Study of the Installation Process of the Subsea Tree Passed Through the Splash Zone

Abstract

The subsea tree is one of the critical pieces of equipment in the subsea production system, and its installation is related to the safe production of offshore oil and gas. Due to the differences in the form of the structures, the speed of entering the water, the marine environment, and other factors, the process of the structure entering the water is exceedingly complicated. During the engineering installation, the most dangerous phase involves the structure passing through the splash zone. Based on the theory of the movement of the subsea tree passing through the splash zone, Lingshui 17-2 subsea tree installation was analyzed with the marine engineering software OrcaFlex, and a sensitivity analysis of the lowering of the subsea tree was performed. During the splash zone phase, the wave height had the highest impact on the subsea tree, affecting the horizontal offset and cable load, which may lead to the oil tree capsizing and cable breakage. Furthermore, the velocity only affected the horizontal offset, and the overall effect was not noticeable. The operational safety window for the subsea tree installation was established according to the operational safety standards. Therefore, the recommended lowering speed was 0.50 m/s, while the flow velocity should not exceed 1.50 m/s, and the wave height should not be higher than 4.5 m.

Dynamic Analysis of Splash-zone Crossing Operation for a Subsea Template

“…Various numerical studies have been performed to analyze the dynamic responses of lifting operations when the lifted objects cross the splash-zone. These stud-ies addressed the dynamic responses during the installation of different subsea assets such as subsea trees [1] , manifolds [2,3] , templates [4] , suction anchors [5] , and spools [6] . In a typical offshore lowering operation, the vessel hull is used to shield the lowered asset from the incident waves.…”

“…Thus, the prediction of the motion responses and the estimation of the slamming loads on the subsea template in the wave zone can be quite challenging. Several numerical studies were conducted to capture the dynamic responses when lowering subsea structures through the splash-zone [1,2,5,6,[13][14][15][16] .…”