Cementing system for riserless abandonment operation

1. A method for abandonment of a subsea well, comprising:

setting a packer of a lower cementing tool against a bore of an inner casing hung from a subsea wellhead at a location adjacent to an outer casing hung from the subsea wellhead;

fastening a pressure control assembly (PCA) to the subsea wellhead;

hanging an upper cementing tool from the PCA and stabbing the upper cementing tool into a polished bore receptacle of the lower cementing tool;

perforating a wall of the inner casing below the packer;

perforating the wall of the inner casing above the packer by operating a perforator of the upper cementing tool; and

pumping cement slurry followed by a release plug through bores of the cementing tools, wherein:

the release plug engages and launches a cementing plug from the lower cementing tool, and

the cementing plug drives the cement slurry through the perforations below the packer and into an inner annulus formed between the inner casing and the outer casing.

2. The method of claim 1 , wherein the wall of the inner casing is perforated below the packer before being perforated above the packer.

3. The method of claim 1 , further comprising:

setting a bore plug in a nipple of the lower cementing tool; and

arming the perforator by opening an isolation sleeve thereof,

wherein the perforator is operated by pressurizing the bores of the cementing tools against the set bore plug.

4. The method of claim 1 , further comprising:

severing an upper portion of production tubing from a lower portion thereof; and

retrieving the severed portion from the subsea well,

wherein the packer is set, the PCA is fastened, the upper cementing tool is hung, the bore is closed, the inner casing is perforated, and the cement slurry is pumped after retrieving the severed portion from the subsea well.

5. The method of claim 4 , wherein the severed portion is retrieved by retrieving a production tree from the subsea wellhead.

6. The method of claim 1 , wherein the PCA comprises a blowout preventer stack.

7. The method of claim 1 , further comprising setting a bridge plug in the bore of the inner casing before setting the packer.

8. The method of claim 1 , further comprising:

fastening a tool housing to the PCA; and

after fastening the tool housing to the PCA:

deploying a second perforator through open sea with a lubricator and wireline;

fastening the lubricator to the tool housing; and

lowering the second perforator through the bores of the cementing tool,

wherein the wall of the inner casing is perforated below the packer by operating the second perforator using the wireline.

9. The method of claim 1 , further comprising perforating walls of the inner and outer casings below the packer after curing of the cement slurry and through the cured cement.

10. The method of claim 9 , further comprising perforating the inner and outer casing walls above the packer by operating a second perforator of the upper cementing tool.

11. The method of claim 10 , further comprising pumping a second cement slurry through the bores of the cementing tools and into an outer annulus formed between the outer casing and a third casing hung from the subsea wellhead.

12. The method of claim 11 , further comprising following the second cement slurry with a second release plug, wherein the second release plug engages and launches a second cementing plug from the lower cementing tool.

13. The method of claim 1 , further comprising deploying the lower cementing tool through open sea to the subsea wellhead before fastening the PCA to the subsea wellhead.

14. The method of claim 1 , wherein the method is performed riserlessly.

15. The method of claim 1 , further comprising, after curing of the cement slurry:

retrieving the PCA and the upper cementing tool;

setting a bridge plug in the bore of the inner casing; and

forming a cement plug on the set bridge plug.

16. A method for abandonment of a subsea well, comprising:

setting a packer of a lower cementing tool against a bore of an inner casing hung from a subsea wellhead at a location adjacent to an outer casing hung from the subsea wellhead;

fastening a pressure control assembly (PCA) to the subsea wellhead;

hanging an upper cementing tool from the PCA and stabbing the upper cementing tool into a polished bore receptacle of the lower cementing tool;

perforating a wall of the inner casing below the packer and adjacent to a lower end of the lower cementing tool;

perforating the wall of the inner casing above the packer by operating a perforator of the upper cementing tool; and

pumping cement slurry through bores of the cementing tools, through the perforations below the packer, and into an inner annulus formed between the inner casing and the outer casing.

17. The method of claim 16 , wherein the packer is located at the lower end of the lower cementing tool.

18. The method of claim 16 , further comprising inflating a second packer of the lower cementing tool.