GB2133059A - Drilling tools - Google Patents

Abstract

A stabiliser has its external blades formed by ribs 19 suitably faced to constitute the external blades of the stabiliser; but the blades, instead of being parallel to the stabiliser axis, form a herringbone pattern when the stabiliser is viewed in side elevation. Preferably the blades run at an angle of from 30 DEG to 60 DEG to the stabiliser axis when the stabiliser is viewed in side elevation. <IMAGE>

Description

SPECIFICATION Drilling tools The invention relates to drilling tools.

The invention is particularly applicable to tools for use in drilling for oil or natural gas, and is especially concerned with the stabilisation of directional drilling in varying bed formation.

The quality and face design of face, of the stabiliser blades is a major factor in deciding the quality and ease of directional drilling when using such tools.

Facings, for example tungsten carbide, can be used on the stabiliser blades if the blades are designed appropriateiy. For example, UK Patent Specification No 1 372 181 (Groom) shows a stabiliser whose blades exhibit external ribs each faced with tungsten carbide and each running parallel to the stabiliser axis.

According to the present invention, a stabiliser has its external blades formed with ribs suitably faced to constitute the external blades of the stabiliser; but the blades, instead of being parallel to the stabiliser axis, form a herringbone pattern when the stabiliser is viewed in side elevation.

Such a stabiliser is believed to give more accurate and easier control and maintenance of drilling direction, especially when key seats or other variations in bed formation are encountered by the descending drill string.

Preferably the blades run at an angle of between 300 and 600 to the stabiliser axis when the stabiliser is viewed in side elevation. The herringbone pattern assists such a range of drilling angles to be adopted whereas this was not, as far as is known, previously possible.

Preferabiy also, each blade changes direction, in defining its "herringbone", about a notional line whose position is variable down the length of the blade depending upon differing drilling conditions and formations to be drilled.

The said line may lie between one-third and one-half the way down the length of the blade, when a build-up of mud pressure is to be avoided, and vice versa when producing the opposite effect.

In the accompanying drawings: Figures 1 to 4 each show, in side elevation, different types of drill stabiliser embodying the invention; and Figure 5, also in side elevation, but drawn to an enlarged scale, shows the bladed body of the stabiliser of Figure 4.

In each of Figures 1 to 4, a drill stabiliser consists essentially of a hollow elongate linear circular-cylindrical body 11, enlarged in diameter about its mid-length region to provide an externally-bladed upset 1 2. The body is reduced in diameter and tapered and screw-threaded at the bottom or "pin" end 13, and taper-bored and internally screw-threaded at the top or "box" end 1 4 (except for a "near-bit" stabiliser which is double "box", ie. bored and internally threaded at both ends). In use, and in well-known manner, stabilisers are screw-threaded into the drill string at strategic positions to centralise the string at fulcrum points to either make, maintain, or drop angle.As the resulting assembled drill "string" of components rotates then the mud and slurry cleared by the drill is recirculated to pass down the inside of the string which is hollow for that purpose. The near-bit stabliliser is important in its design and length of blades to minimise the tendency of the bit to work off to the right.

In Figure 1, the externally-bladed sleeve 12 is a circular-cylindrical sleeve, either shrink on or screwed, which is coaxial with the body 11 and rotates with the body. The blades on the sleeve 1 2 are bevelled at each of their opposite ends, as indicated respectively at 1 5 and 1 6.

In Figure 1, a cylindrical sleeve is initially manufactured separately from the body, has blades welded into it, and is then shrunk on to the body.

In Figure 2, the sleeve 12 is machined, cast, or is a sleeve with welded blades and is manufactured separately from the body 11. It slides on to the body from the pin-end 13 of the body, and then screw-threads on to and over an enlarged-diameter threaded portion 1 7 and hard up against a further-enlarged shoulder 1 8 both machined integrally into the body 11.

In Figure 3, the blades are manufactured separately and welded to the body 11.

In Figure 4 the upset portion 12A and body 11 are again machined integrally from the same piece of bar. In this embodiment, the upset portion is turned to full diameter and the blades 19 are formed by milling inter-blade channels 21 from the sleeve material.

It will be evident that the blades 19 form a herring-bone pattern when the stabiliser is viewed in side elevation. The respective angles A, B, which each portion of the blade makes with the stabiliser axis, preferably lie between approximately 300 and approximately 600. The vee angle C of each blade preferably lies between 900 and 1200. Thus, for example, if the angle C is 900 then the angle A may be 600 and the angle B will then be 300. This angling and patterning of the blades enables the stabiliser to resist the inevitabie tendency to be pushed off its drilling line by variations in the formation being drilled.

Figure 5 also shows that each blade 1 9 changes direction about a notional line 22 which is less than half way down the line of the blade when measuring that length from the pin-end 13 of the stabiliser. In Figure 5 the line 22 lies just over one-third the way down the length of the blade when so measured.

Each blade changes direction about the line 22 in a smoothly-radiused manner as indicated in Figure 5.

In Figures 4 and 5, the blades are flat-faced and the inter-blade channels 21 which separate them are particular in section. In Figure 3, the blades 19 are again flat-faced but the channels 21 are trapezoidal in section.

Methods of facing the blades, and materials suitable for such, can be adapted from UK Patent Specification No 1 372 181 or from UK Patent Specification No 1 293 905 (Lion Oil Tool Holdings) which is relevant to the field of the present invention.

Advantageously the metal carbide fragments may be more densly packed in the brass matrix than is out-lined in Specification 1 293 905. For example, the proportions of metal carbide to brass may be within the range 60:40 to 90:10, but we have found that carbide:brass proportions within the range 75:25 to 85:15 and especially around the proportion 80:20 are to be preferred because in tools of this kind they represent the optimum combination of increased wear surface life and maintain matrix stability.

In Figure 5, in which the line 22 lies just over one-third the way down the length L pf the blade, the lengths of channel 21 above the line 22 are smaller in cross-sectional area than the lengths of channel 21 below the line 22. If the line 22 were half way down the length L, each channel 21 would be the same cross-sectional area along its whole length. If the line 22 were over one-half the way down the length of the blade, for example between one-half and two-thirds the way down the length L measured from the pin-end 1 3 of the stabiliser, then the lengths of channel 21 above that line would be larger in cross-sectional area than the lengths of channel below the line 22; depending in every case on whether or not a build-up of mud pressure is to be avoided or positively created.

Claims (Filed on 23. 11. 83) 1. A stabiliser which has its external blades formed with ribs suitably faced to constitute the external blades of the stabiliser; but in which the blades, instead of being parallel to the stabiliser axis, form a herring-bone pattern when the stabiliser is viewed in side elevation.

2. A stabiliser according to Claim 1 and in which the blades run at an angle of 300 to 600 to the stabiliiser axis when the stabiliser is viewed in side elevation.

3. A stabiliser according to Claim 1 or Claim 2 and in which each blade changes direction, in defining its "herringbone", about a notional line whose position is variable down the length of the blade depending upon differing drilling conditions and formations to be drilled.

4. A stabiliser according to Claim 3 and in which the said line lies between one-third and one-half the way down the length of the blade.

5. A stabiliser substantially as described herein with reference to, and as illustrated in, any appropriate combination of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. Specification No 1 372 181 or from UK Patent Specification No 1 293 905 (Lion Oil Tool Holdings) which is relevant to the field of the present invention. Advantageously the metal carbide fragments may be more densly packed in the brass matrix than is out-lined in Specification 1 293 905. For example, the proportions of metal carbide to brass may be within the range 60:40 to 90:10, but we have found that carbide:brass proportions within the range 75:25 to 85:15 and especially around the proportion 80:20 are to be preferred because in tools of this kind they represent the optimum combination of increased wear surface life and maintain matrix stability. In Figure 5, in which the line 22 lies just over one-third the way down the length L pf the blade, the lengths of channel 21 above the line 22 are smaller in cross-sectional area than the lengths of channel 21 below the line 22. If the line 22 were half way down the length L, each channel 21 would be the same cross-sectional area along its whole length. If the line 22 were over one-half the way down the length of the blade, for example between one-half and two-thirds the way down the length L measured from the pin-end 1 3 of the stabiliser, then the lengths of channel 21 above that line would be larger in cross-sectional area than the lengths of channel below the line 22; depending in every case on whether or not a build-up of mud pressure is to be avoided or positively created. Claims (Filed on 23. 11. 83)

1. A stabiliser which has its external blades formed with ribs suitably faced to constitute the external blades of the stabiliser; but in which the blades, instead of being parallel to the stabiliser axis, form a herring-bone pattern when the stabiliser is viewed in side elevation.

2. A stabiliser according to Claim 1 and in which the blades run at an angle of 300 to 600 to the stabiliiser axis when the stabiliser is viewed in side elevation.

3. A stabiliser according to Claim 1 or Claim 2 and in which each blade changes direction, in defining its "herringbone", about a notional line whose position is variable down the length of the blade depending upon differing drilling conditions and formations to be drilled.

4. A stabiliser according to Claim 3 and in which the said line lies between one-third and one-half the way down the length of the blade.

5. A stabiliser substantially as described herein with reference to, and as illustrated in, any appropriate combination of the accompanying drawings.