A process fluid flow system is provided having an input, an output, and a plurality of fluid circuits disposed between the input and output. At least one valve is disposed to selectably cause process fluid to flow through either a first circuit of the plurality of circuits, or a second circuit of the plurality of circuits. Process fluid flows through the first circuit during normal production, and through the second circuit during process fluid sequestration. A process fluid flow measurement device is operably interposed between the input and output and configured to measure total flow through the system. A separator is disposed in the second circuit and is arranged to allow the process fluid to separate gravitationally over time into immiscible components of the process fluid, the separator having a known internal volume. A guided wave radar level measurement device is preferably disposed to measure heights of interfaces within the separator. A controller is coupled to at least one valve, the process fluid flow measurement system, and the guided wave radar level measurement device. The controller is configured to combine total process fluid flow information from the process fluid flow measurement device with measured height information from the guided wave level measurement device to provide fractional flow rates for at least one immiscible component of the process fluid.