Abstract

This paper presents a discussion of a new buoyant tower design for developing fields in mid-water depths (50 m to 250 m). A tower using this design was installed offshore Peru in the fall of 2012. This new buoyant tower design applied a number of deepwater technologies to shallow water. These technologies include the cellular construction of the hull, a suction pile like foundation, float-over deck installation, air over water ballast system, fixed ballast at the bottom, and unconditionally stable design approach.

Introduction

The buoyant tower concept is not a new idea for the oil business. A number of bottom founded structures held upright by buoyancy were installed in the North Sea years ago. The Brent flare tower and the Beryl articulated loading tower are two examples. All of these early buoyant towers used a mechanical pivot at the base. Some of them used a truss structure to connect the upper buoyancy modules to the base pivot. However, the offshore structure recently installed offshore Peru is the first buoyant tower to be used for drilling and producing operations.

The tower offshore Peru is also different from its predecessors in that the mechanical pivot was replaced with a suction can foundation (SCF). This foundation element performs the same functions as the mechanical pivot in that it allows the tower to rotate about the base in a compliant manner while restraining the base from moving vertically, laterally, and torsionally.

The idea of using a can in the soil to form a pivot also is not new. The test guyed tower installed in the Gulf of Mexico (GOM) in 1975 was supported at the base by a spud can. This spud can effectively formed a pivot in the soil allowing the tower to remain compliant to the wave forces. This tower experienced numerous winter storms during its four year stay offshore with no detectable vertical, lateral, or torsional movement.

This content is only available via PDF.
You can access this article if you purchase or spend a download.