WELLBORE

BACKGROUND OF THE INVENTION

The present invention relates to a method and a system for drilling a sidetrack of an underground wellbore formed in an earth formation.

Wellbores for the production of hydrocarbon fluid generally are provided with steel casings and/or liners to provide stability to the wellbore wall and to prevent undesired flow of fluid between the wellbore and the surrounding earth formation. A casing generally extends from surface into the wellbore, whereas a liner may extend only a lower portion of the wellbore. However in the present description the terms "casing" and "liner" are used interchangeably and without such intended difference.

A production tubing for flow of hydrocarbon fluid from a reservoir zone to surface is arranged in the casing whereby an annular space filled with brine extends between the casing and the production tubing.

It may be required to position one or more wellbore tools in the casing or in the production tubing.

Traditionally, a whipstock is positioned in the casing in order to drill a deviated wellbore section. For such purpose a landing nipple is are generally installed in the casing or production tubing to provide a specific landing location for the whipstock and/or wellbore tools. The deployed landing nipples may have identical internal profiles so as to make them universal for these tools.

US patent application US2003/0213600 discloses an expandable latch profile that supports a whipstock without requiring a packer and US patent application US2010/0193124 discloses a method for lining a wellbore or pipe using an inflatable bladder.

International patent application WO2011072121 discloses a landing nipple for mounting in a string that extends from a surface to a subterranean location for operational support of a tool, comprising a tubular body having a passage defined by a wall and having end connections on the wall for securing the body to a string.

There is a need for an improved method of positioning a wellbore sidetrack drilling tool in a parent wellbore or wellbore tubular, which allows drilling of a sidetrack at a desired relatively large angle away from the parent wellbore and which overcomes the drawbacks of the prior art . SUMMARY OF THE INVENTION

In accordance with the invention there is provided a method for drilling a sidetrack of an underground wellbore, the method comprising:

(a) lowering a landing device in a retracted mode into the wellbore;

(b) expanding the landing device against an inner surface of the wellbore or wellbore liner so as to anchor the landing device to said inner surface;

(c) connecting either before step (a) or after step (b) the landing device to a sidetrack drilling assembly comprising a drill string and a knuckle joint carrying a tiltable drill bit;

(d) after step (c) further lowering the drill string into the wellbore thereby buckling the knuckle joint and inducing the buckled knuckle joint to tilt the sidetrack drill bit towards the inner surface; and

(e) inducing the tilted drill bit to drill the sidetrack.

In accordance with the invention there is furthermore provided a sidetrack drilling assembly for drilling a sidetrack of an underground wellbore comprising a drill string and a knuckle joint carrying a tiltable drill bit, which assembly is configured:

- to be connected to an expandable landing device;

- to buckle the knuckle joint by further lowering the drill string after expansion of the landing device, thereby inducing the buckled knuckle joint to tilt the sidetrack drill bit towards the inner surface; and

- to induce the tilted drill bit to drill the sidetrack.

The landing device may comprise a hydraulically actuated expander and the knuckle joint may comprise upper and lower sections that are each pivotally connected to an intermediate section and wherein the upper section is connected to the drill string by an upper pivot and the lower section is connected to the landing device by a lower pivot and the drill bit is secured to the upper section of the knuckle joint and is pivotally connected to the lower end of the drill string by a swivel joint that permits the sidetrack drill bit to swivel relative to the drill string when the knuckle joint is buckled.

The lower pivot may be connected to the landing tool by a bearing and/or landing nipple assembly that permits rotation of the drill bit and the tilt angle thereof relative to the landing tool by rotating the drill string and the side track drill bit may be an abrasive and/or other jet drill bit comprising a nozzle to which drilling mud is supplied via the drill string.

Suitably said means for installing the wellbore tool in the receiving portion includes one of a wireline and a work string . BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described hereinafter in more detail and by way of example with reference to the

accompanying schematic drawings in which:

Fig. 1 shows a first embodiment of a landing device for use in the sidetracking drilling assembly according to the invention, in longitudinal section;

Fig. 2 shows the first embodiment after expansion of a tubular portion against a wellbore tubular;

Fig. 3 shows the first embodiment after repositioning an expander in the tubular portion;

Fig. 4 shows the first embodiment after further expansion of the tubular portion;

Fig. 5 shows the first embodiment after finalising expansion of the tubular portion;

Fig. 6 shows a modified version of the first

embodiment ;

Fig. 7 shows a second embodiment of a landing device for use in a casing in accordance with the invention, in longitudinal section; and

Fig. 8 shows the landing device of Fig.7 on which the sidetrack drilling assembly according the invention has been landed.

DETAILED DESCRIPTION OF DEPICTED EMBODIMENTS

In the detailed description and the figures, like reference numerals relate to like components.

Referring to Figs. 1-5 there is shown a wellbore 1 formed in an earth formation 2. The wellbore 1 is provided with a wellbore casing 4 and a tubular member in the form of production tubing 6 for the production of hydrocarbon fluid from a reservoir zone of the earth formation to a production facility (not shown) at surface. A landing device in the form of a steel landing nipple 8 is supported in the production tubing 6 on a work string 10. The landing nipple 8 includes a receiving portion 12 for receiving a wellbore tool (not shown) which may be, for example, a lock mandrel, a plug or other flow control tool. The receiving portion 12 has an internal profile 14 adapted to receive and hold the wellbore tool in place. The landing nipple 8 further comprises a tubular portion 16 arranged below the receiving portion 12 and integrally connected thereto. The tubular portion 16 is radially expandable against the inner surface of the production tubing 6.

The work string 10 is at the lower end thereof provided with an expander 18 arranged in the tubular portion 16 of landing nipple 8. The expander 18 is movable between a radially retracted mode and a radially expanded mode and may be, for example, in the form of an inflatable packer. In the radially retracted mode, the expander 18 is

retrievable through the landing nipple 8 and the production tubing 6. Further, the expander 18 is adapted to radially expand the tubular portion 16 upon movement of the expander from the radially retracted mode to the radially expanded mode. Any suitable power source may be used to move the expander 18 between the radially retracted mode and the radially expanded mode. In the present example the expander is operated by a hydraulic power source (not shown) at surface that supplies pressurised hydraulic fluid to the expander via a fluid passage extending through the work string 10. In the position shown in Fig. 1, the expander 18 has been partially expanded in order to allow the expander to support the landing nipple 8 via an internal shoulder 20 thereof .

During normal operation of the first embodiment, the landing nipple 8 is lowered into the production tubing 6 on work string 10 whereby the landing nipple 8 is supported by the partially expanded expander 18 (Fig. 1) .

After the landing nipple 8 has arrived at the desired depth, the hydraulic power source at surface is operated to move the expander 18 to the radially expanded mode thereby radially expanding an upper section 22 of the tubular portion 16 against the inner surface of the production tubing 6. In this manner the landing nipple 8 is anchored to the inner surface of the production tubing 6 (Fig. 2) .

In a next step the hydraulic power source is operated to move the expander 18 to the radially retracted mode, and the expander 18 is then lowered on work string 10 into a yet unexpanded lower section 24 of the tubular portion 16 (Fig. 3) .

Subsequently the hydraulic power source at surface is operated to move the expander 18 again to the radially expanded mode thereby radially expanding the lower section 24 of the tubular portion 16 against the inner surface of the production tubing 6. The cycle of moving the expander 18 to the retracted mode, lowering the expander into another section of the tubular portion 16, and moving the expander to the expanded mode may be repeated as many times as necessary and in accordance with the length of the tubular portion 16. At this stage the tubular portion 16 has been fully expanded against the inner surface of the production tubing 6 (Fig. 4) .

The expander is then radially retracted and retrieved to surface on work string 10 (Fig. 5) . Finally the wellbore tool is lowered through the production tubing 6, for example on wireline, and received into the receiving portion 12 of the landing nipple.

Referring further to Fig. 6 there is shown the wellbore 1 provided with a modified landing nipple 26 which is largely similar to the landing nipple 8 except that the receiving portion 12 is arranged below the radially expandable tubular portion 16. Internal shoulder 20 for supporting the landing nipple 26 during lowering into the wellbore 1 is provided at the upper end of the radially expandable tubular portion 16. The modified landing nipple 26 may be installed in the production tubing 6 in the same manner as described above with reference to the landing nipple 8.

Referring further to Figs 7 there is shown a wellbore 30 formed in an earth formation 32. The wellbore 30 is provided with a wellbore casing 34. A landing device in the form of a steel landing nipple 36 is arranged in the casing 34. The landing nipple 36 includes a receiving portion 38 for receiving a sidetrack drilling assembly 39 (Fig. 8) for drilling a side track in the direction of arrow 45 so as to drill a deviated sidetrack wellbore section. The receiving portion 38 has an internal profile 40 adapted to receive and hold the whipstock 39 in place. Guide keys 42 or a guide profile may be provided at the internal profile 40 to orient the whipstock 39 in the desired direction. The landing nipple 36 further comprises a radially expandable tubular portion 44 arranged below the receiving portion 38 and integrally connected thereto.

Figure 8 illustrates that the sidetrack drilling assembly 38 according to the invention comprises a drill string 46 and a knuckle joint 47 carrying a tiltable drill bit 48 and that the assembly 38 is connected to the expanded landing device 36, wherein after expansion of the landing device 36 at a desired depth the drill string is further lowered into the wellbore as illustrated by arrow 53, thereby buckling the knuckle joint 47 and inducing the buckled knuckle joint 47 to tilt the sidetrack drill bit 48 towards the inner surface of the wellbore 30 or wellbore tubular 34, whereupon the tilted drill bit drills the sidetrack in the direction of arrow 45.

Figure 8 further shows that the knuckle joint 47 comprises upper and lower sections 47A and 47B that pivotably connected to an intermediate section 47C by pivots 50A and 50B that the upper section 47A is connected to the drill string 46 by an upper pivot 50C and that the lower section 47B is connected to the landing device 36 by a lower pivot 50D and the sidetrack drill bit 48 is secured to the intermediate section 47C of the knuckle joint 47 and is connected to the lower end of the drill string 46 by a flex joint 51A, 51B that permits the sidetrack drill bit 48 to pivot relative to the drill string 46 when the knuckle joint 47 is buckled.

Figure 8 also shows that the lower pivot 50D is connected to the landing tool 36 by a landing nipple assembly 52 that also performs as a bearing assembly that permits rotation of the sidetrack drilling assembly 38 within the wellbore 30 by rotating the drill string 46.

In the embodiment shown in Figure 8 the side track drill bit 48 is an abrasive and/or other jet drill bit comprising a nozzle to which drilling mud is supplied via the drill string 46 and flex joints 51A, 51B and which is positioned at a selected tilt angle a and orientation relative to a longitudinal axis and inner surface of the wellbore 30 by buckling the knuckle joint 47 and rotating the bearing assembly 52 by manoeuvring the drill string 46. The tilt angle a can be accurately configured by configuring the lengths Ll and L2 of the intermediate and lower knuckle joint sections 47C and 47B in relation to the width of the internal surface of the wellbore 30 or wellbore liner, so that the sidetrack is drilled at a relatively large and accurately defined tilt angle a.

It will be understood that the expandable setting device 44 may be lowered separately from or together with the side track drilling assembly 38 into the borehole and may be set at a desired depth using a Casing Collar Locator (CCL) or Gamma Ray (GR) log for depth control/correlation. After setting the orientation of expandable setting device 44 may be checked with a separate wireline gyro run. The bottom 52 of the side track drilling assembly 38 may be set in line and adjusted to the orientation of the expandable setting device 44 in order to orientate the jetting direction 45 of the sidetrack drilling assembly.

Centralization of the knuckle joint 47 assembly is done by a bow spring assembly 54 and an inflatable packer 55. The inflatable packer 55 is optional and may be replaced by a second bow spring assembly.