received by the International Bureau on 20 February 2018 (20.02.2018)

What is claimed is:

1. A method for characterizing a hydraulic fracture or network of fractures in a subsurface formation, comprising:

inducing a pressure change in a well drilled through the subsurface formation, the pressure change inducing tube waves in the well;

measuring at a location proximate to a wellhead at least one of pressure and a time derivative of pressure in the well for a selected length of time;

determining a conductivity of at least one fracture, using the measured at least one of pressure and the time derivative of pressure; and

determining a change in the determined conductivity with respect to time.

2. The method of claim 1 wherein the inducing a pressure change comprises pumping a hydraulic fracture treatment.

3. The method of claim 1 wherein the inducing a pressure change comprises inducing water hammer by changing a flow rate of fluid into or out of the well.

4. The method of claim 1 wherein the inducing a pressure change comprises operating an acoustic source which propagates a pressure pulse into fluid within the well.

5. The method of claim 1 further comprising determining a fracture closure rate using the determined change in fracture conductivity with respect to time.

6. The method of claim 5 wherein the fracture closure pressures are determined by aligning pressure measurement with conductivity decrease.

7. The method of claim 5 determining fluid leak off rates by correlating with the conductivity decrease over time.

8. The method of claim 1 further comprising initiating flowback, cleanup and production from the well after the change in conductivity is determined.

9. The method of claim 1 further comprising determining a gel breakdown time from a determined time of substantial increase in fracture conductivity.

10. The method of claim 9 further comprising initiating flowback, cleanup and production from the well after the gel breakdown time is determined.

11. A method for characterizing a hydraulic fracture or network of fractures in a subsurface formation, comprising:

inducing a pressure change in a well drilled through the subsurface formation, the pressure change inducing tube waves in the well;

measuring at a location proximate to a wellhead at least one of pressure and a time derivative of pressure in the well for a selected length of time;

in a computer, determining a conductivity of at least one fracture, using the measured at least one of pressure and the time derivative of pressure; and

in the computer, determining a change in the determined conductivity with respect to time.

12. The method of claim 11 wherein the inducing a pressure change comprises pumping a hydraulic fracture treatment.

13. The method of claim 11 wherein the inducing a pressure change comprises inducing water hammer by changing a flow rate of fluid into or out of the well.

14. The method of claim 1 1 wherein the inducing a pressure change comprises operating an acoustic source which propagates a pressure pulse into fluid within the well.

15. The method of claim 1 1 further comprising, in the computer, determining a fracture closure rate using the determined change in fracture conductivity with respect to time.

16. The method of claim 15 wherein the fracture closure pressures are determined in the computer by correlating pressure measurement with a conductivity change.

17. The method of claim 15 further comprising, determining in the computer fluid leak off rates by correlating with the conductivity decrease over time .

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18. The method of claim 11 further comprising initiating flowback, cleanup and production from the well after the change in conductivity is determined.

19. The method of claim 1 1 further comprising, in the computer, determining a gel breakdown time from a determined time of substantial increase in fracture conductivity.

20. The method of claim 19 further comprising initiating flowback, cleanup and production from the well after the gel breakdown time is determined.

21. The method of claim 11 where measurements are made during flowback and production

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