Subsea autonomous chemical injection system

A subsea chemical injection system comprising:

• a seawater flowline having a seawater inlet and a first seawater outlet;
• a chemical flowline in fluid communication with the seawater flowline between the seawater inlet and first sweater outlet;
• a high-pressure seawater pump disposed along the seawater flowline;
• a first seawater volume flowmeter disposed along the seawater flowline;
• at least one chemical injection flow control mechanism disposed along the chemical flowline;
• and
• at leastonechemicalsubseamassflowmeterdisposedalongthechemicalflowlinebetween the seawater flowline and the chemical injection flow control mechanism, wherein the chemical subsea mass flowmeter comprises a Coriolis tube housed in a pressure vessel;
• and wherein the chemical injection flow control mechanism is housed in the pressure vessel.

A method for injecting chemicals into a subsea hydrocarbon production facility, the method comprising:

• pumping seawater through a chemical injection system disposed adjacent a subsea hydrocarbon production facility;
• measuring the volume of seawater pumped through chemical injection system;
• injecting one or more chemicals into the seawater as the seawater passes through chemical injection system;
• measuring the mass flow of the chemical injected into the seawater passing through chemical injection system, wherein the mass flow of the chemical is measured at a pressure less than the seawater within the chemical injection system;
• comparing the measured volume of seawater to the measured mass flow of the chemical and a predetermined set point;
• and
• adjusting the injection of the one or more chemicals based on the comparison.