AU5290896A - A method and a device for directional drilling - Google Patents

Description

A METHOD AND A DEVICE FOR DIRECTIONAL DRILLING

The invention relates to a method and a device for directional drilling.

In connection with the drilling of holes in the crust of the earth, e.g. gas and oil wells, it is often desirable to be in a position of varying the direction of the bore hole.

In order to utilize a gas or oil field at a relatively large distance from an oil installation, it is necessary to drill wells extending laterally out from the oil installation. Methods and devices for drilling wells having a moderate deviation from a vertical line, are well known. It has become more and more usual, especially in connection with newer fields in the North Sea, to drill wells deviating substantially from the vertical line, and there exist wells of long extents close to horizontal. Optimum utilization of an oil field requires that gas and oil wells can be drilled in a predetermined direction and with a relatively high accurancy. Also, when drawing cables through the ground, there is a need for hole drilling in varying directions.

It is known to place a wedge or key, a socalled whipstock (a guide key) , within a bore hole in order to force the bit laterally outwards in order to achieve a directional change. Such a whipstock has several disadvantages which can be summed up in that they are time-consuming and difficult to use, and it happens that they are difficult to remove or move after use. More modern directional drilling of gas and oil wells uses a downhole motor operating the bit. Then, the drill string does not rotate, it being usual to use coiled tubing as drill string. Directional guidance is achieved in that the rotational axis of the bit forms an angle with the axis of the drill string, the bit thereby trying to point laterally. If the bottom part of the drill string, possibly the downhole motor, is assigned a navigational aid giving the operator information concerning the direction in which the drilling is taking place, the operator may choose a drilling direction through a rotation of the drill string. Also, it is known to dispose a separate downhole directional unit remote operated from the surface, such that the operator can choose drilling direction.

In spite of these known methods and devices, it appears to be difficult to achieve the desired and guided drilling direction. This may have several causes, but variations within the formation in which the drilling is carried out, has a major influence thereon. The bit has a tendency of deviating from a hard zone towards a softer one. If one shall drill laterally out through an existing vertical well, it is often necessary to subject the bit to large and disadvantageous lateral forces. This is particularly the case if the drilling is to be carried out through the side of a lined well.

In connection with horizontal bore holes, it is generally a problem to achieve the desired resting force between bit and formation, and the drilling rate decreases. Increased drilling rate may, however, be achieved through the arrangement of shear jets, e.g. a high speed abrasive liquid flow, such as known from Norwegian patent No. 171,077, within the cutting area of the bit.

The object of the invention is to provide a method and a device giving an easily guidable drilling direction. The object is achieved through features as defined in the following claims.

According to the invention, one or more shear jets are disposed within the shearing or cutting area of the bit, correspondingly to what is known from said Norwegian patent No. 171,077, where the hitting points of the shear jets are symmetrically positioned around a rotational axis around which the shear jets can rotate. In accordance with the invention, the hitting points of the shear jets are asymmetrically disposed in relation to said rotational axis. Using this principle, the bit itself will seek the desired direction where the resistance against drilling is the least.

An examplary embodiment of the invention is described in the following, reference being made to the attached drawings, wherein:

Figure 1 diagrammatically shows a part of a well wherein a drill string and a downhole equipment for directional drilling are disposed;

Figure 2 shows, on a larger scale, from the side and partly in section, a bit having an eccentrically placed and freely suspended nozzle for supplying a shear jet;

Figure 3 shows the same bit as in figure 2 when the bit has • rotated half a revolution;

Figure 4 shows a shearing path for a shear jet, as seen in the direction of drilling.

In figure 1, reference numeral 1 denotes a well where the bottom end of a substantially vertical drill string 2 is coupled to a tubular bend 3 and a downhole motor 4 adapted to operate a bit 5. By means of the bend 3, the rotational axis 6 of the bit 5 deviates from the axis 7 of the drill string 2. Thus, the drilling direction will deviate from the substantially vertical well 1. Upon rotating the drill string 2, the bit 5 may, as known, be brought to drill in another direction.

In the bit 5, as known per se, an eccentrically placed nozzle 9 has been freely suspended in a bearing 10. The nozzle 9 can turn about a rotational axis 11 substantially parallel to the axis 6 of the bit 5. Cutting fluid is supplied to the nozzle 9 through a supply hose 12. Out from the nozzle 9, a jet 13 of abrasive liquid flows. The direction of the jet 13 deviates from the direction of the rotational axis 11 of the nozzle 9. However, the direction of the jet 13 is fixed as it appears from figure 3 where the bit has rotated half a revolution. The nozzle 9 is adapted to rotate about the axis 11 with the same speed as the bit 5 and with a rotational direction opposite of the rotational direction of the bit 5, so that the direction of the shear jets 13 does not change when the bit 5 rotates. Thus, the jet 13 works an area within a limited and eccentrically placed part face of the total working face of the bit 5. The result is reduced resistance against drilling in the direction defined by the eccentric location of said part face. By altering the direction of the jet 13, e.g. by turning the supply hose 12 a little, the part face's location can be changed and, then, the drilling direction will also be changed because the bit 5 seeks towards a place exhibiting a lower resistance against drilling.

In figure 4, the circle 14 denotes the wall of the well 1 as seen in the direction of drilling, while 15 denotes the working path of the jet 13 as the bit 5 rotates. As it appears from figure 4, the jet 13 works on an eccentrically placed part face of the total and substantially circular working face of the bit 5. This is achieved in that the hitting point of the shear jet 13 is eccentrically positioned in relation to the rotational axis 11 of the nozzle 9. If more than one shear jet 13 are used, the hitting points of the shear jets 13 must be asymmetrically situated in relation to the rotational axis 11. Thus, the centre of gravity of the area situated within the hitting points of the shear jets 13 becomes eccentrically located in relation to the rotational axis 11 of the shear jets.

The degree of directional guidance can be made to vary by letting the shear jets 13 be selectively activatable. At a desired point of time, one or more nozzles 9 may be closed by adding particles to the flow within the supply hose 12. The nozzles 9 may have differently sized outlet openings, and adapted to be closed selectively by adding particles larger than one nozzle's 9 outlet opening.

The direction of the shear jets 13 may also be variable and controllable (guidable) in that the nozzles 9 are flexably suspended and by varying the tension on the supply hose 12.

It goes without saying that the invention is not restricted to the use of abrasive liquid jets, but that all suitable shear and cutting jets may be utilized, such as it e.g. appears from Norwegian patent No. 171,077.

Also, it goes without saying that the invention can be used in connection with all kinds of directional drilling.

Claims (2)

C l a i s

1. A method for directional drilling of holes in the crust of the earth, wherein the direction of a hole is changed by eroding a portion of the hole's bottom and, possibly, also wall by means of one or more shear jets, such as liquid jets which are allotted high speed by means of suitable nozzles, c h a r a c t e r i z e d i n that the shear jets (13) erode the hole's (1) bottom and, possibly, wall in the direction in which the hole (1) is desired to be extended, simultaneously as a rotary bit (5) works the non-eroded portion of the hole's (1) bottom, whereby the bit (5) naturally will seek its way in the direction where the bottom/wall of the bore hole (1) is eroded.

2. A device for directional drilling of holes in the crust of the earth in accordance with the method as set forth in claim 1, comprising a rotary bit (5) having at least one nozzle (9) to generate a liquid-based shear jet (13) , wherein the nozzle (9) is rotatable around an axis (11) substantially parallel to the axis (6) of the bit (5) and eccentrically placed in relation to the axis (6) , and wherein the nozzle (9) is adapted to direct at least one shear jet (13) obliquely out from the axis (11) toward the bottom of the hole (1) , c h a r a c t e r i z e d i n that the nozzle (9) is adapted to rotate about the axis (11) with the same speed as the bit (5) and with a rotational direction opposite of the rotational direction of the bit (5) , so that the direction of the shear jets (13) does not change when the bit (5) rotates.