Shaped charge and method of modifying a shaped charge

Abstract

Some embodiments are directed to a shaped charge liner including an apex end and a base end and defining a main liner axis that passes through the apex and base ends, the liner being rotationally symmetric about the main liner axis wherein the liner has discrete rotational symmetry about the main liner axis.

Claims

1. A method of manufacturing an enhanced shaped charge liner design for use in an oil/gas well perforator that is usable to form a desired hole shape in a rock formation, the method comprising comparing the desired hole shape to a library of known liner designs, the library including data relating to a hole shape formed by each of the known liner designs within the library; selecting a liner design from the known liner designs that produces a hole shape optimised to the desired hole shape; varying at least one parameter of the selected liner design to form a modified liner design; modelling the hole shape that the modified liner design produces; repeating the varying and modelling steps until the hole shape of the modified liner design converges towards the desired hole shape to thereby create a final liner design; and forming the enhanced shaped charge liner in accordance with the final liner design.

2. The method as claimed in claim 1, wherein the varying step comprises varying a thickness of the selected liner design.

3. The method as claimed in claim 1, wherein selected shaped charge liner design defines an internal apex angle, and the varying step comprises varying the internal apex angle of the selected liner design.

4. The method as claimed in claim 1, wherein the varying step comprises varying a liner material of the selected liner design.

5. The method as claimed in claim 1, wherein the data for the plurality of liner designs includes the hole shape each of the plurality of liner designs produces in a range of different rock strata, the method further comprising filtering the data for the plurality of liner designs against rock conditions for a particular well environment.

6. The method as claimed in claim 1, wherein the forming step comprises forming the enhanced shaped charge liner to include: a cylindrically shaped lip member that is configured to engage a charge case, one end of the lip member defining a planar face having a diameter and an opposite end of the lip member defining a bottom face, a concavity extending between the planar and bottom faces of the lip member; and a projecting section defined by side walls projecting from the planar face of the lip member to define a linear apex end at a location that is spaced furthest from the planar face in a direction along a main liner axis that passes through the apex end and the lip member, the side walls having both inner surfaces and outer surfaces, wherein a maximum width of the outer surfaces at an end of the projecting section opposite the apex end extends in a direction perpendicular to the main liner axis and is less than the diameter of the planar face of the lip member such that flat surfaces are defined on the planar face of the lip member between all portions of the end of the projecting section and an outer perimeter of the lip member, the projecting section being rotationally symmetrical about the main liner axis such that the projecting section has discrete rotational symmetry about the main liner axis, a cross section of the projecting section in a plane perpendicular to the main liner axis defining an obround shape that is defined in part by two opposing arcuate walls.

7. The method as claimed in claim 6, wherein the forming step comprises forming the enhanced shaped charge liner such that the planar face of the lip member is circular, and the side walls of the projecting section include opposing half cones that define two opposing walls each of which is arcuate in cross-section.

8. The method as claimed in claim 6, wherein the forming step comprises forming the enhanced shaped charge liner such that the concavity of the lip member is contiguous with an aperture of the projecting section so as to form a single contiguous opening.

9. The method as claimed in claim 6, wherein the forming step comprises forming the enhanced shaped charge liner from a wrought metal.

10. The method as claimed in claim 6, wherein the forming step comprises forming the enhanced shaped charge liner from a pressed metal powder, and the metal powder includes tungsten powder.

11. The method as claimed in claim 6, wherein the forming step comprises forming the enhanced shaped charge liner such that the projecting section is hollow.

12. The method as claimed in claim 6, wherein the forming step comprises forming the enhanced shaped charge liner such that the liner constitutes a reactive liner.

13. The method as claimed in claim 6, wherein the forming step comprises forming the enhanced shaped charge liner such that the charge case defines a lower end, and the lip member engages a region of the charge case adjacent the lower end.

14. The method as claimed in claim 6, wherein the forming step comprises forming the enhanced shaped charge liner such that a width of the concavity of the lip member is wider than a width of an aperture of the projecting section in the direction perpendicular to the main liner axis.

15. The method as claimed in claim 6, wherein the forming step comprises forming the enhanced shaped charge liner such that the concavity of the lip member has a smaller volume than an aperture of the projecting section.

16. The method as claimed in claim 1, wherein the forming step comprises forming the enhanced shaped charge liner to include: a cylindrically shaped lip member that is configured to engage a charge case, one end of the lip member defining a planar face having a diameter and an opposite end of the lip member defining a bottom face, a star shaped concavity extending between the planar and bottom faces of the lip member; and a projecting section defined by side walls projecting from the planar face of the lip member to define an apex end at a location that is spaced furthest from the planar face in a direction along a main liner axis that passes through the apex end and the lip member, the side walls having both inner surfaces and outer surfaces, wherein a maximum width of the outer surfaces at an end of the projecting section opposite the apex end extends in a direction perpendicular to the main liner axis and is less than the diameter of the planar face of the lip member such that flat surfaces are defined on the planar face of the lip member between all portions of the end of the projecting section and an outer perimeter of the lip member, the projecting section being rotationally symmetric about the main liner axis such that the projecting section has discrete rotational symmetry about the main liner axis, a cross section of the projecting section in a plane perpendicular to the main liner axis defining a four or five pointed star shape of both the inner surfaces and the outer surfaces of the side walls of the projecting section, wherein all of the inner surfaces and all of the outer surfaces of the side walls of the projecting section are flat, planar surfaces.

17. The method as claimed in claim 16, wherein the forming step comprises forming the enhanced shaped charge liner such that the planar face of the lip member is circular.

18. The method as claimed in claim 16, wherein the forming step comprises forming the enhanced shaped charge liner such that the concavity of the lip member is contiguous with a star shaped aperture of the projecting section so as to form a single contiguous star shaped opening; and the charge case defines a lower end, and the lip member engages a region of the charge case adjacent the lower end.

19. The method as claimed in claim 18, wherein the forming step comprises forming the enhanced shaped charge liner such that a width of the concavity of the lip member is wider than a width of the aperture of the projecting section in the direction perpendicular to the main liner axis.

20. The method as claimed in claim 18, wherein the forming step comprises forming the enhanced shaped charge liner such that the concavity of the lip member has a smaller volume than the aperture of the projecting section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which like reference numerals are used for like parts, and in which:

(2) FIG. 1 shows a known perforator design;

(3) FIG. 2 shows a representation of a well bore and perforator gun;

(4) FIG. 3 shows an array used in firing trials that mimics a down well environment;

(5) FIGS. 4 to 6 show examples of shaped charge liners in accordance with embodiments of the present invention;

(6) FIG. 7 shows a simulation of the shaped charge liner depicted in FIG. 4;

(7) FIG. 8 shows the simulated effects of the jet of FIG. 7 impacting the array of FIG. 3;

(8) FIGS. 9a to 9d show predicted tunnel geometries for the liners depicted in FIGS. 4 to 6;

(9) FIG. 10 shows a charge design in accordance with embodiments of the present invention;

(10) FIG. 11 shows a cross section through the liners of FIG. 4-6;

(11) FIGS. 12a and 12b show simulated tunnel profiles for two liners with differing apex angles based on the design in FIG. 4 for 50° and 60° internal angles respectively;

(12) FIG. 13 shows a photograph of an incursion into a rock made by a liner in accordance with embodiments of the present invention;

(13) FIGS. 14a to 14d show results of measuring jet formation for two liners with differing apex angles over a pair of tests;

(14) FIGS. 15a to 15d correspond to FIGS. 14a to 14d but show the results of modelling the same jet formations;

(15) FIG. 16a shows a flow chart that details the process of generating a library of shape charge liners;

(16) FIG. 16b shows a flow chart that relates to the process of liner/charge optimisation;

(17) FIG. 17 shows an example of the data contained in the library of FIGS. 16a and 16b.

DETAILED DESCRIPTION OF THE INVENTION

(18) In accordance with aspects of the present invention it is noted that improved fracture formation and also preferential directionality of fracture propagation may be achieved by the use of non-circularly symmetric shaped charge liners within the oil/gas perforators used in a down-hole oil/gas well.

(19) Such non-circularly symmetric liners—optionally with and non-circularly symmetric cases—result in the creation of a collapse jet with tuneable, non circular characteristics. This in turn leads to the deliberate creation of non-circular holes (perforation tunnels) in the rock formation, thereby establishing near-bore tunnel geometries and residual stress states that allow greater control over fracture initiation and propagation orientation towards the far field (i.e. at distance from the well-bore rock formation).

(20) The essence of the invention is that the completion engineer can choose the best bespoke charge option to produce the preferred fracture pattern in the rock using the ‘designer hole’ concept, optimised for a given rock strata and borehole well dimensions. Thus it is entirely possible that different charge options would be used for different types/size of boreholes and different rock strata environments. This would empower the completion engineer to make informed decisions as to which charge design is best suited to the situation in that borehole/well configuration.

(21) The figures detail an example where the concept has been demonstrated in principle to produce a slot shaped hole in a specific well casing configuration. The results of simulations and laboratory proof tests of such liners are detailed (in conjunction with FIGS. 3 and 7 to 15 a-d) for a well and bore hole with the following parameters: Metal casing liner internal diameter (ID)=9.96 cm, outer diameter (OD)=11.43 cm, borehole size 20.24 cm.

(22) It is noted that the perforating gun used to deploy the perforating charges (depicted in FIGS. 4 to 6) down-well has to fit readily within the well casing (see FIG. 2). The maximum gun diameter is therefore in the region of 90 mm for this case, which gives a stand-off distance between the shaped charge liner and the well casing of less than 10 mm. In fact it is noted that the perforators will sit within a carrier inside the perforator gun. The wall of the perforating gun is usually scalloped internally (counter-bored) and the perforators are aligned with the scallop pocket to minimise the thickness of gun body that the perforator jet must pass through. The standoff between the perforator and the inside surface of the perforating gun is likely to be of the order of a few mm (since the apex of the perforator body is sitting on the scallop pocket).

(23) It is important to note that in order to avoid fracturing or splitting the perforating gun as a result of firing the perforators, it is essential to ensure that the gun can be withdrawn readily from the well. Furthermore, for reasons of well operational integrity, it is essential to avoid the destruction or failure of any interstitial seals between various sections of the well bore when the perforator gun is fired. There is therefore a trade-off between the net explosive size (NEQ) of the perforator and the integrity of the well casing and well case integrity.

(24) FIG. 3 shows a target 200 which was used in proof of principle laboratory firing trials to evaluate the shaped charge liners in accordance with embodiments of the present invention. The target was designed to mimic the down-hole arrangement of liner casing, cement and rock. Consequently, a thin front plate 202 having a diameter of 500 mm was arranged above a block of cement 204 backed by rock 206.

(25) Byro sandstone was identified as having a density and porosity similar to the rock conditions in a typical well. Byro rock was regarded as representative of the strength of the rock strata in the down well condition. The target was encased in a concrete 208 and steel box 210 to contain any cement and rock to prevent the target from shattering and to contain any localised fractures and thereby facilitate post-firing examination and measurement.

(26) Three geometric configurations of shaped charge liner were investigated, both theoretically and experimentally (against the target shown in FIG. 3). In each instance identical, initiation, liner casing and explosive elements were used (i.e. the liner geometry was the single variable). These liners are shown in FIGS. 4 to 6.

(27) For each of the shaped charge liners depicted in FIGS. 4 to 6 a main liner axis 220 is shown that passes through both the apex 230 and base 240 of the liner in question. Note: although the discussion below is in the context of a liner axis it will be appreciated by the skilled person that the shaped charge liner may comprise a planar axis that passes through both the apex and base of the liner in question. The term liner axis should therefore be read accordingly. In relation to this point see for example FIG. 4 where the axis 220 is actually a planar axis that passes through the line defined by points 250 and 252.

(28) FIG. 4 shows a generally prismatic liner shape 260 in which the ends of the prism have been formed into a “half cone” shape 262. The base end of the shaped charge liner is formed into a lip member 264 which has a circular profile for convenient engagement with the perforator charge casing. The apex 230 of the liner of FIG. 4 is a line rather than a point. It is noted that looking down the main liner axis 220 (from above the apex 230 end of the liner) it can be seen that the liner of FIG. 4 demonstrates rotational symmetry (such that a 180° rotation, 2-fold symmetry will leave the liner unchanged) but does not demonstrate circular symmetry. In other words any angular rotation of the liner of FIG. 4, other than 180° or a multiple thereof, will not result in the liner appearing identical to the start position.

(29) FIG. 5 shows a pyramidal shaped charge liner 270. Again the base 240 of the liner is formed into a lip member 264. Again, viewed from above the liner demonstrates rotational symmetry (4-fold rotational symmetry) but does not display circular symmetry.

(30) FIG. 6 shows a shaped charge liner 280 that has a star-like cross section. The particular liner depicted in FIG. 5 is a four pointed star but it is noted that the liner may be constructed as a five pointed, six pointed or an n-pointed star (where n is an integer). The base 240 of the shaped charge liner is formed into a similar lip member 264 to that of FIG. 4. Again, viewed from above the liner demonstrates rotational symmetry (4-fold rotational symmetry) but does not display circular symmetry.

(31) The liners (260, 270, 280) depicted in FIGS. 4 to 6 are therefore distinguished from known conical or hemispherical liners which exhibit circular symmetry.

(32) FIG. 7 shows a simulation of the shaped charge liner 260 of FIG. 4 when fired from a perforator gun. It can be seen that the jet 290 of ejected material is dispersed into distinctive planes (the left hand and right hand images in FIG. 7 show two perpendicular planes). It is also noted that the rear of the jet (the “slug” 292) is rectangular in shape.

(33) FIG. 8 shows the simulated effects of the jet 290 of FIG. 7 impacting the target arrangement 200 of FIG. 3. It can be seen that the jet 290 is predicted to penetrate through the well casing 202, the cement 204 and into the rock 206. It is noted that FIGS. 7 and 8 represent a shaped charge liner in accordance with FIG. 4. In this case the liner was fabricated from wrought copper but could also be pressed powder or even non-metallic or reactive.

(34) FIG. 9a is a three dimensional representation of the predicted tunnel geometry 300 formed by the jet 290 of FIG. 7 (liner 260 of FIG. 4). It can be seen that the hole 302 in the backing rock is generally slot shaped (i.e. it has a rectilinear geometry). It is also noted that the hole in the well casing is also slot shaped

(35) FIG. 9b shows the predicted tunnel geometry formed for a liner of FIG. 4 fabricated from tungsten powder. It can be seen that the hole of FIG. 9b is also slotted in shape but additionally has two offshoots 304 from the main hole 302 such that the overall jet shape is generally “Y” shaped. The two offshoots provide a mechanism for producing preferential fracture initiation sites in the rock formation.

(36) FIGS. 9c and 9d show the tunnels that result from copper liners according to FIGS. 6 and 5 respectively. The tunnel 306 formed in FIG. 9c can be seen to be generally diamond shaped and the tunnel 308 formed in FIG. 9d can be seen to be generally elliptically shaped.

(37) Variants of the liner 260 depicted in FIG. 4 were then further tested using the in the laboratory tests using the charge design 310 shown in FIG. 10.

(38) The charge design of FIG. 10 used in the laboratory tests comprised a steel charge holder 312 within which was held a main explosive charge of EDC 1(S) 314. One end 315 of the charge holder held the shaped charge liner under test. At the other end of the holder a booster pellet 316 (for initiating the main charge) was mounted so that it was in contact with (in communication with) the high/low voltage detonator 318.

(39) The further testing comprised changing the liner profile of the shaped charge liner of FIG. 4 slightly in order to “tune” the performance of the liner upon detonation. Two different liner profiles were tested. FIG. 11 shows a cross section through the liner 230 of FIG. 4. It is noted that an internal apex angle θ is defined by the prism sides of the liner. The first liner tested had an internal angle of 50° and the second liner tested had an internal angle of 60° although the skilled person will appreciate that other angles could be used. A similar cross section would be apparent for the liners of FIGS. 5 and 6, having an apex angle θ.

(40) The simulated tunnel profiles 330, 332 for the two liners are shown in FIGS. 12a and 12b. FIG. 12a shows the predicted tunnel profile for the EDC1 filled design of shaped charge liner for a 50° internal apex angle and FIG. 12 b shows the predicted tunnel profile for the shaped charge liner for a 60° internal apex angle. It can be seen that the changed apex angle results in a slightly different tunnel profile. In the case of FIG. 12a it can be seen that the primary tunnel 334 is more prominent compared to the offshoots 336. In FIG. 12b the primary tunnel 338 and offshoots 340 are of similar size.

(41) The liner of FIG. 4 with an internal apex angle of 50° was fired into a target consistent with the arrangement of FIG. 3. A slot shaped tunnel 350 was created through the cement layer, through the well casing and with an initial incursion into the rock, as shown in the photograph of FIG. 13. The test firing was repeated with another liner of the same profile. Two further test firings were performed with a liner of the shape of FIG. 4 with an internal apex angle of 60°. The results of the various firings are shown below in Table 1 which show the hole dimensions in each part of the target.

(42) TABLE-US-00001 TABLE 1 Firing Steel plate Cement Rock No Round 202 (mm) 204 (mm) 206 (mm) 1 50° (1) 37 × 32 120 × 35 Slight indent 2 50° (2) 35 × 32 135 × 38 Slight indent 3 60° (1) 32 × 32  59 × 40 58 × 40 × 12 deep 4 60° (2) 33 × 30  72 × 38 53 × 26 × 12 deep

(43) As can be seen from Table 1 the liner trials demonstrate that slot holes can be produced with a prismatic liner 260 with varying internal apex angles. The results are reproducible and also demonstrate that varying the apex angle alters the size of the resultant hole. In the table the slot holes are provided either in the format X×Y (where X=width of slot hole and Y=height of hole) or in the format X×Y×Z (where the X×Y dimensions of the hole are specified at a distance Z beneath the surface of an object).

(44) It is noted that the holes produced in the steel plate 202 are approximately 10 times larger in cross section than holes produced from an equivalent standard perforator charge which are generally 12.5 mm in diameter (as defined in the JRC Shaped Charge Listing performance handbook).

(45) FIGS. 14a to 14d show the results of measuring the jet formation of the liners (firing rounds in Table 1) 1-4 tested above using a flash X-ray radiography set up. FIGS. 14a and 14b show orthogonal flash X-rays for the 50° liner design taken 25 μs after firing. FIGS. 14c and 14d show orthogonal flash X-rays for the 60° liner design taken 25 μs after firing.

(46) It can be seen for the 50° design that there is little liner material between the ‘V’ shape of the jet, whereas for the 60° design there is evidence of thin bands of liner material between the ‘V’ shape. The jet for the 60° design also is more concentrated.

(47) The X-rays all also show that the jet is a ‘blade’ shape in one plane and a narrow jet in the other plane and there is some evidence of the jet splitting. There is also a pronounced slug in the jet. The rounds were reproducible.

(48) FIGS. 15a to 15d correspond to FIGS. 14a to 14b and additionally show the results of computer modelling of the shape of the jet formed from the 50° and 60° liners. It can be seen that there is a good correspondence between simulation and experiment.

(49) FIGS. 3 to 15 show how, according to a first aspect of the present invention, the liner geometry can be customised such that desirable perforation tunnel geometric features are created, to order, within the well casing, cementation layer and rock strata. Such desirable features include (but are not limited to):— tunnel geometries that will promote fracture initiation and propagation at minimal subsequent fracking pressures tunnel geometries that will promote fracture initiation and growth in a specific orientation in relation to the well casing and/or bedding planes. tunnel geometries that will promote maximum flow/flow rate from the rock through the cementation and well casing elements and into the well bore.

(50) Tests (presented above) on the liner 260 variants depicted in FIG. 4 indicated the effects of changing the internal apex angle of the liner. It is noted that additionally, or alternatively, the liner or charge configuration may be varied to produce a designer hole. These are listed below and can be used to customise the hole produced by the charge. wrought metal, powder compact, reactive or non metallic (e.g. polymer based) liner material. Graded density liner using mixtures of materials or thin layers Liner shape Liner thickness variants (e.g. tapered, pointed apex, truncated liners) Varying initiation system (e.g. single, multi-point, waveshaper, plane wave) Varying case material and shape Varying explosive composition

(51) According to a further aspect of the present invention there is provided a method of generating a library of shaped charge liners detailing the performance of such liners in different environmental conditions. According to a yet further aspect of the present invention there is provided a method of optimising a shaped charge liner design for use in an oil/gas well perforator to form a desired hole shape in a rock formation.

(52) The process for this is flexible in being applicable to a whole range of well and gun dimensions and also different rock strata environments (e.g. horizontal, vertical bedding planes).

(53) FIG. 16a is a flow chart 400 that details the process of generating a library of shape charge liners. So the process is to select or calculate the type of hole required for the given strata, gun dimensions, perforator geometrical constraints and well conditions (Step 402—receive desired hole “target” parameters and Step 404—receive environmental parameters). One would then develop a bespoke charge design (Step 406) to produce a ‘designer hole’ based on advanced simulation techniques. As experience is gained this would be expanded into a library of charge configurations/designs suitable for a range of wells that the completion engineer could select for a given application. This library would evolve (Step 408) to encompass more relevant situations encountered by the completion engineer. Additional simulations (e.g. using GRIM) would be performed to expand the library accordingly to account for the new range of well/gun conditions. These simulations would include investigation of liner parameters (e.g. materials, thickness, profile) and also case parameters (e.g. materials, thickness, profile). Also further laboratory experiments may be performed to prove certain designs configurations.

(54) FIG. 16b is a flow chart 410 that relates to the process of liner/charge optimisation.

(55) An example of the data contained in such a library is shown in FIG. 17. It can be seen that four different liner types, A-D, are characterised (there may be, for example, prismatic, star shaped, pyramid, hexagonal liners). For each liner type the performance of different rock types (R1, R2, R3, R4) is detailed and the data on the hole produced includes the type of cross section and the depth that the jet produced by the liner penetrates into the rock around the oil well. This would also be repeated for a range of gun and well dimensions. It should be noted that it is unlikely that the charges can simply be scaled from one gun/well condition to another.

(56) The library may additionally include data on the effect of different liner materials on the performance of such liners (in which case each of the entries against each liner type in FIG. 17 would be repeated for each potential liner material).

(57) It is noted that the data associated with the “liner type” would define the standard dimensions and relevant internal angles of each liner type.

(58) Returning to the optimisation method shown in FIG. 16b, in Step 412, parameters relating to a desired hole to be formed in the rock adjacent to an oil/gas well are received. Such parameters may comprise the required hole depth and the general hole profile required (e.g. “slot like” cross section).

(59) In Step 414 the received hole parameters are compared to the data contained within the library. It is noted that the performance of each liner within the library may be characterised for different rock types (e.g. sandstone, granite etc.) and gun geometry, well conditions and additional constraints. The comparison of Step 414 would include filtering the data contained in the library to relate to the correct environment including rock type and strata conditions (i.e. the rock type that corresponds to the intended rock type that an oil/gas well is located in).

(60) In Step 416, the shaped charge liner within the library that results in a hole that is closest to the desired hole shape is chosen.

(61) In Step 418 a parameter relating to the selected liner is varied. This parameter may be the liner material, the liner thickness, the depth of the liner (or the internal apex angle) or any other relevant parameter.

(62) In Step 420, the performance of the modified liner is modelled. Examples of suitable modelling methods comprise the GRIM hydrocode package.

(63) In Step 422 the hole produced by the modified liner design is compared again to the desired hole profile. Steps 418 and 420 may then be repeated until the liner performance shows no further improvement (or until the liner performance shows no appreciable improvement). In other words the optimisation method checks whether the modified liner performance has converged towards the desired hole shape. The resultant shaped charge liner design represents an optimised design that is suitable for use in the particular down-well environment that relates to the desired hole shape.

(64) Further variations and modifications not explicitly described above may also be contemplated without departing from the scope of the invention as defined in the appended claims.