Methods and apparatus for measuring return flow in a well

1. A method for evaluating the loss circulation in a wellbore made of a casing and an annular with an annular fluid within, comprising:

(i) fixing a reel of wound optic fiber line on an objet, said object defining a plug in said casing;

(ii) fixing the optic line on a first position to a reference point;

(iii) moving the object within the casing so that the optic fiber line is unwound from the reel on a second position;

(iv) generating from the first position a signal along the optic fiber line;

(v) measuring from the first position a change of said signal along the optic fiber line, said signal informing on the second position;

(vi) deducing from said change of said signal a displacement of the object and a flow rate at an object level Q s ;

(vii) measuring the flow rate of the fluid exiting the annular at the surface level Q r ;

(viii) evaluating the loss circulation Q l by comparing the flow rate at the object level Q s with the flow rate at the surface level Q r .

2. The method of claim 1 , further comprising the step of pumping a fluid in the casing at the reference point level and measuring a flow rate of the fluid at a reference point level Q c and evaluating a U-tube effect of the casing by comparing the flow rate at the object level Q s with the flow rate at the reference point level Q c .

3. The method of claim 1 , further comprising fixing means at the second position that is able to create the change of said signal.

4. A method for limiting the loss circulation in a wellbore made of a casing and an annular with an annular fluid within and a pump pumping a fluid in the casing at a reference point level comprising:

(i) performing the evaluation of the loss circulation in the wellbore according to claim 1 ;

(ii) identifying the presence of the loss circulation in the wellbore; and

(iii) adjusting the flow rate of the fluid at the reference point level Q c .

5. The method of claim 1 , wherein the flow rate at the object level Q s is measured by the displacement of the object within the casing by unwinding from the reel.

6. The method of claim 1 , wherein the object is made of a dart or a plug or a foam ball.

7. A method for evaluating the U-tubing effect in a tube, comprising:

(i) fixing a reel of wound optic fiber line on an object, said object defining a plug in said tube;

(ii) fixing the optic fiber line on a first position to a reference point;

(iii) pumping a fluid in the tube at the reference point level;

(iv) measuring the flow rate of the fluid at the reference point level Q c ;

(v) moving the object within the tube thanks to the fluid so that the optic fiber line is unwound from the reel on a second position;

(vi) generating from the first position a signal along the optic fiber line;

(vii) measuring from the first position a change of said signal along the optic fiber line, said signal informing on the second position;

(viii) deducing from said change of said signal a displacement of the object and a flow rate at an object level Q s ;

(ix) evaluating the U-tubing effect of the tube by comparing the flow rate at the object level Q s with the flow rate at the reference point Q c .

8. The method of claim 7 , further comprising fixing means at the second position that is able to create the change of said signal.

9. A method for limiting the U-tubing effect in a wellbore made of a casing and an annular with an annular fluid within and a pump pumping a fluid in the casing at a reference point level comprising:

(i) performing the evaluation of the U-tubing effect in the casing according to claim 7 ;

(ii) identifying the presence of the U-tubing effect in the casing;

(iii) performing an evaluation of loss circulation in the wellbore;

(iv) identifying an absence of the loss circulation in the wellbore;

(v) and adjusting the flow rate of the fluid at the reference point level Q c .

10. The method of claim 7 , wherein the flow rate at the object level Q s is measured by the displacement of the object within the casing by unwinding from the reel.

11. The method of claim 7 , wherein the object is made of a dart or a plug or a foam ball.

12. An apparatus for use in a wellbore made of a casing and an annular with a fluid within, comprising:

a reel of wound optic fiber line fixed to an object within the casing, and

a light transmitter/receiver device able to generate a signal through the optic fiber line and to measure a change of said signal;

wherein the optic fiber line is: (a) on a first position fixed to a reference point linked to the light transmitter/receiver device, and is (b) on a second position unwound from the reel;

wherein the light transmitter/receiver device is able to measure the change of said signal when occurring at the second position; and the apparatus being characterized by having a system able to measure a flow rate of the fluid exiting the annular at a surface level Q r :

wherein the apparatus further comprises an input of fluid in the casing at the surface and a flow meter able to measure the flow rate of said fluid at the reference point level Q c :

wherein a flow rate at an object level Q s is measured by the displacement of the object within the casing by unwinding from the reel.

13. The apparatus according to claim 12 , further comprising an additional element on the second position able to create the change of said signal at the second position.

14. The apparatus according to claim 12 , wherein the light transmitter/receive device is an apparatus in the family of optical time domain reflectometer.

15. The apparatus according to claim 12 , wherein the object is made of a dart or a plug or a foam ball.

16. The apparatus according to claim 12 , wherein the optic fiber line is further linked to a sensor.

17. The apparatus of claim 16 , wherein the sensor is a sensor in the family of Bragg grating sensor.

18. The apparatus according to claim 12 , wherein the optic fiber line is further linked to an actuator located on the object.