Patent Publication Number: US-9885215-B2

Title: Core barrel and related drilling apparatus and method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 13/382,753 filed Jan. 6, 2012, which is a U.S. National Stage Application of International Application No. PCT/EP2010/059845 filed Jul. 8, 2010, which designates the United States and claims benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application Ser. No. 61/223,940 filed Jul. 8, 2009, which are incorporated herein by reference in their entirety. 
    
    
     The present invention relates to drilling apparatus. The invention may find particular application in a core barrel, in particular for use in the field of oil prospecting, comprising
         at least one outer tube and a core bit which form an outer assembly,   at least one inner tube and core removal elements which form an inner assembly, and   a holder for holding the inner assembly in the outer assembly which comprise at least one rolling bearing arranged between them so that these assemblies are reciprocally free in rotation.       

     In a customary core barrel, the outer assembly is driven in rotation and the core bit can therefore dig a core hole. During this time, the inner assembly is held inside the outer assembly in a position fixed in terms of rotation, while being driven axially by the outer assembly. 
     Core barrels may be made to pass through geological layers, thereby generating very high levels of vibration in the core drilling equipment. Often, the tools that exist on the market do not withstand these extreme conditions. This is because the axial vibrations increase the risks of jamming of the system for holding the inner assembly inside the outer assembly. They may also cause damage to the numerous threads which are usually used to join together the outer assembly and inner assembly. Finally, these axial vibrations often have the effect of modifying the axial position of the inner assembly relative to the outer assembly whereas, in order for the core to be removed correctly, it is desirable that the respective depth positions of the core bit and of the core removal elements are appropriately adjusted. 
     It would be desirable to develop a core barrel in which these above-described vibrations which damage the threads are greatly reduced. It would also be desirable to considerably simplify the core drilling equipment and to reduce as far as possible the number of threads and also the number of parts. Finally, it would also be desirable to lock the system for adjusting the axial position of the inner assembly in the outer assembly, so as to prevent any disconnection between these once this position has been adjusted. 
     The present invention has been made in view of the foregoing background. A drilling apparatus according to a first aspect of the present invention is defined in claim  1  below. 
     In one embodiment, the drilling apparatus is realised as a core barrel as indicated in the introduction, and which further comprises at least one spacer element which is housed inside the outer assembly, bearing on the one hand against a bearing surface of one of said inner and outer assemblies and on the other hand against the rolling bearing, the restoring member being a spring member that axially biases said rolling bearing away from the bearing surface. 
     The spring member, which is preferably prestressed, has the effect, when axial vibrations of the inner assembly occur, of absorbing these vibrations and therefore filtering them. 
     According to one embodiment of the invention, the spacer element comprises an upstream tubular part which bears against an aforementioned outer tube, and a downstream tubular part which bears against an aforementioned rolling bearing, said spring member being arranged between these upstream and downstream tubular parts, bearing against each of them and acting thereon axially so as to move them apart, the spacer element additionally comprising retaining features which limit the moving-apart thereof. 
     The terms upstream and downstream in the context of the present invention are to be understood as a function of the core drilling direction, an upstream position or element being closer to the surface and a downstream position or element being closer to the bottom of the core hole. The spring member advantageously consists of spring washers. The latter are preferably arranged so that all the spring washers exert an elastic stress both in the upstream direction and in the downstream direction. Other known spring member can of course be envisaged, for example a helical spring. 
     According to one advantageous embodiment of the invention, one of said upstream and downstream tubular parts has a female tubular end piece and the other has a male tubular end piece capable of sliding axially inside a cavity of the female tubular end piece, and the spring member is housed at the bottom of said cavity, bearing against the male end piece pushed into the female end piece. The spacer element is in this way in an advantageously compact form. 
     Said retaining features, which limit the moving-apart described above, advantageously comprise a plurality of elongate slots provided in the axial direction in the female tubular end piece and locking elements fixed to the male tubular end piece so as to protrude radially into said elongate slots and to lock a predetermined spacing of said tubular parts by bearing against one end of said elongate slots. This arrangement allows a particularly simple and robust installation of the spacer element. 
     According to one particularly advantageous embodiment of the invention, said holder comprises two upstream and downstream rolling bearings placed around an aforementioned inner tube and housed inside an aforementioned outer tube, the downstream rolling bearing being arranged between a downstream-facing first annular bearing surface of the inner tube and an upstream-facing annular stop surface of the outer tube, whereas the upstream rolling bearing is arranged between an upstream-facing second annular bearing surface of the inner tube and said spacer element, said first and second annular bearing surfaces of the inner tube being located between the two rolling bearings. 
     The particular arrangement of an inner tube biased axially in the downstream direction by a spring member and clamped between two rolling bearings makes it possible to eliminate almost all the threads which, in the prior art, were necessary to ensure the connection between the outer assembly and inner assembly. This results in an item of equipment which is particularly robust and resistant to vibrations. The inner tube remains in a very stable position, correctly aligned axially by the two rolling bearings. 
     Advantageously, said first and second annular bearing surfaces of the aforementioned inner tube are provided on an annular flange which protrudes radially therefrom, and this annular flange is clamped between the upstream rolling bearing, spaced apart from the outer assembly under the spacing action of the spring member of the spacer element, and the downstream rolling bearing which is retained by the annular stop surface of the outer tube. 
     According to one particular embodiment of the invention, the aforementioned outer tube is composed of two upstream and downstream sections which are screwed to one another, the spacer element bears between said upstream section and said upstream rolling bearing, and the downstream section has said annular stop surface on which the downstream rolling bearing bears. In this way, due to the clamping which results from screwing these two upstream and downstream sections together, the spring force of the spring member of the spacer element is automatically applied to the inner assembly at a specific value which can be predetermined. 
     According to one embodiment of the invention, said inner tube of the inner assembly is held by said holder inside the outer assembly at an upstream end, and, at its downstream end, it has an outer thread capable of cooperating with an inner thread of another inner tube of the inner assembly in order to fix this inner assembly in an axially adjusted manner in a position of use. 
     The inner assembly can thus be adjusted to a suitable depth relative to the outer assembly in order to remove the core, by using just one single connecting thread, which greatly reduces the risks of damage and jamming. 
     Since unscrewing may occur under the effect of the vibrations, advantageously the core barrel additionally comprises a threaded locking nut, arranged on said outer thread of said downstream end of said inner tube, upstream of the other inner tube, and, in said position of use, this locking nut is clamped to a predetermined clamping torque against said other inner tube. Preferably, the core barrel additionally comprises a locking washer which, in said position of use, is clamped around said threaded downstream end of said inner tube, between a threaded locking nut and said other inner tube, this locking washer being arranged in such a way as to prevent any unscrewing of the nut and of said other inner tube on said threaded downstream end. Such a system, which is effective, safe, compact and easy to use, ensures that the clamping stress of the locking nut is maintained throughout the entire core drilling process. This stress is constant and permanent throughout the entire core drilling process. It therefore ensures the filtration of the cyclic stresses associated with the aforementioned axial vibrations, thereby considerably attenuating the risks of wear of the aforementioned connecting thread due to a mechanical fatigue phenomenon. 
    
    
     
       Other details and particular features of the invention will emerge from the description of an exemplary embodiments of the invention, said description being given below by way of example only, with reference to the appended drawings, in which: 
         FIGS. 1A and 1B  together show a view in axial section of an embodiment of a core barrel according to the invention; 
         FIG. 2  shows a view in axial section of a spacer element used in the embodiment of  FIGS. 1A and 1B ; 
         FIGS. 3 and 4  show the installation of an embodiment of a system for adjusting the position of the inner assembly relative to the outer assembly of a core barrel according to the invention; 
         FIG. 5  shows a plan view of a locking washer of the adjustment system of  FIGS. 3 and 4 ; and 
         FIG. 6  shows a partial view in axial section of a variant embodiment of a spacer element as may be used in a core barrel according to the invention. 
     
    
    
     In the various figures, identical or analogous elements are denoted by the same references. 
     The core barrel shown in  FIGS. 1A and 1B  comprises an outer assembly formed of a plurality of outer tubes  1 ,  2  and  3  which are screwed to one another, and of a core bit  4 . From the surface, this outer assembly is driven in rotation about the axis  5 . The core barrel additionally comprises an inner assembly formed of a plurality of inner tubes  6 ,  7  and  8  which are screwed to one another, and of core removal elements  9  which are known and are shown schematically. Finally, a holder, in the illustrated example two upstream and downstream roller bearings  10  and  11 , are provided for holding the inner assembly in the outer assembly. In this way, these assemblies are reciprocally free in rotation, and the inner assembly remains fixed in rotation while the outer assembly turns about its axis. It would also be possible to provide more than two rolling bearings, or even just one, between the two assemblies. 
     According to the example of embodiment shown in  FIGS. 1A and 1B , the core barrel additionally comprises a spacer element  12  which is shown in detail in  FIG. 2 . 
     The spacer element  12  is housed inside the outer tube  1 . In the illustrated example, it comprises an upstream tubular part  13  which bears against the outer tube  1  and a downstream tubular part  14  which bears against the upstream rolling bearing  10 . In this example, the upstream tubular part  13  is provided with a female tubular end piece  15  while the downstream tubular part  14  has a male tubular end piece  16  which is capable of sliding axially inside the cavity  17  of the aforementioned female end piece. 
     In the illustrated example of embodiment, a spring member  18  formed of a plurality of stacked frustoconical spring washers is housed at the bottom of the cavity  17  of the upstream tubular part  13 , bearing against the male tubular end piece  16  pushed into the female tubular end piece  15 . 
     Retaining features limit the possibilities of moving apart and, in the illustrated case, simultaneously of bringing together the upstream and downstream tubular parts  13  and  14 . These retaining features consist here of a plurality of elongate slots  19  provided in the axial direction on the female tubular end piece  15 , and of locking elements  20 , in the form of bolts for example, which are screwed into the male tubular end piece  16  so as to protrude radially into the elongate slots  19 . The ends of the elongate slots  19  serve as a stop for the locking elements  20  and thus limit a moving-apart of the two parts of the spacer element, beyond a predetermined value. A shoulder  35  is provided on the downstream tubular part  14  so as to prevent the parts  13  and  14  from being brought closer together beyond a certain limit. 
     By virtue of this arrangement, the axial vibrations which may occur as the core barrel passes through hard geological layers are effectively absorbed and damped by the spacer element. 
     As can be seen from  FIGS. 1A and 1B , the holder for holding the inner assembly in the outer assembly advantageously comprise, as indicated above, two upstream and downstream rolling bearings  10  and  11  which are placed around the inner tube  6 , in particular around the upstream end thereof, and are arranged inside the outer tube  1 . 
     In this example of embodiment, the inner tube  6  carries close to its upstream end an annular flange  21  which protrudes radially therefrom. This flange is clamped between the two rolling bearings  10  and  11 . The downstream rolling bearing  11  is housed between the downstream-facing annular bearing surface  22  of the flange  21  and an annular stop surface  23  of the outer tube  1 . The upstream rolling bearing is arranged between the upstream-facing annular bearing surface  24  of the flange  21  and the spacer element  12 , in particular the downstream tubular part  14  thereof. The spring member, by exerting its spacing action between the upstream and downstream tubular parts  13  and  14  of the spacer element, has the effect of pushing in the downstream direction the two rolling bearings  10  and  11  and the flange clamped between them, the downstream rolling bearing  11  being retained by the annular stop surface  23  of the outer assembly. 
     Thus, in the case where the inner assembly ascends towards the surface under the effect of axial vibrations, it can be imagined that the downstream rolling bearing  11  may no longer be in contact with the annular stop surface  23  or the annular bearing surface  22 , or even risks being dislocated due to a disconnection of the elements constituting this downstream rolling bearing  11 . However, according to the invention, the upstream rolling bearing  10  takes over while, in addition, the spring member tends to oppose this ascent. 
     As can be seen from  FIGS. 1A and 1B , in the illustrated example of embodiment, the outer tube  1  is composed of two downstream and upstream sections  25  and  25 ′. These two sections are joined to one another by a robust thread  26 . The downstream section  25  has the upstream-facing annular stop surface  23 . By a suitable screwing of these two sections  25  and  25 ′, it is possible to adjust automatically the return force of the spring member  18  to an appropriate specific value. 
     In the example of embodiment shown in  FIGS. 1A, 1B, 3 and 4 , the core barrel comprises, in a known manner, a system for adjusting the depth position of the inner assembly relative to the outer assembly. At its upstream end, the inner tube  6  is held by the rolling bearings  10  and  11  inside the outer assembly. At its downstream end, it has an outer thread  27  capable of cooperating with an inner thread of the next inner tube  7 . This arrangement makes it possible to fix the inner assembly at an adjustable depth relative to the outer assembly. It should be noted that, in this embodiment, there is a single thread, the outer thread  27 , for forming the connection between the outer assembly and the inner assembly, and for adjusting the position of use of the core barrel. The structure is therefore greatly simplified compared to the core barrels according to the known prior art, which minimises the possibilities for damage. 
     The outer thread  27  is preferably specially designed to be on the one hand robust, so as to minimise the risks of wear on the thread, and on the other hand particularly long, so as to have an extended adjustment length for the inner assembly relative to the outer assembly. 
     In order to prevent any unscrewing from occurring on the adjustment system between the inner tubes  6  and  7  under the effect of the vibrations, it is provided according to the invention to arrange a locking nut  28  which is screwed onto the inner tube  6 , upstream of the inner tube  7 . Once the position of the inner assembly relative to the outer assembly has been adjusted, it is then possible to screw the locking nut  28  against the inner tube  7  to a predetermined clamping torque. This nut substantially prevents any unscrewing of the inner tubes  6  and  7  associated with the vibrations, and thus reduces the causes of damage or breakage of the outer (adjustment) thread  27 . 
     Advantageously, as shown in detail in  FIGS. 3 to 5 , it is possible to provide a locking washer  29  which, in the position of use of the core barrel, is clamped between the locking nut  28  and the upstream end of the inner tube  7 . This washer is preferably arranged so as to prevent any unscrewing of the locking nut  28  and of the inner tube  7 . In the illustrated example, the locking nut  28  has peripheral notches  30  and the upstream end of the inner tube  7  has peripheral notches  31 . The locking washer  29  has corresponding tabs  32  around its periphery. In the screwed position, some of the tabs can be folded in the upstream direction into the notches  30  and some can be folded in the downstream direction into the notches  31 , thus preventing any separation movement between the locking nut  28  and the inner tube  7 . 
     In order that said washer is secured to the inner tube  6  in the angular position while remaining free in terms of axial displacement, two inner tabs  33  have been added to the washer  29  so as to be housed in two axial recesses  34  provided for this purpose on the inner tube  6 . As soon as tabs  32  are engaged in the inner tube  7  and the locking nut  28 , these latter elements  7  and  28  are thus advantageously held in an angularly fixed manner relative to the inner tube  6 . 
     It has also been found that, with a core barrel as designed according to the invention, it became possible to eliminate the seals which were usually required. Even the lubrication of the outer adjustment thread  27  has in fact been found to be unnecessary, and therefore a lubrication chamber at this location has turned out to be superfluous. This therefore results in an increased reliability of the system, and it is thus possible to suppress the temperature limits for use of the core barrel in view of the omission of seals made from rubber or plastomer material. 
     It must be understood that the present invention is in no way limited to the embodiment described above and that many modifications can be made thereto within the scope of the appended claims. 
     For example, according to one advantageous embodiment of the invention, there can be envisaged a core barrel comprising an additional spacer element  36 , as shown in  FIG. 6 . The core barrel of  FIG. 6  is identical to the core barrel of  FIGS. 1 to 5 , except in the respects illustrated in  FIG. 6  and as described below. 
     As stated, the embodiment of  FIG. 6  has additional spacer element  36 . In this example of embodiment, the additional spacer element is a helical spring. The additional spacer element is to be inserted between the downstream rolling bearing  11  and the upstream-facing annular stop surface  23  of the outer tube  1 . When the two sections  25  and  25 ′ of the outer tube  1  are screwed together, the spring is prestressed, which makes it possible to produce a vertical force, directed upwards, on the downstream rolling bearing  11  and to keep the elements of this rolling bearing  11  in compression, so that they remain secured. In the event of upward axial displacement of the inner assembly, the downstream rolling bearing  11  is accompanied in this displacement and it is not subject to any impact upon once again making contact with the stop surface  23 . 
     Although the above description has been made predominantly with respect to a core barrel, the invention may find application in other drilling apparatus where it is desired to provide axial damping between relatively rotatable tubular members, and in cases where it is desirable to be able to securely adjust the length and/or relative position between threadedly connected tubular members, such as drill string components and related equipment, for example in a bottom hole assembly.