Mojo

Hi, I am building a dual porosity model in XT1. Could you please tell me: 1. How the the cumulative surface area of the stagnant zones affect a mineral reaction rate? I have my custom rate and need to know how to revise it to capture this. I have set the surface area of each mineral based on cm2/gr and I call "Surface" in my costume rate law. But certainly this is wrong as the minerals surface areas should be affected by the cumulative surface area of the stagnant zones. 2. Are the minerals equally distributed between the cubes representing the stagnant zones? 3. What is the half-width of the cubes? Is it half of the width of the cube? And what is it for slab? What is the slab thickness? 4. Can we set any arbitrary number for half-width of the cube as long as it is smaller than Node dimensions? For example, if my node cross sectional area is 10*10 cm2, how is it possible to have cubes with half-width of 2 cm while the volume fraction of stagnant zone is 0.9? How the cube can fit the node cross section while honouring their defined sizes and also the volume fraction of stagnant zones? In the manual's example, half-width of spheres defining stagnant zone was much higher than domain surface area, how is that possible? Can you show me the concept in a graphic please? I attached the common concept of dual porosity model to this text. The Spheeris or Cubes should fit the domain. 5. Should not the porosity of fracture considered to be equal to one for the dual porosity model and matrix or stagnant zones have its own porosity? The Node/grid porosity should be calculated from these two values. In the Medium section, does the Porosity refer to overall Node porosity? Many thanks and kind regards Mojo

Hi I am trying to model salting out effect that happens during dry gas injection. I used thermo.tdt in React to model the reactions between the rock and brine at 135 C. The model works just fine when there is no evaporation. But when I considered evaporating >99% of the brine, the model outcomes does not look trustworthy to me as the brine ionic strength is super high (like around 500,000 PPM!). I doubt any brine at this salinity can be stable. I have already read again section 3.2 of the manual and I cannot use thermo_kmw.tdat as the ionic species and minerals I have in my system are not defined in this dataset. Do you have any suggestions how one can model salting out effect in this case? And why model shows such a high salinity brine? Also when I am calculating ionic strength based on the data from "Components in fluid", it does not match what I get from "Ionic strength" listed in "Chemical Paramnters" dropdown menu. And lastly, I am confused between the difference of "components in fluid" and "species concentration". They do not give the same number for any ion (for example check H+). Why is that? Which one shows the true concentration of ions (in particular H+) in brine? Many thanks and kind regards, Mojtaba 20 yrs injection.rea

Hi All, I am running a a React model for studying CO2-brine-rock reactions. I increased the CO2 pressure linearly to my desired number in 2 days and I used the model outcomes for running a new model under constant CO2 pressure from 2 days to 20 yrs. The 20 yrs model has not converged even after 3 days running! I have run parallel models for which I tuned the time step and even put Siderite and Anorthite (the most reactive minerals in the model) at equilibrium condition to help the model converge faster, but it was un-effective. Non of the 20 yrs models converge yet and they are still going on.... Any idea why is that? I am using the most recent version of GWB (2021). Not sure what causes this issue. I faced this issue once in the past when I had Calcite (highly reactive mineral) in my model. And I found that I need to set Calcite in equilibrium so the model that can converge in a few mins. But as I said this trick did not work this time. Attached are both 2 days and 20 yrs models. Also, I wonder why the calculated porosity change in 2 days model is wrong. When I calculate the porosity using the minerals volumes data, and a fix bulk volume (initial bulk volume value), i end up to a different number. It seems bulk volume is changing in the model in each time step. Thanks Seyed 20 yrs injection.rea 2 days injection.rea

Dear Brian and Jia, I have been working with GWB react module for the past few months and I just wanted to let you know that the program does not report the right porosity values when the system gets a little bit complex. For example, when we include evaporation of water into the program for a simple system (water + quartz), as water evaporates during simulation time, porosity decreases! The way porosity is calculated in GWB seems to be wrong. Porosity should be calculated from: phi= pore volume/ bulk volume= (bulk volume- mineral volume)/bulk volume In a porous media, the bulk volume a rock/porous media is always constant, but in GWB it changes! Even when we have reactions, the bulk volume should remain constant. What should change is the mineral volume. For example, when a reaction led to the dissolution of minerals, the mineral volume decreases while the pore volume increases. Therefore, the bulk will remain constant. This is the real physic of porous media. As such, porosity will evolve. Now, for the case of evaporation that I mentioned, since GWB assume pore volume = fluid volume, as soon as evaporation starts, porosity decrease which is wrong and misleading. In reality, the porosity of rock will remain unchanged by evaporation of its pore fluid unless the evaporation of formation fluid led to the precipitation of minerals and an increase in mineral volume. Note that for the simple example that I mentioned, you will see mineral volume will remain unchanged. Another example is the temperature drop. If you make a simple model (water+ quartz) and drop the temperature, a reduction in the volume of fluid would occur which is expected. However, since GWB assumes fluid volume is equal to pore volume, it gives a reduction in system porosity which again is wrong. If there is no reaction or change in mineral volume, porosity should remain constant. Another example is the dissolution of CO2 in brine. If we have a sliding CO2 fugacity in a system without any reactions. We will see fluid volume increase linearly over time as CO2 dissolve in brine and therefore porosity increases! This is wrong if mineral volume remains unchanged. Do you have any feedback on this? Please let me know since it is a major problem that can mislead a lot of users and gives wrong data. This is of great importance for users using GWB for porous media applications such as scaling issues in reservoirs. I look forward to hearing from you. Kind Regards Mojtaba