Fracture Characterisation

• US 20130233537A1
• Filed: 11/30/2011
• Published: 09/12/2013
• Est. Priority Date: 12/01/2010
• Status: Active Grant

• Current Assignee: Optasense Holdings Limited (Luna Innovations, Inc.)
• Original Assignee: Optasense Holdings Limited (Luna Innovations, Inc.)
• Inventors: McEwen-King, Magnus, Hill, David John
• Granted Patent: US 9,416,644 B2
• Time in Patent Office: Days
• US Class Current: 166/250.1
• CPC Class Codes: E21B 43/26 by forming crevices or fractures
• CPC Class Codes: E21B 43/267 reinforcing fractures by propping
• 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: E21B 49/00 Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells

Abstract

This application relates to methods and apparatus for monitoring hydraulic fracturing in well formation and fracture characterisation using distributed acoustic sensing (DAS). The method involves interrogating a optic fibre (102) arranged down the path of a bore hole (106) to provide a distributed acoustic sensor and also monitoring flow properties of fracturing fluid pumped (114) into the well. The acoustic data from the distributed acoustic sensor is processed together with the flow properties data to provide an indication of at least one fracture characteristic.

Claims

1. A method of fracture characterisation of a downwell hydraulic fracturing process comprising:

interrogating a optic fibre arranged down the path of a bore hole to provide a distributed acoustic sensor;

monitoring flow properties of fracturing fluid; and

processing acoustic data from the distributed acoustic sensor together with the flow properties data to provide an indication of at least one fracture characteristic.

2. A method as claimed in claim 1 wherein interrogating the optical fibre comprises launching a series of optical pulses into said fibre and detecting radiation Rayleigh backscattered by the fibre;

and processing the detected Rayleigh backscattered radiation to provide a plurality of discrete longitudinal sensing portions of the fibre.

3. A method as claimed in claim 1 wherein said optic fibre is arranged in the well bore in which hydraulic fracturing is performed.

4. A method as claimed in claim 1 further comprising:

monitoring the acoustic disturbances in the optical fibre generated during perforation of the well prior to fracturing process; and

determining the portions of the optical fibre that correspond to fracture sites.

5. A method as claimed in claim 1 wherein the flow data is correlated with the acoustic data.

6. A method as claimed in claim 5 comprising correlating any acoustic disturbances, or changes in the acoustic signals with a change in flow properties.

7. A method as claimed in claim 1 wherein the flow data comprises at least one of flow rate, flow pressure, proppant concentration or proppant flow rate over time.

8. A method as claimed in claim 1 wherein an increase in fluid flow rate or drop in fluid pressure correlated with an increased acoustic disturbance in a portion of the optical fibre that does not correspond to a fracture site is taken as an indication of proppant wash out.

9. A method as claimed in claim 1 wherein the method comprises determining the amount of fracture fluid and/or proppant supplied to each fracture site.

10. A method as claimed in claim 9 wherein the acoustic data is analysed to determine the relative flow rates of the fracture fluid and/or proppant to individual fracture sites.

11. A method as claimed in claim 9 wherein the flow data is analysed to determine the rate of flow of fracture fluid and/or proppant into the well.

12. A method as claimed in claim 9 wherein the amount of proppant supplied to each individual fracture site is used in controlling the hydraulic fracturing process.

13. A method as claimed in claim 12 wherein the amount of proppant delivered to each fracturing site is used as measure of the degree or extent of fracturing at such site.

14. A method as claimed in claim 13 comprising monitoring the cumulative amount of proppant delivered to each fracture site and stopping the process once a predetermined amount of proppant has been delivered to a fracture site.

15. A method as claimed in claim 1 comprising the step of correlating the fracturing characteristic with data on subsequent production of oil or gas from the well.

16. A method as claimed in claim 15 comprising interrogating the optic fibre to provide a distributed acoustic sensor during in-flow and analysing the acoustic data during in-flow to determine the relative flow from each different fracturing site.

17. A method according to claim 10 wherein analysing the acoustic data to determine relative flows comprises comparing the intensity levels of acoustic disturbances in the vicinity of each of a number of different fracture sites.

18. A method according to claim 17 wherein the average intensity or acoustic energy in each relevant sensing portion of fibre is used to determine the relative flow rates to each fracture site.

19. A method as claimed in claim 17 wherein the acoustic data for a sensing portion of fibre in the vicinity of a fracturing site is divided into one or more spectral bands and the average intensity determined for each of said spectral bands.

20. A method as claimed in claim 19 comprising the step of analysing the data from a plurality of spectral bands to identify a spectral band of interest.

21. A method as claimed in claim 20 wherein said analysing step comprises determining a spectral band in which the intensity of acoustic disturbances in that spectral band in the sensing portions of fibre corresponding to the fracture sites are significantly higher than the intensity in other nearby longitudinal sensing portions.

24. A computer program product on a non-transitory computer readable medium which, when run on a suitably programmed computer connected to or embodied within a controller for an optical interrogator or a downhole fibre optic, performs the method of claim 1.

22. A system for fracture characterisation, said system comprising:

a fibre optic interrogator adapted to provide distributed acoustic sensing on an optic fibre arranged along the path of a bore hole;

a sampler arranged to sample a plurality of channels output from said interrogator to provide acoustic data from a plurality of portions of said fibre at each of a plurality of times;

a flow monitor adapted to monitor the flow properties of fracture fluid into well bore to be fractured and a data analyser adapted to process said sampled acoustic data with said flow data to determine at least one fracture characteristic.

23. A system as claimed in claim 22 wherein the optic fibre is deployed along the exterior of the well casing.