A coring device with an improved core sleeve and anti-gripping collar with a collective core catcher

This invention relates to subsurface well bore equipment, and more particularly to an improved coring apparatus for use in combination with a coring bit and a drill string.

From US-A-3 012 622 such a coring apparatus is known comprising an outer driving structure adapted to be connected at one end to said coring bit for cutting a core in a bore hole and atthe other end to the lower end of said drill string in telescoping and co-rotatable manner therewith, an inner barrel disposed within said outer driving structure and including a lower end portion adjacent to said bit, and means supporting said inner barrel in spaced relationship to said outer driving structure while permitting rotation of said driving structure with respect to said inner barrel. This apparatus uses a rubberlike coring retaining sleeve which grips the core as the core is cut. An elastomeric sleeve operates well for unconsolidated cores, but where the material being cored is fractured rock such as Monterey Shale and Chert, which is comprised of hard and very hard rocks, the alternation of unconsolidated bands with highly fractured unconsolidated sections not only limits the length of the core samples, but provides samples with very sharp edges and crushed granules and pebbles. Such a core sample tends to be jammed within the core barrel and to damage the sleeve material.

From EP-A-0 135 859 (State of art according to Article 54(3)) an apparatus of the kind already described above is known further comprising a woven metal mesh sleeve mounted in surrounding relation on at least a portion of the exterior surface of said inner barrel, said sleeve including a leading portion adapted to be positioned within the inner barrel and initially to receive a core as it is cut, said sleeve having a predetermined normal diameter which is greater than the diameter of the sleeve in tension, means at the free end of said sleeve opposite said loading portion of said sleeve, for maintaining the portion of said sleeve which surrounds said inner barrel in compression and to maintain an inside diameter greater than the outside diameter of said inner barrel of said portion of said sleeve surrounding said inner barrel while the portion of said sleeve positioned inside said inner barrel being in tension to grip and compress a core received within said sleeve and having an outside diameter less than the inside diameter of said inner barrel when in tension, and means positioned within said inner barrel and connected to the leading portion of said sleeve to draw said sleeve within said inner barrrel and to apply tension to the portion of said sleeve within said barrel to encase and grip said core as it is cut.

This apparatus grips the core tightly and eliminates friction by preventing the fracture planes of the core from sliding and acting like a wedge as the wire metal core sleeve being fed around the lower end of the inner core barrel is tensioned in the inner barrel to compress the sleeve around the core to keep the core together, and to prevent the core from touching the inside of the wall, thereby insuring relatively high core recovery, especially with highly fractured formations.

The present invention provides a coring apparatus as described above in connection with EP-A-0 135859 comprising a core catching means at the free end of said sleeve engaging the core when said means is drawn into said inner barrel. In a preferred form said core catching means may include a plurality of annular wedge-shaped segments forming the core catcher when drawn into said inner barrel.

The core catching means apply when drawn into the inner barrel a radially compressive or constricting force about the core not only a serving to retain the entire column of core within the inner barrel, but also serving to crush or cut the core free from the contiguous formation.

In another form an intermediate tube is located between the inner barrel and the driving structure, the woven metal mesh sleeve being mounted in the space between said intermediate tube and said inner barrel and said core catching means further comprises a separate annular weight located between said tube and said barrel. In this way, travel of the sleeve down the outside and around the bottom of the inner barrel is facilitated. In addition, the tension applied to that portion of the sleeve within the inner barrel which grips the core, will not cause contraction of that portion of the wire mesh sleeve on the outside of the inner barrel. The intermediate tube surrounding the woven metal mesh sleeve shieldsthe portion of the sleeve travelling down the outside of the inner barrel thus keeping it free of any attacks from the outside.

• Figure 1 is a diagrammatic longitudinal section of a coring apparatus in accordance with the present invention, with its parts in their relative position prior to the commencement of the actual coring operation.
• Figure 2 is a view similar to Figure 1, illustrating the coring apparatus of the present invention released for the commencement of a coring operation.
• Figure 3a is a diagrammatic view of a portion of a wire mesh core sleeve in accordance with the present invention in a normal diameter condition.
• Figure 3b is a diagrammatic view of a portion of a wire mesh core sleeve in accordance with the present invention in a compressed state.
• Figure 3c is a diagrammatic view of a portion of a wire mesh core sleeve in accordance with the present invention in a state of tension.
• Figure 4 is a view similar to Figure 1 illustrating the coring apparatus of the present invention and illustrating the relative position of the parts of the apparatus as a length of core is being produced.
• Figure 5 is a diagrammatic longitudinal section of the lower portion of a modified coring apparatus in enlarged scale in accordance with the present invention, with the parts thereof illustrated in their relative positions prior to termination to coring operation.
• Figure 6 is a view similar to Figure 5 illustrating the relative position of the parts of the apparatus after a length of core has been produced.

Detailed description of the preferred embodiments

Referring to the drawings which illustrate preferred forms of the present invention, the coring apparatus of this invention may be in the form of a coring device A adapted to be lowered into a well bore B to the bottom C by way of a string of drill pipe D, or the like. While the coring apparatus may take various forms, for the purposes of illustration, a coring device similar to that shown and described in U.S. Patent 3,012,622 will be described, although it is understood that other forms of devices may be used, as will be set forth.

The lower end of the string of drill pipe may be threadably attached to the upper end of an inner mandrel 10 forming a portion of an expanding or telescopic unit 11, the inner mandrel being telescoped within the upper portion of an outer housing 12 to which it is slidably splined. The inner mandrel and the outer housing are rotated by rotation of the drill pipe in the usual manner. The outer housing includes an upper housing section 13 carrying upper and lower side seals 14 adapted slidably to seal against the periphery of the inner mandrel 10 to prevent leakage of fluid in both directions between the inner mandrel and the outer housing. The slidable splined connection includes a plurality of longitudinally and circumferentially spaced grooves 15 in the exterior of the mandrel, each of which receives a spline element 16. The lower end of the inner mandrel includes a wedge assembly 17 cooperating with a groove 19 formed in the inner wall 20 of the upper housing section 13. The lower end 22 of the splines form an upper stop at one end of the groove, while the lower end of the groove 19 including shoulder 23 forming a lower stop at the opposite end of groove 19. Threadably secured to the upper housing section 13 is an outer tube assembly 25, the lower end of which may have mounted thereon a core bit 30.

Mounted on and carried by the inner mandrel is a stripper tube latch assembly 32, with ports 33 located as illustrated for flow of fluid therethrough. Cooperating with the stripper tube latch assembly is a top stripper tube ratchet spring 34 through which passes the upper end 37 of a stripper tube 40. The stripper tube includes circumferential teeth 42 which cooperate with the latch assembly 32 and ratchet spring 34, as will be described.

Located below the upper stripper tube latch assembly is a bottom stripper tube latch assembly 45 supported by a nozzle plate 48, which may form the bottom end of the upper housing section, the nozzle plate 48 which includes a plurality of flow nozzles 49, as shown. Nozzle plate 48 also includes a seal 51 to prevent flow of fluid between the stripper tube 40 and spaced radially therefrom is an inner barrel 50, the latter spaced radially inwardly from the outer tube 12. The upper end of the inner barrel is supported by an inner barrel swivel assembly 55, as shown, so that the inner barrel 50 does not rotate relative to the outer tube or housing 12. Fluid then flows through nozzles 49 below shoulder 59 into the annular space between outer tube 12 and intermediate tube 58 to the core bit 30, the latter being provided with passage 63, to permit flow into the bottom of the well bore to remove cuttings and to convey them laterally of the bit, and to cool the bit. The fluid and cuttings then flow around the exterior of the outer tube 12 and drill pipe D to the top of the well bore.

In the form shown, the outer tube 12 rotates while inner barrel 50 does not rotate. The stripper tube 40 also normally rotates with outer tube 12. The lower end of the stripper tube 40 may be provided with a stripper tube swivel assembly 67 cooperating with an anchor assembly 70 which does not rotate with the stripper tube 40 and which, like the inner barrel, is nonrotatable.

As illustrated, bit 30 may include diamond cutting elements 76 on its lower portion and side portions for cutting the bottom of the hole and to form a core which passes upwardly, relative to bit 30 as will be described.

For further details of the structure and operation of the apparatus thus far described, reference is made to U.S. Patent 3,012,622, which is representative of coring devices to which this invention relates, although it is to be understood that other forms of coring devices may be used, as will become apparent.

In general, the operation of the device thus far described, involves conditioning the well as described in U.S. Patent 3,012,622. In the relative position of the parts as shown in Figure 1, the coring device A is in the extended condition, the mandrel 10 being held upwardly by the upper stripper tube latch assembly 32 which may include a plurality of spring arms which engage the upper end of the stripper tube, as is known. Thus, rotation of the drill pipe D is transmitted through the inner mandrel 10 and through the splined connection to the outer housing to rotate the bit 30, and the stripper tube 40, all of which rotate together, while the inner barrel 50 and the anchor assembly 71 do not rotate. Drilling mud or fluid is circulated as described. No core can be formed since the stripper tube 40 is fixed axially and cannot move axially since it is held by the upper stripper tube latch assembly 32, and the core cannot enter the inner barrel 50. In the form shown, the mandrel 10 may move axially about 0.60 m (two feet) with respect to the outer housing, once released, while the inner barrel 50 may have an axial length of 6-18 m (twenty to sixty feet), for example.

Coring is commenced by dropping or pumping a release plug 100 shown in Figure 2 down through the string of drill pipes, the plug 100 passing through the mandrel 10 to release the fingers of the upper stripper tube latch assembly 32. The mandrel 10 may now move downwardly and along the stripper tube to the maximum extent, limited by the engagement of the stop ring 17 on the shoulder 23. With the release of the latch assembly 32, coring may now take place since the stripper tube 40 is no longer locked axially with respect to the outer housing, and relative downward movement of the outer tube and bit relative to the stripper tube 40 may take place, since stripper tube 40 is axially stationary with respect to the formation being cored. The above described apparatus and operation are for illustrative purposes so that the general environment of this invention may be understood.

Referring again to Figure 1, in accordance with this invention the overall operation of coring devices of various types may be significantly improved by the use of a woven or braided wire mesh core sleeve 105 which may be mounted in surrounding relation and radially outwardly of the inner barrel 50 and radially inwardly of the outer tube 12. In one preferred form, the wire mesh core sleeve is positioned in the annular chamber 65 formed between the intermediate inner barrel 50 and intermediate tube 58. The wire mesh core sleeve 105 includes a leading portion 110 positioned at the open bottom end 112 of the inner barrel 50, the leading end of the mesh sleeve being secured at 114 to the anchor plate, as shown, although various other means may be used to secure the sleeve to the plate. Thus, the wire mesh core sleeve does not rotate because of the stripper tube swivel assembly 67 but is able to move axially as the stripper tube moves axially relative to the outer tube.

As shown in Figure 3a, the wire mesh core sleeve is composed in one form of bundles of wires 120 and 121 in a diamond weave or braid at about 90° to each other at about 45° to the longitudinal axis of the sleeve. In a normal relaxed condition, free of compression or tension, the sleeve has a predetermined diameter which is less than the diameter of the sleeve in compression (Figure 3b) and greater than the diameter of the sleeve in tension (Figure 3c). Similarly, in compression the length of the sleeve is less than its normal length. The wires forming the bundles may preferably be flexible, corrosion-resistant stainless steel, for example, stainless steel 304; have a hardness sufficient to resist being cut by sharp edges of hard abrasive rock; and are strong enough to lift the core but sufficiently flexible to bend around the lower end 112 of the inner barrel. Materials with a yield strength of 1760 kg/cm² (25,000 Ib./inch squared) have been found to provide these qualities. The wire may be about 0.4 mm (.016) of an inch in diameter with thirteen wires to a bundle and forty-eight bundles being used. This provides a weave able to easily flex through a radius of 4.8 mm to 6.4 mm (3/16 to 1/4 of an inch), which is the typical radius at the lower end 112 of the inner barrel 50.

As seen in Figures 1, 2 and 4, the normal diameter of the wire mesh core sleeve is approximately equal to the diameter of the core E, and the mesh is assembled over the inner barrel 50 in a compressed condition such that the inner surface of the sleeve is spaced from the outer surface of the inner barrel 50.

A preferred manner of applying a compressive force to the sleeve when assembled to the inner barrel in accordance with this invention, is to provide a weight 126 on the upper end of the core sleeve as diagrammatically shown in the Figures. The weight 126 is sufficiently heavy to exert a downward force on the sleeve 105. Weight 126 freely travels down the annular space 65 until it contacts an annular shoulder 127 at the lower end 112 of the inner barrel 50. As shown in Figure 5, the weight 126 is separate from the sleeve 105 and has an outside diameter less than the inside diameter of the intermediate tube 58 and an inside diameter greater than the outside diameter of the inner barrel 50. Thus, the weight 126 is freely movable vertically in the space 65 formed between the barrel 50 and the tube 58. In practice, the length of the annular weight 126 may be as long as 1.2 m (four feet) in order to maintain the core sleeve compressed and to bear downwardly on the sleeve 105. This downward push on the sleeve 105 significantly assists in assuring that the portion 125 of the sleeve which passes around the lower end 112 of the inner barrel 50 is not placed in tension until it enters the inside of the inner barrel 50. In other words, while the core urges the sleeve 105 downwardly and maintains that portion of the sleeve 105 which is in space 65 into compression. In this way, the tendency of the sleeve 105 to grip the outer surface of the inner barrel 50 is substantially eliminated. Thus, it is preferred to use a weight 126 which has a sufficient axial length to prevent cocking of the sleeve in the chamber. Although the weight is shown in one piece, a plurality of weights may be used, if desired.

Referring now to Figures 2 and 4, Figure 2 illustrates the condition of the coring device upon release of the upper stripper tube latch assembly 32 by the stripper release plug 100, as described. The coring apparatus is rotated by the drill pipe D while fluid is pumped downwardly through it. The pressurized fluid flows through the flow path as described, and exerts a downward pressure on the core bit 30, thereby imposing proper drilling force or weight against the bottom C of the well bore. As drilling proceeds, the drill bit 30 and the outer housing 12, as well as inner barrel 50, move downwardly with respect to the stripper tube 40 and the mandrel 100. The mandrel 100 is not moved downwardly at all, but remains in the position that it had when it was first shifted downwardly within the housing, as illustrated in Figure 2. The components surrounding the stripper tube 40 can all move downwardly, along the stripper tube 40, as permitted by the bottom stripper tube latch assembly 67. As the bit 30 forms a core E (see Fig. 4), and moves downwardly to form a hole and a core, the inner barrel 50 moves downwardly along with the bit 30 the lower end 112 of the inner barrel 50 forcing the wire mesh core sleeve 105 downwardly, assisted by the weight 126, around the lower end 112 and then upwardly into the inner open portion of the inner barrel 50. As this takes place, a tension is applied to the core sleeve 105 within that portion thereof located within the interior or the inner barrel 50, with the result that the sleeve 105 tightly grips the core by attempting to assume the diameter which the sleeve assumes when under tension. This is illustrated in Figure 4, where the annular clearance 130 is created between the outer surface of the sleeve 105 and the inner surface of the inner barrel 50.

One of the unique advantages of this invention is that core jamming, especially as may take place with fragmented hard abrasive rock is significantly reduced. As mentioned before, core jamming is caused by friction between the core and the inner barrel.

In situations where no elastic core sleeve or stripper tube is used, the newly cut core must push that portion of the core, which is already cut, up the core barrel. Core is essentially "lost" by a cessation of coring caused by the jam before a full core sample can be cut.

In a second situation where elastic or rubber sleeves and stripper are used, the sleeve is not strong enough to prevent the fractured core from spreading, wedging and then jamming, or sharp pieces simply sever the rubber sleeve. Elastomeric core sleeves and other equivalent core sleeves tend to grip the core due to the natural resilience of the material of which the sleeve is made. Being elastomerically resilient, any fracture in the core tends to distend or deform the elastomeric tube due to its natural resilience with the result that the fractured pieces still act as a wedge. In this case, the "normal force", which is one of the elements giving rise to friction between the core and the barrel, is created by the angle of the fracture and the force which is pulling the core upwardly into the elastomeric sleeve in the interior of the barrel 50. Each fracture approximately doubles (assuming the same angle of fracture) the frictional forces which must be overcome as new core enters the barrel. Eventually, this force will exceed the strength of the elastomeric sleeve and it is pulled in two or cut by sharp pieces of rock. The result is that the core becomes jammed as with conventional coring equipment and can fall out of the bit on the way out of the hole because the sleeve is no longer attached to the stripper tube.

The core sleeve of this invention markedly reduces the tendency to jam by tightly gripping the core with significantly greater force than is the case with elastomeric core sleeves. Moreover, since the sleeve 105 is of metal and is capable of gripping the core to provide a clearance between the sleeve 105 and inside surface of the barrel 50, jamming is markedly reduced. Another factor is that the core sleeve 105 of this invention, being affixed to a stripper tube 40, results in the tube lifting the core within the sleeve 105 since the latter grips the core tightly and has significant mechanical strength as compared to an elastomeric or equivalent core sleeve. Another factor is that the core sleeve of this invention resists being cut by the sharp pieces of broken, fractured core. In addition the wire mesh sleeve does not have simply three conditions, namely compressed, normal and tensioned, but a full range of conditions therebetween. The diameter of the sleeve, or the radial force exerted by the sleeve on the core is proportional to the amount of tension or compression exerted on the sleeve.

Moreover, the percentage of core recovery of fractured hard rock, using the wire mesh sleeve of this invention, is substantially greater than that achieved with conventional coring devices in the same formation. The average percentage of recovered core is significantly higher than has been achieved with conventional coring equipment of the prior art. It is believed that the comparatively high core recovery rate is due, at least in part, to the wire mesh sleeve 105 tightly gripping the core and, in the case of formations with many fractures, the tight gripping which results from the tension on the sleeve 105 and tends to reduce the diameter, results in the improved sleeve keeping these fractured pieces in their original in-situ position and keeping them from spreading or falling out of the core sleeve 105 of this invention. Even in instances of unstabilized bottom hole conditions, i.e., core barrel which is undersized with respect to bottom hole diameter, the percentage improvement in core recovery under these adverse conditions is striking.

In a sense, the improved core sleeve of this invention is nonelastic as compared to elastomer or plastic sleeves or stockinette materials as may have been described in the prior art. Even though wire metal cloths have been described, none responds to the application of a tensile force which tends to reduce the diameter of the sleeve in order to grip the core, thereby to maintain a clearance between the outer surface of the sleeve 105 and the inner wall of the inner barrel 50. Thus, even if a jam does occur, for example, in the core catcher or throat of the bit, or even if the core sleeve 105 of this invention should tear at some point along its length, the portion of the core located in that portion of the sleeve attached to the stripper tube 40 is still usually recovered because of the tension-induced tight grip of the sleeve 105 on the core, and because in the preferred embodiment, the sleeve in the relaxed state is slightly smaller than the core.

The coring device may be further improved according to the present invention by forming plurality of wedged shaped annular segments 125 best illustrated in connection with Figures 5 and 6. Segments 125 may be coupled to sleeve 105 in any manner known in the art, such as welding, brazing, riveting of the like. In the illustrated embodiment segments 125 fully overlap sleeve 105 and are brazed to sleeve 105. Segments 125 are separated by portions of sleeve 105 which are flexible and expandable. Those portions of sleeve 105 brazed to segments 125 are, of course, rigid so that the initial inverted separation and later collective formation of segments 125 into a core catcher is accomplished by the expansion of the unattached portions of sleeve 105 between segments 125. The woven mesh of the end of sleeve 105 to which segments 125 are attached may thus be altered in a conventional manner to increase the radial flexibility of the unattached portions of sleeve 105.

Turning now to Figure 5, weight 126 is illustrated just at the point where core sleeve 105 had drawn the plurality of segments 125 around end 112 of inner barrel 50. The upper end 202 of annular segments 125 have just contacted core E and the outer surface 204 of segments 125 are being brought into sliding contact with the inner surface 206 of inner barrel 50. As illustrated in Figure 6 as the core is continued to be cut and moves upwardly in inner barrel 50 with sleeve 105 also moving upwardly with the core, outer surface 204 of segments 202 will be wedged or jammed against inner surface 206 of inner barrel 50 thereby causing segments 125 to constrict and to apply a radially compressive or constricting force about the core. This radially compressive force not only serves to retain the entire column of core within inner barrel 50, but also serves to crush or cut the core free from the contiguous formation, thereby ultimately allowing retrieval of the core according to the ultimate purpose of the coring device.

Although end 112 of inner barrel 50 is shown in Figures 1, 2 and 4 as a rounded end of a circular cylinder of substantially uniform diameter, it is also within the scope of the present invention as illustrated in Figures 5 and 6, that end 112 could be slightly flared outwardly to provide a bell-shaped termination to assist and ease the plurality of segments 200 as they are drawn upwardly within inner barrel 50 and compressed to form a core catcher. In addition, the flared bell serves to stop and hold weight 126 on inner barrel 50. Furthermore, although shown only in sectional sideview in the Figures, plurality of segments 125 collec- tivelyform a multiply split core catcher. One end of each of the segments 125 which collectively form the core catcher, are attached to sleeve 105. When in the configuration of Figures 1, 2 and 4, the segments are separated and positioned upside-down outside inner barrel 50. However, as sleeve 105 moves into inner barrel 50, segments 125 are drawn downwardly along the outside of inner barrel 50, still retaining their upside-down and separated configuration. By the time the core operation has reached the configuration as illustrated in Figure 5, segments 125 begin to be drawn into inner barrel 50 and are inverted to assume their normal orientation as they are drawn upward into the interior of inner barrel 50 to collectively form the core catcher. The core catcher is essentially formed when plurality of segments 125 assume the configuration shown in Figure 6 wherein split segments 125 are wedged by contact with the inner surface of inner barrel 50 to form a tight constricting wedge-shaped cylindrical, annular band.

As described above, sleeve 105 is drawn upwardly under tension and constricts about the core thereby assuming a smaller diameter. The shrinkage in diameter of sleeve 105 serves to assist in the compressive force exerted by the plurality of segments 125 upon the lower end of the core, thereby allowing the core catcher collectively formed by segments 125 to crush and cut the core.

The various modifications previously described may also be used with the embodiments shown in Figures 5 and 6, and it will also be apparent that various other modifications may be made, as will be apparentto those skilled in the art, based on the foregoing specification and described drawings, without departing from the invention as set forth in the appended claims.