CA2248683C - Underwater installation and method for building of an underwater installation - Google Patents
Underwater installation and method for building of an underwater installation Download PDFInfo
- Publication number
- CA2248683C CA2248683C CA002248683A CA2248683A CA2248683C CA 2248683 C CA2248683 C CA 2248683C CA 002248683 A CA002248683 A CA 002248683A CA 2248683 A CA2248683 A CA 2248683A CA 2248683 C CA2248683 C CA 2248683C
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- CA
- Canada
- Prior art keywords
- seabed
- wells
- hollow body
- well
- casing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 238000009434 installation Methods 0.000 title claims abstract description 23
- 238000000034 method Methods 0.000 title claims abstract description 12
- 229930195733 hydrocarbon Natural products 0.000 claims abstract description 24
- 150000002430 hydrocarbons Chemical class 0.000 claims abstract description 24
- 238000004873 anchoring Methods 0.000 claims abstract description 18
- 238000005553 drilling Methods 0.000 claims abstract description 14
- 239000004215 Carbon black (E152) Substances 0.000 claims abstract description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 9
- 239000004020 conductor Substances 0.000 description 5
- 238000007667 floating Methods 0.000 description 5
- 239000003921 oil Substances 0.000 description 4
- 238000010420 art technique Methods 0.000 description 3
- 238000007796 conventional method Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 239000000346 nonvolatile oil Substances 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 230000000284 resting effect Effects 0.000 description 1
- 239000003981 vehicle Substances 0.000 description 1
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- Earth Drilling (AREA)
Abstract
An underwater installation for use in offshore drilling of and production from, respectively, oil and/or gas wells at deep and moderate deep water comprises an intermediate station in the form of a buoyancy based hollow body (16) tensio n strut anchored at the seabed (10) and located at a depth substantially closer to t he surface of the sea than the seabed (10). At least one hydrocarbon conveying pipeline extends between the buoyancy body (16) and seabed depth, for the transfer of hydrocarbons from the reservoir to said buoyancy body (16). At least one casing liner string (18a-18h) constitutes the tension leg/strut anchoring of the buoyancy body (16). The invention also relates to a method for the building of an underwater installation.</SD OAB>
Description
Underwater installation and method for building of an underwater installation.
The invention relates to an underwater installation for use in offshore recovery of oil and gas, particularly at large depths of the ocean.
Oil drilling from floating vessels is a well established technique which can be carried out even at large depths of the ocean. Conventionally, production of oil and gas has taken place by means of fixed installation resting on the seabed. It is difficult to build fixed installations at large depths. Therefore, technique has been developed wherein wellhead and valves belonging thereto are placed on the seabed, and where risers carry hydrocarbons to a vessel at the surface.
Seadbed based equipment is to a high degree remote controlled and adapted to the use of a remote control vehicle (a RCV or a ROV) for maintenance, etc. This prior art technique can be used at moderate depths. Using known technique, large depths are difficult to access, and a finished installation will be very expensive.
From Norwegian patent application No. 924962, it is previously known to dispose wellheads on a submerged buoyancy body, from where conductor pipes extend downwardly to wells on the seabed. From the wellhead, hydrocarbons are conducted upwardly to a vessel as previously known. Thus, the buoyancy body serves as an artificial seabed, wherein well completion and production are carried out using prior art technique. If the artificial seabed has a sufficient buoyancy, it may in itelf carry a common fixed oil installation.
According to this technique, production wells are drilled in two phases. By means of a floating vessel, a well is drilled to a part of the planned length, e.g. until a 13 3/8 inches casing is set, whereafter the well is plugged and left.
Thereafter, neighbour wells are drilled in the same manner.
The last set casings are, at the upper ends thereof, provided with fasteners in order to be extendable upwardly, e.g. in the form of internal or external threads, to be screwed together with another pipe.
A submerged buoyancy body is anchored above the well area and conductor pipes extend from the buoyancy body and downwardly to the wells, where the conductor pipes are attached to the last set casings. The buoyancy body is positioned at a depth so deep that the wave influence becomes insignificant, the body being attached to the seabed by means of tension struts, such as known from floating tension leg platforms.
On the top of the conductor pipe, within the buoyancy body, a blowout valve is mounted as previously known, risers extending upwardly to a drilling vessel. Drilling of the wells may, thus, continue by means of prior art technique, but now from a substantially less depth than the first phase of the drilling, e.g. one hundred and fifty metres. Second drilling phase which is introduced by drilling out the plug set in the first phase may, thus, be carried out by means of simpler equipment than during the first phase.
Finished drilled wells are completed and put in production as previously known.
The invention relates to an underwater installation for use in offshore recovery of oil and gas, particularly at large depths of the ocean.
Oil drilling from floating vessels is a well established technique which can be carried out even at large depths of the ocean. Conventionally, production of oil and gas has taken place by means of fixed installation resting on the seabed. It is difficult to build fixed installations at large depths. Therefore, technique has been developed wherein wellhead and valves belonging thereto are placed on the seabed, and where risers carry hydrocarbons to a vessel at the surface.
Seadbed based equipment is to a high degree remote controlled and adapted to the use of a remote control vehicle (a RCV or a ROV) for maintenance, etc. This prior art technique can be used at moderate depths. Using known technique, large depths are difficult to access, and a finished installation will be very expensive.
From Norwegian patent application No. 924962, it is previously known to dispose wellheads on a submerged buoyancy body, from where conductor pipes extend downwardly to wells on the seabed. From the wellhead, hydrocarbons are conducted upwardly to a vessel as previously known. Thus, the buoyancy body serves as an artificial seabed, wherein well completion and production are carried out using prior art technique. If the artificial seabed has a sufficient buoyancy, it may in itelf carry a common fixed oil installation.
According to this technique, production wells are drilled in two phases. By means of a floating vessel, a well is drilled to a part of the planned length, e.g. until a 13 3/8 inches casing is set, whereafter the well is plugged and left.
Thereafter, neighbour wells are drilled in the same manner.
The last set casings are, at the upper ends thereof, provided with fasteners in order to be extendable upwardly, e.g. in the form of internal or external threads, to be screwed together with another pipe.
A submerged buoyancy body is anchored above the well area and conductor pipes extend from the buoyancy body and downwardly to the wells, where the conductor pipes are attached to the last set casings. The buoyancy body is positioned at a depth so deep that the wave influence becomes insignificant, the body being attached to the seabed by means of tension struts, such as known from floating tension leg platforms.
On the top of the conductor pipe, within the buoyancy body, a blowout valve is mounted as previously known, risers extending upwardly to a drilling vessel. Drilling of the wells may, thus, continue by means of prior art technique, but now from a substantially less depth than the first phase of the drilling, e.g. one hundred and fifty metres. Second drilling phase which is introduced by drilling out the plug set in the first phase may, thus, be carried out by means of simpler equipment than during the first phase.
Finished drilled wells are completed and put in production as previously known.
Use of a submerged buoyancy body forming an artificial seabed makes it possible to recover oil and gas from substantial depths of the ocean. However, the state of the art, such as represented by said NO 924962, falls unnecessarily expensive, substantially due to a very expensive anchoring.
The present invention is directed towards the provision of a reasonable anchoring of submerged buoyancy bodies of the kind serving as bases for wellheads to wells at larger depths of the ocean.
In accordance with one aspect of the present invention, there is provided an underwater installation for offshore drilling of a hydrocarbon well or wells in the seabed for the production of hydrocarbons from a reservoir below the seabed, the well or wells having an exposed casing or casings on the seabed, the installation comprising an intermediate station in the form of a buoyancy based hollow body, the body being totally submerged below the surface of the water and above the seabed at a depth at which the influence from waves is small, the hollow body being positioned over the well or wells; a tension leg anchoring means for anchoring the hollow body to the seabed over the well or wells, the anchoring means comprising at least one hydrocarbon conveying pipeline formed of a casing extension pipe string extending between, and being coupled to, the exposed casing or casings of the well or wells on the seabed and the hollow body for forming a tension leg anchoring means for the hollow body and for transferring hydrocarbons from the reservoir in the seabed to the hollow body, the tensioning leg anchoring means forming.the sole means for anchoring the submerged hollow body to the seabed; and 3a means for supplying hydrocarbons from the hollow body to the surface of the water.
In accordance with another aspect of the present invention, there is provided a method for constructing an underwater installation for offshore drilling of a hydrocarbon well or wells for the production of hydrocarbons from a reservoir below the seabed, the installation having a totally submerged, intermediate station in the form of a buoyance based hollow body with an upwardly extending production hose for the hollow body for the transfer of the hydrocarbons to,a surface of the water, the method comprising the steps of: a) using a seabed frame, drilling one or more wells in the seabed to leave an exposed casing at the well or wells and thereafter temporarily plugging the well or wells; b) submerging the hollow body beneath the surface of the water and above the seabed to a depth at which the influence from waves is small; c) positioning the hollow body over the well or wells; d) retaining the body over the well or wells by means of guys attached to the frame on the seabed and the hollow body; e) forming a hydrocarbon conveying casing pipe string extension from the exposed casing of cne or more wells to the hollow body; f) removing the guys to tension the casing pipe string extension so that the casing becomes a tension leg forming the sole means for anchoring the submerged hollow body to the seabed; and g) removing the plugging of the well or wells to supply hydrocarbons to the casing pipe string extension.
3b A characteristic features of the invention consist in that the buoyance body is anchored to the seabed by means of conductor pipes extending between one of the casings of the well and the buoyance body.
An example of a diagrammatically shown embodiment of the invention is shown in a perspective view when an underwater installation occupies a production phase.
On the seabed 10, a subsea frame 12 has been installed in an introduction phase, forming an anchor for lines 14 for submerging and lateral positioning of a buoyancy based hollow body 16.
The underwater installation according to the invention is suitable for use at large depths of the ocean, e.g. 400 -4000 metres, and the submerged buoyancy body 16 may e.g. be placed at a depth of e.g. 150 metres, where the influence from the waves is very small, causing a moderate variation in the load on tension struts for the anchoring of the buoyancy body 16 on the seabed.
After e.g. eight wells are predrilled to 13 3/8 inches, casing liner strings 18a, 18b, 18c, 18d, 18e, 18f, 18g, 18h are lowered from a floating platform (not shown) to be screwed to the upper threaded end of last set casings, during which the liner strings 18a - 18h pass through vertically aligned passages, not shown, in the buoyancy body 16. In the production phase, the buoyancy body 16 is closed uppermost, except for a central opening for a production hose 20. After having been screwed to said upper end of last set casings, these casing liner strings 18a - 18h, the number of which corresponds to the number of wells, are attached to the buoyancy body 16 with the upper end thereof. During this attachment, the temporary anchor lines 14 may be tightened for, thereafter, to be slackened, transferring the tension strain to "the tension struts" 18a - 18h according to the invention which, thus, are tensioned and tightened.
The temporary anchor lines 14 may be removed when the underwater installation is ready for production.
As mentioned, one or more casing-liner strings 18a - 18h have a double function, namely as a casing and a tension strut. In the embodiment shown, the wells upon completion are considered as being continuous from the reservoir up to the buoyancy based, tension leg/strut anchored, submerged hollow body which is positioned at a depth of another order than the seabed. The invention represents large simplifications in relation to known and conventional technique, and enables the utilization of already established technology such as operations associated to drilling at very large depths of the ocean as well as socalled floating production.
The present invention is directed towards the provision of a reasonable anchoring of submerged buoyancy bodies of the kind serving as bases for wellheads to wells at larger depths of the ocean.
In accordance with one aspect of the present invention, there is provided an underwater installation for offshore drilling of a hydrocarbon well or wells in the seabed for the production of hydrocarbons from a reservoir below the seabed, the well or wells having an exposed casing or casings on the seabed, the installation comprising an intermediate station in the form of a buoyancy based hollow body, the body being totally submerged below the surface of the water and above the seabed at a depth at which the influence from waves is small, the hollow body being positioned over the well or wells; a tension leg anchoring means for anchoring the hollow body to the seabed over the well or wells, the anchoring means comprising at least one hydrocarbon conveying pipeline formed of a casing extension pipe string extending between, and being coupled to, the exposed casing or casings of the well or wells on the seabed and the hollow body for forming a tension leg anchoring means for the hollow body and for transferring hydrocarbons from the reservoir in the seabed to the hollow body, the tensioning leg anchoring means forming.the sole means for anchoring the submerged hollow body to the seabed; and 3a means for supplying hydrocarbons from the hollow body to the surface of the water.
In accordance with another aspect of the present invention, there is provided a method for constructing an underwater installation for offshore drilling of a hydrocarbon well or wells for the production of hydrocarbons from a reservoir below the seabed, the installation having a totally submerged, intermediate station in the form of a buoyance based hollow body with an upwardly extending production hose for the hollow body for the transfer of the hydrocarbons to,a surface of the water, the method comprising the steps of: a) using a seabed frame, drilling one or more wells in the seabed to leave an exposed casing at the well or wells and thereafter temporarily plugging the well or wells; b) submerging the hollow body beneath the surface of the water and above the seabed to a depth at which the influence from waves is small; c) positioning the hollow body over the well or wells; d) retaining the body over the well or wells by means of guys attached to the frame on the seabed and the hollow body; e) forming a hydrocarbon conveying casing pipe string extension from the exposed casing of cne or more wells to the hollow body; f) removing the guys to tension the casing pipe string extension so that the casing becomes a tension leg forming the sole means for anchoring the submerged hollow body to the seabed; and g) removing the plugging of the well or wells to supply hydrocarbons to the casing pipe string extension.
3b A characteristic features of the invention consist in that the buoyance body is anchored to the seabed by means of conductor pipes extending between one of the casings of the well and the buoyance body.
An example of a diagrammatically shown embodiment of the invention is shown in a perspective view when an underwater installation occupies a production phase.
On the seabed 10, a subsea frame 12 has been installed in an introduction phase, forming an anchor for lines 14 for submerging and lateral positioning of a buoyancy based hollow body 16.
The underwater installation according to the invention is suitable for use at large depths of the ocean, e.g. 400 -4000 metres, and the submerged buoyancy body 16 may e.g. be placed at a depth of e.g. 150 metres, where the influence from the waves is very small, causing a moderate variation in the load on tension struts for the anchoring of the buoyancy body 16 on the seabed.
After e.g. eight wells are predrilled to 13 3/8 inches, casing liner strings 18a, 18b, 18c, 18d, 18e, 18f, 18g, 18h are lowered from a floating platform (not shown) to be screwed to the upper threaded end of last set casings, during which the liner strings 18a - 18h pass through vertically aligned passages, not shown, in the buoyancy body 16. In the production phase, the buoyancy body 16 is closed uppermost, except for a central opening for a production hose 20. After having been screwed to said upper end of last set casings, these casing liner strings 18a - 18h, the number of which corresponds to the number of wells, are attached to the buoyancy body 16 with the upper end thereof. During this attachment, the temporary anchor lines 14 may be tightened for, thereafter, to be slackened, transferring the tension strain to "the tension struts" 18a - 18h according to the invention which, thus, are tensioned and tightened.
The temporary anchor lines 14 may be removed when the underwater installation is ready for production.
As mentioned, one or more casing-liner strings 18a - 18h have a double function, namely as a casing and a tension strut. In the embodiment shown, the wells upon completion are considered as being continuous from the reservoir up to the buoyancy based, tension leg/strut anchored, submerged hollow body which is positioned at a depth of another order than the seabed. The invention represents large simplifications in relation to known and conventional technique, and enables the utilization of already established technology such as operations associated to drilling at very large depths of the ocean as well as socalled floating production.
Claims (4)
1. An underwater installation for offshore drilling of a hydrocarbon well or wells in the seabed for the production of hydrocarbons from a reservoir below the seabed, the well or wells having an exposed casing or casings on the seabed, said installation comprising an intermediate station in the form of a buoyancy based hollow body, said body being totally submerged below the surface of the water and above the seabed at a depth at which the influence from waves is small, said hollow body being positioned over the well or wells; a tension leg anchoring means for anchoring the hollow body to the seabed over the well or wells, said anchoring means comprising at least one hydrocarbon conveying pipeline formed of a casing extension pipe string extending between, and being coupled to, the exposed casing or casings of the well or wells on the seabed and the hollow body for forming the tension leg anchoring means for the hollow body and for transferring hydrocarbons from the reservoir in the seabed to the hollow body, said tensioning leg anchoring means forming the sole means for anchoring said submerged hollow body to the seabed; and means for supplying hydrocarbons from the hollow body to the surface of the water.
2. An underwater installation according to claim 1 further including a frame on the seabed for the exposed casing or casings of the well or wells.
3. A method for constructing an underwater installation for offshore drilling of a hydrocarbon well or wells for the production of hydrocarbons from a reservoir below the seabed, the installation having a totally submerged, intermediate station in the form of a buoyance based hollow body with an upwardly extending production hose for said hollow body for the transfer of said hydrocarbons to a surface of the water, said method comprising the steps of:
a) using G seabed frame, drilling one or more wells in the seabed to leave an exposed casing at the well or wells and thereafter temporarily plugging the well or wells;
b) submerging the hollow body beneath the surface of the water and above the seabed to a depth at which the influence from waves is small;
c) positioning the hollow body over the well or wells d) retaining the body over the well or wells by means of guys attached to the frame on the seabed and the hollow body;
e) forming a hydrocarbon conveying casing pipe string extension from the exposed casing of one or more wells to the hollow body f) removing the guys to tension the casing pipe string extension so that the casing becomes a tension leg forming the sole means for anchoring the submerged hollow body to the seabed; and g) removing the plugging of the well or wells to supply hydrocarbons to the casing pipe string extension.
a) using G seabed frame, drilling one or more wells in the seabed to leave an exposed casing at the well or wells and thereafter temporarily plugging the well or wells;
b) submerging the hollow body beneath the surface of the water and above the seabed to a depth at which the influence from waves is small;
c) positioning the hollow body over the well or wells d) retaining the body over the well or wells by means of guys attached to the frame on the seabed and the hollow body;
e) forming a hydrocarbon conveying casing pipe string extension from the exposed casing of one or more wells to the hollow body f) removing the guys to tension the casing pipe string extension so that the casing becomes a tension leg forming the sole means for anchoring the submerged hollow body to the seabed; and g) removing the plugging of the well or wells to supply hydrocarbons to the casing pipe string extension.
4. A method as set forth in claim 3, including the steps of providing a fastener in the form of threads on the exposed end or ends of the casing or casings and connecting said end portion to an adjacent end of a pipe comprising the casing pipe string extension, the opposite end of said pipe being anchored to the hollow body.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NO960997 | 1996-03-12 | ||
| NO19960997A NO303028B1 (en) | 1996-03-12 | 1996-03-12 | The subsea installation |
| PCT/NO1997/000068 WO1997034074A1 (en) | 1996-03-12 | 1997-03-07 | Underwater installation and method for building of an underwater installation |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2248683A1 CA2248683A1 (en) | 1997-09-18 |
| CA2248683C true CA2248683C (en) | 2006-04-18 |
Family
ID=36250936
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002248683A Expired - Fee Related CA2248683C (en) | 1996-03-12 | 1997-03-07 | Underwater installation and method for building of an underwater installation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2248683C (en) |
-
1997
- 1997-03-07 CA CA002248683A patent/CA2248683C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2248683A1 (en) | 1997-09-18 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |
Effective date: 20170307 |