Patent Application
20110311179
Many forms of measurements performed with a fiber optic sensor can be taken as a distributed measurement of a parameter that is incident along the length of the optical fiber. For instance, in the hydrocarbon production industry, various downhole parameters, such as temperature, pressure, and fluid flow, may be monitored before or during production and/or before, during or after a well treatment using a distributed fiber optic sensor. Data gathered in this manner can provide useful information about characteristics of the hydrocarbon production. In addition, distributed fiber optic sensors may also be deployed in a wellbore during a seismic survey to provide information relating to the characteristics of an earth formation. In such applications, the fiber optic sensor typically is deployed in an environment in which the sensor is exposed to corrosive materials, as well as elevated temperatures and pressures. Thus, the fiber optic sensor is generally configured as a cable in which one or more sensing fibers are encased in a jacket or coating that protects the fiber from the environment. The jacket or coating is made of materials that allow certain measurement parameters (e.g., temperature, vibration, etc.) to naturally transfer through the jacket/coating to the sensing fiber or fibers. However, partially due to the protective characteristics of the outer jacket, not all parameters naturally transfer through the cable, thus limiting the spectrum of fiber optic distributed monitoring that may be performed.
Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying drawings illustrate only the various implementations described herein and are not meant to limit the scope of various technologies described herein. The drawings are as follows:
In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.
In the specification and appended claims: the terms “connect”, “connection”, “connected”, “in connection with”, and “connecting” are used to mean “in direct connection with” or “in connection with via another element”; and the term “set” is used to mean “one element” or “more than one element”. As used herein, the terms “up” and “down”, “upper” and “lower”, “upwardly” and downwardly“, “upstream” and “downstream”; “above” and “below”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the invention.
Individual sensors and sensor arrays have long been deployed in wellbores for use in both temporary and long-term or permanent monitoring installations. In recent years, conventional fixed sensors and sensor arrays have been commonly replaced by distributed fiber optic sensors that are configured to respond along the length of the fiber to a parameter of interest. In such installations, the distributed measurements typically are limited to parameters that can naturally transfer through the cable to the sensing fiber or fibers, such as temperature and vibration. As a result, measurements of various parameters that could otherwise provide useful information related to hydrocarbon production, such as pressure and gas composition/concentration, but which do not readily transfer through the cable's protective coating or jacket in a manner in which they can generate a response in the optical fiber, have not been readily attainable.
Accordingly, embodiments of the invention provide for a fiber optic sensor cable that is configured to enhance the exposure and increase the sensitivity of the sensing fiber or fibers to conditions in the sensing environment (e.g., in a wellbore) so as to provide for measurements of a wide range of parameters, including temperature, vibration and pressure. Although providing greater exposure to the parameters of interest, the fiber optic sensor cable also is configured to provide sufficient protection to the sensing fiber or fibers from the sensing environment so that the fiber optic sensor cable may be deployed in a permanent installation, if desired.
Towards that end, an illustrative embodiment of such a fiber optic sensor cable 100 is shown in
The outer protective layer 106 may be a coating or a jacket that protects the inner tube 102 and sensing fiber 104 from the environment in which the cable 100 is deployed. At the same time, the protective layer 106 is configured such that a parameter of interest can transfer through the layer 106 to the inner tube 102. For instance, in some embodiments, the protective layer 106 may be a metal armor having multiple ports or openings 108 therethrough to allow transfer of the sensed parameter to the inner tube 102. In the embodiment shown in
In the embodiment shown in
In the illustrative embodiment of
In other embodiments of the fiber optic sensor cable 100, such as in embodiments in which a parameter other than pressure is of interest, the inner tube 102 is compartmentalized into discrete sensing elements 118 but is configured to be resistant to pressure. For instance, the inner tube 102 may have a circular cross section that is substantially inflexible when exposed to pressure. In addition, each compartment 114 may be filled with a transmission medium 112 other than a pressure-transmitting liquid, e.g., air. For instance, in applications in which gas composition or gas concentration detection is of interest, the sensing fiber 104 may be configured to respond to various chemicals that are present in the monitored environment. In such applications, the outer armor 106 may include the ports 108, which allow the gas to readily impinge on the inner tube 102/sensing fiber 104 and/or may be made of a material that is nonresistant to the chemicals of interest.
Regardless of the application, the sensor cable 100 is constructed such that the sensing fiber 104 extends within the inner tube 102, which is segregated from the outer protective layer 106. The outer protective layer 106 provides protection from the environment so that the cable 100 may be included in a permanent monitoring installation, if desired. At the same time, the outer protective layer 106 is configured to allow transfer of the parameter of interest to the sensing fiber 104. To provide for point measurements of the parameter at each of a plurality of locations along the length of the sensing fiber 104, the inner tube 102 includes the series of compartments 114 that are separated from each other by the seals 116, thus creating the individual sensing elements 118 that extend along the length of the sensor cable 100. Any suitable material may be used for the outer protective layer 106, the inner tube 102, the seals 116, and the parameter transmission medium 112, and the particular materials may vary depending on the particular application and the characteristics of the environment in which the fiber optic sensor cable 100 is employed.
The length of each of the separately sealed sensing elements 118 also may vary depending on the application. For instance, the length of each sensing element 118 may be in the range of a few centimeters to several tens of meters. Likewise, the spacing between elements 118 may range between a few centimeters to tens of meters. The sensing elements 118 may be evenly spaced and their lengths may be uniform, or the spacing and lengths may vary along the length of the sensor cable 100 as may be suitable for the particular measurement and/or type of measurement being made.
In yet other embodiments, additional optical fibers and/or electronic conductors may also be incorporated in the sensor cable 100. One such embodiment is shown in the transverse and longitudinal cross-sectional views in
Conventional manufacturing methods can be used to construct the sensor cables 100 and 200. As an example, the compartmentalized sensing elements 118/212 can be constructed by blowing, pumping, laying or otherwise disposing a sensing optical fiber 104/204 into the conduit or tube 102/210. Sealing elements 116/213 and transmitting media 112/209 suitable for enhancing transfer of the parameter of interest then may be installed. For instance, to fabricate a pressure-sensitive sensor cable, a pressure-transmitting fluid 112/209, such as a liquid metal, may be pumped into the elliptical, flexible tube 102/210 through which the sensing fiber 104/204 extends. The pressure-transmitting fluid 112/209 may be alternated with a slow set sealing fluid that is pumped into the tube 102/210 at regular intervals (e.g., every 10 meters) so that, when set, a series of the separate sensing elements 118/212 are formed. In an alternative embodiment, the tube 102/210 may be filled with the parameter-transmitting fluid 112/209 and then a sealing fluid may be injected through the wall of the tube 102/210 at selected locations (e.g., regular intervals of 10 meters) and allowed to set to form seals 116/213. It should be understood that the foregoing examples are illustrative only and that the compartmentalized sensing elements 118/212 may be formed in other manners using other manufacturing techniques and materials that are suitable for the particular application in which the sensor cable will be employed.
Regardless of the manner in which the compartmentalized sensing elements 118/212 are formed, the tube 102/210 containing the elements 118/212 is contained within the outer protective armor 106/202: As an example, a flat sheet of protective material, such as a metal protective armor, may be pre-drilled with spaced-apart openings to form the ports 108/208. The openings may be drilled in a regular pattern so that one or more of the openings will align with a sensor element 118/212. The compartmentalized tube 102/210 may be laid on the drilled armor sheet, and the armor sheet then rolled about the tube 102/210 and the edges welded together to form the protective outer layer 106/202. In embodiments which include additional sensing fibers and/or electrical conductors, these additional components may be spiraled together with the compartmentalized tube 102/210 before placing them into the protective armor 106/202. In general, the finished sensor cable 100/200 may have an outer diameter on the order of ¼ inch.
Again, the example provided above for encasing the compartmentalized tube 102/210 in a protective outer layer is illustrative only and other techniques may be used. For instance, for hydrocarbon production applications, the outer protective layer 106/202 may be provided by a perforated control line or wireline into which the compartmentalized inner conduit 102/210 may be pumped or otherwise deployed.
As shown in
The backscattered optical signals generated by the optical fiber 104 in response to the interrogating optical signal may be detected and converted to an electrical signal at the receiver 276. This electrical signal may be acquired by a signal acquisition module 278 (e.g., an analog-to-digital converter) and then transferred as data representing the backscattered signals to an output module 280 for outputting the data to the processing subsystem 268. The processing subsystem 268 may process the data to determine characteristics of the parameter of interest (e.g., amount of pressure present at various locations in the monitored environment).
More particularly, the backscattered light is affected by the pressure that is incident on the optical fiber 104 due to simple elongation of the fiber that occurs when subjected to a strain (such as from pressure that is incident on the fiber). This elongation changes the relative position between the scattering centers of the optical fiber and also changes the refractive index of the glass. Both these effects alter the relative phase of the light scattered from each scattering center. As a result, characteristics of a parameter of interest that is incident on and strains the sensing fiber 104 may be determined by acquiring and processing data from the backscattered signal that is generated in response to an interrogating optical signal.
In embodiments in which the sensor cable 100 also includes electrical conductors, the control system 264 may also be arranged to transmit and receive control and status signals to and from various downhole components deployed in the wellbore 256. Data acquired from the sensor cable 100 by the control system 264 may be transmitted to a remote data center, if desired, for further processing, analysis, and/or storage.
The processing subsystem 268 of
Data and instructions are stored in respective storage devices, which are implemented as one or more computer-readable or machine-readable storage media. The storage media include different forms of memory including semiconductor memory devices such as dynamic or static random access memories (DRAMs or SRAMs), erasable and programmable read-only memories (EPROMs), electrically erasable and programmable read-only memories (EEPROMs) and flash memories; magnetic disks such as fixed, floppy and removable disks; other magnetic media including tape; optical media such as compact disks (CDs) or digital video disks (DVDs); or other types of storage devices. Note that the instructions discussed above can be provided on one computer-readable or machine-readable storage medium, or alternatively, can be provided on multiple computer-readable or machine-readable storage media distributed in a large system having possibly plural nodes. Such computer-readable or machine-readable storage medium or media is (are) considered to be part of an article (or article of manufacture). An article or article of manufacture can refer to any manufactured single component or multiple components.
The sensor cable 100 may be deployed in the wellbore 256 in any of a variety of conventional manners. For instance, the cable 100 may be laid against either the inside or the outside of the completion tubing and deployed in the wellbore along with the completion components. Alternatively, the cable 100 may be deployed in the production tubing after completion is finished. Yet further, the installation of the cable 100 may be permanent or temporary and may be used, for instance, to monitor parameters during production or before, during and/or after a well treatment.
Although the foregoing embodiments have been described with respect to monitoring parameters in a hydrocarbon production well, it should be understood that embodiments of the sensor cable may also be used in any application in which measurement of a particular parameter at a plurality of separate locations distributed along a sensing fiber is desired. Moreover, while the foregoing embodiments have been described in the context of pressure monitoring and gas composition detection, it should be understood that embodiments of the sensor cable may be configured to monitor other types of parameters.
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. It is intended that the appended claims cover such modifications and variations as fall within the true spirit and scope of the invention.
