Monitoring of Hydraulic Fracturing Operations

• US 20160146962A1
• Filed: 07/14/2014
• Published: 05/26/2016
• Est. Priority Date: 07/12/2013
• Status: Abandoned Application

• Current Assignee: Fotech Group Limited (BP PLC)
• Original Assignee: Fotech Solutions Limited
• Inventors: Hayward, Peter John
• Application Number:
  US14/904,362
• Publication Number:
  US 20160146962A1
• Time in Patent Office: Days
• CPC Class Codes: E21B 2200/06 Sleeve valves
• CPC Class Codes: E21B 34/10 operated by control fluid supplied from outside the borehole
• CPC Class Codes: E21B 43/26 by forming crevices or fractures
• CPC Class Codes: E21B 47/00 Survey of boreholes or wells monitoring pressure or flow of drilling fluid E21B21/08
• CPC Class Codes: E21B 47/005 Monitoring or checking of cementation quality or level
• CPC Class Codes: E21B 47/107 using acoustic means
• CPC Class Codes: E21B 47/135 using light waves, e.g. infrared or ultraviolet waves
• CPC Class Codes: G01V 1/307 for determining seismic attributes, e.g. amplitude, instantaneous phase or frequency, reflection strength or polarity
• CPC Class Codes: G01V 1/42 using generators in one well and receivers elsewhere or vice versa G01V1/52 takes precedence

Abstract

There are disclosed methods and apparatus for monitoring hydraulic fracturing operations, using a distributed optical fibre sensor to detect relevant acoustic signatures, such as acoustic signatures of cement washout and of events involving a valve drive component.

Claims

1. A method of monitoring a hydraulic fracturing operation comprising using a distributed optical fibre sensor to detect an acoustic signature of washout of cement surrounding a casing of a wellbore.

2. The method of claim 1 further comprising detecting a spatial extent of said washout from a spatial distribution said acoustic signature.

3. The method of claim 1 comprising:

using the distributed optical fibre sensor to detect an acoustic signal from the wellbore; and

identifying the acoustic signature of washout of cement from the acoustic signal.

4. The method of claim 3 wherein identifying the acoustic signature comprises identifying a central region proximal to an egress point in the casing, and identifying one or more branch regions each of which moves away from the egress point over time in association with related cement washout activity progressing along the wellbore.

5. The method of claim 4 wherein identifying the acoustic signature comprises identifying two said branch regions which simultaneously move away from the egress point in opposite directions along the wellbore.

6. The method of claim 4 comprising recognizing the central region and the one or more branch regions initiating together at a time of opening of a valve to permit fracture fluid to pass through an egress point in the casing.

7. The method of claim 6 further comprising identifying from the acoustic signal a pressure wave front propagating rapidly in both directions along the wellbore, and associating the origin of the wave front with the opening of the valve.

8. The method of claim 4 further comprising measuring a spatial extent of said washout from spatial extent of the one or more branch regions.

9. The method of claim 1 wherein identifying the acoustic signature comprises identifying an acoustic frequency peak in the acoustic signal detected by the distributed optical fibre sensor.

10. The method of claim 9 comprising recognising the acoustic frequency peak as located in a said branch region of the acoustic signature.

11. The method of claim 9 wherein the acoustic frequency peak has a height of at least double the associated background acoustic signal.

12. The method of claim 9 wherein the acoustic frequency peak has a full width at half maximum (FWHM) of less than 100 Hz.

13. The method of claim 9 wherein the apex of the acoustic frequency peak lies between 40 Hz and 300 Hz.

14. The method of claim 9 comprising determining extent of the cement washout by determining a spatial position of the acoustic frequency peak

15. The method of claim 9 comprising determining packoff of cement washout by determining diminishment of the acoustic frequency peak.

16. The method of claim 1 further comprising automatically generating an alarm signal or an alert when an acoustic signature of cement washout is identified.

17. Apparatus for monitoring a hydraulic fracturing operation comprising:

a distributed optical fibre sensor comprising a sensor optical fibre disposed along a wellbore; and

a washout detector arranged to receive an acoustic signal from the distributed optical fibre sensor and to detect from the acoustic signal an acoustic signature of washout of cement surrounding a casing of a wellbore.

18. The apparatus of claim 17 wherein the washout detector is arranged to detect in the acoustic signal a central region proximal to an egress point in the casing, and one or more branch regions each of which moves away from the egress point over time in association with related cement washout activity progressing along the wellbore.

19. The apparatus of claim 17 wherein the washout detector is arranged to detect an acoustic frequency peak in the acoustic signal and to use the acoustic frequency peak in detecting the acoustic signature of washout.

20. A method of monitoring a hydraulic fracturing operation in a wellbore, the hydraulic fracturing operation including delivering a valve drive component along the wellbore to a valve arranged to permit fracturing fluid to egress from the wellbore, comprising using a distributed optical fibre sensor having one or more sensing fibres disposed along the wellbore to detect an acoustic signal from the wellbore, and identifying from the acoustic signal an acoustic signature of the valve drive component.

21. The method of claim 20 wherein the acoustic signature is an acoustic signature of the valve drive component passing along the wellbore.

22. The method of claim 21 further comprising deriving a track of the valve drive component from the acoustic signature.

23. A method of monitoring a hydraulic fracturing operation in a wellbore as set out in claim 20, the wellbore being within a rock formation, the hydraulic fracturing operation including delivering a valve drive component along the wellbore to a valve located in the wellbore within the rock formation, the method comprising:

identifying from the acoustic signal an acoustic signature of the valve drive component engaging with the valve.

24. The method of claim 23 wherein the valve is a sliding sleeve valve and the valve drive component is a ball.

25. The method of claim 24 wherein the acoustic signature of the valve drive component engaging with the valve is an acoustic signature of the ball becoming seated in the sliding sleeve valve.

26. The method of claim 23 further comprising identifying from the acoustic signal an acoustic signature of fracture events in the rock formation resulting from the valve drive component engaging with the valve and consequent successful operation of the valve.

27. The method of claim 23 further comprising identifying from the acoustic signal a lack of acoustic signature fracture events in the rock formation resulting from a failure of the valve to operate successfully.

28. The method of claim 20 wherein the wellbore is within a rock formation, and identifying from the acoustic signal an acoustic signature of the valve drive component comprises detecting an acoustic signature of a failure of prior engagement of the valve drive component with the valve.

29. The method of claim 28 further comprising detecting an acoustic signature of fracture events in rock formations downstream of the valve subsequent to detecting an acoustic signature of a failure of prior engagement of the valve drive component with the valve, and determining whether the failure was due to penetration of the valve drive component through the valve or due to disintegration of the valve drive component dependent upon a length of delay between the two acoustic signatures.

30. The method of claim 20 wherein properties of an event involving the valve drive component are calculated from aspects of the acoustic signature propagating away from the event along the wellbore.

31. The method of claim 20 wherein the acoustic signature of the valve drive component represents one or two wave fronts triggered at the same time by an event involving the valve drive component, the wave fronts propagating in one or both directions along the wellbore.

32. The method of claim 31 wherein the method comprises determining an origin of the two wave fronts and identifying the position and/or time of the event as the origin of the wave fronts.

33. Apparatus for monitoring a hydraulic fracturing operation comprising:

a distributed optical fibre sensor comprising a sensor optical fibre disposed along a wellbore; and

a valve drive component detector arranged to receive an acoustic signal from the distributed optical fibre sensor and to detect from the acoustic signal an acoustic signature of the valve drive component.

34. The apparatus of claim 33 wherein the valve drive component detector is arranged to generate a position or a track of the valve drive component.

35. The apparatus of claim 33 wherein the valve drive component detector is arranged to recognise an impact of the valve drive component at a valve.

36. The apparatus of claim 33 wherein the valve drive component detector is arranged to recognise, from the acoustic signal, failure of a valve to open after recognised impact of the valve drive component at a valve.

37. The apparatus of claim 33 wherein the valve drive component detector is arranged to recognise, from the acoustic signal, failure of a valve drive component.

38. The apparatus of claim 37 wherein the recognised failure is identified by the valve drive component as a failure by extrusion of the valve drive component through the valve.

39. The apparatus of claim 37 wherein the recognised failure is identified by the valve drive component as a failure by disintegration of the valve drive component.

40. The apparatus of claim 33 wherein the valve drive component detector is arranged to recognise from the acoustic signature two wave fronts triggered at the same time by an event involving the valve drive component, the wave fronts propagating in both directions along the wellbore, and to identifying the position and/or time of the event as the origin of the wave fronts.

41. (canceled)

42. (canceled)

43. A method of monitoring a hydraulic fracturing operation in a wellbore within a rock formation, the method comprising:

using a distributed optical fibre sensor having one or more sensing fibres disposed along the wellbore to detect a seismic signature of a fracture event in the rock formation, the fracture event resulting from the hydraulic fracturing operation.

44. The method of claim 43 further comprising detecting one or more properties of the fracture event from the seismic signature.

45. The method of claim 44 wherein one or more of the properties are detected from the spatial development over time of the seismic signature as detected at the one or more sensing fibres.

46. The method of claim 44 wherein one or more of the properties are detected from the spatial propagation over time of the seismic signature along the one or more sensing fibres.

47. The method of claim 44 wherein the one or more properties include one or more of:

a location of the fracture event;

a position along the one or more sensing fibres of the fracture event;

a (for example radial) distance from the one or more sensing fibres of the fracture event; and

a magnitude of the fracture event.

48. The method of claim 43 comprising detecting a distance of the fracture event from the one or more sensing fibres using a shape of the seismic signature in a plane having dimensions of time and position along the one or more sensing fibres.

49. The method of claim 48 wherein the distance of the fracture event from the one or more sensing fibres is detected from a curve shape of the seismic signature in a plane having dimensions of time and position along the one or more sensing fibres.

50. The method of claim 43 comprising detecting a position along the one or more sensing fibres of the fracture event from the position of an apex of a curved shape of the seismic signature in a plane having dimensions of time and position along the one or more sensing fibres.

51. The method of claim 43 comprising using the distributed optical fibre sensor to detect seismic signatures of a plurality of such fracture events in the rock formation, and monitoring the hydraulic fracturing operation using the detected seismic signatures.

52. The method of claim 51 comprising monitoring a distribution of the fracture events along a fracture zone.

53. The method of claim 52 further comprising detecting or measuring pack off from the distribution of fracture events along a fracture zone.

54. The method of claim 53 wherein pack off in a particular region of the fracture zone is detected or measured from a diminishment over time in detected fracture events in that region.

55. The method of claim 51 further comprising:

identifying a suboptimal fracture distribution along a fracture zone;

including a diverter in the fracture fluid injected into the rock formation for hydraulic fracturing of the fracture zone; and

monitoring the effectiveness of the diverter in mitigating the suboptimal fracture distribution using the detected seismic signatures.

56. The method of claim 55 wherein the suboptimal fracture distribution is also identified using the detected seismic signatures.

57. (canceled)