Method for Autonomous Control of a Chemical Injection System for Oil and Gas Wells

摘要

A method for injection a liquid phase chemical into a well the method comprises steps of inputing a desired flow rate; computing a time required to dispense a known volume of fluid at the desired flow rate; opening a variable orifice to dispense the said fluid in less than the time computed; timing the dispensing of the fluid; adjusting the said orifice to ensure the time to dispense the fluid is less than the computed time. Preferably, a control program for a positive displacement metering system measures the time required for the travel of a free piston 22 in a cylinder of known volume to determine an average flow rate during a full stroke of the piston. Also inlet and outlet pressures 49, 49' or the differential pressure between the fluid inlet and outlet are measured. A four-way valve 15 may function as an adjustable metering orifice in response to the measured average flow rate and/or changes in the inlet and outlet pressures to achieve the desired flow rate. The system may automatically compensate for changes in fluid properties and fluid pressure.