Differential pressure indicator for downhole isolation valve

1. A differential pressure indicator (DPI), comprising:

a tubular mandrel for assembly as part of a casing string and for receiving a tubular string, the tubular mandrel includes a mandrel stop shoulder and a mandrel piston shoulder;

a tubular housing for assembly as part of the casing string and for receiving the tubular string, wherein a terminal end of the tubular mandrel fits into a terminal end of the tubular housing, the tubular housing movable relative to the tubular mandrel between an extended position and a retracted position, wherein the tubular housing includes a housing stop shoulder and a housing piston shoulder;

a hydraulic chamber formed between the housing piston shoulder and the mandrel piston shoulder; and

a coupling in communication with the hydraulic chamber and for connection to a sensing line;

wherein the tubular housing is movable relative to the tubular mandrel and to the extended position in response to tension exerted on the tubular housing by the casing string, wherein a volume of the hydraulic chamber reduces in response to the movement of the tubular housing to the extended position.

2. The DPI of claim 1 , wherein:

the coupling is a hydraulic coupling, and

the DPI further comprises a hydraulic passage providing the communication between the hydraulic chamber and the hydraulic coupling.

3. The DPI of claim 2 , wherein:

the hydraulic chamber is operable to move the tubular housing relative to the tubular mandrel and to the retracted position,

the mandrel stop shoulder and housing stop shoulder are engaged in the retracted position, and

the housing piston shoulder and mandrel piston shoulder are engaged in the extended position.

4. The DPI of claim 1 , wherein the tubular housing is longitudinally movable relative to the tubular mandrel between the positions.

5. The DPI of claim 1 , wherein:

each of the tubular mandrel and the tubular housing have a torsional coupling, and

the torsional couplings are engaged in and between the positions.

6. The DPI of claim 5 , wherein:

each of the tubular housing and the tubular mandrel includes a piston and an adapter fastened together, and

the mandrel piston shoulder is formed in an outer surface of the mandrel piston, and

the housing piston shoulder is formed in an inner surface of the housing piston.

7. The DPI of claim 6 , wherein:

the mandrel stop shoulder is a lower end of the mandrel adapter, and

the housing stop shoulder is formed in an inner surface of the housing piston.

8. The DPI of claim 6 , wherein:

the housing torsional coupling is formed in a lower end of the housing piston, and

the mandrel torsional coupling is formed in an outer surface of the mandrel piston.

9. The DPI of claim 6 , wherein a hydraulic passage is formed in a wall of and along the housing piston.

10. A system for use in drilling a wellbore, comprising:

the DPI of claim 1 ; and

an isolation valve, comprising:

a second tubular housing for connection to the tubular housing of the DPI;

a flapper disposed in the second tubular housing and pivotable relative thereto between an open position and a closed position; and

a flow tube longitudinally movable relative to the second tubular housing for opening the flapper;

the sensing line for connecting the coupling of the DPI to a control station;

the control station comprising a microcontroller (MCU) operable to calculate a differential pressure across the flapper.

11. The system of claim 10 , wherein:

when the flapper is in the open position, the DPI is configured to move from the extended position toward the retracted position when a hydraulic fluid in the hydraulic chamber is at a threshold pressure; and

when the flapper is in the closed position, an upward force generated by the differential pressure across the flapper moves the DPI toward the retracted position, causing the pressure of the hydraulic fluid to decrease to an indication pressure;

wherein the MCU calculates the differential pressure across the flapper from the difference between the threshold pressure and the indication pressure.

12. The DPI of claim 1 , wherein the DPI has a first length when the tubular housing is in the extended position and a second length when the tubular housing is in the retracted position, wherein the second length is less than the first length.

13. The DPI of claim 1 , wherein the casing string is stretched by the DPI as the DPI moves from the extended position to the retracted position.

14. The DPI of claim 1 , wherein the tubular housing is moveable relative to the tubular mandrel and to the retracted position in response to a fluid pressure in the hydraulic chamber, wherein the movement of the tubular housing to the retracted position increases the volume of the hydraulic chamber.

15. A method of constructing a wellbore, comprising:

deploying a tubular string into the wellbore through a casing string disposed in the wellbore, the casing string having an isolation valve in a closed position and a hydraulic sensing line extending along the casing string;

equalizing pressure across the isolation valve, including using the hydraulic sensing line to determine tension in the casing string to determine differential pressure across the isolation valve;

opening the isolation valve; and

lowering the tubular string through the open isolation valve.

16. The method of claim 15 , wherein the differential pressure is determined using pressure of the sensing line.

17. The method of claim 16 , wherein:

the casing string further has a differential pressure indicator (DPI) connected to the hydraulic sensing line and the isolation valve, and

the method further comprises, before equalization, injecting hydraulic fluid into the hydraulic sensing line, thereby retracting the DPI.

18. The method of claim 17 , wherein the DPI is in an extended position before deployment of the tubular string.

19. The method of claim 17 , wherein a stroke of the DPI decreases a length of the DPI.

20. The method of claim 17 , wherein:

the casing string has a free portion and a portion cemented into the wellbore, and

the isolation valve and the DPI are part of the free portion.

21. The method of claim 15 , wherein the differential pressure is determined using fluid volume into or from the hydraulic sensing line.

22. The method of claim 15 , wherein the casing string further has a control line extending therealong for opening the isolation valve.

23. The method of claim 15 , further comprising monitoring the differential pressure during deployment of the tubular string.

24. An isolation valve for use in drilling a wellbore, comprising:

a tubular housing for assembly as part of a casing string and for receiving a drill string, wherein the tubular housing has a shoulder formed in an inner surface thereof;

a tubular member including a seat, wherein the tubular member and the seat are disposed in the tubular housing, and wherein the tubular member and the seat are longitudinally movable and longitudinally movable relative to the tubular housing, wherein the seat has a shoulder formed in an outer surface thereof;

a flapper pivotally connected to the seat between an open position and a closed position;

a flow tube longitudinally movable relative to the seat and the tubular housing for opening the flapper;

a first hydraulic chamber formed between the flow tube and the tubular housing and receiving a piston of the flow tube, wherein the flow tube is movable to open the flapper in response to a fluid pressure in the first hydraulic chamber;

a hydraulic passage in fluid communication with the first hydraulic chamber and a hydraulic coupling; and

a differential pressure indicator (DPI) linked to the seat for responding to force exerted on the seat by the flapper in the closed position, the DPI including a second chamber formed between the shoulder of the tubular housing and the shoulder of the seat, wherein the second chamber is further formed between the tubular member and the tubular housing.

25. The valve of claim 24 , wherein the second chamber is a second hydraulic chamber, and wherein a hydraulic passage disposed in the tubular housing extends from the second hydraulic chamber to a hydraulic coupling.

26. The valve of claim 25 , wherein the DPI further comprises a compression spring disposed in the second hydraulic chamber of the DPI and having a first end bearing against the shoulder of the tubular housing and a second end bearing against the shoulder of the seat.

27. A system for use in drilling a wellbore, comprising:

the valve of claim 26 ; and

a sensing line for connecting the hydraulic coupling of the DPI to a control station;

a control line for connecting the hydraulic coupling to a hydraulic manifold; and

the control station for operating the hydraulic manifold and comprising a microcontroller (MCU) operable to calculate a differential pressure across the flapper by monitoring volume of hydraulic fluid into or from the sensing line.

28. A system for use in drilling a wellbore, comprising:

valve of claim 26 ; and

a sensing line for connecting the hydraulic coupling of the DPI to an accumulator of a control station, the control station further including a microprocessor operable to calculate a differential pressure across the flapper; and

a level sensor in communication with the microprocessor, the level sensor configured to monitor a hydraulic fluid level in the accumulator.

29. A system for use in drilling a wellbore, comprising:

the valve of claim 25 ; and

a sensing line for connecting the hydraulic coupling of the DPI to a control station;

a control line for connecting the hydraulic coupling to a hydraulic manifold; and

the control station for operating the hydraulic manifold and comprising a microcontroller (MCU) operable to calculate a differential pressure across the flapper using a pressure of the sensing line.

30. The valve of claim 24 , wherein

the DPI further comprises:

a compression spring disposed in the second chamber and having a first end bearing against the housing shoulder and a second end bearing against the seat shoulder;

a sensor for measuring a length of the spring; and

leads extending from the sensor to an electrical coupling.

31. The valve of claim 30 , wherein the sensor is a proximity sensor.

32. The valve of claim 30 , wherein the sensor is a position sensor.