A petroleum well tracer release flow shunt chamber in an annulus space about a base pipe and method of estimating one or more pressure differences or gradients, wherein the flow shunt chamber extending generally axial-parallel with the base pipe, and provided with a shunt flow passage for holding a shunt chamber fluid, and including a tracer system exposed to and arranged for releasing unique tracer molecules at a generally even release time rate to the shunt chamber fluid, a first inlet aperture for receiving a first fluid, a second outlet aperture for releasing the shunt chamber fluid to a fluid, a flow restrictor allowing a pressure gradient between the inlet and outlet apertures driving the shunt chamber fluid out via the flow restrictor.