WO2004070167A1

WO2004070167A1 - Method and system for the use of a distributed temperature system in a subsea well

Info

Publication number: WO2004070167A1
Application number: PCT/GB2003/005515
Authority: WO
Inventors: Euan Drummond
Original assignee: Sensor Highway Limited
Priority date: 2003-02-04
Filing date: 2003-12-18
Publication date: 2004-08-19
Also published as: GB0302499D0; MXPA05008055A; BR0318072A; AU2003295127A1; NO20053950L; NO20053950D0; GB2398444A; NO339526B1; GB2398444B

Abstract

A system and method to transmit information to or from a sub sea well (12), comprising deploying an ROV (60), towards the sub sea well, optically connecting a first optical fiber (66) that is carried by the ROV with a second optical fiber (36) that is located along a section of the sub sea well, and transmitting information along the optical fibers to or from a remote location. The information may comprise a temperature profile along the section, data from sensors functionally connected to the second optical fiber, or a command.

Description

METHOD AND SYSTEM FOR THE USE OF A DISTRIBUTED TEMPERATURE SYSTEM

IN A SUBSEA WELL

BACKGROUND

The invention generally relates to oil and gas wells. More particularly, the invention relates to a system and method used to provide selective optical communication between a remote location, such as a vessel at the ocean surface, and a subsea well. The optical communication can be used to enable the operation of a distributed temperature system in the subsea well.

Subsea wells provide unique challenges to the oil and gas industry. They are located in extremely harsh environments and, being a substantial distance from the ocean surface, are hard to reach. Nevertheless, despite the environment and location, operators must still obtain as much information from the subsea well as possible (such as temperature, pressure, and chemical properties) in order to monitor the well and take corrective action if necessary. Obtaining this information, however, should be done with as little intervention as possible so as to not disrupt the production of the well.

Thus, there exists a continuing need for an arrangement and/or technique that, addresses one or more of the problems that are stated above.

SUMMARY A system and method transmit information to or from a subsea well, comprising: deploying an ROV towards the subsea well, optically connecting a first optical fiber that is carried by the RON with a second optical fiber that is located along a section of the subsea well, and transmitting information along the optical fibers to or from a remote location. The information may comprise a temperature profile along the section, data from sensors functionally connected to the second optical fiber, or a command.

BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a schematic of a subsea well including one embodiment of this invention. Fig. 2 is a schematic of an RON in optical communication with a subsea well through a connector subassembly on the subsea tree.

DETAILED DESCRIPTION

Figure 1 shows a component of the present invention. Tubing 10 is deployed within a subsea well 12 that may include a casing 15. Subsea well 12 extends from the ocean floor 14 below the ocean surface 16. Tubing 10 is typically suspended from a wellhead 18 by a tubing hanger 20 and may terminate at a subsea tree 22. For purposes of clarity, subsea tree 22 is not shown in detail since it is known in the art. A pipeline 24 is in fluid communication with the tubing 10 and provides fluid communication between the tubing 10 and a remote location (such as the ocean surface 16 or land) so as to enable the transportation of hydrocarbons from the well 12. The well 12 intersects at least one formation 26. Hydrocarbons flow from the formation 26 into the tubing 10. Casing 15 includes perforations 28 to allow such flow.

A conduit 30 may be disposed along or within the tubing 10 and may be attached to tubing 10 such as by clamps. Alternatively, conduit 30 may be deployed within or behind casing 15. Conduit 30 is in fluid communication with a passageway 32 in the tubing hanger 20 and then a passageway 34 in the wellhead 22. Conduit 30 and passageways 32 and 34 provide a continuous channel that houses at least one optical fiber 36. Optical fiber 36 exits subsea tree 22 at an outlet 38. The position of the outlet 38 is dependent on the subsea tree vendor and type of subsea tree, be it a horizontal or vertical subsea tree. It is understood that to enable the continuous channel and the housing of the optical fiber 36, various hydraulic and/or optical connectors may be required through the tubing hanger 20, wellhead 18, and subsea tree 22, particularly to maintain a seal of the channel in relation to the exterior environment. Thus, optical fiber 36 may actually be formed from a plurality of components. The term optical fiber 36 herein refers to all of such components that are in optical communication.

A subsea tree connector subassembly 40 is associated with and may be connected to the subsea tree 22. The optical fiber 36 (or a component thereof) extends from the outlet 38 to the subassembly 40 and may be housed between such two points by a tube 42. Subassembly 40 includes connectors 44 that are mateable with corresponding connectors to be deployed on a remotely operated vehicle (RON), as will be disclosed.

Optical fiber 36 can carry optical signals indicative of data or commands. Such optical signals can thus extend to and from the bottom of the optical fiber 36 to the subassembly 40, at which point they may be passed on to the RON via the connectors 44, as will be disclosed.

It is noted that certain subsea trees 22 already include passageways and outlets similar to passageway 34 and outlet 38, particularly for use with electrical components and gauges. Such electrical passageway and outlet may be used to house the optical fiber 36, or the optical fiber 36 may be housed in an additional passageway 34 and outlet 38.

Figure 2 shows the deployment of an ROV 60 from a remote location, such as a vessel 62 (a ship). ROV 60 is connected to the vessel 62 by way of cable 64. Cable 64 includes at least one optical fiber 66 that extends from the ROV 60 to an opto-electronic unit 68 that may be located on the vessel 62 (or another remote location). Cable 64 may also provide power to ROV 60. ROV 60 includes thrusters 70 that enable its maneuverability and control from a remote location, such as vessel 62.

ROV 60 includes an ROV connector subassembly 72 that includes connectors 74 that are selectively mateable with the connectors 44 on the tree connector subassembly 40. Depending on the design desired by the operator, the tree connectors 44 may be the male connectors and the ROV connectors 74 may be the female connectors, or vice versa. ROV 60 also provides optical communication, by way of additional or the same optical fiber, from optical fiber 66 through ROV 60 and to ROV connectors 74. Thus, when tree connectors 44 are appropriately mated to ROV connectors 74, optical communication exists from the bottom of the optical fiber 36 housed in the conduit 30 to the unit 68.

The purpose of providing optical communication from the subsea well 12 to the unit 68 via the ROV 60 is to enable the selective transmission of information to and from the subsea well 12 without requiring a permanent optical communication cable or subsea opto-electronics unit. Optical communication to and from the subsea well 12 can provide a large number of benefits to an operator.

For instance, the optical fibers 36, 66 and unit 68 may comprise a distributed temperature sensor (DTS)-based temperature measurement system that can provide temperature data that is spatially distributed over many thousands of individual measurement points inside the well. Optical fiber 36 can be deployed downhole so that the optical fiber 36 extends into the region where temperature measurements are to be made (within the subsea well 12). An optical time domain reflectometry (OTDR) technique may be used to detect the spatial distribution of temperature along the length of the optical fiber 36. OTDR techniques used to measure a temperature profile along a location, such as a well, are known. More specifically, pursuant to the OTDR technique, optical energy is introduced by the unit 68 into optical fiber 66, through ROV 60, through mated connectors 74 and 44, and into optical fiber 36 in the subsea well 12. The optical energy that is introduced into the optical fiber 36 produces backscattered light. The phrase "backscattered light" refers to the optical energy that returns at various points along the optical fiber 36 back to the unit 68. More specifically, in accordance with OTDR, a pulse of optical energy typically is introduced into optical fiber 66, through ROV 60, through mated connectors 74 and 44, and into optical fiber 36, and the resultant backscattered optical energy that returns from the optical fiber 36 to the unit 68 is observed as a function of time. The time at which the backscattered light propagates from the various points along the optical fiber 36 to the unit 68 is proportional to the distance along the optical fiber 36 from which the backscattered light is received.

In a uniform optical fiber, the intensity of the backscattered light as observed from the unit 68 exhibits an exponential decay with time. Therefore, knowing the speed of light in the optical fiber 36 yields the distances that the light has traveled along the optical fiber 36. Variations in the temperature show up as variations from a perfect exponential decay of intensity with distance. Thus, these variations are used to derive the distribution of temperature along the optical fiber 36. In the frequency domain, the backscattered light includes the Rayleigh spectrum, the Brillouin spectrum and the Raman spectrum. The Raman spectrum is the most temperature sensitive with the intensity of the spectrum varying with temperature, although all three spectrums of the backscattered light contain temperature information. The Raman spectrum typically is observed to obtain a temperature distribution from the backscattered light. A temperature profile along the subsea well 12 may be beneficial for a variety of reasons, as known in the art. For instance, a temperature profile along the formation 26 may be used to determine where and whether hydrocarbons are flowing from the formation 26 into the well 12.

An operator may also choose to observe the temperature profile along the optical fiber 66. In this case, the optical fiber 66 and unit 68 may be configured so that backscattered light from the optical fiber 66 is also analyzed at the unit 68, as previously disclosed.

As an alternative to OTDR, another technique that may be used in conjunction with a DTS -based temperature measurement system is an optical frequency domain reflectometry (OFDR) technique. As is known in the art, OFDR is not time domain based like the OTDR technique. Rather, OFDR is based on frequency.

Optical fiber 36 may also be in functional communication with other types of sensors (not shown), such pressure sensors, acoustic sensors, resistivity arrays, flow sensors, chemical property sensors, optical fluid analyzers, water detection sensors, gas detection sensors, oil detection sensors, differential pressure sensors, relative bearing sensors, strain sensors, distributed strain sensors, distributed pressure sensors, accelerometers, or induction sensors. Such sensors may be electrical or optical. Thus, when ROV 60 is appropriately mated to tree subassembly 40, data from such sensors may be transferred optically to the unit 68. Status data of any downhole tool or sensors may also be sent via the optical pathway.

Optical communication between unit 68 and subsea well 12 may also be used to send commands to and from the unit 68. Thus, an optical command may be sent to a downhole tool, such as a packer 80, which is received and interpreted by a module in the packer 80 to take a certain action, such as setting the packer 80. Other downhole tools that may be optically activated may include pumps, valves, separators, anchors, and chokes, to name a few. In operation, then, an ROV 60 is launched from the vessel 62 and is maneuvered to mate with tree subassembly 40 so that optical communication is established through mated tree connectors 44 and ROV connectors 74. Once optical communication is established, transmission of information takes place through the optical fibers 36 and 66, as previously disclosed. Thus, a temperature profile along optical fiber 36 (and/or optical fiber 66) or data from another sensor/tool may be obtained at the unit 68 and vessel 62. Or, commands may be sent from the unit 68 to downhole or from downhole to the unit 68. In any case, once the transmission of optical signals is completed, the ROV 60 is disengaged from the tree subassembly 40 and is maneuvered back to the vessel 62 or the subsea tree of another nearby subsea well to repeat the procedure at such well.

Another benefit of an all optical transmission and sensing, such as measuring a temperature profile using OTDR techniques, is that no electronic components are used thereby increasing the life of the system. In addition, in one embodiment of the present system and method, a memory storage is not required. Thus, the ROV 60 essentially collects the relevant information from the subsea well 12 on a real-time (or near real-time) basis whenever the ROV 60 and ROV connectors 74 is/are engaged. The selective engagement and transmission of information using ROV 60 benefits an operator since the operator does not have to include additional, costly, and power-consuming subsea infrastructure (such as a subsea opto-electronic unit or an additional subsea power and communication module) to enable the functionality of the system. In addition, any subsea tree can be retrofitted to be used with the ROV 60 and the invention disclosed herein. In an alternative embodiment, a memory module (not shown) is provided adjacent or in the subsea tree 12 in order to capture data at various points in the life of the well. In this embodiment, the ROV 60 downloads such data from the module when engaged.

While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. For instance, although only one optical fiber 36 and 66 is shown, a plurality of optical fibers 36 may be deployed in the subsea well 12 and a plurality of optical fibers 66 may be contained in the cable 64. In addition, the invention can be used with any subsea well (such as injector and/or water wells) and not just those wells that carry hydrocarbons or produce fluids. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the invention.

Claims

CLAIMSWhat is claimed is:

1. A method to transmit information to or from a subsea well, comprising: deploying an ROV towards the subsea well; optically connecting a first optical fiber that is carried by the ROV with a second optical fiber that is located along a section of the subsea well; and transmitting information along the optical fibers to or from a remote location.

2. The method of claim 1 , further comprising: launching an optical signal through the optical fibers; and analyzing the backscattered light provided by the second optical fiber to determine a temperature profile along the section.

3. The method of claim 1 , wherein the information is a temperature profile along the section.

4. The method of claim 1 , further comprising optically connecting the first optical fiber to a unit located on a vessel.

5 The method of claim 1 , wherein the information is data from sensors functionally connected to the second optical fiber.

6. The method of claim 1 , wherein the information is a command.

7. A system to transmit information to or from a subsea well, comprising: an ROV including at least one ROV connector; a subsea well with a subsea tree including at least one tree connector; the at least one ROV connector selectively mateable to the at least one tree connector; the at least one ROV connector in optical communication with a vessel through a first optical fiber; the at least one tree connector in optical communication with a second optical fiber located along at least a section of the subsea well; and wherein, when the at least one ROV connector is mated to the at least one tree connector, optical communication is established to transmit information along the optical fibers.

8. The system of claim 7, wherein an opto-electrical unit located on the vessel is connected to the first optical fiber.

9. The system of claim 7, wherein the second optical fiber measures a temperature profile along the section.

10. The system of claim 7, wherein the information is a temperature profile along the section.

11 The system of claim 7, wherein the information is data from sensors functionally connected to the second optical fiber.

12. The system of claim 7, wherein the information is a command.