Failure analysis of horizontal injection pump and Countermeasures

Horizontal injection pump has been widely applied in Tarim Oilfield. In this paper, the fault in the operation of a horizontal water injection pump in the Tazhong area is described in detail, and the corresponding countermeasures are put forward, which provides a good guiding significance for the follow-up production operation.

Since the water injection system was put into operation in a certain block in Tazhong operation area in 2011, there have been many problems in the horizontal injection pump, resulting in the intermittent stop of water injection. In the past two years, we have explored and summarized the field problems, and applied our valuable experience to other water injection blocks.

1. field condition

Working principle of 1.1 level water injection pump

The horizontal injection pump is a multi-stage centrifugal pump, which is driven by the impeller at high speed by the motor. Under the centrifugal force, the liquid filled with the impeller is flung from the impeller center along the blade path to the impeller. As the liquid is affected by the blade, the pressure and speed are increased simultaneously, through the guide case. The runner is introduced to the secondary impeller. In this way, all the impeller and guide shells are gradually passed through, thus increasing the pressure energy of the liquid. The liquid gradually flows through all the impellers and deflector in the pump, and the pressure is superimposed by step by step, so that the outlet can obtain certain pressure energy.

1.2 level water injection pump system composition

The integral pump of a horizontal water injection pump in the tower is equipped with a skid mounted structure. Under the premise of ensuring overall rigidity, it can be hoisted and lifted according to need. Its structure is mainly composed of eight parts, such as control cabinet, motor, motor base, coupling, suction assembly, horizontal pump, pump support, concrete foundation or steel frame foundation.

Operation condition of 1.3 level water injection pump

In normal operation, the inlet pressure of the injection pump is 0.3Mpa, the outlet pressure of the pump is 23Mpa, and the wellhead pressure is 22Mpa. The process system is equipped with overload, under load, inlet pressure and pump outlet temperature protection.

Common malfunction of 2. level water injection pump

The horizontal water injection pump in Tazhong oilfield has repeatedly stopped for various reasons since it was put into operation. The common failures are mainly overload and stopping pump, under load stop pump, pump body heating and operation, and the vibration and abnormal noise occur during the operation. Through exploration and practice in operation, we have carried out the cause analysis and experience summarization of all kinds of failures.

Analysis of 2.1 fault causes

2.1.1 overload stop pump

The starting delay is short and the overload setting is too small. Due to the influence of instrument signal and process conditions, the injection pump may have false signals during the start-up process, and it will be able to return to normal in operation. If the delay is too short and the overload value is too low, the injection pump will stop the pump because of the fact that the actual current is higher than the overload current protection value in a short time.

Mechanical failure. In the process of horizontal injection pump operation, if the card blockage occurs, the pump will overload and chain will stop. The possible causes of mechanical failure are motor bearing or suction bearing with dead point, stuck between the guide wheel or relative sliding between the guide wheel and the shell.

The voltage of the power grid is too low. Low voltage causes the output power of the motor to be less than the rated value, and the torque is reduced. If the rated load is still required, the working current of the motor will be increased, the speed is down, and the temperature will rise. If the voltage is too low, the working current will increase rapidly and the temperature of the motor will rise suddenly. When the motor has no overcurrent protection, the motor will be blocked, the temperature rises sharply, and the motor will burn up quickly. The water injection pump in Tazhong oilfield is equipped with overcurrent protection device, and when the current is overloaded, the water injection pump chain is shut down.

Human control factors. When the pump is started, if the operator controls the opening of the outlet valve of the pump too large, it will cause the flow and power of the pump to be very big when starting, and the motor and the rotating part of the pump run from rest to high speed, which requires a lot of acceleration, which will cause the large start current and the overload to stop the pump.

2.1.2 under load stop pump

The startup delay is short and the under load is set too high. If the start-up delay is set too low and the under load value is too high, the injection pump will stop the pump due to the fact that the actual current is less than the under load current protection value in a short time.

Mechanical failure. If the pump is broken during the start or operation of the pump, the pressure of the pump outlet will be reduced or zero. At the same time, the motor current will be smaller and the pump temperature is higher. As the operating current of the injection pump decreases, when the running current value falls below the under load protection value, the water injection pump will be cascading to stop pump due to underload protection.

Other reasons. There will be a drop in the displacement of water injection pump in the inner sand tank of the tank, the falling of the gate valve gate of the water injection pump and the inflow pressure, the blocking of the single flow valve tongue plate at the outlet of the water injection pump, the opening of the outlet valve and the pressure of the wellhead higher than the pump pressure. At this point, the current value will decrease as the displacement of the injection pump decreases. When the running current value falls below the under load protection value, the water injection pump will be cascading to stop pump due to underload protection.

Local fever of 2.1.3 injection pump

The heat of the water injection pump exit is no difference. This is mainly due to the fact that the wellhead pressure is equal to or higher than the outlet pressure of the injection pump, resulting in more difficult water injection. When the pump outlet temperature is higher than the set value of 70 C, the temperature protection stops the pump. Secondly, the outlet valve of the water injection pump is too small or scaling to make the drainage volume too small, which will also cause the pump outlet section to generate heat.

The local fever of the water injection pump is accompanied by abnormal noise. This situation is mostly friction between the pump shell and the impeller shell. Each guide shell of the water injection pump is fixed by the front and back compression rings. Under normal circumstances, the impeller of the water injection pump is in the guide shell.