RU2745457C1 - Offshore gravity structure for arctic conditions - Google Patents

Abstract

FIELD: hydraulic structures.SUBSTANCE: invention relates to hydraulic structures, and more specifically to the structures of marine gravity structures for the development of the continental shelf in arctic conditions. The novelty in the claimed offshore gravity structure for arctic conditions, containing an annular reinforced concrete displacement support base 1 and a topside installed on it in the form of an ice-resistant metal drilling platform 2, having a conical inclined surface 3 to resist ice loads, a drilling tower 4 and a drilling shaft 5 with pipelines and the equipment passing through the platform 2 and the said support base 1, is that the ice-resistant metal platform 2 is equipped with a metal cone catcher 9 mounted for interaction with the guide cone 10 installed in the central part of the support base 1, which is adequate to the cone catcher 9 to ensure alignment with a reinforced concrete support base 1. The angle between the cone catcher 9 of the metal platform 2 and the central guide cone 10 of the support base 1 is selected from the condition of avoiding jamming depending on the coefficient of friction between the surfaces of the contact act of the mentioned catcher and guide cone. In the borehole 5 of the ice-resistant support base 1, an underwater production complex 12 is mounted.EFFECT: technical result of the invention is the expansion of operational capabilities by providing the possibility of exploration drilling while increasing manufacturability and reducing labor intensity.4 cl, 7 dwg

Description

The claimed invention relates to hydraulic structures, and more specifically to the structures of marine gravity structures for the development of the continental shelf in Arctic conditions.

Known offshore gravity structure (see US patent No. 4245929, IPC E02B 17/00 from 1981) in the form of an ice-resistant drilling platform having a conical inclined surface to resist ice loads, an oil rig and a drilling shaft, and the lower part of the specified known platform consists from the upper and lower sections, the outer conical walls of which are inclined to the horizon at different angles.

The disadvantage of this known analogue is the impossibility of relocating the structure for use as a mobile tool for exploration drilling.

It is also known a marine gravity structure (see US patent No. 4486125, IPC E02B 17/02 from 1982 - a prototype of the present invention), which includes an annular reinforced concrete displacement support base and a topside installed on it in the form of an ice-resistant metal drilling platform having a conical inclined surface to resist ice loads, an oil derrick and a well shaft passing through the platform and said support base.

The disadvantage of the prototype is significant labor intensity due to the fact that the support base is in the zone of constant ice contact. This requires the design and construction of a ditch in the seabed to provide high resistance to horizontal shear loads. In addition, the disadvantages of the prototype include the complexity of the technology of submersion of the support base, requiring the installation of additional structures (buoyancy towers), ensuring stability during installation on the bottom and ascent for reuse, as well as the complexity of using the prototype for exploration drilling, due to the need to pump sand suspension into the inner space of the lower part of the support base to provide the required clamping load.

The technical result of the claimed invention is to expand operational capabilities by providing the possibility of exploration drilling while increasing manufacturability and reducing labor intensity.

This is achieved in an offshore gravity structure for arctic conditions, which includes an annular reinforced concrete displacement support base and an ice-resistant metal drilling platform installed on it in the form of an ice-resistant metal drilling platform, which has a conical inclined surface to resist ice loads, an oil rig and a drilling shaft with pipelines and equipment. passing through the platform and said support base, in that said ice-resistant metal platform is equipped with a metal cone catcher mounted with the possibility of interaction with a guide cone installed in the central part of said support base, adequate to said cone catcher to ensure alignment with a reinforced concrete support base, and the angle between the mentioned cone catcher and the guiding cone is selected from the condition of avoiding jamming depending on the coefficient of friction between the contact surfaces of the said catcher and the guiding about the cone, while an underwater production complex was mounted in the drilling shaft of the ice-resistant support base.

The specified technical result is also achieved by the fact that the drilling shaft of the support base is equipped with a closure, as well as the fact that for servicing the subsea production complex the ice-resistant support base is made with a channel leading from the outer perimeter to the well.

In addition, the specified technical result is also achieved by the fact that the drilling shaft is made with the possibility of drainage by means of submersible pipelines

FIG. 1 schematically shows a general view of the proposed offshore structure for arctic conditions with a partial section;

in fig. 2 - section A-A of Fig. 1 (section along the bottom of the support base and tanks for receiving liquid ballast);

in fig. 3 - the process of submersion of the support base on the seabed;

in fig. 4 - support base installed on the bottom;

in fig. 5 - positioning the drilling platform and preparing it for diving.

in fig. 6 - the process of installing the drilling platform on the support base while maintaining positive stability;

in fig. 7 - support base as a protective structure for the subsea mining complex.

The declared offshore gravity structure for arctic conditions refers to offshore drilling platforms that are installed on the bottom and provide year-round operation in harsh arctic conditions when exposed to waves and ice formations characteristic of the area.

The declared offshore gravity structure is intended for operation at depths of up to 60 m.

The declared offshore gravity structure consists of two main parts: a reinforced concrete support base, designed to create the necessary support due to the sufficient mass of the structure and the area of contact with the subgrade; a steel drilling platform designed for operation in arctic conditions and providing drilling of exploration wells or a cluster of production wells, as well as performing operations for lowering and installing equipment for subsea production complexes.

The claimed offshore gravity structure for arctic conditions includes an annular ice-resistant reinforced concrete displacement support base 1 and a topside installed on it in the form of an ice-resistant steel drilling platform 2, having a conical inclined surface 3 to resist ice loads, a drilling tower 4 and a drilling shaft 5 with a drilling rig column 6, offshore drilling risers 7 and pipelines 8 passing through platform 2 and support base 1. To ensure alignment with the base 1, platform 2 is equipped with a guide catcher 9, mounted with the ability to interact with the steel centering cone 10 installed in the central part of the base 1, adequate to the guide catcher 9. In this case, the angle α between the guide catcher 9 and the steel centering cone 10 is selected from the condition of avoiding jamming, depending on the coefficient of friction between the contact surfaces of the guide catcher 9 and the centering cone 10. To ensure the floor For the first contact between the platform 2 and the base 1, rubberized plates 11 are installed between them, which also increase the value of the coefficient of friction on the contact surface of steel and concrete. Drilling shaft 5 allows the descent and installation of equipment of the subsea mining complex 12, for which the ice-resistant reinforced concrete support base 1, after commissioning, is a protective structure that excludes the impact of ice formations on the equipment and systems of the subsea mining complex 12. Drilling shaft 5, at the level of the centering cone 10 is equipped with a closure 13. For servicing the subsea production complex 12 during operation, the support base 1 is made with a technological channel 14 leading from the outer perimeter to the drill shaft 5. For installation and commissioning of the subsea production facility 12 without the use of diving operations and diving equipment, the drilling shaft 5 is made with the possibility of draining it by means of pipelines 8 due to the operation of the pump room (not shown) of the steel drilling platform 2. When using a reinforced concrete base 1 as a protective structure for an underwater mining complex 12, technological to Port 14 is used to connect pipelines and control umbilicals 15.

The submersion of the base 1 on the seabed is carried out by receiving liquid ballast into the tanks 16.

The construction process of the proposed offshore gravity structure is divided into two stages:

- installation of a reinforced concrete support base 1;

- installation of a steel drilling platform 2.

Installation of reinforced concrete base 1 begins with transportation to the installation site in the water area. Reinforced concrete support base 1 has sufficient buoyancy and stability to be towed afloat by means of a towing order (not shown) without additional structures.

After the towing is completed, the towing order is changed to a holding one (not shown) and the liquid ballast necessary for immersion and the creation of a downward load is taken into the tanks 16 intended for this.

The shape of the reinforced concrete base 1 and the area of contact with the ground are sufficient to ensure stability when placed on an unprepared base composed of both sandy and clayey soils.

For installation on the seabed and to create the necessary pressure load stability conditions, outboard water is taken into the ballast tanks 16.

The installation of the steel drilling platform 2 begins with its towing (not shown) to the installation site. Steel drilling platform 2 has sufficient buoyancy and stability to be towed afloat without additional structures.

After arriving at the installation site of the steel drilling platform 2, the towing order is changed to a holding one (not shown) and preparation for positioning and diving is made.

To ensure the alignment of the reinforced concrete base 1 and the steel drilling platform 2, mating units are provided.

Reinforced concrete base 1 has a steel centering cone 10, steel drilling platform 2 - a guide cat 9, adequate to the dimensions of the centering cone 10.

The steel centering cone 10 and the guide catcher 9 have an inclination angle selected from the condition of avoiding jamming when the centering cone 10 and the guide catcher 9 come into contact during diving. The tilt angle and height of the centering cone 10 ensure the alignment of the support base 1 with the steel drilling platform 2 with a positioning accuracy of up to ± 2.0 m.

After the final ballasting of the steel drilling platform 2, ensuring full contact and stability with respect to the reinforced concrete base 1, the proposed offshore gravity structure for Arctic conditions can begin drilling operations.

The inventive offshore gravity structure for arctic conditions can carry out exploration drilling with subsea or dry well completion. The riser and drill string 6 is placed in the drill shaft 5.

When using the proposed offshore gravity structure for arctic conditions for production drilling in the drill shaft 5 is placed a grid of wells with offshore drilling risers 7.

When using the proposed offshore gravity structure for arctic conditions for drilling and subsequent operation using an underwater mining complex 12, the drilling shaft 5 can be drained using pumping pipelines 8, for the possibility of lowering and installing equipment without using diving equipment. The tightness of the connection is ensured, among other things, through the use of rubberized plates 11 at the contact between the reinforced concrete base 1 and the steel drilling platform 2. After drilling the required number of wells, connecting pipelines and control umbilical cables 15 and putting the subsea production complex 12 into operation, the steel drilling platform 2 pops up by deballasting in the reverse order of the immersion process. After surfacing, the steel drilling platform 2 can be towed to a new place of operation or sludge.

When operating a reinforced concrete base 1 as a protective structure for an underwater mining complex 12, an additional closure 13 is installed on the drilling shaft 5, which excludes damage to the underwater mining complex 12 when large objects fall from above or coarse soil transferred with ice formations.

During the operation of the subsea mining complex 12, its maintenance with the help of divers and diving equipment is carried out through the technological channel 14. If a major repair or replacement of units and equipment of the subsea mining complex 12 is required, work is performed through the drilling shaft 5 with the closure removed 13.

Upon completion of operation or moving to a new drilling site, the reinforced concrete base 1 is deballasted and floats. Under air pressure, the ballast tanks 16 are purged, followed by ascent. The simplified form of the reinforced concrete base 1, its overall dimensions and design, as well as the absence of technological equipment in any way sensitive to excessive accelerations and inclinations, make it possible to ascend at an acceptable level of risks in conditions of negative initial stability and with a minimum level of process control.

After surfacing, the reinforced concrete support base 1 is towed to a new place of operation or sludge.

The technical and economic advantage of the proposed offshore gravity structure lies in expanding operational capabilities and increasing mobility while ensuring a high level of reliability, simplifying the design and construction technology. The declared offshore gravity structure is considered as a universal complex that provides year-round exploration drilling in ice conditions. Upon completion of exploration drilling and making a decision on the method of field development, the claimed offshore gravity structure can be used as an operational platform or protective structure for an underwater production complex, while a long transition from the exploration stage to the operation stage is not required.

Claims (4)

1. An offshore gravity structure for arctic conditions, including an annular reinforced concrete displacement support base and a topside installed on it in the form of an ice-resistant metal drilling platform having a conical inclined surface to resist ice loads, an oil derrick and a drilling shaft with pipelines and equipment passing through through the platform and said support base, characterized in that said ice-resistant metal platform is equipped with a metal cone catcher mounted with the possibility of interaction with a guide cone installed in the central part of said support base, adequate to said cone catcher to ensure alignment with a reinforced concrete support base, and the angle between the mentioned cone catcher and the guide cone is selected from the condition of avoiding jamming, depending on the coefficient of friction between the contact surfaces of the said catcher and the guide cone, while an underwater production complex was mounted in the drilling shaft of the ice-resistant support base. 2. Offshore gravity structure for arctic conditions according to claim 1, characterized in that the drilling shaft of the support base is equipped with a closure. 3. The offshore gravity structure for arctic conditions according to claim 1, characterized in that for servicing the subsea production complex, the ice-resistant support base is made with a channel leading from the outer perimeter to the borehole. 4. Offshore gravity structure for arctic conditions according to claim 1, characterized in that the borehole is made with the possibility of drainage by means of submersible pipelines.

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