Abstract:
A sensor assembly that responds to temperature of fluids within an annulus formed by an outer surface of a borehole instrument and the wall of a borehole. The sensor assembly is removably installed preferably in the wall of the borehole instrument. Installation and removal are from outside of the borehole instrument thus eliminating the need to disassemble the borehole instrument. The sensor assembly comprises a temperature transducer that is hermetically sealed within a housing designed to obtain maximum thermal exposure of the transducer. Power to the temperature transducer is supplied from a separate electronics package in the borehole instrument through a rotary connector within the sensor housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority under 35 U.S.C. § 119(e) to U.S. provisional patent application Ser. No. 60/650,185, filed Feb. 7, 2005, which is incorporated herein by reference in its entirety 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention is directed toward the measure of temperature, and more particularly toward a sensor for measuring temperature of well borehole environs in the vicinity of a borehole instrument that is conveyed along the borehole. The temperature sensor is removably disposed preferably within the wall of the borehole instrument. The sensor can be embodied in a wide variety of borehole exploration and testing equipment including measurement-while-drilling, logging-while-drilling, and wireline systems.  
       FIELD OF THE INVENTION  
       [0003]     Borehole geophysics encompasses a wide variety of measurements made with an equally wide variety of apparatus and methods. Measurements can be made during the drilling operation to optimize the drilling process, where borehole instrumentation is conveyed by a drill string. These measurements are made with systems commonly referred to as measurement-while-drilling or “MWD” systems. It is also of interest to measure, while drilling, properties of formation materials penetrated by the drill bit. These measurements are made with systems commonly referred to as logging-while-drilling or “LWD” systems, and borehole instrumentation is again conveyed by a drill string. Subsequent to the drilling operation, borehole and formation properties can be made with systems commonly referred to as “wireline” systems, with borehole instrument being conveyed typically by a multiconductor cable. Various types of formation testing is also performed both during the drilling of the borehole, and after the borehole has been drilled or “completed”, using drill string conveyed and wireline conveyed instrumentation.  
         [0004]     The temperature of fluid within the borehole is a parameter of interest in virtually all types of geophysical exploration. A measure of temperature of liquid or gas within the annulus formed by the borehole wall and the borehole instrument is of particular interest. A variation in annulus temperature at a particular depth within the borehole can indicate formation liquid or gas entering or leaving the borehole at that depth. Such information can, in turn, be related to formation fracturing, formation damage, wellbore tubular problems, and the like. A measure of annulus temperature as a function of depth can define thermal gradients which, in turn, can be related to a variety of geophysical parameters and conditions of interest. Certain electromagnetic, acoustic and nuclear formation evaluation logging systems, both drill string and wireline conveyed, require corrections for annulus temperature in order to maximize measurement accuracy and precision.  
         [0005]     From the brief discussion above, it is apparent that methods and apparatus for measuring annulus temperature are critical to a wide variety of geophysical operations. It is desirable that an annulus temperature measurement system be accurate and precise. It is further desirable for the measurement system to respond rapidly to any changes in temperature. Ruggosity is required for the harsh conditions typically encountered a borehole environment. Operationally, it is desirable to dispose an annulus temperature sensor in the wall of the borehole instrument defining the annulus. Furthermore, it is operationally advantageous if the sensor can be easily removed and replaced from the outside of the borehole instrument therefore removing the need to dismantle the instrument. As an example, sensors may be designed for maximum response in a given temperature range. If the range is exceeded, it is advantageous to replace the sensor optimized for another range. Ease of replacement is also operationally advantageous in the event of sensor failure.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     The present invention comprises a sensor assembly that responds to temperature of fluids within an annulus formed by an outer surface of a borehole instrument and the wall of a borehole. The sensor assembly is removably installed preferably in the wall of the borehole instrument. Installation and removal are from outside of the borehole instrument thus eliminating the need to disassemble the instrument. The sensor assembly comprises a temperature transducer that is hermetically sealed within a housing. The housing is designed to obtain maximum thermal exposure of the transducer. This yields optimum thermal response of the transducer to temperature variations in the surrounding annulus environment. The sensor is designed to operate at high temperature, high pressure, and high vibration/shock typically encountered in the borehole environment. The sensor assembly housing has a locking feature to ensure that it remains in the borehole instrument during operation. Power to the temperature transducer is supplied from a separate electronics package in the borehole instrument through a rotary connector within the sensor housing. Response of the temperature transducer is received, through the same rotary connector, by the electronics package for processing and transmission via a suitable telemetry system to the surface of the earth. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     So that the manner in which the above recited features, advantages and objects the present invention are obtained and can be understood in detail, more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.  
         [0008]      FIG. 1  is a cross sectional view of the temperature sensor assembly;  
         [0009]      FIG. 2  is an exploded view of major elements of the temperature sensor assembly;  
         [0010]      FIG. 3  is a sectional view of the temperature sensor assembly mounted in a cylindrical receptacle in the wall of a borehole instrument;  
         [0011]      FIG. 3A  is a sectional view of the temperature sensor assembly mounted in a thermal isolator insert and within a cylindrical receptacle in the wall of a borehole instrument and  
         [0012]      FIG. 4  illustrates conceptually the temperature sensor assembly disposed in a well borehole for measuring temperature of borehole fluids. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]      FIG. 1  is a cross sectional view of the temperature sensor assembly  10 . Internal elements of the assembly  10  are hermetically sealed within a cylindrical housing  12 . The housing material is preferably beryllium-copper, although other metals or alloys such as Inconel can be used. The top or “outer” end of the housing  12 , as will be shown in subsequent illustrations, is exposed to borehole fluid. This outer end comprises a protrusion  13 . A temperature transducer  14  is disposed inside of the housing and positioned within the protrusion  13 . The transducer  14  is in thermal contact with the housing  12 , and is preferably soldered to the housing to insure good thermal contact. This arrangement surrounds, as much as practical, the temperature transducer  14  with borehole fluid thereby maximizing the response of the temperature transducer to borehole fluid temperature. Electrical leads  16   a  and  16   b  from the temperature transducer  14  extend through an “upper” connector assembly. The upper connector comprises an upper insulating base member  24 , and outer electrical contact  22 , and an inner electrical contact  18 . The electrical leads  16   a  and  16   b  terminate at the electrical contacts  18  and  22 , respectfully.  
         [0014]     Still referring to  FIG. 1 , a large spring  28  and a small spring  26  are positioned coaxially within the housing  12 . The upper end of the large spring  28  is in electrical contact with the outer electrical contact  22 , and the upper end of the small spring  26  is in electrical contact with the inner electrical contact  18 . Opposing or lower ends of the large spring  28  and small spring  26  contact a rotary connector assembly. The rotary connector assembly or “rotary connector” is illustrates as a whole in  FIG. 2 , and designated by the numeral  41 . The assembly  41  comprises an outer sensor contact  30  which is in electrical contact with the large spring  28 , and an inner sensor contact  34  which is in electrical contact with the small spring  26 . An insulator ring  31  separates the two sensor contacts  30  and  34 . The large and small springs  28  and  26 , respectively, serve as electrical conductors between the temperature transducer  14  and the rotary connector assembly  41 . Both springs also provide a mechanical load to the rotary connector assembly  41 . The rotary connector assembly  41 , large spring  28  and small spring  26  are retained in the housing  12  by a retaining ring  40 . The rotary connector assembly  41  also comprises an electrical insulating base member  36  forming an insulating ring  31  containing alignment indentions  33 . The insulating base member  36  defines the lower or “inner” end of the sensor  10 , and is penetrated by extensions of the sensor contacts  30  and  34  in the form of protrusions, as shown in  FIG. 1 . These protrusions are hermetically sealed with O-rings rings  44 . The insulating base  36  is hermetically sealed to the interior of the housing  12  by an O-ring  46 . The insulating base  36  also has an alignment tab  54  which properly aligns the rotary connector assembly  41  within the borehole instrument wall in which it is received. Alignment will be discussed in a subsequent section of this disclosure.  
         [0015]     The temperature sensor assembly  10  is threaded into a cylindrical receptacle in the wall of the borehole instrument via the threads  42 . Hermetic sealing between the housing  12  and the borehole instrument receptacle is provided by O-rings  50  and cooperating back-up rings  52 .  
         [0016]      FIG. 2  is an exploded view of major elements of the temperature sensor assembly  10 , and best illustrates the functionality of the rotary connector assembly which allows the temperature sensor to be inserted and removed from the wall of a borehole instrument. The housing  12 , transducer  14 , upper base member and connector assembly  24 , large spring  28 , and small spring  26  all rotate with respect to the rotary connector assembly  41 . As the housing  12  is threading into or out of the borehole instrument wall, the O-ring  46  maintains a hermetic seal within the housing  12  as it is rotated with respect to the rotary connector assembly  41 . The rotary connector assembly  41  is held fixed with respect to the wall of the borehole instrument by the alignment tab  54  which is received in a slot within the wall of the borehole instrument. Hermetic seal between the outer surface of the sensor housing  12  and the cylindrical borehole instrument receptacle is maintained by the O-rings and back-up rings  50  and  52 , respectfully, as the sensor assembly  10  is threaded into or out of the wall of the borehole instrument. The outer end of the housing  12  is fabricated to receive an appropriate means for turning, such as an Allen wrench or the like.  
         [0017]      FIG. 3  is a sectional view of the temperature sensor assembly  10  mounted in a cylindrical receptacle  62  in the wall  60  of a borehole instrument. O-rings  50  and back-up rings  52  are shown hermetically sealing the housing  12  within the wall  60  of the borehole instrument. The lower portion of the temperature sensor assembly  10  is cut away to show the cooperation of the elements of the rotary connector assembly  41  with elements of the borehole instrument wall. The male threads  42  on the housing  12  are received by corresponding female threads cut at the base of the receptacle  62 . The alignment tab  54  is received by a slot in the borehole instrument wall  60  so that the rotary connector assembly is held fixed with respect to the instrument wall. The alignment tab  54  is also positioned so that the sensor contacts  30  and  34  are aligned and make electrical contact with corresponding borehole instrument or “tool” contacts  72  and  70 , respectfully. Power for the temperature transducer  14  (see  FIGS. 1 and 2 ) is supplied by an appropriate power supply in an electronics package  78  via electrical leads  74  and  76  which terminate at the tool contacts  72  and  70 , respectively. The electronics package  78  and leads  74  and  76  are hermetically sealed within the borehole instrument wall. The sensor and tool contact arrangement allows the temperature sensor  10  to be inserted into and removed from the instrument wall  60  without disturbing the “tool” hermetic seal of elements within the instrument wall  60 . Response of the temperature transducer  12  is conveyed from the sensor assembly  10  via the sensor contacts  30  and  34  through the tool contacts  72  and  70  and to the electronics package  78  via the leads  74  and  76 . Temperature sensor response is typically telemetered from the electronics package  78  to the surface of the earth for processing and use, as illustrated conceptually with the arrow  79 . Optionally, the sensor response can be processed within the electronics package  78 . These processed results can be recorded in the electronics package, or used to control or correct functions of other sensors or equipment disposed within the borehole instrument.  
         [0018]     As shown in  FIG. 3 , the housing  12  is disposed entirely within a radius defined by the outer surface of the borehole instrument wall  60 . Alternately, the housing  12  can protrude outside of the radius defined by the outer surface of the borehole instrument wall  60 .  
         [0019]     It is advantageous for the temperature sensor assembly  10  to respond to changes in drilling fluid temperature as quickly as possible. The wall  60  of the borehole instrument is typically massive and does not, therefore, rapidly reach thermal equilibrium with the drilling fluid temperature. Response of the temperature sensor assembly  10  to changes in drilling fluid temperature can, therefore, be maximized by thermally isolating the temperature sensor assembly  10 , and the transducer  14  therein, from the wall  60  of the borehole instrument. One method for thermal sensor assembly isolation is shown in  FIG. 3A . The cylindrical receptacle  62  in the wall  60  of the borehole instrument is lined with a thermal isolator insert  51 . The thermal isolator insert  51  is fabricated from any suitable temperature insulating material, such as composite graphite or thermal plastic, that can function within the typically harsh borehole environment. The male threads  42  on the housing  12  are received by corresponding female threads  42   b  cut at the base of the thermal isolator insert  51 . The alignment tab  54  is received by a slot in the thermal isolator insert  51  so that the rotary connector assembly is held fixed with respect to the instrument wall, as is the case in the embodiment shown in  FIG. 3 . Once again, the alignment tab  54  is positioned so that the sensor contacts  30  and  34  are aligned and make electrical contact with corresponding contacts  72  and  70 , respectfully. Power for the temperature transducer  14  is again supplied by an appropriate power supply in an electronics package  78  via electrical leads  74  and  76 . The leads  74  and  76  are disposed within the borehole instrument wall  60  and within the thermal isolator insert  51 , and terminate at the tool contacts  72  and  70 , respectively.  FIG. 3A  illustrates one means for thermally isolating the temperature transducer  14  from the wall  60  of the borehole instrument. It should be understood that the desired thermal isolation of the temperature transducer  14  can be obtained using other embodiments, such as fabricating the housing  12  with a thermally insulating material.  
         [0020]      FIG. 4  illustrates conceptually the temperature sensor assembly  10  disposed in a well borehole for measuring temperature of borehole fluids. A borehole instrument  84  is suspended in a well borehole  92  that penetrates earth formation  90 . The borehole instrument is operationally connected to a lower end of a data conduit  82  by a suitable connector  83 . The upper end of the data conduit  82  is operationally connected to a conveyance means  80  at the surface  96  of the earth. The conveyance means  80  is operationally connected to surface equipment  89  which can power and transmit down-link data to the borehole instrument  10 , and receive and process up-link data transmitted from the temperature sensor assembly  10  and other instrumentation within the borehole instrument  84 . The temperature sensor  10  responds primarily to temperature of borehole fluid in the annulus defined by the outer surface of the borehole instrument  84  and the wall  94  of the borehole  92 .  
         [0021]     As mentioned previously, the temperature sensor assembly  10  can be embodied in LWD, MWD, wireline and other types of borehole systems. If embodied in an LWD or MWD system, the borehole instrument  84  is typically a drill collar, the data conduit  82  is a drill string, and the conveyance means  80  is a rotary drilling rig which incorporates an appropriate telemetry system, such as a mud pulse system. If embodied in a wireline system, the borehole instrument  84  is typically a cylindrical pressure housing, the data conduit  82  is a logging cable cooperating with a suitable up-hole and down-hole telemetry system, and the conveyance means  80  is a wireline draw works assembly.  
         [0022]     While the foregoing disclosure is directed toward the preferred embodiments of the invention, the scope of the invention is defined by the claims, which follow.