Catriona Posted May 2, 2013 Share Posted May 2, 2013 Hello, I have been working in React building a model of fluid rock interaction between host rock minerals and a measured surface water that I sampled dripping from a tunnel roof - this fluid has flowed through a few hundred meters of cold rock. I reacted this fluid with the rocks at increasing temperatures to ~200 degrees. To constrain the model I have analyses of geothermal spring waters in the area, which is what essentially comes out the other end of the system - I have only used these analyses to compare with the modelled fluid compositions and I have not involved them in the model. The rock compositions used were based on "average" rocks the fluid would interact with based on various thin section observations of the different rock types and their proportions in the area. By doing this I aim to: 1. investigate the strongest controls on fluid chemistry to try and explain the differences in chemistry between the springs I have analysed and 2. investigate alteration mineral assemblages and the how much water, time, etc it would take to alter the rocks to varying degrees that we see in the field. Starting out with a basic equilibrium model I quickly realised that I needed to set kinetic constraints on mineral dissolution and so included the built in kinetic rate laws (constrained by specifying pre-exp and Ea)for all minerals involved other than halite and graphite (kinetic minerals = Quartz, K-feldspar, Anorthite, Albite, Phlogopite, Annite, Muscovite, Epidote, Tremolite, Calcite, Clinochlore14-A and Pyrite). This model runs and converges when I increase temperatures from 10 (measured fluid temperature) to 200 degrees (>maximum temperatures of spring fluids at depths) over different timescales in the range of 20-200 years and allow minerals to precipitate (with inappropriate minerals suppressed). I should/will at some point involve kinetic mineral precipitation too. However, this is not very realistic as the fluid is moving through the rock pile to probably >2km depth and therefore back reaction with minerals already precipitated is not realistic - but when I tell the model to "flow-through" it does not converge or simply gets stuck trying to solve at a particular stage. Additionally the fluids are flowing through the system and interacting with more and more rock as they go, so the system will not "run out" of any of the reactant minerals. To try and get around this I broke up the reaction path and asked it to first of all solve the model for temperatures increasing from 10 to 20 degrees over 1 year, and several other options with the intention of pickingup this fluid and interacting with more fresh reactants. However, the model gets stuck trying to solve for one stage (normally about Xi=0.02), or sometimes the model gets stuck then the message "Successful completion of react path." pops up, yet in reality it has only run for <5 days. I think the problem may be do to with step size while using kinetics as the model solves when run over ~20 years up to 200 degrees but not for the same temperature change over 15 years, or the smaller time steps when I try to break down the reaction paths. Please could you advise on what may be causing these problems or how I could fix them? I have attached the .rea file for more details - it takes 15-30 minutes to solve under the saved conditions in that file. Av tunnels-simple kinetics posted.rea Thanks, Catriona Quote Link to comment Share on other sites More sharing options...
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