Geochemist's Workbench Support Forum

# Alkali Flood simulation

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Hi there

I am trying to redo the alkali flooding simulation on page range 443-447 in Geochemical and Biogeochemical Reaction modeling book.

Is the volume change on Y axis (Fig. 30.4) expressed as "delta"? If yes, I have a couple of questions on values found in Table 30.2

Consider NaOH flood, how did you calculate the change in pore volume (delta % and Alkali consumed (%)?

Thanks

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And as a follow-up to the above questions, when calculating carbonate (mineral) volume change, did you take into account both calcite and dolomite minerals or calcite only. With a +42 value, it looks like it's calcite. If it's only calcite, why didn't you consider dolomite? and if you summed up both calcite and dolomite volume change, does it mean that you minimized their difference in kinetics?

Thanks for the clarification.

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Hello,

The calculation for the pore volume change assumes a constant bulk volume for the initial and final state of the system. For the NaOH flood example, the initial bulk volume is the sum of the fluid volume (1064.535) and the mineral volume (6050) at 7114.53 cm^3. Calculate the initial porosity by dividing the initial mineral volume (1064.535 cm^3) by the bulk volume to get 0.149628.

After 20 days of flushing the system, calculate the final porosity by taking the initial bulk volume (7114.53 cm^3) and subtract the initial mineral volume (6050) and the additional mineral volume precipitated during the simulation (98.74367 cm^3) and then divide by the initial bulk volume. This will get you a final porosity of 0.135748.

Calculate the change in porosity by taking the difference and dividing by the initial porosity: (0.135748-0.149628)/0.149628 = -0.092763

To calculate the fraction of alkali consumed, you can look at the increase in moles of Na+ in the rock (under the Variable type Components in rock) and divide it according to the moles of Na+ in the reactant fluid. In the NaOH flood simulation, the Na+ in the rock component increased by 3.926 moles. We know that 5 moles of Na+ were added to the system (recall that the reactant times factor was set to 10). The fraction of alkali consumed is 3.926/5 = 0.7852.

With regards to your follow up question, I think you missed accounting for dawsonite in your carbonate totaling. Since the kinetic rate law was only set for Quartz, all other minerals in this system are precipitating and dissolving according to simple thermodynamics.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

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Thank you so much, Jia!

Just a quick question about the value of fluid volume of 1064.535 cm^3 while the text says "1 Kg of water...". Is that value (1064.535 cm^3) from standard conditions?

Thanks

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The fluid volume comes from an estimate of fluid density based on a NaCl fluid of the same TDS as the fluid in the example. Note, the exact numbers quoted in the forum response for fluid volume refer to a variation of the calculation in which density was calculated according to the Phillips et al method, which was previously the default in the GWB. The new default method starting with GWB14 is the Batzle-Wang equation. The results shouldn’t be too different, though. You can compare them by changing the method on the Config > Options… dialog. For more information, please see Appendix A.10 Fluid density and viscosity in the GWB Essentials Guide, as well the density command in the GWB Command Reference.

Regards,

Brian Farrell
Aqueous Solutions

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Thanks Brian. Do you know of any paper (or resource) that can be helpful in estimating the fluid volume from TDS values? Or should I consider 1Kg of water though the groundwater has high TDS value.

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You're welcome. Like I said, React calculates density (and thus volume) from TDS using either the Phillips or Batzle-Wang methods, both of which are cited in the appendix to the GWB Essentials Guide. You can find various configured and calculated system properties in the output, such as solvent and solution mass, volume, and density, under Chemical parameters and Physical parameters.

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Hi Brian

I am sorry; It appears that there is some misunderstanding. The volume of 1064.535 cm^3 does not seem to have been retrieved from React since it was used from the beginning (before running React) to calculate the volume of the solid matrix ,hence the volume of each mineral phase (Quartz, Calcite, Dolomite, Muscovite and Kaolinite). I was asking how that value was estimated because I try to find the density of the fluid from GSS (physical parameters....> density), It just gives blank cells with no values.

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Modeling is quite often done in steps. It's an iterative process. You can get an estimate of fluid density in React by supplying the major components defined for the fluid:

```T    = 70
pH   = 5
Na+  = 1  molal
Ca++ = .2 molal
Cl-  = 1  molal
```

Or, for a more accurate calculation, you can configure a fluid in equilibrium with arbitrary amounts of the reservoir minerals to calculate the density accounting for all the components of the fluid. So, the swapping steps are the same as in the textbook example, but the mineral volume/mass constraints don't matter for that part of the problem.

If you'd prefer, you can specify volume% of each mineral, rather than an absolute volume, along with a porosity for the system.

As for GSS, you can supply the values of certain analytes or in some cases you can calculate them. If you want to calculate fluid density in GSS from your fluid analysis, choose +analyte > Calculate with SpecE8.... If that's what you're doing and you're still having issues, please attach your spreadsheet. For more information, please see 3.2.5 Calculating analytes in the GWB Essentials Guide.

Regards,

Brian

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Thanks Brian. I now get it!!

You're welcome.

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