EA004841B1 - A method for installing submerged oil and gas wells, and apparatus for the same - Google Patents

Abstract

1. A method for installing wells in shallow waters, where there is a risk for ice drift comprising the steps of: a) a vessel (10) brings a hollow structure (1) to an installation site, and lower it down to the seabed (2) in an upright vertical position, b) the structure (1) is driven down in the seabed (2) by hammering or vibration means, until an upper end of the structure (1) is essentially level with the seabed, c) material is removed from within the structure (1), d) the interior of the structure (1) is filled with concrete, thereby forming a base slab (4) and the slab (4) is levelled, e) a drilling template (5) having drilling guides is placed on the slab (4), and f) then a desired number of wells are drilled and completed through the drilling template (5) drilling guides. 2. A method of claim 1, wherein the hollow structure's (1) upper end is closed with a lid (3). 3. A method of claim 1, wherein a hole (9a) is formed in the wall of the structure (1), and flow lines and/or umbilicals are drawn from the outside to the interior of the structure (1) through the hole (9a). 4. An apparatus for installation of wells in shallow waters, where there is a risk for ice drift, comprising a hollow structure (1) with open ends and adapted to be driven down in the seabed (2), and designed to accommodate a template (5) with associated equipment, as manifold (6) and Christmas trees (8) for several wells, wherein it further comprises a base in form of a cast slab (4) within the hollow structure (1), which slab (4) serves as a foundation for the template. 5. An apparatus according to claim 4, wherein the hollow structure (1) comprises a hole (9a) in the side wall for inducting a flow line or similar. 6. An apparatus according to claim 4 or 5, wherein the cast base slab (4) comprises anchoring or fastening means for the template (5). 7. An apparatus according to any of the claims 4-6, wherein the hollow structure (1) comprises a lid (3). 8. An apparatus according to any of the claims 4-7, wherein the hollow structure (1) comprises guides arranged to the internal wall to guide the template into its correct position on the slab (4). 9. An apparatus according to any of the claims 4-8, wherein the hollow structure (1) is cylindrical. 10. An apparatus according to any of the claims 4-9, wherein the hollow structure (1) is polygonal.

Description

FIELD OF THE INVENTION

The invention relates to subsea oil and gas wells, in particular, to a method and apparatus used in relation to subsea oil and gas wells in shallow water, where floating ice can destroy structures located on the seabed and where conventional semi-submersible pontoon drilling rigs cannot be used by conventional way. In the proposed device and method, the equipment associated with the wellhead, in the process of drilling the well, as well as in the process of subsequent operation of the well, is located in a shaft structure located below the bottom of the reservoir.

State of the art

In such external conditions, protection of the mouths of subsea wells is extremely important. Previously, they tried to use underwater caissons of large diameter in the Arctic regions, however, this was largely unsuccessful mainly due to difficulties associated with the installation of such caissons. The deepening of the bottom with the formation of open funnels is practiced today, however, this procedure is expensive and does not protect the equipment from eroded rock. To protect the subsea wells from the gear of fishing vessels and anchors, pile frame constructions were used, however, they are bulky structures, the installation of which is difficult and costly.

Thus, usually the mouth of a subsea well is located at the level of the seabed and is associated either with a blowout preventer during the drilling phase, or with a valve block and flow line connector during well operation. The wellhead and associated equipment protrude to a certain height above the seabed, resulting in damage.

Any equipment located at the bottom of the ocean is exposed to various kinds of dangers. In coastal waters with hydrocarbon deposits, the main threat to underwater equipment comes from the trawls of fishing vessels, as well as the anchors of vessels serving wells, barges for laying underwater pipelines, drilling vessels and other floating equipment. As for the hydrocarbon deposits in regions with cold water, it is necessary to take into account the new danger that ice creates on the seabed. For example, in the Beaufort Sea region, the scolding effect of ice occurs in regions outside the ice shelf, where ice forms with sharp edges, often affecting the seabed. In Canada’s eastern coastal waters, severe damage to the seabed occurs when icebergs break off. Thus, when designing a well, it is necessary to provide for the possibility of providing control over its work even in such an extreme situation when moving ice will blow the upper part of the well.

One way to solve this problem is to install pressure control devices (for example, a fountain valve, системаδν system, etc.) and wellhead equipment together with sealing devices below the bottom damage zone, as well as appropriate fasteners to guarantee well integrity. To implement this method, there are a large number of options. One of them is to dig an open funnel in the seabed that is deep enough to install all the pressure control devices in the well below the bottom damage zone. Such an open funnel is a good technical solution, but it cannot be called economically attractive. Another solution to this problem is the development of fountain fittings, which could be installed inside the wellbore at the required depth with protective equipment located above the pressure control devices in the well. The fountain fittings introduced inside were designed to minimize the height of equipment above the bottom. However, it is not yet known whether the equipment located between the surface and the pressure control devices in the well will perform a protective function.

However, between these two extreme methods described above, there are a large number of other ways to solve this problem. They consist mainly of installing a caisson of a sufficiently large size to accommodate a standard marine bottom fountain armature inside it. The success of this decision depends on the ability to install such a caisson.

To overcome some of these problems, it was proposed to manufacture a caisson of a sufficiently large size so that a blowout device could be installed in it. A method for installing a caisson of this type is described in US Pat. Nos. 3,344,612 and 3,796,273. Patent No. 3,344,612 describes the technology of the erosion jet for caissons installed in soft seabed soil, and Patent No. 3,796,273 describes rotary drilling technology for hard rock of the seabed. In the latter design, cutting teeth are provided on the surface of the caisson bottom, and the entire caisson rotates, drilling a recess for itself. Although this technology is feasible, it requires a very expensive drilling rig, as well as cementing to ensure the strength of the structure, since the surrounding rock is largely disturbed. In the case of a rotating caisson, the feasibility of rotating such a large body closer to the moment of completion of its immersion is in question, since in this case there is a large surface area with a large radius.

US Pat. No. 3,344,612 describes a caisson suitable for supporting a drilling process from a drilling vessel and subsequent well operation in the coastal zone. The main goal of the caisson described in this patent is to artificially lower the bottom of the reservoir above the well construction site so that the blowout preventer, usually connected to the wellhead during drilling, can be located at a distance from the bottom of the drilling vessel performing drilling operations. The blowout preventer that needs to be installed when drilling offshore wells has a significant height. A blow-out device is a mechanism for sealing a well in the event of an increase in oil pressure or in the case of gas pockets that occur when drilling a well in a geological formation. Drilling vessels usually have in their hull a central shaft through which drilling is carried out using a drilling rig mounted on a vessel above the shaft. In the shallow water area, the height of the blowout preventer may be greater than the distance between the wellhead and the bottom of the drilling vessel. In this case, during the drilling process, the drilling vessel will be rigidly attached to a blowout preventer, as a result of which it will not be able to move away from the well in the event of a storm or accident.

In US patent No. 3344612 it is shown that in such shallow water the bottom of the reservoir can be artificially lowered by the caisson, so that the distance between the wellhead located in the area of the caisson bottom and the bottom of the drilling vessel will exceed the height of the blowout preventer. Thus, in case of danger, the drilling vessel can be diverted from the well construction site even before the operation valve is installed instead of the blowout preventer after completion of drilling (known in industry as “fountain fittings”). The main purpose of installing the caisson described in this patent is to lower the bottom of the reservoir sufficiently to ensure that the blowout preventer is below the hull of the drilling vessel. The upper part of the blowout pipe connected to the wellhead during the drilling operation may protrude above the bottom of the reservoir.

US Pat. No. 4,189,255 discloses an underwater wellhead that includes a substantially cylindrical hollow retaining wall structure, wherein the upper cylindrical edge part of the structure forms an upper hole and the lower edge part forms a bottom hole. Fasteners are installed on the upper edge part for attaching the fixing wall structure to the corresponding crane lowering the underwater wellhead shaft to the seabed from the drilling vessel. An annular air ejector located next to the lower edge part is installed inside the fixing wall structure. In the annular air ejector, means are provided for connecting it to a source of compressed air. The annular air ejector includes a large number of air nozzles directed mainly vertically upward. A large number of exhaust pipes are installed essentially inside the fixing wall structure. These pipes comprise upper outlet parts protruding outward from the structure, and lower inlet parts located at least partially above the nozzles to direct air, water and particulate matter upward and outward from the fixing wall structure. The underwater retaining wall structure described in this patent is installed as follows. First, a hole is drilled approximately in the center of a given section of the ocean floor, which must be cleared. The jet device is subsequently used to supply a jet of compressed air or other gas into the area of the drilled hole to expand this hole to a size sufficient to install a fixing wall structure. Inside the partially cleaned hole, a T-section jet injection device can also rotate, providing an outward direction through a large number of nozzles of the injected medium to weaken the soil of the seabed. The weakened soil is removed by suction in the exhaust pipes mounted on a fixing wall structure.

All these inventions relate to the traditional method of drilling and completion of wells by drilling, namely the drilling of single wells, when the guide casing is cemented into the ground and connected to the wellhead. However, in recent years there has been growing interest in the use of base plates for drilling, when several wells can be drilled in one place. But the base plate for drilling requires a good foundation, in addition, before drilling, it must be firmly fixed. None of the above methods can be used together with such a base plate.

Another problem is the connection of flow lines and composite hoses with the wellhead. These lines and hoses are usually connected to the top of the fountain, therefore they are at risk of being cut off and damaged by moving ice. Thus, all existing solutions to these problems comprise the so-called "weak link", i.e. flow lines and composite hoses will usually be torn in the connector when touched by ice.

Disclosure of invention

The present invention provides an efficient, simple, economical, and reliable method and apparatus for constructing a hollow structure such as a shaft, such as an underwater wellhead, which is to be used together with a base plate for drilling. In the future, such a shaft hollow structure will also be called a shaft. Of particular note, the present invention provides an improved shallow water shaft that can be installed by using simple impact means or vibration means. Shallow waters are deeper than 10 m and especially below 5 m.

According to the proposed method, the shaft hollow structure or shaft is first installed essentially vertically. Next, the shaft is lowered until its lower end rises to the seabed, and then it is driven into the ground until the top edge of the shaft is located approximately at the top of the soil formation, i.e. bottom of the reservoir. Then rock or soil is removed from the mine and a concrete slab is formed at the bottom of the mine. A base plate for drilling is installed on the concrete base, after which the required wells are drilled in the soil formation through conductors (guide pipes) for drilling the wells with which the base plate is equipped.

The device includes a hollow structure such as a shaft with an open top and bottom. The inner area of the mine is a chamber, the size of which allows you to completely place in it a base plate for drilling, associated with equipment for several wells, for example, piping. A concrete slab is placed near the base of the shaft, serving as the foundation for the base plate. Fountain fittings, piping and other related equipment are fixed to the base plate for drilling. Flow lines and / or composite hoses pass into the shaft through an opening in the side wall.

Brief Description of the Drawings

The above, as well as other features of the invention, are more fully set forth in the description of a preferred embodiment of the invention below with reference to the accompanying drawings, in which FIG. 1 is a schematic exploded view of the main components of an underwater wellhead shaft;

in FIG. 2 - wellhead shaft installed below the seabed;

in FIG. 3 is a flowchart of an installation method.

The implementation of the invention

In FIG. 1 shows an underwater wellhead in the form of a shaft hollow structure 1, which is preferably in the form of a cylinder, but may also have a different shape, for example a rectangular, octagonal or even asymmetric shape. Preferably, the hollow structure 1 is made of steel, however, if soil conditions permit, it can be made of concrete. The hollow structure 1 can be formed from several smaller structures made up to the required height. Hereinafter, the hollow structure is referred to as shaft 1.

The cover 3, which is a protective roof, can be installed on top of the shaft 1, closing the upper passage of the shaft 1 to protect the equipment of the wellhead located inside the shaft 1.

The base plate 4 is arranged to fit inside the shaft 1. This plate is preferably made of concrete and is preferably cast in place after all material has been removed from the shaft 1. Plate 4 is the foundation for the base plate 5 for drilling. Plate 4 is cast in place, so that it provides a level base for the base plate 5, eliminating the need to horizontally align the base plate. The alignment procedure of the base plate 5 in the traditional mine construction method is a laborious operation and takes a lot of time. Through the use of a leveled base to place the base plate, this procedure is much simplified or even eliminated. The base plate 4, especially if it is cast in place, protects the shaft 1 from water seeping into it during installation of the equipment and drilling, or subsequently, during well maintenance. This expands the ability to conduct work on the well, mainly in a dry environment. In addition, the base plate 4, in the case when the seabed is loose, for example, is formed by silt, sand or a similar material, provides a solid base for performing various tasks. In the base plate 5 for drilling, guide bodies are installed for guiding the drill string during drilling and placement of wellhead equipment and fountain fittings 8, as well as associated piping 6.

Discharge lines or composite hoses are preferably laid in the seabed to prevent damage by ice. To connect the flow line to the piping, it is preferable to pass this line through the hole

9a. Preferably in the hole 9a

Ί a mortise plug 9 is installed to seal the hole and to allow the flow line or integral hose to pass inside the shaft 1. Alternatively, the mortise plug 9 may include connectors located both inside and outside. A flow line or a composite hose is inserted into the tube from the outside, while the piping is connected to the tube by means of a short flange connection from the inside of the shaft 1.

Furthermore, as shown in FIG. 1, hollow extension elements 7 can be placed over the shaft structure, as a result of which the shaft will rise above the water level. Due to this, water from the mine can be pumped out, and all work, such as equipment maintenance, can be performed in dry conditions.

As shown in FIG. 2, after the construction of the well is completed, the downhole equipment will be in a safe environment inside the mine, thus it will be protected from exposure to floating ice or fishing equipment that could cause damage.

The subsea wellhead system is intended to be used in conjunction with a special drilling vessel 10 capable of lowering the shaft 1, as well as ensuring the tightness of the shaft 1 and the shaft 12 in the body of the drilling vessel for ambient water. Thanks to this, it is possible to install and connect equipment in dry conditions.

The construction method is shown in FIG. 3 in the form of a schematic flowchart. During the installation of the underwater wellhead shaft, the mine 1 is removed from the barge or other similar vessel 10 and raised to a vertical position. Next, the shaft 1 is first lowered to be placed in a vertical position on the seabed 2. In order to immerse the shaft 1 in the seabed, shock or vibration equipment, well known in the art and not requiring further description, is preferably used. These operations in FIG. 3 are not shown.

In FIG. 3 (1) shows the stage in which the shaft 1 is already crammed into the seabed 2. After the shaft 1 has been sunk into the seabed, the material inside the shaft is scooped out or dug out, FIG. 3 (2), resulting in the formation of a pit zone 11. After that, the drilling vessel 10 is located above the shaft 1 and lowered so that its drilling shaft 12 sits on the seabed 2. As shown in FIG. 3 (3), the ship’s drill shaft 12 may be equipped with protruding skirts that are buried a short distance into the seabed 2, making it possible to pump water from the drill shaft 12, as well as the shaft 1.

Next, a base plate 4 is placed in the mine, either by lowering a prefabricated concrete slab from the vessel, or, preferably by pouring concrete into the shaft 1 to form a plate 4, which serves as the foundation for the base plate 5 for drilling. Since at this stage it is possible to work in dry conditions, with the help of concreting, an even horizontal foundation can be made. After that, the base plate 5 for drilling is lowered into the shaft. The slab can be anchored in concrete using standard technical means. Drilling can now be carried out in the usual way using conduits for drilling wells that the base plate is equipped with. At the end of drilling, a piping 6 is installed on the base plate 5, and fountain fittings 8 are installed on each well, FIG. 3 (4).

If necessary, the inner walls of the shaft 1 can be equipped with vertical guides (not shown in the drawings), with which the base plate 5 is sent for installation on the base plate in the correct position. In addition, during the casting process, anchor or fasteners can be laid in concrete to secure the base plate for drilling.

After completion of drilling and completion activities, the roof is lowered in the form of a cover 3 to protect the shaft 1 from ice and other external factors, FIG. 3 (5).

During the installation of the base plate 5 for drilling and piping, a pipe can be installed that goes from the piping 6 to the mortise plug 9 in the shaft wall for subsequent connection of the flow line.

At the final stage of construction or later, if there is a need for a major overhaul of the well, the cover 3 is removed and hollow extension rings 7 are installed over the shaft, FIG. 1, protruding above the surface of the water, thereby ensuring work in dry conditions.

Claims (10)

CLAIM 1. A method of constructing wells in shallow water in areas where there is a threat from drifting ice, which includes the following stages: a) the vessel (10) delivers the hollow structure (1) to the well construction zone and lowers the structure in the known manner onto the seabed (2) in a vertical position; b) immerse the structure (1) in the seabed (2) by means of shock or vibration means until the upper edge of the structure (1) is located substantially flush with the seabed; c) remove the material from the inside of the structure (1); d) fill the inside of the structure (1) with concrete with the formation of a flattened slab (4) of the base; d) install in a known manner on the plate (4) the base plate (5) for drilling, equipped with conductors for drilling wells; and f) drill and complete a predetermined number of wells through said conductors of a base plate (5). 2. The method according to claim 1, in which the lid (3) is closed with the upper edge of the hollow structure (1). 3. The method according to claim 1, in which a hole (9a) is made in the wall of the structure (1) through which flow lines and / or composite hoses are passed from outside the structure (1) into its internal region. 4. A device for constructing wells in shallow water in areas where there is a threat from drifting ice, used in the method claimed in claim 1, containing a hollow structure (1) with open ends, made with the possibility of immersion in the seabed (2) and placing in it a base plate (5) for drilling associated with equipment such as piping (6) and a fountain - FIG. one FIG. 2 nd reinforcement (8) for several wells; a base in the form of a molded plate (4) located inside the hollow structure (1), the plate (4) serving as the foundation for said base plate. 5. The device according to claim 4, in which a hole (9a) is made in the side wall of the hollow structure (1) for introducing a flow line or similar device. 6. The device according to claim 4 or 5, in which the cast plate (4) of the base contains anchor or fastening means for the base plate (5). 7. The device according to any one of claims 4 to 6, in which the hollow structure (1) is equipped with a cover (3). 8. The device according to any one of claims 4 to 7, in which the hollow structure (1) contains guides attached to the inner wall for guiding the base plate to the corresponding position on the plate (4). 9. The device according to any one of claims 4 to 8, in which the hollow structure (1) has a cylindrical shape. 10. The device according to any one of claims 4 to 9, in which the hollow structure (1) has a polygonal shape.