Offshore Shallow Water Platforms and Methods for Deploying Same

Abstract

An offshore structure for drilling and/or producing a subsea well includes a hull having a longitudinal axis, a first end, and a second end opposite the first end. The hull includes a plurality of parallel elongate columns coupled together. Each column includes a variable ballast chamber positioned axially between the first end and the second end of the hull and a first buoyant chamber positioned between the variable ballast chamber and the first end of the hull. The first buoyant chamber is filled with a gas and sealed from the surrounding environment. The offshore structure also includes an anchor fixably coupled to the second end of the hull and configured to secure the hull to the sea floor. The anchor has an arrow-shaped geometry and a central axis coaxially aligned with the longitudinal axis of the hull. The anchor includes angularly-spaced penetration members extending radially from the central axis of the anchor. In addition, the offshore structure includes a topside mounted to the first end of the hull.

1 . An offshore structure for drilling and/or producing a subsea well, the structure comprising:
 a hull having a longitudinal axis, a first end, and a second end opposite the first end;   wherein the hull includes a plurality of parallel elongate columns coupled together, wherein each column includes a variable ballast chamber positioned axially between the first end and the second end of the hull and a first buoyant chamber positioned between the variable ballast chamber and the first end of the hull;   wherein the first buoyant chamber is filled with a gas and sealed from a surrounding environment;   an anchor fixably coupled to the second end of the hull and configured to secure the hull to the sea floor, wherein the anchor has an arrow-shaped geometry and a central axis coaxially aligned with the longitudinal axis of the hull, wherein the anchor includes angularly-spaced penetration members extending radially from the central axis of the anchor; and   a topside mounted to the first end of the hull.   
     
     
         2 . The offshore structure of  claim 1 , wherein anchor tapers to a pointed tip at the second end of the anchor. 
     
     
         3 . The offshore structure of  claim 1 , wherein each penetration member comprises a body and a plurality of stiffeners extending from the body. 
     
     
         4 . The offshore structure of  claim 3 , wherein each body is a plate extending axially from the first end of the anchor to the second end of the anchor;
 wherein a first set of the plurality of stiffeners extend from a first planar side of each plate and a second set of the plurality of stiffeners extend from a second planar side of each plate.   
     
     
         5 . The offshore structure of  claim 4 , wherein the plurality of stiffeners are oriented parallel to each other;
 wherein each stiffener is an elongate plate extending axially from the first end of the anchor to the second end of the anchor.   
     
     
         6 . The offshore structure of  claim 4 , wherein the plate of each body has a trapezoidal shape. 
     
     
         7 . The offshore structure of  claim 3 , wherein each penetration member is angularly spaced 90° from each circumferentially adjacent penetration member. 
     
     
         8 . The offshore structure of  claim 1 , wherein the plurality of columns are uniformly circumferentially-spaced about the longitudinal axis of the hull, and wherein the plurality of columns are uniformly radially spaced from the longitudinal axis of the hull. 
     
     
         9 . The offshore structure of  claim 8 , wherein each column is spaced from each circumferentially-adjacent column by a distance D that is at least 1.0 m. 
     
     
         10 . The offshore structure of  claim 1 , wherein each column has a central axis, a first end disposed at the first end of the hull, and a second end proximal the second end of the hull;
 wherein each column includes a radially outer tubular wall extending axially from the first end of the column to the second end of the column and an end plate coupled to the outer tubular wall at the second end of the column; and   wherein at least a portion of the end plate of each column is oriented at an acute angle α relative to a reference plane oriented perpendicular to the longitudinal axis of the hull.   
     
     
         11 . The offshore structure of  claim 10 , wherein the angle α is between 0° and 20°. 
     
     
         12 . The offshore structure of  claim 1 , further comprising a cell fixably coupled to the plurality of columns and positioned between the plurality of columns proximal the second end of the hull, wherein the cell has a central axis coaxially aligned with the longitudinal axis of the hull;
 wherein the cell comprises a fixed ballast chamber; and   wherein the first end of the anchor is fixably attached to the cell.   
     
     
         13 . A method, comprising:
 (a) positioning a buoyant platform at an offshore installation site, wherein the platform includes a hull, a topside mounted to a first end of the hull, and an anchor fixably coupled to a second end of the hull, wherein the anchor includes a plurality of angularly-spaced penetration members extending radially outward from a central axis of the hull;   (b) ballasting the hull;   (c) penetrating the sea floor with the penetration members of the anchor; and   (d) allowing the platform to pitch about the second end of the hull after (c).   
     
     
         14 . The method of  claim 13 , wherein (d) comprises allowing the platform to pitch to a maximum pitch angle relative to vertical that is less than 10°. 
     
     
         15 . The method of  claim 13 , wherein (a) comprises:
 (a1) transporting the hull and the topside to the offshore installation site;   (a2) floating the hull at the sea surface in a horizontal orientation;   (a3) transitioning the hull from the horizontal orientation to a vertical orientation with the first end disposed above the second end; and   (a4) mounting the topside to the hull above the sea surface to form the platform.   
     
     
         16 . The method of  claim 13 , wherein the hull includes a plurality of circumferentially-spaced, parallel columns disposed about the central axis of the hull, wherein an end wall of each column disposed at or proximal the second end of the hull includes at least a first portion oriented at an acute angle α relative to a reference plane oriented perpendicular to the central axis of the hull to the first portion. 
     
     
         17 . The method of  claim 16 , wherein the first portion of the end wall of at least one column engages the sea floor during (d). 
     
     
         18 . The method of  claim 16 , wherein each end wall includes a second portion oriented parallel to the reference plane, wherein the second portion of the end wall of each column is radially positioned between the first portion of the end wall and the central axis of the hull. 
     
     
         19 . The method of  claim 16 , wherein the entire end wall of each column is oriented at the acute angle α. 
     
     
         20 . An offshore structure for drilling and/or producing a subsea well, the structure comprising:
 a hull having a longitudinal axis, a first end, and a second end opposite the first end;   wherein the hull includes a plurality of parallel elongate columns coupled together, wherein each column includes a variable ballast chamber positioned axially between the first end and the second end of the hull and a first buoyant chamber positioned between the variable ballast chamber and the first end of the hull, wherein each column includes an end wall positioned at or proximal the second end of the hull, wherein at least a first portion of each end wall is oriented at an acute angle α relative to a reference plane oriented perpendicular to the longitudinal axis of the hull;   wherein the first buoyant chamber is filled with a gas and sealed from a surrounding environment;   an anchor fixably coupled to the second end of the hull and configured to secure the hull to the sea floor, wherein the anchor has a central axis coaxially aligned with the longitudinal axis of the hull; and   a topside mounted to the first end of the hull.   
     
     
         21 . The offshore structure of  claim 20 , wherein the acute angle α of the first portion of each end wall is less than 20°. 
     
     
         22 . The offshore structure of  claim 21 , wherein each acute angle α is the same. 
     
     
         23 . The offshore structure of  claim 21 , wherein the end wall of each column includes a second portion oriented parallel to reference plane, wherein the second portion of each end wall is radially positioned between the first portion and the longitudinal axis of the hull. 
     
     
         24 . The offshore structure of  claim 21 , wherein the entirety of each end wall is oriented at the acute angle α.