From April 22 to June 20, 2014, Shenzhen Shanye Industrial Co., Ltd. organized and implemented the replacement of 9 upper anchor cables in the anchor cable maintenance project of FPSO South China Sea endeavour STP (underwater turret production system) of Wenchang 13-1 / 13-2 oilfield for the owner Shenzhen COOEC Underwater Technology Co., Ltd.

During the operation, the upper part of the STP is separated from the FPSO, and the bottom of the STP is connected with 9 anchor cables and suspended in the water at a certain depth in a state of natural tension buoyancy. During the operation, the depth of the STP changes with the tension change caused by the replacement of 9 anchor cables. The water depth at the bottom of the STP is at least 12m and up to 41m. The project fully adopts the air diving operation mode supported by dp-ii mother ship. Our company fully carries out the operation in accordance with the requirements of "diving operation on dynamic positioning mother ship" in IMCA international diving code. We are equipped with diving equipment such as open Diving Bell and its hoisting system, emergency diving cage and its hoisting system, two-way wired communication and video monitoring system with bridge and ROV operation control room, During the implementation of DP ship status warning system, in full compliance with the requirements of IMCA international diving code, bell people are equipped to take care of the bell underwater, and emergency divers are equipped on the surface.

DP support has its advantages for the operation with large depth, but for the diving operation when the STP water depth is shallow, the DP operation with very shallow water depth has its unique risks to be considered and the risk control measures to be improved. On the one hand, it is necessary to consider the taut wire release safety at the starboard bow position (there are 9 anchor cables, 4 oil pipes and cables underwater radiating outward with STP as the center), on the other hand, it is also necessary to ensure that DP ship cuts into the working position at a certain bow position (New / old anchor cables are connected to the bottom of STP at the starboard stern inlet bridge), which poses a certain degree of challenge to the positioning of ship's working position. Moreover, the controlled umbilical length of DP operation in very shallow water and deep water conflicts with the requirements of divers' operation radius, which brings challenges to the formulation of field procedures and operation management of diving.

The FPSO under the influence of wind and current is in use all year round, resulting in uneven stress on 9 anchor cables connected to it and unequal clearance at the connection and bite parts. During the replacement operation, the operation support ship needs to be positioned in a certain bow direction. However, when the bow is downward, the action direction of wind, wave and current is easy to affect the support ship, resulting in continuous unstable factors for underwater disassembly and connection. During the operation, we made concerted efforts to constantly challenge various new situations and solve new problems, and completed the project safely and smoothly. (contributed by Underwater Engineering Department)