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

Research on the Performance of Deep Water Jack-up Preloading in Wave
Chang Gao1, Fei Wang2, Hongtao Li1
Offshore Engineering Technology Center of China Classification Society 1, China Oilfield Services Limited2
Tianjin1, Hebei2 China

operating in deep water, punch-through in preloading process may
cause high speed tilting of platform, casualties, equipment damage, oreven cause the whole platform overturning. HSE (InternationalConference on Health, Safety and Environment) has found (Burd, 1997)
that punch-through damage accounted for 53% of the total number ofaccidents, and every year occurrence of punch-through accident isincreased by 1 or 2. About 1 million USD to 10 million USD are lostfor one accident. In October 2009, when the “Sapphire Driller” carriedout preloading in west Africa ivory coast, punch-through for the bow
leg happened and several leg nodes were damaged by punching shear,making the platform tilted 7.8 degrees. In May 2009, during thepreloading operation of "HYSY941" in the South China Sea, thepenetration of the bow leg caused the hull to tilt 6.2 degrees, and thefour diagonal braces and two internal horizontal braces were greatlydeformed.

ABSTRACT
In order to prevent the overturning of the platform caused by punchthrough accident, the deep water jack-up may preload with hull close to
the water surface which is called "preloading in wave". The platform
operates under wave impact loads, which exert influence on legs, localstructure of the hull, jacking system and so on. Under severe condition,
it will cause damage to the structure. Therefore, it is necessary toanalyze the performance of jack-up preloading in wave and determine
the critical sea state. In this paper, for example, a 400ft jack-up
preloading in wave is analyzed. First, the example jack-up is simulated
as a floating body with spring restraint during preloading operation inanalysis. Then using three dimensional potential flow theory andconsidering non-linear effect such as second-order wave force caused
by water surface fluctuation and local slamming pressure, the shortterm statistics of motion response and wave load in random waves arecalculated for two conditions which include the certain draft andpositive air gap. Then the strength of legs, hull structures and jacking
system is analyzed to determine bearable wave load level for example
jack-up. Finally, using the iterative searching method, the critical sea
states during "preloading in wave" can be obtained, and compared withthe model test data, several useful conclusions are drawn. The above
method of preloading in wave, may have a high practical value which isimportant for deep water jack-up to reduce the risk of punch-through,and will provide useful guidance to the designers and operators.

For deep water jack-up drilling platforms, preloading with the hullclose to sea surface is advised in order to reduce the risk of structural
damage. In this way, the puncture distance and speed can be reduced by
the sea buoyancy when punch-through happens. This course is called“preloading in wave”. For example, for 400ft deep water operating
jack-ups of an offshore oil and gas exploration company, the distanceof 0.5 meters from platform bottom to the sea surface is considered as
maximum value in the process of preloading. But it can cause wave
impact to platform, sequentially exerting an influence on legs, local
structure of the hull, jacking system and so on. In severe condition, it
will cause damage to the structure, so that it is necessary to analyze theperformance of platform and determine the critical sea state.

KEY WORDS: jack-up platform; preloading in wave; slamming;
critical sea states.

In the analysis, a 400ft deep water jack-up is simulated as a floating
body with spring restraint for preloading condition. Using three
dimensional potential flow theory and considering non-linear effectsuch as second-order wave force caused by water surface fluctuationand slamming pressure, the short term statistics of motion response andwave load in random waves are calculated for two conditions which
include the certain draft and positive air gap. Then the strength of legs,
hull structures and jacking system is analyzed to determine bearable
wave load level for example jack-up. Finally, using the iterativesearching method, the critical sea state during "preloading in wave" canINTRODUCTION
Jack-up drilling unit is the platform whose hull can be elevated along
the leg to the certain height above the sea for drilling operation. Jackups have been widely used in offshore oil and gas exploration becauseof their high efficiency, convenient operation and low cost (Chen andLi, 2007; Chen, 2008). When jack-up during preloading encounters anupper stiff layer and below this a softer layer soil stratum, it is likelythat the leg rapidly penetrates through the upper stiff layer into the soft
soil layer, which is called punch-through (Kellezi, 2012). For jack-up

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