Technical Challenges of Design for Installation of Reel-Layed Pipe-In-Pipe System for a Deepwater Application

Sriskandarajah, T. (Subsea 7) | Mackay, Don (Subsea 7) | Rao, Venu (Subsea 7) | Zhou, Daowu (Subsea 7) | Ragupathy, P. (Subsea 7) | Kashani, Shahryar (Subsea 7) | Power, Brian (Murphy Exploration & Production)



The Murphy Dalmatian development is one of the frontier developments in deepwater, consisting of a 6.625” (168.3 mm) / 10.75” (273.1 mm) pipe-in-pipe system in 5,831 – 6,391 ft (1,780-1,948 m) water depth installed successfully by reel-lay method using Seven Oceans reel-lay vessel. Reel-lay is a proven highly efficient and cost-effective method of pipe-lay. This paper presents some of the additional engineering performed to get all the design details right for installing the Pipe-in-Pipe system efficiently by reel-lay method. The paper presents the methods used to analyse the installation sequences, shows the results of the analysis and provides details of the solutions obtained from the analysis.

The Dalmatian South is located in Desoto Canyon Block 134. The PIP system is approximately 12 km long and will be used to connect several wells via existing subsea infrastructure to the Petronius platform.

The PIP is a sliding system with centralisers at 2.15 m intervals along its length and is designed to operate with design pressure 482 barg and design temperature 93°C.

The PIP system was reel laid and safe installation in deepwater required careful evaluation of the maximum load transfer through the centralisers, particularly as the PIP traversed the aligner wheel. Detailed evaluation of the centraliser integrity incorporated evaluation of compression, slippage, creep, abrasion and centraliser bolt relaxation. The effect of reel-lay induced plastic deformation of thermal insulation on the overall heat transfer coefficient, which needed to be maintained during operation, was also evaluated in detail design.

Waterstops were designed to be fit-for-purpose in the unlikely event of water ingress in the annulus during installation.

Numerical simulations were used to obtain axial strain ratcheting and differential elongation between the inner and outer pipes of the PIP system during installation. This information provided essential guidance on the extent of available slack in the inner pipe for connecting In-line Tee and laydown PLET.