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Gtplot discrepancy between delta cm3 and delta vol% plots


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Hi, I noticed that for my plots of a reaction path model there was a large difference between the delta cm3 and the delta vol%. I expected that the delta vol% would equate with the change in cm3 of a mineral to the total vol of minerals but that cannot be the case. Can you explain to me what I am looking at in the vol% plot?

 

Cheers

Dirk

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Hello Dirk,

The delta mineral volume % is calculated relative to the initial mineral volume %. For any given mineral, the delta volume % =100* ((mineral vol at current step / bulk volume at current step) - (mineral vol at step 0 / bulk volume at step 0)).

You can plot and export the bulk volume numerical value under variable type "Physical parameters" and the mineral volume (make sure that you select the linear scale) and perform the calculation in Excel to verify that they match what is shown for delta volume%.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

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Hi Jia. Thanks for the quick response. Yes, the calculation works but I need to know how porosity is impacted and the entire change in quartz for instance is due to the increase in the bulk volume which is due to an increase in the fluid volume (density increase) not to the mineral volume. In the subsurface the result would be a pressure increase and either fluid flow or fracturing, but without fracturing the the volume% change would reflect the porosity change where in this case it does not. Is there a way to set this up so that the bulk volume stays the same? See column J in the spreadsheet.delta vol calc.xlsx

 

Dirk

delta vol calc.xlsx

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Hello Dirk,

Thanks for attaching the excel file. The porosity is calculated as the fluid volume divided by the bulk volume of the system. The bulk volume is composed of the mineral volume, fluid volume, and any inert volume that may be prescribed at each time step. So if your overall mineral volume decreases, the total bulk volume will decrease and the porosity will increase in React.

In React, there's no way to fix the bulk volume of your system. The reactive transport model applications, X1t and X2t, on the other hand require the user to set a domain, which has a fixed bulk volume for each node. If you want, you might want to consider trying your model in one of the RTM apps.

Hope this helps,
Jia

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