Riserless well systems and methods

Abstract

A riserless well abandonment system includes a surface vessel, a first mast extending from the surface vessel, a second mast extending from the surface vessel, wherein the second mast is spaced from the first mast, a running tool extending from the first mast, wherein a subsea intervention device is coupled to the running tool, and a concentric drill string extending from the second mast, wherein the concentric drill string includes an inner drill pipe disposed within an outer drill pipe.

What is claimed is: 
     
         1 . A riserless well abandonment system, comprising:
 a surface vessel;   a first mast extending from the surface vessel;   a second mast extending from the surface vessel, wherein the second mast is spaced from the first mast;   a running tool extending from the first mast, wherein a subsea intervention device is coupled to the running tool; and   a concentric drill string extending from the second mast, wherein the concentric drill string comprises an inner drill pipe disposed within an outer drill pipe.   
     
     
         2 . The riserless well abandonment system of  claim 1 , wherein the subsea intervention device comprises:
 a ram blowout preventer configured to seal a bore of the subsea intervention device;   an annular blowout preventer; and   a rotating control device configured to seal against the concentric drill string when the drill string extends through the subsea intervention device and is rotating relative to the subsea intervention device.   
     
     
         3 . The riserless well abandonment system of  claim 1 , wherein the concentric drill string comprises an inner drill pipe disposed within an outer drill pipe. 
     
     
         4 . The riserless well abandonment system of  claim 3 , wherein the subsea intervention device is coupled to a wellhead disposed on the sea floor. 
     
     
         5 . The riserless well abandonment system of  claim 3 , wherein:
 when the concentric drill pipe extends into a borehole extending from the wellhead, an inlet fluid flowpath is formed between an annulus disposed between the inner drill pipe and the outer drill pipe and the borehole;   when the concentric drill pipe extends into the borehole, a return fluid flowpath is formed between the inner drill pipe and the borehole.   
     
     
         6 . The riserless well abandonment system of  claim 5 , wherein the concentric drill string further comprises a crossover port to provide fluid communication between the borehole and the inner drill pipe. 
     
     
         7 . The riserless well abandonment system of  claim 5 , further comprising a drill bit coupled to the concentric drill pipe, wherein fluid communication is provided between the inlet fluid flowpath and the borehole through the drill bit. 
     
     
         8 . The riserless well abandonment system of  claim 5 , further comprising:
 a top drive coupled to the second mast and configured to rotate the concentric drill string; and   a swivel coupled to the second mast and configured to provide fluid communication between the inlet fluid flowpath and a surface system disposed on the surface vessel.   
     
     
         9 . The riserless well abandonment system of  claim 5 , further comprising:
 a casing string extending into the borehole from the wellhead; and   a perforating gun coupled to the concentric drill string, wherein the perforating gun is configured to form perforations in the casing string.   
     
     
         10 . A method of permanently abandoning a well using a riserless well abandonment system, comprising:
 extending a subsea intervention device from a first mast disposed on a surface vessel;   extending a drill string from a second mast disposed on the surface vessel and spaced from the first mast while the subsea intervention device is extended from the first mast;   coupling the subsea intervention device to a wellhead disposed on the sea floor;   extending the drill string through the subsea intervention device; and   circulating cement through a borehole extending from the wellhead using the drill string.   
     
     
         11 . The method of  claim 10 , further comprising sealing against the drill string with a rotating control device of the subsea intervention device as the drill string rotates relative to the subsea intervention device. 
     
     
         12 . The method of  claim 10 , further comprising drilling through a cement plug disposed in the borehole using a drill bit coupled to the drill string. 
     
     
         13 . The method of  claim 10 , further comprising:
 forming a first perforation in a casing disposed in the borehole using a first perforating gun coupled to the drill string; and   forming a second perforation in the casing axially spaced from the first perforation using a second perforating gun coupled to the drill string.   
     
     
         14 . The method of  claim 13 , further comprising circulating fluid through an annulus formed around the casing using the drill string. 
     
     
         15 . The method of  claim 14 , further comprising:
 circulating fluid into the borehole through an inner drill pipe of the drill string; and   circulating fluid from the borehole through an annulus formed between the inner drill pipe and an outer drill pipe of the drill string.   
     
     
         16 . A method of permanently abandoning a well using a riserless well abandonment system, comprising:
 coupling a subsea intervention device to a wellhead disposed on the sea floor;   extending a concentric drill string through the subsea intervention device;   circulating fluid into a borehole extending from the wellhead through an inlet fluid flowpath extending through an inner drill pipe of the concentric drill string;   circulating fluid from the borehole through a return fluid flowpath extending through an annulus formed between the inner drill pipe and an outer drill pipe of the concentric drill string; and   circulating cement through the borehole using the concentric drill string.   
     
     
         17 . The method of  claim 16 , further comprising:
 extending the subsea intervention device from a first mast disposed on a surface vessel; and   extending the concentric drill string from a second mast disposed on the surface vessel and spaced from the first mast while the subsea intervention device is being extended from the first mast.   
     
     
         18 . The method of  claim 16 , further comprising:
 forming a perforation in a casing disposed in the borehole using a perforating gun coupled to the concentric drill string; and   circulating fluid into an annulus surrounding the casing through the perforation using the concentric drill string.   
     
     
         19 . The method of  claim 18 , further comprising pumping cement into the annulus using the concentric drill string. 
     
     
         20 . The method of  claim 18 , further comprising:
 forming a first cement plug in a bore of the casing using the drill string; and   forming a second cement plug in the bore of the casing using the drill string, wherein the second cement plug is axially spaced from the first cement plug.