Submersible pump monitoring
In order to address the above noted problems, embodiments of the present invention use distributed acoustic sensing to monitor the fluid level in an ESP activated well so as to monitor the condition and performance of the ESP. Embodiments of the invention use the ESP as an acoustic source in order to monitor the annulus fluid level within the well and to monitor the frequency of the ESP. Additionally, embodiments of the present invention may use distributed acoustic sensing to monitor the flow rates of the production fluid above and below the ESP to determine the pump's efficiency. In particular, some embodiments utilize one or more optical fibers to measure the acoustic waves generated by the ESP, wherein the fiber cabling has already been deployed along the length of the well. As such, the present invention is a non-invasive, in-situ method for monitoring the condition and performance of an ESP.
1. A method of in-well fluid level detection around an in-well submersible pump using an optical fiber distributed acoustic sensor having an optical fiber deployed in-well, the method comprising:
a) measuring a propagation of acoustic waves within fluid in a vicinity of the submersible pump using the optical fiber distributed acoustic sensor, wherein the acoustic waves are generated by the submersible pump when in operation, the speed of sound of the acoustic waves being measured along a length of the optical fiber within the vicinity of the submersible pump to measure the propagation therefrom; and
b) detecting an in-well fluid level by determining, in dependence on the measurements by the optical fiber distributed acoustic sensor of the propagation of the acoustic waves generated by the submersible pump, a location of a fluid interface within the well with respect to the submersible pump to thereby further determine whether the submersible pump is submerged in the fluid, wherein determining the location of the fluid interface in the well includes detecting a change in the speed of sound measurements, wherein a spatially abrupt change in the speed of sound measurements as a result of weak acoustic coupling is indicative of acoustic energy propagating above the fluid interface.
2. A method according to claim 1 , wherein measuring the propagation of acoustic waves includes detecting one or more reflections of an acoustic wave.
3. A method according to claim 1 , wherein determining the location of the fluid interface in the well comprises measuring the propagation of acoustic waves from a known location of the submersible pump to the fluid interface to determine the distance from the known location to the interface.
4. A method according to claim 1 , wherein the propagation of acoustic waves generated by the submersible pump are measured below and/or above the pump.
5. A method according to claim 1 , wherein the optical fibre distributed acoustic sensor is further arranged to measure one or more operating frequencies of the submersible pump.
6. A method according to claim 5 , wherein the operating frequencies are measured during start-up and/or the operation of the submersible pump.
7. A method according to claim 5 , wherein the optical distributed acoustic sensor detects any changes in the operating frequencies.