A reservoir boundary that allows some flow across it is called Leaky.

• A. No-flow
• B. Constant-Pressure
• C. Leaky
• D. Composite Limits

Answer: (C)

Boundary conditions describe how fluid can cross the edge of a reservoir. A boundary that prevents any crossing is a no-flow boundary, where the flux across the boundary is zero. A boundary with fixed pressure sets the boundary pressure to a specific value, regardless of what happens just inside the boundary. When the boundary allows some flow, but not completely, it’s described as leaky. This is modeled as a Robin or mixed condition: the flux across the boundary is related to the pressure difference between the reservoir and the adjacent region, meaning the boundary offers a finite resistance to flow. In practice, a leaky boundary represents partial communication with neighboring formations or aquifers, so fluid can exchange across the edge but not freely or at a fixed pressure. The term composite limits isn’t a standard boundary type here, so it doesn’t match the idea of partial cross-edge flow.