4D chemical fingerprint well monitoring

A method for well monitoring, the method comprising:

• inserting a sensing system downhole to a desired depth, wherein the sensing system comprising an evanescent field sensing element that is in direct contact with a downhole fluid and provides partial or total internal reflection of a beam which interacts with the downhole fluid at an interface between the evanescent field sensing element and the downhole fluid;
• wherein the sensing system comprises:
• at least one light source, having at least one frequency comb generator, that emits the beam;
• a first optical switch configured to split the beam into a reference beam and a sensing beam;
• a waveguide;
• wherein the frequency comb generator is configured to modify the reference beam into a reference comb beam and to modify the sensing beam into a sensing comb beam,
• wherein the sensing comb beam interacts with the downhole fluid to form at least a portion of an interacted beam;
• a second optical switch that combines the sensing comb beam after interacting with the downhole fluid and the reference comb beam to form the interacted beam having an interferogram,
• wherein the downhole fluid is arranged between the first optical switch and the second optical switch,
• wherein the sensing comb beam interacts with the downhole fluid at the evanescent field sensing element, and the reference comb beam bypasses the downhole fluid, and
• a detector configured to obtain a spectral distribution of at least one of the following:
• the beam, the sensing comb beam, the reference comb beam, the interacted beam, or a combination thereof;
• detecting, by the detector, spectral distribution of the interacted beam to monitor a composition of the downhole fluid in real-time;
• and
• controlling an actuator with an inflow and injection control device (ICD) based on the composition of the downhole fluid.