The invention relates to a method and a device for injecting profile control online. The method includes that a plugging agent is injected in a water
injection well. The plugging agent injected in the water
injection well is injected online and the steps are that: (A) the plugging agent is stored into a
liquid storage tank; (B) the plugging agent is simultaneously injected along with the injected water by a special
injection device; (C) the plugging agent is mixed into an online water injection pipeline through a metering
plunger pump; (D) the plugging agent is mixed with the injected water in the water injection pipeline, injected into the well together and reach an oil layer; (E) the total injecting flow and injecting pressure on the well opening are measured by a flowmeter and a pressure gauge. The device includes the
liquid storage tank, a control valve, the metering
plunger pump, an injection agent tube, the water injection pipeline, a
throttle valve, the flowmeter, the pressure gauge and the water
injection well. One end of the injection agent tube is connected on the water injection pipeline and the other end is connected with the metering
plunger pump, the control valve and the
liquid storage tank in sequence. The water injection pipeline is connected with the water injection well through the
throttle valve and the flowmeter. The method and the device have the function of controllable water injection and simultaneous injection and are broadly applied into the water injection technique of
petroleum exploitation.