A flowmeter apparatus is for determining a volumetric flowrate for a well flow out from a wellbore, by means of a mass flowmeter, which is configured for receiving well flow and for measuring a mass flow rate of the well flow. At least one mass density measuring apparatus, is fluidly connected to the mass flowmeter upstream of a first inlet or downstream of a first outlet, or both. The mass flow rate of the well flow can be measured using a measuring wheel rotatably arranged below a funnel second section arranged to receive at least a portion of the well flow. A system for determining a volumetric flowrate for a well flow out from a wellbore includes the flowmeter apparatus arranged on a platform, rig, vessel, or other topside location, and connected between a riser and downstream processing equipment.

A flowmeter apparatus is for determining a volumetric flowrate for a well flow out from a wellbore, by means of a mass flowmeter, which is configured for receiving well flow and for measuring a mass flow rate of the well flow. At least one mass density measuring apparatus, is fluidly connected to the mass flowmeter upstream of a first inlet or downstream of a first outlet, or both. The mass flow rate of the well flow can be measured using a measuring wheel rotatably arranged below a funnel second section arranged to receive at least a portion of the well flow. A system for determining a volumetric flowrate for a well flow out from a wellbore includes the flowmeter apparatus arranged on a platform, rig, vessel, or other topside location, and connected between a riser and downstream processing equipment.