Method for estimating either flowback or the reservoir fluid production rate from either one individual inlet or the contribution from several inlets separated by intervals in a wellbore located in an oil and/or gas reservoir (Ω), said wellbore (W) being extended along a path (P) at least from a point of the surface of the reservoir (Ω) until a point in the subsurface, the wellbore (W) comprising:
- a casing (T) comprising a plurality of inlet ports (I) distributed according to a first arrangement along the path (P) allowing the entrance of fluid into the casing (T) and, the casing (T) also comprising a plurality of magnetic irregularity elements (C) distributed according to a second arrangement along the path (P);
- at least one sensor element (S) wherein the sensor element (S) is adapted to record in time the magnetic perturbation generated by a magnetic irregularity element (C) when the at least one sensor element (S) is moving within the casing (T) and passing through a section of the wellbore (W) where the said magnetic irregularity element (C) is located according to the path (P) direction;
- wherein the method comprises:
- delivering at least one sensor element (S) to flowing fluid in the wellbore (W) within the casing (T) during either flowback or the production of fluid at a location of the wellbore (W) located in the subsurface and where the fluid flows, wherein the sensor element (S) is dragged by the flow of surrounding fluid;
- recording by the at least one sensor element (S) the magnetic perturbations caused when the sensor element (S) dragged by the flowing fluid passes near each magnetic irregularity element (C) with known spacing between them, wherein the recording is timestamped by the sensor element (S) at each magnetic perturbation along the path (P);
- when the sensor element (S) has completed a length of the path (P) to be measured, transmitting the timestamped magnetic perturbation recorded data from the sensor element (S) to a control center or a computer system that is exterior to the wellbore;
- determining from the timestamped transmitted magnetic perturbations recorded data the estimation of the velocity of the fluid flow as the velocity of the sensor element (S) being dragged by said flow of either flowback or the production of fluid;
- and
- determining the estimation of the flow rate of the flowback or the reservoir fluid production from either one individual inlet port (I) or the contribution from several inlet ports (I) along the path in the wellbore located in the oil and/or gas reservoir (Ω) from the estimation of the velocity of the fluid flow;
- and
- wherein the section of the wellbore (W) through which the sensor element (S) is traveling is horizontal, and the sensor element (S) has a weight determined to show a buoyancy or a sink effect when being submerged within the fluid in order to cause the position of the sensor element (S) in respect to the radial direction of the casing (T) when being dragged by the flow different to the central position of the section of the casing (T) allowing to estimate the velocity of the flow along the radial direction.