Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Application of SSIV on SEMI-Submersible Platform to Facilitate Structural Integrity
by Wet Tow Method
Gang Li, Ning He, Yuyang Fan, Lixin Liu, Rubin Zhang
Engineering Company, Offshore Oil Engineering Co. Ltd.
Tanggu, Tianjin, China

east manifolds will converge at Manifold EAST1 and then betransported to LS17-2 SEMI for process through two 12” SCR risers.
After processing, qualified natural gas shall be pressurized andtransported to subsea pipelines from YC13-1 platform to Hong Kongthrough a 18” subsea export pipeline. Condensate oil shall be sent tothe storage tank on LS17-2 SEMI and be exported by DP Shuttle oiltanker.

ABSTRACTThe SSIVs were located on the pontoon of SEMI, which shall be towed
to site offshore by wet-tow method, and which case was the first-of-itskind in China. the SSIVs shall moving up and down near the seasurface, so all the SSIV related facilities would be exposed to severe
environmental conditions. This paper presents the system design ofSSIV, the protection method and shows the analysis process against thechallenge mentioned above. This can provide a good reference to thesimilar projects

KEY WORDS: SSIV, SEMI, Wet-tow, Pontoon, Protection.
NOMENCLATURECOOEC = China Offshore Oil Engineering Corporation
SCR=SSEMI= Semi-Submersible Platform
SSIV= Subsea Isolation Valve
TUTA = Topside Umbilical Termination Assembly
UTA= Umbilical Termination Assembly

Fig. 1: LS17-2 Gas Field Layout
P.J. Comer (1991) proposed that assessing the risk of riser and pipeline
failures on offshore installations is necessary and suggested the QRA
method. From safety view, the SSIVs were decided to be installed inLS17-2 project during FEED. For the location of SSIV, there are twoselections. One is on the seabed, and the other is on the pontoon ofSEMI. The quantitative study was conducted by Qin Sun (2018) andthe result was that the second option was better. So, five SSIVs wereinvolved at the SCR ends which located on the pontoon of SEMI andprovide a means of isolating the topside from gas in the production andexport pipeline.

INTRODUCTION
Lingshui17-2 (hereinafter referred to as LS17-2) gas field is located in
the northern part of the Qiongdongnan Basin in the western continental
shelf of the northern South China Sea, with water depth of 1220m to1560m. LS17-2 gas field is approximately 149km away from Sanya,Hainan Province, about 160km southeast from existing Yacheng 13-1
gas field, and about 90 km from gas export pipeline (YC13-1 to HongKong). The distance between LS17-2 gas field and the nearest onshore
terminal (Nanshan terminal of YC13-1 gas field) is approximately
156km.

SYSTEM DESIGN
LS17-2 project includes five (5) SSIVs according to the quantity of
SCR: two sets of 10inch SSIV, two sets of 12inch SSIV, and one set of
18inch SSIV, which be classified into three sets of SSIV systems, as 18inch export system, 12 inch East input and 10 inch West input system.
In order to reduce the costs, the three systems adopt standardized
design with the same configuration. Taking 12inch SSIV system as anexample, the 12 inch east area input system is mainly composed of 2The development of LS17-2 gas field consists of subsea production
system, one SEMI and subsea pipelines. The subsea production systemcomprises one west manifold and three east manifolds. The SEMI
platform is located near Manifold EAST1. Well fluid from west
production loop will be transported to LS17-2 SEMI for process
through two 10” pipelines and two 10” SCR risers. Well fluid from all735