Described herein is a “cross-over” connector that can be used with core barrel outer tubes to prevent damage and destruction when they are connected to one another by automated equipment on a rig floor, for example, automated rig-floor torque wrenches. Standard core barrel outer tubes having a pin connector and a box connector are modified by adding “cross-over” sub elements to the pin and box connectors to increase their effective strength. The sub elements include portions which engage respective ones of the pin and box connections. The sub elements are designed to be the contact points for the automated equipment, so that it they are damaged, they can readily be replaced at a lower cost when compared to the scrapping and replacement of the core barrel outer tubes themselves.

FOREIGN PRIORITY 
     This application claims foreign priority to Great Britain Application No. 1210197.8 filed Jun. 11, 2012, the contents of which are hereby incorporated by reference in their entirety. 
     FIELD OF INVENTION 
     The present invention relates to improvements relating to core barrel outer tubes. 
     BACKGROUND TO THE INVENTION 
     Core barrel outer tubes have relatively thin walls at the American Petroleum Institute (API) standard connectors that are used to connect them together in the field. The API connectors comprise “pin”, “male” or screw connectors and “box”, “female” or socket connectors as is well-known. These API connectors are inserted into or formed in the open ends of the core barrel outer tubes. Typically, a “pin” connector is provided at one end of the core barrel outer tube and a box” connector at the other end of the core barrel outer tube. In the field, for example, on a rig floor, a pin connector is joined to a box connector to join two core barrel outer tubes together. 
     “Rig-tongs” have conventionally been used for making the connections between core barrel outer tubes. The pressure applied to the core barrel in the vicinity of the “pin” and “box” connectors by “rig-tongs” is not normally sufficient to cause serious damage to the core barrel outer tubes as they are being connected to one another. However, for reasons of safety, these “rig-tongs” are being replaced by automated equipment, in particular, automated rig-floor torque wrenches. When making connections using automated rig-floor torque wrenches, the core barrel outer tubes may be damaged or destroyed due to one or more of the pressure applied to the thin walls during the connection process; the small distance between automated tongs that causes the tongs to grip directly over the outer tube connection where the wall thickness is the thinnest; and excessive pressure exerted by jaws of such automated tongs to achieve the required torque for a satisfactory connection between the tubes. 
     A conventional way of overcoming the problems created by automated equipment is to replace the entire core barrel outer tube with a stronger, thicker core barrel outer tube. This has the disadvantage of increasing the cost of each core barrel outer tube due to the increased raw material needed to make the stronger, thicker core barrel outer tube, as each core barrel out tube has a typical length of between 8 m and 10 m (between approximately 26 ft and 32 ft). 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a cross-over connection that can resist the pressure applied by automated equipment, and, in particular, automated rig-tongs. 
     In accordance with a first aspect of the present invention, there is provided a connector for core barrel outer tubes having pin and box connectors, the connector comprising: a first portion connectable to one of a pin connector and a box portion; and a second portion connectable to the other of the pin connector and the box connector, the second portion having a second connecting portion and a second outer wall portion; the first and second outer wall portions spaced from the respective first and second connecting portions and substantially thicker than walls of the core barrel outer tubes in the vicinity of the respective pin and box connectors. 
     Advantageously, the connectors of the present invention have much lower material cost than that required to provide stronger core barrel outer tubes. Their use allows commonly-used core barrel outer tubes to be adapted to resist the pressure applied by automated tools when connections are being made, and, hence damage to and destruction of the core barrel outer tubes. 
     Additionally, the connectors of the present invention can easily be adapted for any change in automated equipment, for example, automated rig-floor torque wrenches, used for connecting core barrel tubes together. 
     In one embodiment, the first portion may be connectable to the pin connector and the first connecting portion may include a threaded portion for engagement with the pin connector. In this embodiment, the second portion may be connectable to the box connector and the second connecting portion may include a threaded portion for engagement with the box connector. 
     In an alternative embodiment, the first portion may be connectable to the box connector and the first connection portion may include a threaded portion for engagement with the box connector. In this embodiment, the second portion may be connectable to the pin connector and the second connecting portion may include a threaded portion for engagement with the pin connector. 
     In another embodiment, the first connecting portion of the first portion may comprise a box connector and the first portion may provide a box connector for connection to the second portion. In this embodiment, the second connecting portion of the second portion may comprise a pin connector and the second portion provides a pin connector for connection to the first portion. 
     Preferably, the first and second portions may each include a substantially centralised bore. 
     In accordance with another aspect of the present invention, there is provided a core barrel outer tube having a connector as described above, the first portion being connected to one end of the core barrel outer tube and the second portion being connected to the other end of the core barrel outer tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, reference will now be made, by way of example only, to the accompanying drawings in which: 
         FIG. 1   a  illustrates an end of a conventional core barrel outer tube having a pin connector; 
         FIG. 1   b  illustrates an end of a conventional core barrel outer tube having a box connector; 
         FIG. 1   c  illustrates connected ends of the core barrel outer tubes shown in  FIGS. 1   a  and  1   b;    
         FIG. 2   a  illustrates an end of a core barrel outer tube having a top “cross-over” sub element in accordance with the present invention; 
         FIG. 2   b  illustrates an end of a core barrel outer tube having a bottom °cross-over” sub element in accordance with the present invention; 
         FIG. 2   c  illustrates connected ends of the core barrel outer tube shown in  FIGS. 2   a  and  2   b ; and 
         FIGS. 3   a ,  3   b  and  3   c  illustrate respective assembly stages for the top and bottom cross-over sub element in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. 
     It will be understood that the terms “vertical” and “horizontal” are used herein refer to particular orientations of the Figures and these terms are not limitations to the specific embodiments described herein. In addition, the terms “top” and “bottom” are used to distinguish one end of a core barrel outer tube from the other. 
     In the drilling industry, the term “top” tends to refer to the part of the drilling equipment that is nearest to the surface and the term bottom” tends to refer to the part of the drilling equipment that is furthest from the surface. 
     In accordance with the present invention, a “cross-over” connector is provided which comprises two sub elements which, when connected together, provide a connection for core barrel outer tubes which withstands the pressure exerted by automated equipment used for assembling such core barrel outer tubes. 
     It is known to use a pin with a lateral aperture to secure a core sampler to its associated drill string in core sampling apparatus as described in U.S. Pat. No. 6,095,259. Here, the core sampler is attached to the drilling string by means of a connector that is screwed to the drill string at one end and has the lateral aperture at the other end. The core sampler has a tang in which a lateral aperture is formed that, when aligned with the lateral aperture in the connector, can receive a pin to secure the core sampler to the connector. 
     This particular connector addresses the problem of minimising the amount of time and manpower necessary to retrieve a gathered core sample thereby minimising the impact of core sample retrieval on drilling efficiency. This is achieved by not having to break a threaded connection with the drill string to remove the core sampling apparatus. In this connector, the pin is removed from the aligned lateral apertures of the connector and tang to release the tang and allow the core sampler to be easily be extracted. 
     U.S. Pat. No. 6,860,514 discloses a connector for a drill string in which an adaptor is attached to a starter rod by means of a tapered threaded portion engaging a corresponding tapered threaded socket with inter-engaging profiled surfaces or spline profiles transferring the torque from the starter rod to the adaptor. The end of the adaptor remote from the starter rod includes any conventional coupling or joint that can be used to connect underground directional drilling tools. 
     The use of such an adaptor addresses the problem of severe torque loadings and longitudinal stresses of joints in a drill string and tool due to the mechanical stresses and abrasive conditions in which the drill string and tool operated. These conditions tend to wear threaded joints rapidly requiring frequent replacement as failure of a joint due to thread wear or joint loosening can result in a tool being stuck in a borehole or pipe. 
     In U.S. Pat. No. 6,860,514, the problem of torque loading and longitudinal stresses is addressed by the use of front and rear tapered pilot portions in conjunction with the tapered threaded portion and the tapered threaded socket portion. The use of these pilot portions enables the joint to be further tightened to compensate for thread wear, the threaded end portion being further tightened into the threaded socket by advancing over tapered shoulders of the pilot portions. This engagement with the tapered pilot portions provides additional being moment loading. 
     EP-A-1411207 describes an adaptor coupling for connecting a sail sampler barrel to a drill rod, the adaptor coupling having a barrel adaptor and a rod adaptor for connecting to respective ones of the soil sampler barrel and the drill rod. The adaptor coupling also includes an isolating mechanism which isolates the sampler barrel from any upward vibratory movement of the drill rod so that it only receives downward motion from the drill rod. 
     The problem addressed by this adaptor coupling is to minimise the amount of disturbance of soil samples taken with vibratory drill systems and to reduce the amount of friction between the barrel sampler and the ground. The isolating mechanism in the adaptor coupling overcomes this problem. 
     Whilst various types of connectors are described in U.S. Pat. No. 6,095,259, U.S. Pat. No. 6,860,514 and EP-A-1411207, none of these connectors address the problem of the present invention, that is, to prevent damage and destruction to core barrel outer tubes during their assembly on a drill rig. 
     Referring initially to  FIG. 1   a , a conventional core barrel outer tube  100  is shown having an end  110  having a pin connector  120 .  FIG. 1   b  shows a second core barrel outer tube  100 ′ which is to be connected to the core barrel outer tube  100  shown in  FIG. 1   a . The core barrel outer tube  100 ′ has an end  130  having a box connector  140 . It will be appreciated that the core barrel outer tubes  100 ′ may be identical and each has a pin connector at one end and a box connector at the other end (not shown). When the core barrel outer tubes  100 ,  100 ′ are to be connected, the pin connector  120  of tube  100  is connected to the box connector  140  of tube  100 ′ to form a joint  150  as shown in  FIG. 1   c.    
     In accordance with the present invention, a “cross-over” sub connector is provided. The “cross-over” sub connector comprises sub elements which are attached to core barrel outer tubes so that the core barrel outer tubes can resist the pressure applied to them by automated rig-floor torque wrenches when they are being assembled. The “cross-over” sub elements are effectively paired so that a “top” sub element of one core barrel outer tube is connected to a “bottom” sub element of another core barrel outer tube. By using these “cross-over” sub elements, the core barrel outer tubes remain unaltered and the connections between the “cross-over” sub elements and the tube itself can be made under controlled conditions in a warehouse or other suitable location before sending the core barrel equipment to the rig. On the rig, two core barrel outer tubes are connected to one another so that the sub elements are effectively paired, that is, a “top” sub element is connected to a “bottom” sub element, using automated rig-floor torque wrenches. 
       FIG. 2   a  illustrates a “top” sub element assembly  200  in which a “top” sub element  210  is inserted into an end  220  of a core barrel outer tube  230 . As shown, the “top” sub element  210  has a region  240  that has a thicker wall than the wall of the core barrel outer tube  230 . It is with this region  240  that the automated rig-floor torque wrench (not shown) engages to make the connection between two core barrel outer tubes. 
     It will be appreciated that the end  220  of the core barrel outer tube  230  may comprise a box connector into which the “top” sub element  210  is inserted. The region  240  is spaced from the portion of the “top” sub element  210  that engages with the box connector (not shown). In this way, the pressure applied to the “top” sub element in the region  240  does not damage the core barrel outer tube  230  in the vicinity of the box connector. 
       FIG. 2   b  illustrates a “bottom” sub element assembly  250  in which a “bottom” sub element  260  is inserted into an end  270  of a core barrel outer tube  230 ′. As shown, the “bottom” sub element  260  has a region  280  that has a thicker wall than the wall of the core barrel outer tube  230 ′. It is with this region  280  that the automated rig-floor torque wrench (not shown) engages to make the connection between two core barrel outer tubes. 
     It will be appreciated that the end  270  of the core barrel outer tube  230 ′ may comprise a pin connector into which the “bottom” sub element  260  is attached. The region  280  is spaced from the portion of the “bottom” sub element  260  that engages with the pin connector (not shown). In this way, the pressure applied to the “bottom” sub element in the region  280  does not damage the core barrel outer tube  230  in the vicinity of the pin connector. 
       FIG. 2   c  illustrates two core barrel outer tubes  230 ,  230 ′ connected together by means of respective “top” and “bottom” sub elements  210 ,  260  to form a joint  290 . 
     Although the “top” sub element  210  and the “bottom” sub element  260  are described as connecting to the core barrel outer tube by means of respective box and pin connectors, it will be appreciated that the “top” sub element  210  and the “bottom” sub element  260  may connect to a pin and a box connector respectively. 
     In another embodiment, the core barrel outer tubes may comprise either box or pin connectors only, and in this case, the “cross over” sub elements may comprise either pin or box connectors only as appropriate. 
     Each of the “top” and “bottom” sub elements of the connector of the present invention may comprise a “pin-to-pin” sub element where one pin engages a box connector of the core barrel outer tube and the other pin engages a box connector of the other sub element. 
     Similarly, each of the “top” and “bottom” sub elements of the connector of the present invention may comprise a “box-to-box” sub element where on box engages a pin connector of the core barrel outer tube and the other box engages a pin connector of the other sub element. 
     However, it may be preferred that each of the “top” and “bottom” sub elements comprise conventional “pin-to-box” and/or “box-to-pin” sub elements. In the former case, the pin engages the box connector of the core barrel outer tube and the box engages the pin connector of the other sub element, and in the latter case, the box engages the pin connector of the core barrel outer tube and the pin engages the box connector of the other sub element. 
       FIGS. 3   a ,  3   b  and  3   c  illustrate respective stages in the assembly of the sub elements with a core barrel outer tube in a warehouse or other suitable location. 
       FIG. 3   a  shows a conventional core barrel outer tube  300  having a pin connector  310  at one end and a box connector  320  at the other end. 
       FIG. 3   b  illustrates a “bottom” sub element  330  being added to the pin connector  310  with the “bottom” sub element  330  having a portion  340  which engages and surrounds the pin connector  310 . Similarly, at the other end, a “top” sub element  350  is added to the box connector  320  with the “top” sub element  350  having a portion  360  that engages with the box connector  320  as shown. 
     In  FIG. 3   c , an assembled core barrel outer tube  300 ′ with respective “top” and “bottom” sub elements  330 ′,  350 ′ is shown. 
     Once the core barrel outer tubes  300 ′ are on the rig, they can be assembled using the stronger and thicker connections provided by the “top” and “bottom” sub elements so that the core barrel outer tube itself is not damaged. 
     The use of the sub elements provides stronger and thicker connections than the ones provided between pin and box connectors of core barrel outer tubes. Whilst the inner diameter of each sub element is substantially the same as the core barrel outer tube itself, their outer diameter is larger than the outer diameter of the tube thereby providing thicker walls which are stronger for engaging with automated rig-floor torque wrenches when connecting one core barrel outer tube to another. 
     Each core barrel outer tube is inspected after each run, and, if the sub elements do not pass inspection criteria, they can be scrapped rather than having to scrap an entire core barrel outer tube. 
     Each sub element pair, namely, a “top” and a ‘bottom” sub element, can be configured to meet the changing needs of automated rig-floor torque wrenches. This means that it is possible to react rapidly to any change in the type of torque wrenches used on the rig floor at reduced cost as only the “cross-over” connector or sub element pair needs to be modified and not the core barrel outer tube itself. 
     Additionally, current stocks of core barrel outer tubes that were designed for conventional non-automated tools can be updated by the simple addition of the sub element pairs so that they can readily be used with automated tools without having to be redesigned. 
     The “cross-over” sub elements can be made from a different material to the core barrel outer tube due to their substantially shorter lengths, a wider range of materials and raw material stock sizes being available for the shorter lengths. 
     The weakest part of a conventional core barrel outer tube is its threaded connections as the cross-section through the tube at these points is reduced. Frequent connections and disconnections increase the wear of the tube and therefore decrease its useful life. The use of the “cross-over” sub connections increases the useful life of each core barrel outer tube with which they are used. Each core barrel outer tube can effectively be refurbished when the “cross-over” sub element forming the “cross-over” sub connection can be replaced without damaging the core barrel outer tube itself. 
     Although the present invention is described in relation to core barrel outer tubes, it will be appreciated that the “cross-over” connectors as described above can be used in any situation where pressure is applied to a relatively weak portion of a drill string during its assembly.