EP0176180B1

EP0176180B1 - Hole opener

Info

Publication number: EP0176180B1
Application number: EP85305111A
Authority: EP
Inventors: Neil Andrew Abercrombie Simpson; Alan Martyn Eddison; Ian Alexander Millar
Original assignee: Diamant Boart NV SA
Current assignee: Diamant Boart NV SA
Priority date: 1984-07-27
Filing date: 1985-07-18
Publication date: 1988-11-30
Also published as: NO169609B; NO169609C; EP0176180A1; NO852975L; DE3566564D1

Description

This invention relates to a hole opener for enlarging well bores.
In the process of drilling wells for hydrocarbon minerals or geothermal energy, there are many situations where an existing well bore has to be enlarged. This can be achieved in a variety of different ways. For example a first hole enlarger of the type described in US-A-3,237,705 can be run. It relates to a drilling apparatus comprising a string of drill pipe, a drill bit on the lower end of the drill pipe and a cylindrical body coupled into the string of drill pipe above the drill bit to straighten or enlarge the bore hole drilled by the drill bit.
Extending from only one side of the cylindrical body is a lateral projection having a reaming face of appreciably half-circumferential cross section at one side of the string of drill pipe to provide an upflow passageway on the trailing and advance sides ofthe reaming face. An aperture through the housing wall of the cylindrical body and the lateral projection emerges between the diamond cutting elements which are set in the reaming face to be forced into cutting contact with the wall of the bore hole.
The lateral projection of the cylindrical body is preferably formed of a powdered metal sleeve extended around a reduced portion of the cylindrical body. The bond between the cylindrical body and the powdered metal sleeve is insured by means of a plurality of protuberances tightly inset within sockets drilled into portions of the cylindrical body.
By rotation of the cylindrical body, the reaming face of the lateral projection gyrates in a circular path about the axis of rotation of the cylindrical body. The apparatus is stabilised by having its lower diameter the same as the pilot hole so as to bear against the pilot hole in use, but the pilot hole tends to be non-uniform and rough-walled and severe vibration of the tool can result.
It is also known by US-A-2,249,732, an off center reamer used in drilling to straighten out drilling hole. The apparatus comprises a hollow drilling stem which is internally threated at its lower end, a hollow coupling member having nipples position at an angle with respect to the longitudinal axis of both the stem and a drill bit engaged in the lower end of the coupling member.
The coupling is provided with a discharge opening for discharging water during the drilling operation. The coupling has a lateral projection formed of a vertical extending blade having a reinforcing lug at its rear side. This lateral projection constitutes a reamer which thanks the offset position of the coupling, cuts one side only of the hole.
In this drilling apparatus, the coupling is employed onlywhere it is desired to straighten out the hole being drilled.
The apparatus cannot be used for enlarging drilling wells to greater bore hole sizes but has only a reaming action.
A third drilling apparatus to enlarge well bores for oil drilling is disclosed in US-A-2028910. It concerns a rotatable well reamer including a sleeve having a plurality of radially projecting cutting teeth preferably integral with the sleeve. Various teeth are circumferentially spaced around the sleeve, so that their combined cutting contact constitutes an appreciable arc of the circumference of the well bore. Each circumferentially successive tooth longitudinally overlaps and projects below the next preceding tooth emerging from the peripherical wall of sleeve. They are arranged in vertical rows widening out from the small cutting teeth of the lower end of the sleeve to the large cutting teeth of the upper end of the sleeve. Vertical channels are formed between the rows of cutters for upflow passage of cuttings, adapted to engage the wall of a well bore for enlarging it to gauge throughout the circumference determined by the cutting teeth of the upper end of the sleeve.
The particular arrangement of the cutting teeth procures a radially inwardly and upwardly slanting peripheral edge, which is relatively sharp adopted for shearing cut into the formation.
The drawback of this reamer is the back of efficiency in some layers of terrain such as clay soils that clogs the surface of the tool.
The weak conicity of the apparatus brakes the rotation of the blades under the weight of the drilling stem and the tool, which has a propensity to wedge. The blades undergo premature near the tear and suffer deterioration and crack due to shocks to certain parts of the blades against the wall of the drill hole.
It has also been proposed to use a self-stabilizing drill collar for producing straighten bore holes, for example in US-A-3,908,771. The drill collar comprises a heavy cylindrical rigid member converted end-to-end above the drill bit in prolongation of the drilling string to prevent deviating from a vertical course.
The cylinder member is provided with an arrangement of elongated slots in which some nozzles are located for jetting drilling mud from the central passageway into the annular gap between the drilling collar and the bore hole.
The drill collar optionally includes a plurality of radially extending flanges provided with a plurality of apertures to reduce its turning resistance.
The flanges perform a reaming function to shape the bore hole and cut away any solid obstructions such as rock that may project into it.
According to the present invention there is provided a hole opener for enlarging well bores, comprising
a tubular housing, showing side walls,
a plurality of cutters extending outwardly of the housing and having cutting edges for engaging a well bore wall,
and a central passageway formed by a hollow portion of the housing for delivery of pressurised fluid, through at least one aperture arranged in the side walls of the housing perpendicularly to the rotation axis of the housing, in the form of a nozzle for providing a jet of said fluid in a direction lateral of the housing and at generally the same level on the housing as said cutting edge.
This tool is characterized in that the plurality of cutters are interchangeably secured within a slot in a staggered arrangement in such a way that they have each circumferentially-spaced cutting edges extending along a portion of the tubular housing.
Preferably a plurality of apertures are provided for the passageway.
The aperture is preferably in the form of a nozzle for providing a jet of fluid from the passageway laterally outwardly against the well bore. In this way localised pressure is exerted on the borehole wall in the area of cutting, increasing locally the pore pressure. The provision of the aperture at the same level as the cutting edge maximises this effect and also ensures that cuttings are immediately caught in the flow of fluid, keeping the cutting edge clear of debris.
The housing above the cutter has at least a portion whose diameter is substantially the same as the diameter produced by the outer extremity of the cutter on rotation of the housing.
Preferably a plurality of cutters are provided at spaced intervals around the housing and the diameter of the housing above the cutter is at its maximum substantially the same as the diameter of the enlarged well bore produced by the cutters on rotation of the housing.
An embodiment of this invention will now be described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is a side view of a tool for enlarging well bores in accordance with the invention;
Fig. 2 is a part-sectional angled side view of the tool of Fig. 1; and
Fig. 3 is a sectional view on the line A-A of Fig. 1.

Referring to the drawings, the tool of this embodiment of the invention has a housing generally indicated at 1 of which top and bottom cylindrical sections 2, 3 of 241 mm outside diameter and a middle cylindrical section 4 is of 444 mm outside diameter at its upper portion 4A. The housing 1 has an overall length of 2121 mm.
A lower portion 4B of the middle section is of reduced outside diameter and has three equispaced slots 5 cut into it, the slots receiving cutters 6 having cutting edges 6A, 6B and 6C which have synthetic polycrystalline Compax, Stratax or Diapax diamond wafers 7 along them to provide hardness and wear resistance. On rotation of the housing the outermost cutting edges 6C describe a circle having a diameter of 444 mm, i.e. the same as the diameter of the upper portion 4A of the housing middle section 4.
Each cutter 6 is secured within its slot 5 by means of two screwed pins 12 passing through the cutter 6 and screwing into the portion 4B of the housing 1 (see Fig. 3) which forces the cutter 6 against a side face of the slot 5, thereby preventing vibration of the cutter 6 in the slot. Each screwed pin 12 is prevented from loosening by means of an eccentric locking disc 12A.
At their lower portion the cutters 6 are forked at 11, the cutting edges 6 being provided on each fork.
A through bore 8 extends axially through the housing and apertures 9, 10 open from the bore 8 radially outwardly into the slots 5 between the forks 11 of each cutter 6. The apertures 9, 10 are disposed at the same level on the housing 1 as the cutting edges 6C, 6A respectively.
The apertures 10 are directed along the cutting edges 6A.
Located within the apertures 9, 10 are removable sleeves 14 which are aligned with the bore 8 by dowel pins 13. Nozzles 15 are disposed within the sleeves 14 and sealed against their innerfaces to provide a reducing cross-sectional area for the apertures 9, 10 as they emerge from the bore 8. The nozzles 15 are removable and interchangeable, and their total area at their outer ends is 0.9 c_m2.
In use, the tool of this embodiment of the invention is screwed at its upper end lower ends into a drill string, so that the bore 8 communicates with fluid passageways above and below it. The string carries at its lower end a drill bit (not shown) which forms a pilot hole 16 (Fig. 2) in the sea bed on rotation of the string, or a bullnose which will follow an existing pilot hole.
Drilling fluid is pumped through the drill string and passes through the bore 8 to the drill bit and, being under pressure, is forced in part through the nozzles 15, emerging from them at a velocity of 60-100 metres per sec. The pressure drop across the nozzles 15 is around 70 kg per cm². The rate of fluid flow through the nozzles is 5455 litres per minute.
As the fluid is jetted through the nozzles 15 it forces debris away from the cutting edges 6A, 6B, 6C, with direct action along the edge 6A. Cuttings are then entrained in the upward flow of fluid from the drill bit, which is joined by the fluid from the nozzles 15. Further, the high velocity of the fluid from the nozzles 15 against the wall of the well bore assists the cutting action of the cutters by causing initial weakening and breakage of the wall; as the fluid flow from the nozzles is lateral of the well bore it acts directly against the bore well generally in the plane of rock strata, thus producing a disruptive effect on the wall. The localised high pressure created by the fluid from the nozzles also reduces the "chip hold-down" effect of a substantially downwardly-directed jet, thus reducing wear on the cutting edges 6A, 6B, 6C.
Thus the pilot hole 16 is opened to a wider diameter by the cutters 6, providing a drill hole 17 (Fig. 2) of about 444 mm diameter. As the tool rotates, therefore, the upper portion 4A of the housing's middle section bears against the wall of the drill hole 17, providing stabilisation for the tool. The face of the newly-formed drill hole 17 is smoother and has more integrity than that of the pilot hole 16, and therefore provides better stabilisation for the tool than conventional arrangements in which the stabilisation is effected against the pilot hole.
There are several reasons for the high level of performance achieved by the tool of this embodiment:

1) The impact of the high velocity jet was breaking down the ledge.
2) The lateral jet was carrying away the cutting effectively as it only had to turn 90° to be travelling up the hole as opposed to 180° as in normal jet nozzle bits or hole openers.
3) Creating a wash-out situation relieved the cutters of much of their work.
4) Creating localised high formation pressure reduced the chip hold down effect.

It is a well-known fact that chip hold down is affected greatly by over-balance and if the lateral jetting is causing formation pressure to be increased to a level above the hydrostatic pressure of the mud column, then a substantial increase in rate of penetration will certainly take place.
This now remains to be proved under laboratory conditions.
Increases in ROP have been achieved in the past using nozzles to reduce bottom hole pressure but this method of increasing the ROP has been accompanied with the increased risk of causing an influx by reducing or removing the over-balance excited by the mud column. In the case of lateral jetting in the present invention this is not the case as the formation pressure is being increased locally at the point of cutting which would effectively reduce the risk of an influx but still reduce or remove the over-balance exerted by the mud column.
Modifications and improvements may be made without departing from the scope of the invention as claimed.

Claims

1. A hole opener for enlarging well bores, comprising a tubular housing (1) showing side walls, a plurality of cutters (6) extending outwardly of the housing (1) and having cutting edges (6A, 6B, 6C) for engaging a well bore wall, and a central passageway (8) formed by a hollow portion of the housing (1) for delivery of pressurised fluid through at least one aperture (9, 10) arranged in the side walls of the housing (1) perpendicularly to the rotation axis of the housing (1), in the form of a nozzle (15) for providing a jet of said fluid in a direction lateral of the housing (1) and at generally the same level on the housing (1) as said cutting edge (6A, 6B, 6C) characterized in that the plurality of cutters (6) are interchangeably secured within a slot (5) in a staggered arrangement in such a way that they have each circumferentially spaced cutting edges (6A, 6B, 6C) extending along a portion of the tubular housing (1).

2. A tool according to claim 1, characterized in that each cutter is interchangeably secured within its slots by means of snap-rings or screwed pins passing through the cutter and screwing into the portion of the housing (1) which forces the cutter against a side face of the slot (5).

3. A tool according to any one of the preceding claims, characterized in that at least one aperture provided through the side walls of the housing (1), emerges between two adjacent cutting edges (6A, 6B, 6C) at the level of the lower extremity of the cutting edges (6A, 6B, 6C).

4. A tool according to any one of the preceding claims, characterized in thatthe upper portion (4A) of the housing (1) is the body of an integral stabiliser which bears against the wall of the drill hole (17).