This invention relates to whipstocks. In Figs. 1, 47, 48 and 58 of our International Patent Application No. PCT/GB94/01979 (Publication No. WO 95/07404) we disclose a whipstock with a concave which is provided with a support assembly. When the whipstock is correctly positioned in a tubular the support assembly is actuated to cause several spaced apart bars to move radially outwardly from the concave to engage the wall of the tubular and support the con¬ cave.

The disadvantage of this arrangement is that it cannot effectively support the concave when the distance between the concave and the tubular varies along the length of the concave. This will often be the case, if the whipstock is of significantly smaller diameter than the tubular in which it is set.

According to the present invention there is provi¬ ded a tapered support member which accommodates a plur- ality of spacers which can be moved from an inoperative position in which they project outwardly from said support member to support said support member character¬ ised in that said spacers are shaped and disposed so that when they are moved to project outwardly from said support member they project by different distances.

Preferably said spacers are pivotally mounted on said tapered support member.

Advantageously, said whipstock includes an actua¬ ting bar which co-operates with said spacers to move them from their inoperative position to their operative position.

Preferably, said spacers are each provided with one of a stud and an elongated slot, and said actuating bar is provided with a plurality of the other of said stud and said elongate slot, each said stud projecting into a

respective one of said elongate slots.

Advantageously, one of said tapered support member and said actuating bar is provided with a cam pin and the other of said tapered support member and said actua- ting bar is provided with a cam profile which engages said cam pin.

Preferably, said cam profile includes a projection. Advantageously, said cam profile comprises a first end and a second end which are disposed to either side of said projection.

Preferably, said actuating bar forms part of an actuating linkage, said actuating linkage comprising a member slidably mounted on said concave, and a link pivotally mounted to said member and said actuating bar so that said actuating bar can move outwardly from said concave.

Advantageously, said whipstock includes a detent for engaging said actuating bar and holding said spacers in their operative position. Preferably, said whipstock includes a recess adap¬ ted to receive said detent and shaped so that said detent will withdraw from said recess when said whip¬ stock is lifted during a recovery operation.

For a better understanding of the present inven¬ tion, reference will now be made, by way of example, to the accompanying drawings, in which: -

Fig. 1 is a side view, partly in section, showing one embodiment of a whipstock in accordance with the invention in a first position in a tubular;

Fig. 2 is a view similar to Fig. 1 but with the whipstock and tubular omitted for clarity;

Fig. 3 is a view similar to Fig. 2 but with the parts in a second position;

Fig. 4 is a view similar to Fig. 3 but on an en¬ larged scale and with the parts in a third position;

Fig. 5 is a view similar to Fig. 4 but with the parts in a fourth position; Fig. 6 is a view similar to Fig. 5 but showing the whipstock and tubular;

Fig. 7 is a view, on an enlarged scale, of part of Fig. 6;

Fig. 8 is an exploded view, on an enlarged scale, of part of Fig. 2; and

Fig. 9 is a fragmentary view, partly in section and on an enlarged scale, of a detail of Fig. 2.

Referring to Fig. 1, there is shown a whipstock, which is generally identified by reference numeral 1. The whipstock 1 comprises a concave 2 comprising a tapered support member 3. The front 4 of the tapered support member 4 is arcuate and part is provided with a sacrificial bearing 5 of brass.

The back 6 of the support member 3 accommodates a plurality of spacers 7, seven of which are shown. Each spacer 7 is pivotally mounted on the support member 3 by a shaft 8.

The whipstock 1, which is shown set in a tubular comprising a casing 9, is mounted on the bottom of a setting tool assembly 10 via a shear bolt 11.

A rod 12 projects downwardly from the setting tool assembly 10 and is provided at its lower end with a nut and washer which support a spring 13. The spring 13 acts against the head 15 of a shear bolt 14 which is slidably mounted on the rod 12.

The shear bolt 14 is threadedly attached to the uppermost member 16 of an actuating linkage which is generally identified by reference numeral 17. The uppermost member 16 of the actuating linkage 17 is provided with a slot 18 (Fig. 8) which accommodates the shaft of a guide bolt 19. The guide bolt 19 holds the uppermost member 16 to the concave 2 whilst allowing it to slide relative thereto within the confines of the slot 18. The actuating linkage 17 further comprises an actuating bar 20 which is pivotally connected to the uppermost member 16 via a short link 21.

The actuating bar 20 is provided with seven elongate slots 23 which are spaced apart along the length of the actuating bar 20 and which accommodate respective studs 22 mounted on each spacer 7.

A cam pin 24 is mounted on the concave 2 just below each spacer 7. Each cam pin 24 rests in a respective cam profile 25 formed in the actuating linkage 17. The cam profile 25 includes an upper end 26, a lower end 27, and a projection 28 therebetween.

The operation of the whipstock 1 will now be described. Firstly, the whipstock 1 is lowered down the casing 9 on the setting tool assembly 10 on a workstring or coil tubing (not shown). It is then set in the casing 9. This operation is more fully described in WO 95/07404.

Once the whipstock 1 is set in place the setting tool 10 is raised. This shears the shear bolt 11. As the setting tool 10 is raised the spring 13 acts

on the shear bolt 14 and raises it. Initially the actuating linkage 17 moves to the position shown in Fig. 3 where the bottom of the elongate slots 23 engage the studs 22 and the cam pins 24 move away from the upper ends 26 of their cam profiles 25.

As the setting tool 10 is further raised the actua¬ ting linkage 17 rises and the projections 28 pass over the cam pins 24. This causes the actuating linkage 17 to move outwardly. This, in turn, causes the spacers 7 to start to pivot clockwise about their shafts 8 to the position shown in Fig. 4. This outward movement of the actuating linkage 17 is facilitated by the short link 21.

As the setting tool 10 is further raised the spa- cers 7 pivot to the outwardly extending position shown in Fig. 5. It will be noted that the cam pins 24 have now passed over the projections 28 in their respective cam profiles 25 so that the actuating linkage 17 has moved inwardly. This action causes the cam pins 24 to occupy a position at the upper end of their respective elongate slots 23.

As the setting tool 10 is further raised two spring loaded detents 29 engage in recesses 30 in the actuating bar 20 to hold the actuating bar 20 in juxtaposition with respect to the concave 2 (Figs. 6 and 7).

The shear bolt 14 fails on further upward movement of the setting tool assembly 10 which is then removed leaving the whipstock 1 well supported and ready to receive a starting mill (not shown). It will be noted particularly from Figs. 5 and 6 that the length of the spacers 7 increases progressively so that the back 6 of the concave 2 is well supported. This helps ensure that the new well is drilled in the desired direction and also inhibits the concave 2 being distorted.

If the whipstock 1 is to be permanently left in the casing 9 the recesses 30 can simply be bores. However, if the whipstock 1 is to be retrievable the recesses 30 can be shaped so that the detents 29 can be freed. In particular, in order to retrieve the whipstock 1 a fishing tool is lowered in to the casing 9 and man¬ oeuvred until a hook on the fishing tool engages in an elongate slot (not shown) in the top of the concave 2. When the fishing tool is raised the spring loaded de- tents 29 will ride out of their respective recesses 30 and the spacers 7 will collapse back to a retracted position.

In a typical embodiment for use in casing 9 having a diameter of 18cm (7 inches) the actuating bar 20 is about 335cm (11 feet) long. The spacers 7 increase progressively in length from 5cm (2 inches) at the top to 12.7cm (5 inches) at the bottom and project from the concave 2 by about 1.3cm (0.5 inches) at the top to about 7.6cm (3 inches) at the bottom. Various modifications to the embodiment described with reference to the drawings are envisaged, for exam¬ ple the length of the spacers 7 may be varied so that the concave 2 adopts a predetermined curvature in use. This variant is however not recommended. If desired, the studs 22 could be mounted on the actuating bar 20 and the elongate slots 23 formed in the spacers 7.

If desired, the cam pins 24 could be mounted on the actuating bar 20 and the cam profiles 25 formed in the tapered support member 3 of the concave 2. However the arrangement described is believed easier to fabricate.

Whilst the spacers 7 are actuated by withdrawal of the setting tool assembly 10 it is noted that the embo¬ diment could be modified so that the spacers 7 are actuated on the application of downward pressure on the

setting tool assembly 10. Such an embodiment would be particularly advantageous where the setting tool inclu¬ ded a starting mill bolted to the whipstock by a shear bolt similar to shear bolt 11. After shearing the shear bolt 11 downward movement of the starting mill would actuate the spacers 7. The starting mill could then be started without the necessity of a separate trip.

* * *

As used herein the term "concave" is used to refer to the tapered part of a whipstock regardless of whether the surfaces on which the starting mill bears is arcuate or flat.