Unpowered automatic-liquid-drainage metering device and metering method thereof

The invention relates to the technical field of oilfield surface produced liquid metering, in particular to an unpowered automatic-liquid-drainage metering device and a metering method thereof. The unpowered automatic-liquid-drainage metering device comprises a vertical metering separator and a control module. According to the unpowered automatic-liquid-drainage metering device and the metering method thereof, the requirement for metering produced gas and produced liquid under different working conditions is met, and especially, the significant advantages are achieved aiming at metering, gathering and transportation under the severe working conditions that the gas-oil ratio is low and associated gas slug is serious; by controlling a differential pressure control valve, a certain pressure difference is maintained in the vertical metering separator, and it is ensured that a metered liquid phase is drained normally; by utilizing pressure energy of a wellhead, the unpowered automatic-liquid-drainage gathering and