PorousFlow 2D models: should injection rate and thermal power be interpreted “per unit out-of-plane”?

[Yulongggggg]

Hi MOOSE/PorousFlow team,

I’m running a Cartesian 2D (x-y) PorousFlow ThermoHydro model for a geothermal doublet-like setup on a planar fracture network. I’m confused about how to interpret injection rate and extracted thermal power in 2D, and whether I must scale results by an assumed out-of-plane thickness H to represent a 3D reservoir.

Questions:
1. In a 2D (x-y) PorousFlow model, are well/source terms (e.g., PorousFlowPointSourceFromPostprocessor or PorousFlowPeacemanBorehole) implicitly defined per unit out-of-plane thickness?
2. Similarly, is thermal power computed in 2D (e.g., heat_J_this_step / dt) actually W per meter thickness, so that a 3D-equivalent thermal power should be:Q3D = Q2D * H

[GiudGiud]

Hello

A 2D simulation is effectively infinite in the 3rd dimension. So 3D results (with this limitation that they are not truly 3D) can be obtained by scaling the 2D slice by the length in the 3rd dimension.

Similarly for imposing a local 3D source in a 2D simulation, you divide by the length in the 3rd dimension.
So yes to 1 and 2, and I'll let porous flow experts weigh in on 3.

The easier way to conceptualize this is to normalize everything by volume. E.g. instead of passing the power from 3D to 2D, you compute the power density, and impose that same quantity in 2D and 3D.

[Yulongggggg]

Hello

A 2D simulation is effectively infinite in the 3rd dimension. So 3D results (with this limitation that they are not truly 3D) can be obtained by scaling the 2D slice by the length in the 3rd dimension.

Similarly for imposing a local 3D source in a 2D simulation, you divide by the length in the 3rd dimension. So yes to 1 and 2, and I'll let porous flow experts weigh in on 3.

The easier way to conceptualize this is to normalize everything by volume. E.g. instead of passing the power from 3D to 2D, you compute the power density, and impose that same quantity in 2D and 3D.

Thank you so much, now it makes much sense to me