WO1994009244A1

WO1994009244A1 - Underreamer

Info

Publication number: WO1994009244A1
Application number: PCT/NO1993/000153
Authority: WO
Inventors: Tor Jan Eriksen; Rune Woie; Egil Kristiansen
Original assignee: Target Drilling Services As
Priority date: 1992-10-14
Filing date: 1993-10-13
Publication date: 1994-04-28
Also published as: NO923978D0; NO923978L; AU5345894A

Abstract

A knee-shaped underreamer (3) is provided with external cutting inserts and is adapted to be fitted within a drill string (2) above a bit (4). Weight from the drill string (2) urges the bit (4) against the bottom of a bore hole (1). Due to the knee-shape, the underreamer (3) is pressed out toward the wall of a bore hole (1). When the drill string (2) rotates, the underreamer (3) describes a circle, and the external cutting inserts of the underreamer (3) scrape off material from the wall of the bore hole (1) at the same time as the bit (4) lengthens the bore hole (1). A motor (6) drives the bit (4), independently on the rotation of the drill string (2). A stabilizer (5) having variable diameter is fitted within the drill string (2) above the underreamer (3). The stabilizer (5) assists in increasing the bearing force of the underreamer (3) against the wall of the bore hole (1), simultaneously reducing the risk of having the drill string (2) hurled out toward the wall of the bore hole (1).

Description

UNDERREAMER

The invention relates to an underreamer for use in oil drilling, as well as an arrangement in a drill string wherein the underreamer is included.

When drilling for oil, it is sometimes an advantage to increase the diameter of the bore hole beyond the diameter of the bit, and it is known to dispose underreamers within the drill string above the bit. Known underreamers have cutting inserts disposed on arms which are swung out toward the hole wall when the bit occupies the working position, and which are swung in toward the drill string when this is being withdrawn from the hole. Thus, the hole diameter is widened subsequent to a pilot hole being drilled in a usual way.

Known underreamers are complex and consist of many movable and partly sensitive parts. Also, it iε a disadvantage with known underreamers that a hole section has to be drilled two times.

An object of the invention is to provide an underreamer wherein said disadvantages are avoided. Further, it is an object to provide an underreamer for use with a bit driven by a downhole motor, whereby controlled directional drilling can be achieved.

In accordance with the invention, the objects are achieved through the features as defined in the following claims.

Three examples of embodiments of the invention are described in the following, reference being made to the attached drawings, wherein:

Figure 1 shows, in side elevational view, partly in section, a portion of a bore hole; bit and underreamer being working;

Figure 2 shows the same as figure 1, after the drill string has rotated half a rotation around its own axis;

Figure 3 shows an underreamer having a rotary end adapted to be rotated by a motor;

Figure 4 shows a combined downhole drill mud motor and under¬ reamer.

In the drawings, reference numeral 1 denotes a bore hole, 2 a drill string, 3 a knee-shaped underreamer equipped with external cutting inserts, not shown, 4 a bit and 5 a stabilizer. As known, the drill string 2 is suspended from a drilling equipment adapted to raise and lower the drill string 2 and to rotate the drill string 2 around the longitudinal axis. The bearing force of the bit 4 against the bottom of the bore hole 1 is, as known, controlled by lowering the drill string 2 until the weight of the drill string 2 urges the bit 4 against the bottom of the bore hole 1 with a desired force. In accordance with the invention, extra weights may be fitted into the drill string 2 in the usual way. When the drill string 2 is lowered gradually, thereby transferring weight to the bit 4, the drill string 2, because of the knee-shape of the underreamer 3, will yield a little, so that the underreamer 3 is urged against the wall of the bore hole 1. When the drill string 2 is rotated around the longitudinal axis, the bore hole 1 is lengthened by means of the bit 4. Simultaneously, the underreamer 3 carries out a circular movement, whereby the external cutting inserts of the underreamer will scrape off material from the wall of the bore hole 1, increasing the diameter of the bore hole 1. The stabilizer 5 which, preferably, is of the type wherein the diameter can be varied assists in increasing the bearing force of the underreamer 3 against the wall of the bore hole 1, and in reducing the risk of having the rotating drill string 2 hurled out toward the wall of the bore hole 1 due to the eccentricity created by the underreamer 3.

In figure 3, it is shown a motor 6 fitted within the drill string 2, and one end 7 of the underreamer 3 is adapted to be rotated around a longitudinal axis 8 by the motor 6 through a transmission, not shown. Thus, the motor 6 is adapted to operate the bit 4, independently on the drill string 2 and the underreamer 3. Due to the directional deviation from the drill string 2 and the bearing force between the underreamer 3 and the wall of the bore hole 1, the bit 4 will be diverted toward the side of the bore hole 1. If the drill string 2 is rotating around its own axis, the side diverting of the bit 4 will be evenly distributed, and the bore hole will be extended along a nearly straight line. Stopping the rotation of the drill string 2 periodically, εaid side diverting may be utilized intentionally in order to obtain a change of direction of the bore hole 1.

Figure 4 shows an underreamer according to the invention, combined with a downhole motor 9 having a knee-shaped enclosure and an outgoing drive shaft 10 adapted to rotate the bit 4 around the axis 8. The drive shaft 10 may be sleeve-shaped in order to allow drill mud to pasε. The enclosure of the motor 9 is provided with external cutting inserts scraping off material from the wall of the bore hole 1 when the drill string 2 is rotated. Besides, the mode of operation will be as explained above for figure 3.

Claims

C l a i m s

1. An underreamer to be fitted into a drill string (2), char a ct er i z ed in that the underreamer (3) is formed as a knee and provided with external cutting inserts adapted to εcrape off material from a bore hole'ε (1) wall when the drill εtring (2) .is rotated.

2. An underreamer as set forth in claim 1, c h a r a c t e r i z e d i n that one end (7) of the underreamer (3) is adapted to be rotated around a longitudinal axiε (8) forming an angle in relation to the longitudinal axiε of the drill εtring (2) .

3. An underreamer as set forth in claim 2, c h a r a c t e r i z e d i n that the rotary end (7) of the underreamer (3) is adapted to be driven from a motor (6) .

4. An underreamer aε set forth in one or more of the preceding claims, c h a r a c t e r i z e d i n that a motor's (9) enclosure is formed as a knee and provided with external cutting insertε adapted to scrape off material from a bore hole's (1) wall when the enclosure of the motor is rotated, simultaneously as the motor (9) has an outgoing drive shaft/drive sleeve (10) adapted to drive a bit (4) .

5. An arrangement in a drill string, c h a r a c t e r i z e d i n that a stabilizer (5) is placed above an underreamer (3) within a drill string (2) , whereby the stabilizer (5) assists in centering the drill string (2) within a bore hole (1) and, thus, in increasing the bearing force between the underreamer (3) and the wall of the bore hole (1) .