Application Note

Chemical Injection Application

Source: ABB Measurement & Analytics
ChemicalInjectionApp.jpg

This program starts with the well open and the chemical pump off until the flowrate drops below the setpoint. Once below the setpoint, the well is closed and the slug and pump run times are calculated. The pump turns on and runs for this amount of time. When the pump time expires, there is a user settable mix time. After the mix time expires, the program checks to ensure that the pressure is greater than the setpoint prior to opening. Once the well is open, it flows until it starts to load up. In the open cycle, there are setpoints to determine when the cap gas is depleted, when the slug is unloaded and when the well is starting to load up. The well then closes and restarts the cycle again.

This program is designed to assist plunger lift. It will lighten the load, thus requiring less bottom hole pressure to lift the plunger. Once the well is closed (valve is controlled by plunger lift) the chemical pump is turned on. The pump on time is determined by the slug size, pump speed and chemical-to-slug ratio. Mixing time is set by the timer option in the closing valve state of plunger lift.

The chemical pump is controlled based on the gas flowrate. The lower the flowrate, the longer the pump will run in a one minute window. If the flowrate is above the highest setpoint the pump will not run. The user will enter the number of flowrate setpoints and the pump on times for each setpoint. If the tubing pressure is above a designated setpoint, the last pump on time will be frozen until the pressure drops below that setpoint.