Analysis of common faults in a submersible electric pump well

1. Ground management factors

(1) There are too many times of starting and stopping the well, and based on experience in production practice, it can be confirmed that damage to the electrical system is the main cause, and motor burning in the electric pump well is the most common. Frequent startup greatly affects the lifespan of the unit, with the main consequence accelerating the failure of the motor protector.

(2) Long well shutdown time, easy to overload and shut down during startup

During the production process of the oil field, sand is produced from the oil well, and the well fluid corrodes to form debris and scale. The specific gravity of these substances is relatively higher than that of oil and water. During normal production of the electric pump well with a large displacement of lifting liquid, debris is discharged from the wellbore along with the well fluid. However, when the electric pump well is shut down for a long time, a large amount of debris is deposited on the single flow valve. Due to the higher specific gravity than oil and water, debris falls into the centrifugal pump at the moment of opening the well. In addition, after the well is shut down, some sand particles and debris are also deposited in the guide shell of the centrifugal pump, and the upper oil pipe wax oil sleeve annulus is also prone to forming dead oil.

2. Underground unit factors

After repeated use of the unit for a period of time, the cables of the unit deteriorated severely and were not properly updated (including components). During the repair process, quality inspection was not standardized, execution standards were not detailed, and execution was not strict. The insulation of the unit will be relatively low, and the reliability will also be relatively poor.

3. Geological factors

(1) The impact of sand production and scaling in the formation, as well as the large displacement production of the electric pump well, can easily cause sand production in the formation during the production process. The excessive sand content in the well fluid directly leads to the pump being stuck and shut down. A low sand content in the well fluid can cause wear and tear on the centrifugal pump impeller, guide vanes, and pump casing of the electric pump unit, which, together with corrosion in the well fluid, can lead to impeller wear or pump body puncture.

(2) The impact of well fluid corrosion, with the improvement of oil field exploitation, according to the analysis of wellhead sampling, the average mineralization degree of electric pump wells with corrosion phenomenon reached 36345.58mg/L. Chemical corrosion is very serious, especially after the local wear of the surface strengthening layer of the parts, under the dual effects of chemical corrosion and electrochemical corrosion, pitting corrosion occurs, further accelerating the corrosion rate, causing the unit casing or anti inversion block to corrode and fail, leading to the collapse of the well.

(3) The impact of insufficient liquid supply in the formation, the insufficient liquid supply capacity of the oil well, and the inability to dissipate a large amount of heat during the production process, resulting in the burning of the motor.

4. Impact of downhole tools

The main manifestations are oil pipe leakage and damage to the single flow valve. The oil pipe with thread damage forms a leakage channel when it is lowered into the well due to the production pressure difference. The channel continues to increase due to water excitation, ultimately leading to oil pipe leakage. The electric pump unit can operate normally due to oil pipe leakage, but the pump does not produce liquid or the liquid volume is low. Severe oil leakage leads to a decrease in the strength of the oil pipe, which can cause downhole failure of the unit when it falls into the well.

5. Impact of well repair construction

Due to the non-standard quality of well repair construction, the well has been lying down, mainly manifested as incomplete well cleaning, dirty wellbore, and non-standard installation and operation of the unit.

6. Grid voltage fluctuations

The instantaneous fluctuation of power grid voltage makes the working voltage of the underground motor unstable, leading to the destruction of the motor magnetic field and the generation of partial reverse magnetic field, resulting in a decrease in the positive torque and speed of the motor, leading to a decrease in the pump efficiency of the centrifugal pump. In addition, the electric pump operates underground for a long time, and the insulation of the cables and the unit decreases with the extension of time. After the insulation decreases, the voltage fluctuation of the power grid will directly cause cable breakdown or unit burning.