Monolithic blade stabiliser tool for drill string

Abstract

A drilling string stabilizer tool comprises a cylindrical body and a plurality of stabilizer blades machined as an integral component forming in this way a monolithic blade stabilizer tool. The stabilizer blades have an elongated shape and are aligned in the direction of the axis of the cylindrical body. The blades are disposed in such a way to result in an almost constant flow-by-area.

Claims

1. A monolithic blade stabiliser tool (30) for a drilling string comprising a cylindrical body part of radius (r) and a length (L) defining a longitudinal axis (X) and comprising a plurality of stabiliser blades (1), wherein said stabiliser blades (1) and said cylindrical body part are machined as an integral component defining a monolithic blade stabiliser tool, said stabiliser blades (1) extending radially outwardly from a surface of said cylindrical body part, and defining with their most outwardly extended surface an ideal cylinder coaxial with said cylindrical body part and having a radius (R), wherein R>r; each of said stabiliser blades (1) having an elongated shape extending parallel to said longitudinal axis (X) and having a length (I), wherein I<L; each of said stabiliser blades (1) comprising a front section (4), a back section (5) and a central section, an upper surface (6) having the shape of a dome defining a contact area, and vertical side walls (7), wherein said back section (5) tapers from said central section towards a substantially semi-circular back end and the front section (4) has substantially the shape of a semicircle, and wherein said upper surface (6) of the stabiliser blades slopes downwards near and towards the end of the front section (4) and also near and towards the end of the back section (5) till the upper surface (6) meets the surface of said cylindrical body part, each stabiliser blade including opposite rounded edges (8) between the vertical side walls (7) and the upper surface (6) beginning adjacent the front section (4) and moving toward the back section (5) and each rounded edge (8) terminating such that the contact area of the upper surface (6) and each vertical side wall (7) shares a respective common edge adjacent to the back section (5).

2. The monolithic blade stabiliser tool according to claim 1, wherein centers of said stabiliser blades are located along at least two coaxial spaced apart circles on the surface of said cylindrical body.

3. The monolithic blade stabiliser tool according to claim 2, wherein the plurality of stabiliser blades include more than three stabiliser blades and along each ideal cylinder there are placed at least a group of three stabiliser blades.

4. The monolithic blade stabiliser tool according to claim 3, wherein the average width of the front section of said stabiliser blades is substantially greater than the average width of the back section of said stabiliser blades.

5. The monolithic blade stabiliser tool according to claim 4, wherein front ends of each of said stabiliser blades on both cylinders extend in opposite directions, away from both cylinders.

6. The monolithic blade stabiliser tool according to claim 5, wherein the back section of the two groups of stabiliser blades are arranged in between each other such that oblique channels are formed between the back sections of each neighboring pair of stabiliser blades, defining a flow-by-area between the blades.

7. The monolithic blade stabiliser tool according to claim 6, wherein the flow-by-area is constant within 10% of its mean value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention will be more apparent in light of the detailed description of preferred, but not exclusive, embodiment, of a drilling string stabiliser illustrated by way of a non-limitative example, with the aid of the accompanying drawings, in which:

(2) FIG. 1 is a schematic drawing of a drilling assembly (bottom hole assembly);

(3) FIG. 2 is a perspective view of a stabiliser blade according to the state of the art;

(4) FIG. 3 is a perspective view of a stabiliser tool showing the grooves for mounting a monolithic type of stabiliser blade;

(5) FIG. 4 is a perspective view of a monolithic blade to be mounted on the stabiliser tool of FIG. 3;

(6) FIG. 5 is a perspective view of a monolithic stabiliser tool according to the invention;

(7) FIG. 6 are planar views of a monolithic stabiliser tool according to the invention.

(8) FIG. 7 shows a comparison regarding the surface contact area between the monolithic stabiliser tool according to the invention and the one with replaceable blades represented in FIG. 3.

(9) FIG. 8 shows details of the contact line for the monolithic stabiliser tool according to the invention and for the one with replaceable blades represented in FIG. 3.

(10) FIG. 9 shows the flow-by-area percentage in monolithic stabiliser tool compared with a stabiliser tool having replaceable blades (as the one depicted in FIG. 3).

(11) The same reference numbers in the drawings identify the same elements or components.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(12) A stabiliser tool according to the invention is shown in FIG. 5 and FIG. 6. Said stabiliser tool 30 comprises a cylindrical body part of radius r and length L defining a longitudinal axis X. The monolithic stabiliser tool 30 comprises three or more upper stabiliser blades 1 and three or more lower stabiliser blades. The blades 1 and the cylindrical body part are machined as an integral component forming in this way a monolithic blade stabiliser tool. The blades 1 extend radially outwardly from the surface of the cylindrical body part defining with their most outwardly extended surface an ideal cylinder coaxial with said cylindrical body part and having a radius R>r. The stabiliser blades 1 are preferably all of identical shape and we describe only one stabiliser blade. In this description we refer conventionally to the triangle-shaped part of the stabiliser blades as the back (or rear) section of the stabiliser blade only for ease of description, without giving any limiting meaning to these adjectives.

(13) The stabiliser blade 1 according to the invention has an elongated shape with a length I, shorter than L, defining a longitudinal axis parallel to the axis of the monolithic stabiliser tool, with a front section 4, a back section 5, a central section, and vertical side walls 7. The upper surface 6 of the blade, having the shape of a dome, defines the contact area. The back section 5 tapers from the central section towards a substantially semi-circular back end, while the front section 4 has substantially the shape of a semicircle. The upper surface 6 of the stabiliser blade 1 slopes downwards near and towards the end of the front section 4 and also near and towards the end of the back section 5 till it meets the surface of the cylindrical body part of the monolithic stabiliser tool. The stabiliser blade has the overall shape of a wing. Preferably, all edges 8 between the side vertical walls and the upper surface are rounded and similarly a rounding of the edges of all other walls having a border with the upper surface is also performed.

(14) In the embodiment described in FIGS. 5 and 6 six stabiliser blades are machined in an axially aligned manner on the cylindrical surface of the cylindrical body part. A first group of three stabiliser blades have their centers arranged and equally distributed on a first circle on said cylindrical surface and a second group of three stabiliser blades have their centers arranged and equally distributed on a second circle, which second circle is spaced apart from the first circle. The front ends 4 on both circles extend in opposite directions, away from both circles, such that the front area of the forward moving stabiliser tool is provided with the wider front ends 4 of the stabiliser blades 1, irrespective of the direction in which the drilling string is being moved. The back sections of the two groups of stabiliser blades 1 are arranged in between each other, where the back ends 5 reach, in axial direction, approximately towards the centers of the neighboring stabiliser blades 1. Thereby oblique channels are formed between the back halves of each neighboring pair of stabiliser blades 1, defining the free flow area between the blades.

(15) The stabiliser bladesthree or more upper and three or more lowerare suitably positioned to optimise the hydrodynamic efficiency of the tool. This arrangement assists in streamlining the mud flow around the stabiliser blades, minimising the restriction of cuttings being carried out of the hole and enhancing hole cleaning, while maintaining all round centralisation of the bottom hole assembly in the borehole.

(16) The shape of the stabiliser blades is such that they efficiently displace the drilling fluids and drilling cutting around the stabiliser blades, and greatly reduce the balling up and packing off of the stabiliser tool with drilled cuttings.

(17) The tapered shape of the stabiliser blades reduce friction, and enhance the stabilisers performance while sliding in the oriented mode.

(18) The function of the cross sectional taper of the blade is to reduce rotary torque and minimise undercutting when drilling in the rotary mode.

(19) The toe and heel angle of the stabilised blades are preferably machined at approximately 20 degrees to minimise hanging-up and reduce up and down drag in the borehole.

(20) Flow paths can be milled into the cylindrical body to create a self-cleaning and jetting effect, accelerating cuttings transportation over the cylindrical body upset area. The self-cleaning action, i.e. the jet effect, has shown minimised mud build up, homogeneous drilling fluid flow, and minimised balling up.

(21) The monolithic stabiliser blade has a large surface contact area, greater than the surface contact area of the state-of-the-art stabiliser tool with replaceable blades resulting in an improved stability. FIG. 7 shows two stabilizer tools having the same diameter, the one on the left representing a monolithic stabiliser according to the invention, while the stabiliser tool on the right represents a stabiliser having replaceable blades, like the one of FIG. 3. The surface contact area are shown as shadow lines. From the figure it is possible to see that the surface contact area of the blade of the monolithic stabiliser tool is greater than the surface contact area of the replaceable blade.

(22) FIG. 8 shows a more detailed comparison between the monolithic stabiliser tool depicted in the left hand side of the figure and the replaceable blade stabiliser tool of FIG. 3, depicted in the right hand side. The contact line is longer in the current invention (monolithic design) than the one of the stabiliser tool with replaceable blades of FIG. 3. This feature is expected to improve stabilisation. At the same time the available opening for mud/cuttings to flow is larger in the current invention, improving the hydrodynamics further as compared to the replaceable blades stabiliser tool.

(23) In wells that do not have an adequate hole cleaning further accumulation of cuttings can occur. This is common in directional or horizontal wells. Increasing circulating pressure while drilling, or increase in drag when tripping are indications of a problem. In the current invention, the monolithic construction allows a better flexibility in choosing the value of the free flow area, also called the flow-by-area, which is an important design parameter. This flexibility feature may be advantageous in specific applications, such as in almost horizontal drilling, where as long as the bypass area is greater than the cuttings bed area, then tripping without circulation is possible, allowing also small radius drill string stabiliser.

(24) The flow-by-area should be 35% of the hole area for hole size of 10? (inches) and above, and 25% of the hole area for hole sizes below 10? (inches).

(25) As soon as we decide on a relation between the flow-by-area, e.g. 55%, and the contact area, e.g. 45%, then the aim is to keep the flow-by-area as constant as possible.

(26) In FIG. 9 the graph shows the relation between the flow-by-area of a replaceable blade stabiliser tool (the one depicted in FIG. 3) and the monolithic one of the present invention. The elimination of the mounting components in the monolithic stabiliser tool allows better results in term of constancy of the flow-by-area. From the graph it results a flow-by-area that is constant within 10% of the mean value.

(27) Whereas the invention is described by way of a preferred embodiments, the man skilled in the art will appreciate that modifications can be made within the scope of the invention as defined by the claims.