# Questions regarding boundary conditions and source terms

**URL:** <https://discourse.opengeosys.org/t/questions-regarding-boundary-conditions-and-source-terms/1781>\
**Category:** Help & Support\
**Created:** [December 19, 2025, 12:12pm UTC](https://discourse.opengeosys.org/t/questions-regarding-boundary-conditions-and-source-terms/1781 "2025-12-19T12:12:59Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![marosaro](https://discourse.opengeosys.org/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@marosaro](https://discourse.opengeosys.org/u/marosaro)\
**Post date:** [December 19, 2025, 12:12pm UTC](https://discourse.opengeosys.org/t/questions-regarding-boundary-conditions-and-source-terms/1781/1 "2025-12-19T12:12:59Z")

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Hello everybody, I have 2 questions if somebody could give some inputs.

1. What is the (functional) difference between source term and Neumann pressure boundary condition?  
e.g. in the context of material/fluid inflow at a point - if we want to simulate fluid injection (or production) into the reservoir, and represent the injection place as a point, will the results be the same if we define the flow as a source term or as a Neumann pressure boundary condition (in that point)?

2. Regarding temperature source terms - if we have a wellbore (represented as a 1D line mesh) in the domain, and want to dynamically simulate heat exchange between the reservoir and the wellbore (through python script).. Can we just calculate heat exchange values and define them as temperature source terms along the nodes of the wellbore 1D mesh, or do we need to also take into account the volume of cells connected to the node?

Thank you and best regards

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**Author:** ![chleh](https://discourse.opengeosys.org/user_avatar/discourse.opengeosys.org/chleh/32/854_2.png) [@chleh](https://discourse.opengeosys.org/u/chleh)\
**Post date:** [January 7, 2026, 8:07am UTC](https://discourse.opengeosys.org/t/questions-regarding-boundary-conditions-and-source-terms/1781/2 "2026-01-07T08:07:09Z")

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Hi marosaro,

1. A volumetric source term and a Neumann BC behave identically in OGS: The integrand will be integrated over the provided geometry and added to the rhs of the global equation system. However, you can define a [`Nodal`](https://doxygen.opengeosys.org/stable/d0/d2c/ogs_file_param __prj__ process_variables __process_variable__ source_terms __source_term__ Nodal.html) source term if you want to simulate injection at a single point.

2. I’m not entirely sure what you mean. If you use a [Python BC](https://doxygen.opengeosys.org/stable/da/dc2/ogs_file_param __prj__ process_variables __process_variable__ boundary_conditions __boundary_condition__ Python.html) or [Python source term](https://doxygen.opengeosys.org/stable/d1/d12/ogs_file_param __prj__ process_variables __process_variable__ source_terms __source_term__ Python.html) on the 1D line mesh, there the fluxes you compute in the Python script will be integrated over the 1D line elements by OGS, i.e., in that sense you don’t have to worry about the volume of the adjacent (3D) cells.

Best regards,  
Christoph