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Hi Jason, The potential drop across the length of the domain is the driving force for flow. The program uses it, along with the permeability and viscosity, to calculate flow according to Darcy’s law. A boundary might be open to flow, closed to flow (no flow), or water might be set to enter at a specified value of specific discharge. For more information, please see 2.14 Groundwater flow, 3.2 Setting flow rate, and 4.3 Calculating the flow field in the GWB Reactive Transport Modeling Guide. The program uses a correlation to calculate the log of permeability from the porosity, and optionally, the volume fraction of one or more minerals. Permeability is always a positive number. Log permeability, on the other hand, can be negative. For details of the correlation, please see 2.13 Permeability correlation in the same guide. If you’d like to set permeability directly, the porosity multiplier (A) should be set to 0. In your example, set B to 3.6987 mdarcy (the log of 5000). Yes, you can plot permeability in the x and y directions in Xtplot. It’s a good idea to verify that the permeability the program calculates is what you expect. You can use a combination of equilibrium and kinetic minerals, if necessary, to define the minerals that exist in your system. For a good example, see the Weathering and Steam examples in the Reactive Transport Modeling guide (3.8 Example: weathering in a soil profile and 3.11 Example: steam flood). In the future, please post on the main GWB forum (the front page), not the archive of old posts. Regards, Brian Farrell Aqueous Solutions LLC

Hi Coralie, Well, it’s easiest if you have a complete fluid analysis. In that case you’d just run the fluid through SpecE8 or React to calculate saturation indices for every possible mineral. That way you could figure out what you need to swap into your basis. When you’re working with limited data, as you’re doing, it’s much more difficult. You can try different assemblages of minerals you’ve observed, and at least try to rule out unlikely assemblages when you can’t get the initial system to converge. You might also be able to use some experience or consult some stability diagrams to rule out combinations of minerals that aren’t likely to be in equilibrium together under particular conditions. You can add minerals as simple reactants, in which case they’re continuously “titrated” into the system at a constant rate, or as kinetic reactants, in which case the rate of dissolution is set by a kinetic rate law. Reactant minerals in transport models are probably set as kinetic reactants more commonly, but you should make that decision yourself. For more information, please see sections 3 Tracing Reaction Paths and 3.1 Titration paths, as well as 4 Kinetic Reaction Paths, 4.1 Setting kinetic reactions, and 4.2 Kinetics of precipitation and dissolution in the GWB Reaction Modeling Guide. Sure, you can approximate reactive transport in a very simplistic way with React’s flush and flow-through configurations. The flush configuration follows the point of view of a section of porous media through which water flows. You might be interested in alteration products as a reactant fluid flows in and reacts with the existing minerals. The flow-through configuration, conversely, follows a packet of fluid as it migrates. Precipitated minerals aren’t allowed to re-dissolve into the fluid because the fluid packet travels downstream, away from the immobile minerals. You might try either of them before moving to X1t. But the very first step should be to find an initial system that you’re happy with, using Go Initial in React. Hope this helps, Brian

Hi Coralie, Go Initial is primarily for testing out your initial chemical system (what you specify on the Basis pane of SpecE8/ React or the Initial pane of X1t). It calculates the initial state before any reactants are added or boundary fluids flow in. It’s a convenient way to understand the starting point for your calculation without having to worry about the complexity that will be added during the reaction path. Since there are no minerals in the Basis pane of the React script you attached, and the fluid isn’t supersaturated with respect to any minerals, doing a Go Initial will leave you with only a fluid. The reactant minerals haven’t been added yet. There are various ways to conceptualize models like this. If you think that one or more minerals are in equilibrium with the porewater at the very start of your transport model, you should swap those into the Basis. Not all observed minerals are necessarily in equilibrium with the pore fluid, though, so only those that are truly in equilibrium with your fluid should be swapped into the basis. That’s why I suggested trying out different basis configurations and using Go Initial - so you don’t have to worry about the transport or other complexities. You could add the non-equilibrium minerals as reactants later on, after the initial system is sorted out. If, on the other hand, you think the starting point for your transport model is the water-rock system resulting from the titration of your basalt minerals into a brine (the React script you attached), then run the React script to completion (Go, not Go Initial). There should be minerals in the resulting equilibrium system, which you might transfer to the Initial pane of X1t as described previously. Hope this helps, Brian

Hi Coralie, Thanks for changing the thermo dataset. I think part of the problem is that one or more of the minerals swapped into the basis of the Initial pane are not in equilibrium with the fluid. I think a good strategy would be to focus on setting up the starting point for your model, using SpecE8 or React, then moving onto a transport once that’s working. The Initial pane (or Basis pane in SpecE8 and React) is where you specify your initial equilibrium system. If a mineral is present in the field but not in equilibrium with the fluid, it shouldn’t be swapped into the basis. It could be left out, to start, or it could be set as a reactant on the Reactants pane. Try working on the initial system in this way (you can use the Run > Go Initial option in React) to try to find a plausible equilibrium assemblage. If you have more data about the porewater chemistry, you could try calculating the saturation indices of the various minerals observed in the field. Hope this helps, Brian

Hi Coralie, Do the minerals swapped into the Initial system represent the complete mineralogy of the basalt? Are they all in equilibrium with the initial porewater? Usually you include minerals in equilibrium with the porewater in the Initial pane. Minerals that are present but not in equilibrium can be set with kinetic rate laws on the Reactants pane. Then the infiltrating boundary fluids can react with those equilibrium and kinetic minerals. Adding the oxide components of the rock as simple reactants, as you've done, is much less common. And if you're just duplicating the composition of rocks in the Initial pane, you probably don't need to do it. I'm not sure what you mean with the ??? for minerals. I don't see that in your script anywhere. If you'd like to work on this script a little more and have someone take another look, please attach your custom thermo dataset as well. Regards, Brian Farrell Aqueous Solutions LLC

Hi I want to simulate the compatibility between HCl acid and additives such as corrosion inhibitors which are used in petroleum industry, but i don't know which module is suitable for this. Also how can i find the hydrolysis of various compounds in G-WB software? I will be grateful if anyone can help me.

Hi Anastasia, Are you sure the constraints you've specified (concentration values and units) for the Initial system and Inlet fluid are correct? The K+, for example, is .00362 mg/l in the Initial system and .00362 molal in the Inlet fluid. Perhaps this is just a coincidence, but maybe one of the values or units is wrong. You might also think about your conceptual model of the system. For example, you've specified that both the Initial and Inlet fluids are in equilibrium with Quartz and K-feldspar, but you've also set kinetic rate laws for these minerals. Are you sure that both of these fluids are supposed to be in equilibrium with each other? On a different note, it's sometimes easier to converge upon a solution when you charge balance on a cation than on an anion. In your fluid, if balancing on Cl- fails, you might try Na+. Regards, Brian