Characterizing lubricant oil degradation using fluorescence signals

1. A method to diagnose lubrication oil deterioration, the method comprising:

generating a continuous wave collimated light beam;

chopping the continuous wave collimated light beam into a plurality of step light beams, each step light beam having a constant intensity for a particular time interval;

irradiating a fresh lubrication oil sample obtained from a hydrocarbon well equipment with the plurality of step light beams such that a first light-induced fluorescence is emitted from the fresh lubrication oil sample in response to irradiation by each step light beam;

detecting a first light-induced fluorescence signal from the fresh lubrication oil sample;

irradiating a deteriorated lubrication oil sample obtained from the hydrocarbon well equipment with the plurality of step light beams such that a second light-induced fluorescence is emitted from the deteriorated oil sample in response to irradiation by each step light beam;

detecting a second light-induced fluorescence signal from the deteriorated lubrication oil sample;

determining a lubrication oil parameter from the first light-induced fluorescence signal and from the second light-induced fluorescence signal, wherein each of the lubrication oil parameters are associated to at least one of an oil viscosity of the respective lubrication oil sample, a damping ratio of the respective fluorescence signal, and or an undamped natural frequency of the respective fluorescence signal; and

determining an amount of lubrication oil deterioration of the deteriorated lubrication oil sample by correlating the lubrication oil parameter from the first light-induced fluorescence signal and from the second light-induced fluorescence signal to a calibration curve.

2. The method of claim 1 , wherein determining the lubrication oil parameter comprises determining a temporal variation of a fluorescence intensity from the light-induced fluorescence-signal.

3. The method of claim 2 , wherein determining the lubrication oil parameter comprises determining a steady-state of the light-induced fluorescence-signal from the temporal variation of the fluorescence intensity.

4. The method of claim 3 , wherein determining the lubrication oil parameter comprises determining the lubrication oil parameter from the steady-state of the light-induced fluorescence-signal.

5. The method of claim 2 , wherein the fluorescence intensity is represented as a second order dynamic system corresponding to one of an over-damped oscillator with a damping factor larger than 1 or an under-damped oscillator with a damping ratio smaller than 1.

6. The method of claim 1 , further comprising collecting the lubrication oil sample from the hydrocarbon well equipment.

7. The method of claim 1 , further comprising guiding the light beam at an acute angle on a front surface of a container holding the lubrication oil sample.

8. The method of claim 1 , further comprising filtering the light-induced fluorescence signal.

9. The method of claim 1 , further comprising capturing the light-induced fluorescence signal by a fast photodiode.

10. The method of claim 1 , further comprising:

comparing the oil parameter to previously measured oil parameter to determine an oil deterioration rate; and

determining an estimate of a useful remaining lifetime of the hydrocarbon well equipment associated to the lubrication oil sample based on the oil deterioration rate, wherein the hydrocarbon well equipment is in use in a hydrocarbon-producing well during determining the estimate of the useful remaining lifetime of the hydrocarbon well equipment.

11. The method of claim 10 , wherein the hydrocarbon well equipment is a submersible pump configured to pump fluid uphole from the hydrocarbon-producing well and wherein the submersible pump is disposed within the hydrocarbon-producing well.

12. The method of claim 1 , wherein the light beam is generated by a laser source.

13. A system, comprising:

a light beam generator configured to generate a continuous wave collimated light beam;

a chopper configured to chop the continuous wave collimated light beam into a plurality of step laser beams, each step laser beam having a constant intensity for a particular time interval;

a container configured to hold a lubrication oil sample;

an optical equipment configured to guide the plurality of step laser beams to a face of the container;

a fast photodiode configured to detect light-induced fluorescence signal from the lubrication oil sample in response to irradiation by the plurality of step light beams; and

a hardware processor interoperably coupled with a memory and configured to:

detect a first light-induced fluorescence signal from a fresh lubrication oil sample obtained from a hydrocarbon well equipment;

detect a second light-induced fluorescence signal from a deteriorated lubrication oil sample obtained from the hydrocarbon well equipment;

determine a lubrication oil parameter from the first light-induced fluorescence signal and from the second light-induced fluorescence signal, wherein each of the lubrication oil parameters are associated to at least one of an oil viscosity of the respective lubrication oil sample, a damping ratio of the respective fluorescence signal, and an undamped natural frequency of the respective fluorescence signal; and

determine an amount of lubrication oil deterioration of the deteriorated lubrication oil sample by correlating the lubrication oil parameter from the first light-induced fluorescence signal and from the second light-induced fluorescence signal to a calibration curve.