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Title:
ROTARY CORING APPARATUS
Document Type and Number:
WIPO Patent Application WO/2016/191792
Kind Code:
A1
Abstract:
A coring bit (5) suitable for use in coring apparatus (100). The coring bit (5) comprising a main body (40) and a cutting head (45) at one end (41) of the main body (40). The cutting head (45) comprising a generally cylindrical side wall (46) and an annular peripheral rim (22) remote from the main body (40). The rim (22) having an outer annular surface (48) providing for a cutting surface (49), the annular surface being generally continuous or uninterrupted.

Inventors:
PAYOR STEPHEN DAVID (AU)
Application Number:
PCT/AU2015/050599
Publication Date:
December 08, 2016
Filing Date:
October 02, 2015
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
BENTHIC GEOTECH PTY LTD (AU)
International Classes:
E21B10/02; E21B10/60; E21B25/06; E21B25/10; E21B25/18
Foreign References:
US2532716A1950-12-05
US4300643A1981-11-17
US2503561A1950-04-11
JP2005113383A2005-04-28
CN204175218U2015-02-25
US20100133014A12010-06-03
Attorney, Agent or Firm:
DAVIES COLLISON CAVE (255 Elizabeth StreetSydney, New South Wales 2000, AU)
Download PDF:
Claims:
The claims.

1. A coring bit (5) for use in coring apparatus (100), the coring bit (5) comprising a main body (40), and a cutting head (45) at one end (41) of the main body (40), the cutting head (45) comprising an annular peripheral rim (22), the rim (22) having an outer annular surface (48) providing a cutting surface (49), and the outer annular surface (48) is substantially continuous or uninterrupted.

2. The coring bit according to claim 1, wherein the main body (40) is generally tubular, and the main body (40) and the outer annular surface (48) are coaxially aligned along a central axis (110).

3. The coring bit according to claim 2, including a generally cylindrical side wall (46) and a plurality of passageways (23), the passageways (23) arranged around the side wall (46) and extending through the side wall (46).

4. The coring bit according to claim 3, wherein the passageways (23) are angled with respect to the central axis (110).

5. The coring bit according to claim 3 or claim 4, wherein each passageway (23) is associated with a slot (51) in the cutting head (45).

6. The coring bit according to claim 5, including a shoulder (56) on the inner surface of the side wall (46) adjacent said one end.

7. The coring bit according to any one of claims 1 to 6, wherein the coring bit is of a thin- kerf type.

8. A coring apparatus (100) comprising:

a rotatable head (2), the rotatable head (2) comprising a bearing assembly (8); an outer tubular member (1) operatively connected to the rotatable head (2) to be rotatable about a central rotation axis (110);

an inner tubular member (3) disposed within the outer tubular member (1) and arranged to remain stationary relative to the outer tubular member (1) when the outer tubular member (1) is rotating during operation of the apparatus (100), and the inner tubular member (3) being operatively connected to the bearing assembly (8);

a coring bit (5) operatively connected to the outer tubular member (1) for rotation therewith during operation of the apparatus (100);

a core catcher assembly (4) disposed within the coring bit (5) and located adjacent the inner tubular member (3); and,

a spindle (9) to which the bearing assembly (8) is operatively mounted so as to facilitate externally accessible axial adjustment relative to the outer tubular member (1).

9. The coring apparatus according to claim 8, wherein the core catcher assembly (4) comprises a first core catcher (20) and a second core catcher (21).

10. The coring apparatus according to claim 8 or 9, including an annular passage (12) between the inner tubular member (3) and the outer tubular member (1), and including a fluid inlet (11) through which fluid can be delivered to the annular passage (12), a valving arrangement associated with the fluid inlet (11), the valving arrangement being capable of adopting a first mode of operation in which fluid is inhibited from flow through the inlet to the annular passage and a second mode of operation in which back flow of fluid from the passage through the inlet is inhibited.

11. The coring apparatus (100) according to any one of claims 8 to 10, wherein the coring bit (5) is in accordance with any one of claims 1 to 7.

12. The coring apparatus according to any one of claims 8 to 11, wherein the first core catcher (20) is suitable for handling relatively hard rigid materials and the second core catcher (21) is suitable for handling relatively soft unconsolidated materials, and the core catcher assembly (4) comprises a core catcher casing which includes an extension (25) at one end which is adapted to be located adjacent a shoulder (56) on the inner surface of a side wall (46) when in an assembled position.

13. A double-tube coring assembly that comprises:

an outer tube (1), a rotating head (2) containing a spindle (9), a bearing assembly (8) rotatable and axially movable on the spindle (9), and a tube adapter (7) connected to the bearing assembly (8);

a non-rotating disposable inner tube (3) of substantially rigid material connected at an upper end to the tube adapter (7);

a core catcher case (19) connected to a lower end of the inner tube (3); at least one core catcher (20, 21); and

a coring bit (5) connected to the outer tube (1), the coring bit (5) having a continuous smooth cutting rim (22).

14. The double-tube coring assembly of claim 13, wherein the disposable inner tube (3) has ends that push fit into the tube adapter (7) and the core catcher case (19).

15. The double-tube coring assembly of claim 13 or 14, wherein the inner tube (3) is vented by passages (13) to an annular passage (12).

16. The double-tube coring assembly of any one of claims 13 to 15, wherein the lower edge of the core catcher case (19) forms a spigot that engages an opposing inner shoulder (26) of the coring bit (5) in close proximity to the cutting rim (22).

17. The double-tube coring assembly of any one of claims 13 to 16, wherein the coring bit (5) has a plurality of outwardly directed fluid passages (23) connecting from the annular space (12) between the inner tube (3) and the outer tube (1) to the perimeter of the coring bit (5).

18. The double-tube coring assembly of any one of claims 13 to 17, including a first core catcher (20) and a second core catcher (21).

19. The double-tube coring assembly of claim 18, wherein the second core catcher (21) has the same external diameter as the inner tube (3) and when fully open has the same internal diameter as the inner tube (3).

20. The double-tube coring assembly of any one of claims 13 to 19, wherein the spindle (9) is axially adjustable by external access to threaded connection and a locknut (10).

21. The double-tube coring assembly of any one of claims 13 to 20, including a dual function valve, with a first function as a stop valve to shut off downward flow of drilling fluid and a second function as a non-return valve to stop upward backflow through the coring assembly.

22. The double-tube coring assembly of claim 21, wherein the dual function valve includes a compressible resilient lip seal (14).

23. The double-tube coring assembly of claim 21, wherein the dual function valve includes at least one ball check valve assembly (17).

24. The double tube coring assembly of claim 18, wherein the second core catcher (21) comprises a plurality of fingers (27) of spring biased sheet material.

25. The double tube coring assembly of claim 24, wherein the fingers (27) are attached at their lower ends (28) to a mounting sleeve (26) and geometrically arranged such that adjacent edges overlap substantially along their full length.

26. The double tube coring assembly of claim 25, wherein inner exposed edges of the fingers (27) trail a direction of rotation of the coring assembly, and the free ends of the fingers (27) are spring biased upwards and radially inwards. The double tube coring assembly of claim 25 or 26, wherein the fingers (27) are formed from a one-piece cut-out of sheet material (31) with a notched profile (32) to create an overlap of individual fingers when double-wrapped and fixed inside the mounting sleeve (26).

Description:
ROTARY CORING APPARATUS

Technical Field

This disclosure relates to apparatus for obtaining geotechnical core samples of rock and soil, and more particularly relates to a coring apparatus which is suitable for sampling weak and fragile formations.

Background Art

Extraction of rock and soil samples for geotechnical or geoscientific investigation widely relies on the use of rotary diamond coring tools. Thin-kerf double-tube core barrels are well known in practice. These have a rotating outer tube with an annular cutting bit on the leading edge and a stationary inner tube which receives the cylindrical core sample as the barrel assembly advances into the borehole. The objective is to recover the core sample as completely as possible and with as little disturbance to its original stratigraphic arrangement as possible. A core lifter or catcher is provided at the end of the barrel to retain the core in the inner tube when the laden barrel is lifted from the hole. Drilling fluid (water, mud or water/synthetic polymer solution) for the purpose of cooling the cutting face of the bit and removing the cuttings, is pumped through an annular passage between the outer and inner tubes to exit at the bit. The fluid may discharge either radially through an annular gap inside the core bit or axially through a number of passages in the face of the bit.

The advent of small portable drilling rigs that are remotely deployed on the seafloor for geotechnical investigation of sub- seabed formations creates a requirement for specialized coring tools. Such seabed drilling and sampling platforms can carry only a limited quantity of tools, therefore to maximize sub-seabed penetration capability they must preferably use relatively small diameter coring tools of compact, lightweight construction and be capable of achieving maximum recovery of high quality core samples. Significant problems are encountered when coring certain types of weak, fragile formations such as variable reef limestone and calcarenite that may contain features (fractures and voids) larger than the core diameter and interspersed layers of unconsolidated material. Adaptation of the thin-kerf barrel offers the most appropriate solution to this situation. For a given tool diameter, reducing the kerf width (the width of material removed by the cut) to a minimum dramatically alters the balance of forces at the bit in favour of greater strength of the core, while simultaneously reducing the forces trying to fracture the core. Reducing the kerf width also enhances productivity by reducing the amount of material needed to be cut from the borehole per unit length of core. Typically, core samples greater than approximately 70mm diameter are preferred for geotechnical evaluation and are cut using tools with kerf widths in the range 7 to 11mm. This typically represents the kerf accounting for 30% to 45% of the total material drilled.

Known thin-kerf coring tools characteristically have "crowned" cutting bits, in which the cutting face is divided into a number of arcuate segments. The segments are separated by radial channels or slots for passage of drilling fluid to the cutting elements from nozzles discharging around the core or at the face. Cutting surfaces may be variously a plurality of poly cry stalline diamond teeth, surface set diamonds or impregnated diamond matrix material.

The disadvantages of these known thin-kerf tools are significant particularly when applied to coring fragile, weakly cemented formations. Any coring bits with "teeth" or projecting elements, such as surface set diamonds, tend to apply excessive loads that tear the formation apart and disrupt the core structure. For similar reasons, bits with slots in the cutting face also give poor results.

A further disadvantage of the conventional double-tube barrel is that the drilling fluid exits inside the bit and is directed inwards towards the core. This can result in scouring or washout of soft core samples, to the detriment of good core recovery and quality. Moreover, in some known types of coring barrels the inner tube is vented externally, allowing high pressure drilling fluid to push loose flakes of core to the top of the tube, invariably resulting in delaminated and totally disturbed core in some types of formation such as soft shales. Conventional friction collet types of core lifter or catcher used in rotary core barrels are suited for gripping relatively competent rock, but are often ineffective for retaining the sample when coring weaker formations. The friction core lifter or catcher relies on capturing a plug of hard material to close the end of the barrel and prevent the core sample falling out during retrieval of the barrel from the borehole and subsequent handling. If the sample happens to consist of weak or unconsolidated material, the sample can easily be lost through the core lifter. Alternative core catcher designs are known in which a number of thin wedge shaped segments are arranged to hinge or spring radially inwards, acting as a one-way "valve". The segments are intended to open and allow free upward movement of the core but engage the core in downward movement and close off the tube. However the wedge-shaped segments move apart on opening, are individually weak, can be easily damaged or jam, and may be only partially effective in retaining the core sample. Other types of positively driven mechanical or hydraulic core catchers are also known, however these tend to be complex and difficult to implement on small diameter tools.

To maximize productivity together with penetration capability it is also desirable to maximize the length of core capacity relative to the overall length of each core barrel. Conventional types of rotary core barrels are disadvantageous in that the head assembly and stabiliser occupy a significant portion of the total tool length, leaving a less than desirable length for core recovery in the barrel. For example a typical 3 metre long core barrel will hold only about 77% of its length in core. Moreover, conventional rotary core barrels require the use of spacer washers or internal adjustment of the head assembly to accommodate manufacturing tolerances during mechanical assembly. This results in an inconvenient procedure requiring trial assembly and disassembly to fit spacer washers or to access internal adjustment features.

A particular problem encountered in coring fine sands is the backflow of water from the formation that occurs when the drilling fluid flow must be shut off during drill rod changing. This backward flow up through the core barrel and drill string, due to residual excess water pressure in the borehole formation, can carry fine sand into the narrow passages of the core barrel. When downward flow of drilling fluid is resumed, the fine sand can block the passages and consequently cause a sudden high pressure in the annular space between the outer and inner tubes, with a tendency to crush the inner tube. Summary of the Disclosure

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

According to one aspect, embodiments are disclosed of a coring bit for use in coring apparatus, the coring bit comprising a main body, and a cutting head at one end of the main body, the cutting head comprising an annular peripheral rim, the rim having an outer annular surface providing a cutting surface, and the outer annular surface is substantially continuous or uninterrupted.

In example embodiments, the main body is generally tubular, and the main body and the outer annular surface are coaxially aligned along a central axis.

In example embodiments, the main body is generally tubular having a central axis, the annular cutting surface being coaxial with the central axis and facing away from the main body.

In example embodiments, the coring bit includes a plurality of passageways, the passageways being arranged around the periphery of the side wall and extending through the side wall.

In example embodiments, the passageways are angled, e.g. angularly inclined, with respect to the central axis, preferably towards the rim. In example embodiments, each passageway is associated with a slot, preferably in the cutting head or in an outer surface of the side wall.

In example embodiments, the coring bit includes a shoulder on the inner surface of the side wall adjacent said one end.

In example embodiments, the coring bit is of a thin-kerf type. According to another aspect, embodiments are disclosed of a coring apparatus comprising: a rotatable head; an outer tubular member operatively connected to the rotatable head to be rotatable about a central rotation axis; an inner tubular member disposed within the outer tubular member, and arranged to remain stationary relative to the outer tubular member when the outer tubular member is rotating during operation of the apparatus; a coring bit operatively connected to the outer tubular member for rotation therewith during operation of the apparatus; and a core catcher assembly disposed within the coring bit and located adjacent the inner tubular member.

In example embodiments, the head comprises a bearing assembly, the inner tubular member being operatively connected to the bearing assembly.

In example embodiments, the apparatus includes a spindle to which the bearing assembly is operatively mounted so as to facilitate externally accessible axial adjustment relative to the outer tubular member. In certain embodiments a locknut is provided which is associated with the spindle and facilitates external accessible adjustment.

In example embodiments, the core catcher device comprises a first core catcher suitable for handling relatively hard rigid materials and a second core catcher suitable for handling relatively soft unconsolidated materials.

In example embodiments, the coring apparatus includes an annular passage between the inner and outer tubular members.

In example embodiments, the coring apparatus includes a fluid inlet through which fluid can be delivered to the annular passage, a valving arrangement associated with the fluid inlet the valving arrangement being capable of adopting a first mode of operation in which fluid is inhibited from flow through the inlet to the annular passage and a second mode of operation in which back flow of fluid from the passage through the inlet is inhibited. In example embodiments, the core catcher assembly comprises a core catcher casing which includes an extension at one end which is adapted to be located closely adjacent the inner shoulder of the cutting bit when in an assembled position providing for a small running clearance.

The disclosure in another example aspect comprises a double-tube coring assembly that includes a rotating outer tube and head assembly, an internal bearing assembly and a disposable inner tube adapted at its upper end to attach to the bearing assembly, allowing the inner tube to remain stationary. The inner tube is adapted at its lower end to attach to a core lifter assembly comprising a core lifter case with provision for a dual core catcher arrangement of a soft soil type catcher and a conventional rock core lifter in series. Pressurised drilling fluid, typically seawater in the case of marine drilling operations, flows in an annular passage formed between the inner and outer tubes, while a venting passage provides pressure equalization between the inside of the inner tube and the annular passage.

In example embodiments, the outer tube has a conventional type of reamer at the lower end. A special thin-kerf coring bit attaches to the reamer to complete the coring assembly. The outer tube assembly has overall length to suit the length of the inner sample tube. The head and bearing assemblies are arranged in a way that minimizes their length in proportion to the overall length of the coring assembly and that also provides easy external access for adjustment to accommodate assembly tolerances in the length of component parts. By way of example, a coring assembly 3m long x 88mm outer diameter with a thin kerf of 8mm produces 72mm diameter core to 92% of the overall length of the tool assembly. For servicing and lubrication, the bearing assembly is provided with an externally accessible grease nipple, or alternative self- sealing connector or solid plug or cap.

In example embodiments, the thin-kerf cutting bit is preferably diamond impregnated material, and provided with an extended portion in the form of a continuous (unsegmented) smooth- edged cutting rim. A number of holes form connecting passages through to the perimeter of the bit from the annular passage between the outer and inner tubes. Drilling fluid flow is thereby dispersed away from direct contact with the core, but is sufficient to cool and lubricate the smooth-edged cutting rim and remove the cuttings. The core catcher case overlaps the inner shoulder of the cutting bit to form a rotating bearing and seal that minimizes fluid influx to prevent erosion of soft or unconsolidated core. An extended portion of the core lifter case reaches within 3 to 4mm of the cutting face. This limits the distance the core must travel inside the rotating bit before entering the non-rotating spigot portion of the core lifter case, thus minimizing exposure of fragile cores to disruptive forces.

In example embodiments, the second core catcher is contained directly above the lower core lifter and is a type of soft soil catcher such as a finger, diaphragm, spoon or sock type catcher. A preferred type of catcher comprises a number of thin fingers or strips of lightly spring biased material, fixed such that their edges overlap along their full length and their free ends project upwards and radially inwards, forming a type of iris diaphragm. These spring fingers readily move aside while remaining overlapped, to allow free upward passage of the core sample without significant disturbance. When the laden barrel is lifted and the core tends to fall downwards under gravity, in the case of soft or unconsolidated core, the spring fingers engage the core and move inwards to a closed position under the weight of core resting above. In the case of solid cores where the spring fingers do not grip sufficiently, the conventional lower rock core lifter engages to hold the core in place. In example embodiments, the inner diameter of the or each core catcher is the same as that of the inner tubular member.

In example embodiments, the disposable liner tube is removed from the coring assembly with the core intact, and a fresh tube fitted into the assembly for further use. The core laden sample tube can be sealed and stored with minimal handling and disturbance of the contents. With an inner tube of clear plastic, this is particularly advantageous for visually inspecting the core while preserving its integrity, especially when dealing with weak or friable samples and small diameter cores.

Overall, it will be appreciated that the features embodied in the embodiments disclosed provide one or more advantages of maximized core diameter, simpler construction, easier maintenance and assembling, and higher productivity, combined with the advantages that a disposable inner tube offers for core visualisation and better handling. The dual core catcher provides the capability to capture cores reliably through sequences of hard and soft or poorly consolidated material which may be encountered in layered formations. The thin-kerf coring bit with a smooth, continuous rim, outwardly directed drilling fluid passages and minimal distance of the core passing unsupported through the bit substantially reduces the possibility of core disturbance or erosion.

Other aspects, features, and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying figures, which are a part of this disclosure and which illustrate, by way of example, principles of one or more inventions disclosed.

Brief Description of the Figures

Notwithstanding any other forms which may fall within the scope of the example embodiments as set forth in the Summary, specific example embodiments will now be described, by way of illustrative example, and with reference to the accompanying figures.

Figure 1 is a sectional side elevation of an example coring apparatus;

Figure 2 is a sectional side elevation of part of the coring apparatus shown in figure 1 ;

Figure 3 is a further embodiment of coring apparatus of the type shown in figure 1;

Figure 4 is a side view of an example coring bit;

Figure 5 is an end view of the coring bit shown in figure 4;

Figure 6 is a sectional view of the coring bit shown in figures 4 and 5 together with an example core catcher assembly;

Figure 7 is a detailed view of part of the coring bit circled in figure 6;

Figure 8 is a top view of an example core catcher in one operating position;

Figure 9 is a sectional view of the core catcher shown in figure 8;

Figure 10 is a bottom view of the core catcher shown in figures 8 and 9;

Figure 11 is a plan view of the core catcher shown in figures 8, 9 and 10 in another operating position;

Figures 12 and 13 are sectional views of the catcher in the position shown in figure 11 ; and - Si -

Figure 14 shows the development of an example one-piece double wrap profile of an example core catcher.

Detailed Description of Preferred Embodiments

The following modes, given by way of example only, are described in order to provide a more precise understanding of the subject matter of a preferred embodiment or embodiments. In the figures, incorporated to illustrate features of an example embodiment(s), like reference numerals are used to identify like parts throughout the figures. Fig. 1 illustrates an improved double-tube coring apparatus 100 according to one embodiment. When the coring apparatus is in operation the coring apparatus is generally disposed in a generally upright position. Thus the use of terms such as upper and lower are used in this context. The coring apparatus includes an outer tube 1 and head assembly 2, at an upper end of coring apparatus 100, for connection to a rotating drill string (not shown), an inner tube 3 for receiving cut core, a core catcher device 4 and a coring bit 5, preferably a thin-kerf coring bit 5, at the lower end of coring apparatus 100. A reamer 6 of known type may be connected between coring bit 5 and outer tube 1. The outer tube and other rotating components which are caused to rotate with the drill string about a rotation or central axis 110 which is generally longitudinal in extent relative to coring apparatus 100.

Inner tube 3 is disposable (preferably, though not necessarily, non-reusable), typically a cylindrical extrusion of metal or preferably clear plastic material such as polycarbonate, with plain ends. Inner tube 3 is terminated at the upper end with a push fit onto a tube adapter 7 and at the lower end with a push fit into core catcher device 4.

Tube adapter 7 is mounted on bearings 8 and a spindle 9 such that inner tube 3 and core catcher device or assembly 4 may remain stationary while outer tube 1, reamer 6 and coring bit 5 rotate when coring apparatus 100 is in operation. Spindle 9 has a threaded connection to head assembly 2 with a locknut 10 arranged such that locknut 10 is readily accessible externally for length adjustment using concentric tube spanners or similar tool inserted from the open, upper end of head assembly 2, thus providing an example of an externally accessible axial adjustment.

During a coring operation, fluid is pumped down inside the drill string and passes through holes 11 to flow through an annular passage 12 formed between inner tube 3 and outer tube 1 , to reach coring bit 5. Annular passage 12 has only a small radial clearance (typically 0.5mm) between inner tube 3 and outer tube 1, thus stabilising inner tube 1 against buckling. Venting passages 13 provide pressure equalization between the inside of inner tube 3 and annular passage 12.

Thus there is provided coring apparatus 100 comprising rotatable head 2 and outer tubular member 1 operatively connected to rotatable head 2 to be rotatable about a central rotation axis. The inner tubular member 3 is disposed within outer tubular member 1 and arranged to remain stationary relative to outer tubular member 1 when outer tubular member 1 is rotating during operation of the apparatus. Coring bit 5 is operatively connected to outer tubular member 1 for rotation therewith during operation of the apparatus. Core catcher assembly 4 is disposed within coring bit 5 and is located adjacent inner tubular member 3.

In one embodiment as shown in Fig. 2, spindle 9 includes a valve assembly 50 in the form of a compressible lip seal 14 of resilient material such as polyurethane that serves a dual function. In its normal uncompressed state, lip seal 14 remains in contact with the wall of outer tube 1. During a coring operation, when pressurized drilling fluid is pumped downwards through the coring assembly, lip seal 14 deflects away from inner tube 1 allowing drilling fluid to pass into annular passage 12. When inner tube 3 becomes either filled with core or jammed with fractured core, upward displacement of adapter 7 on spindle 9 causes lip seal 14 to compress and deform to activate a first function 15a of shutting off the downward fluid flow in annular passage 12, with a subsequent increase in fluid supply pressure alerting the drilling operator that the coring assembly needs to be changed. This scenario is illustrated on the left side of Fig. 2. On the other hand, during "washdown" operation, when the drilling fluid flow is stopped for drill rod addition, resilient lip seal 14 returns into contact with outer tube 1 to activate a second function 15b as a non-return valve. Backflow of fluid into the coring assembly due to residual excess pressure in the surrounding formation forces lip seal 14 in its uncompressed state against the wall of outer tube 1 and thus prevents upward backflow from the borehole carrying fine particulates that can cause blockage in the coring assembly when pressurized downward flow is subsequently resumed. This scenario is illustrated on the right side of Fig. 2.

In another embodiment providing a valve assembly 50 as shown in Fig. 3, a stop valve 16 provides a first function of shutting off downward flow of drilling fluid. Ball check valves 17 are located in holes 11 to provide a second function of allowing downward flow in the valves open state 18a and preventing upward backflow in their closed state 18b.

As shown in Figs. 4 to 7, core catcher assembly 4 includes a core catcher case 19, a first core catcher 20, of any known type such as a friction collet type rock core lifter held in the lower end of core catcher case 19, and a second core catcher 21, preferably though not necessarily comprising an iris diaphragm type assembly held in core catcher case 19. Second core catcher 21 is positioned adjacent or next to first core catcher 20, for example second core catcher 21 is positioned immediately above first core catcher 20.

The coring bit 5, preferably a thin-kerf coring bit 5, comprises a generally tubular main body 40 with a cutting head 45 at the lower end 41 thereof. The cutting head 45 comprises a generally cylindrical side wall 46 and an annular peripheral rim 22 having an outer annular surface 48 which forms a cutting surface 49. The outer surface of side wall 46 also forms a cutting surface. The annular surface 48 is generally continuous or uninterrupted or unsegmented or smooth. A plurality of passageways 23 are arranged around the side wall 46 and extend therethrough, i.e. through side wall 46. The passageways are angled, e.g. angularly inclined, with respect to the central axis 110 of coring apparatus 100. The inner surface of side wall 46 may be inwardly stepped and there may be more than one step forming one or more shoulders on the inner surface for reasons which will become apparent. In one example, coring bit 5 is preferably of impregnated diamond matrix material and as shown in Figs. 4 to 7, has an extended portion in the form of a continuous (unsegmented) smooth-edged cutting rim 22 that is absent of any channels or slots typical of prior art coring bits. A number of holes 23 allow drilling fluid to flow from annular passage 12 through to outwardly angled nozzles 24 at the periphery of coring bit 5. Each hole or nozzle has a slot 51 associated therewith in the outer surface of the side wall 46. The coring bit 5 has a smooth and continuous rim.

Thus, in one example there is provided a coring bit 5 suitable for use in coring apparatus 100. The coring bit 5 comprises main body 40 and cutting head 45 at one end 41 of main body 40. Cutting head 45 comprises a generally or substantially cylindrical side wall 46 and an annular peripheral rim 22 remote from the main body 40. Rim 22 has an outer annular surface 48 providing for a cutting surface 49, where the annular surface is continuous or uninterrupted, or is substantially continuous or uninterrupted. The annular surface can be said to be substantially smooth and/or substantially continuous. Main body 40 is substantially tubular having a central axis, the annular cutting surface being coaxial with the central axis and facing away from the main body 40. Coring bit 5 can include a plurality of passageways 23, where the passageways 23 are arranged around the periphery of side wall 46 and extend through side wall 46. Preferably passageways 23 are angled with respect to central axis 110.

An extended rim 25 of core catcher case 19 overlaps the inner shoulder or shoulders 56 of coring bit 5, with coaxial mating surfaces forming a water-lubricated bearing and seal that stabilizes core catcher case 19 and minimizes inward fluid impingement into the region of the core where it may erode fragile core samples. Extended rim 25 typically reaches to within about 3mm to about 4mm of the cutting face on cutting rim 22, thus limiting the distance the core must travel unsupported inside rotating cutting rim 22 before entering the spigot portion of non-rotating core lifter case 19.

As shown in Figs. 8 to 10, second core catcher 21 comprises a mounting sleeve 26 and a number of fingers 27, i.e. a plurality of fingers 27, made up of, for example, strips of sheet material. In Figs. 8 and 10, the plurality of fingers 27 are shown in a closed state. As shown in Fig. 9, fingers 27 are attached at the lower ends 28 to the inside of mounting sleeve 26 and are geometrically arranged such that their edges overlap along their full length and their free ends project upwards and radially inwards. Fingers 27 are spring biased such that the overlapping strips form a type of iris diaphragm that closes symmetrically towards the centre of the assembly as shown in Figs. 8 and 10. The diameter and wall thickness of catcher assembly 21 match those of inner tube 3 so that when fingers 27 are in the fully open state there is a smooth continuous bore from coring bit 5 through first core catcher 20 and second core catcher 21 to inner tube 3. In Figs. 8 to 10, the number of fingers 27 shown is illustrative only and the actual number of fingers 27 used can vary to provide the optimum, or any desired, overlap according to the diameter of the catcher.

A further aspect of core catcher 21 is that fingers 27 have a direction of overlap with respect to the catcher assembly axis of symmetry such that the fingers tend to open when in rotational contact with the core. Thus, in the close-up view box of Fig. 11, in normally clockwise rotation (arrow 62), viewed from above, fingers 27 are overlapped with trailing edges 29 innermost. Fig. 11 shows fingers 27 in an open state. Fig. 12 shows a partial assembly with fingers 27 in an open state. Fig. 13 shows a sectional view of catcher 21 with fingers held in an open state. In Figs. 11 to 13, the number of fingers 27 shown is illustrative only and the actual number of fingers 27 used can vary.

In some soil conditions it is possible that loose, coarse particles may initially pass through second core catcher 21 ahead of hard consolidated core sample. The coarse particles may settle between mounting sleeve 26 and the closed or semi-closed fingers 27, preventing them from fully opening to allow passage of the consolidated core. As shown in Fig. 13 a loose retaining ring 30 is provided to initially hold fingers 27 fully open. Retaining ring 30 is held in position by the spring bias of fingers 27 until consolidated core enters catcher 21 and pushes ring 30 ahead of it into inner tube 3.

Construction of core catcher 21 may be achieved as shown in Fig. 12 by welding individual fingers of sheet material into sleeve 26 in the above described configuration. Alternatively a one-piece cut-out 31 of sheet material as shown in Fig. 14 may be double wrapped and welded inside mounting sleeve 26, with notched profiles 32 creating the overlap of individual fingers 27. The strip of excess material 33 is trimmed off. In a further alternative, mounting sleeve 26 may also be an attached part of cut-out 31 and formed as a third wrap outside the double- wrapped, notched profile.

The apparatus is deployed in the manner of a conventional core barrel. When lowered to the bottom of a borehole on a drill string (not shown) the coring assembly is rotated while applying downward force and pumping drilling fluid to coring bit 5, removing an annular section of the formation and leaving an intact central core. As the coring assembly advances into the borehole the cut core enters through core catcher assembly 4 into inner tube 3. Inner tube 3 does not rotate relative to the core, being held stationary by friction against the core and with rotation of the outer tube being accommodated by bearings 8 in head assembly 2.

As the core enters second core catcher 21, fingers 27 are easily deflected outwards to the full diameter of the core, allowing the core to move freely into inner tube 3. When inner tube 3 is filled, or partially filled if desired, rotation is stopped and the coring assembly is lifted from the borehole. The action of the dual core catcher then comes into effect, depending on the properties of the core present in the catcher. If the core is hard and consolidated material the conventional friction collet of first core catcher 20 will tighten on the core under slight downward movement and weight of core above. The captured core plug thus holds the core in inner tube 3. If the core present in the catcher assembly is soft or unconsolidated material, the core cannot be gripped effectively by first core catcher 20, but with slight downward movement under gravity the core will engage with lightly gripping fingers 27 of second core catcher 21. The overlapping arrangement of fingers 27 along their full length prevents them from jamming on each other and allows any localised force on one or two fingers to be transferred successively to adjacent fingers, thus forcing closure of the catcher assembly 4 as a whole to retain the core sample in inner tube 3.

Core-laden inner tube 3 is recovered from the coring assembly by the steps of removing coring bit 5 from outer tube 1, removing core catcher assembly 4 and sliding out inner tube 3 from outer tube 1. The core sample in removed inner tube 3 remains undisturbed and can be capped and sealed for storage. In the case of a clear plastic inner tube 3, the core sample can be visually inspected without requiring extraction. The coring assembly may then be fitted with a new disposable inner tube 3 and returned to service. In the foregoing description of preferred embodiments, specific terminology has been resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "top" and "bottom", "front" and "rear", "inner" and "outer", "above" and "below", "upper" and "lower" and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

In this specification, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

In addition, the foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

Furthermore, invention(s) have been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention(s). Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment.

Table of Parts

Coring assembly 100

Central rotation axis 110

Outer tube 1 Head assembly 2

Inner tube 3

Core catcher assembly 4

Coring bit 5

Reamer 6 Tube adaptor 7

Bearings 8

Spindle 9

Locknut 10

Holes 11 Annular passage 12

Venting passages 13

Valve assembly 50

Lip seal 14

First function (operating mode) 15a Second function (operating mode) 15b

Stop valve 16

Ball check valves 17

Open state (operating mode) 18a

Closed state (operating mode) 18b Core catcher case 19

First core catcher 20

Second core catcher 21

Continuous cutting rim 22

Holes 23 Extended rim (of catcher case) 25

Inner shoulder (of coring bit) 56 Cutting face (of cutting rim) 49

Mounting sleeve 26

Fingers 27

Lower end 28 Trailing edges 29

Retaining ring 30

One piece cut-out 31

Notched profiles 32

Excess material 33 Slots 51

Main body 40

Cutting head 45

End 41

Side wall 46 Annular surface 48

Passageway 23

Direction of rotation 62