Jack-up spudcan pullout is an important process to transmit the platform from elevated condition to floating condition. In this process, enough pull out force is needed to resist the loads from seabed. In practice, jack-up rigs are prone to damage in this condition, so the spudcan pullout condition is a critical case for the structure and jacking system of jack-up. But there is no standard analysis method to simulate it so far. In this paper, an available analysis method is studied for the spudcan pullout condition, which provide recommended practice for the design of the jack-up and also provides guidance to platform operation.
Jack-up drilling unit is the platform whose main hull can be elevated along the leg to a certain height above the sea surface for drilling operation. Jack-ups are widely used in offshore oil and gas exploration because of high efficiency, convenient operation and low cost. According to statistics(Hou and Zeng, 2014), by the beginning of 2016, there were about 330 contracted jack-up platforms, which accounts for 60% of the whole drilling platform market. In addition to the widely use in exploiting of oil and gas, jack-up platforms also play an important role in offshore wind turbine installation, submarine cable laying, artificial island and sea tunnel construction.
The complete operating cycle for jack-up rigs includes towing, installation, preloading, jacking-up, operating/survival, lowering hull and spudcan pullout. Spudcan pullout is an important process in the transition from elevated condition to floating condition. In order to increase the submarine support area and get enough foundation bearing capacity, most of jack-ups are designed to have a larger box called spudcan at the bottom of each leg. After the drilling operation is completed, the spudcan will be pulled out from the seabed by hull buoyancy and raised to the bottom of the hull at a predetermined height. In real condition, due to the different soil characteristics of the seabed, deep penetration of spudcan often occur, which will make spudcan more difficult and time consuming to be pulled out. Even spudcan excessive pulling may lead to serious structural damage. However, the industry has not yet developed a mature method for spudcan pullout condition design, and not all operating manuals can give a clear restriction for this operation.