# US 7,464,774 B2 · Drill bit and system for drilling a borehole

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- Number: US 7,464,774 B2
- Document ID: US7464774B2
- Status: Granted
- Kind: B2
- Application number: 10/557,324
- Filed: 2004-05-18
- Published: 2007-05-10
- Granted: 2008-12-16
- Earliest claimed: 2003-05-21
- Assignees: Shell Oil Company
- Inventors: Jean-Michel Claude Gaston Savignat; Djurre Hans Zijsling
- Web page: https://patentgrep.com/patent/US7464774B2

## CPC

- E21B 7/068: {drilled by a down-hole drilling motor (down-hole drives per se E21B4/00, E21B7/067 takes precedence)}
- E21B 7/062: {the tool shaft rotating inside a non-rotating guide travelling with the shaft (E21B7/067 and E21B7/068 take precedence)}
- E21B 7/067: {with means for locking sections of a pipe or of a guide for a shaft in angular relation, e.g. adjustable bent sub}
- E21B 10/26: Drill bits with leading portion, i.e. drill bits with a pilot cutter; Drill bits for enlarging the borehole, e.g. reamers (percussion drill bits with leading portion E21B10/40)
- E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS

## Abstract

A drill bit for drilling a borehole in an object, the drill bit having a central longitudinal axis and comprising: a pilot section for drilling a pilot bore section of the borehole in the object; an under-reaming section in a following position with respect to the pilot section, the cutting diameter Du of the under-reaming section being larger than the cutting diameter Dp of the pilot section; a connecting shaft extending between the pilot section and the under-reaming section; and a stabilising section located between the pilot section and the under-reaming section, wherein the stabilising section fits inside the pilot bore section and is capable of laterally stabilising the drill bit relative to the object while allowing rotation of at least the pilot section relative to the object.

## Claims

### Claim 1

A drill bit for drilling a borehole in an object, having a central longitudinal axis and comprising:
a pilot section with a cutting diameter Dp for drilling a pilot bore section of the borehole in the object;
an under-reaming section with a cutting diameter Du in a following position with respect to the pilot section, the cutting diameter Du of the under-reaming section being larger than the cutting diameter Dp of the pilot section;
a connecting shaft extending between the pilot section and the under-reaming section;
a stabilising section located between the pilot section and the under-reaming section, wherein the stabilising section fits inside the pilot bore section and laterally stabilizes the drill bit relative to the object while allowing rotation of at least the pilot section relative to the object,
wherein the stabilising section and the pilot section are substantially concentrally arranged; and
wherein the pilot section is rotatable about the central longitudinal axis relative to the stabilising section;
further including a locking means for selectively disabling rotation of the pilot section about the central longitudinal axis relative to the stabilising section.

### Claim 2 (depends on 1)

The drill bit of claim 1, wherein said rotation comprises rotation about the central longitudinal axis of the drill bit.

### Claim 3 (depends on 1)

The drill bit of claim 1, wherein said rotation comprises rotation about an axis extending in lateral direction of the drill bit.

### Claim 4 (depends on 3)

The drill bit of claim 3, wherein the pilot section is rotatable about said lateral axis relative to the stabilising section.

### Claim 5 (depends on 1)

The drill bit of claims 1, wherein the pilot section and the under-reaming section are rigidly connected to each other via the connecting shaft.

### Claim 6 (depends on 1)

The drill bit of one of claim 1, wherein the stabilizing section is positioned such that L1 is larger than L2, wherein
L1=the distance between the operative center of the stabilising section and the operative centre of the pilot section;
L2=the distance between the operative center of the stabilising section and the operative center of the under-reaming section.

### Claim 7 (depends on 6)

The drill bit of claim 6, wherein the cutting diameter (Dp) of the pilot section is larger than half the cutting diameter (Du) of the under-reaming section, and wherein the stabilising section is positioned such that L2 is larger than half L1.

### Claim 8 (depends on 6)

The drill bit of claim 6, wherein the stabilising section is positioned such that the ratio L2/L1 is substantially equal to the ratio Dp/Du.