Detection of well fluid contamination in sealed fluids of well pump assemblies

1. An apparatus for pumping well fluid from a well, comprising:

at least one submersible well pump assembly for lowering into the well to pump well fluid, the at least one submersible well pump assembly comprising:

a rotary pump;

an electrical motor operably connected to the pump;

a sealed fluid contained in the well pump assembly;

a seal section operably connected between the motor and the pump for reducing a pressure differential the sealed fluid contained in the motor and the well fluid in the well;

at least one sensor mounted to the well pump assembly that detects contamination of the sealed fluid by the well fluid encroaching into contact with the sealed fluid;

a well fluid contamination first sensor mounted to the submersible well pump assembly and a well fluid contamination second sensor mounted to the submersible well pump assembly at an axial distance from the first sensor, relative to a longitudinal axis of the submersible well pump assembly, each of the first and second sensors being of a type that will detect a presence of well fluid encroachment into the sealed fluid; and

means for receiving signals from the first and second sensors indicating a presence of well fluid encroachment into the sealed fluid and for determining a time delay between a well fluid presence signal received by the first sensor and a well fluid presence signal received by the second sensor to estimate how fast well fluid is leaking into the sealed fluid.

2. The apparatus according to claim 1 , wherein:

the first and second sensors are mounted in the motor; and

the sealed fluid comprises motor oil located in the motor and in the seal section.

3. The apparatus according to claim 1 , wherein:

the first and second sensors are mounted in the seal section; and

the sealed fluid comprises motor oil located within the seal section.

4. The apparatus according to claim 1 , wherein the at least one submersible well pump assembly comprises:

a primary well pump assembly and a secondary well pump assembly, the secondary well pump assembly adapted to be suspended in the well along with the primary well pump assembly, but initially in a non operating mode;

the secondary well pump assembly having a barrier to prevent entry of well fluid into the rotary pump during the non operating mode;

the sealed fluid comprises a buffer fluid located in the rotary pump of the secondary well pump assembly while in the non operating mode; and

at least one of the first and second sensors is mounted in the buffer fluid in the pump of the secondary well pump assembly.

5. The apparatus according to claim 1 , wherein each of the first and second sensors comprises:

a light source;

a photo detector mounted opposite the light source for receiving a light beam emitted by the light source, the light source and the photo detector being mounted so as to pass the light beam through the sealed fluid; and

a circuit configured to determine attenuation of the light beam.

6. The apparatus according to claim 1 , wherein the seal section comprises:

a housing having a chamber with a well fluid entry port;

a flexible element located in the chamber having an interior filled with the sealed fluid in fluid communication with the sealed fluid in the motor and an exterior for contact with the well fluid in the chamber; and wherein

the first sensor is located in the interior of the flexible element.

7. The apparatus according to claim 6 , wherein:

the seal section has a labyrinth chamber; and

the second sensor is located in the labyrinth chamber.

8. An apparatus for pumping well fluid from a well, comprising:

a primary submersible well pump assembly and a secondary submersible well pump assembly for lowering as an unit into the well, the secondary submersible well pump assembly being initially in a non operating mode, the secondary submersible well pump assembly comprising:

a rotary pump filled with a buffer fluid and having an intake initially closed with a barrier to prevent entry of well fluid into the buffer fluid;

well fluid contamination upper and lower sensors mounted in the rotary pump within the buffer fluid, the upper sensor being mounted above the lower sensor, each of the sensors being configured to sense well fluid leaking into the buffer fluid;

an instrument panel adapted to be mounted adjacent a wellhead and linked to the upper and lower sensors for receiving signals from the upper and lower sensors indicating sensing a presence of well fluid in the buffer fluid; and

means in the instrument panel for determining a time delay between receiving a well fluid presence signal from the upper sensor and receiving a well fluid presence signal from the lower sensor so as to indicate how fast well fluid is leaking into the rotary pump.

9. The apparatus according to claim 8 , further comprising a pressure sensor mounted in the buffer fluid in the rotary pump, the pressure sensor configured to sense a buffer fluid pressure.

10. The apparatus according to claim 8 , wherein each of the upper and lower sensors comprises:

a light source that transmits a light beam along a path through the buffer fluid, the light beam having a wavelength selected that has a different absorption rate for well fluid than for the buffer fluid; and

a photo detector that detects a strength of the light beam, the strength being indicative of well fluid encountered along the path.

11. A method of pumping well fluid from a well, comprising:

providing at least one submersible well pump assembly comprising a rotary pump, an electrical motor operably connected to the rotary pump, a seal section operably connected between the motor and the rotary pump, a longitudinal axis, and a sealed fluid contained in the at least one submersible well pump assembly;

mounting a well fluid contamination first sensor to the at least one submersible well pump assembly and a well fluid contamination second sensor to the at least one submersible well pump assembly at an axial distance from the first sensor;

lowering said at least one submersible well pump assembly into the well; and

receiving signals from the first and second sensors indicating a presence of well fluid in the sealed fluid and determining a time delay between a well fluid presence signal received by the first sensor and a well fluid presence signal received by the second sensor to estimate how fast well fluid is leaking into the sealed fluid.

12. The method according to claim 11 , wherein:

the sealed fluid comprises motor oil located in the motor and the seal section; and

the first and second sensors are mounted in the motor oil.

13. The method according to claim 11 , wherein:

providing the at least one submersible well pump assembly comprises:

providing a primary well pump assembly and a secondary well pump assembly, the secondary well pump assembly having a barrier to prevent entry of well fluid into the rotary pump during the non operating mode, and the sealed fluid comprises a buffer fluid located in the rotary pump of the secondary well pump assembly;

lowering the at least one submersible well pump assembly comprises:

simultaneously lowering both the primary well pump assembly and the secondary well pump assembly into the well along with the primary well pump assembly; and the method further comprises:

operating the primary well pump assembly and leaving the secondary well pump assembly non operating with the buffer fluid located therein; and

detecting with the first and second sensors any encroachment of well fluid into contact with the buffer fluid.