Bulk volume input parameter in React

[Zhidi Wu]

Hello!

I'm trying to set up a batch reaction model on a shale sample in React. My shale core sample has a porosity of 8.85% and a bulk volume of 57.78 ml. Plus, the fluid volume in my batch experiment is 100 ml. Therefore, in the Medium tab, I set porosity to 0.0885, bulk volume to 57.78 ml, and permeability constants A=1 and B=-3.0885. The model has difficulty in convergence due to the porosity in node 0 being too small. I played around with the parameters in the Medium tab and found that the model runs when the bulk volume is higher than a certain value (~1400 ml). So, is the bulk volume in the Medium tab different from the bulk volume of my sample? Looking into the output file, the bulk volume seems to be the sum of fluid, mineral, and inert volumes. I realized that the bulk volume in the model is different from what I first assumed. How do I correctly set up the bulk volume to match the mineral, fluid, and pore volumes in my experiment?

Many thanks,

Zhidi

[Jia Wang]

Hello Zhidi,

The bulk volume in the Medium pane refers to the bulk volume of your entire system and not the mineral bulk volume. As you have discovered, the bulk volume in React is composed of the mineral volume, fluid volume, and any inert volume that may be prescribed at each time step. The porosity is calculated as the fluid volume divided by the bulk volume of the system.

I cannot see what your input pane looks like, but generally it is recommended to use relative units for your constraints. For example, you can set your mineral composition as a volume percentage of your system and the concentration of dissolved components in units like mmolal or mmol/l. This way you can easily scale the bulk system to the desired total volume in the Medium tab.

It sounds like the bulk volume of your system is 57.78 ml (mineral) + 100 ml (fluid) = 157.78ml. You can enter this on your Medium pane to scale the whole system to this volume. Note that the volume of a React node will change depending on what type of reactions you are using. If you are adding minerals or fluid, that will increase the bulk volume for your system.

You can find more information about the bulk volume, or any other command, in the GWB Command Reference.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

[Zhidi Wu]

Hi Jia,

That's helpful. I also looked into GWB Command Reference, and it answers most of my questions. 

However, I still have another question on how React calculates the mineral mass and volume. If I type wt% of the mineral in the Reactants tab and assign porosity and bulk volume in the Medium tab, the output file returns a mineral mass, a very small mineral volume, and a very large inert volume. I understand that the inert volume is ignored once porosity is defined according to Command Reference, but this results in an extremely large mineral density (~90 g/cm3), which is not realistic. I tried to use absolute mass unit instead of relative unit in the Reactant tab and the results are more realistic. My question is: how mineral and inert volumes are calculated in this case?

Thanks,

Zhidi

[Jia Wang]

Hi Zhidi,

I am glad you found the guide helpful.

I think the Porosity explanation in the Command Reference will help, it explains that...

Use the “porosity” command to set (as a volume fraction) the initial porosity of the system. Porosity, the fraction of the system occupied by fluid, is the ratio of fluid volume to the sum of fluid, mineral, and inert volume.

When you specify the porosity, the program will figure the difference between the volume of a system of the given porosity and fluid volume, and the volume taken up initially in the system by minerals and fluid. The program assigns this difference as inert, non-reactive volume (see the “inert” command). In this case, the program ignores any settings that may have been made with the “inert” command.

When you do not specify an initial porosity with the “porosity” command, on the other hand, the program calculates it from volumes in the system of fluid, minerals, and inert space. To restore this default behavior, enter the command with an argument of “?”.

For example, if you specify 5 free volume % of Quartz and a porosity of 0.1. Then the program will include 5 free volume % of inert mineral to achieve 0.1 porosity.

The program draws information from the thermodynamic dataset for its calculation. Mineral density information is provided from the thermodynamic dataset. You can open the dataset loaded for your current React run by going to File -> View -> open the file that ends with .tdat. If density information is not available, then the software converts between mass and volume assuming a density of 2.65 g/cm3. This is the same density used for converting between inert mass and volume. If you are checking density from your calculation, please make sure you are looking at the individual mineral mass (under Variable type "Mineral") and not the total mineral mass volume reported under Variable type "Physical parameters".

Hope this helps,
Jia

[Zhidi Wu]

Hi Jia,

I still don't think I understand. In your example, there are vol. 5% quartz (mineral volume fraction) and 10% porosity (fluid volume fraction). Should the program automatically include vol. 85% inert mineral (non-reaction phase volume fraction) to sum the three components (fluid, mineral, and inert) up to 100%?

Thanks,

Zhidi

[Jia Wang]

Hi Zhidi,

Sorry about my mistake above. You are right. The inert volume should be 85% and the fluid volume would be 10%. I had a mix up with the porosity in the math.

Best regards,
Jia