Modified Wellbore Casing Trajectories

Abstract

An oil and gas casing includes an upper section, a curved section, and a lower section. The upper section extends down from a seafloor to the curved section. The curved section is curved between the upper section and the lower section. The lower section extends from the curved section toward a reservoir. At least a portion of the upper section includes multiple curved sub-sections.

What is claimed is: 
     
         1 . A wellbore casing, comprising:
 an upper section;   a curved section; and   a lower section, wherein the upper section extends down from a seafloor to the curved section, wherein the curved section is curved between the upper section and the lower section, wherein the lower section extends from the curved section toward a reservoir, and wherein the upper section includes multiple curved subsections.   
     
     
         2 . The casing of  claim 1 , wherein a curvature of at least one curved subsection of the upper section corresponds to at least a 1-degree per 100 feet curvature. 
     
     
         3 . The casing of  claim 1 , wherein a curvature of at least one curved subsection of the upper section corresponds to at least a 2-degrees per 100 feet curvature. 
     
     
         4 . The casing of  claim 1 , wherein a curvature of at least one curved subsection of the upper section corresponds to at least a 6-degrees per 100 feet curvature. 
     
     
         5 . The casing of  claim 1 , wherein at least one curved subsection of the upper section has a vertical length of approximately 1000 feet long. 
     
     
         6 . The casing of  claim 1 , wherein the lower section includes vertical undulations. 
     
     
         7 . The casing of  claim 1 , wherein the casing is disposed in a wellbore and wherein a curvature of at least one curved subsection of the upper section substantially matches a curvature of a curved section of the wellbore. 
     
     
         8 . The casing of  claim 1 , wherein a maximum deviation of a center line of at least one curved subsection of the upper section from a vertical axis extending through a center of an equivalent straight subsection is at least approximately one fourth of an inner diameter of the casing. 
     
     
         9 . The casing of  claim 1 , wherein radii of curvature of the curved subsections are large enough to allow a single relief well to stop a gas blowout through the casing. 
     
     
         10 . The casing of  claim 1 , wherein the casing is disposed in a wellbore, wherein a curvature of at least one curved subsection of the upper section is formed by using a de-centralizer disposed outside of the casing within a wellbore to deviate a center of a portion of the casing from a vertical axis extending through a center of the wellbore. 
     
     
         11 . The casing of  claim 1 , wherein a curvature of a first curved sub-section proximal to the curved section of the casing is larger than a curvature of a second curved sub-section that is distal from the curved section. 
     
     
         12 . A wellbore casing, comprising:
 an upper section including a spiral section;   a curved section; and   a lower section, wherein the upper section extends down from a seafloor to the curved section, wherein the curved section is curved between the upper section and the lower section, wherein the lower section extends from the curved section toward a reservoir, and wherein the upper section includes the spiral section.   
     
     
         13 . The casing of  claim 12 , wherein the spiral section completes a 360-degree rotation in approximately 1000 feet vertical length. 
     
     
         14 . The casing of  claim 12 , wherein a portion of the spiral section that is proximal to the curved section has a larger diameter than a portion of the spiral section that is proximal to the seafloor. 
     
     
         15 . The casing of  claim 12 , wherein the spiral section has a radius of curvature that allows a single relief well to stop a blowout through the casing. 
     
     
         16 . A method of drilling, the method comprising:
 drilling an upper section of a wellbore;   drilling a curved section of the wellbore;   drilling a lower section of the wellbore, wherein the upper section of the wellbore extends down from a seafloor to the curved section of the wellbore, wherein the lower section of the wellbore extends from the curved section of the wellbore toward a reservoir, and wherein the upper section of the wellbore includes curved subsections of the wellbore; and   inserting a casing into the wellbore, wherein inserting the casing into the wellbore forms curved subsections of the casing in an upper section of the casing.   
     
     
         17 . The method of  claim 16 , wherein the upper section of the wellbore has a corkscrew spiral portion that includes the curved subsections of the wellbore. 
     
     
         18 . The method of  claim 16 , wherein inserting the casing into the wellbore forms a corkscrew spiral portion of the casing in the upper section of the casing and wherein the corkscrew spiral portion of the casing includes the curved subsections of the casing.