Repairing wellbores with fluid movement behind casing

1. A method comprising:

milling a section of casing within a wellbore;

after milling the section of the wellbore, underreaming the section of the wellbore through to a next layer of casing;

after underreaming the section of the wellbore and before installing a scab liner over the section, squeezing a setting fluid into the section, the setting fluid penetrating micro-channels exposed by the milling and underreaming;

after squeezing the setting fluid into the section, installing the scab liner over the section; and

after installing the scab liner over the section, securing the scab liner within the wellbore.

2. The method of claim 1 , wherein securing the scab liner comprises:

expanding a packer encircling the scab liner, the expanded packer contacting the next layer of casing; and

cementing the scab liner.

3. The method of claim 2 , further comprising:

sealing, by the packer, an uphole section of an annulus, defined by an outer surface of the scab liner and an inner surface of the next layer of casing, from a downhole section of the annulus.

4. The method of claim 1 , wherein the setting fluid comprises resin or cement.

5. The method of claim 1 , further comprising curing the setting fluid.

6. The method of claim 1 , wherein squeezing the setting fluid comprises:

setting a plug downhole of the section;

setting a retainer uphole of the section;

pressurizing fluid by the retainer; and

flowing the setting fluid into channels responsive to pressurizing the fluid.

7. The method of claim 6 , further comprising:

drilling out the retainer.

8. The method of claim 6 , further comprising:

drilling out the plug.

9. The method of claim 1 , further comprising injecting or producing fluid by the wellbore after securing the scab liner within the wellbore.

10. A method of repairing cracks within or behind a wellbore casing, the method comprising:

receiving a mill by the wellbore, the mill being received at a target depth, the mill enlarging a section of the wellbore at the target depth;

after receiving the mill by the wellbore, receiving an underreamer by the wellbore, the underreamer being received at the target depth, the underreamer enlarging the section of the wellbore to a next layer of casing;

after the underreamer enlarges the section of the wellbore, receiving a pressurized setting fluid by the section of the wellbore, wherein the pressurized setting fluid flows into cracks within or behind the wellbore casing; and

after receiving the pressurized setting fluid, receiving a scab liner by the section of the wellbore.

11. The method of claim 10 , wherein receiving the pressurized setting fluid comprises:

receiving a plug downhole of the section;

receiving a retainer uphole of the section;

receiving pressure by the retainer; and

flowing the setting fluid into channels responsive to the received pressure.

12. The method of claim 10 , wherein the setting fluid comprises resin or cement.

13. The method of claim 10 , further comprising curing the setting fluid.

14. The method of claim 10 , further comprising injecting fluid by the wellbore after receiving the scab liner.

15. The method of claim 10 , further comprising producing fluid by the wellbore after receiving the scab liner.

16. The method of claim 10 , wherein receiving the scab liner comprises:

cementing the scab liner within the wellbore; and

expanding a packer encircling the scab liner, the expanded packer contacting the next layer of casing.

17. The method of claim 16 , further comprising:

sealing, by the packer, an uphole section of an annulus, defined by an outer surface of the scab liner and an inner surface of the next layer of casing, from a downhole section of the annulus.

18. The method of claim 17 , further comprising sealing the annulus, by the cement, from a primary flow passage defined by an interior surface of the scab liner.