Brian Farrell

Hi Lauren, Can you please post the entire X1t input file so that I'm better able to take a look? Thanks, Brian Farrell Aqueous Solutions LLC

Hi Terry, The forum doesn’t send notifications when new topics are added to the archive of old posts. I’ve moved your post from the archive to the front page of the forum. Please ensure you post to the main page in the future so that your questions don’t get missed. To add a new mineral in TEdit, just right-click on the Minerals section of the tree structure (or any of the minerals listed under it) and select “Add”. You can then supply the mineral’s name, mole weight and volume, species to form a reaction, and a log K for the reaction at one or more temperatures. Click Apply when the entry is complete then save your dataset with a new name. For more information on the TEdit thermo data editor, please see section 9, Using TEdit, in the GWB Essentials Guide. By the way, the dataset itself is still just an ascii file so you’re free to edit it in a text editor like Notepad if that’s what you prefer. Just right-click on the dataset and select “Edit” if available, or “Open with –> Notepad”. Hope this helps, Brian Farrell Aqueous Solutions LLC

Hi Sebastian, The “flow-through” configuration might be used to follow a packet of fluid as it migrates through an aquifer, or to trace the evaporation of seawater. In either case, the program isolates minerals that form over the reaction path and prevents them from back reacting. With the “flush” configuration, the program tracks the evolution of a water-rock system (a volume of porous media) through which a fluid migrates. An even simpler model, the “titration” path, is like pouring one fluid into a bucket of another. Section 2.2.5, Local equilibrium models, in the Geochemical and Biogeochemical Reaction Modeling text contains a more complete description and diagrams of these and other conceptual models. Please see as well Section 3, Tracing Reaction Paths, in the GWB Reaction Modeling Guide. You’ll have to think about your conceptual model and which would be the best choice. Does the second fluid displace the original fluid, or does it all pool together? It may be helpful to set up very simple examples of each (perhaps just Na+, Cl-, and Temperature for your fluid(s)). Gtplot can be very helpful here. Pay attention to how water mass changes (or doesn’t change) in each configuration, for example, or use temperature or Na+ and Cl- as tracers as you mix one fluid into another. Another way to prevent minerals from re-dissolving into the fluid is to implement dissolution/ precipitation kinetics using a custom rate law. Your rate law would depend on the saturation state of the mineral. There’s an example in section 5.2, Rate law scripts, in the GWB Reaction Modeling Guide that should be useful. By the way, there’s an example of fluid mixing at hydrothermal vents in section 22.2, Black smokers, in the GBRM text. This sounds pretty similar to what you’re trying to do. Hope this helps, Brian Farrell Aqueous Solutions LLC

Hi, Currently there is no way to add a multiplier to a Ternary or Piper plot. You might try another plot, like the Schoeller diagram, which uses a log scale to compare the concentrations of various components in different samples. You might also manually change the concentration of Cl- in your spreadsheet. Be careful with this option, though. You obviously shouldn't do any calculations with the modified values and you should make sure to designate on the plot in post-processing the change you'e made. Hope this helps, Brian Farrell Aqueous Solutions LLC

Hi Tom, Yeah it looks like the space before the "(aq)" in CaSeO4 (aq) in the reaction to form the surface species is problematic. I'll talk with the team and see what can be done about it. In the meantime, you can remove the space from CaSeO4 (aq) in thermo_minteq.tdat, then remove it from the reaction for the surface species. Luckily you're dealing with an aqueous species, not a basis species, otherwise there would be more places to make the change. I think the space in the name of the surface species itself is okay, though. After these quick edits to the thermo and surface datasets I can type a command (with quotes) like explain ">CaSeO4 (aq)" and get the expected results. Thanks for bringing this to our attention. Best, Brian

Hi, I haven't been able to take a good look at this yet but I hope to do so soon. Regards, Brian Farrell Aqueous Solutions LLC

Dear GWB users, We are pleased to announce our latest maintenance release, GWB 11.0.4. The 11.0.4 update allows plot datasets larger than 2 Gb, fixes a potential race condition in the multithreaded codes, and resolves all known issues with GWB11 and ChemPlugin. Update from 11.0 - 11.0.3 at no charge to ensure you have all the newest features and bug fixes. Existing installations should automatically update to this release, unless auto-update is disabled. In that case, users should update their installations from the Support tab of the GWB dashboard. Regards, Brian Farrell Aqueous Solutions

Hi Ross, I'm glad to hear that the recommendations helped. Cheers, Brian

Hi Zeno, Glad to hear that it helped. Yes, you’re calculating in mol/sec. I think either the mass or moles internal parameters should work, as should the mass(“ ”) helper function. FYI, (moles(“ ”) isn’t listed in the documentation but it works too. Also, the internal parameters are specific to each kinetic reactant. In a rate law for Siderite, for example, the mass internal parameter always refers to the number of moles of Siderite while in a rate law for Calcite that same parameter would refer to Calcite. With a helper function, though, you can refer to any species of interest (using the (“ ”)) from any rate law, for example mass(“Siderite”), mass (“Calcite”), or mass(H+”). The Q/K values for all minerals in the Mineral saturation list correspond to how they’re written in the thermo dataset (as destruction reactions, i.e. dissolution, dissociation, etc.). The Q/K values for kinetic reactants in the Kinetic parameters (or System parameters, pre-GWB11) correspond to how the rate law is set up. Using the default method of forward reactions (destruction reactions like dissolution and dissociation), the Q/K will appear like those in Mineral saturation, but for reverse reactions (formation reactions, like precipitation and association) you’ll see the inverse. Take a look and confirm this for yourself. I played around a little with different ways of writing the rate law. Using the normal forward (dissolution) option, I found reasonable-looking, but not necessarily correct results (siderite dissolved and calcite precipitated near the inlet) using rate = (-6.75e-10) * (QoverK - 1) or rate = (6.75e-10) * (1 - QoverK) I’m not sure how the rate law in your reference was derived or whether the assumptions about parameters and reaction direction match up with what GWB expects. I recommend checking out the original paper and running a simple test in a batch system to make sure you have everything straight. You should also take a look at section 4.3, Forward and reverse reactions, in the GWB Reaction Modeling Guide for more information. Hope this helps, Brian

Hi Ross, In troubleshooting a model like this, it’s typically a good idea to scan through plots of various system parameters just to make sure everything looks okay. When I look at the mass of solvent water or solution, I notice that the value in the first interior node decreases drastically with time. Porosity similarly decreases to the point where there is almost no pore space remaining. Looking at minerals vs. time in the first interior node, you’re precipitating more and more as your inlet fluid flushes through, which is causing the pore space to disappear. At that point it’s understandable that the program fails to converge. You might consider conceptualizing the problem a little differently. Perhaps you need to account for minerals that precipitate according to a kinetic rate law instead of remaining in equilibrium with the fluid. Hope this helps, Brian

Hi Ross, I'd be happy to take a look if you attach your X1t script. Regards, Brian Farrell Aqueous Solutions LLC

Hi Zeno, You’re required by the program to enter a value for specific surface area with kinetic minerals, but if you’re using a custom rate law that doesn’t make use of surface area then the value you specify will be ignored. Take a look at example 3.7, quartz precipitation in a vein, in the GWB Reactive Transport Modeling Guide for an example that should prove useful. Similarly, the programs expect you to enter a rate constant, but you don't need to use it (or the internal parameter "rate_con" that corresponds to it). If both were in the same units this would make sense, but since they're not you can just define a variable, MyRateConstant, in your custom rate law script. Or, in a less elegant solution, you could hard-code the value of the rate constant into the rate law. By the way, you can multiply siderite's mass in moles by the internal parameter mw (or the mw("Siderite") helper function) instead of typing the number in yourself. Either way it should work, though. Take a look at Tables 5.1 and 5.2 in the GWB Reaction Modeling Guide for a list of internal parameters and helper functions you can utilize if you wish. Hope this helps, Brian Farrell Aqueous Solutions LLC

One more reminder: If you’re attending Goldschmidt 2016 in Yokohama, all workshop bookings close on May 26. Register through the conference for our Reactive Transport Modeling workshop for only ¥13400 – about US$120, or €110. After May 26, you can register with the organizers for $699, or $599 if you’re a student. Regards, Brian

Dear GWB Users, Just a gentle reminder: May 31 is the last day to early register for the International Geological Congress in Cape Town. IGC registrants are eligible to attend our Geochemical Reaction Modeling workshop for a discounted fee of only R4900, and by registering early for the conference you’ll save even more. If you are not registering for the conference but would like to participate in the workshop, the regular fee is R5900. We hope to see you there! Regards, Brian Farrell Aqueous Solutions LLC

Hi John, The composition of the flushing fluid remains constant, so you don't need to do anything to maintain the CO2 activity in the pre-saturated brine. If I run your "Kazuba input-flush model" and plot CO2(aq) activity as a function of the amount of mass reacted, I see the CO2(aq) activity of the system approaches and levels off at a value of 3.114, which is just about the same activity as that calculated for the flushing fluid in " Kaszuba input-equilibrate with CO2". The activity of CO2(aq) in the system changes because it's a mixture of the initial porewater and incoming fluid, in addition to the effects of reaction with the rock matrix. The activity asymptotically approaches the value in the flushing brine, though, as more and more brine is flushed through. Hope this helps, Brian

Hi, The GWB's plotting programs display data from a single calculation at a time, so there's no way to plot multiple calculations together. If this was allowed, it would significantly complicate how the user operates the plotting programs. You can easily export your plots to programs like PowerPoint, Excel, or Illustrator, though, to display the results of multiple calculations in a single plot. Our tutorials page contains some tips that will be useful to you. Check out the "How do I overlay my diagrams?" and "How do I retrieve numerical data from my plots?" tutorials within the Using GWB section. Hope this helps, Brian Farrell Aqueous Solutions LLC

Hi, If you only have access to GWB8 (no TEdit app) then you'll need to modify the dataset in a text editor like Notepad. It would be best to use one of the datasets installed with GWB8 (compiled at the same principal temperatures) as a guide. The changes you'll need to make include: If the dataset has a .tdat extension, you'll need to change it to .dat. You'll need to change the dataset format (second line of the dataset) from oct13 to oct94. You'll need to add four reactions (log k for Eh reaction, O2 gas solubility, h2 gas solubility, n2 gas solubility) to the tables section of the thermo dataset (so after the c h2o 4 table). It's probably easiest to copy these from one of the datasets that come installed with GWB8 You'll need to delete the Free electron reaction, which is located between the aqueous species and the minerals. This reaction, in modified form, appears in the log k for Eh reaction. If you changed the redox pivot [H2(aq) instead of O2(aq)] or the species used to balance redox coupling reactions [O2(g), e-, H2(aq), H2(g) instead of O2(aq)] then you'll need to rebalance those reactions and recalculate the log Ks. The Rxn app will be useful. If all of your redox coupling reactions are written in terms of O2(aq), as was required for GWB8, then there's nothing else to do. For more information, Appendix A.1.5 in the GWB Reference Manual describes redox pivoting and redox coupling reactions in the new format thermo datasets (Releases 10 and 11). And Appendix A.1.12 describes the differences between the current (oct13) and older(oct94) formats. If you have access to TEdit (you're running Release 10 or 11), then, as long as O2(aq) is still the redox pivot and redox coupling reactions are written in terms of O2(aq), you can simply go to the Header section of the dataset and change the dataset format to oct94, then click Apply, then save as a .dat file. The program will take care of the four reaction tables and the free electron reaction. BTW, I moved your post from the archive of older topics to the front page of the GWB forum. Please be sure to post on the front page in the future so that your posts are more visible. Hope this helps, Brian Farrell Aqueous Solutions LLC

Hi John, Have you tried using a fixed activity buffer? If the system is configured such that the CO2(aq) activity is at its desired level, you can go to the Reactants pane and click add - Fixed - Aqueous... - CO2(aq). For more information, see section 3.5, Buffered paths, in the GWB Reaction Modeling Guide. Section 14.2, Fixed activity and fugacity paths, in the Geochemical and Biogeochemical Reaction Modeling text contains a more detailed explanation. Hope this helps, Brian Farrell Aqueous Solutions

Dear GWB users, I’m writing to alert you to the first-ever Reactive Transport Modeling Summer School, to be held at Heriot-Watt University in Edinburgh, Scotland on August 1-4. We are very excited to announce the Summer School is open for registration! The Summer School is designed to help postgraduate students in the geosciences learn the techniques of reactive transport modeling as applied to geoscientific research, and for advanced students to share the results of their work with other students, in a relaxed, collegial, non-threatening environment. The Summer School will feature a welcoming reception, hands-on instruction from world leaders in the field, a field excursion each day, opportunity for participants to present posters or 5-minute talk capsules, and many chances for interaction among participants. You may download the Summer School brochure and registration form here, or from the event’s webpage. Please forward this message to your network of colleagues and of course to any students who might be interested in participating. Brian Farrell On behalf of the organizers: Eric MacKay, Heriot-Watt University Craig Bethke, University of Illinois

Hi Tyler, It sounds like you have this figured out and working to your satisfaction. I'll leave you with one last tip for now that may be useful for simulating titrations or other reaction processes in the future. Sometimes one sets the initial fugacity of a gas then lets it evolve during a reaction path. Other times it's desirable to "fix" the fugacity of a gas if the external reservoir is sufficiently large and maintains equilibrium with the fluid over the course of the reaction path. You can take a look at 15.3, Gas buffers, in the GBRM text for more info. Best, Brian

Is your measured acidity a "total acidity"? In addition to the water acidity (H+ + OH- = H2O) and carbonate acidity (CO2 + OH- = HCO3-) of a fluid, "mineral acidity" can sometimes be quite substantial (for example, Al+++ + 4 OH- = Al(OH)4-). What you enter for the HCO3- component (whether CO2 is swapped into the basis or not) should be the sum of the concentration of carbonate species (CO2 + HCO3- + CO3-- + NaHCO3 + ...). If you're entering acidity titration directly for a fluid with substantial mineral acidity, that could be the source of your problem. Section 15.1 of the Geochemical and Biogeochemical Reaction Modeling textbook describes an example in which a titration model is used to interpret an alkalinity measurement and determine the carbonate component concentration, which is what you want. You could do the same thing to interpret an acidity measurement. Finally, you're using alkalinity units for the HCO3-/CO2, but at a pH of 2 you should basically have no alkalinity. You should enter the carbonate concentration in normal concentration units, like moles/kg or mg/kg. Hope this helps, Brian

Hi Tyler, When you are constraining your system, especially under extreme conditions, it sometimes helps the program converge when the species that are swapped into the basis are somewhat predominant. For example, at very low pH, you might want to swap in CO2(aq) for HCO3-, or at high pH, swap in CO3-- for HCO3-. Hope this helps, Brian Farrell Aqueous Solutions LLC

Dear GWB users, We are pleased to announce our latest maintenance release, GWB 11.0.3. The 11.0.3 update gives the user options to install a GWB desktop icon and open the GWB dashboard when installing and updating; improves auto-sizing and plot spacing when displaying multiple special plots on a page; polishes pasting behavior in TEdit; fixes glitches in Isotopes and Stepping dialogs in React; puts more graphics types on clipboard, and increases bitmap resolution, when copying plots in Act2 and Tact; resolves a problem in Act2 and Tact when more than one speciating ion does not speciate; corrects a problem reading the sixth coefficient in the temperature expansion of beta2 from HMW datasets; fixes various minor issues when making X-Y plots in Gtplot;. Update from 11.0 - 11.0.2 at no charge to ensure you have all the newest features and bug fixes. Existing installations should automatically update to this release, unless auto-update is disabled. In that case, users should update their installations from the Support tab of the GWB dashboard. Regards, Brian Farrell Aqueous Solutions

Hi again, I thought about this a little more and set up a simple model in React. H2O = 1 free kg SiO2(aq) = 1e-6 mg/kg react 10 mg of Quartz printout basis = long About 6 mg of Quartz dissolve into the fluid before it reaches saturation and starts to accumulate in the system. At the end of the reaction there are about 4 mg of the mineral Quartz. When the Quartz reaches saturation, it is swapped into the basis in place of SiO2(aq). You can see this on the Results pane and also in the text output file where the "Basis components" (current basis) and "Original basis" are listed. The "printout basis = long" command is used to show the composition in terms of the current basis (the default setting is to show only the original basis). You can also type "report basis original" and "report basis current" to see what components are used. When you type "report mass Quartz", I think it's reporting the amount of the component Quartz, rather than the mineral. And since you haven't specified the full argument (fluid, system, sorbed, stagnant, or colloid) it's going with the first option: fluid. So in my example, "report mass Quartz", "report mass current Quartz", "report mass current fluid Quartz", "report mass original SiO2(aq)", and "report mass original fluid SiO2(aq)" all give me the same answer for the amount of dissolved silica, about 6 mg. The commands "report mass current system Quartz" and "report mass original system SiO2(aq)" give the total amount of silica either dissolved or in a mineral phase, about 10 mg. To get just the amount of the mineral Quartz, about 4 mg, you should use "report mass minerals Quartz". Regards, Brian

Hi, What do you mean the number is not correct? Are you comparing with mineral mass in Xtplot or X1t's text output file? Since you're using X1t, are you making sure to specify the correct nodal block? You would use report set_node 0 report set_node 99 to get results for the first or last node, respectively, in a domain consisting of 100 nodal blocks. Hope this helps, Brian Farrell Aqueous Solutions LLC