Patent Publication Number: US-6341656-B1

Title: Core barrel

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a core barrel, particularly in the field of oil exploration, comprising, on the one hand, at least an outer tube and a coring bit which form an outer assembly and, on the other hand, at least one inner tube which, with a drilled core possibly present therein, and possibly with some of the formations under the base of the drilled core, forms an inner assembly, suspension and/or guidance means being provided to keep the inner assembly inside the outer assembly. 
     2. Background of the Prior Art 
     Numerous core barrels of this kind are known. Their suspension and/or guidance means form, between the outer assembly and the inner assembly, mechanical connections of the type involving a bearing, of the radial and step type, and of the double-acting thrust type. It is thus common practice to have at least one upper mechanical connection therein, often of the thrust-bearing type, at the rear end of the inner tube, when considering a direction of advance S of the core barrel into the ground, and to have a lower mechanical connection of the step bearing type (in the bit, for example) at the front end of the inner tube. There may also be intermediate mechanical connections, usually of the step bearing type, particularly when core drilling is to be performed in a position which is steeply inclined with respect to the vertical or even in a horizontal position. 
     In searching for a core barrel capable of supplying a drilled core sample which is as intact as possible and as representative as possible of the formations being probed, the person skilled in the art tends to make the mechanical connections between the abovedescribed outer and inner assemblies very severe, that is to say to make them have close tolerances, so as to obtain the most efficient possible guidance of the inner tube around the drilled core. 
     It has, however, been found that the drilled cores obtained could be greatly damaged as the result of the vibrations and jolts transmitted through the string of core-barrel control rods, by the phenomenon known as whirling of the coring bit in its hole, about its axis of rotation, and from the rotation of the latter about the axis of the hole, against the pseudocylindrical interior wall of the hole, which has a diameter greater than that of the bit, and by the catching of the latter in the formation that is to be sampled, etc., that is to say as the result of an unfavourable action of the outer assembly on the inner assembly. 
     SUMMARY OF THE INVENTION 
     The inventors of the present invention have resolutely chosen to go against the practice explained hereinabove and consider that the inner tube and the drilled core, which is received therein as core drilling progresses, need to be relieved of the stresses that the abovementioned outer assembly experiences during this same core-drilling operation and transmits to the inner assembly. 
     To this end, according to the invention, the suspension and/or guidance means are arranged in such a way that the inner assembly retains, at least at the location of these means, with respect to the outer assembly, a predetermined freedom of axial and/or radial and/or angular movement which is greater than usual. 
     As a result of this, it has thus been found, surprisingly, that harsh stresses on the outer assembly are no longer transmitted, or are transmitted to a very reduced extent, to the drilled core, whose integrity is only better preserved as a result. 
     It has also become apparent, as a result of this, that the material of the core barrel experiences markedly lower stresses and is better preserved than was the case in the past as regards destruction by impact, by the forcing of parts onto one another, and onto the drilled core. 
     According to one embodiment of the invention, the suspension and/or guidance means comprise at least one rotary thrust bearing for suspending and/or supporting the inner tube in the outer tube, this thrust bearing being mounted therein with a radial and/or axial and/or angular clearance that is greater than the usual clearance. 
     According to a particular embodiment of the invention, the suspension and/or guidance means comprise hydrostatic bearing means in which pressurized core-drilling fluid forms, during core drilling, one or more elastic cushions for the radial and/or axial and/or angular location. 
     According to an advantageous embodiment of the core barrel of the invention, means are arranged therein so as, during core drilling, and in collaboration with the effects of the pressure of the core-drilling fluid on the inner assembly, to keep the latter hydrostatically suspended within the outer assembly within the limits of the said freedom of movement and/or of the aforementioned clearance. 
     Other details and particular features of the invention will emerge from the secondary claims and from the description of the drawings which are appended to this text and which illustrate, by way of nonlimiting examples, some advantageous embodiments of the invention, which are depicted diagrammatically in axial section unless otherwise indicated, with cutaway, and possibly to different scales. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a front end of a core barrel in which the present invention can be implemented. 
     FIG. 2 shows the core barrel of FIG. 1 at the location of the rear end of the inner tube and its suspension in the outer tube. 
     FIG. 3 shows the location of the said suspension of the inner tube in the outer tube, on a larger scale. 
     FIG. 4 shows the front ends of the inner and outer tubes and the coring bit, on a larger scale. 
     FIG. 5 shows one embodiment of an intermediate guide means implementing the present invention. 
     FIG. 6 shows another embodiment of the suspension of the inner tube in the outer tube. 
     FIG. 7 shows another alternative form of the means for suspending and/or guiding the inner tube in the outer tube. 
     FIG. 8 shows a cross section on the plane VII—VII of FIG.  7 . 
     FIG. 9 shows, at the location of the rear end of the inner tube and of the suspension thereof in the outer tube, a core barrel of the so-called wireline type, the front end of which may be similar to the one depicted in FIG.  1 . 
     FIG. 10 shows, in a view similar to that of FIG. 9, one embodiment of a core barrel, the inner tube of which cannot be withdrawn from the outer tube using the wireline technique. 
     FIG. 11 shows, on a larger scale, the location of the aforementioned suspension of FIG. 10, the inner tube occupying a position supported in the outer tube. 
     FIG. 12 shows, on the same scale as FIG. 11, the same suspension location, the inner tube occupying a position in which it is said to be hydrostatically suspended in the outer tube. 
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     In the various figures, the same reference notation is used to denote elements which are identical or similar. 
     The core barrel  1  (FIGS. 1 and 2) of the invention comprises, on the one hand, an outer tube  2  and a coring bit  3  which may be considered as forming an outer assembly  4  and, on the other hand, at least one inner tube  5  which may be considered as forming, with a drilled core  6  possibly present therein, an inner assembly  7 . It may also be considered that at least some of the formations arranged under the base of the drilled core  6  form part of the inner assembly  7 . Means  9  for suspending and/or guiding the inner assembly  7 , essentially the inner tube  5 , in the outer assembly  4 , are provided. 
     According to the invention, the suspension and/or guidance means  9  are arranged in such a way that the inner assembly  7  retains, at least at the location of these means, with respect to the outer assembly  4 , a predetermined freedom of movement which is greater than usual, whether this be axially and/or radially and/or angularly with respect to the longitudinal axis of the outer assembly  4 . 
     This predetermined freedom, or this less severe connection than usual between the outer assembly  4  and inner assembly  7 , prevents harsh movements, of a defined amplitude, of the outer assembly  4  from being communicated with the inner tube  5  and from the latter to the drilled core  6  which would thus be damaged by these harsh movements and/or would each time be broken off, at its base, from those of the formations located under this base. A drilled core  6  thus broken exhibits artificial discontinuities by comparison with the formation being drilled, and does not therefore show its true nature. A drilled core  6  thus broken and/or damaged also carries a considerable risk, which is directly associated with the number of discontinuities produced, of jamming in the inner tube  5 , by comparison with a continuous, if possible one-piece, drilled core  6 . 
     In one embodiment of the invention, the suspension and/or guidance means  9  comprise (FIG. 3) at least one rotary thrust bearing  12 , for example ball bearing, for suspending and/or supporting the inner tube  5  in the outer tube  2 . According to the invention, this thrust bearing  12  is mounted with a radial and/or axial and/or angular clearance that is greater than the clearance usually selected in the art. To achieve this, the thrust bearing  12  is held, with a chosen axial clearance, 
     -on the side of its inside diameter, between two elements  13  and  14  screwed home, for example, one inside the other and supporting the actual inner tube  5  (not depicted) on a male thread  15 , and 
     -on the side of its outside diameter, between two clamping elements  16  and  17  of the outer tube  4  which are also screwed one into the other and which secure a thrust ring  18  (of the circlip type). 
     In order to be screwed one into the other, it is merely a matter of choice and/or of construction constraints as to whether it is the element  13  which for this purpose will have a male thread (FIG. 3) and the element  14  which will have a female thread, or vice versa. 
     As FIG. 3 shows, a radial clearance may also be provided between the said rotary thrust bearing  12  and, on the one hand, the elements  13  and  14  and, on the other hand, the clamping elements  16  and  17 . 
     The combination of the axial and radial clearances described in respect of FIG. 3 gives this assembly an angular clearance between the axis of the inner tube  5  and that of the outer tube  2 . 
     In another embodiment, separately from or in addition to the foregoing, the suspension and/or guidance means  9  comprise at least one bearing  20  (FIGS. 1 and 4) and/or  21  (FIG. 5) for radially supporting the inner tube  5  in the outer assembly  4 , this bearing  20 ,  21  being arranged in such a way as to allow a radical clearance (FIGS. 1 and 4) and/or an axial clearance (FIGS. 4 and 5) and/or an angular clearance (by combining the radial and axial clearances greater than the clearances usually set) between the outer tube  2  and inner tube  5 . 
     In FIG. 5, the bearing  21  exhibits, for the part of the inner tube  5  which constitutes the shaft thereof, a barrel shape so as to increase the angular clearance it is possible to have between the axes of the inner tube  5  and outer tube  2 , and therefore flexibility of the mechanical connection at this point. 
     According to one particular embodiment of the invention, the suspension and/or guidance means  9  may comprise (FIG. 6) elastic means  22 . These elastic means  22 , which are also intended to make the mechanical connection between the outer assembly  4  and inner assembly  7  more flexible and to deaden the transmission of jolts, may comprise rubber or synthetic rings  23  arranged, for example, above and below the rotary thrust bearing  12  mounted, moreover, like the one in FIG.  3 . These rings  23  may have annular beads  23 A intended to collaborate with grooves in the surrounding parts with a view to providing the constituent elements thus stacked with a suitable location with respect to each other. 
     Advantageously, the suspension and/or guidance means  9  may comprise (FIG. 7) hydrostatic bearing means  24  in which pressurized core-drilling fluid, arriving from the surface through a central duct  25  and leaving via radial ducts  26  forms, during core drilling, between a cylindrical or conical interior wall  27  of the outer assembly  4  and, opposite it, a cylindrical or conical exterior wall  28  of the inner assembly  7 , one or more elastic cushions for providing this inner assembly  7  with radial and/or angular location with respect to the outer assembly  4 . The fit and the distribution of the flow of core-drilling fluid between the radial ducts  26  and the usual connecting ducts  29  leading the fluid from the central duct  25  into the gap between the outer tube  2  and inner tube  5  makes it possible to obtain a pressure difference causing centrifugal radial flow from the radial ducts  26 , for example into oblong chambers  21 , one dimension (the longitudinal dimension) of which is visible in FIG. 7, and the other dimension of which is visible in FIG.  8 . Each oblong chamber  31  may thus generate a fluid cushion between the walls  27  and  28 . 
     FIG. 9 shows one instance of a core barrel  1  of the wireline type, in which the inner tube  5  is suspended in the outer assembly  4  under the effect of its own weight and the pressure of the core-drilling fluid arriving at  32  from the surface of the ground. In particular, in this type of core barrel, means  33  may be arranged so as, during core drilling, and in collaboration with the effects of the pressure of the core-drilling fluid pushing the inner tube  5  downwards and with the friction of the drilled core  6  entering this inner tube  5 , to keep the latter hydrostatically suspended within the outer assembly  4  within the limits of the said freedom of movement and/or of the aforementioned clearance. 
     To this end, the means  33  may comprise, for example, a collection of bristles, or some other coating (not depicted) arranged on the interior wall of the inner tube  5 , to offer known resistance to the entry of the drilled core  6  into this tube  5 . 
     As an alternative, the means  33  may comprise means for regulating the escape of a fluid contained in the inner tube  5 , these means being designed so that by controlled escape they thus offer known resistance to the entry of the drilled core  6  into the tube  5 . 
     The means  33  may comprise a combination of passages  34  for the core-drilling fluid, the outlet orifices  35  of which passages open onto a peripheral surface of the inner assembly  7 , and of interior surfaces  36  and  37  of the outer assembly  4 , which have different diameters. 
     At rest, the fluid outlet orifices  35  occupy a position, depicted in FIGS. 9 and 11, in which they face an interior surface  36  which is some distance away, so as to allow the core-drilling fluid to leave them without being throttled. 
     Through the action of the said known resistance, the inner tube  5  will tend to be pushed back by the drilled core  6  in the opposite direction to the direction of advance S for core drilling, so as no longer to rest against a suspension shoulder  38  (FIGS. 9 and 11) of the outer assembly  4 . Thus, the orifices  35  occupy a position depicted in FIG. 12, in which they gradually come to face another interior surface  37  which is less distance from the orifices  35 , so as gradually to throttle the outlet of core-drilling fluid and thus increase its pressure upstream of the orifices  35  as the innner assembly  7  rises up inside the outer assembly  4 . The increase in pressure will tend to push the inner assembly  7  back in the direction of advance S of core drilling, and a state of equilibrium will thus be sought, away from the shoulder  38 , between opposing thrusts due to the said known resistance and to the increase in fluid pressure which results from its gradually being throttled. 
     When the inner assembly  7  leaves the shoulder  38 , there is in fact a leak of fluid at this point (FIG.  12 ). The “hydrostatic” equilibrium obtained for hydrostatic suspension therefore results from the self weight of the inner tube  7  and of its suspension means, from the said known resistance, from the flow rate of core-drilling fluid and leaks thereof, including through the orifices  35 . Any change which occurs in the pressure of the fluid is visible at the surface to the operator of the core barrel  1 , who can therefore take appropriate action in order, for example, having deduced that the drilled core  6  has jammed in the inner tube  5 , to alter this pressure and attempt thereby to unjam the drilled core  6 . 
     In FIG. 9, the inner assembly  7  comprises, at the rear end of its suspension and/or guide means  9 , a means  39 , known per se in the art of wirelines, for grasping the inner tube  5  in order to at least withdraw it (with a drilled core  6 ) from the outer tube  2 . 
     In FIG. 10, the inner assembly  7  is similar to the one in FIG. 9, except that it has no means  39  for grasping because, for example on account of a restricted inside diameter of the outer tube  4  upstream of the inner assembly  7  (when considering the direction of flow of core-drilling fluid through the core barrel), the inner assembly  7  cannot be raised using the said wireline technique. As a result of that, the configuration of the ducts for the passage of core-drilling fluid from the point  32  and directed towards the front end of the core barrel  1  may differ from that of FIG. 9 and, for example, have the shape of a funnel. The pressure of this fluid at the point  32  is converted into a force which thrusts the inner tube  5  in the direction S towards the said front end of the core barrel  1 , in the core-drilling position, to the exclusion of any mechanical means. 
     FIG. 7 shows, by way of an alternative form, that the suspension and/or guidance means  9  may comprise a spherical thrust bearing  40  to increase the flexibility of the mechanical connections between the outer assembly  4  and the inner assembly  7 . 
     It must be understood that the invention is not in any way restricted to the embodiments described and that many modifications may be made thereto without departing from the scope of the present invention. 
     Thus, FIG. 4 shows that the bit  3  advantageously has an internal passage  41 , the diameter of which is greater than the diameter exhibited by one or more cutters  42  closest to its axis of rotation and intended to determine the outside diameter of the drilled core  6 . The purpose of this is to provide clearance at this point, so as to reduce the enclosure of the drilled core  6  in the bit  3  and thus not subject this drilled core  6  to unfavourable reactions of the bit  3  during work. This extent of enclosure may also be reduced by reducing the axial length of what is known as the internal clearance  48  (FIGS. 1 and 4) of the bit  3  (that is to say the passage provided therein for the drilled core  6 ) as far as possible. 
     This falls within the scope of the objectives of the invention, namely the search for an optimum minimum number of elements and/or points of mechanical connection or of contact between what has been defined hereinabove as being the outer assembly  4  and the inner assembly  7 . Likewise, and for the same purpose, the geometric dimensions of the suspension and/or guidance means  8  are preferably optimized particularly to increase the clearances between the outer assembly  4  and inner assembly  7 , to reduce the diameters and/or lengths (for example to reduce or avoid enclosures) by comparison with what, hitherto, had tended to be common practice for the person skilled in the art. 
     A labyrinth seal  49 , arranged on part of the body  50  of the suspension means  9 , below the rotary thrust ball bearing  12  (or, as appropriate, spherical thrust bearing) may be noticed, particularly in FIGS. 11 and 12. The labyrinth seal  49  may for example consist of an annular seal  51 , mounted tightly on the body part  50 , and a bearing ring  52  which, for example, collaborates with the suspension shoulder  38  as is described hereinabove and which has an annular groove in which the annular seal  51  may be housed with annular clearances. 
     When the bearing ring  52  is resting against the suspension shoulder  38 , core-drilling fluid passing between the outer tube  2  (FIG. 11) and the screwed element  13  is practically prevented from passing to the support point but will tend to pass through the thrust ball bearing  12  and the assembly clearances between the latter and the body part  50  and between the latter and the bearing ring  52 . This may markedly restrict the flow rate of fluid along the mentioned path, according to the annular gaps organized between these parts. 
     In one embodiment, not described, an intermediate tube located between the outer tube  2  and the inner tube  5  and approximately coaxial therewith may, as the case may be, form part of the outer assembly  4  or of the inner assembly  7 . 
     Key to Figures 
     S direction of advance of core drilling 
       1  core barrel 
       2  outer tube 
       3  coring bit 
       4  outer assembly 
       5  inner tube 
       6  drilled core 
       7  inner assembly 
       9  suspension and/or guidance means 
       12  rotary thrust bearing 
       13  screwed element of  7 ,  5   
       14  screwed element of  7 ,  5   
       15  male thread of  14   
       16 clamping element of  4 ,  2   
       17  clamping element of  4 ,  2   
       18  thrust ring 
       20  bearing of  9   
       21  bearing of  9   
       22  elastic means of  9   
       23  ring of  22   
       23 A annular bead of  23   
       24  hydrostatic bearing of  9   
       25  central duct of  1   
       26  radial ducts of  24   
       27  cylindrical or conical interior wall of  4 ,  2   
       28  cylindrical or conical exterior wall of  7 ,  5   
       29  connecting ducts of  7 ,  5   
       31  oblong chambers of  24   
       32  point at which pressurized core-drilling fluid arrives 
       33  hydrostatic suspension means of  5 ,  7   
       34  core-drilling fluid passages of  23   
       35  orifices of  34   
       36  interior surface of  4 ,  2   
       37  interior surface of  4 ,  2   
       38  suspension shoulder 
       39  means of grasping of  5 ,  7   
       40  spherical thrust bearing 
       41  internal passage of  3   
       42  cutters of  3   
       48  internal clearance of  3   
       49  labyrinth seal 
       50  body part of  9 ,  14  (FIG. 11) 
       51  annular seal on  50   
       52  bearing ring of  7 ,  5