So you plan to inject produced gas to well "A" with the objective increase production in well "B".
I would prefer such a solution when the reservoir is still above the bubble point. In this case your gas goes again into solution lowering the viscosity and maintain reservoir pressure.
If you already have a gas cap, things get more complicated and economics needs to be run.
- gas can be reinjected right there (into gas cap) trying to balance fluid production and keep the reservoir pressure. BUT remember - gas is not sweeping efficient, you might bypass the oil and never get it back. By the way, Sgi is irreducible gas saturation.
- You can close gas producers and start pressure maintenace with water injection