MXPA00012659A - Non-intrusive fiber optic pressure sensor for measuring unsteady pressures within a pipe - Google Patents

Abstract

Non-intrusive pressure sensors (14-18) for measuring unsteady pressures within a pipe (12) include an optical fiber (10) wrapped in coils (20-24) around the circumference of the pipe (12). The length or change in the length of the coils (20-24) is indicative of the unsteady pressure in the pipe. Bragg gratings (310-324) impressed in the fiber (10) may be used having reflection wavelength&lgr;that relate to the unsteady pressure in the pipe. One or more of sensors (14-18) may be axially distributed along the fiber (10) using wavelength division multiplexing and/or time division multiplexing.

Description

NON-INTRUSIVE OPTICAL FIBER PRESSURE SENSOR FOR MEASURING IRREGULAR PRESSURES WITHIN A PIPE Cross-references to related applications This application is a continuation of part of the co-pending co-pending North American patent application, serial No. 09 / 105,525, entitled? Non -Intrusive Fiber Optic Pressure Sensor For Measuring Pressure Inside, Outside and Across Pipes ", filed on June 26, 1998. TECHNICAL FIELD This invention relates to the detection of pressure in pipes and more particularly to a fiber pressure sensor non-intrusive optics to measure irregular pressures inside a pipeline BACKGROUND OF THE ART It is known in the oil and gas industry that the measurement of fluid pressure in an extraction pipeline is useful for the exploration and production of oil and gas However, typical pressure sensors require the drilling of a hole in the pipe to connect the pres sensor, or require that the sensor or a part of it be deployed in the pipeline. Drilling holes in pipes can be an expensive process and can cause system failures. Accordingly, it would be desirable to measure the pressure in the pipe in a non-intrusive manner.

COMPENDIUM OF THE INVENTION The objects of the present invention include the provision of a non-intrusive pressure sensor for measuring irregular pressures within pipelines. In accordance with the present invention, a pressure sensor for measuring an irregular pressure (ac, dynamic or varying over time) in at least one location along a pipeline comprises an optical fiber wrapped around the circumference of the pipe. In accordance with the present invention, a length of said optical fiber changes when the pressure to be measured changes. Accordingly, still in accordance with the present invention, a reflective element is placed within said fiber having a reflection wavelength related to the pressure. The present invention offers a significant improvement compared to the prior art by providing a non-intrusive pressure sensor for measuring irregular pressure in a pipe using a fiber optic sensor. Likewise, the present invention eliminates the need for electronic components in the perforation, thus improving the reliability of the measurement. In addition, the present invention is inherently safe and explosion-proof compared to electrical systems. The present invention may also provide an average pressure around the circumference and / or an irregular pressure axially averaged over a predetermined axial length of pipe. The circumferential average naturally filters out pressure alterations such as alterations related to pipe transverse vibrations, flow noise, and larger dimensional acoustic oscillations. This attribute is useful for measuring the propagation of one-dimensional acoustic waves. Thus, the present invention allows the measurement of irregular pressure in real time for exploration and production of oil and gas and for other applications where a fluid (liquid or gas) is flowing in a pipe or duct. The foregoing objects as well as other objects, features and advantages of the present invention will be apparent taking into account the following detailed description of exemplary embodiments of said invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of a pipe having an optical fiber wrapped around the pipe at each irregular pressure measurement location and a pair of Bragg grids around each optical shell, in accordance with the present invention. Figure 2 is a cross-sectional view of a pipe showing the internal pressure Pin and the external pressures Pout, in accordance with the present invention.

Figure 3 is a side view of a pipe having an optical fiber wrapped around the pipe at each irregular pressure measuring location with a unique Bragg grid between each pair of optical envelopes, in accordance with the present invention. Figure 4 is a side view of a pipe having an optical fiber wrapped around the pipe at each irregular pressure measurement location without Bragg grids around each of the wraps, in accordance with the present invention. Figure 5 is an alternative geometry of an optical shell of Figures 1,3 of a radiator tube geometry, in accordance with the present invention. Figure 6 is an alternative geometry of an optical envelope of Figures 1,3 of a race track geometry in accordance with the present invention. Figure 7 is a cross-sectional end view of a pipe wrapped with an optical fiber of Figures 5, 6, in accordance with the present invention. Figure 8 is a side view of a pipe having a pair of grids at each axial detection location, in accordance with the present invention. Figure 9 is a side view of a pipe having a single grid at each axial detection location, in accordance with the present invention.

PREFERRED MODE OF THE INVENTION With reference to Figure 1, a pipe (or duct) 12 is provided with several pressure sensors 18-24 based on non-intrusively distributed fiber grids located along the pipe 12. Each of the pressure sensors 18-24 comprises corresponding windings 302-308 having a predetermined length wrapped around the pipe 12. Each of the sensors 14-18 comprises one or more Bragg grids 310-324 having predetermined reflection lengths ??,? 2,? 3 /? associated with them. The grids 310-324 are similar to those described in U.S. Patent No. 4,725,110, entitled "Method for Impressing Gratings Within Fiber Optics ", by Glenn et al, however, any grid with tunable wavelength or reflector element integrated in fiber 10 can be used, if desired.A Bragg grid, as is known, reflects a band of light of a predetermined wavelength having a central peak reflection wavelength? b, and passing the remaining wavelengths of the incident light (within a predetermined wavelength range). 40 propagates along the fiber 10 to the sensors 14-18 and the louvers 310-324 reflect the light 42 back along the fiber 10.

Still with reference to Figure 1, fiber optic pressure sensors 18-24 can be Bragg grid-based pressure sensors, such as those described in co-pending US Patent Application Serial No. 08 / 925,598, 'entitled "High Sensitivity Fiber Optic Pressure Sensor for Use in Harsh Environments", presented on September 8, 1997. Alternatively, sensors 18-24 can be optical strain gauges fixed on the external wall or on the internal wall of the pipe or integrated into the internal wall or the external wall of the pipe, which measure the deformation of the wall of the pipe. In one embodiment of the present invention, fiber optic pressure sensors 18-24 may be individually connected or may be multiplexed along one or more optical fibers using wavelength division multiplexing (WDM), multiplexing time division (TDM), or any other optical fiber multiplexing technique (discussed in more detail below). With reference to Figure 2, optical fiber pressure sensors 18-24 (Figures 1,3,4,7,8,9), can measure irregular pressure variations (either dynamic or ac) Pin inside the pipe 12 by measuring the elastic expansion and contraction, in accordance with that represented by the arrows 350, of the diameter (and therefore of the circumference represented by the arrows 351) of the pipe 12. In general, the strain gauges measure the deviation of the wall of the pipe in any direction in response to uneven pressure within the pipe 12. The elastic expansion and contraction of the pipe 12 is measured at the location of the strain gauge as changes in internal pressure Pin and thus measures the local strain (axial deformation, deformation of ring or deformation off axis), caused by deviations in the directions indicated by the arrows 351, in the pipe 12. The amount of change in the circumference is determined in a variable manner by the ring resistance of the pipe 12, the Internal pressure Pin the external pressure Pout outside the pipe 12, the thickness T of the pipe wall 352, and the stiffness or modulus of the pipe material. Thus, the thickness of the pipe wall 352 and the pipe material in the sensor sections 14,16 (Figure 1) can be established based on the desired sensitivity of the sensors and other factors and can be different from the wall thickness or material of pipe 12 outside the detection regions 14,16. With reference to Figures 1,3,4, alternative arrangements of fiber optic strain gauge pressure sensors are shown. The fiber optic pressure sensors 18-24 can be configured using an optical fiber 300 which is coiled or wrapped around and fixed on the pipe 12 at each of the pressure sensor locations in accordance with that indicated by the windings or wraps 302 -308 for the pressures Pi, P2, P3, P4, respectively. The fiber wrappers 302-308 are wrapped around the pipe 12 such that the length of each of the fiber wrappers 302-308 changes with changes in the deformation of the pipe ring in response to irregular pressure variations inside the pipe 12 and therefore the internal pressure of the pipe at the respective axial location is measured. Such changes in fiber length are measured using known fiber optic measurement techniques in accordance with what is discussed below. Each of the casings substantially measures the circumferentially averaged pressure in line 12 at the corresponding axial location in line 12. Likewise, the casings provide axially averaged pressure over the axial length of a given envelope. While the structure of the pipe 12 offers some spatial filtering of short wavelength alterations, we have found that the basic operating principle of the invention remains substantially the same as the basic operating principle of the point sensors described above. With reference to Figure 1, for embodiments of the present invention where the wraps 302-308 are connected in series, pairs of Bragg (310,312), (314,316), (318,320), (322,324) grids should be placed throughout of the fiber 300 at opposite ends of each of the wrappers 302, 304, 306, 308, respectively. The grid pairs are used to multiplex the pressure signals Pl f P2, P3, P4 to identify the individual envelopes of the optical return signals. The first pair of grids 310, 312 around the casing 302 can have a common reflection wavelength? I, and the second pair of grids 314, 316 around the casing 304 can have a common reflection wavelength? , but different from the wavelength of the first pair of grids 310, 312. Similarly, the third pair of grids 318, 320 around the casing 306 has a common reflection wavelength? 3, which is different from? j.,? 2, and the fourth pair of grids 322, 324 around the wrapper 308 has a common reflection wavelength?, which is different from? i, ?2. 3. With reference to Figure 2, instead of having a different pair of reflection wavelengths associated with each envelope, a series of Bragg 360-368 grids can be employed with only one grid between each of the wraps 302-308 each having a common reflection wavelength? i. With reference to Figures 1 and 3, the wraps 302-308 with the grids 310-324 (Figure 1) or with the grids 360-368 (Figure 3) can be configured in numerous known ways to accurately measure the fiber length or fiber length change, such as an interferometric array, Fabry Perot array, flight time fix, or other known fixes. An example of a Fabry Perot technique is described in U.S. Patent No. 4,950,883, "Fiber Optic Sensor Arrangement Having Reflective Gratings Responsive to Particular Wavelenghts," by Glenn. An example of flight time • (or multiplexing by time division; TDM) is a case in which an optical pulse having a wavelength is released by the fiber 300 and a series of optical pulses are reflected back along the fiber 300. The length of each envelope can then be determined by the time delay between each return pulse. Alternatively, a portion or all of the fiber between the grids (or including the grids, or the entire fiber, if desired, can be doped with a rare earth contaminant (erbium) to create a tunable fiber laser, according to as described in U.S. Patent No. 5,317,576, "Continuosly Tunable Single Mode Rare-Earth Doped Laser Arrangement", by Ball et al or in accordance with U.S. Patent 5,513,913, "Active Multipoint Fiber Laser Sensor", by Ball et al, or in accordance with US Pat. No. 5,564,832, "Birefringent Active Fiber L be Sensor", by Ball et al, which are incorporated herein by reference, while the grids 310-324 are shown axially oriented relative to the pipe 12, in figures 1,3 they can be oriented along the pipe 12 axially, circumferentially, or any other orientation.According to the orientation, the grid can measure deformations in the pipe wall. ía 352 with several levels of sensitivity. If the grid reflection wavelength varies with the changes in internal pressure, such variation may be desired for certain configurations (eg, fiber laser) or it may be compensated in the optical instrumentation for other configurations, for example, allowing a predetermined range of reflection wavelength displacement for each pair of grids. Alternatively, instead of each of the wraps being connected in series, the wraps can be connected in parallel, for example, by the use of optical couplers (not shown) before each of the wraps, each coupler is coupled to each other. the common fiber 300. With reference to Figure 4, alternatively, the sensors 18-24 can also be formed as a purely interferometric sensor by wrapping the pipe 12 with the wrappers 302-308 without using Bragg gratings where separate fibers 330, 332, 334, 336 can be fed to the separate wraps 302, 304, 306, 308, respectively. In this particular embodiment, known interferometric techniques can be used to determine the length or change in length of the fiber 10 around the pipe 12 due to pressure changes, such as for example Mach Zehnder or Michaelson interferometric techniques, such as those described. in U.S. Patent No. 5,218,197, entitled "Method and Apparatus for the Noninvasive Measurement of Pressure Incide Pipes Using a Fiber Optic Interferometer Sensor" by Caroll. The interferometric envelopes can be multiplexed in accordance with that described in Dandridge, et al, "Fiber Optic Sensors for Navy Applications", IEEE, February 1991, or Dandridge, et al, "Multiplexed Interferometric Fiber Sensor Arrays", SPIE, vol. . 1586, 1991, pages 176-183. Other techniques to determine the change in fiber length can be used. Likewise, optical reference windings (not shown) can be used for certain interferometric approaches and can also be placed in the pipe 12 or around the pipe 12 but can be designed in such a way that they have not been sensitive to pressure variations. With reference to FIGS. 5 and 6, instead of wrappers 302-308 being wound with optical fibers fully wrapped around the pipe 12, the wrappers 302-308 may have alternative geometries, such as, for example, a "coil" geometry. of radiator "(Figure 5) or a" racetrack "geometry (Figure 6), which are shown in a side view as if the pipe 12 were cut axially and placed in a flat manner. In this particular modality, the fiber optic pressure sensor 302 is not necessarily wound 360 ° around the pipe as best seen with reference to Figure 7, but can be placed on a predetermined portion of the circumference of the pipe 12 represented by the arrow 50. The fiber optic pressure sensor 302 will have a sufficient length to optically detect changes in the circumference of the pipe. Other geometries for wrappers and fiber optic sensor configurations can be used, if desired. Likewise, for any geometry of the wraps described herein, more than one layer of fiber can be used according to the overall fiber length desired. The desired axial length of any particular envelope is established according to the characteristics of the ac pressure that is to be measured, for example the axial length or coherence of a pressure alteration caused by a vertex to be measured. With reference to Figures 8 and 9, embodiments of the present invention include configurations wherein instead of employing the wrappers 302-308, the fiber 300 may have shorter sections placed around at least a portion of the circumference of the pipe. 12 that can optically detect changes in the circumference of the pipe. Within the scope of the present invention is the fact that sensors may comprise an optical fiber 300 placed in a helical pattern (not shown) around the pipe 12. As discussed above, the orientation of the deformation detection element varies the sensitivity to the deviations in the wall of the pipe 352 caused by irregular pressure transients in the pipe 12. With reference to figure 8, in particular, the bragg grid pairs (310,312), (314,316), (318,320) are placed. , (322,324) along Figure 300 with sections 380-386 of the fiber 300 between each of the grid pairs, respectively. In this case, known Fabry Perot techniques, interferometric, time of flight, or fiber laser detection can be used to measure the deformation in the pipeline, in a manner similar to that described in the aforementioned references. Referring to Figure 9, alternatively, individual grids 370-376 can be placed on the pipe and used to detect irregular variations in pipeline 12 (and consequently uneven pressure within the pipe) at the detection locations. When a single grid per sensor is used, the grid reflection wavelength shift will be an indication of changes in pipe diameter and consequently pressure. Any other technique or configuration for an optical strain gauge can be employed. The type of optical strain gauge technique and optical signal analysis approach is not a critical factor for the present invention, and the scope of the invention is not limited to a particular technique or a specific approach. For all the modalities described here, the pressure sensors can be fixed on the pipe through adhesive, glue, epoxy substances, tape, or any other type of suitable fixation to ensure adequate contact between the sensor and the pipe 12. Sensors can alternatively be removable or fixed permanently through known mechanical techniques such as mechanical fastener, spring loaded arrangement, stapling, clamps, strapping, or other equivalent. Alternatively, the optical fibers and / or grids can be integrated into a composite pipe. If desired, for some applications, the grids can be detached from the pipe 12 (either acoustically isolated or for deformations), if desired. The present invention can be used to measure any parameter (or characteristics) of the content of the pipe that is related to irregular pressure (ac, dynamic or variable over time) for example, the present invention can be used to measure through of the sensor when a jet of liquid or a solid passes through the pipeline thanks to the dynamic pressure wave created. Also, instead of a pipeline, any conduit for transporting a fluid (where the word "fluid" refers to a liquid or a gas) can be used if desired. Likewise, it should be understood that the present invention can be used in reflection and / or optical transmission. Also, even though the invention has been illustrated using four pressure sensors, it will be understood that a greater or lesser number of sensors can be used, depending on the application. It will be understood that other features, alternatives or modifications described as to a particular embodiment may also be applied, used or incorporated with other modalities described herein. Even though the invention has been described and illustrated in relation to exemplary embodiments thereof, the foregoing embodiments as well as various other additions and omissions may be made without departing from the spirit and scope of the present invention.

Claims (1)

1. CLAIMS An apparatus for measuring an irregular pressure inside a pipe, the apparatus comprises: an optical fiber wrapped around a circumference of the pipe and which provides a signal indicating said irregular pressure. The apparatus according to claim 1, wherein a length of said optical fiber changes in response to said irregular pressures within said pipe. The apparatus according to claim 1, further comprising a reflector element positioned within said fiber having a reflective wavelength related to said irregular pressure. The apparatus according to claim 1, further comprising a reflector element positioned within said fiber having a reflecting wavelength that changes in response to said irregular pressure. The apparatus according to claim 1, wherein said optical fiber measures an irregular pressure circumferentially averaged in an axial position along said pipe. The apparatus according to claim 1, wherein said optical fiber measures an irregular pressure averaged axially along a predetermined axial length of said pipe. An apparatus for the non-intrusive measurement of an irregular pressure at least at an axial location along a pipe, said apparatus comprises: an optical fiber having at least a portion of said fiber positioned around at least a part of a circumference of the pipe; and a reflective element positioned within said fiber having a reflection wavelength related to said irregular pressure in the pipe. The apparatus according to claim 7, wherein said reflection wavelength changes in response to said irregular pressure. The apparatus according to claim 7, wherein said reflector element comprises a Bragg grid • fiber. An apparatus for measuring an irregular pressure inside a pipe, the apparatus comprises: various fiber optic sensors wrapped around a circumference of said pipe, each of said sensors provides a signal indicative of said irregular pressure. The apparatus according to claim 10, wherein said sensors are placed in a different axial position along said pipe and measure said irregular pressure in each of said axial positions. A method for measuring an irregular pressure inside a pipe, the method comprises: wrapping a predetermined length of an optical fiber around the pipe; measuring a change in said length of said optical fiber due to the pressure; and determining said irregular pressure from said length of said optical fiber. The apparatus according to claim 12, wherein said fiber has a reflector element integrated therein. The apparatus according to claim 12, wherein said reflector element comprises a grating of Bragg fiber. The apparatus according to claim 12, wherein said method further comprises measuring a pressure circumferentially averaged at a given axial location along the pipe. The apparatus according to claim 12, wherein said method further comprises measuring an axial average pressure along a given axial length of the pipe.