Patent Publication Number: US-9429013-B2

Title: Optical window assembly for an optical sensor of a downhole tool and method of using same

Description:
BACKGROUND 
     The present disclosure relates generally to wellsite operations. In particular, the present disclosure relates to formation evaluation involving testing, measuring, sampling, monitoring and/or analyzing downhole fluids using, for example, optical sensors. 
     Wellbores are drilled to locate and produce hydrocarbons. A downhole drilling tool with a bit at an end thereof is advanced into the ground to form a wellbore. As the drilling tool is advanced, drilling mud is pumped through the drilling tool and out the drill bit to cool the drilling tool and carry away cuttings. The fluid exits the drill bit and flows back up to the surface for recirculation through the drilling tool. The drilling mud is also used to form a mudcake to line the wellbore. 
     During or after a drilling operation, various downhole evaluations may be performed to determine characteristics of the wellbore and surrounding formations. In some cases, the drilling tool may be provided with devices to test and/or sample the surrounding formation and/or fluid contained in reservoirs therein. In some cases, the drilling tool may be removed and a downhole wireline tool may be deployed into the wellbore to test and/or sample the formation. These samples or tests may be used, for example, to determine whether valuable hydrocarbons are present. Production equipment may be positioned in the wellbore to draw located hydrocarbons to the surface. 
     Formation evaluation may involve drawing fluid from the formation into the downhole tool for testing and/or sampling. Various devices, such as probes or packers, may be extended from the downhole tool to establish fluid communication with the formation surrounding the wellbore and to draw fluid into the downhole tool. Downhole tools may be provided with fluid analyzers and/or sensors to measure downhole parameters, such as fluid properties. Examples of downhole tools are provided in U.S. Pat. No. 7,458,252, the entire contents of which are hereby incorporated by reference. The downhole tool may also be provided with sensors, such as optical sensors, for measuring downhole parameters. Examples of sensors are provided in Nos. 2007/0108378 U.S. Pat. Nos. 5,167,149, 5,167,149, 5,201,220, 5,331,156, and 7,687,770, the entire contents of which are hereby incorporated by reference. 
     SUMMARY 
     In at least one aspect, the disclosure relates to an optical window assembly of an optical sensor of a downhole tool positionable in a wellbore penetrating a subterranean formation. The downhole tool has a housing with a flowline there through to receive downhole fluid therein. The optical sensor is positioned about the flowline to measure light passing there through. The optical window assembly includes a tubular sensor body positioned in the housing (the sensor body having a sensor-end and a flanged signal-end with a passage there through), an optical window positioned in the passage of the sensor body to pass the light from the flowline to the optical sensors, a seal disposed about the sensor body, and a backup ring disposed about the sensor body between the flanged signal-end and the seal to support the seal about the sensor body whereby the downhole fluid is prevented from leaking between the seal and the sensor body. 
     The sensor body has a tapered inner surface. The optical window assembly may also include a brazing between the optical window and the sensor body. The seal may be an o-ring. The backup ring may be made of polyether ether ketone. The sensor body may be made of a non-metallic material. The optical window may include a metalized sapphire. A leakage gap may be defined between the seal and the housing. 
     In another aspect, the disclosure relates to a downhole tool positionable in a wellbore penetrating a subterranean formation. The downhole tool includes a housing with a flowline to receive downhole fluid therein, a light source to pass light through the flowline, a pair of optical sensors positioned in the housing to measure the light passing through the flowline, and a pair of optical window assemblies operatively connectable to the pair of optical sensors. Each of the optical window assemblies includes a tubular sensor body positioned in the housing (the sensor body having a sensor-end and a flanged signal-end with a passage there through), an optical window positioned in the passage of the sensor body to pass the light from the flowline to the optical sensors, a seal disposed about the sensor body, and a backup ring disposed about the sensor body between the flanged signal-end and the seal to support the seal about the sensor body whereby the downhole fluid is prevented from leaking between the seal and the sensor body. 
     The downhole tool may also include a spacer positionable between the optical sensors, an optical converter operatively connectable to the optical sensors, fiber optics to operatively connect the optical sensors to the optical converter and the light source. The optical converter may include a lens, a filter, and a photo diode. The housing may include a chassis layer and at least one additional layer about the chassis layer. The chassis layer may have the optical sensors and the optical window assemblies therein. The downhole tool may also include at least one downhole sensor, a surface unit and/or a downhole unit operatively connectable to the optical sensors to receive measurements therefrom. 
     Finally, in another aspect, the disclosure relates to a method of sensing downhole parameters of downhole fluid about a wellbore penetrating a subterranean formation. The method involves deploying a downhole tool into the wellbore. The downhole tool includes a housing with a flowline there through, a light source, a pair of optical sensors positioned in the housing, and a pair of optical window assemblies operatively connectable to the pair of optical sensors. Each of the optical window assemblies includes a tubular sensor body positioned in the housing (the sensor body having a sensor-end and a flanged signal-end with a passage there through), an optical window positioned in the passage of the sensor body, a seal disposed about the sensor body, and a backup ring disposed about the sensor body between the flanged signal-end and the seal. The method may also involve measuring light passing through downhole fluid in the flowline and through the optical window with the optical sensors and preventing the downhole fluid from leaking between the seal and the sensor body by supporting the seal about the sensor body with the backup ring. 
     The method may also involve receiving downhole fluid in the downhole tool through the flowline, passing light from the light source through the flowline and the optical window and to the optical sensors, and/or absorbing forces of the downhole fluid against a tapered inner surface of the sensor body. 
     This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the optical fluid analyzer calibration method are described with reference to the following figures. The same numbers are used throughout the figures to reference like features and components. 
         FIGS. 1.1 and 1.2  depict schematic views, partially in cross-section, of a wellsite with a downhole drilling tool and a downhole wireline tool, respectively, with an optical sensor assembly in accordance with embodiments of the present disclosure; 
         FIG. 2  depicts schematic views illustrating a portion of a downhole wireline tool having an optical sensor assembly therein in accordance with embodiments of the present disclosure; 
         FIGS. 3A-3C  are schematic, assembly and cross-sectional views illustrating a portion of a downhole tool having an optical sensor assembly therein in accordance with embodiments of the present disclosure; 
         FIGS. 4A-4B  are schematic plan and perspective views of a cross-section of an optical window assembly in accordance with embodiments of the present disclosure; and 
         FIG. 5  is a flow chart illustrating a method of sensing downhole parameters in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The description that follows includes exemplary apparatuses, methods, techniques, and instruction sequences that embody techniques of the inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details. 
     The present disclosure relates to a downhole optical window assembly usable with optical sensors positioned about a downhole tool for measuring parameters of downhole fluids. The optical window assembly includes a sensor body (e.g., a ceramic body) with an optical (e.g., sapphire) window therein, and a seal and backup ring thereabout. The optical window may be metalized (e.g., sapphire) and tapered to absorb force applied thereto. The backup ring supports the seal about the sensor body to prevent fluid from passing there between and to permit fluid to pass through a leakage gap between the optical window assembly and the downhole tool. 
     The optical window assembly is configured to control and/or restrict fluid leakage thereabout. The optical window assembly may be capable of use in environments having pressures of up to, for example, about 30 Kpsi (2413.7 Bar) or more. The configuration of the optical window assembly may also be used to reduce the size of the optical window and/or to increase the light intensity used with the optical window assembly. 
     ‘Formation evaluation’ as used herein relates to the measurement, testing, sampling, and/or other analysis of wellsite materials, such as gases, fluids and/or solids. Such formation evaluation may be performed at a surface and/or downhole location to provide data, such as downhole parameters (e.g., temperature, pressure, permeability, porosity, seismic, etc.), material properties (e.g., viscosity, composition, density, etc.), and the like. 
     ‘Fluid analysis’ as used herein relates to a type of formation evaluation of downhole fluids, such as wellbore, formation, reservoir, and/other fluids located at a wellsite. Fluid analysis may be performed by a fluid analyzer capable of measuring fluid properties, such as viscosity, composition, density, temperature, pressure, flow rate, optical parameters, etc. Fluid analysis may be performed using, for example, optical sensors (e.g., spectrometers), gauges (e.g., quartz), densitometers, viscometers, resistivity sensors, nuclear sensors, and/or other fluid measurement and/or detection devices. 
       FIGS. 1.1 and 1.2  depict environments in which subject matter of the present disclosure may be implemented.  FIG. 1.1  depicts a downhole drilling tool  10 . 1  and  FIG. 1.2  depicts a downhole wireline tool  10 . 2  that may be used for performing formation evaluation. The downhole drilling tool  10 . 1  may be advanced into a subterranean formation F to form a wellbore  14 . The downhole drilling tool  10 . 1  may be conveyed alone or among one or more (or itself may be a) measurement-while-drilling (MWD) drilling tools, a logging-while-drilling (LWD) drilling tools, or other drilling tools. The downhole tool  10 . 1  is attached to a conveyor (e.g., drillstring)  16  driven by a rig  18  to form the wellbore  14 . The downhole tool  10 . 1  includes a probe  20  adapted to seal with a wall  22  of the wellbore  14  to draw fluid from the formation F into the downhole tool  10 . 1  as depicted by the arrows. 
     The downhole drilling tool  10 . 1  may be withdrawn from the wellbore  14 , and the downhole wireline tool  10 . 2  of  FIG. 1.2  may be deployed from the rig  18  into the wellbore  14  via conveyance (e.g., a wireline cable)  16 . The downhole wireline tool  10 . 1  is provided with the probe  20  adapted to seal with the wellbore wall  22  and draw fluid from the formation F into the downhole tool  10 . 2 . Backup pistons  24  may be used to assist in pushing the downhole tool  10 . 2  and probe  20  against the wellbore wall  22  and adjacent the formation F. 
     The downhole tools  10 . 1 ,  10 . 2  may also be provided with a formation evaluation tool  28  with an optical sensor assembly  30  for measuring parameters of the formation fluid drawn into the downhole tool  10 . 1 ,  10 . 2 . The formation evaluation tool  28  includes a flowline  32  for receiving the formation fluid from the probe  20  and passing the fluid to the optical sensor assembly  30  for measurement as will be described more fully herein. A surface unit  34  may be provided to communicate with the downhole tools  10 . 1 ,  10 . 2  for passage of signals (e.g., data, power, command, etc.) therebetween. 
     While  FIGS. 1.1 and 1.2  depict specific types of downhole tools  10 . 1  and  10 . 2 , any downhole tool capable of performing formation evaluation may be used, such as drilling, coiled tubing, wireline or other downhole tool. Also, while  FIGS. 1.1 and 1.2  depict one optical sensor assembly  30  in a downhole tool, it will be appreciated that one or more optical sensor assemblies  30  and/or other sensors may be positioned at various locations about the downhole tool and/or wellbore. Data and test results from various locations and/or using various methods and/or apparatuses may be analyzed and compared. 
       FIG. 2  is a schematic view of a portion of downhole tool  10  which may be either of the downhole tools  10 . 1  or  10 . 2  form  FIGS. 1.1 and 1.2 . The probe  20  may be extended from the downhole tool  10 . 2  for engagement with the wellbore wall  22 . The downhole tool  10  includes a tool housing  234  which may include one or more housing layers, such as a drill collar  238 . 1 , mandrel  238 . 2 , and chassis  238 . 3  as shown and/or other layers. 
     The formation evaluation tool  28  may be provided with one or more flowlines  32  for drawing fluid into the downhole tool  10  through the probe  20 . While one probe  20  is depicted, one or more probes, dual packers and related inlets may be provided to receive downhole fluids and pass them to one or more flowlines  32  (e.g., a high pressure flowline). Examples of downhole tools and fluid communication devices, such as probes, that may be used are depicted in U.S. Pat. No. 7,458,252, previously incorporated herein. 
     The flowline  32  extends into the downhole tool  10  to pass downhole fluid to the formation evaluation tool  28 . The formation evaluation tool  28  may be used to analyze, test, sample and/or otherwise evaluate the downhole fluid. The optical assembly  30  is positioned about the flowline  32  and exposed to the downhole fluid passing therethrough. 
     The optical sensor assembly  30  includes a light source  240  (e.g., a halogen lamp), an optical fiber  242 , an optical converter  244 , a pair of optical sensors  245 , and a pair of optical window assemblies  246 . In some cases, the light source  240  may be integral with the optical sensor(s)  245 . The optical fiber  242  operatively connects the light source  240 , the optical converter  244 , and/or the optical sensors  245 . The optical converter  244  includes a lens  247 , a filter  249 , and a photo diode  251 . 
     The light source  240  passes light through the optical window assemblies  246  and the flowline  32  therebetween. The optical sensors  245  measure light passing through the fluid between the optical window assemblies  246 . The optical sensors  245  may measure, for example, intensity of the light passing through the fluid. Changes in intensity may be measurable and used to determine fluid parameters of the downhole fluid. A signal containing the measurements is passed through the lens  247 , filter  249  and photo diode  251 . 
     A sample chamber  243  is also coupled to the flowline  32  for receiving the downhole fluid. Fluid collected in the sample chamber  243  may be collected therein for retrieval at the surface, or may be exited through an outlet  248  in housing  234  of the downhole tool  10 . Optionally, flow of the downhole fluid into and/or through the downhole tool  10  may be manipulated by one or more flow control devices, such as a pump  252 , the sample chamber  246 , valves  254  and/or other devices. 
     One or more downhole sensors S may optionally be provided to measure various downhole parameters and/or fluid properties. The downhole sensor(s) may include, for example, gauges (e.g., quartz), densitometers, viscometers, resistivity sensors, nuclear sensors, and/or other measurement and/or detection devices capable of taking downhole data relating to, for example, downhole conditions and/or fluid properties. 
     Optionally, a surface and/or downhole unit  34  may be provided to communicate with the formation evaluation tool  28 , the optical assembly  30 , and/or other portions of the downhole tool  10  for the passage of signals (e.g., data, power, command, etc.) therebetween. These units  34  may include, for example, a measurement while drilling tool, a logging while drilling tool, a processor, a controller, a transceiver, a power source and other features for operating and/or communication with the formation evaluation tool  28  and/or the optical assembly  30 . 
     The surface and/or downhole unit  34  may include, for example, a database and a processor for collecting and analyzing the downhole measurements. As fluids are drawn from the formation into the formation evaluation tool  28  by the probe  20 . The fluids may be analyzed by directing light at the fluids and detecting the spectrum of the transmitted and/or backscattered light. Information may be collected and/or processed (e.g., based on information in the database relating to different spectra) in order to characterize the formation fluids. In an example, light may be reflected from a window/fluid flow interface at certain specific angles to determine the presence of gas in the fluid flow. In another example, optical density (OD) measurements of the fluid stream may be taken at certain predetermined energies, and oil and water fractions of a two-phase fluid stream quantified. Examples of analysis are provided in U.S. Pat. Nos. 5,167,149; 5,201,220; and 5,331,156 previously incorporated by reference herein. 
       FIGS. 3A-3C  depict various views of a portion of the downhole tool  10  with the optical sensor assembly  30  therein.  FIG. 3A  shows an exterior view of the downhole tool  10 .  FIG. 3B  shows an exploded view of the downhole tool  10 .  FIG. 3C  shows a cross-sectional view of the downhole tool  10  of  FIG. 3A  taken along line  3 C- 3 C. 
     As shown in these figures, the light source  240  and the optical fibers  242  may be positioned within and/or about a light housing  360 , and attached to the chassis layer  238 . 3  inside the downhole tool  10 . As shown in this view, the light housing  360  and the optical sensor  245  are integral. The optical converter  244  may also be packaged in a converter housing  362  and attached to the chassis layer  238 . 3  inside the downhole tool  10 . 
     The chassis layer  238 . 3  may have the flowline  32  passing therethrough and a sensor receptacle  364  for receiving the optical sensors  245  and light housing  360  therein. The optical sensors  245  and light housing  360  are positioned in the sensor receptacles  364  of the chassis layer  238 . 3  about the flowline  32 . The optical sensors  245  are operatively connected to the light source  240  and the optical converter  244  by the optical fibers  242 . 
     As also shown in  FIGS. 3B and 3C , the optical window assemblies  246  are positioned adjacent the optical sensors  245 . The optical window assemblies  246  include a tubular body  366 , an optical window  367 , a backup ring  370 , and a seal  371 . The optical window assemblies  246  are positioned in the sensor receptacle  364  of the chassis layer  238 . 3 . The optical window assemblies  246  have a spacer  372  therebetween to support the optical window assemblies  246  about flowline  32 . 
     Each optical window assembly  246  has a sensing end  374  positioned about the flowline  32  and a flanged signal-end  376  operatively coupled to the optic fiber  242 . The tubular body  366  has the backup ring  370  and seals  371  thereabout to prevent leakage of fluid there between. Fluid may be permitted to leak between the optical window assembly  246  and the chassis layer  238 . 3 . 
       FIGS. 4A and 4B  depict additional views of the optical window assembly  246 . As shown in  FIG. 4A , the tubular body  366  includes has the optical window  367  therein. The tubular body  366  is generally tubular with a tapered inner surface  480  extending from the flanged signal-end  376  to the sensor-end  374 . The inner surface  480  tapers such that the inner surface increases in diameter as the inner surface extends away from the flanged signal-end  376 . 
     The tubular body  366  may be of titanium or a non-metallic material, such as a ceramic body. The optical window  367  may be made of a metallic material, such as a metalized sapphire. A brazing layer  484  may be provided between the tubular body  366  and the optical window  367 . The optical window  367  may be connected via a brazing process to the tubular body  366 . The optical window  367  may be, for example, a metalized sapphire window. Examples of sapphire windows are provided in US Publication No. 2007/0108378, previously incorporated by reference herein. 
     The backup ring  370  and seal  371  are positioned about an outer surface of the tubular body  366 . The backup ring  370  is positioned adjacent the flanged signal-end  376 . The seal  371  is positioned adjacent the backup ring  370 . The backup ring  370  may be made of, for example, a non-metallic material, such as PEEK (polyether ether ketone). The seal  371  may be, for example, an o-ring made of an elastomateric material. Additional seals may optionally be provided. 
       FIG. 4B  shows the flow of fluid from the flowine  32  and about the optical window assembly  246 . The fluid may be high pressure of up to about 30 Kpsi (2413.7 Bar) or more. As shown in  FIG. 4B , the optical window assembly  246  may be configured to restrict and/or direct fluid flow thereabout. For example, the optical window assembly  246  may be used to seal pressure for passage of light from the light source therethrough during measurement. The inner surface  480  of the tubular body  366  is tapered to absorb force from hydraulic pressure of fluid passing therein. The taper of the inner surface  480  may be provided at a desired shape and angle to deflect at least some of the hydraulic fluid pressure. 
     The backup ring  370  is disposed about the tubular body  366  between the flanged signal-end  376  and the seal  371  to support the seal  371  about the tubular body  366  and to prevent fluid from leaking there between. The backup ring  370  may support the seal  371  about the outer surface of the tubular body  366  and spacer  372  to restrict fluid flow there between. Fluid from flowline  32  passes in a leakage gap  475  between the optical window assembly  246  and the chassis layer  238 . 3  as indicated by the arrows. The leakage gap  475  may extend about a periphery of the optical window assembly  246 . Fluid is prevented from passing between the outer surface of the tubular body  366  and the seal  371  or the backup ring  370 . This configuration may be used to direct leakage paths to a single path between the optical window assembly  246  and the chassis layer  238 . 3  and/or to eliminate additional leakage paths thereabout. 
       FIG. 5  depicts a method  500  of sensing downhole parameters of downhole fluid about a wellbore penetrating a subterranean formation. The method involves deploying ( 590 ) a downhole tool into the wellbore. The downhole tool may include a housing with a flowline there through, a light source, a pair of optical sensors positioned in the housing, and a pair of optical window assemblies operatively connectable to the pair of optical sensors (e.g., as in  FIGS. 2-3C ). Each of the optical window assemblies may include a tubular sensor body positioned in the housing (the sensor body having a sensor-end and a flanged signal-end with a passage there through), an optical window positioned in the passage of the sensor body, a seal disposed about the sensor body, and a backup ring disposed about the sensor body between the flanged signal-end and the seal. The method may also involve measuring (592) light passing through downhole fluid in the flowline and through the optical window with the optical sensors and preventing ( 594 ) the downhole fluid from leaking between the seal and the sensor body by supporting the seal about the sensor body with the backup ring. 
     The method may also involve, for example, receiving ( 596 ) downhole fluid in the downhole tool through the flowline, passing ( 598 ) light from the light source through flowline and the optical window and to the pair of optical sensors, and/or absorbing ( 599 ) forces of the downhole fluid against a tapered inner surface of the sensor body. 
     The method may be performed in any order, and repeated as desired. 
     Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter. 
     Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.