Abstract:
An apparatus for supporting a retrievable downhole component within a drill collar of a downhole drilling tool deployed from a rig into a wellbore penetrating a subterranean formation is provided. The apparatus includes a sleeve that is positionable about the downhole component and is within said drill collar. The sleeve is adapted to limit the lateral movement of the downhole component. The sleeve is formed of a series of fins or is lined with an energy absorbing material which protects the downhold component from shock and vibration while at the same time, allowing the component to be retrieved should the drill string become stuck in the borehole.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to downhole drilling tools that are used in wellbore operations. More particularly, the present invention relates to a protective support for isolating downhole drilling tools from high shock and vibration intrinsic to the drilling process in a wellbore penetrating a subterranean formation.  
       BACKGROUND OF THE RELATED ART  
       [0002]     Wellbores are drilled at wellsites 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, a drilling mud is pumped from a surface mud pit, 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 tool. The drilling mud is also used to form a mudcake to line the wellbore.  
         [0003]      FIG. 1  illustrates a wellsite system  1  which includes a surface system  2 , a downhole system  3  and a surface control unit  4 . In the illustrated embodiment, a borehole  11  is formed by rotary drilling in a manner that is well known.  
         [0004]     The downhole system  3  includes a drill string  12  suspended within the borehole  11  with a drill bit  15  at its lower end. The surface system  2  includes the land-based platform and derrick assembly  10  positioned over the borehole  11  penetrating a subsurface formation F. The assembly  10  includes a rotary table  16 , kelly  17 , hook  18  and rotary swivel  19 . The drill string  12  is rotated by the rotary table  16 , energized by means not shown, which engages the kelly  17  at the upper end of the drill string. The drill string  12  is suspended from a hook  18 , attached to a traveling block (also not shown), through the kelly  17  and a rotary swivel  19  which permits rotation of the drill string relative to the hook.  
         [0005]     The surface system further includes drilling fluid or mud  26  stored in a pit  27  formed at the well site. A pump  29  delivers the drilling fluid  26  to the interior of the drill string  12  via a port in the swivel  19 , inducing the drilling fluid to flow downwardly through the drill string  12  as indicated by the directional arrow  9 . The drilling fluid exits the drill string  12  via ports in the drill bit  15 , and then circulates upwardly through the region between the outside of the drill string and the wall of the borehole, called the annulus, as indicated by the directional arrows  32 . In this manner, the drilling fluid lubricates the drill bit  15  and carries formation cuttings up to the surface as it is returned to the pit  27  for recirculation.  
         [0006]     The drill string  12  further includes a bottom hole assembly (BHA), generally referred to as  100 , near the drill bit  15  (in other words, within several drill collar lengths from the drill bit). The bottom hole assembly includes capabilities for measuring, processing, and storing information, as well as communicating with the surface. The BHA  100  thus includes, among other things, an apparatus  110  for determining and communicating one or more properties of the formation F surrounding borehole  11 , such as formation resistivity (or conductivity), natural radiation, density (gamma ray or neutron), and pore pressure.  
         [0007]     The BHA  100  further includes drill collars  130 ,  150  for performing various other measurement functions. Drill collar  150  houses a measurement-while-drilling (MWD) tool. The MWD tool further includes an apparatus  160  for generating electrical power to the downhole system. While a mud pulse system is depicted with a generator powered by the flow of the drilling fluid  26  that flows through the drill string  12  and the MWD drill collar  150 , other power and/or battery systems may be employed.  
         [0008]     Sensors are located about the wellsite to collect data, preferably in real time, concerning the operation of the wellsite, as well as conditions at the wellsite. For example, monitors, such as cameras  6 , may be provided to provide pictures of the operation. Surface sensors or gauges  7  are disposed about the surface systems to provide information about the surface unit, such as standpipe pressure, hookload, depth, surface torque, rotary rpm, among others. Downhole sensors or gauges  8  are disposed about the drilling tool and/or wellbore to provide information about downhole conditions, such as wellbore pressure, weight on bit, torque on bit, direction, inclination, collar rpm, tool temperature, annular temperature and toolface, among others. The information collected by the sensors and cameras is conveyed to the surface system, the downhole system and/or the surface control unit.  
         [0009]     The MWD tool  150  includes a communication subassembly  152  that communicates with the surface system. The communication subassembly  152  is adapted to send signals to and receive signals from the surface using mud pulse telemetry. The communication subassembly may include, for example, a transmitter that generates a signal, such as an acoustic or electromagnetic signal, which is representative of the measured drilling parameters. The generated signal is received at the surface by transducers, represented by reference numeral  31 , that convert the received acoustical signals to electronic signals for further processing, storage, encryption and use according to conventional methods and systems. Communication between the downhole and surface systems is depicted as being mud pulse telemetry, such as the one described in U.S. Pat. No. 5,517,464, assigned to the assignee of the present invention. It will be appreciated by one of skill in the art that a variety of telemetry systems may be employed, such as wired drill pipe, electromagnetic or other known telemetry systems.  
         [0010]     Downhole tools, such as those in BHA  100 , are subjected to high shock and extreme vibration intrinsic to the drilling process. These high shock and vibration loads can significantly reduce the efficiency, accuracy and reliability of the tools. Shock and vibration may be of particular concern when the tools carry delicate and sensitive electronics equipment, such as the measuring and communications assemblies described above. MWD tools and their associated sensors may, for example, especially susceptible to damage and inaccurate performance in high shock and vibration environments.  
         [0011]     The borehole depicted in  FIG. 1  is oriented vertically in a downward direction from ground level as is typical at a wellsite. Boreholes are, however, often required to be formed in a diagonal, horizontal or upward direction with respect to the drilling surface. Despite the orientation, the drilling tools are typically subjected to significant shock and vibration. Those of ordinary skill in the art, given the benefit of this disclosure, will appreciate that the present invention also finds application in drilling applications other than conventional wellsites as illustrated in  FIG. 1  and this invention is not limited thereto.  
         [0012]     The industry has attempted to address the adverse effects of shock and vibration on downhole tools in a number of ways, such as the use of specially designed drill collars to protect the delicate components in the drilling tools. While such collars provide a measure of protection against shock and vibration, they are often expensive to make, to deploy in the borehole and to maintain. Moreover, the special design and expense of these protective collars can limit their use at other locations in the drill string.  
         [0013]     Drill collars primarily are designed to provide structure to the drill string and to serve as a passageway for the drilling tools and drilling mud into the borehole as illustrated in  FIG. 1 . Drill collars are a required fixture at most drill sites and come in various lengths and diameters. It is not uncommon for a wellsite to require several hundred drill collars in order to complete the borehole to the required depth.  
         [0014]     Thus, the industry has developed manufacturing techniques and economies for making drill collars for their conventional and passive purposes relatively inexpensively. When drill collars must also perform an active function, such as protecting drilling tools from the harmful effects of shock and vibration from the drilling operation, the special design and materials required for these purposes greatly increases the cost of the drill collar and discourages their use for more conventional purposes.  
         [0015]     Some protective drill collars have been used in an attempt to limit the internal displacement of the various tool components within the collar. The tool components are typically installed inside the protective collar and physically attached to its interior. While this approach may provide a measure of protection, the protective collar and the tool components are typically very expensive and often cannot be retrieved if stuck. Thus, while some degree of protection may be achieved, the costs of such a protective collar and its tool components can be very expensive. The risk of such a financial loss often deters the use of protective collars for expensive tool components, such as MWDs. Even in cases where retrievability is possible by providing a protective collar, the impact on the cost to operate the service can become prohibitive in many situations.  
         [0016]     Various techniques have been developed for protecting various downhole components within drilling tools. See, for example, U.S. Pat. Nos. 6,761,230; 4,265,305 and 4,537,067. Some such techniques involve the use of centralizers or rings positioned within the drill collar to protect internal components.  
         [0017]     Despite the development and advancement of various approaches to protecting downhole components within drill collars or other housings of downhole tools, there remains a need to provide such protection in a more economical manner. It is desirable that a protection system be provided that permits the retrievable of the downhole components should the downhole tool become stuck in the borehole. It is further desirable that such a protection system not require the use of specially designed and/or expensive drilling collar. Preferably, such as protection system provides one or more of the following, among others: retrievability of the downhole components reduced manufacturing costs, reduced maintenance costs, enhanced component protection, reduced shock and/or vibration.  
       SUMMARY OF THE INVENTION  
       [0018]     In at least one aspect, the present invention relates to an apparatus for supporting a retrievable downhole component within a drill collar of a downhole drilling tool deployed from a rig into a wellbore penetrating a subterranean formation. The apparatus includes a support or sleeve that is positionable about the downhole component and is located within the drill collar. The sleeve is adapted to limit the lateral movement of the downhole component within the drill collar.  
         [0019]     In another aspect, the invention relates to a downhole drilling tool for supporting a retrievable downhole component therein. The downhole drilling tool is deployed via a drill string from a rig into a wellbore penetrating a subterranean formation. The drilling tool includes at least one drill collar operatively connected to the drill string, a retrievable downhole component that is removably positionable within the drill collar and a sleeve that is positionable within the drill collar. The sleeve is adapted to limit the lateral movement of the retrievable downhole component within the drill collar.  
         [0020]     Finally, in another aspect, the invention relates to a method of supporting a retrievable downhole component within a downhole drilling tool that is deployed from a rig into a wellbore penetrating a subterranean formation. The method includes operatively connecting a drill collar of the downhole tool to a drill string and positioning a sleeve in the downhole tool about the retrievable downhole component such that the sleeve limits the degree of lateral movement of the retrievable downhole component within the drill collar. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     So that the above recited features and advantages of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof that are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0022]      FIG. 1  is a schematic view, partially in cross-section of a prior art MWD tool and wellbore telemetry device connected to a drill string and deployed from a rig and into a wellbore.  
         [0023]      FIG. 2  is a longitudinal cross-sectional view of a drill collar and drilling tool component, the drilling tool component having a protective sleeve thereabout.  
         [0024]      FIG. 3  is a horizontal cross-sectional view of the drill collar, a drilling tool component and protective sleeve as depicted in  FIG. 2  taken along line  3 - 3 .  
         [0025]      FIG. 4  is a horizontal cross-sectional view of the drill collar, a drilling tool component and protective sleeve as depicted in  FIG. 2  taken along line  4 - 4 .  
         [0026]      FIG. 5  is a perspective view of another fin of a protective sleeve.  
         [0027]      FIG. 6  is a horizontal cross-sectional view the drill collar, drilling tool component and protective sleeve of  FIG. 2 , taken along line  6 - 6 , with the fin of  FIG. 5 .  
         [0028]      FIG. 7  is a horizontal cross-sectional view of the drill collar, drilling tool component and protective sleeve of  FIG. 6 , with the fin of  FIG. 5  having three lobes.  
         [0029]      FIG. 8  is a perspective view of another fin used to form a protective sleeve as illustrated in  FIG. 2 .  
         [0030]      FIG. 9  is a horizontal cross-sectional view of the drill collar, drilling tool component and protective sleeve of  FIG. 2  taken along line  9 - 9 , with the fin of  FIG. 8 .  
         [0031]      FIG. 10  is a perspective view of the fin of  FIG. 8  having separate lobes.  
         [0032]      FIG. 11  is a perspective view of the fin as depicted in  FIG. 10  with a centralizing tube attached thereto.  
         [0033]      FIG. 12  is a longitudinal cross-sectional view of a drill collar and a drilling tool component, the drill collar having an alternative protective sleeve lining an inner surface thereof  FIG. 13  is a horizontal cross-sectional view the drill collar, a drilling tool component and protective sleeve as depicted in  FIG. 12  taken along line  13 - 13 .  
         [0034]      FIG. 14  is a longitudinal cross-sectional view of a drill collar and a drilling tool component, the drilling tool component having a protective sleeve lining an outer surface thereof.  
         [0035]      FIG. 15  is a horizontal cross-sectional view of a drill collar, a drilling tool component and a protective sleeve as depicted in  FIG. 14  taken along line  15 - 15 .  
         [0036]      FIG. 16  is a longitudinal cross-sectional view of a drill collar and a drilling tool component deployed into a wellbore from a rig via a drill string, the drill collar having a helically shaped protective sleeve positioned therein.  
         [0037]      FIG. 17  is a horizontal cross-sectional view of a drill collar, a drilling tool component and a protective layer as depicted in  FIG. 16  taken along line  17 - 17 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]     Presently preferred embodiments of the invention are shown in the above identified figures and described in detail below. In describing the preferred embodiments, like or identical reference numerals are used to identify common or similar elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.  
         [0039]     Referring to  FIG. 2 , a protective sleeve  1  for a downhole component  7  of a downhole tool, such as the downhole tool  100  of  FIG. 1 , is provided. While  FIG. 1  depicts a drilling tool, it will be appreciated that such a protective sleeve may be used in a variety of downhole tools, such as a drilling, wireline, coiled tubing, completions or other downhole tool.  
         [0040]     As shown, the protective sleeve is positioned in a drill collar  2  and an adjacent landing sub  4  for supporting a downhole component. However, the protective sleeve may be positioned within one or more drill collars and/or landing subs, or other modules or housing depending on the application. The drill collar and/or sub may be machined and/or cut to the desired length to meet the needs of the wellbore application. Such cuts may be made to the drill collar for maintenance, repair and/or manufacture. Re-cuts and re-threads may be performed as desired.  
         [0041]     The protective sleeve  1  includes a centralizing tube  10  and a plurality of fins  11 . The protective sleeve preferably supports the component  7  therein from wellbore and/or drilling conditions. The protective sleeve is preferably adapted to restrict the movement of downhole components, and/or isolate the component from shock and vibration.  
         [0042]     The tube, generally indicated by reference number  10 , is preferably positioned inside the drill collar. The drill collar may be, for example, a conventional low cost monel drill collar  2 . Drill collar  2  preferably has a threaded downhole end  3  for threadedly connecting to an adjacent drill collar as is known in the art. Landing sub  4  likewise has a threaded downhole end  5  for threadedly connecting to an adjacent downhole drill collar (not shown) in order to continue the drill string structure in the downhole direction. Drill collar  2  also has an uphole treaded end  6  for threadedly connecting to an adjacent uphole drill collar (not shown) in order to continue the drill string structure in the uphole direction.  
         [0043]     The downhole component for which sleeve  1  serves to protect can be one of a number of difference components, such as an MWD and/or telemetry tool, a gyroscopic tool, etc. The example used in  FIG. 2 , for illustrative purposes only, is an MWD telemetry tool  7 . MWD tool  7  is inserted into drill collar  2  and extends into landing sub  4 ..  
         [0044]     Landing sub  4  includes an integrally formed landing shoulder  8  which serves as downhole support and orientation for drilling tool components such as MWD tool  7  shown in  FIG. 2 . MWD tool  7  has a corresponding resting pad  9  which rest upon landing shoulder  8 . Preferably, the weight of MWD tool  7 , landing shoulder  8  and/or the forces and pressures within the drill string maintain MWD tool  7  in its desired location.  
         [0045]     Centralizing tube  10  is preferably formed of tubular construction. The tube is preferably of sufficient length to enclose the drilling tool component to be protected. Tube  10  may be made of metal, such as stainless steel or a steel alloy. In fact, centralizing tube  10  may also be a low cost monel drill collar positionable within low cost monel drill collar  2 .  
         [0046]     Centralizing tube  10  includes a plurality of centralizer fins  11 ,  11   a,    11   b  attached to its exterior diameter and which extend outward to the interior diameters of Drill collar  2  and landing sub  4 . The fins preferably extend between sleeve  10  and drill collar  2  to support the sleeve and the component housed therein.  
         [0047]     The number, type and position of fins  11  needed to maintain centralizing tube  10  in a stable position is a matter of design choice for one of ordinary skill in the art. Four sets of fins are depicted in  FIG. 2 , but the invention is not limited to this number. A fewer or a larger number of fins can be used, depending on the particular needs of the drilling operation. A variety of types, geometries and configurations may be used as will be described more fully below.  
         [0048]     Fins  11  may be made of the same material as centralizing tube  10  or may be formed of any other material of suitable strength and rigidity necessary to maintain centralizing tube  10  in a stable position within Drill collar  2  and landing sub  4  in the presence of shock and vibration caused by the drilling operation. Fins  11  may be attached to centralizing tube  10  using a number of conventional attachment techniques, such as, molding, adhesives, or interference press fits.  
         [0049]     Various fin configurations are shown in greater detail in  FIGS. 3-1 . Each of fins  11  are arranged about centralizing tube  10  as illustrated in the cross-sectional views shown in  FIGS. 3 and 4 .  FIGS. 3 and 4  are taken along line  3 - 3  and line  4 - 4 , respectively, in  FIG. 2 . Fin  11  can be positioned around centralizing tube  10  so that each fin is aligned with respect to vertically adjacent fins as shown in  FIG. 3  or may be offset by some number of degrees from immediately adjacent fins as shown in  FIG. 4 . As shown, the fins of  FIGS. 3 and 4  are rectangular. However, other geometries are possible.  
         [0050]      FIG. 5  depicts the construction of a fin  11  a in greater detail. Fin  11  a has a left lobe  41  and a right lobe  42  with a void area  43  separating the lobes. The void area  43  permits the passage of mud between the lobes when the fin is positioned in a drill collar. The fin also includes a center hole  44  through which centralizing tube  10  is positioned.  
         [0051]     The fin shown in  FIG. 5  may be molded from a hard rubber or other elastomer material. The fin may be integrally formed with centralizing tube  10  using known molding techniques. Alternatively, the fin may be separate from the centralizing tube and operatively connected thereto.  
         [0052]      FIG. 6  is a horizontal cross-sectional view of the drill collar of  FIG. 2  taken along line  6 - 6  with fin  1  la of  FIG. 5  positioned therein.  
         [0053]     Arrows  12  in  FIG. 2  indicates the flow of drilling mud through drill collar  2  and land sub  4 . Note that the flow of mud travels between the inside walls of drill collar  2  and landing sub  2  and the outside wall of centralizing tube  10 . Voids  43  allow the drilling mud to easily flow pass fin  11 . Upper surface  46  of fin  11  also is preferably formed with an aerodynamic profile to aid the flow of the drilling mud pass fin  11 .  
         [0054]     The type of material used to make fin  11  and the length of outer portions  51  and  52  of lobes  41  and  42 , which come into contact with the interior diameters of drill collar  2  and landing sub  5 , may be selected to provide sufficient lateral support to centralizing tube  2 . The lobes  41  and  42  are preferably configured to substantially absorb the shock and vibrations incident to the drilling operation. Some shock and vibration may also be absorbed by centralizing tube  2 . Preferably, a minimum amount of shock and vibration, if any, reaches the downhole components, such as MWD  7 , positioned within the drill collar thus protecting the tools from these harmful effects.  
         [0055]     In some drilling operations, it might be sufficient for fin  11  to be formed with two lobes  41  and  42  as shown in  FIGS. 5 and 6 . In other drilling operations that require more support for centralizing tube  10 , fin  11  may be formed with additional lobes, such as lobes  71 ,  72  and  73  illustrated in  FIG. 7 . The number of lobes required for a particular operation is a matter of design choice for the person of ordinary skill in the art. Note that as pointed out above, boreholes may be formed in diagonal, horizontal and vertical directions as well as the conventional downward direction at a conventional wellsite. Thus, the amount of support necessary for centralizing tube  10  will depending on the particular drilling operation.  
         [0056]     The upper surface of lobes  71 - 73  also preferably have an aerodynamic profile to aid the flow of drilling mud pass each lobe through voids  74 .  
         [0057]      FIG. 8  depicts the configuration of fin  11   b  in greater detail. This fin has two lobes  92  and  93 , with a center passage  91  through which centralizing tube  10  can pass. The outer ends of lobes  92  and  93  of the fin extends out to the exterior diameter of centralizing tube  10  to provide support as illustrated in  FIG. 9 .  
         [0058]     The upper surface  94  of the fin is preferably formed with an aerodynamic profile to aid the flow of drilling mud pass the fin.  
         [0059]      FIG. 9  is a horizontal cross-sectional view of drill collar  2  taken along line  9 - 9  in  FIG. 2  where two fins  11   a  are formed of the construction depicted in  FIG. 8 . As shown in  FIG. 9 , fins  11   b  is arranged around centralizing tube  10  so that vertically adjacent fins are offset from each other. Positioning the fins in this manner provides uniform support to centralizing tube  10  in the presence of shock and vibration during the drilling operation.  
         [0060]     Like the configurations of fin  11  a depicted in  FIG. 5-7 , the fin  11   b  shown in  FIGS. 8 and 9  may be formed of the same material as centralizing tube  10  or may be formed of any material of suitable strength and rigidity necessary to maintain centralizing tube  10  in a stable position within drill collar  2  and landing sub  4  in the presence of shock and vibration caused by the drilling operation.  
         [0061]      FIG. 10  depicts fin  11   b  having separate lobes  80  and  81  In this configuration, lobes  80  and  81  are of the same construction. The lobes may then be attached to the exterior wall of centralizing tube  10  as depicted in  FIG. 11 .  
         [0062]     Each fin member  80  and  81  may be formed of hard rubber or other elastomer material. Fin  11   b  may be formed by way of injection molding using a process well known in the art. Each fin member may be attached to centralizing tube  10  using a number of attachment techniques, such as adhesives, rivets, nuts and bolts and screws in cooperation with corresponding elements attached to centralizing tube  10 .  
         [0063]     Centralizing tube  10  and associated fins  11 ,  11   a,    11   b,  as illustrated in  FIGS. 2-11  preferably minimize shock and vibration transmission into the MWD tool  7  by significantly reducing the relative motion between drill collar  2  and the MWD tool. This restriction in motion also reduces the potential for high shock impact between the two. Thus, very delicate and expensive downhole drilling tools, such as MWD tool  7 , are protected from physical damage that otherwise would occur in the drilling environment.  
         [0064]     Use of centralizing tube  10  and associated fins  11  may be used to eliminate the need for specially designed and expensive drill collars. However, should a drill collar be used for centralizing tube  10 , the collar can be of the low cost rental monel type that is customarily used throughout the drill string. In the event that the drill string becomes stuck in the borehole, the drilling tool components can easily be retrieved from the inside of centralizing tube  10 . Thus the tool component is not sacrificed at the expense of providing protection from shock and vibration in the borehole.  
         [0065]     A plurality of fins  11 ,  11   a  and/or  11   b  may also be attached directly to the drilling tool component, thus eliminating the need for centralizing tube  10 . Ideally, the method of attachment should be such that the fins can easily break away or shear off so that the drilling tool component can be retrieved from the borehole should the drill string become stuck. Methods of attachment that provide such functionality are well know to those in the art and include adhesives, breakable plastic and/or glass fasteners and the like. Here again, the retrievability of the drilling tool is not sacrificed by providing the tool with protection from shock and vibration in the borehole.  
         [0066]      FIG. 12  depicts an alternate protective sleeve  101  positioned on an inner surface of a drill collar  2 . The inside wall  100  of drill collar  2  is lined with protective sleeve  101  in the form of an energy absorbing layer  101 , such as rubber. Other materials may also be used which have energy absorbing characteristics.  
         [0067]     A number of techniques are known in the art for applying layer  101  to the inside of drill collar  2 . Such techniques include extruding layer  101  onto the interior of drill collar  2  using an internal mandrill and various thermo setting processes known to those of skill in the art. Layer  101  may also be attached using adhesives or may be formed of a sleeve and inserted inside of drill collar  2 .  
         [0068]      FIG. 13  is a horizontal cross-sectional view taken along line  13 - 13  in  FIG. 12 . This figure illustrates the position of layer  101  with respect to drill collar  2  and MWD tool  7  being protected. This figure shows that the protective sleeve or layer  101  is positioned between the collar  2  and the downhole component  7 . In this position, the layer  101  may be used to absorb any impact between the downhole component and the drill collar, thereby reducing the effects of an impact therebetween on the downhole component.  
         [0069]      FIG. 14  illustrates another a protective sleeve  120  positioned in a drill collar  2 . MWD tool  7  is itself covered by the protective sleeve or layer  120 . Preferably, the protective sleeve is made of energy absorbing material, such as rubber. Like the sleeve or layer depicted in  FIGS. 12 and 13 , MWD tool  7  may, alternatively, be covered with other materials that have energy absorbing characteristics.  
         [0070]     A number of techniques are known in the art for applying layer  120  to MWD tool  7 . Such techniques include molding the layer onto tool  7  or using various other thermo setting processes known to those of skill in the art.  
         [0071]      FIG. 15  is a horizontal cross-sectional view taken along line  15 - 15  in  FIG. 14 . This figure shows the position of layer  120  with respect to drill collar  2  and MWD tool  7  being protected. This figure shows that the protective sleeve or layer  120  is positioned between the collar  2  and the downhole component  7 . In this position, the layer  101  may be used to absorb any impact between the downhole component and the drill collar, thereby reducing the effects of an impact therebetween on the downhole component.  
         [0072]      FIG. 16  shows another version of a protective sleeve  130  positioned in a drill collar  2 . The outer surface of the downhole component  7  has a layer  130  made of an energy absorbing material, such as rubber. Layer  130  is formed in a helix profile along the length of drill collar  2 . The helical profile is illustrated by the flow of drilling mud through drill collar  2  and indicated by arrow  12 . The layer  130  may be positioned on the inner surface of the drill collar  2  and/or the outer surface of the downhole component.  
         [0073]      FIG. 17  is a horizontal cross-sectional view of the drill collar  2  taken along lines  17 - 17  in  FIG. 16 . This figure illustrates the profile of lobes  131 ,  132  and  133  with respect to drill collar  2  and the MWD tool  7  being protected.  
         [0074]     Layer  130  can be attached permanently to the interior of drill collar  2  or insert loaded into the collar using techniques know in the art. Some examples of helical rubber liners used in motor stators and techniques for making such motors are described in U.S. Pat. No. 9,931,389. Lobes  131 ,  132  and  133  provide a surface for centralizing MWD tool  7 , and thus minimize shock transmission to tool  7 . Space between the lobes is also provided to permit the passage of mud therethrough.  
         [0075]     The sleeves illustrated in  FIG. 12-17  may also be used to eliminate the need for specially designed and expensive drill collars while at the same time allowing the drilling tools, such as MWD tool  7 , to be retrieved should the drill string becomes stuck in the borehole.  
         [0076]     Various combinations of the sleeves depicted in  FIGS. 2-17  may be used. For example, the sleeve  101  of  FIG. 12  may be positioned on drill collar  2 , and an additional sleeve  120  may be positioned on downhole component  7 . Other combinations may be envisioned. Moreover, multiple layers of material may be used to make up portions of the sleeves and/or tubes. Reinforcements may also be provided therein.  
         [0077]     It will be understood from the foregoing description that various modifications and changes may be made in the various embodiments of the present invention without departing from its true spirit. Thus, this description is intended for purposes of illustration only and should not be construed in a limiting sense. The scope of this invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. “A,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded.