Abstract:
Presented are systems and methods for dampening vibrations transmitted to a sensor assembly based on well drilling operations. Vibration isolators are distributed around a sensor assembly and retained in their desired location. The sensor assembly and retained vibration isolators are inserted in a shrinkable thin-walled tube and the thin-walled tube is shrunk to constrict the inner surface of the thin-walled tube, and the retained vibration isolators against the outer surface of the sensor assembly. Additionally, the constricted thin-walled tube restrains a wiring harness associated with the sensor assembly in a wire well traversing the axial direction of the sensor assembly.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to down-hole remotely operated oil well wireline and MWD/LWD (Measure While Drilling/Log While Drilling) tools and, more specifically, to a low-profile vibration-dampening mounting system for suspending logging sensors within a down-hole MWD tool. 
       BACKGROUND 
       [0002]    The ever increasing use of fossil fuels has led to the development of drilling technologies that were unimaginable in the recent past. For instance, the ability to determine the geological strata and the probability of drilling a producing well can be determined from sensing devices placed near the bit head of a well drill. In certain cases the delicate nature of the active element of a sensing device can place requirements on vibration-dampening mounting systems that state of the art technology is unable to meet. 
         [0003]    In one example, a gamma radiation detecting sensor is mounted close to the bit head of a well drill. The sensitivity of nuclear logging equipment is directly related to the volume and therefore the diameter of the active sensing element. In the case of a gamma radiation detector, the active sensing element is typically a thallium-doped sodium iodide crystal that is sensitive to mechanical vibration and shock. If the active element receives too much vibration then false readings and a general degradation of the mechanically delicate active element can occur. In extreme cases, if the active element receives too great a shock then mechanical failure of the crystal sensing element can occur. 
         [0004]    Obtaining maximum sensitivity of the active element requires that the portion of the sensing element containing the active element be assembled from relatively thin-walled components that do not permit the implementation of typical sensor suspension methods. Current methods of vibration dampening and suspension of logging sensors within cylindrical pressure housings generally rely on a series of large cross-section O-rings installed around the sensor housing along and perpendicular to the axial length of the sensor assembly. In another current method of vibration dampening and logging sensor suspension, a series of metallic leaf springs, extending along the axis of the sensor assembly, are installed between the outer surface of the sensor housing and the inner surface of the pressure housing. 
         [0005]    The O-ring suspension method divides the sensor into sections that can be tuned to a high enough resonant frequency to be unaffected by the vibrations of typical operating conditions. The resonant frequency tuning requirement is at odds with the requirement to maximize the sensing element volume and therefore produces active element tube lengths longer than desirable between O-ring supports. In a typical installation, the sensing crystal is positioned at the center of an O-ring to O-ring gap and receives the maximum displacement from the induced vibrations. Consequently, as described above, sensor behavior ranging from false counts to sensing crystal failure can occur. Further, O-ring placement around the outer surface of the sensor assembly can interfere with the passage of the electrical conductors along the axial surface of the sensor assembly. 
         [0006]    In the leaf spring suspension method, the leaf springs are fabricated from formed sheetmetal sections. Based on the mechanical properties of the sheetmetal, the stiffness required to produce a sufficiently high resonant frequency consequently produces a greater than desirable insertion/extraction force on the sensor assembly as it is inserted into or extracted from the pressure housing. The mechanical stresses therefore can result in deformation of the sensor assembly or significant shock to the sensor active element. In either case, premature failure of the active sensor element can occur. Further, the assembler should take care when inserting the sensor assembly into the pressure housing to prevent the leaf spring suspension system from damaging the electrical conductors running along the axial surface of the sensor assembly. 
         [0007]    Under the above described well sensor operating conditions, a system and associated methods are desired allowing the damping of vibration while permitting the largest possible diameter crystal sensing element and its associated optically matched photomultiplier tube. The system should allow a longer useful life of the active sensing element and reduce the amount of error generated because of excessive vibrations and false counts. The system should provide uninterrupted and uncompromised passage of electrical conductors and permit visible inspection of the electrical harness. The ability for end user assembly and disassembly for sensor element servicing is also desired. 
       SUMMARY 
       [0008]    Systems and methods according to these exemplary embodiment descriptions address the above described needs by providing a series of strips or loops, of a relatively small cross-section, acting as isolators between the outer surface of the sensor assembly and the inner surface of a shrinkable thin-walled tube. After shrinking, the exemplary embodiment thin-walled tube constricts the isolators against the outer surface, holding the isolators in place during insertion into the pressure shell and allowing the isolators to compress against the pressure shell. In a further aspect of the exemplary embodiment, the thin-walled tube encloses and protects the electrical harness, extending along the axial length of sensor assembly, and constrains the electrical harness in a shallow wire well. 
         [0009]    According to an exemplary embodiment of a low-profile well sensor suspension system, a series of vibration isolators are used to dampen vibrations generated from well drilling and exerted on the sensor assembly. The exemplary embodiment includes a retainer for attaching the vibration isolators to their desired locations and restraining them in these positions. Further, the exemplary embodiment continues by including a shrinkable thin-walled tube for encasing the vibration isolators and the sensor assembly. After shrinking the included thin-walled tube, the exemplary embodiment constricts the vibration isolators against the outer surface of the sensor assembly. 
         [0010]    According to another exemplary embodiment, a method for positioning and retaining a series of vibration isolators between a sensor assembly and a shrinkable thin-walled tube, encasing the vibration isolators and the sensor assembly, is presented. Continuing with the exemplary embodiment method, the series of vibration isolators are positioned around a circumference of an outer surface of the sensor assembly. In the next step of the exemplary embodiment method, the positioned vibration isolators are retained against the outer surface of the sensor assembly. Further in the exemplary embodiment method, the sensor assembly, including the retained vibration isolators, is inserted into a shrinkable thin-walled tube. Continuing with the exemplary embodiment method, shrinking the shrinkable thin-walled tube until the thin-walled tube constricts the vibration isolators against the outer surface of the sensor assembly. 
         [0011]    In a further exemplary embodiment, a system for protecting well sensor instrumentation is described. The exemplary embodiment includes a means for dampening vibrations delivered to a sensor assembly based on well drilling operations. The exemplary embodiment further includes a means for retaining a series of vibration isolators associated with dampening the vibrations. Continuing with the exemplary embodiment, included is a means for encasing the vibrations isolators and the sensor assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The accompanying drawings illustrate exemplary embodiments, wherein: 
           [0013]      FIG. 1  depicts a sensor low-profile suspension system with a strip (pinstripe) isolator arrangement; 
           [0014]      FIG. 2  depicts an enlarged cross-section view of a sensor low-profile suspension system with a pinstripe isolator arrangement; 
           [0015]      FIG. 3  depicts a sensor low-profile suspension system with a pinstripe isolator arrangement wherein the isolators are taped in position for wrapping; 
           [0016]      FIG. 4  depicts a sensor low-profile suspension system with an oval (racetrack) isolator arrangement; 
           [0017]      FIG. 5  depicts an enlarged cross-section view of a sensor low-profile suspension system with a racetrack isolator arrangement; 
           [0018]      FIG. 6  depicts a sensor low-profile suspension system with a racetrack isolator arrangement and the sensor low-profile suspension system with a racetrack isolator arrangement encased in a pressure housing; 
           [0019]      FIG. 7  depicts an enlarged cross-section view of a sensor low-profile suspension system with a racetrack isolator arrangement encased in a pressure housing; and 
           [0020]      FIG. 8  is a flowchart depicting a method for reducing the operational vibration of a well down-hole sensor encased in a pressure housing shell. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The following detailed description of exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. 
         [0022]    Looking to  FIG. 1 , a detailed diagram of an exemplary embodiment of a low-profile logging sensor suspension system  100  is presented. The exemplary embodiment includes a sensor assembly  108 , a shrinkable thin-walled tube  102 , a first plurality of vibration isolators  104  placed around a first circumferential location of the sensor assembly  108  and a second plurality of vibration isolators placed around a second circumferential location of the sensor assembly  108 . It should be noted in this exemplary embodiment that the sensor assembly  108  and the vibration isolators  104 ,  106  are encased in the shrinkable thin-walled tube  102  and the shrinkable thin-walled tube is already constricted. Further, in this exemplary embodiment, it should be noted that the encased sensor assembly is inserted in a pressure housing  718  (see  FIG. 7 ) and the pressure housing  718  (see  FIG. 7 ) is connected to a well drill and lowered into a well as part of the well drilling operation. It should also be noted, as illustrated in this exemplary embodiment, that the low-profile logging suspension system  100  can be used with existing O-ring  110  technology. 
         [0023]    In general, this exemplary embodiment depicts two series of vibration isolators  104 ,  106  placed in locations around two different circumferential positions on the outer surface of the sensor assembly  108 . In this exemplary embodiment, the vibration isolators  104 ,  106  are equally spaced from adjacent vibration isolators  104 ,  106  in their cross-sectional plane. It should be noted that other exemplary embodiments can have any number of vibration isolators  104 ,  106  arranged in other locations not equally spaced or symmetrical with respect to the outer surface of the sensor assembly  108  or other vibration isolators  104 ,  106 . 
         [0024]    Continuing with the exemplary embodiment, the vibration isolators  104 ,  106  are cylindrical strips in shape and of a length optimized for vibration reduction based on the number of strips employed and the composition of the strips. A non-limiting example of a material for constructing vibration isolators  104 ,  106  is a fluoroelastomer. 
         [0025]    In another aspect of this exemplary embodiment, after shrinking, the thickness of the thin-walled tube is such that the vibration isolators  104 ,  106  have a greater thickness than the thin-walled tube and extend above the radial height of the thin-walled tube when compared to a location where the thin-walled tube is constricted directly to the outer surface of the sensor assembly. In this regard, the exemplary embodiment thin-walled tube  102  acts to restrain the vibration isolators  104 ,  106  and as a smooth surface facilitating insertion of the thin-walled tube  102  encased sensor assembly  108  into a pressure housing  718  (see  FIG. 7 ). 
         [0026]    Looking now to  FIG. 2 , an exemplary embodiment is depicted of a cross-section  200  of a low-profile logging sensor suspension system  100  (see  FIG. 1 ). The exemplary cross-section  200  is shown from position A-A on the low-profile logging sensor suspension system  100  (see  FIG. 1 ). The exemplary embodiment cross-section  200  includes a sensor assembly  202 , a plurality of vibration isolators  204  in isolator channels  216 , a shrinkable thin-walled tube  206 , a retainer  208 , a wiring harness  210  in a wire well  212  and the active element  214  of the sensor assembly  202 . 
         [0027]    In an exemplary embodiment, the sensor assembly  202  outer surface can have isolator channels  216  made (e.g., cut, stamped, pressed, rolled, etc.) to a depth sufficient to retain the vibration isolators  204  in place when the thin-walled tube  206  encased sensor assembly  202  is inserted or removed from the pressure housing  718  (see  FIG. 7 ) and to allow a vibration isolator of sufficient thickness to dampen operational vibrations to an acceptable level. It should be noted that in other exemplary embodiments the sensor assembly  202  does not have isolator channels  216  made for the vibration isolators  204  and the vibration isolators rest against the outer surface of the sensor assembly  202 . 
         [0028]    Continuing with the exemplary embodiment, a retainer  208  can retain the vibration isolators against the sensor assembly  202  until the shrinkable thin-walled tube  206  shrinks around the sensor assembly  202  and attached vibration isolators  204 . In this exemplary embodiment, the retainer  208  can be cellophane tape wrapped around the sensor assembly  202  and over the plurality of vibration isolators  204 .  FIG. 3  depicts an exemplary embodiment  300  of a first band  302  of cellophane tape and a second band  304  of cellophane tape restraining vibration isolators  204  against the sensor assembly  202 . It should be noted that in other exemplary embodiments, the retainer  208  can be an epoxy resin applied between the vibration isolators  204  and the sensor assembly  202  or an elastic band wrapping the vibration isolators  204  and the sensor assembly  202 . 
         [0029]    Returning to  FIG. 2 , the exemplary embodiment depicts a shrinkable thin-walled tube  206  constricting the vibration isolators  204  against the sensor assembly  202 . The cross-section  200  illustrates the shrinkable thin-walled tube  206  after shrinking, however, before shrinking the shrinkable thin walled tube&#39;s  206  inner diameter is greater than the diameter of the sensor assembly  202 /vibration isolators  204  pair allowing for easy insertion of the sensor assembly  202 /vibration isolators  204  pair into the shrinkable thin-walled tube  206 . As described previously, the shrinkable thin-walled tube  206  can restrain the vibration isolators  204  from movement during insertion into or removal from the pressure housing  718  (see  FIG. 7 ) and can provide a smooth seamless surface for reducing the force required to insert or remove the sensor assembly  202 /vibration isolators  204  pair from the pressure housing  718  (see  FIG. 7 ). 
         [0030]    In a non-limiting exemplary embodiment, a shrinkable thin-walled tube  206  can be manufactured from polytetrafluoroethylene. It should be noted that in other exemplary embodiments, the shrinkable thin-walled tube  206  can be manufactured from an aromatic polyamide. Further, in another exemplary embodiment, the vibration isolators  204  can be attached to the inner surface of the shrinkable thin-walled tube  206  and secured to the outer surface of the sensor assembly  202  by the constrictive forces generated by shrinking the shrinkable thin-walled tube  206  around the sensor assembly  202 . 
         [0031]    Continuing with the exemplary embodiment, a wiring harness  210  can reside in a wire channel  212  and restrained by the retainer  208  and the shrinkable thin-walled tube  206 . In this exemplary embodiment, the wiring harness is protected from cutting or chafing because the wiring harness  210  cannot escape from its protective covered wire channel  212  and become pinched between the outer surface of the sensor assembly and the inner surface of the pressure housing  718  (see  FIG. 7 ) during insertion into or removal from the pressure housing  718  (see  FIG. 7 ) of the sensor assembly  202 . It should be noted in this exemplary embodiment that the vibration isolators  204  and the shrinkable thin-walled tube can be replaced as required during periodic field inspection and service. 
         [0032]    Continuing now to  FIG. 4 , a detailed diagram of an exemplary embodiment of a low-profile logging sensor suspension system  400  is presented. The exemplary embodiment includes a sensor assembly  408 , a shrinkable thin-walled tube  402  and a plurality of vibration isolators  404  placed around a circumferential location of the sensor assembly  408 . It should be noted in this exemplary embodiment that the sensor assembly  408  and the vibration isolators  404  are encased in a shrinkable thin-walled tube  402  and the shrinkable thin-walled tube is already constricted. Continuing with the exemplary embodiment, the vibration isolators  404  can be oval in shape and can be of sufficient number to provide the amount of dampening required by the active element of the associated sensor assembly  408  or by other conditions associated with the well drilling operations. 
         [0033]    Looking now to  FIG. 5 , an exemplary embodiment of a cross-section  500  of a low-profile logging sensor suspension system  500  is depicted. The exemplary cross-section  500  is shown from position A-A on the low-profile logging sensor suspension system  400  (see  FIG. 4 ). The exemplary embodiment cross-section  500  includes a sensor assembly  502 , a plurality of vibration isolators  504  in isolator channels  516 , a shrinkable thin-walled tube  506 , a retainer  508 , a wiring harness  510  in a wire well  512  and an active element  514  of the sensor assembly  502 . It should be noted that in this exemplary embodiment, vibration isolators  504  is illustrated in cross-section  500  as  504   a  and  504   b , showing that vibration isolators  504  is a one-piece oval in shape. In one aspect of the exemplary embodiment, the retainer  508  acts to restrain the vibration isolators  504  in their selected positions. For example, the selected positions can be in isolator channels  516  made for the shape of the vibration isolators  504  and the retainer  508  can be cellophane tape wrapped around the vibration isolators  504  and the sensor assembly  502 . 
         [0034]    In another aspect of the exemplary embodiment, isolator channels  516  that can retain the oval vibration isolators  504  can be made in the outer surface of the sensor assembly  502 . It should be noted in this exemplary embodiment, the oval vibration isolators  504  can be attached to the outer surface of the sensor assembly without making isolator channels  516  in the outer surface of the sensor assembly  502 . In a further non-limiting exemplary embodiment, the oval shaped vibration isolators  504  can be attached to the inner surface of the shrinkable thin-walled tube  506 . It should also be noted in this exemplary embodiment that the vibration isolators  504  are not limited to cylindrical strips or ovals but can be any other shape acceptable for vibration reduction. 
         [0035]    Turning now to  FIG. 6 , a detailed diagram of an exemplary embodiment of a low-profile logging sensor suspension system  600  is presented. The exemplary embodiment includes a sensor assembly  606 , a shrinkable thin-walled tube  602 , a plurality of vibration isolators  604  placed around a circumferential location of a sensor assembly  606  and a pressure housing  608 . It should be noted in this exemplary embodiment that the sensor assembly  606  and the vibration isolators  604  are encased in a shrinkable thin-walled tube  602  and the shrinkable thin-walled tube is already constricted. 
         [0036]    Continuing with the exemplary embodiment, the sensor assembly  606 , encased with the vibration isolators  604  by the shrinkable thin-walled tube  602 , can be inserted into a pressure housing  608  which can be part of down-hole well drill. Further, in this exemplary embodiment, after insertion into the pressure housing  608 , the vibration isolators  604  are compressed and exert a symmetrical force on the shrinkable sensor assembly  606 , holding the sensor assembly  606  centered in the pressure housing  608  and isolated from the pressure housing  608  vibrations. In another aspect of the exemplary embodiment, the vibration isolators  604  can be placed at locations capable of preventing unacceptably low resonant frequencies, therefore eliminating vibration induced false counts and preventing damage to the active element of the sensor assembly  606 . 
         [0037]    Looking now to  FIG. 7 , an exemplary embodiment of a cross-section  700  of a low-profile logging sensor suspension system  700  inserted in a pressure housing  718  is depicted. The exemplary cross-section  700  is shown from position B-B on the low-profile logging sensor suspension system  600  of  FIG. 6 . The exemplary embodiment cross-section  700  includes a sensor assembly  702 , a plurality of oval vibration isolators  704  in isolator channels  716 , a shrinkable thin-walled tube  706 , a retainer  708 , a wiring harness  710  in a wire well  712  and an active element  714  of the sensor assembly  702 . 
         [0038]    Continuing with the exemplary embodiment, the sensor assembly  702  and the oval vibration isolators  704 , encased by the shrinkable thin-walled tube  706  are inserted in the pressure housing  718 . In another aspect of the exemplary embodiment, the oval vibration sensors  704  are under compression by the inner surface of the pressure housing  718  and have centered the sensor assembly  702  in the pressure housing  718 . In a further aspect of the exemplary embodiment, vibrations generated by the drilling operations and transferred to the pressure housing  718  are dampened by the vibration isolators  704  before reaching the sensor assembly  702  and the active element enclosed inside the sensor assembly  702 . 
         [0039]    In another aspect of the exemplary embodiment, the shrinkable thin-walled tube  706  allows for a larger cross-section of vibration isolators  704  to be installed in the shallow isolator channels  716  than would be possible without the shrinkable thin-walled tube  706 . In a further aspect of the exemplary embodiment, the protrusion of the vibration isolators  704  and the shrinkable thin-walled tube  706  from the sensor assembly  702  contact the inside surface of the pressure housing  718  and the supporting force of the vibration isolators  704  limits the exposure of the sensor assembly  702  to transverse vibration, prevents impingement of the sensor assembly  702  on the inner surface of the pressure housing  718  and produces a frictional force that dampens axial motion of the sensor assembly  702  in the pressure housing  718 . 
         [0040]    Continuing with another aspect of the exemplary embodiment, the vibration isolators  704  and the shrinkable thin-walled tube  706  are replaceable as required during existing field inspection and service. Further, the exemplary embodiment vibration isolators  704  can be constructed of different materials and to different dimensional specifications to tune the frequency response of the suspended sensor assembly  702  based on operational vibration characteristics and operational temperatures. 
         [0041]    Continuing now to  FIG. 8 , an exemplary method embodiment  800  for positioning and retaining a plurality of vibration isolators  204  between a sensor assembly  202  and a shrinkable thin-walled tube  206  encasing the plurality of vibration isolators  204  and the sensor assembly  202  is depicted. Starting at exemplary method embodiment step  802 , the vibration isolators  204  are positioned around the outer surface of the sensor assembly  202 . In this exemplary method embodiment, the vibration isolators can be cylindrical strips placed in isolator wells  216  cut into the outside surface of the sensor assembly  202 . In another exemplary method embodiment, the vibration isolators  204  can be placed on the outer surface of the sensor assembly. In a further exemplary method embodiment, the vibration isolators  204  can be oval in shape and placed either in oval shaped isolator wells  516  cut into the outer surface of the sensor assembly  502  or on the outer surface of the sensor assembly  502 . Continuing with another exemplary method embodiment, the vibration isolators can be positioned around the inner surface of the shrinkable thin-walled tube  206 . 
         [0042]    Next at exemplary method embodiment step  804 , the vibration isolators  204  can be retained in the selected positions. In one exemplary method embodiment, the vibration isolators can be retained with cellophane tape wrapped around the vibration isolators and the sensor assembly  202  as depicted in exemplary embodiment  300 . In another exemplary method embodiment, the vibration isolators  204  can be retained by applying an epoxy resin between each vibration isolator  204  and the sensor assembly  202 . In another exemplary method embodiment, an elastic band can be stretched around the vibration isolators  204  and the sensor assembly  202  or the vibration isolators  204  can be inserted into pockets in the elastic band and the elastic band can be stretched around the sensor assembly. In another exemplary method embodiment, the vibration isolators can be attached to the inner surface of the shrinkable thin-walled tube  206 . 
         [0043]    Next at exemplary method embodiment step  806 , the sensor assembly  202 , with the positioned and attached vibration isolators  204 , can be inserted into the shrinkable thin-walled tube  206 . In this exemplary method embodiment, the shrinkable thin-walled tube  206  can be initially of inner diameter larger than the outer diameter of the sensor assembly  202  and attached vibration isolators  204  to allow easy insertion without disturbing the positions of the vibration isolators  204 . In another exemplary method embodiment, the sensor assembly  202  can be inserted in the shrinkable thin-walled tube  206 , with the vibration isolators  204  attached to the inner surface of the shrinkable thin-walled tube  206 . 
         [0044]    Next at exemplary method embodiment step  808 , the shrinkable thin-walled tube  206  can be constricted around the sensor assembly  202  and the vibration isolators  204  compressing the vibration isolators  204  against the outer surface of the sensor assembly  202 . In one exemplary method embodiment, the shrinkable thin-walled tube  206  can be constricted by heating the shrinkable thin-walled tube  206 . In another exemplary method embodiment, the shrinkable thin-walled tube  206  can be constricted by exposure to appropriate chemicals or vapors based on the material used to manufacture the shrinkable thin-walled tube  206 . 
         [0045]    The disclosed exemplary embodiments provide a system and a method for dampening vibrations experienced by a down-hole well sensor assembly during drilling operations. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details. 
         [0046]    Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. 
         [0047]    This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.