Adding volumetric pressure source_term represents injection rate in TH2M module

Usability
1

Hi all,
I want to add a pressure source term which represents an unit injection rate in TH2M module. From the OGS conventions page, I learned that volumetric pressure ST represents a volumetric mass source in the model domain and in THM module pressure refers to liquid pressure(Pw). However, in TH2M process there is no process_variable named pressure. Instead, there are gas pressure(Pg) and capillary pressure(Pc). I think the source term setting must be different form that of THM module but I have no idea how to choose the correct process_variable block and set suitable parameters.

I know under Dirichlet boundary condition, Pg=non-wetting fluid pressure(whose unit is Pa) and Pc=Pg-Pw. But for gas_pressure and capillary_pressure variable block, what does source_term refers to? Can I set two respective source term values for Pg and Pc and the liquid pressure source term i.e.unit injection rate equals to the difference between them? Or is there any other way to set an injection rate in TH2M module?

Maybe someone can give me some help.

Best
Yuhao

2

Hi Yuhao,

a quick look at the FEM assembler of TH2M process shows that the conservation equations are in the order of: gas phase main component, liquid phase main component, temperature and displacement. (You can find this information in the code comments). From your last post, I think you already know that the order of primary variables here is Pg,Pc, T and sigma. Thus, there is a one to one relationship between the PVs and the balance equations. For instance, if you have a water source term, then this should be prescribed for Pc with a unit of M/L3/T, I think.

Reg,
Boyan

3

Hi Boyan
Thanks for your advice. I have prescribed a source term in Pc variable block. However, sometimes the calculation does not converge. I think the reason is that the calculation process is too sensitive to the setting of some pre-processing parameters, like permeability, porosity and so on. I will try to set correct parameters and make the whole process converge. :fist:

Best
Yuhao