Method and System for Downhole Clock Synchronization

• US 20050035875A1
• Filed: 08/10/2004
• Published: 02/17/2005
• Est. Priority Date: 08/13/2003
• Status: Active Grant

• Current Assignee: IntelliServ, LLC (NOV, Inc.)
• Original Assignee: Intelliserv, Inc. (NOV, Inc.)
• Inventors: Johnson, Monte, Hall, David R., Bartholomew, David B., Moon, Justin, Koehler, Roger O.
• Granted Patent: US 7,142,129 B2
• Time in Patent Office: Days
• US Class Current: 340/853.100
• CPC Class Codes: E21B 47/12 Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling
• CPC Class Codes: G01V 1/26 Reference-signal-transmitting devices, e.g. indicating moment of firing of shot
• CPC Class Codes: G01V 11/002 Details, e.g. power supply systems for logging instruments, transmitting or recording data, specially adapted for well logging, also if the prospecting method is irrelevant means for transmitting well survey signals E21B47/12; signal transmission systems in general G08C; transmission in general H04B

Abstract

A method and system for use in synchronizing at least two clocks in a downhole network are disclosed. The method comprises determining a total signal latency between a controlling processing element and at least one downhole processing element in a downhole network and sending a synchronizing time over the downhole network to the at least one downhole processing element adjusted for the signal latency. Electronic time stamps may be used to measure latency between processing elements. A system for electrically synchronizing at least two clocks connected to a downhole network comprises a controlling processing element connected to a synchronizing clock in communication over a downhole network with at least one downhole processing element comprising at least one downhole clock. Preferably, the downhole network is integrated into a downhole tool string.

Claims

1. A method for synchronization of at least two clocks connected to a downhole network comprising:

determining total signal latency between a controlling processing element comprising a synchronizing clock and at least one downhole processing element comprising at least one downhole clock;

the controlling processing element sending a request to the downhole processing element to set the downhole clock to a synchronizing time adjusted to compensate for latency.

2. The method of claim 1, wherein the downhole network is integrated into a downhole tool string.

3. The method of claim 2, wherein the downhole network comprises a plurality of downhole components, wherein each downhole component comprises a conductor connecting a first communication element in one end and a second communication element in another end.

4. The method of claim 3, wherein the first and second communication elements are selected from the group consisting of inductive coils, optical fiber couplers, and electrical contacts.

5. The method of claim 4, wherein the inductive coils are encapsulated in circular, magnetically conducting, electrically insulating troughs.

6. The method of claim 1, wherein electronic time stamps are used to measure transmission latency between processing elements.

7. The method of claim 1, wherein at least one of the downhole processing elements is selected from the group consisting of computer systems, electronic processors, and integrated circuits.

8. The method of claim 1, wherein at least one of the clocks is located outside of the well bore.

9. The method of claim 1, wherein at least one of the downhole clocks is attached to the tool string.

10. The method of claim 1, wherein the downhole clocks are distributed along the tool string.

11. The method of claim 1, wherein the downhole clocks are associated with tools selected from the group consisting of mud motors, turbines, jars, repeaters, amplifiers, nodes, mud hammers, shock absorbers, reamers, under-reamers, fishing tools, steering elements, MWD tools, LWD tools, seismic sources, seismic receivers, sensors, modems, swivels, pumps, perforators, other tools with an explosive charge, mud-pulse sirens, well casing, blow-out preventors, bottom hole assemblies, switches, routers, multiplexers, piezoelectric devices, optical transmitter, optical regenerators, optical receivers, and wireless transceivers.

12. The method of claim 1, wherein at least one of the processing elements is connected to an information source through a medium selected from the group consisting of global positioning systems, computer networks, and wireless networks.

13. The method of claim 1, wherein at least three clocks are concurrently electrically synchronized.

14. The method of claim 1, wherein at least one of the processing elements comprises hardware that fixes the computational latency to a known constant.

15. The method of claim 1, wherein the method to determine the total signal latency comprises:

the controlling processing element sending a first request to the downhole processing element to set the downhole clock to time t_n;

the controlling processing element sending a second request to the downhole processing element to relay a time t_z back to the controlling processing element, time t_z being the time according to the downhole clock at the approximate instant the response to the second request is transmitted;

the controlling processing element receiving time t_z from the downhole processing element and recording a time t_x, time t_x being the approximate instant time t_z arrives from the downhole processing element, according to the synchronizing clock;

approximately determining a total signal latency between the controlling processing element and the downhole processing element by logical computations using time t_z and time t_x.

16. The method of claim 15, wherein the controlling processing element sends the second request multiple times to determine an approximate average total signal latency.

17. The method of claim 15, wherein the first request from the controlling processing element is made at time t_n.

18. A method for synchronization of at least two clocks connected to a downhole network comprising:

a controlling processing element comprising a synchronizing clock sending a first request to a downhole processing element comprising at least one downhole clock to set the downhole clock to time t_n;

the controlling processing element sending a second request to the downhole processing element to relay a time t_z back to the controlling processing element, time t_z being the time according to the downhole clock at the approximate instant the second request is received;

the controlling processing element receiving time t_z from the downhole processing element and recording a time t_x, time t_x being the approximate instant time t_z arrives from the downhole processing element, according to the synchronizing clock;

approximately determining a total signal latency between the controlling processing element and the downhole processing element by logical computations using time t_z and time t_z;

the controlling processing element sending a request to the downhole processing element to set the downhole clock to a synchronizing time adjusted to compensate for total signal latency.

19. The method of claim 18, wherein the downhole network is housed within a downhole tool string.

20. The method of claim 19, wherein the downhole network comprises a plurality of downhole components, wherein each downhole component comprises a conductor connecting a communication element in one end and a second communication element in another end.

21. The method of claim 20, wherein the first and second communication elements are selected from the group consisting of inductive coils, optical fiber couplers, and electrical contacts.

22. The method of claim 21, wherein the inductive coils are encapsulated in circular, magnetically conductive, electrically insulating troughs.

23. The method of claim 18, wherein electronic time stamps are used to determine transmission latency between processing elements.

24. The method of claim 18, wherein at least one of the processing elements comprises hardware that fixes the computational latency to a known constant.

25. A method for determining total signal latency between at least two processing elements connected to a downhole network comprising:

a controlling processing element comprising a first clock sending a first request to a downhole processing element comprising a downhole clock to set the downhole clock to time t_n;

the controlling processing element sending a second request to the downhole processing element to relay a time t_z back to the controlling processing element, time t_z being the time according to the downhole clock at the approximate instant the second request is received;

the controlling processing element receiving time t_z from the downhole processing element and recording a time t_x, time t_x being the approximate instant time t_z arrives

from the downhole processing element, according to the first clock;

the controlling processing element approximately determining a total signal latency between itself and the downhole processing element by logical computations using time t_z and time t_x.

26. The method of claim 25, wherein the downhole network is housed within a downhole tool string.

27. The method of claim 26, wherein the downhole network comprises a plurality of downhole components, wherein each downhole component comprises a conductor connecting a first communication element in one end and a second communication element in another end.

28. The method of claim 27, wherein the first and second communication elements are selected from the group consisting of inductive coils, optical fiber couplers, and electrical contacts.

29. The method of claim 28, wherein the inductive coils are encapsulated in circular, magnetically conducting, electrically insulating troughs.

30. The method of claim 25, wherein at least one time t_z and at least one time t_x are measured to determine an approximate average total signal latency between the first and second devices.

31. The method of claim 25, wherein at least one of the processing elements comprises hardware that fixes the computational latency to a known constant.

32. A system for synchronizing at least two clocks connected to a downhole network comprising:

a controlling processing element in electronic communication with a synchronizing clock in communication over a downhole network with

at least one downhole processing element in electronic communication with at least one downhole clock.

33. The system of claim 32, wherein the downhole network is housed within a downhole tool string.

34. The system of claim 33, wherein the downhole network comprises a plurality of downhole components, wherein each downhole component comprises a conductor connecting a first communication element in one end and a second communication element in another end.

35. The system of claim 34, wherein the first and second communication elements are selected from the group consisting of inductive coils, optical fiber couplers, and electrical contacts.

36. The system of claim 35, wherein the inductive coils are encapsulated in magnetically conducting, electrically insulating troughs.

37. The system of claim 32, wherein the processing elements are capable of affixing electronic time stamps to data that are transmitted and received between devices.

38. The system of claim 32, wherein at least one of the processing elements is selected from the group consisting of computer systems, electronic processors, and integrated circuits.

39. The system of claim 32, wherein at least one of the processing elements is connected to an information source through a medium selected from the group consisting of global positioning systems, computer networks, and wireless networks.

40. The system of claim 32, wherein at least one clock is located outside of the well bore.

41. The system of claim 32, wherein at least one clock is attached to the drill string.

42. The system of claim 32, wherein at least one clock comprises a clock source selected from the group consisting of at least one crystal, at least one transistor, at least one oscillator, at least one RC circuit, at least one LC circuit, and at least one RLC circuit.

43. The system of claim 32, wherein at least one of the devices comprises hardware that fixes the computational latency to a known constant.

44. The system of claim 32, wherein at least three clocks are concurrently electrically synchronized.