A3 Léa Lévy Electrical conduction of low-salinity hydrothermal systems: a quantitative measure of the smectite and chlorite content
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This document summarizes a study on using electrical conductivity measurements to quantify the smectite and chlorite content in rock cores from Krafla, Iceland. The study finds that electrical conductivity, when normalized by formation factor and porosity, correlates strongly with smectite content as determined by cation exchange capacity measurements. Smectite has weaker molecular bondings than chlorite, allowing it to contribute more to electrical conductivity. Between 7-20% clay content corresponds to 5-18% chlorite in whole rock samples. The ability to measure smectite content electrically could help locate transitions between hydrothermal heat convection and conduction zones.
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A3 Léa Lévy Electrical conduction of low-salinity hydrothermal systems: a quantitative measure of the smectite and chlorite content
- 1. ELECTRICAL CONDUCTION: A QUANTITATIVE MEASURE OF THE SMECTITE AND CHLORITE CONTENT? STUDY BASED ON CORES FROM KRAFLA 24.11.2016 Léa Lévy - GEORG conference 1 LÉA LÉVY IN COLLABORATION WITH: ÓLAFUR G. FLÓVENZ GYLFI PÁLL HERSIR FREYSTEINN SIGMUNDSSON BENOIT GIBERT AND MANY MORE
- 2. What is clay? • CEC = Cation Exchange Capacity • Between T sheets „Internal exchange“ • Only in smectite • On the edges „External exchange“ • Minimal compared to internal • Unit = meq/100g or C/kg • Measured by chemical titration 24.11.2016 Léa Lévy - GEORG conference 2 Chlorite Illite Smectite • Phyllosilicates • T = tetrahedral sheet (Si) • O = octahedral sheet (Al or Mg) • Sequences T-O-T • Substitutions Negative charge • Compensation between sheets From multiple sources. Ex: Lyklema, 2001
- 3. Charge and mobility 24.11.2016 Léa Lévy - GEORG conference 3 Internal CEC (meq/100g) 100 Smectites Illite Chlorite # water layers 0 1 2 |Total charge|0 0.70.50.3 10.9 2 T-O No charge T-O-T low charge T-O-T high charge higher charge stronger bondings structure more stable Stability Brucitic layer Cation with 2 water shellsNothing Cations with 1 water shell Cations with 0 water shell Weak Coulombian attraction Van der Waals bondings of increasing strength H bondings Montmorillonite 2 water shells From Meunier, 2000 Beidellite 1 water shell
- 4. The smectite chlorite transition • Kinetic vs thermodynamics • Intermediary step • Hydrothermal convection vs heat conduction • Presence/absence of smectite 24.11.2016 Léa Lévy - GEORG conference 4 „Smectite is a kinetic step in the formation of chlorite by hydrothermal convection.“ Electrical conduction Unstable smectite Weak bondings Low charge
- 5. Context of the study 24.11.2016 Léa Lévy - GEORG conference 5 (b) KH-5 (a) 288m – Epidote, quartz, wairakite. (b) 279 m – Epidote overprinted by laumontite. (c) (d) KH6. 594 m – Zeolite transforming into wairakite. (b) KH-3 – 273 m. Precipitation of MLC and chlorite in vesicles. KH-1. 74 m – Stilbite and smectite. Map by Þorbergsson and Víkingsson, 2016
- 6. Clay content and CEC 24.11.2016 Léa Lévy - GEORG conference 6 0 5 10 15 20 25 30 35 40 45 50 0% 10% 20% 30% 40% 50% CECmeq/100g Clay fraction (XRD) CEC and clay fraction of whole rock samples Based on XRD {d(001) + d(002)}
- 7. Clay content and CEC 24.11.2016 Léa Lévy - GEORG conference 7 y = 109.55x R² = 0.9669 y = 85.673x R² = 0.9959 0 5 10 15 20 25 30 35 40 45 50 0% 10% 20% 30% 40% 50% CECmeq/100g Clay fraction (XRD) CEC and clay fraction of whole rock samples Based on XRD {d(001) + d(002)} 100% smectite 75% smectite 𝐶𝐸𝐶0 = 110 meq/100g
- 8. Clay content and CEC 24.11.2016 Léa Lévy - GEORG conference 8 y = 109.55x R² = 0.9669 y = 85.673x R² = 0.9959 y = 67.361x R² = 0.9863 0 5 10 15 20 25 30 35 40 45 50 0% 10% 20% 30% 40% 50% CECmeq/100g Clay fraction (XRD) CEC and clay fraction of whole rock samples Based on XRD {d(001) + d(002)} 100% smectite 75% smectite 60% smectite 𝐶𝐸𝐶0 = 110 meq/100g
- 9. Clay content and CEC 24.11.2016 Léa Lévy - GEORG conference 9 y = 109.55x R² = 0.9669 y = 85.673x R² = 0.9959 y = 67.361x R² = 0.9863 y = 41.798x R² = 0.9567 y = 22.927x R² = 0.9509 0 5 10 15 20 25 30 35 40 45 50 0% 10% 20% 30% 40% 50% CECmeq/100g Clay fraction (XRD) CEC and clay fraction of whole rock samples Based on XRD {d(001) + d(002)} 100% smectite 75% smectite 60% smectite 40% smectite 20% smectite 𝐶𝐸𝐶0 = 110 meq/100g
- 10. Clay content and CEC 24.11.2016 Léa Lévy - GEORG conference 10 y = 109.55x R² = 0.9669 y = 85.673x R² = 0.9959 y = 67.361x R² = 0.9863 y = 41.798x R² = 0.9567 y = 22.927x R² = 0.9509 y = 11.465x R² = 0.6641 0 5 10 15 20 25 30 35 40 45 50 0% 10% 20% 30% 40% 50% CECmeq/100g Clay fraction (XRD) CEC and clay fraction of whole rock samples Based on XRD {d(001) + d(002)} 100% smectite 75% smectite 60% smectite 40% smectite 20% smectite 10% smectite 𝐶𝐸𝐶0 = 110 meq/100g
- 11. Conductivity and CEC 24.11.2016 Léa Lévy - GEORG conference 11 𝜎 𝑏𝑢𝑙𝑘 = 𝜎 𝑤 𝐹 + 𝜎𝑠 y = 3.75x-1.89 R² = 0.76 10 100 1,000 1% 10% 100% Formationfactor Porosity Formation factor and porosity 1.E-03 1.E-02 1.E-01 1.E+00 0.01 0.1 1 10 Bulkconductivity(S/m) Fluid conductivity (S/m) Bulk conductivity vs fluid conductivity 𝑚 = 1.89 1/F 𝜎𝑠 R² = 0.888 R² = 0.637 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 0 1 10 100 Conductivity(S/m) CEC (meq/100g) Interface conductivity vs CEC Cs*F*Por Cs m Rock type Published in 1.33 Seafloor MAR Pezard, 1990 1.74-2.43 Shaly sands Waxman & Smits, 1968 2.45 Hawaiian basalt Revil et al., 2016 2.75 Icelandic basalt Flóvenz et al., 2005 Fluid conductivity Formation factor Clay „Interface“ conductivity 𝜎𝑠 = f(CEC, F, ∅) 𝐹 = a∅−𝑚 Porosity (Waxman & Smits, 1968) (Archie, 1942) Contribution of clay Small Moderate High
- 12. Conductivity and smectite 24.11.2016 Léa Lévy - GEORG conference 12 𝜎𝑠 ∗ F ∗ ∅ = f CEC = f(smec%) 1.E-03 1.E-02 1.E-01 1.E+00 1% 10% 100% Clay fraction in the whole rock (XRD) Normalized interface conductivity vs clay% Clay >50% smectite Clay 20-50% smectite Clay < 20% smectite Whole rock < 2% smectite Between 7 and 20% of clay 5 to 18% chlorite in whole rock R² = 0.912 1.E-03 1.E-02 1.E-01 1.E+00 0% 1% 10% 100% Conductivity(S/m) Smectite fraction in the whole rock (CEC) Normalized interface conductivity vs smectite% Meaningful smectite content (> 1 %) Clay < 20% smectite 𝑤𝑡%(𝑠𝑚𝑒𝑐) = 𝐶𝐸𝐶 𝐶𝐸𝐶0 𝜎𝑏𝑢𝑙𝑘 = 𝜎 𝑤 𝐹 + 𝜎𝑠 𝜎𝑠 = f(CEC, F, ∅) 𝐶𝐸𝐶0 = 110 meq/100g
- 13. Conclusions • Electrical conductivity measures the smectite content • At low-salinity • Normalized by F*φ • Independent of chlorite content • Weak bondings in smectite are a key in geothermal exploration • Smectite content is a measure of hydrothermal activity (unstability) • Smectite content can be measured by electrical conduction (CEC) Could we use the evolution of the smectite content to locate the transition between heat convection and heat conduction? 24.11.2016 Léa Lévy - GEORG conference 13
- 14. Thank you ! OTHER SCIENTISTS I WOULD LIKE TO ACKNOWLEDGE INCLUDE PHILIPPE PEZARD PIERRE BRIOLE SIGURÐUR SVEINN JÓNSSON ÞRÁINN FRIÐRIKSSON HELGA M. HELGADÓTTIR HJALTI FRANZSON ANDRÉ REVIL ALAIN MEUNIER PHILIPPE COSENZA 24.11.2016 Léa Lévy - GEORG conference 14
- 15. Appendix 24.11.2016 Léa Lévy - GEORG conference 15
- 16. Complex conductivity 24.11.2016 Léa Lévy - GEORG conference 16 𝜎𝑏𝑢𝑙𝑘 ∗ = 𝜎′ + 𝑖𝜎′′ Carry an electrical current Stores electrical charges 𝜎′′ = 𝑓𝐿𝐹 𝜎 𝑤, CEC, F, ∅ +𝑓𝐻𝐹 𝜎′ = f(𝜎 𝑤, CEC, F, ∅) (𝜎𝑏𝑢𝑙𝑘 = 𝜎 𝑤 𝐹 + 𝜎𝑠) y = 0.001x0.457 R² = 0.544 1.E-03 1.E-02 1.E-01 1.E+00 1.E+02 1.E+03 1.E+04 1.E+05 QuadratureConductivity(S/m) CEC (C/kg) Correlation of quadrature conductivity (using different correction factors) and CEC C''*F 10 Hz Cw=1,5 S/m
- 17. Comparison between borehole conductivity (from the 64'' resistivity log) and CEC from cuttings in borehole KJ-18 Conductivity and CEC in borehole KJ-18 CEC (cuttings) and conductivity (borehole log) 24.11.2016 Léa Lévy - GEORG conference 17
- 18. Thermodynamics of cation exchange 0 5 10 15 20 25 30 35 40 0 100 200 300 400 500 600 700 800 CECapparent(meq/100g) mass of rock / initial concentration in mg/(mol/L) Variation of apparent CEC with rock mass Initial concentration of Cu-trien varies between 1.52x10-3 and 1.73x10-3 mol/L L81 L82 L96 L40 L31 L22 L16 L14 L11 L09 L06 L99 24.11.2016 Léa Lévy - GEORG conference 18
- 19. 0 5 10 15 20 25 30 0 50 100 150 200 L22 - CEC and K Determination K = 100 CEC = 24,2 (e) 0 5 10 15 20 25 30 35 40 0 50 100 150 200 Cu(trien)consumedbythe reactioninmeq/100g L14 - CEC and K Determination K = 20 CEC = 38 0 5 10 15 20 25 30 35 40 0 100 200 L09 - CEC and K Determination K = 25 CEC = 37 0 5 10 15 20 25 30 35 0 50 100 150 200 Cu(trien)consumedbythereactionin meq/100g 2VCi/m = Initial Cu(trien) content in meq/100g L06 - CEC and K Determination K = 20 CEC = 32.8 0 5 10 15 20 25 30 35 40 0 100 200 2VCi/m = Initial Cu(trien) content in meq/100g L99 - CEC and K Determination K = 30 CEC = 34 (a) (c) (d)(b) 0 5 10 15 20 25 0 50 100 150 200 2VCi/m = Initial Cu(trien) content in meq/100g L11 - CEC and K Determination K = 50 or 25 CEC = 23,2 or 21,8 (f) Analytical fit of experimental observations 24.11.2016 Léa Lévy - GEORG conference 19
- 20. Normalization of interface conductivity 24.11.2016 Léa Lévy - GEORG conference 20 R² = 0.845 R² = 0.888 R² = 0.637 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 0 1 10 100 Conductivity(S/m) CEC (meq/100g) Interface conductivity vs CEC Cs*F Cs*F*Por Cs
- 21. References • Flóvenz, Ó. G., Spangenberg, E., Kulenkampff, J., Árnason, K., Karlsdóttir, R. and Huenges, E. (2005). The role of electrical interface conduction in geothermal exploration. World Geothermal Congress, Ankara, Turkey, 2005. • Lyklema, J. (2001). Fundamentals of Interface and Colloid Science. Volume II Solid-Liquid Interfaces. Academic Press. • Meier, L. and Kahr, G. (1999). Determination of the Cation Exchange Capacity (CEC) of Clay Minerals Using the Complexes of Copper(II) Ion with Triethylenetetramine and Tetraethylenepentamine. Clays and Clay Minerals 47(3), 386–388. • Meunier, A. (2013). Les argiles par la pratique. Vuibert • Pezard, P. A. (1990). Electrical properties of mid-ocean ridge basalt and implications for the structure of the upper oceanic crust in Hole 504B. Journal of Geophysical Research 95(B6), 9237. • Vinegar, H. J. and Waxman, M.H. (1984). Induced polarization of shaly sands. Geophysics 49(8), 1267–1287. • Revil, A., Le Breton, M., Niu, Q., Wallin, E., Haskins, E. and Thomas, D.M. (2016). Induced polarization of volcanic rocks. I. Surface versus quadrature conductivity. In press. • Waxman, M. H. and L. J. M. Smits (1968). Electrical conductivities in oil-bearing shaly sands. Soc. Pet. Eng. J. 8, 107–122. 24.11.2016 Léa Lévy - GEORG conference 21
- 22. Clay content and CEC 24.11.2016 Léa Lévy - GEORG conference 22 y = 92.23x R² = 0.91 y = 67.86x R² = 0.98 y = 36.02x R² = 0.77 y = 9.20x R² = 0.30 0 5 10 15 20 25 30 35 40 45 50 0% 10% 20% 30% 40% 50% CECmeq/100g Clay fraction (assuming the highest has 50% of clay) CEC and clay fraction – based on the sum of d(001) and d(002) areas – of whole rock samples Clay >90% Smectite MLC with 50-90% smectite MLC with 20-50% smectite Chlorite with 0-20% smectite 𝐶𝐸𝐶0 = 110 meq/100g
Editor's Notes
- 30 sec I am Léa Lévy, I am doing a PhD in collaboration with these institutions here. In this talk there will be two main things: an overview of the physics linking clay minerals and electrical conduction and then my laboratory results showing to what extent the clay content can be quantified by electrical conductivity measurements. I decided to include a condensate of knowledge about clay physics because when I started my work on this topic, I couldn‘t find that. I had to go back and forth between physicists and mineralogists to finally understand what is so special about clays in hydrothermal contexts. and my goal today is to show you some of the physics between clay minerals and electrical conductivity first from a theoretical angle and then from an experimental angle, with laboratory results. Clays are fascinating because they are both geothermometers and electrical media. But when I first tried to understand why, I faced a deep intellectual void. Yes there is a conceptual void when you want to use a unique logic to jump from one scale to another. So I decided to start my presentation today with an overview of what makes clays so special for geothermal exploration. Then I will present laboratory results showing to what extent
- 50 sec 0) Well for soil scientists, it‘s the fraction below 2 um. But for mineralogists clay means clay minerals, also called phyllosilicates 1) Silicates because the building bricks are silicon tetrahedra and phyllo because the mineral is organized in sheets, actually an alternance of octahedral and tetrahedral sheets. 2) Let‘s look at smectite for example, tetrahedral: pink/yellow and octahedra: green. We see clearly here the TOT sequence, followed by a space filled with cations and water, where fascinating things are happening. And again TOT 3) Then we have chlorite with a different layer between the TOT sequences. 4) And illite with a big green potassium cation between the TOT sequences. Some clays are not organized in TOT but we are not interested in them here. The main difference between all clays is the degree of substitution in the T and O sheets, which means the replacement of an atom (say Si) by an atom of similar size but lower charge in the crystal lattice. Each replacement creates a negative charge in the crystal. 5) The more substitutions the higher the charge. Depending on the level of the charge you will have or not mobile cations compensating the charge in the interlayer space. In smectite you have mobile cations but in illite the cations are not mobile and in chlorite, we don‘t have cations but a whole octahedral layer with a positive charge. This mobility can actually be quantified, it is what we called the CEC. The cation exchanges can also take place somwhere else than in the interlayer, but these other contributions are minimal so no detail here. A word about the unit: chemists tend to use the meq/100g while physicist use the Coulomb/kg. So far this is quite known. But by the way how does the charge of the structure affects the mobility of cations? What do you think: high charge means high CEC or the contrary? Let‘s see.
- 1 min What is the link between the degree of substitution and the mobility of cations? The degree of substitution determines the negative charge in the crystal lattice and it‘s the intensity of this charge that will allow or not the mobility of cations. What do you think: if the charge increase (in absolute value) is the CEC lower or higher? Let‘s check that out. Let‘s imagine an axis With an increasing absolute charge. Let‘s now see how the different clays are distributed according to their charges Three groups of charges. Kaolinite Hop Smectite hope illite/micas hop Chlorite A first difference between these clays is their affinity for having water between the T sheets. It‘s the natural state of cations to be surrounded by water, but the water mocules, and especially the oxygen, eats a bit of the cation‘s charge. So if the charge to compensate in the clay is high, the water molecules are not welcome, because the whole cation is required to compensate the chagre. As the charge decreases, the tolerance to water increases in the interlayer. For example we have here two types of smectite that have different tolerance to water. The invitation of water molecules to the party affects a lot the strength of the bondings between the cations and the sheets. From H bondings when no cations are involved to VdW bondings when cations are alone and to weak Coulombian attraction when water is present. And what happens if the bondings are weak? The cations are mobile. So the answer is low charge = weak bondings = increased CEC. Now again, why is that interesting? For two reasons. First it means that an external force (let‘s say electrical) can remove the cations from the clay. Imagine you are a formula driver and you hit an obstacle. It‘s a force. If you have a normal belt, you will stay at your place, but if you have a poorly designed belt, say in paper, it will easily break and you will be ejected. It‘s pretty much how I see cations in clays. The second reason is because weak bondings also means unstability. Yes the cations are the bolt mainting the whole clay structure. If they can leave the boat like that, the structure is not stable. And that brings us to my last slide about clays.
- 1 min Let‘s sum up what‘s going on in smectite Low substitution level Low charge in the crystalline structure Weak bondings between the structure and compensating cations Mobility of cations and ability to spread an electrical current on one side On the other side, as I just mentionned, unstability of the whole structure. Why is this instability important? Pause. Read sentence. Yes the present understanding of chlorite formation in a context of hydrothermal convection is that it‘s a kinetic process, which begins by the formation of smectite. Just to clarify Kinetic reaction is different from thermodynamic, because it involves time. The formation of chlorite is not triggered immediately when the right species are saturated in water, it will first form an itnermediary product, unstable, the smectite. Smectite is always a first step in chlorite formation but the higher the temperature, the shorter this step. This is also true for permeability: the higher fluid renewal, the shorter this step. That can explain why at high temperature or in highly permeable rock, you will see a chlorite/smectite ratio much higher. Another key word in this sentence is hydrothermal convection. Because chlorite can also form in a thermal gradient, when heat conduction is the dominating process. In this case, the temperature is much higher but the flux lower and smectite does not seem to be involved. The presence of smectite is therefore a hint for an on-going hydrothermal activity: there must be a hydrothermal fluid not very far away in the time-space around the smectite. It‘s only a hint because smectite can be metastable: in some particular cases it can remain even after the hydrothermal activity is gone But let‘s close the chain: if you have hydrothermal convection you will see smectite precipitate as a first product, before chlorite precipitates. We see that the low charge of smectite, causing also its high CEC, is actually tightly related to its function in the chlorite formation process. So to conclude about the clays: we know that the variation of the smectite/chlorite ratio is a useful information about the temperature and permeability of the reservoir, even though it‘s not 100% reliable as such. And we also have a way to distinguish whether a clay is smectite-rich or chlorite-rich. If I had to summarize the rest of my presententation with one sentence I would say that actually smectite is the only conductor in hydrothermal systems and that the conductivity of rocks linearly increases with the smectite content. Let‘s get there step by step.
- 30 sec. I am working with core samples from four boreholes in Krafla, with different alteration stages and temperature. The maximujm depth is 700 m. Here we can see low temperature alteration in KH1, which is observed in the whole borehole. KH3 has high temperature alteration but shows a maximum temperature of 30°C KH5 has very high temperature alteration but maximum temperature of 150°C and overprinting of epidote by laumontite is observed. This section of the reservoir is likely colder now than in the past KH6 is only 2km from KH5 but has the ivnerse trend: the temperature seems to be increasing. A gradient Smectite to MLC is clearly seen, as well as a gradient zeolite to wiarakite. The rest of the presentation consists in laboratory measurements on these cores: conductivity, cation exchange capacity, quantitative Xray diffraction and also thin section observations. All samples I am going to talk about are altered, at different degree. None of them are fresh.
- 2 min The first results I am going to talk about is the straight relationship between the CEC and the clay content, and more aprticularly the role of smectite. First let‘s consider all samples. They all have clay, as we can see on the XRD scans. Let‘s assume that the maximum clay fraction is 50%, which is a qualitative estimation, to start witth. Some of the samples have almost no smectite and some have 100% smecite in the clay. We can observe some trend here but it is a bit fuzzy. Actually if you look behind the main trend you can see different sub-trends. Two independant and simple measurements: CEC and XRD on whole rock. Separation between smectite ~100% vs contains some chlorite layers is straight forward (red/blue XRD curves). CEC measurements very uncertain below 2 meq/100g and uncertainty being dealt with for high values: importance of thermodynamic factor + heterogeneity. That‘s why the trend at high clay content is not so good. The clay fraction can be greatly improved with better quantification, so this is just preliminary but I decided to present it here to show that the relation is quite straight forward with simple manipulation. Relative values: would need a reference sample to be absolute. Planned: use a sample that contain a lot of smectite and no zeolite and measure the weight loss during dehydration. Proper XRD Quantitative with standards is given in weight ratio. Here it‘s unclear. Of course when I say more than 50% smectite I don‘t know if it is in the mix-layer clay itself or if it is in the mixture of clays. Beware: low-smectite content can mean very crystalline rock, not much altered (then we have a low clay fraction, can be seen with XRD of course) or a lot of chlorite and a high level of alteration. So again my work focuses on how to quantify the smectite content. Then how to interprete the smectite content is another question.
- 2 min The first results I am going to talk about is the straight relationship between the CEC and the clay content, and more aprticularly the role of smectite. First let‘s consider all samples. They all have clay, as we can see on the XRD scans. Let‘s assume that the maximum clay fraction is 50%, which is a qualitative estimation, to start witth. Some of the samples have almost no smectite and some have 100% smecite in the clay. We can observe some trend here but it is a bit fuzzy. Actually if you look behind the main trend you can see different sub-trends. First two trends with samples containing mainly smectite, 100% in orange and about 75% in blue. If we assume that only one mineral phase gives the CEC signal (it has to be the smectite), we can deduce an average CEC for our smectite here from the orange curve. We obtain 110 meq/100g, which is in agreement with the litterature and strengthen our first hypothesis of a maximum of 50% of clay. Based on this value we can compute a smectite fraction in the whole rock, by comparing the CEC of whole rock to this index CEC. And then we can estimate the smectite fraction in the clay. Methods? Two independant and simple measurements: CEC and XRD on whole rock. Separation between smectite ~100% vs contains some chlorite layers is straight forward (red/blue XRD curves). CEC measurements very uncertain below 2 meq/100g and uncertainty being dealt with for high values: importance of thermodynamic factor + heterogeneity. That‘s why the trend at high clay content is not so good. The clay fraction can be greatly improved with better quantification, so this is just preliminary but I decided to present it here to show that the relation is quite straight forward with simple manipulation. Relative values: would need a reference sample to be absolute. Planned: use a sample that contain a lot of smectite and no zeolite and measure the weight loss during dehydration. Proper XRD Quantitative with standards is given in weight ratio. Here it‘s unclear. Of course when I say more than 50% smectite I don‘t know if it is in the mix-layer clay itself or if it is in the mixture of clays. Beware: low-smectite content can mean very crystalline rock, not much altered (then we have a low clay fraction, can be seen with XRD of course) or a lot of chlorite and a high level of alteration. So again my work focuses on how to quantify the smectite content. Then how to interprete the smectite content is another question.
- 2 min The first results I am going to talk about is the straight relationship between the CEC and the clay content, and more aprticularly the role of smectite. First let‘s consider all samples. They all have clay, as we can see on the XRD scans. Let‘s assume that the maximum clay fraction is 50%, which is a qualitative estimation, to start witth. Some of the samples have almost no smectite and some have 100% smecite in the clay. We can observe some trend here but it is a bit fuzzy. Actually if you look behind the main trend you can see different sub-trends. First two trends with samples containing mainly smectite, 100% in orange and about 75% in blue. If we assume that only one mineral phase gives the CEC signal (it has to be the smectite), we can deduce an average CEC for our smectite here from the orange curve. We obtain 110 meq/100g, which is in agreement with the litterature and strengthen our first hypothesis of a maximum of 50% of clay. Then we start to observe MLC in thin sections, as well as some charcteristic peaks in XRD. MLC has smectite and chlorite layers with different propotions. Here we look at the global balance in the clay: how many layers of smectite, how many of chlorite, regardless whether they are in discrete smec/chl or in MLC minerals. A category with 60% smectite in the total clay can be seen. Methods? Two independant and simple measurements: CEC and XRD on whole rock. Separation between smectite ~100% vs contains some chlorite layers is straight forward (red/blue XRD curves). CEC measurements very uncertain below 2 meq/100g and uncertainty being dealt with for high values: importance of thermodynamic factor + heterogeneity. That‘s why the trend at high clay content is not so good. The clay fraction can be greatly improved with better quantification, so this is just preliminary but I decided to present it here to show that the relation is quite straight forward with simple manipulation. Relative values: would need a reference sample to be absolute. Planned: use a sample that contain a lot of smectite and no zeolite and measure the weight loss during dehydration. Proper XRD Quantitative with standards is given in weight ratio. Here it‘s unclear. Of course when I say more than 50% smectite I don‘t know if it is in the mix-layer clay itself or if it is in the mixture of clays. Beware: low-smectite content can mean very crystalline rock, not much altered (then we have a low clay fraction, can be seen with XRD of course) or a lot of chlorite and a high level of alteration. So again my work focuses on how to quantify the smectite content. Then how to interprete the smectite content is another question.
- 2 min The first results I am going to talk about is the straight relationship between the CEC and the clay content, and more aprticularly the role of smectite. First let‘s consider all samples. They all have clay, as we can see on the XRD scans. Let‘s assume that the maximum clay fraction is 50%, which is a qualitative estimation, to start witth. Some of the samples have almost no smectite and some have 100% smecite in the clay. We can observe some trend here but it is a bit fuzzy. Actually if you look behind the main trend you can see different sub-trends. First two trends with samples containing mainly smectite, 100% in orange and about 75% in blue. If we assume that only one mineral phase gives the CEC signal (it has to be the smectite), we can deduce an average CEC for our smectite here from the orange curve. We obtain 110 meq/100g, which is in agreement with the litterature and strengthen our first hypothesis of a maximum of 50% of clay. Then we start to observe MLC in thin sections, as well as some charcteristic peaks in XRD. MLC has smectite and chlorite layers with different propotions. Here we look at the global balance in the clay: how many layers of smectite, how many of chlorite, regardless whether they are in discrete smec/chl or in MLC minerals. A category with 60% smectite in the total clay can be seen. Then we jump to clay phases that are dominated by chlorite, but where smectite layers are still present and participating to the signal. Methods? Two independant and simple measurements: CEC and XRD on whole rock. Separation between smectite ~100% vs contains some chlorite layers is straight forward (red/blue XRD curves). CEC measurements very uncertain below 2 meq/100g and uncertainty being dealt with for high values: importance of thermodynamic factor + heterogeneity. That‘s why the trend at high clay content is not so good. The clay fraction can be greatly improved with better quantification, so this is just preliminary but I decided to present it here to show that the relation is quite straight forward with simple manipulation. Relative values: would need a reference sample to be absolute. Planned: use a sample that contain a lot of smectite and no zeolite and measure the weight loss during dehydration. Proper XRD Quantitative with standards is given in weight ratio. Here it‘s unclear. Of course when I say more than 50% smectite I don‘t know if it is in the mix-layer clay itself or if it is in the mixture of clays. Beware: low-smectite content can mean very crystalline rock, not much altered (then we have a low clay fraction, can be seen with XRD of course) or a lot of chlorite and a high level of alteration. So again my work focuses on how to quantify the smectite content. Then how to interprete the smectite content is another question.
- 2 mn The first results I am going to talk about is the straight relationship between the CEC and the clay content, and more aprticularly the role of smectite. First let‘s consider all samples. They all have clay, as we can see on the XRD scans. Let‘s assume that the maximum clay fraction is 50%, which is a qualitative estimation, to start witth. Some of the samples have almost no smectite and some have 100% smecite in the clay. We can observe some trend here but it is a bit fuzzy. Actually if you look behind the main trend you can see different sub-trends. First two trends with samples containing mainly smectite, 100% in orange and about 75% in blue. If we assume that only one mineral phase gives the CEC signal (it has to be the smectite), we can deduce an average CEC for our smectite here from the orange curve. We obtain 110 meq/100g, which is in agreement with the litterature and strengthen our first hypothesis of a maximum of 50% of clay. Then we start to observe MLC in thin sections, as well as some charcteristic peaks in XRD. MLC has smectite and chlorite layers with different propotions. Here we look at the global balance in the clay: how many layers of smectite, how many of chlorite, regardless whether they are in discrete smec/chl or in MLC minerals. A category with 60% smectite in the total clay can be seen. Then we jump to clay phases that are dominated by chlorite, but where smectite layers are still present and participating to the signal. We have a final category of samples with about 10% smec in the clay and the rest is not classified. Here the red trend is not very satisfying. There is little smectite that the uncertainty of these low CEC values plays a big role. What is aprticvularly interesting is the consistent behavior of the five first groups: they have an average smectite content in the clay and an average CEC, regardless whther they have a lot of lay or not. Let‘s now see how that can be translated in terms of electrical conductivity. Relative values: would need a reference sample to be absolute. Planned: use a sample that contain a lot of smectite and no zeolite and measure the weight loss during dehydration. Beware: low-smectite content can mean very crystalline rock, not much altered (then we have a low clay fraction, can be seen with XRD of course) or a lot of chlorite and a high level of alteration. So again my work focuses on how to quantify the smectite content. Then how to interprete the smectite content is another question.
- 2mn 1) Standard equation for cond 1 was measured in laboratory F was deduced from the slope here Cs was taken as the lowest value CEC measured in the laboratory,s ame values as we have shown before. In Krafla the salinity is below 0,1 S/m so we are in the flat part of the graph and the value at 0,02 S/m is a rather good estimate of what we would measure in the field. Classic method, just done with a lot of Icelandic samples here (new).
- 2mn It‘s actually the same data as the cond/CEC, but using the assumtpion that only smec gives the CEC, we translate that into smec content The blue part of the graph regroups the samples which have a meaningful smectite content, more than 1% in the whole rock. The samples that are not on the blue part have between 0 and 1% of smectite, according to the CEC. The variations are thus subject to high uncertainty and they have been separated from the graph, to focus on the blue part. If we take all the blue samples, the comparison cond/smec content yields a very good correlation. Let‘s look at the red part, where the clay contains less than 20% smectite, meaning at least 80% chlorite. So we have a nice trend for samples contasining at least one percent smectite, which means more or less that the CEC is more than 1 meq/100g. But what‘s happening in the rest of the samples? Do they have little smectite because they have a lot of chlorite instead or because they don‘t have a lot of clay in general? We cannot know that based only on this plot. We just see in red samples with a low smectite/chlorite ratio and in blue samples with lot of smectite in the whole rock. There is actually an overlap: 5 samples have up to 2% of smectite in the whole rock but this 1-2% represents less then 20% of the clay so they have up to 18% chlorite in the whole rock. My assumption was that smectite was only conducting mineral, how can I know if it is true? I would need to see the evolution of the conductivity for samples with a relatively constant smectite content and an increasing chlorite content. Let‘s do that. Here we use a different dataset: the clay content comes from XRD. The red samples are the same red samples as in the other plot: the clay contains at least 80% chlorite. What does it tell us? Well those samples, as we see on the left graph have a relatively constant smectite content in the whole rock, less than 2%, but a chlorite content that varies between 5 and 18%. The conductivity does not seem to be correlated to this evolution. Therefore we conclude that the assumption of smectite being the only conductor is relevant. It means that the normalized conductivity is a direct emasurement of the smectite content and that we can track the smectite content in the reservoir. But it‘s a bit difficult to measure F or even the porosity from the surface. How do we do then? I am just going to mention here a possibility on how to proceed. The measurements are still going-on so results were still very preliminary, but the main idea is that you can constrain your itnerpretation by looking at the impedance signal as a whole, instead of only the amplitude ratio. Yes because in the field or in the lab you measure both an amplitude ratio and a phase, which is the definition of a complex number.And wWhen you look separately at the real and imaginary part of this complex number you have two values, which are pretty much dependant on the same variables and can help reseolve the ambiguity mentioned here: F, porosity, smectite-content. That‘s waht I am working on at the moment.
- 1 mn One big idea that I want people to leave with? Have good closing. Stress the novelty of the work and why the results are important. Stress the take-home message. The so-called normalized interface conductivity is directly proportional to the smectite content, with a constant baseline for samples with almost no smectite. The comparison of smectite and chlorite electrical behavior, based on three different types of laboratory quantification, that is conductivity, CEC & XRD, is completely new. It is shown here in the particular case of Icelandic altered basalt. According to my results I conclude that if you see a CEC signal in the chlorite zone it is likely due to the presence of a small fraction of smectite, and not to the CEC of chlorite. Which emphasizes the fact that smectite is the key in that whole problem, through the weak bondings between cations and crystal structure The weak bondings relate the role of smectite in chlorite precipitation, through its unstability and the electrical conduction by cation exchange. And before I end this talk I would like to raise an open question. We have seen that the presence of smectite itself can be misleading, in the case smectite is metastable. But could we use the evolution of the smectite content to locate the transition? Thanks for your attention !
- 1 min Interest in the delay time of current carriage, due to polarization, i.e. charges storage because it is both tightly related and complementary to electrical conductivity. Interpretation of conductivity alone is ambiguous, whether it is CEC or porosity. But the imaginary part has the potential to clear the ambiguity because it brings a second equation on CEC/porosity/F. Cs‘‘=f(freq): various phenomena visible. Cs‘‘ = f (CEC) Trend less robust? A new parameter is taken into account: the pyrite (removed from the graph). Done on sedimentary rock, very new on volcanic rock (Revil). Comparison with Revil trend: no chlorite in his samples, one with zeolites – but this is a non CEC zeolite (natrolite). All the rest is smectite with sometimes illite. This is the first study of complex conductivity vs CEC for volcanic rocks with alteration ranging in smectite-chlorite.
- Depth uncertainty on cuttings 30 sec
- 2 min Methods? Two independant and simple measurements: CEC and XRD on whole rock. Separation between smectite ~100% vs contains some chlorite layers is straight forward (red/blue XRD curves). CEC measurements very uncertain below 2 meq/100g and uncertainty being dealt with for high values: importance of thermodynamic factor + heterogeneity. That‘s why the trend at high clay content is not so good. The clay fraction can be greatly improved with better quantification, so this is just preliminary but I decided to present it here to show that the relation is quite straight forward with simple manipulation. Relative values: would need a reference sample to be absolute. Planned: use a sample that contain a lot of smectite and no zeolite and measure the weight loss during dehydration. Proper XRD Quantitative with standards is given in weight ratio. Here it‘s unclear. Of course when I say more than 50% smectite I don‘t know if it is in the mix-layer clay itself or if it is in the mixture of clays. Beware: low-smectite content can mean very crystalline rock, not much altered (then we have a low clay fraction, can be seen with XRD of course) or a lot of chlorite and a high level of alteration. So again my work focuses on how to quantify the smectite content. Then how to interprete the smectite content is another question.