silicate phase was also observed in WC (Figure d). Fesulphides have rarely been observed in previous SEM surveys of Precipice Sandstone samples. The dashed highlighted area in Figure e following the reaction of WC with CO /SO /NO indicates minor corrosion. Minor corrosion of Ferich chlorite was observed in WC11 following reaction with CO /SO /NO (Figure a,b). Similar morphological changes were observed following reaction of an adjacent Precipice Sandstone sample (WC11) with CO /NO, as reported in Milestone 1.1 (Turner et al., 1). Overall, the mineral morphological changes observed following experiments with CO /NO and CO /SO /NO were minor. The reaction of WC11 with CO /SO appeared to show the most significant changes, predominantly in the form of Fesulphide and Fehydroxide precipitants. 1

17 Significantly longer reaction periods would likely be required in order for visible quartz alteration, for example, to occur (Rathnaweera et al., 1). (a) WC191 preco /NO (b) WC191 preco /NO (c) WC191 postco /NO Figure. SEM images of WC191 before (a,b) and after (c) reaction with CO /NO. S = KCa sulfate, Q = quartz, M = muscovite and K = kaolinite. Figure. WC191 offcuts and PEEK sample holder following reaction with CO /NO. The majority of the brown precipitate (indicator of Feoxide) is dispersed on the surface of the PEEK sample holder. 1

18 Counts Counts (a) WC11 preco /SO (b) WC11 postco /SO 1 9 Si Al Fe ONa S Cl K Ca Ti Fe Fe kev (c) WC11: postco /SO (d) WC11: postco /SO Al Si Fe Fe O S Cl Fe kev Figure. SEM images and EDS spectra of WC11 before (a) and after (bd) reaction with CO /SO at 1 MPa and 1 C. Ti = rutile, Ch = FeMg chlorite, Q = quartz, Fe = Feoxides and Fesulphides. (a) WC pre CO /NO (b) WC pre CO /SO /NO (c) WC pre CO /SO /NO Figure. SEM images of WC before (a,b) and after (c) reaction with CO /NO. Q = quartz, M = muscovite, Ti = rutile and K = kaolinite. 1

19 Counts (a) WC pre CO /SO /NO (b) WC pre CO /SO /NO (c) WC post CO /SO /NO (d) WC pre CO /SO /NO (e) WC post CO /SO /NO 1 EDS spot analysis: 1 9 Si S Fe Fe O Al Ti Fe kev Figure. SEM images of WC before (a,b,d) and after (c,e) reaction with CO /SO /NO. EDS spot analysis of Fesulphide mineral in (e) also shown. M = muscovite, K = kaolinite, Ti = rutile, Ox = oxyphlogopite (Ti bearing) and S = Fesulphide. Dashed regions in (e) highlight some areas of minor Fesulphide corrosion. (a) WC11 pre CO /SO /NO (b) WC11 pre CO /SO /NO (c) WC11 post CO /SO /NO Figure. SEM images of WC11 before (a,b) and after (c) reaction with CO /SO /NO. K = kaolinite, Ch = Ferich chlorite, Q = quartz, Ti = rutile.. Water chemistry A summary of experimental water chemistry during batch experiments is shown in Table. Data for the WC11 experiment with CO /NO (as previously discussed in Milestone 1.) is shown for comparison. Incremental water chemistry data for WC11 is also shown in Appendix II for further reference. All major dissolved cations increased following reaction with either CO /NO, CO /SO or CO /SO /NO. The is significantly lower in the CO /SO experiment in comparison to CO /NO ( compared to.), due to the production of the strong sulfuric acid, which can be generated via disproportionation (Eq. 1), in the presence of O (Eq. ) or an oxidising agent such as Feoxide minerals (Eq. ) (Pearce et al., 1a): 19

20 SO (g) H O HSO H H S (1) SO (g) Fe O (Feoxide) H HSO H Fe H O () SO (g) H O 1/O (g) HSO H () From Table, elemental mobilisation from the rock cores is greatest for WC11 and lowest for WC. Changes in incremental cation and anion chemistry are described in the proceeding sections. Table. Summary of initial, postn equilibration and end fluid composition (mg/l) and during batch leaching experiments. WC191 and WC11 were equilibrated with N for days prior to injection of CO /NO and CO /SO respectively, whereas WC11, WC and WC were equilibrated for 1 days prior to the injection of CO /SO /NO or CO /NO. Sample Time Gas (days) Al Ca Fe K Mg Mn Na S Si WC CO /NO WC CO /NO WC CO /SO WC11 1. <DL <DL <DL <DL <DL <DL.1 <DL <DL CO /SO /NO. <DL. 1.. <DL WC 1.9 <DL <DL <DL <DL <DL <DL. <DL.1 CO /NO. <DL <DL <DL. <DL WC 1. <DL <DL <DL <DL <DL <DL.1 <DL <DL CO /SO /NO. <DL <DL.9.9 <DL WC191 CO /NO The concentration of Ca, K and S increased immediately during WC191 equilibration with a low salinity water and inert N (Figure a) due to the dissolution of CaK type sulfates. The increase was more gradual following the introduction of CO /NO, and remained relatively stable after approximately 1 days. Concentration of Si and Fe both declined from days but increased thereafter (Figure b). Of the minor elements, Si concentration was highest. The increase in Al during CO /NO reaction was minor and remained < mg/l throughout the experiment, indicative of the low reactivity of kaolinite and muscovite. It has been suggested that muscovite reactivity in

21 CO /NO is equivalent to weathering processes in low temperature and acidic environments (Wilke et al. (1)). The increase in Mg over time is thought to be due to the minor corrosion of Mg bearing clays e.g. FeMgchlorite. These were not observed during SEMEDS scans and are thought to be present in only minor amounts. The dissolved concentration of NO increased to approximately 1 mg/l during N equilibration with low salinity water and WC191 core, and up to mg/l days after CO /NO gas injection (Figure c), indicating that HNO formation and dissociation to NO and H had taken place rapidly in solution. NO declined to mg/l after days before gradually increasing up to 1 mg/l for the remainder of the experiment. NH was <1 mg/l throughout the experiment and NO only increased above 1 mg/l from to days reaction with CO /NO. This suggests that HNO is unstable in solution and HNO is preferentially formed and dissociates to NO. The concentration of HCO increased from mg/l at the start of CO /NO injection up to a maximum of 1 mg/l after 1 days (Figure d). It is possible that the high variability of HCO was due to the slow exsolving of CO from solution after sampling. Solution declined from. to. following CO /NO injection, due to the generation of carbonic and nitric acid. Solution buffering was minimal, consistent with the low carbonate content present in WC191. 1

22 Concentration (mg/l) Concentration (mg/l) Concentration (mg/l) Concentration (mg/l) (a) Ca K S Al Fe Mg Si N CO /NO N CO /NO (b) (c) N NO NO NH CO /NO 1 1 (d) N HCO CO /NO Figure. Incremental water chemistry of selected elements (a,b), dissolved nitrogen species (c) and bicarbonate (d) during reaction of WC191 with CO /NO... WC11 CO /SO The concentration of dissolved Ca, K and S increased during equilibration of WC11 with N due to the dissolution of residual CaK sulfates (as in the reaction of WC191) (Figure 9a). A further increase in K was not observed after injection of CO /SO, suggesting complete dissolution of CaK sulfates. However, a minor increase in Ca concentration from 11 to mg/l was observed during the first days of CO /SO reaction. This was mirrored by a gradual increase in Mg from. to mg/l over the same period (Figure 9b). This suggests minor corrosion of CaMgFe clays or ion exchange may have occurred during this period. The concentration of Al and Si increased rapidly up to day of CO /SO injection after which their rate of increase declines. The concentration of Al is greater than Si throughout CO /SO injection, suggesting greater corrosion of kaolinitic type clays or incongruent dissolution. The increase in Fe from the corrosion of Ferich clays was most significant for the first days of CO /SO reaction (Figure 9a). Subsequently Fe decreased from a maximum of 1 mg/l to

23 Concentration (mg/l) Concentration (mg/l) Concentration (mg/l) Concentration (mg/l) mg/l after days. The decline in Fe was mirrored by a decline in S over the same period, indicating pyrite precipitation via the following reaction (De Silva et al., 1): Fe (aq) SO (aq) HS FeS H O () The modelled phase stability diagram for the FeCO SO system provides information as to the final state of the minerals containing Fe, S and CO (Figure 1). This diagram indicates that pyrite is the only thermodynamically stable mineral at the final experimental conditions. Pyrite precipitation was also confirmed in the post reaction SEM images (Figure b d). Hematite precipitation is more likely to occur at higher and O fugacity, as confirmed by the stability diagram in Figure 1 and observed elsewhere experimentally by Renard et al. (1). (a) Ca Fe K S (b) Al Mg Mn Si 1 N CO /SO 1 N CO /SO (c) SO SO SO S 1 N CO /SO (d) 1 1 HCO 1 N CO /SO Figure 9. Incremental water chemistry (a, b), dissolved sulfur species (c) and HCO concentration (d) during reaction of WC11 with CO /SO.

24 log f O (g) 1 9 Fe HSO SO S Fe H S(aq) Hematite Pyrite Siderite 1 bar C log(a Fe ) =. log(a SO ) =. fco (g) = bar HS S Diagram Fe, T = C, P = 1 barș a [main] = 1., a [H O] = 1, f [CO (g) ] = , a [SO ] = 1. ; Suppressed: ( species) Figure 1. Calculated phase stability diagram of versus log fo (g) for reaction of WC11 with CO /SO at C and 1 bar. The black boxes show mineral stability fields and red boxes S speciation in solution. The activities of Fe and SO were computed using the Spec module of GWB using their experimentally measured concentration as the input. The green circle denotes the position of the system at the end of the experiment, indicating that pyrite is thermodynamically stable at these experimental conditions... WC CO /NO Changes in incremental cation release during the reaction of WC with CO /NO are shown in Figure 11ac. Major cations Na, K and S all increased during N equilibration (Figure 11a), likely due to the dissolution of residual sulfatetype minerals. All cations increased and decreased from. to.1 during the initial period of CO /NO injection. Solution increased from.1 after 1 day to. after days, indicating some minor buffering by mineral dissolution. Si had the largest relative increase in concentration, followed by Fe and Ca (Figure 11b). Minor elements Mg, Mn and Al showed some incongruent dissolution (Figure 11c). Incremental NOx dissociation species concentration for up to days reaction in CO /NO are displayed in Figure 11d. NO increased up to a maximum mg/l after days, before declining to mg/l after days then returning to mg/l at days. The variable nature of NO concentration was observed in WC191 (Figure c), albeit over a shorter timescale. NO increased to. mg/l after 1 day, before declining exponentially and falling below.1 mg/l after 1 days. The rate of NO decline was similar for all CO /NO experiments (WC11, WC191 and WC). A number of studies have discussed control by Fe on NOx speciation. This is discussed further in Section..

25 Concentration (mg/l) Concentration (mg/l) Concentration (mg/l) Concentration (mg/l) (a) K Na S N CO /NO (c) Al Mg Mn N CO /NO (b) 1 (d) 1 1 NO NO NH 1 N N Ca Fe Si CO /NO CO /NO Figure 11. NOx species evolution during reaction of WC with CO /NO. Note that the initial water solution contained 1 ppm NaCl and 1 ppm NaHCO... CO /SO /NO blank reaction Little is known about NOx or combined NOx and SOx behaviour at CO storage conditions. Blank experiments containing no rock core with CO /NO/SO and low salinity water were performed to provide a better understanding of NO and SO dissociation behaviour in water at high pressure and temperature. It should be noted that the water salinity during CO /SO /NO experiments was slightly lower than that used during previous CO /NO experiments i.e. ppm NaCl/1 ppm NaHCO instead of 1 ppm NaCl/1 ppm NaHCO. A study by Ting et al. 1 was performed at much lower temperature and pressure to investigate reactions in CO capture systems. Although the conditions are different, several reactions including NO were assumed to occur. proceed as follows (Ting et al., 1): The relevant reactions within a CO /SO /NOwater system may NO(g) O (g) NO (g), slow () NO (g) N O (g), fast ()

26 Concentration (mg/l) Concentration (mg/l) NO (g) H O(l) HNO (aq) HNO (aq), slow () HNO (aq) HNO (aq) NO(g) H O(l), fast () CO (aq) H O HCO H (9) NO (g) SO (g) NO(g) SO (g), fast (1) SO (aq) H O(l) H SO (aq) (11) NO formed during Reaction () acts as a catalyst for the conversion of SO to H SO in R1 and R11. Assuming all the dissolved NO and SO formed HNO and H SO, the concentration of NO and SO in solution would be approximately mg/l and 1 mg/l respectively. In the blank experiment performed here, NO concentration increased up to mg/l after day 1 (Figure 1a), indicative of near complete dissolution of NO in solution and conversion to HNO (R). NO declines slightly to 1 ± 1 mg/l from day to, before increasing to mg/l after day. NO concentration remained <1 mg/l throughout the reaction, whilst NH was < mg/l. SO increased up to 1 mg/l after day 1, also indicative of near complete dissolution of SO in solution. However, SO subsequently declined to. mg/l up at day, where it remained stable until the termination of the experiment. This shows that more complicated processes are occurring at CO storage conditions than suggested by Ting et al. (1) at lower PT conditions. (a) NO NO NH (b) 1 SO SO SO S Figure 1. NOx (a) and SOx (b) species evolution during blank reaction with CO /SO /NO and low salinity water with no rock core... WC CO /SO /NO Changes in incremental water chemistry during the reaction of WC with CO /SO /NO are shown in Figure 1. The addition of CO /SO /NO at days resulted in a reduction from. to. and a general increase in ions released into solution. The increase in K and S was most significant (Figure

27 Concentration (mg/l) Concentration (mg/l) Concentration (mg/l) 1a), followed by Si and Ca (Figure 1b). The increase in Fe was minor (Figure 1b) and only slightly greater than the value measured after 1 days with N only. The increase in Al, Mg and Mn was also minor and mostly below 1 mg/l (Figure 1c). (a) N K Na S CO /SO /NO (b) N Ca Fe Si CO /SO /NO (c) N Al Mg Mn CO /SO /NO Figure 1. Incremental water chemistry of selected elements during reaction of WC with CO /SO /NO. NOx and SOx species evolution during reaction of WC with CO /SO /NO are displayed in Figure 1. In general, NOx and SOx species concentration were higher than those measured in the blank experiment (Figure 1). NO concentration increased up to 1 mg/l after 1 day in CO /SO /NO, followed by a sudden decrease to 1 mg/l and further gradual increase up to mg/l after days (Figure 1a). The rapid decline of NO after 1 day in WC was also observed after days during reaction of WC191 with CO /NO (Figure c). The magnitude of NO decline in WC is greater than that observed during the blank CO /SO /NO experiment (Figure 1a), suggesting some interaction with the rock sample or components in solution from the rock. The presence of the rock core may accelerate NO dissolution into solution and fixing of the species in solution through subsequent reactions. As discussed later, Buchwald et al. (1) show that the heterogeneous surfaces of minerals can accelerate reactions of N species in solution.

28 Concentration (mg/l) Concentration (mg/l) The increase of SO up to mg/l during the N equilibration stage is likely due to the dissolution of sulfate type salts (Figure 1b). SO concentration increased from to mg/l after 1 day in CO /SO /NO, equivalent to near complete dissolution of SO in solution. The additional SO increase to 9 mg/l after days may be representative of further sulfatesalt dissolution. SO declined after day and varied between and mg/l for the remainder of the experiment. The remaining SOx species (SO, S O, S ) were <1 mg/l, excluding the slight increase in S O to mg/l after days. (a) NO NO NH 1 N CO /SO /NO (b) SO SO SO S 1 N CO /SO /NO 1 1 Figure 1. NOx (a) and SOx (b) species evolution during reaction of WC with first N then CO /SO /NO gas. Note that due to water sample shortage, no SOx species were analysed at t = days... WC11 CO /SO /NO Changes in incremental water chemistry during the reaction of WC11 with CO /SO /NO are shown in Figure 1.The majority of elements increased during the N equilibration stage, in particular K and Na (Figure 1a), due to the dissolution of soluble sulfate minerals. As expected, the concentration of total S increases sharply during the initial period of CO /SO /NO reaction (Figure 1b). Mineral dissolution increased during the CO /SO /NO stage, most significantly for Ca, Si (Figure 1b) and Mg (Figure 1c). Fe declined throughout the CO /SO /NO reaction stage (Figure 1c), likely due to the precipitation of Feoxide type minerals.

29 Concentration (mg/l) Concentration (mg/l) Concentration (mg/l) (a) N K Na CO /SO /NO (b) 1 1 N Ca S Si CO /SO /NO (c).. Al Fe Mg Mn N CO /SO /NO Figure 1. Incremental water chemistry of selected elements during reaction of WC11 with CO /SO /NO NOx and SOx species evolution during reaction of WC with CO /SO /NO gas are displayed in Figure 1. NOx and SOx species concentrations were higher than those measured in the blank experiment (Figure 1), but lower than those measured during the reaction of WC (Figure 1). Dissolved NO increased up to mg/l after days and was highly variable thereafter (Figure 1a). This variance was not observed in the NO concentration, which declined steadily from. mg/l after day 1 to <.1 mg/l after day. NH increased during the period of NO decline up to a maximum of. mg/l after days. The SO concentration after 1 days reaction of rock in low salinity water and N was. mg/l (Figure 1b) and approximately x lower than that measured at the same point for WC (Figure 1b). This suggests that the WC core subsample contained a higher composition of highly soluble sulfate minerals, also confirmed by XRD or that more were dissolved by the SO /NO gas stream (Table ). SO increased from. to 1. mg/l after 1 day following CO /SO /NO gas addition, then steadily declined from day onwards to 1. mg/l. The remaining SOx species (SO, S O, S ) were <1 mg/l throughout the experiment. 9

30 Concentration (mg/l) Concentration (mg/l) 1 (a) NO NO NH N CO /SO /NO (b) 1 1 SO SO SO S N CO /SO /NO Figure 1. NOx (a) and SOx (b) species evolution during reaction of WC11 with first N then CO /SO /NO.. NOx species evolution The distinctive NO and NO trends observed during CO /NO and CO /SO /NO suggests the presence of an underlying mechanism influencing NOx speciation, possibly controlled by mineral dissolution or mineral surface promoted reactions. The reduction of nitrate or nitrite coupled to the oxidation of Fe(II) has been observed during studies of both soils (Buchwald et al., 1) and postulated within the context of CO sequestration (Tanaka et al., 1a). These are discussed further in the proceeding sections...1 Fe and NO Tanaka et al. (1b) postulated that Fe, leached from Ferich clays such as chlorite, may act as a reducing agent for NO via the following reaction: Fe Fe e (1) NO H e NO H O (1) All core samples contained variable amounts of Febearing clays such as FeMgchlorite and illite that may contribute to the above mechanism. It would be expected that NO would decline with increasing Fe concentration if the mechanism suggested by Tanaka et al. (1b) was true for the current system. Dissolved Fe and NO concentration are plotted for CO /NO and CO /SO /NO experiments in Figure 1. The initial NO concentration measured after 1 day during CO /NO experiments was similar for all samples at approximately mg/l (Figure 1a). NO increased further for WC191 and WC and was significantly larger throughout in comparison to WC11. Fe concentration was similar for

31 NO (mg/l) Fe (mg/l) NO (mg/l) Fe (mg/l) WC191 and WC11 but approximately x lower for WC11 (Figure 1b). It can be concluded that the greatest NO concentration is observed for the sample with the overall lowest Fe release during CO /NO experiments, though the relationship is not clear. NO and Fe evolution during CO /SO /NO experiments are plotted in Figure 1c and d respectively. A large spike in NO concentration was observed for WC11, followed by a decline after days then gradual increase up to days (Figure 1a). A similar NO trend was observed for WC191 (Figure 1a). A gradual increase in NO concentration was observed for WC up to 1 days, after which it stabilised to mg/l, similar to the initial concentration measured for CO /NO experiments (Figure 1a). Fe concentration was highly variable for both WC11 and WC (Figure 1d) and could not be correlated to NO concentration. It should be noted that the abundance of Fe bearing minerals was considerably higher in the Tanaka et al. (1b) experiment i.e. >. wt.%, in comparison to < wt.% for this study. Previous reservoir scale geochemical modelling studies with the Precipice Sandstone formation have found no sink for the NO produced during sequestration of a CO /NO stream, resulting in very high (up to mol/kg over 1 years) concentrations and low (Haese et al., 1). The removal of NOx by Fe cycling may be a favourable reaction to prevent formation of the very low. (a) CO /NO WC191 WC11 WC (c) CO /SO /NO 1 WC11 1 WC (b) 9 WC191 WC11 WC CO /SO /NO WC11 (d) CO /NO CO /NO 1. WC Figure 1. NO (left column) and Fe (right column) concentration changes over time during CO /NO (ab) and CO /SO /NO (cd) experiments. 1

32 .. Fe and NO Buchwald et al. (1) presented evidence for the abiotic reduction of NO by Fe at atmospheric pressure and room temperature conditions at and. Anaerobic batch experiments were performed with an initial NO concentration of μm (9. mg/l) and aqueous Fe ranging from. to.1 mm (.9 to. mg/l). In some cases, the mineral goethite (FeOOH) was added. They observed goethite, magnetite or ferrihydrite formation. They considered the following primary net reactions during their experiments: Fe NO H O FeOOH N O(g) H (1) Fe NO H O FeOOH 1/N (g) H (1) The above mechanism supports the precipitation of Fe(hydr)oxide type minerals, as observed in reaction of WC191 with CO /NO (Figure ). Faster rates of nitrite reduction were observed by Buchwald et al. (1) at higher Fe concentrations, higher (of rather than ) and in the presence of added goethite (FeOOH). NO reduction over time for experiments with CO /NO and CO /SO /NO are shown in Figure 1a and b respectively. The data was fitted to the following first order exponential reduction curve: y = A exp(k 1 x) (1) where A (mg/l) is a fitting parameter based on the initial concentration of NO, k 1 (day 1 ) is the pseudo first order rate constant and x is the time (day). These fitting parameters and linear regression coefficients have been summarised in Table. The rate constant for NO reduction during CO /NO experiments was greatest in WC191 and lowest for WC11 i.e. k 1WC191 > k 1WC > k 1WC11. The estimated initial concentration of NO at t = days (A) decreased from WC11 to WC19. Similarly, k 1WC was larger than k 1WC11 and A WC was lower than A WC11 during the CO /SO /NO experiments. The influence of the total Fe composition of samples (as calculated by whole rock digestion in mg/kg) on A is shown in Figure 19. A decreases with Fe composition for both the CO /NO and CO /SO /NO experiments. Additionally, A is lower in the low salinity CO /SO /NO experiments than the high salinity CO /NO experiment. It is apparent than NO concentration is influenced by the rock, fluid and initial gas composition. The concentration of Fe was not well constrained during the current series of experiments i.e. rock samples were heterogeneous, the available reactive surface area likely differed and dissolved Fe concentration continually changed with either mineral dissolution or precipitation. Additional CO /NO experiments with a well constrained aqueous Fe concentration would facilitate further

33 NO (mg/l) NO (mg/l) investigation of the mechanisms controlling NOx speciation at CO sequestration conditions relevant to the Surat Basin ( C and 1 MPa). The influence of Fe and Fe bearing minerals on NOx reactions is important as a sink or fate for NOx subsurface is currently not well constrained in models which has led to predicted generation of low especially in the near well bore (Haese et al., 1). A sink for NOx species other than nitric acid or nitrate may be favourable. The Evergreen Formation overlying the Precipice Sandstone contains more abundant Febearing minerals such as chlorite and other redox sensitive elements including Mn have been shown to be released in higher concentrations during previous experimental reactions (Pearce et al., 1, Dawson et al., 1). The behaviour of NOx if it interacts with the Evergreen Formation may differ with higher concentrations of available Fe and warrants further investigation. Table. Summary of fitting parameters for NO reduction during CO /NO and CO /SO /NO experiments. Sample Gas A k 1 R (mg/kg) (day 1 ) WC11 CO /NO WC191 CO /NO WC CO /NO WC CO /SO /NO WC11 CO /SO /NO (a) WC11 (b) WC 1 WC191 WC WC Figure 1. NO evolution during (a) CO /NO and (b) CO /SO /NO experiments.

34 Initial NO, A (mg/l) WC11 WC11 WC y =.x 11. R² =.99 WC191 WC CO/NO CO/SO/NO 1 WR Fe content (mg/kg) Figure 19. Influence of initial sample Fe content (as measured by whole rock digestion) on initial measured NO concentration (A). CO /NO and CO /SO /NO experiments have been separated from each other... Influence of O fugacity on NOx speciation Though the water solution was deoxygenated and the entire system purged with N prior to experiments for both samples, differences in O fugacity may have contributed to the difference in NO. For example, a larger O fugacity in the WC19 system may have resulted in greater conversion of NO(g) to NO (g) and consequent dissolution in water to form HNO : NO(g) O (g) NO (g) (1) NO (g) H O(l) HNO (aq) HNO (aq) (1) HNO (aq) HNO (aq) NO(g) H O(l) (19) Variable amounts of oxide minerals or other oxidising rock components (e.g. Feoxides, Tioxides) can affect the system especially in solution. It expected that the contribution of O fugacity differences are minor and variable sample mineralogy are predominantly responsible for the differences in NOx species concentration for all samples. Pyrite production in the reaction of WC19 indicates the presence of reduced Fe which could be coupled to oxidised N species.. SOx species evolution A comparison SOx species evolution during the reaction of WC11 and WC with CO /SO /NO is shown in Figure. The SO concentration is approximately x higher for WC than WC11 after 1 days equilibration with N (Figure a). This is expected due to the greater proportion of soluble sulfatetype minerals (e.g. Lazurite) in WC compared to WC11. SO increases by approximately 1 mg/l for both WC11 and WC after 1 day reaction with CO /SO /NO. This indicated that the majority of injected SO gas dissolved into solution (assuming oxidative reduction