Title of Invention

SYSTEM AND METHOD FOR MAKING A HOLE IN AN OBJECT

Abstract

System and method for making a hole (1) in an object, the system comprising jet means for generating an abrasive jet (10) formed of a mixture of a fluid and abrasive particles, and for blasting the abrasive jet with an erosive power into impingement with the object in an impingement area, thereby eroding the object in the impingement area. The system further comprises rotating means for moving the impingement area along a selected circular trajectory in the hole (1) about its circumference, and modulation means for modulating the erosive power of the abrasive jet (10) while the impingement area is being moved along the selected trajectory.

Full Text

- 1 - SYSTEM AND METHOD FOR MAKING A HOLE IN AN OBJECT The present invention relates to a system for making a hole in an object, more particularly for making a hole in a subterranean earth formation. In particular, the system comprises jet means for generating an abrasive jet of a mixture containing a fluid and a quantity of abrasive particles and for blasting the abrasive jet with an erosive power into impingement with the object in an impingement area, thereby eroding the object in the impingement area. The invention also relates to a method of making a hole in an object, more particularly for making a hole in a subterranean earth formation. In particular, the method comprises steps of generating an abrasive jet of a mixture containing a fluid and a quantity of abrasive particles and for blasting the abrasive jet with an erosive power into impingement with the object. In US patent 5,944,123 a drilling method is described involving the rotation of a drilling member, whereby drilling fluid is supplied to the drilling member to issue therefrom via an orifice provided, therein. Off axis advance of the drilling member is achieved by modulating the rotational speed of the drilling member as it rotates. Due to increasing friction with the bore hole wall at greater depths, the directional stability of this arrangement is expected to reduce when drilling a bore hole at relatively great depth, such as is generally required for drilling of a well for production of mineral hydrocarbons. In accordance with the present invention there is provided a system for making a hole in an object, the 25 _ 3 - friction between the drilling arrangement and the bore hole wall surrounding the drilling arrangement. The friction causes frictional forces acting on the drilling system, which forces depend on movement of the system in the hole. When the directional control relies on the modulation of the rate of movement of the drilling system, the mentioned friction therefore disturbs the directional stability of the system. An advantage of modulating the erosive power of the abrasive jet is that thereby the material removal rate from the object is modulated while the direct mechanical contact between the drilling tool and the bore hole wall does not have to change. The erosive power of the abrasive jet can be modulated by modulating the power vested in kinetic energy of the abrasive particles present in the abrasive jet. This can be done by modulating the mass flow rate of the abrasive particles in the abrasive jet, for instance by modulating the quantity of the abrasive particles in the abrasive jet, or by modulating the velocity of the abrasive particles in the abrasive jet, which can be done for instance by modulating an acceleration pressure drop of the fluid in the jet means, or by combining these. Preferably, the modulation means are coupled to modulation control means arranged to control the modulation means such that the erosive power is modulated in relation with the position of the impingement area on the selected trajectory. This way, the modulation can be arranged such that the erosive power is be increased when the abrasive jet is impinging the formation where more erosion is required, and, vice versa, the erosive power can be decreased when the abrasive jet is impinging the formation where less erosion is required. - 5 - in the hole about a rotary axis, which rotary axis essentially coincides with a longitudinal direction of the hole. Since the impingement area is located eccentric with respect to the rotary axis, rotating the abrasive jet in the hole results in the jet and the impingement area moving along an essentially circular trajectory in the hole. Preferably, the eccentric impingement area overlaps with the centre of rotation, so that also the middle of the bore hole is subject to the erosive power of the abrasive jet. The drill string 8 is also provided with a controller unit 12, such that the controller unit is located inside the hole. Alternatively, the controller unit can be positioned at the surface 13. The controller unit 12 can house equipment such as modulation means to modulate the erosive power of the abrasive jet 10 impinging the formation 2. Modulating the erosive power includes controlling the erosive power. In operation, the system works as follows. A stream of drilling fluid is pumped by a suitable pump (not shown) through the longitudinal passage of the drill string 8. Part or all of the drilling fluid is led to the jet means where an abrasive jet 10 is generated. The abrasive jet is blasted into impingement with the formation. The formation is eroded in the impingement area as a result of the abrasive jet 10 impinging the formation 2. Simultaneously, the abrasive jet is rotated about the rotary axis. Thus, the impingement area is moved along a circular trajectory in the hole so that the formation can be eroded at all azimuths. By modulating the erosive power of the abrasive jet a high degree of directional control can be achieved. By keeping the erosive power of the abrasive jet constant, the formation is eroded evenly on all sides of - 7 - providing a signal indicative of the direction of the device relative to a reference vector; a positional sensor providing a signal indicative of one or more positional coordinates relative to a reference point; a formation density sensor providing information on a distance to a change of formation type or formation content nearby; or any other suitable sensor. The mechanical forces on the drilling system that is based on abrasive jetting are much smaller than is the case for systems based on mechanical rock removal. This has the advantage that the sensors can be located very close to the excavating tool, making early and accurate signal communication possible to the modulation control means. The sensors can for instance be provided in the same chamber as the modulation control means. Alternatively, the position and and/or the direction of progress through the formation of the abrasive jet can be determined on the basis of parameters available on the surface 13, including torque on the drill string 8 and azimuthal position of the drill string 8, and axial position and velocity of the drill string 8. A decision to change or correct drilling direction may also be taken via the operator of the directional system at surface. In case of the signal originating from a down-hole measurement while drilling sensor, a laud-pulse telemetry system or any other suitable data transfer system can be employed to transfer the data to the surface. Via similar means of data transfer a control signal can be sent to the down hole control means triggering a series of control actions required for the desired direction drilling correction. A thruster (not shown) is advantageously provided for pressing the abrasive jetting system upon the bottom of the hole 1. Best results are obtained when the pressing force is not much higher than what is required to keep - 9 - particles in the mixture does not influence the mechanical contact forces between the drilling system and the formation. Still referring to Fig. 1, the abrasive particles will be entrained in a return stream of drilling fluid through the excavated hole, running for instance through an annular space 16 between the hole 1 and the drilling system (6,12,8) . In order to reduce the concentration of abrasive particles to be transported all the way back to the surface, it is preferred to provide the drilling system, preferably the excavation tool 6, with recirculation means arranged to recirculate at least a part of the abrasive particles from the return stream down stream impingement with the formation back into the abrasive jet 10 again. The abrasive particles to be recirculated can be mixed with the fresh stream of drilling fluid, for instance in a mixing chamber to which both the fresh stream of drilling fluid and the recirculated abrasive particles are admitted. The quantity of the abrasive particles in the mixture can be modulated by modulating the rate at which the abrasive particles are recirculated to the mixing chamber. Fici. 2 schematically shows a preferred embodiment of an excavating tool 6 with recirculation capability, suitable for use in the system of Fig. 1 when applying abrasive particles containing a magnetisable materialr such as for instance steel shot or steel grit. The preferred excavating tool 6 is provided with a longitudinal drilling fluid passage 11, which is at one end thereof in fluid communication with the drilling fluid channel provided in the drill string 8 and at the other end thereof in fluid communication with jet means. The jet means comprises a mixing chamber 9 that is - 11 - The drilling fluid passage 11 is fixedly arranged relative to the support surface 15 and the mixing chamber 9. The drilling fluid passage 11 has a lower end arranged near the inlet 4 for abrasive particles. In the present embodiment the drilling fluid passage 11 is formed inside a ridge in the axial direction which ridge is in protruding contact with the support surface 15. The drilling fluid passage 11 may alternatively be arranged freestanding from the support surface in a manner similar to that shown and described in International Publication WO 02/34653 with reference to Fig. 4 therein, or in a off-axial direction. The inlet 4 for abrasive particles is located at the lower end of the ridge. The cylindrical magnet 7 is formed of eight smaller magnets 7a to 7h stacked together. A different number of smaller magnets can also be used. Each magnet 7a to 7h has diametrically opposed N and S poles, and the magnets are stacked in a manner that two essentially helical diametrically opposing bands are each formed by the N and S poles. For the purpose of this specification, a magnetic pole is an area on the magnet surface or on the support surface where magnetic field lines cross the magnet surface or the support surface thereby appearing as an area of source or sink for magnetic field lines. Directly adjacent to the diametrically opposing bands formed by the poles, helical recesses are provided for achieving helical bands having lower magnetic permeability than the helical bands including the poles. Due to the higher magnetic permeability of the magnet material than the less magnet material that fills up the recesses (a gas, a fluid, or a solid) the internal magnetic field lines predominantly follow the material of the magnet rather than the material contained in the recess. Thus, there exists a strong gradient zone between - 13 - The slanted phantom lines in Fig. 3b indicate the transition between the circular contours and the essentially straight contours. In Fig. 3c, vertically is set out the height of the magnet, which is divided in smaller magnets 7a to 7h, and horizontally the surface at all azimuths between 0 and 360° is visible. As can be seen, the smaller magnets 7a to 7h are arranged such that their individual poles align in two helical bands, in the order of NSSNNSSN or SNNSSNNS. The angle 9 of the helical recess 26 with the plane perpendicular to the shaft 18 is 53°. In operation, the preferred excavating tool of Fig. 2 works as follows. The tool is connected to the lower end of the drill string 8 that is inserted from the surface 13 into the borehole. A stream of drilling fluid is pumped by a suitable pump (not shown) at surface, via the drilling fluid channel of the drill string 8 and the fluid passage 11 into the mixing chamber 9. During pumping, the stream is provided with a small amount of abrasive particles suitable in the form of steel shot. The inlet 3 is arranged with a flow restriction, over which a pressure drop is present driving the acceleration of the drilling fluid. The stream flows from the mixing chamber 9 via mixing nozzle 5 and is thereby jetted against the borehole bottom. Simultaneously, the drill string 8 is rotated in the way described above. The return stream of fluid and abrasive particles flows from the borehole bottom through the annulus 16 in the bore hole in a direction back to the surface. Thereby the return stream passes along the sleeve 15. The magnet 7 induces a magnetic field extending to and beyond the outer surface of the sleeve 15. As the stream passes along the sleeve 15, the abrasive particles in the stream are separated out from the stream by the magnetic forces from the magnet 7 which - 15 - surface 13, such fraction can be replaced via the stream of fluid flowing through the drill string 8. A jet pump mechanism in the mixing nozzle 5 generates a strong flow of drilling fluid from the mixing chamber 9 to the mixing nozzle 5. The jet pump mechanism auxiliarily supports the flow of magnetic particles into the mixing chamber 2. A larger diameter of the mixing nozzle 5 compared to a drilling fluid inlet nozzle (between inlet 3 and the mixing chamber 9) results in adequate entrainment of drilling fluid and the magnetic abrasive particles entering into the mixing chamber via second inlet 4. The interaction between the entrained drilling fluid and the magnetic particles contributes to the efficiency of the release of particles from the support surface 15 into the mixing chamber 9 as well. If provided, the magnetic body 14 on the side opposite from the abrasive particle inlet 4 draws part of the magnetic field generated by the magnet 1 into the mixing chamber 9. As a result, the magnetic force attracting the magnetic abrasive particles to the support surface 15 is less strong for magnetic particles that enter the region of the abrasive particle inlet 4. Thereby, entry of the magnetic abrasive particles through abrasive particle inlet 4 into the mixing chamber 2 is further facilitated. The magnetic abrasive particles have a tendency to form chains from the lower end of the support surface 15 towards the magnetic body 14 that cross through the mixing chamber 9. At the same time the particles in these chains interact with the stream of drilling fluid passing through the mixing chamber 9 from inlet 3 to mixing nozzle 5f and thereby these particles will be entrained by this stream. In a preferred embodiment, one or more relatively short essentially axially oriented ridge sections are provided onto the support surface whereby the support )5/005767 - 17 - Part name Reference size number Outer diameter of foot part 19 73 mm Axial length of magnet 7 120 mm Outer diameter of magnet 7 29 mm Diameter in lower part of 15 34 mm support surface Diameter in upper part of 15 52 mm support surface As an alternative for the cylindrical magnet 7 in Fig. 2, the outer diameter of the magnet and the inner diameter of the inside wall of support sleeve 15 can be made to reduce with decreasing axial height. The smaller magnets from which the magnet is assembled can be of a frustoconical shape to obtain a tapered shape of the separator magnet. The gap between the magnet and the inside wall of the support sleeve may also decrease, as well as the wall thickness of the support sleeve. The drilling fluid in the abrasive jet may contain a concentration of typically up to 10 % by volume of magnetic abrasive particles. The magnet is preferably driven at a rotational frequency exceeding the rotational frequency of the drill string, such that modulation of the magnet rotational frequency can modulate the recirculation rate of the abrasive particles with in a single rotation of the excavation tool 6. Typically the magnet can be driven at a rotational frequency of between 10 and 4 0 Hs. The rotation of the drill string, or at least the excavating tool, is typically between 0.3 and 3 Hz. Generally, in a system comprising conveyor means for supplying abrasive particles to the abrasive jet, the quantity of abrasive particles in the abrasive jet can be modulated by modulating the rate of transport by the - 19 - A second, alternative, type of down hole power system (not shown) comprises a passive hydraulic motor, such as for instance a turbine or a positive displacement motor (PDM) section, drivable by the drilling fluid flow, of which passive hydraulic motor an output shaft is coupled to the conveyor means. Means are provided for controlling the power on the output shaft. Such means can be provided in the form of flow control means controlling the flow of drilling fluid through the passive hydraulic motor, such as an adjustable valve, preferably an electronically adjustable valve, in series with the passive hydraulic motor and/or in parallel in a bypass channel bypassing the passive hydraulic motor. A possible parallel bypass channel is disclosed in US patent 4,396,071. Alternatively, a generator can be mounted around the output shaft and act as a controlled brake that is electronically adjustable by adjusting the load in the generator circuit. The electronically adjustable valve or load may be controlled by an electronic control system. In both the first (example in Fig. 4) and second type systems, the erosive power of the abrasive jet with the abrasive jet can be modulated via the electronic control system 22. The electronic control system may be arranged to receive a signal indicative of the position of the impingement area of the abrasive jet along its trajectory on the bottom of the hole 1, which it can then use to modulate the erosive power of the abrasive jet in dependence on the position, along the trajectory. The signal can be received directly from a down hole positional sensor located in the vicinity of the excavating tool. The positional sensor can suitable be housed together with the electronic control system 22. The electronic control system 22 may include an electronic memory module that stores data including one or more of motor voltage, current, rotational frequency, - 21 - forward, or normal, direction of movement. Advantageously, the conveyor means is switched to reverse movement again just prior to ending an excavation operation. This may be automatically triggered by a drop in flow rate, for instance. 0 3. 05. 2005 © CLAIMS 1. System for making a hole in an object, the system comprising jet means for generating an abrasive jet comprising a fluid and for blasting the abrasive jet with an erosive power into impingement with the object in an impingement area, thereby eroding the object in the impingement area, the system further comprising scanning means for moving the impingement area along a selected trajectory in the hole, and modulation means for modulating the erosive power of the abrasive jet while the impingement area is being moved along the selected trajectory, characterized in that the abrasive jet comprises a mixture containing said fluid and a quantity of abrasive particles, and that the modulation means is arranged to modulate the quantity of abrasive particles in the mixture. 2. The system of claim 1, wherein the scanning means comprises rotary means for rotating the abrasive jet about a rotary axis, whereby the impingement area is positioned off-axis with respect to the rotary axis. 3. The system of claim 1 or 2, wherein the modulation means comprises modulation control means arranged to control the modulation means such that the erosive power of the abrasive jet is modulated in relation with the position of the impingement area on the selected trajectory. 4. The system of any one of claims 1 to 3, comprising a positional sensor for providing a signal indicative of the position of the impingement area on the selected trajectory. 5. The system of any one of claims 1 to 4, comprising a navigational sensor for providing a signal indicative of a direction under which the making of the hole in the object progresses. 6. The system of any one of claims 1 to 5, wherein the modulation means comprise means for modulating the power vested in kinetic energy of the abrasive particles . 7. The system of any one of claims 1 to 6, wherein the modulation means comprises velocity control means arranged to modulate the velocity of the abrasive particles in the abrasive jet. 8. The system of claim 7, wherein the jet means comprises an acceleration nozzle across which a pressure drop is maintainable, whereby the velocity control means comprises pressure control means arranged to modulate the pressure drop. 9. The system of claim 1, comprising a mixing chamber for mixing the fluid with the abrasive particles, and further comprising abrasive particle supply means for supplying the abrasive particles to the mixing chamber, whereby the modulation means is arranged to modulate the rate at which the abrasive particle supply means supplies the abrasive particles to the mixing chamber thereby modulating the quantity of abrasive particles in the mixture. 10. The system of claim 9, wherein the abrasive particle supply means comprises recirculation means arranged to recirculate at least a part of the abrasive particles from a return stream of the mixture downstream impingement with the object into the mixing chamber, whereby the modulation means is arranged to modulate at least the recirculation rate. 11. The system of claim 9 or 10, wherein the abrasive particle supply means comprises conveyor means, preferably in the form of a movable magnet, arranged such that operation of the conveyor means induces transport of the abrasive particles, whereby the modulation means is arranged to modulate at least the rate of transport induced by the conveyor means. 12. The system of claim 11, wherein the conveyor means is movable, whereby movement of the conveyor means induces the transport of the abrasive particles. 13. The system of claim 11 or 12, wherein the conveyor means are coupled to a controllable down hole power system for operating the conveyor means, preferably for driving the conveyor means into movement. 14. The system of claim 13, wherein the controllable down hole power system comprises an electric power generator drivable by a fluid flow, an electric motor mechanically coupled to the conveyor means for driving the conveyor means into movement, whereby the electric motor is electrically coupled to the electric power generator via an electronic control system. 15. Method of making a hole in an object, the method comprising steps of generating an abrasive jet comprising a fluid; blasting the abrasive jet with an erosive power into impingement with the object in an impingement area, thereby eroding the object in the impingement area; moving the impingement area along a selected trajectory in the hole; and modulating the erosive power of the abrasive jet while the impingement area is being moved, characterized in that the abrasive jet comprises a mixture containing said fluid and a quantity of abrasive - " ~ V particles, and that the modulation means modulates the quantity of abrasive particles in the mixture. 16. The method of claim 15, wherein modulating the erosive power of the abrasive jet comprises modulating the power vested in kinetic energy of the abrasive particles.

Documents:

22-chenp-2006-abstract.pdf

22-chenp-2006-claims.pdf

22-chenp-2006-correspondence others(po).pdf

22-chenp-2006-correspondence others.pdf

22-chenp-2006-discription complete.pdf

22-chenp-2006-drawings.pdf

22-chenp-2006-form 18.pdf

22-chenp-2006-form 3.pdf

22-chenp-2006-form 5.pdf

22-chenp-2006-pct.pdf