SU981505A1 - Method of withdrawing from soil deeply immersed columns of self-raising floating installation - Google Patents

Description

The invention relates to offshore oil and gas production and can be used in the operation of self-lifting floating installations. This invention is intended primarily; but for use in the operation of over-floating floating instruments that are not used for drilling oil and gas wells.

A known method for extracting a marine structure from the seabed consists in extracting it with the help of lifting devices and additional floating equipment t

The disadvantages of it are the difficulty of lifting, the additional costs of lifting devices and the complexity of the foundation structure. There is also known a method for extracting deeply submerged support columns from the ground by a self-lifting floating installation, consisting in applying a vertical force to the support column from the buoyancy of a submerged body 1.21.

The disadvantage of this method is the limitation of the penetration of the supporting columns into the ground, since it is impossible to control the magnitude of the moments placed on them when lifting from the ground.

t Therefore, in the method for ensuring the integrity of the column, restrictions are imposed on the depth of the columns in the ground, which limits the necessary forces for lifting the columns. Limit angles of heel and trim, defined in

10 depending on the gaps between the columns and the hull of the self-lifting floating rig (SPVU).

As a result of the accepted restrictions, the use of HLDCs is limited to their use only in areas where the upper ground spans have sufficient bearing capacity;

20 destruction of the supporting columns, since the assumed limits are determined for average conditions and do not take into account the most unfavorable combinations of conditions.

25

The aim of the invention is to increase the reliability and expansion of the field of operation in waters with deep bedding of the bearing soil.

This goal is achieved by

30 that the hull immersion is carried out at

its inclination, which applies a permissible moment to a supporting column or a group of supporting columns, after which water overboard ballast is received in the direction of the hull opposite to the inclined, while maintaining the permissible moment applied to the supporting column or a group of supporting columns, and the permissible moment is determined according to the formula

Aa- m- ,,

where M is the moment allowed by the strength conditions of the support column,

y is the trim angle; 9 - roll angle.

And - the coefficient of compliance of the column, immersed in the ground.

Through the operation of the lifts of all the supporting columns, the casing is immersed in water to obtain excess buoyancy. Having stopped the lift of the column being lifted from the ground, the columns of the other columns gradually unload these columns, which results in an increase in the load on the column being lifted. The increase in heel and trim is controlled.

Upon reaching the limiting inclination angles calculated by the specified formulas and measured by an inclinometer and a differential meter installed on a FSSP, the further loading of the raised column is suspended. The following measures are taken to reduce the inclination of the hull: receiving water ballast from the side, pumping water beshlast from one compartment to another, etc.

After reducing the corners of the corners of the hull, the work of the lifts load the lifting column.

These operations are repeated to reduce the effort required to lift the columns from the ground.

For a four-pod SPBU, in order to reduce the inclination of the hull, the ascent is performed by simultaneously loading two columns located on the same diagonal. In this case, the inclination of the hull resulting from the difference in forces applied to the raised columns is controlled.

The feasibility of the method lies in the possibility of expanding the areas of operation of each type of SCU.

Claims (2)

1. Patent QUA 4118942, cl. E 02 B 17/00, 1978, 2. Instructions for operation and ballasting No. 1540,901.097 IE Sevastopol, 1976.