[OLD] Dynamic modelling

[webmaster]

From: Joel Brugger

Subject: Dynamic modelling

I am trying to repeat the calculations of Sverjensky D. A. (1987) [The role of migrating oil field brines in the formation of sediment-hosted Cu-rich deposits. Econ. Geol. 82, 1130-1141.]. The first step involves titration of an evaporite (hematite+quartz+anhydrite) into an oil field brine.

My problem is that many things happen when you add the first 1% of the evaporite. This is due mainly to the increased in reduced sulphur that causes precipitation of sulphides. These sulphides quickly redissolve as the fluid gets more oxidised. 100% evaporite addition corresponds to the point where the brine becomes saturated with anhydrite. Problem:

Looking at minerals precipitation/dissolution is best done on a log-log plot. If I don't want to miss a phase, I have to calculate about 100,000 steps (delxi =3D 0.0001, dxplot=3D0). GTPLOT reports an error when trying to read the huge resulting plot file. Is there a way to define non-linear step increments? Even better, is there a way to have REACT choose the right number of steps for me? For example, REACT could perform additional steps if some variables change more than a certain amount between two steps. In my case, I would ask REACT to monitor the amounts the pyrite, sphalerite, and galena in the system, as well as Eh. As a cheaper option, it would be good if REACT could choose the calculations exported to the plot file according to such rules. Or may be I just missed a point somewhere (I am using version 3.0.3a) ?

 

From: Craig Bethke

Subject: Re: Dynamic modelling

The easiest way to make this plot is to react the first 1% of the reactants, pick up the results of the run, set a new suffix (so you don't write over the results of the first part of the run), and then run the rest of the path. Then run two instances of Gtplot using log-log coordinates, one for each part of the run, and combine the resulting plots using PowerPoint. Alternatively, save the x-y points from the Gtplot plots to spreadsheet files, import them to Excel, and render them in a plot. A more expensive option to to increase the memory on your computer, so Gtplot can run on your large output file.