| 1. | 1 A core barrel system comprising an outer core barrel, an inner core barrel mounted within the outer core barrel, a core receiving means mounted within the inner core barrel, and support formations extending into the inner core barrel, the inner core barrel comprising a number of tubular members coupled by coupling means in end to end relationship, and the core receiving means comprising a number of tubes mounted end to end within the inner core barrel on said support formations which extend to support the core receiving means against movement in a direction parallel to the longitudinal axis of the inner core barrel. |
| 2. | A core barrel system as claimed in Claim 1, wherein at least one support formation is located adjacent an end of each tubular member forming the inner core barrel. |
| 3. | A core barrel system as claimed in Claim 2, wherein the support formations are in the form of support members which are located between adjacent ends of adjacent tubular members forming the inner core barrel when the tubular members are coupled to each other. |
| 4. | A core barrel system as claimed in any preceding Claim, wherein each of said support formations is in the form of an annular ring which extends inwardly from the inside surface of the inner core barrel. |
| 5. | A core barrel system as claimed in Claim 4, wherein the annular ring is a split ring configured so as to permit removal of one section of the ring from the inner core barrel while another section of the ring is retained between adjacent tubular members. A core barrel system as claimed in any preceding Claim, wherein the coupling means comprises an annular nut which engages threads on an end of one tubular member and a shoulder formation on an adjacent end of another tubular member. A core barrel system as claimed in any preceding Claim, wherein the core receiving means comprises a number of tubular sections, each tubular section being located between adjacent support formations. A core barrel system as claimed in any preceding Claim, wherein the core receiving means has a number of apertures therein to permit gas located within the core receiving means to pass from the inside of the core receiving means to the outside of the core receiving means. A core barrel system as claimed in any preceding Claim, wherein the core receiving means is mounted substantially concentrically within the inner core barrel. A core barrel system as claimed in any preceding Claim, wherein the apparatus also comprises centralising means to centralise the inner core barrel within the outer core barrel. A core barrel system as claimed Claim 10, wherein the centralising means is located on the external surface of the coupling means coupling the members to each other. A core barrel system as claimed in any preceding Claim, wherein the core receiving means is in the form of a liner which may be expendable and may be manufactured from a plastics material, such as polycarbonate, or from glass reinforced plastic, fibreglass, aluminium or steel. A core barrel system substantially as hereinbefore described with reference to and as shown in the accompanying drawings. |
The invention relates to a core barrel system and in particular, a core barrel system for obtaining geological core samples from a borehole during drilling of the borehole.
Conventional core barrel systems use an outer steel barrel and an inner barrel mounted within the outer barrel. As the borehole is drilled, the core sample enters the inner core barrel through a central aperture in the drill bit and as the hole is bored, the core slides up inside the inner barrel.
Typically, the inner barrel comprises a number of tubes coupled together by threaded joints. Typically, the tubes are manufactured from steel where the inner core barrel is reusable, or aluminium or fibreglass where the inner core barrel is intended to be expendable.
In recent years it has also become an option to use a plastic liner inside the outer barrel, the plastic liner typically being polycarbonate. However, one of
the problems with plastic liners is that, although the cost is reduced, the compression loading performance of the plastic liner is poor in relation to the compression loading capabilities of steel, aluminium or fibreglass. Hence, the use of plastic liners has only been successful for cores up to 60 feet long. However, due to the time involved in pulling a drill string out of a borehole and running the drill string back into the borehole, it is desirable to have core barrel systems which can produce core lengths of at least 90 feet in length, and preferably over 100 feet long.
While core lengths of over 100 feet can be achieved using inner core barrels made of steel, aluminium or fibreglass there are also problems associated with these conventional inner barrels .
In particular, a typical core will be located within a number of tubes which are joined together end to end to form the inner core barrel. Therefore, it is necessary to split the tubes forming the core barrel in order to retrieve the core from the inner core barrel. Rotation of the inner core barrel tubes with respect to each other to separate the joints causes rotational stress on the core within the inner tubes and can cause damage and break-up of the core. In addition, the tubes within which the core is located have to be separated in order to pass a conventional shear plate between adjacent tubes in order that each tube and corresponding core can be removed from the drill string. The insertion of the shear plate through the core and the pulling apart of the adjacent tubes can also cause damage to the core within the tubes.
Furthermore, debris from a damaged core will often
collect in the box thread at the top of the next tube to be removed. Any debris located in the box thread must be removed from the thread prior to insertion of a lifting cap into the box thread to lift the tube up in order to permit these to be separated from the next lower tube.
There is also the problem with existing core barrel systems of safely venting gases which may be present in the core sample obtained. Typically, in the borehole, gases in the rock formation are at a pressure which is greater than the pressure at the surface. As the core sample is brought to the surface, the pressure of any gas within the core sample remains at its original pressure in the rock formation and separation of the tubes on the surface can cause a sudden and unpredictable release of the gas. This can result in injury or damage if the gas pressure is sufficient to blow off a tube as it is being disconnected.
In accordance with the present invention, a core barrel system comprises an outer core barrel, an inner core barrel mounted within the outer core barrel, a core receiving means mounted within the inner core barrel, and support formations extending into the inner core barrel, the inner core barrel comprising a number of tubular members coupled by coupling means in end to end relationship, and the core receiving means comprising a number of tubes mounted end to end within the inner core barrel on said support formations which extend to support the core receiving means against movement in a direction parallel to the longitudinal axis of the inner core barrel.
Preferably, at least one support formation is located
adjacent an end of each tubular member forming the inner core barrel.
Typically, the support formations may be in the form of support members which are located between adjacent ends of adjacent tubular members forming the inner core barrel when the tubular members are coupled to each other.
Preferably, the support formations may be in the form of an annular ring which extends inwardly from the inside surface of the inner core barrel.
Typically, the annular ring may be a split ring configured so as to permit removal of one section of the ring from the inner core barrel while another section of the ring is retained between adjacent tubular members.
Preferably, adjacent tubular members are coupled together by an annular nut which engages threads on an end of one tubular member and a shoulder formation on an adjacent end of another tubular member.
Preferably, the core receiving means comprises a number of tubular sections, each tubular section being located between adjacent support formations.
Preferably, the core receiving means may have a number of apertures therein to permit gas located within the core receiving means to pass from the inside of the core receiving means to the outside of the core receiving means.
Preferably, the core receiving means is mounted
substantially concentrically within the inner core barrel.
Preferably, the apparatus also comprises centralising means to centralise the inner core barrel within the outer core barrel.
Preferably, the centralising means is located on the external surface of the coupling means coupling the members to each other.
Typically, the core receiving means may be in the form of a liner which may be expendable and may be manufactured from a plastics material, such as polycarbonate, or from glass reinforced plastic, fibreglass, aluminium or steel.
An example of a core barrel system according to the invention will be described with reference to the accompanying drawings, in which:-
Fig. 1 is a cross-sectional view through a core barrel system; and, Fig. 2 is a perspective view of shear plate clamp for use with the system shown in Fig. 1.
Fig. 1 shows a core barrel system 1 which comprises an outer core barrel 2, an inner core barrel 3 formed from a number of steel tubular members 4 (only two shown 4a, 4b) . Each tubular member 4 has a shoulder end portion 5 at one end and threaded end portion 6 at the other end. A threaded nut 7 is held captive on the shoulder end portion 5 by shoulder 8 on the shoulder end portion 5 and an end 9 of the tubular member 4, which traps a shoulder portion 10 on the nut 7. The opposite end of
the nut 7 from the end 10 has a female thread 11 formed on it which engages with a male thread 12 on the external surface of the threaded end portion 6.
Located between the adjacent ends of the shoulder portion 5 and threaded portion 6 is a split ring 13 which comprises two half portions 13a, 13b. A plastic tubular liner 14a, 14b abuts against each side of the split ring 13.
Formed on the outside of the nut 7 are ribs 15 which act as a centraliser to centralise the inner barrel 3 within the outer barrel 2.
In operation, the end portions 5, 6 are permanently attached to opposite ends of each of the steel tubes 4a, 4b. In order to assemble the core barrel system 1, plastic liner 14a is inserted into lower tube 4a. Upper tube 4b, with the threaded end portion 6, is then lowered into position trapping split ring 13 between the adjacent ends of the portions 5, 6 of the lower tube 4a and the upper tube 4b, respectively. The nut 7 is then moved upwards and rotated to engage the threads 11, 12 so as to securely clamp the split ring 13 between the portions 5, 6. The upper liner 14b can then be inserted into tube 4b and as the inner core barrel 3 is moved down within the outer core barrel 2, the upper tube 4b and upper liner 14b become the lower tube and liner when they are lowered so that end portion 5 of the tube 4b is in the position corresponding to the end portion 5 of tube 4a in Fig. 1. A further split ring 13 and tube 4 are then added and the process is then continued until the desired length of inner core barrel 3 is obtained. The upper end of the outer barrel 2 is then coupled on to
the lower end of the upper drill string.
The core barrel system 1 is then run in the usual manner into a borehole above a drill bit. During drilling the core sample enters into the liners 14 and passes upwards through the liners 14.
After the desired core length has been reached the drill string can be retrieved from the borehole and the inner core barrel 3, with the liners 14, removed from the outer core barrel 2.
Each liner 14 has a number of apertures 17 which permit gas within core sample in the liner members 14 to pass from the inside of the liners 14 into annulus 16 between the inner core barrel 3 and the liners 14.
As the nut 7 is unscrewed in order to release the upper tube 4b from the lower tube 4a any excess gas pressure is controllably released during unscrewing of the nut 7.
After the nut 7 has been unscrewed from thread 12 on the threaded end portion 6, one half 13a of the split ring 13 may be removed and a shear plate clamp 20 (see Fig. 2) may be placed around the threaded end portion 6 and shoulder end portion 5. The clamp 20 comprises two half sections 21, 22 coupled together by a hinge 23. A shoulder 24 on each half 21, 22 abuts against shoulder 25 on the threaded end portion 6 and prevents downward movement of the clamp 20 after the clamp 20 has been secured around the inner core barrel 3.
The clamp 20 is secured in position by a conventional bolting system which secures the two halves
diametrically opposite the hinge 23. Each clamp half 21, 22 has a slot 26 therein and, with the clamp 20 secured around the inner core barrel 3 with the shoulder 24 engaging the shoulder 25, the slot 26 corresponds to the position of the split ring 13. This permits a conventional shear plate (not shown) to be inserted into the slot 26 to split the core sample within the liner 14. As the shear plate is pushed through the core sample, the other half 13b of the split ring 13 is pushed out of the liner 14 and inner core barrel 3 so that the shear plate separates the core sample in the upper liner 14b from the core sample in the lower liner 14a.
The upper tube 4b with the clamp 20 still attached can then be removed from the lower tube 4a and the core sample in the liner 14b subsequently removed from the liner 14b.
The operation is then repeated for the core sample within the lower liner 14a by engaging a core barrel lifting cap with female thread 11 on the nut 7 in order to pull the lower tube 4a upwards to permit a shear clamp 20 to be placed around threaded end portion 6 of the tube 4a so that the core sample within the liner 14a and tube 4a can then be removed in a similar manner to that described above for the core sample in liner 14b.
The advantages of the invention are that during removal of the core sample there is no relative rotation of the adjacent tubes 4a, 4b and tubes 4a, 4b do not require to be moved axially in order to insert the shear plate. In addition, the liners 14 are supported against axial movement and against axial forces by the split ring 13
located between adjacent tube liners 14a, 14b.
Furthermore, the apertures 17 provide for venting of gases within the core sample in a controllable manner and ribs 15 on the exterior surface of the nuts 7 centralise the inner barrel 3 within the outer barrel 2.
Modifications and improvements may be incorporated without departing from the scope of the invention.