Concept of Inverted Jacket for Brown Field Extension of Offshore Platforms in Shallow Water

Abstract This paper proposes a new concept of installing an inverted jacket with battered legs to connect with an existing fixed offshore structure for brown-field projects that require significant amount of additional deck space for new facilities. Use of an inverted jacket will allow more spacing between legs at the top of the jacket implying a larger deck space to accommodate more equipment. However, piles are separated from the legs to avoid convergence of the piles within the seabed. Piles will be driven through separate long sleeves and the annulus between the pile and the sleeve will be grouted before installation of the deck. Rigid/welded connections between the new and the existing deck structure helps in reducing the number and diameter of the new piles. Numerical studies demonstrate the cases of two real-life structures with inverted jacket extensions at 28m and 35m water depths. Results show that a 2-level deck of size 30mx30m can be safely connected to the existing structure to withstand all gravity and environmental loads applicable for the two sites. The extended deck space can accommodate up to 700 MT of equipment and other facilities. The extended structure has adequate strength and the required minimum reserve strength. The proposed design requires considerably less structural steel compared to the conventional jackets to create the same amount of deck space.