WO2024184470A1

WO2024184470A1 - Drill bit and method for directional drilling

Info

Publication number: WO2024184470A1
Application number: PCT/EP2024/056045
Authority: WO
Inventors: Jan Jette Blange
Original assignee: Canopus Drilling Solutions Holding B.V.
Priority date: 2023-03-08
Filing date: 2024-03-07
Publication date: 2024-09-12

Abstract

The invention provides a drill bit, methods, and a system for directional drilling of a subterranean earth formatting by simultaneous abrasive jet drilling and mechanical drilling by cutting It provides in subsequent rotations of the bit, consistently, simultaneous erosion and excavation of the borehole bottom. For example it provides differential hole making by providing more erosion in respective zones of the borehole bottom angularly extending continuously over respective opposing azimuthal ranges by the respective radially inwards and outwards abrasive jets than outside of these zones, for example such as to bring about substantially no excavation in these zones and/or predominant excavation by the cutters outside of these zones.

Description

P36197PC00 Title: DRILL BIT AND METHOD FOR DIRECTIONAL DRILLING The present invention relates to the field of drilling into an object, in particular into an earth formation, e.g. a subterranean earth formation. In particular, the present invention provides a drill bit for, and a method of, directional drilling of a borehole into said object by means of a combination erosion of the borehole bottom by an abrasive jet and mechanical cutting of the borehole bottom, by varying concentrations of abrasive particles in a stream of drilling fluid mixed with abrasive particles, passed as an abrasive jet through abrasive nozzles of a drill bit along rotations thereof, to vary the erosive power of the stream along angular sections of the borehole bottom. Directional drilling involves drilling into said object around a bend, producing curved borehole sections therein. This enables to establish a borehole trajectory in said object with one or more curved sections, e.g. adjoined by straight borehole sections which, as a consequence, extend at a mutual angle. The ability to produce a borehole with such curved trajectories in subterranean earth formations allows in practice e.g. to drill into a subterranean reservoir in a non-vertical direction, e.g. in a slanted or even horizontal direction. For the purpose of directional drilling, drilling equipment is used which is capable of removing material at the end of a borehole in an intended direction that is slanted with respect to the directly preceding direction of the borehole. Performing directional drilling continuously over a certain borehole length produces a tangent or curved predetermined borehole trajectory. For directional drilling, it is known from WO2021069694 by the present applicant to provide a drill bit comprising a bit face, which during use faces the borehole bottom, a bit fluid inlet port, one or more abrasive jet nozzles, and an intermediate space between the bit fluid inlet port and the one or more abrasive jet nozzles. The abrasive jet nozzles are configured for ejecting a stream of drilling fluid mixed with abrasive particles into impingement with the borehole bottom in the form of an abrasive jet. The drill bit comprises multiple abrasive jet nozzles arranged at different azimuthal positions. Each of the abrasive jet nozzles have a nozzle inlet for fluid communication with the intermediate space, from which each of the nozzle inlets extends at least during rotation of the drill bit. The mechanical drill bit further comprises wash nozzles, mechanical cutters, and a strainer. The strainer is configured and arranged within the drill bit such that the abrasive particles from the stream are deflected into the abrasive jet nozzles only, and the drilling fluid from the stream passes into both the abrasive jet nozzles and into the wash nozzles. The present invention provides a drill bit according to claim 1. The present invention furthermore provides methods of directional drilling according to claim 10, and to claim 11 with preferred use of the claimed drill bit. The present invention furthermore provides a system according to claim 20, which comprises a particularly suitable embodiment of the drill bit, namely according to claim 2. Possible and advantageous embodiments are defined in the subclaims thereof and in the description with reference to the figures – although other embodiments are envisaged within the scope of the invention. The drill bit according to the invention is suitable for directional drilling of a subterranean earth formation simultaneously by abrasive jet drilling and mechanical cutting. Thereto it comprises both cutters and abrasive jet nozzles, so as to form a hybrid drill bit. The cutters of the inventive hybrid drill bit are in itself already capable of excavating the borehole bottom in said shape by rotation of the drill bit. Even so, also the abrasive jet nozzles are in itself capable of eroding the borehole bottom in this same shape. An inventive configuration of the nozzles and the abrasive jet nozzles enables an enhanced deepening of the borehole bottom, achieving a rate of penetration (ROP) which is more than the sum of the deepening by the erosion and excavation when applying abrasive jets or cutting in isolation. This is because the erosion, besides in itself deepening the borehole bottom, also works in support of the excavating action. Furthermore, the erosion increases the efficiency of cutters which are less supported by the erosion than other cutters, because a larger portion of the weight-on-bit (WOB) is applied on these cutters than on the other cutters. The cutters are, after all, provided over the whole radial range. For example cutters which are located radially further away from the center of a jet, may be supported less by the erosion by this jet. The radial range of a jet depends on its erosivity: a larger erosivity means a larger radial range covered thereby. In embodiments the radial ranges of the jets from the nozzles cover substantially the whole radial range. In the configuration of the drill bit according to the invention, for example the cutters radially centrally in between the centers of the jets may receive less support from the erosion than the cutters radially close to the jet centers, evenas for example cutters radially respectively inwards and outwards from the centers of the center and gauge jet. If this is the case, these cutters being subjected to a relatively larger portion of the WOB may result in a more efficient operation thereof, since the ROP generally increases with increasing WOB. This results in a more efficient operation of the bit with the same WOB. Thus, with the inventive configuration, the ROP of the drill bit may advantageously be increased in two ways relative to a drill bit with only cutters, or with only abrasive jets. Firstly the erosion supports the excavation, so that there is an amplified effect of deepening which exceeds the sum of the deepening by individual erosion and individual excavation. Secondly the increased portion of the WOB being applied on the cutters less supported by the erosion makes the cutters, and thus the drill bit as a whole, excavate more efficiently. Both increase the ROP of the bit. Besides an increased ROP, the inventive configuration may yield a further advantage in the form of an increased redundancy and lifetime. In the unfortunate case that a cutter unduly becomes damaged, or has worn out faster than other cutters, the excavation thereby declines relative to the other cutters. In the inventive configuration, this results in an increase of erosion by the abrasive jet(s) at the radial position of the cutter, which now increases the support thereby of the (declined) excavating action of the damaged cutter. Any decline in the performance of the bit by the damage of the cutter may thereby be reduced. In the inventive drill bit, the nozzles cover different radial portions of the borehole bottom, with the center nozzle(s) being directed to a radially inwards portion, and the gauge nozzle(s) to a radially outwards portion of the borehole bottom the bit faces. This leads to a particularly advantageous support of the radially offset cutters by erosion along the radial range of the bit, with additional control of the extent of the support along the radial range, e.g. through variation of the extent of the erosion along the nozzles. Therewith for example the shape of the borehole bottom and the loading of the cutters may be better controllable. The abrasive jet nozzles of the drill bit enable differential holemaking for providing a steering effect in applications wherein this is desired. Differential holemaking by means of abrasive jetting through drill bit nozzles is in general known from the art, e.g. from WO2021069694 by the present applicant. Therein the erosive power of a single nozzle is varied along the rotation of the bit, so that the resulting erosion of the borehole bottom is higher in a certain angular target zone of the rotation and lower in a remaining angular zone. This over a number of consecutive rotations gives a directional effect – with a bent borehole as a result. Because in the inventive drill bit with the center nozzle(s) being directed to a radially inwards portion, and the gauge nozzle(s) to a radially outwards portion, the target zones of the center and gauge nozzle(s) should thus be diametrically opposed when performing directional drilling. In addition to the above discussed enhanced ROP in disregard of such an directional effect, the inventive configuration of the nozzles and the cutters now also enables that in applications wherein directional drilling is applied, both the steering effect itself ánd the control thereof is enhanced. The enhancement is achieved in multiple ways. With the abrasive jets supporting the excavating action of the cutters, providing more erosive power in the opposed, respective target zones of the respective center and gauge nozzles along the rotation not only leads to an increased erosion in these zones by the respective center- and gauge jets itself, but also leads to a higher support of the excavating action in these zones. This makes that the deepening is further increased in the target zones relative to the remaining zones, resulting in an enhanced differential holemaking, and thus, an enhanced steering effect. The steering effect is however furthermore enhanced in a second way. The erosive power in the target zone of the rotation being higher than in the remaining zone of the rotation, makes that the excavating cutters experience a higher reaction force in the remaining zone dan in the target zone. Over each full rotation, this results in a net resultant reaction force that biases the bit in the steering direction, enhancing the steering effect. This is explained in more detail with reference to the figures. This enhancement thus results from the presence of the cutters, by means of which the bit experiences the reaction force of the borehole bottom, and of the abrasive jets, an consistently angularly varied erosive power of which causes an consistently angularly varied reaction force so as to create a net resultant force over a full rotation biasing the drill bit in the desired direction. Because the enhancement results from the presence of both the cutters ánd the abrasive jets, and the above described use thereof, the steering effect is more than the sum of what can in this regard be achieved by abrasive jets or cutters alone. It makes that the cutting action also leads to a steering effect, whereas without the abrasive jets the cutters would in itself not be able to provide a steering effect at all. The enhanced steering effect makes, that advantageously, a larger differential holemaking may be achieved by means of the same supply stream of drilling fluid mixed with abrasive particles. A third effect is achieved by the inventive configuration. As earlier explained, when a larger portion of the WOB is applied to a cutter, this cutter operates more efficiently, since the ROP generally increases with increasing WOB. In the remaining zone in which the cutters experience less support from the erosion, they are also subjected to a larger portion of the WOB. As an effect, the cutters operate more efficiently in this target zone relative to the remaining zone of the borehole bottom. This may lead to a further increase of the mentioned net resultant force in the steering direction, and thus an even further enhancement of the steering effect. With regard to the control, the biasing effect due to the net resultant force on the cutters comes on top of the directional effect resulting from the differential holemaking by the variation of the erosive power of the abrasive jets. Therewith, an enhanced control is achieved through the variation of the erosive power, which in the inventive configuration influences both the differential holemaking ánd the net resultant force further biasing the bit by pushing. The (enhanced) steering effect increases when the difference in the extent of erosion between the target zones and the remaining zones is larger. In a possible directional drilling method using the inventive drill bit, the abrasive jets erode the target zones only, and do not provide erosion of the borehole bottom outside of these zones. In another possible directional drilling method using the inventive drill bit, the abrasive jets erode the borehole bottom over the whole angular range of the rotation, but erode the borehole bottom more in the target zones than in the remaining zones. In such embodiment, the cutters benefit from the enhanced ROP throughout the rotation, and benefit from the enhanced steering effect including a further enhanced ROP in the target zones relative to the remaining zones. In a possible directional drilling method using the inventive drill bit, the extent of erosion by the abrasive jets in the target zone of at least the gauge nozzle is such that there is substantially no excavation in the zone(s). The influence on the steering effect of the abrasive jet(s) of the gauge nozzle(s) advantageously is/are larger than that/those of the center nozzle(s), due to the radially more outwards position, and thus longer rotational path, thereof. For example, the gauge nozzle(s) erode(s) 3-5, e.g.4 times more than the center nozzle(s). The enhanced steering effect is facilitated by the fact that the drill bit is configured for creating a borehole bottom in the shape of a cone encircled by an annular groove which radially connects to the cone. This makes that there are practically only two upstanding walls in the borehole, namely the outer wall defining the borehole and an inner wall defining the cone. Therein, to create a directional effect, it is these two walls which should in the deepening of the borehole be extended with an incline – wherein of course the inner wall substantially maintains its axial extension. The at least one center nozzle is positioned and directed such that it creates the incline of the inner wall and the at least one gauge nozzle is positioned and directed such that it creates the incline in the outer wall during deepening. The at least one center nozzle thereto jets from the center in a radially outwards direction, and is thereto positioned and oriented to extend diametrically opposite to its jet. The at least one gauge nozzle is positioned and oriented at the same diametrical side as its jet. After all, as the inner and outer walls are opposite to one another, i.e. facing one another, the at least one gauge nozzle should be usable to have its target zone of the rotation diametrically opposite to the target zone of the center nozzle. The fact that in the inventive drill bit, the nozzles cover different radial portions of the borehole bottom, may improve the steering relative to a drill bit wherein the nozzle(s) are directed to the same or substantially overlapping radial portions, in particular to the annular groove encircling the cone. The nozzles may be directed more towards respectively the inner and outer walls, so that the drill bit is more directly enabled to incline radially, towards the eroded parts of the walls. In an embodiment of a drill bit according to the invention, the at least one central nozzle and the at least one gauge nozzle are positioned, oriented and configured such that during use the recoils of the jets jetted by the respective nozzles generate a resultant jet recoil force that is directed at an angle to the central rotation axis of the drill bit and towards a section of the drill bit comprising the at least one gauge nozzle, such that the resultant jet recoil force pushes the section of the drill bit comprising the at least one gauge nozzle in a radially outward direction, and thus during use towards the wall of the borehole. It is submitted that by increasing the concentration of abrasive particles in the stream of drilling fluid that is jetted by the nozzle, the recoil generated by that jet is increased. Thus, by increasing the abrasive particles to the fluid that is jetted by the nozzles, the resultant jet recoil force is increased. The resultant jet recoil force is thus at a maximum while the abrasive action of the abrasive jets is at its maximum. Thus the jet recoil force advantageously increases the steering effect of the abrasive jets, in particular increases the abrasive effect of the abrasive jet jetted by the at least one gauge jet, by pushing the section of the drill bit with the at least one gauge jet in a radially outward direction, i.e. towards the wall of the borehole, while the abrasive effect of the jet jetted by the gauge jet is maximal. In an embodiment according to the invention the at least one center nozzle is at an angle with the central rotation axis and the gauge nozzle, and the gauge nozzle is at an angle to the central rotation axis, and the angle enclosed by the at least one centre nozzle and the central rotation axis is larger than the angle enclosed by the at least one gauge nozzle and the central rotation axis. Therefore, the jet recoil force generated by the jet jetted by the central nozzle has a laterally directed component that is larger than a laterally direct component of a jet recoil force generated by the at least one gauge nozzle. Preferably, it is the laterally directed component of the jet recoil force of the at least one central nozzle that forms the main component of the resultant jet recoil force that pushes the part of the drilling bit with the at least one gauge nozzle in a radially outward direction. The drill bit according to the invention is hereinafter explained with reference to the appended figures, of which figure 1a schematically illustrates an embodiment of a drill bit according to the invention in a view on the face thereof, figure 1b schematically illustrates the same embodiment of the drill bit in the same view, figure 2 schematically illustrates the same embodiment of the drill bit inside a borehole, with the face of the drill bit facing the borehole bottom in a diametrical cross- section, with the orientation of the nozzles being indicated, figure 3 schematically illustrates the same embodiment of the drill bit in a view on the face thereof, with the orientation of the nozzles being indicated, evenas the inner and outer sections, figure 4 schematically illustrates for the same embodiment in the same view, the respective paths of the cutters during over a drill bit rotation, figures 5a,b schematically illustrates for the same embodiment, in respectively the same and a diametrical cross-sectional view, the jetting over a drill bit rotation, figure 6 schematically illustrates the same embodiment in a view on the face thereof, with faced zones of the borehole bottom being indicated, figure 7 schematically illustrates the same embodiment in the same view during different stages of a rotation during a use of the drill bit, figure 8 schematically illustrates the same embodiment in the same view with resulting forces indicated during the same use of the drill bit, figure 9 schematically illustrates the same embodiment in the view on the face thereof during jetting, and figure 10 schematically illustrates a method and system according to the invention. In particular, figures 1-9 illustrate schematically a drill bit 1 according to an advantageous embodiment of the drill bit according to the invention. A method and system according to the invention is explained in relation to figure 10, depicting an example of both. Figure 1a illustrates schematically the drill bit 1 in a view of the face of the drill bit 1, indicating its parts. Figure 1b illustrates a 3D render of the same drill bit 1 in the same view. Figure 2 illustrates in a side view highly schematically the drill bit 1 according to this embodiment during use in a borehole 103a - see figure 10 - in a subterranean earth formation 100. As shown in figure 2, the drill bit 1 is configured to create a borehole bottom in the shape of a cone 101 encircled by an annular groove 102 which radially connects to the cone 101. It is shown that the cone 101 of the borehole bottom axially faces a radially inwards center section 1i of the drill bit 1 around a central rotation axis A₁ of the drill bit 1. The annular groove 102 axially faces a radially outwards section 1o of the drill bit 1. Thus, considered from a central rotation axis of the drill bit, the depth of the borehole substantially increases continuously in a radially outwards direction from the rotation axis A1 of the drill bit 1 to the annular groove 102. The annular groove 102 is bounded by a radially outward wall 102w which in use of the drill bit 1 extends the inner side wall 100w of the borehole 103a, and by a radially inward wall 101w of the cone 101. The inner and outer sections 1i and 1o are also schematically illustrated in the bottom view of figure 3. Now referring again to figures 1 and 2, the drill bit 1 comprises a cylindrical body 10. This cylindrical body 10 is at one axial side of the drill bit 1, in figure 2 the upper side, connectable to a drilling system. For example the drill bit 1 has at this axial side a connector for connection to a drill string, to a bottomhole assembly, or as is preferred, to a steering sub as disclosed by WO2021069694. At this axial side the cylindrical body 10 is provided with a fluid inlet port (not shown) for receiving a stream of drilling fluid mixed with abrasive particles. Preferably, one fluid input port is provided, but in embodiment multiple fluid input ports may be provided. The cylindrical body 10 is at a face of the drill bit 1 at the other axial side of the drill bit, which is in figure 2 the bottom side, provided with three blades 11, 12, 13 disposed on the body 10 - see again figure 1. The blades are angularly distributed evenly with respect to the rotation axis A1 of the drill bit 1. Embodiments are envisaged with more than three blades, for example four or five blades. An uneven number of blades is however preferred to reduce vibrational effects while drilling. The blades 11, 12, and 13 define slots angularly between them. Each blade has multiple mechanical cutters 11c1,2,3, 12c1,2,3, 13c1,2,3 provided thereon. It is these cutters which excavate the borehole bottom to extend the borehole 103a in the drilling direction δ_1A, i.e. forwards along the rotation axis A₁ in the direction from the bit 1 to the borehole bottom 101,102. Furthermore, a center cutter 10c is additionally provided directly on the body 10 centrally between the blades near the rotation axis A₁ of the drill bit 1. This center cutter 10c has the function of regularly cutting off a cutting of the formation for transportation with drilling fluid through the slots between the wings into the annulus, and further towards the surface, for further geological analysis. By the cutting action of the center cutter 10c a cutting is obtained which is larger than regularly obtained by the cutting action of the excavating cutters only, which makes it more suitable for the geological analysis. The center cutter is close enough to the center axis for ensuring that even without erosion, the rate of penetration (ROP) is not hampered by insufficient cutting action in the center. It is illustrated in figure 4 in a bottom view of the drill bit 1, that the excavating cutters on the blades are provided in positions which are radially offset from one another such, that the total of cutters together substantially covers the radial extension of the drill bit 1. This makes that the drill bit 1 is already by cutting capable of forming and deepening the borehole bottom in the shape of the cone 101 with the radially connecting encircling groove 102. In figure 4, the dashed circles illustrate the rotational path of the radial center of, respectively from the inner to the outer circle, the cutters 10c, 12c1, 11c1, 13c1, 12c2, 11c2, 13c2, 12c3, 11c3, and 13c3. From this figure 4, in particular in comparison with figures 2 and 3 indicating the inner and outer sections 1i and 1o of the drill bit 1, it can be verified that the excavating cutters cover almost the entire radial extension of the drill bit 1 so that as an effect, the borehole bottom is excavated continuously in this range. The drill bit 1 further comprises two abrasive jet nozzles 21, 22. These abrasive jet nozzles 21, 22 are suitable for each jetting the stream of fluid mixed with abrasive particles, received through the fluid inlet port, as an abrasive jet 201,202 towards the borehole bottom 101,102 for impingement thereof, in a respective jetting direction δ201,δ202. Each of the nozzles forms the outlet of a respective channel extending through the cylindrical body 10 for fluid connection with the fluid inlet port. This may in embodiments be via an intermediate space as in WO2021069694, or for example via a simple splitting of a single channel from the inlet port into the two channels ending in the nozzles. The abrasive jet nozzles 21,22 firstly comprise a center nozzle 21, extending in the inwards section 1i of the drill bit 1, and having an opening extending close to the rotation axis A₁, i.e. at a maximum distance of its diameter. See in particular figures 1, 2 and 3. In alternative embodiments, there may be more than one center nozzle 21. The center nozzle 21 is configured for eroding the cone 101 and a radially inwards part 102i of the encircling annular groove 102 of the borehole bottom, by jetting the abrasive jet 201 from the rotation axis A₁ radially outwards to the radially inwards part 102i of the groove 102 of the borehole bottom for impingement of this radially inwards part 102i ahead of the cutters that are facing the radially inwards part 102i. The center nozzle 21 thereto extends substantially at a diametrical side with respect to the rotation axis A₁ which is opposite to that at which the abrasive jet 201 jetted by the nozzle 21 substantially extends. The latter is in particular visible in figures 2, 3, and 7. The center nozzle 21 extends in figure 2 substantially at the left side of the rotation axis A₁, whereas the abrasive jet jetted thereby extends substantially at the right side thereof. In figure 3, this is shown in a bottom view: when considering the diameter of the drill bit through the opening of the nozzle 21 and the rotation axis A1, the center nozzle 21 extends therealong at one side of the rotation axis A1, and the jet 201 ejected therefrom at the other side. It is noted that in the context of the present disclosure, the terms ‘ahead’ and ‘behind’ are to be considered with respect to the axial drilling direction, in the figures denoted by δ1A, thus in a direction along the rotation axis of the drill bit forwards from the face of the drill bit towards the borehole bottom. The abrasive jet nozzles 21,22 secondly comprise a gauge nozzle 22, which has an opening in the radially outwards section 1o of the drill bit 1, see again figures 1, 2 and 3. In alternative embodiments, there may be more than one gauge nozzle 22. The gauge nozzle 22 is configured for eroding a radially outwards part 102o of the encircling groove 102 of the borehole bottom, by jetting the abrasive jet 202 from the radially outwards section 1o of the drill bit 1 to the radially outwards part 102o of the annular groove 102 of the borehole bottom for impingement of this radially outwards part 102o ahead of the cutters facing the radially outwards part 102o. The gauge nozzle 22 thereto each extends at a diametrical side with respect to the rotation axis A₁ which is the same as that at which the abrasive jet 202 jetted by the nozzle 22 substantially extends. The latter is in particular visible in figures 2, 3, and 7. The center nozzle 21 extends in figure 2 substantially at the left side of the rotation axis A₁, and the abrasive jet jetted thereby also extends substantially at the left side thereof. In the bottom view of figure 3, considering the diameter of the drill bit 1 through the opening of the gauge nozzle 22 and the rotation axis A₁, the gauge nozzle 22 extends at one side of the rotation axis A₁, and the jet 201 ejected therefrom at the same side. In figure 2 it is illustrated that the abrasive jet 201 from the center nozzle 21 is positioned and oriented to erode the cone 101 at its wall 101w and the inwards part 102i of the annular groove 102, and the abrasive jet 202 from the gauge nozzle 22 is positioned and oriented to erode the outwards part 102o of the annular groove 102 including the wall 102w thereof. Figures 5a and 5b illustrate respectively in a bottom view and a diametrical cross-section of the drill bit 1 a part of the abrasive jets 201 and 202, cut off transversely at a length approximately corresponding to the impingement positions P₂₀₁, P₂₀₂, when ejected over a full rotation ω₁ of the drill bit 1 around the rotation axis A₁. It shows that the jets 201, 202 radially connect, to erode connecting respective zones Z201 and Z202 of the borehole bottom. It is remarked, that whereas the erosion is straight in front of the nozzle, the fluid cleans the bit 1 and borehole bottom in a much larger area. The radial range over which the erosion takes place, is partly dependent on the erosivity of the associated abrasive jet and thus partly depends on the use of the drill bit. The inventive drill bit 1 however enables radially connecting jets 201,202. Considering the axial drilling direction, the nozzles 21, 22 are configured to jet the respective abrasive jets 201, 202 such that the impingement positions P201, P202 thereof are at least ahead of the excavating cutters in the parts 101,102i,102o of the borehole bottom that the nozzles 21, 22 are configured to erode. The impingement positions are the axial positions along the directions δ201, δ202 where the abrasive jets impinge the borehole bottom. This location may vary with fluid and stream properties, however, the scope of the present invention is, as defined in the claims, limited to abrasive jets of drilling fluid which have a reach such as to at least impinge the borehole bottom ahead of the cutters – limiting the scope to a certain range of fluid properties and pressures to achieve such abrasive jet. In particular, abrasive jets 201, 202 are envisaged having a reach of around 15-25, e.g.18-22, preferably 20, times the nozzle diameter, when ejected in air. The result is a jet which during drilling of subterranean earth formations has its position of impingement with the borehole bottom 1.5-10 times the nozzle diameter, e.g.2-8 cm in case of a 10.5 cm drill bit and a nozzle diameter of 4-20 mm, from the nozzle opening in the jetting direction. See figure 9, wherein the impingement positions P₂₀₁, P₂₀₂ are indicated during a use of the depicted embodiment, a part of each jet being simply illustrated by a cylinder extending in the jetting direction δ₂₀₁, δ₂₀₂ from the nozzle openings to these impingement positions P₂₀₁, P₂₀₂. As explained, an effect of the positions, orientations and configurations of nozzles 21, 22 and the excavating cutters is that when during use of the drill bit the erosion by the abrasive jets is such that there is still an excavating action by the cutters, the erosion additionally supports the cutting action. This results in an enhanced rate of penetration (ROP), which is higher than the sum of the rate of penetration resulting from erosion and cutting in isolation, because of an increased torque and consequent higher bit aggressivity. As known, the erosive power of the abrasive jets can be modulated by modulating the concentration of abrasive particles, the pressure, velocity, fluid properties, particle properties, etc. Also during the use of the inventive drill bit 1, the extent of erosion can be adjusted in the same manner to support the excavating action. As also explained, a second effect of the positions, orientations and configurations of the nozzles 21, 22 and the excavating cutters, is that when the erosive power of the abrasive jets 201, 202 are during use of the drill bit 1 ejected by the nozzles 21, 22 varied along the drill bit rotation, in particular consistently along subsequent drill bit rotations, differential holemaking may be achieved. This effect is explained in relation to the figures by means of an example use wherein the erosion is provided only in a selected angular range of the drill bit rotation ω1, which extends over around half of the rotation, thus a range of around 180°. Therein, each jet erodes the borehole bottom in this selected angular range to such an extent that the excavating cutters are substantially not excavating the borehole bottom in the selected angular range. The difference in erosion between the selected angular range, e.g. selected half of the rotation, and the remaining angular range, e.g. remaining half, of the rotation already provides differential holemaking for a directional effect towards the selected angular range in the way known from the prior art. Consequently, the drill bit 1 may incline slightly in this direction since the increased depth in the selected angular range gives slightly more room to the drill bit to descend in the corresponding zone than in the remaining angular range. Repeating this use of the drill bit over subsequent rotations leads to a further inclination of the borehole bottom extending the borehole, resulting in a bent borehole and a correspondingly altered drilling direction of the drill bit 1. The cutting action in the remaining angular range may, as a second effect of the positions, orientations and configurations of the nozzles 21, 22 and the excavating cutters according to the invention, enhance, and furthermore provide an additional means of control of, the directional effect. That is, in addition to the erosion by the abrasive jet 202, and the control thereof by modulation of the erosive power of abrasive jet 202 and/or of the angular ranges in which these are ejected. The first and second effect are explained in relation to these figures 6, 7 and 8, for an example use of the drill bit 1 which is illustrated in figure 6, which may be further visualized with the help of figure 2.The phenomenon caused by the inventive principles that are to the basis of the enhancement of the directional effect and the additional control means is explained with reference to figures 7 and 8. Figure 6 illustrates an example use of the drill bit 1, wherein the abrasive jet 201 from the center nozzle 21 is ejected only in the angular range α₂₀₁, which is approximately 180°, and the abrasive jet 202 from the gauge nozzle 22 is ejected only in the angular range α₂₀₂ of approximately 180° complementary to the angular range α201. Now considering again figure 2, this corresponds in this figure to erosion by the abrasive jet 201 of the right half of the cone wall 101w and the inner part 102i of the annular groove 102, i.e. zone Z201, and to erosion by the abrasive jet 202 of the left half of the outwards part 102o of the annular groove including the groove wall 102w, i.e. zone Z202. The halves of the cone wall 101w and groove wall 102w are excavated by cutting only, to a less extent, and thus a shallower depth, than the erosion. The result is that the directional effect is to the left side as indicated: the drill bit 1 is thus biased radially towards the drill bit radial direction δ1R. Now concerning the second effect, figure 7 illustrates the mechanical forces exerted by, in particular, the outwards part 102o of the annular groove 102 of the borehole bottom on the drill bit 1 as a result of the above explained use of the drill bit 1. The forces on the bit 1 by the cone 101 and the inwards part 102i of the annular groove 102 only have a minor influence on the second effect when compared to the forces on the bit 1 by the outwards part 102o of the annular groove 102, so that these are in these figures ignored for now, purely for the sake of comprehensibility of the origin of the second effect. In the angular range α₂₀₂, see figure 6, substantially no force is exerted by the groove part 102o on the cutters in the outwards section 1o of the drill bit 1 facing it, because the abrasive jets 201 erodes zone Z₂₀₁ ahead of the cutters. In the angular range α₂₀₁ however, the groove part 102o does exert a resistive force on the cutters in reaction to the excavating action thereof. In figure 7 these reaction forces on the cutters disposed on each of the blades 11, 12, 13 are, in the left side of the figure in six successive positions from above to below during the half rotation ω₁ of the bit 1 wherein the gauge nozzle 22 is ejecting jet 202, and in the right side of the figure in six successive positions from above to below during the subsequent half of the rotation ω₁ of the bit 1 wherein the gauge nozzle 22 is not ejecting jet 202, respectively indicated by arrows F₁₁, F₁₂, F₁₃ which point to the direction of the respective reaction forces on the respective cutters. Where the gauge nozzle 22 is ejecting abrasive jet 202 in the left side of the figure, its opening is shaded black. To the right of each illustrated rotational position, the direction of the resultant force F₁ on the bit 1, i.e. the sum of the reaction forces F₁₁, F₁₂ and F₁₃, is shown. It can be verified from figure 7 that, as a consequence of the defined rotation direction ω₁ and the angular range α₂₀₁ of zone Z₂₀₂, the components of the reaction forces F₁₁, F₁₂ and F₁₃ perpendicular to the radial steering direction δ_1R, in the angular range α₂₀₂ is, consistently directed correspondingly to the effective angular velocity component V1N of the drill bit rotation ω1 in the zone Z202 eroded by the gauge nozzle 22 - see figures 6. This results in a force component of a resulting force F1 on the bit averaged over a complete rotation, that is in the direction of the velocity component V1N. The components of the reaction forces F11, F12 and F13 parallel to the steering direction δ1R, are however opposed along the rotation of the drill bit 1, and substantially cancel each other out – so that averaged over a rotation of the bit, there is substantially no force component of the resulting force F1 on the bit 1 parallel to the steering direction δ1R. In effect, an effective average resultant reaction force F1,AVG on the drill bit 1 averaged over a full rotation ω1 of the drill bit 1, is directed substantially parallel to the velocity component V1N. This average resultant reaction force F1,AVG applies on the bit 1 in the outwards section 1o thereof. This is indicated in figure 6. The effective average resultant reaction force F1,AVG has the result that the drill bit 1 is pushed against the annular groove wall 102w in the direction of this force F1,AVG. This effectuates a contact point RP between the drill bit 1 and the groove wall 102w – see figure 8. The force moment driving the rotation ω1 of the drill bit 1 around the rotation axis A1, causes firstly an effective average frictional force FC,AVG exerted on the bit 1 by the groove wall 102, which is oppositely directed to the radial steering direction δ_1R, and secondly an effective average force moment M_C,AVG around the contact point R_P which therefore forms the rotation point R_P thereof. The force moment M_C,AVG results in a correspondingly directed movement of the bit 1 around the rotation point R_P, which effectively moves the bit in the steering direction δ_1R – thereby enhancing the directional effect. It may be envisaged from the discussed example, that this second effect may be generalized to other uses as well, e.g. wherein the angular ranges are chosen differently, or wherein the jets are ejected over the whole azimuthal range but with varying concentrations. Such uses may result in effective average forces and effective average force moments achieving similar effects, for example to a different extent. The second effect from the position, orientation and configuration of the excavating cutters and abrasive jet nozzles forms additional means of control of the directional effect. First of all, modulation of the erosive power and/or zones eroded by the abrasive jets, has an enhanced influence on the extent of the directional effect emanating from the reaction forces on the cutters. Furthermore, the positions, orientations, and individual properties of the cutters may be modulated along designs of the drill bit 1 to provide a particular influence on the directional effect with a certain use of the drill bit 1, e.g. adapted to certain drilling conditions or desired steering. It is also envisaged that cutters may be switchable on and off, e.g. individually, e.g. during use, to influence the discussed reaction forces on the drill bit 1 and thus the directional effect. It is envisaged that adjustment of the direction of the jet, in particular that ejected by the gauge nozzle 22 as it has the largest influence on the directional effect, may additionally be used as a control variable, through its influence on the reaction force on the cutters and thus the extent of the directional effect. For example, the gauge nozzle 22 may be provided in the body 10 such that the orientation δ202 of the gauge nozzle 22 is adjustable. Such adjustment can in practice be made prior to drilling, the direction being kept constant whilst drilling. Other examples are thinkable as well to influence the directional effect by influencing the reaction forces on the cutters. Now that the enhancement of the directional effect has been explained considering only the outwards section 1o of the drill bit 1 including the gauge nozzle 22, and the corresponding outwards part 102o of the annular groove of the borehole bottom, a nuance can be made concerning the inwards section 1i of the drill bit 1. Referring again to figure 6, in the discussed use of the drill bit 1 the zone Z201 is eroded by the center nozzle 21 ahead of the excavating cutters in the inwards section 1i, so that these cutters do substantially not experience a reaction force of the borehole bottom in that zone Z₂₀₁. The term ‘substantially’ herein covers a situation visible in figure 5a, wherein one of the cutters is still partly ahead of the impingement position of the jet 201. The reaction forces by the borehole bottom on the inner section 1i of the drill bit 1 thus now occur substantially only in the angular range α₂₀₂ which is not eroded by the jet 201. It can be verified following the same line of analysis as discussed for the outer section 1o, that an effective average reaction force is now caused in the direction opposite to the velocity component V_1N in the angular range α₂₀₂ of zone Z₂₀₁. Thus, directed oppositely to the reaction force F_1,AVG applied in the outer section 1o of the drill bit 1, and applying now in the inner section 1i of the drill bit 1. The influence on the directional effect is minor relative to that of the outer section 1o, so that the directional effect is still predominantly caused by the outer section 1o as illustrated by figures 7 and 8 and discussed in relation thereto. The difference between the opposing influences of the inner section 1i including the center nozzle 21 and of the outer section 1o including the gauge nozzle 22, does however provide a further control means of the directional effect. For example, by modulating the erosive power of the jet 202 ejected by the gauge nozzle 22, increasing the directional effect with increasing erosive power, relative to the erosive power of the jet 201 ejected by the center nozzle 21, decreasing the directional effect with increasing erosive power. Thus, as now explained in relation to the example in the figures, to enable the combination of the first and second effect, according to the invention the abrasive jet nozzles 21,22 are configured to jet the abrasive jets 201,202 such that these together erode the borehole bottom 101,102 over substantially the entire radial extension thereof, in particular continuously, and as such being configured to provide the directional effect by differential holemaking, when the erosive power of the abrasive jets 101,102 jetted thereby is selectively varied between, opposing, e.g. complementary, azimuthal ranges α201, α202 which are consistent during subsequent rotations ω1 of the drill bit 1 around the rotation axis A1. Both the nozzles and the cutters are individually capable of forming and deepening the borehole bottom in the shape of the cone encircled by the annular groove. The abrasive jets can however provide the differential holemaking, whereas the cutters are not. The position, orientation and configurations of the excavating nozzles and the cutters may in uses of the drill bit provide enhancement of the directional effect, and/or provide additional control means thereof by influencing the reaction forces of the borehole bottom on the cutters through modulation of the jets along the rotation, and/or along the abrasive jet nozzles. The substantially corresponding axial locations of the openings of the nozzles behind the cutters in particular facilitates that, e.g. with the same fluid pressure, the jets form the encircling groove 102 together, cooperatively, achieve a substantially continuous depth thereof. The discussed radially offset positions of the cutters, evenas the positions, orientations and configurations of the abrasive jet nozzles facilitate that the drill bit 1 according to the invention achieves a particularly favorable quality of the borehole wall and bottom. The slots of the drill bit angularly defined between blades 11, 12, and 13 enable the fluid mixed with abrasive particles of the jets 201, 202 to after impingement with the borehole bottom, to escape therethrough to the annulus of the borehole, and along the borehole against the drilling direction δ_1A to the surface. Preferably, the cutters of the drill bit are of polycrystalline diamond material, so that the drill bit is a hybrid polycrystalline diamond compact drill bit (hybrid PDC drill bit). In embodiments of the drill bit according to claim 2, of which the depicted embodiment is an example, the center nozzle 21 and gauge nozzle 21 are oriented, firstly, such that the abrasive jet 201 directed by the center nozzle 21 is, at least at an axial impingement position P201 along its jetting direction δ201 at the opposite diametrical side as an axial impingement position P202 of the abrasive jet 202 jetted by the gauge nozzle 22 along the jetting direction δ202 thereof, and secondly, such that the impingement positions P201,P202 of the abrasive jets are diametrically substantially aligned with each other and with the rotation axis A1. This feature may for the depicted embodiment in particular be verified in the figure 3. This feature provides particular advantages to the drill bit 1, which may lead to a more simple and effective use thereof. As explained before, the abrasive jet 201 jetted by the center nozzle 21 erodes the inner, slanted wall 101w of the cone 101, radially bounding the inner part 102i of the groove 102o, and the abrasive jet 202 jetted by the gauge nozzle 22 forms the outer wall 102w bounding the outer part 102w of the groove 102 which extends the wall of the borehole behind the bit 1 running up to the surface. In order to steer the bit 1 in a certain direction, both the inner and outer wall 101w, 102w need increased erosion in complementary azimuthal ranges, since any annular location of the outer wall 102w corresponding to a certain radial steering direction δ1R is opposite to the angular location of inner wall 101w corresponding to this steering direction δ1R, with respect to the rotation axis A₁. The effect of the feature according to claim 2 is, that when providing the abrasive jets 201, 202 with an increase or decrease in erosive power simultaneously over a certain part of the rotation in order to steer the bit in a certain direction, the abrasive jets simultaneously effectuate an increased or decreased erosion at complementary azimuthal ranges. This means that with this feature the steering effect can be obtained by means of synchronous modulation of the erosive power of both abrasive jets along the rotation of the drill bit, that is, when considering the timing of impingement of both jets. Thus if at a certain angular position of the drill bit 1 along the rotation, the gauge nozzle is in an azimuthal range which needs more erosion, the center nozzle will needs more erosion as well at that angular position. In one possible use of the drill bit, the erosive power of the abrasive jets is modulated along the rotation thereof by feeding stream portions with alternatingly high and low concentrations of abrasive particles to the bit, which stream portions respectively result in high and low erosive power when impinging the borehole bottom. Therein every highly concentrated stream portion is jetted to the borehole bottom during a first part of a rotation, and every lowly concentrated stream portion is jetted to the borehole bottom during a complementary second part of the rotation. This principle is explained in the application WO2021069694. The feature of claim 2 now enables an example of this use of the drill bit 1 wherein the alternating stream portions are generated in one single stream, which thereafter splits into two parts for forming the respective jets. This splitting is in an embodiment within the drill bit, having one single fluid inlet port for receiving the single stream with the alternating stream portions, a connecting channel splitting inside the body into two channels of which the respective nozzles form the respective outlets. The splitting is in another embodiment upstream of the drill bit channels, so that the drill bit has two fluid inlet ports connected to two channels through the body of which the respective nozzles form the respective outlets. In another possible use of the drill bit, the erosive power of the abrasive jets is modulated along the rotation thereof by providing the nozzles with the stream of fluid with abrasive particles only in the first part of the rotation, e.g. of which the use discussed in relation to figures 6, 7, and 8 is an example. In that case there is only abrasive erosion in the parts of the borehole bottom that need more subtraction, and mechanical cutting applied to the complementary parts of the borehole bottom. The feature of claim 2 now enables an example of this use wherein stream portions are fed to the bit at certain time intervals which lead to jetting in the desired azimuthal ranges. The feature of claim 2 now enables an example of this use wherein the intermittent generation of these portions is done in a single stream, which thereafter splits into two stream parts for forming the respective jets. This splitting may again be inside or outside the bit, the bit being correspondingly provided with either one or two fluid inlets, respectively, connecting to one or two channels through the body, wherein in case of one channel this channel splits inside the body into channels of which the respective nozzles form the outlets and in case of two channels the respective nozzles form the outlet thereof. In embodiments of the drill bit according to claim 3, of which the depicted embodiment is an example, in a bottom view of the drill bit 1, the center nozzle 21 is oriented to have its jetting direction δ₂₀₁ extending substantially radially, and the gauge nozzle 22 is oriented with its jetting direction δ₂₀₂ at an angle with the jetting direction δ₂₀₁ of the center nozzle 21, an angular component of its jetting direction δ₂₀₂ being directed towards the jetting direction δ₂₀₁ of the center nozzle 21. See in particular figure 3. As a result of the feature of claim 3, the channels and nozzles are in a bottom view at a distance from one another, extending such as to not cross one another, enabling a favourable fit in this particularly small part of the body 10 in order to leave ample solid body material in between them for providing strength and robustness, while leaving some flexibility in the practical realization, e.g. for providing a slight adjustability of the nozzle directions and/or diameters. It is preferred, that the gauge nozzle 22 does furthermore not overlap with the center nozzle 21 in the bottom view in order to enhance this effect. In embodiments, of which the depicted drill bit 1 is an example, the jetting direction of the center nozzle 21 is at an angle β21 with the rotation axis A1 of the drill bit 1 in the range of 40 – 60°, and the jetting direction of the gauge nozzle 22 is at an angle β22 with the rotation axis A1 of the drill bit 1 in the range of -10° – 10°, for example adjustable in the range of -5° – 5°. Such embodiments lead in use to a favorable shape of the borehole bottom. In embodiments, of which the depicted drill bit 1 is an example, the nozzles 21, 22 each have an inner diameter of at least 4 mm, thus accommodating an abrasive jet of drilling fluid mixed with abrasive particles with a reach of at least 8 cm when ejected in air. The effect is that the nozzles are suitable for jetting abrasive particles with an effective diameter of 0.8-1.2 mm. In embodiments, the center nozzle and gauge nozzle have approximately equal diameters, the gauge nozzle and the center nozzle so being configured to erode equal volumes of the borehole bottom considering a full rotation of the drill bit and considering equal fluid pressures. In general this will lead to the jet 202 ejected by the gauge nozzle 22 covering around 20% of the borehole bottom radius and the jet 201 ejected by the center nozzle 21 covering around 80% of the borehole bottom radius. In embodiments, the length of the center nozzle 21 is 1.2 – 2 times larger than the length of the gauge nozzle 22, e.g.1.5 times larger. In embodiments, the drill bit is, in particular at the sides of the blades, provided with side cutters for excavating the wall of the borehole along the full rotation of the drill bit, irrespective of any jetting during parts of the rotation. Alternative drill bits according to the invention are envisaged having more than one center nozzle, e.g. two, and/or more than one gauge nozzle, e.g. two. A bit with more than two nozzles is envisaged, wherein in addition to a first center nozzle and a first gauge nozzle, one or more further center and/or gauge nozzles are provided which are positioned, oriented and configured to respectively erode the mentioned respective radial portions of the borehole bottom. In use of such drill bit, the nozzles eroding the same radial portions can both be used to erode the mentioned zones. In an example use, the erosion by the abrasive jets of the further nozzles is substantially the same as the two first nozzles, the work being simply divided over the first and further nozzles. In other example uses for directional drilling, the further nozzles merely support the differential erosion of the two previously mentioned nozzles. In preferred embodiments of such drill bits with the feature of claim 2, it is considered that in order for the feature of claim 2 to be effective, the openings therein lie relatively close to one another, in particular leaving a maximum angle of around 10° with respect to the rotation axis A1 therebetween, the impingement points of the jets ejected thereby effectively being substantially diametrically aligned with the opening of the center nozzle(s), so that this alignment principle discussed in relation to figures 3 and 9 is effectively maintained. In example uses of drill bits with more than two nozzles, wherein the erosion is in support of the cutting action without directional effect, the stream may be fed simultaneously to the nozzles, for example providing substantially the same amount of erosion - and thus enhancement of the ROP. In example uses of the drill bit for directional drilling, wherein the stream is fed intermittently to the nozzles to erode the zones over their azimuthal ranges, the stream may be fed simultaneously to the associated nozzles during the intervals, for example providing substantially the same amount of erosion. Furthermore, it must be realized that it is the cross-sectional area of the nozzles together, or the Total Flow Area, which proportionally determines the jetting power, so that in case of multiple nozzles the same jetting power as with a single nozzle is achieved by letting these multiple nozzles each have a decreased diameter relative to the single nozzle, such that the Total Flow Area remains the same. For example in case of the addition of a second nozzle to a first nozzle, for equal jetting power of the first and second nozzle combined, the Total Flow Area must remain the same. In case the two nozzles are to have the same diameter, the diameter of both of the two nozzles must be decreased by a factor √2 relative to the original diameter of the single nozzle. In embodiments, the blades of the drill bit 1 are exactly three blades, alike the depicted drill bit 1 with blades 11, 12, 13, or exactly five blades. An effect of an uneven number of blades is a reduction of undue vibrations in use of the drill bit due to rocking of the drill bit along every rotation of the bit 1 about diametrical pivot axes through oppositely positioned blades with respect to the rotation axis A1, caused by e.g. the depth differences along the borehole bottom during directional drilling. In embodiments, the nozzle openings are positioned between the blades. This facilitates embodiments with favorable dimensions, in particular axially, of the blades and excavating cutters provided thereon, achieving the impingement of the jets ahead of these cutters. Figure 10 illustrates, highly schematically, a drilling system 30 during a directional drilling process, wherein use is made of the drill bit 1 according to the invention in the drilling system 30. Therein a curved borehole 103a is being drilled by the system 30 in the subterranean earth formation 100. The drilling has progressed through a limestone layer and a sandstone layer into a rock layer of the subterranean earth formation. As best seen in the magnification of the system 30, the system 30 is connected to a drill string 33, which is rotated by top drive 36 of drilling tower 37 at the surface 104. Within the cement casing of a main, vertical borehole 103, an anchor 35 is arranged and a whipstock 34, which guides the drill string 33 through the casing to deviate into borehole 103a. Borehole 103a is the last of four curved boreholes 103a, 103b, 103c, 103d deviating from the main borehole 103 being drilled. All deviating curved boreholes 103a, 103b, 103c, 103d comprise a curved section and a subsequent straight section. System 30 is currently deepening the straight section of borehole 103a. Borehole 103a has the borehole bottom 101,102. At the surface 104, besides the tower 37 and top drive 36, a pump 39 is provided which pumps drilling fluid 205 through a particle injection device 38. In particle injection device 38, magnetic abrasive particles 204 from an abrasive particles supply S₂₀₄ are combined with the drilling fluid 205 to form a stream 200 of drilling fluid 205 mixed with abrasive particles 204. The stream 200 has a substantially constant flow rate and concentration of abrasive particles 204. The stream 200 is passed through a supply channel that runs through the drill string 33 into the system 30, inside which it runs subsequently through a steerable sub 32 and a recirculation sub 31 and drill bit 1. After passing the drill bit 1, the stream 200 impinges the borehole bottom 101,102 in the form of the abrasive jets 201, 202 of the stream 200, so as to erode the borehole bottom 101, 102 as described herein before. After this impingement, the stream 200 progresses upwardly again towards the surface 104, moving inside the annulus in between the cylindrical borehole wall 100w and the system 30. While passing the recirculation sub 31, a portion of the abrasive particles 204 inside the stream is captured by the recirculation sub 31, and recirculated within the recirculation sub as a recirculation stream into the stream 200. After the capture of the abrasive particles 204 by the recirculation sub from the stream 203, it progresses further towards the surface as return stream 203. The particles 204 still left in the return stream 203 are filtered at the surface 104 to join the supply S204 of abrasive particles 204. The drill bit 1 according to the invention is particularly suitable for use in such directional drilling processes. With this context in mind, it may be envisaged that the drill bit 1 is particularly suitable for use in methods according to claims 10 and 11 in general. The use of in particular a drill bit 1 in the method according to claim 11, according to claim 2 facilitates a method according to claim 18, because the orientations of the nozzles relative to one another enable angularly opposing zones being eroded by jets ejected at the same time. Thus, it suffices to supply parts of the same stream portion to the respective jet nozzles at the same time, to establish that the jets thereof are directed to angularly opposing azimuthal zones. The stream 200 can thus be supplied to the drill bit via the fluid port as one single stream 200, the stream being split inside the drill bit body 10 into two parts for each being fed to a respective one of the abrasive jet nozzles 21,22 without further measures to time the ejections in correspondence with the zones. In other embodiments, wherein the nozzles are not oriented to jet towards angularly opposing locations along the borehole bottom, it would be necessary to jet the erosive stream portions in the respective jets at timings offset from one another to achieve angularly opposed erosion. In the method according to the invention, the abrasive particles are preferably magnetic, most preferably steel shot. The particles preferably have a substantially spherical shape. The abrasive particles preferably have a diameter of 0.8-1.2 mm, most preferably 0.9 or 1.0 mm. An example of a system according to the invention is indicated in figure 10. It is particularly useful in the context of the drilling process as described in relation to figure 10, although other applications are envisaged as well. The system 20 comprises a steering sub 32 and the drill bit 1 according to claim 1, and optionally, also a recirculation sub 31. The system therein being connectable to a drill string 33 for driving a rotation of the system 30 such that the drill bit rotates around the rotation axis A1 of the drill bit 1 for deepening the borehole. As defined in claim 20, the steering sub 32 is configured for generating, in the stream 200, stream portions thereof for feeding to the drill bit 1 in synchronisation with its rotations, such that erosion of the borehole bottom by the abrasive jets 201, 202 formed out of the stream 200 takes place ahead of the cutters only in the zones Z201, Z202. The system comprises a drill bit 1 according to claim 2, enabling angularly opposing zones being eroded by jets ejected at the same time. This particularly facilitates the modulation of the stream in the steering sub being effective for providing the directional effect without requiring further offsetting timings of feeding parts of the created stream portions to the different abrasive jets. Suitable embodiments of the system are defined in claims 21-23, although other embodiments are possible as well within the scope of the invention, for example wherein the modulated stream is continuous and consisting of succeeding stream portions which alternatingly, contain sufficient abrasive particles for erosion ahead of the cutters and substantially do not contain abrasive particles, so that substantially only drilling fluid is jetted to the borehole bottom outside the zones Z₂₀₁, Z₂₀₂ with the sole purpose of aiding the drilling by cutting there. Or, for example wherein the intermittence and the lowly and highly concentrated stream portions are combined in the stream 200. Or, wherein the differential holemaking is not applied in each rotation, but only in a part of the rotations during a certain time period – therein reducing the directional effect for a less sharp bend of the borehole. Or, wherein the erosive power of the abrasive jets is varied by other means than the variation of the particle concentration between succeeding stream portions. For example, the type of particles, pressures etc. may also be modulated to control the directional effect. Suitable embodiments of the steering sub are described in WO2021069694. in the system 30 according to claims 22 and 23, in embodiments thereof, in particular envisaged to be embodied accordingly. Suitable embodiments of the recirculation sub are described in WO2021069694. The system 30 according to claims 22 and 23, in embodiments thereof, in particular envisaged to be embodied accordingly. Systems with the recirculation sub are in particular useful in applications of the system wherein the abrasive particles in the stream 200 are magnetic, e.g. of steel. List of reference symbols 1 drill bit 1i radially inwards section of the face of 1 1o radially inwards section of the face of 1 A1 central rotation axis of 1 ω1 (driven) rotation of 1 δ1A axial drilling direction of 1 δ1R radial steering direction of 1 10 body of 1 10c1 center cutter 11 first blade 11c1-3 cutters on first blade 12 second blade 12c1-3 cutters on second blade 13 third blade 13c1-3 cutters on third blade 21 center nozzle 22 gauge nozzle 30 drilling system 31 recirculation sub of 30 32 steering sub of 30 33 drill string 34 whipstock 35 anchor 36 top drive 37 tower 38 particle injection device 39 pump for 205 100 subterranean earth formation 100w wall of borehole 101 cone of the borehole bottom 101w wall of 101 102 annular groove encircling and radially connecting to 101 102w wall of 102 102i radially inwards part of 102 102o radially inwards part of 102 103 main, straight, vertical borehole 103a-d curved boreholes 104 surface 200 supply stream of drilling fluid mixed with abrasive particles 201 abrasive jet ejected by 21 202 abrasive jet ejected by 22 203 return stream of drilling fluid mixed with abrasive particles 204 abrasive particles 205 drilling fluid Z₂₀₁ zone of the borehole bottom eroded by 201 Z₂₀₂ zone of the borehole bottom eroded by 202 α₂₀₁ angular range eroded by 201 α₂₀₂ angular range eroded by 202 β₂₁ angle between δ₂₀₁ and A₁ β₂₂ angle between δ₂₀₂ and A₁ δ1A axial, drilling direction of 1 δ1R radial, steering direction of 1 δ201 direction of 201 δ202 direction of 202 P201 impingement position of 201 P202 impingement position of 202 AIP axis through P201 and P202 F11 force exerted by hole bottom on cutters on blade 11 F12 force exerted by hole bottom on cutters on blade 12 F13 force exerted by hole bottom on cutters on blade 13 F1 resultant force on 1 F1,AVG resultant force on 1 averaged over full rotation of 1 M_C,AVG force moment exerted on 1 by cutting action, averaged over full rotation of 1 R_M,AVG averaged rotation point of M_C,AVG F_C,AVG force exerted on 1 by 102w at R_M,AVG S₂₀₄ supply of 204 at 104

Claims

C L A I M S 1. Drill bit (1) for directional drilling of a subterranean earth formation (100) simultaneously by abrasive jet drilling and mechanical cutting, the drill bit (1) being configured to create and deepen a borehole bottom in the shape of a cone (101) encircled by a, radially connecting, annular groove (102), the cone (101) in use of the drill bit (1) axially facing a radially inwards center section (1i) of the drill bit (1) around a central rotation axis (A1) of the drill bit, and the annular groove (102) axially facing a radially outwards section (1o) of the drill bit, the drill bit (1) comprising ^ a cylindrical body (10) having at one axial side of the drill bit, connectable to a drilling system for being rotated around the rotation axis (A₁), a fluid inlet port for receiving a stream of drilling fluid mixed with abrasive particles, and being, at a face of the drill bit at the other axial side of the drill bit, provided with ^ three or more blades (11,12,13) disposed on the body (10), the blades o being angularly distributed evenly with respect to the rotation axis (A1) of the drill bit, o defining slots angularly between them, and o each having two or more mechanical cutters (11c1,2,3, 12c1,2,3, 13c1,2,3) provided thereon, o the cutters being provided in positions which are radially offset from one another such, that the total of cutters together substantially covers the radial extension of the drill bit, wherein the drill bit (1) further comprises ^ two or more abrasive jet nozzles (21,22), each being o fluidly connected to the fluid inlet port and having a respective opening at the face of the drill bit, o suitable for jetting a respective part of the stream of fluid mixed with abrasive particles as an abrasive jet (201,202) towards the borehole bottom (101,102), for impingement thereof, in a respective jetting direction (δ201,δ202), the abrasive jet nozzles (21,22) comprising o at least one center nozzle (21), each extending in the center section (1i) of the drill bit (1), having an opening close to the rotation axis (A1) such as to be positioned, oriented and configured for eroding the cone (101) and a radially inwards part (102i) of the encircling annular groove (102) of the borehole bottom, by jetting the abrasive jet (201) from the rotation axis (A1) radially outwards to the radially inwards part (102i) of the groove (102) of the borehole bottom for impingement of this radially inwards part (102i) ahead of the cutters that are facing the radially inwards part (102i), the at least one center nozzle (21) thereto each extending at a diametrical side with respect to the rotation axis (A₁) which is opposite to that at which the abrasive jet (201) jetted by the nozzle (21) substantially extends, o at least one gauge nozzle (22), each of which has an opening in the radially outwards section (1o) of the drill bit, and is furthermore oriented and configured for eroding a radially outwards part (102o) of the encircling groove (102) of the borehole bottom, by jetting the abrasive jet (202) from the radially outwards section (1o) of the drill bit to the radially outwards part (102o) of the annular groove (102) of the borehole bottom for impingement of this radially outwards part (102o) ahead of the cutters facing the radially outwards part (102o), the at least one gauge nozzle (22) thereto each extending at a diametrical side with respect to the rotation axis (A₁) which is the same as that at which the abrasive jet (202) jetted by the nozzle (22) substantially extends. 2. Drill bit according to claim 1, wherein the center nozzle (21) and gauge nozzle (21) are oriented - such that the abrasive jet (201) jetted by the center nozzle (21) is, at least at an axial impingement position (P201) along its jetting direction (δ201) that is ahead of the cutters, at the opposite diametrical side as an axial impingement position (P202) of the abrasive jet (202) jetted by the gauge nozzle (22) along the jetting direction (δ202) thereof, and - such that the impingement positions (P201,P202) of the abrasive jets are diametrically substantially aligned with each other and with the rotation axis (A1). 3. Drill bit (1) according to claim 2, wherein in a bottom view of the drill bit (1), the center nozzle (21) is oriented to have its jetting direction (δ201) extending substantially radially, and the gauge nozzle (22) is oriented with its jetting direction (δ202) at an angle with the jetting direction (δ201) of the center nozzle (21), an angular component of its jetting direction (δ202) being jetted towards the jetting direction (δ201) of the center nozzle (21), e.g. wherein the gauge nozzle does not overlap with the center nozzle, e.g. wherein the angle is around 5-30°, e.g. around 20°. 4. Drill bit (1) according to any of the preceding claims, wherein the center nozzle (21) is at an angle (β₂₁) with the rotation axis (A₁) of the drill bit (1) in the range of 40 – 60°, and the gauge nozzle (22) is at an angle (β₂₂) with the rotation axis of the drill bit in the range of -10° – 10°, e.g. adjustable in the range of -5° – 5°. 5. Drill bit (1) according to any one or more of the preceding claims, wherein the gauge nozzle (21) has an inner diameter that is larger than the inner diameter of the center nozzle, e.g.1.2-1.5 times as large. 6. Drill bit (1) according to any one or more of the preceding claims, wherein the blades of the drill bit are exactly three blades (11, 12, 13), or exactly five blades. 7. Drill bit (1) according to any of the preceding claims, wherein the openings of the abrasive jet nozzles (21,22) are provided in between the blades. 8. Drill bit (1) according to any of the preceding claims, wherein the abrasive jet nozzles are positioned, oriented and configured to erode the borehole bottom over substantially the entire radial range of the borehole bottom, e.g. the entire borehole bottom. 9. Drill bit (1) according to any one or more of the preceding claims, further comprising, directly on the body (10) centrally between the blades (11,12,13) close to the rotation axis (A1) of the drill bit, a center cutter (10c) for providing a cutting action at the top of the cone (101), and the abrasive jet nozzles (21,22) are positioned, oriented and configured to jet the abrasive jets (201,202) such that these the abrasive jets together erode the borehole bottom (101,102) over at least the radial extension thereof between the center cutter (10c) and the outer circumference of the annular groove (102), e.g. the entire borehole bottom. 10. Method for directional drilling, wherein use is made of a drill bit (1) according to any one or more of the preceding claims. 11. Method for directional drilling of a borehole, with a borehole bottom (101,102) in the shape of a cone (101) encircled by an annular groove (102) radially connecting with the cone (101), in a subterranean earth formation (100), the method comprising: ^ providing a drill bit (1), a body (10) of said drill bit accommodating, for jetting a stream (200) of a drilling fluid (205) mixed with abrasive particles (204) supplied to the drill bit at one axial side of the drill bit, as abrasive jets to the borehole bottom, two or more abrasive jet nozzles (21,22) forming respective outlets for said stream at a face of the drill bit at the other axial side thereof, and cutters (11c1-3, 12c1-3, 13c1-3) of said drill bit being provided at the face of the drill bit, wherein o the abrasive jet nozzles comprise at least one center nozzle (21) positioned, oriented and configured for jetting an abrasive jet (201) eroding the cone (101) and an inwards part (102i) of the annular groove (102), and at least one gauge nozzle (22) positioned, oriented and configured for jetting an abrasive jet (202) eroding an outwards part (102o) of the annular groove, o the abrasive jet nozzles (21,22) being positioned, oriented and configured to jet the abrasive jets (201,202) such that these together erode the borehole bottom (101,102) over substantially the entire radial extension thereof, and o the cutters are positioned, oriented and configured to together, at least without erosion by the abrasive jets (201,202), excavate the borehole bottom over substantially the entire radial extension thereof, ^ supplying the stream (200) to the abrasive jet nozzles through a fluid connection between the abrasive jet nozzles drill bit and a supply for the stream (200) at an axial side of the drill bit (1) opposite to the face, ^ rotating the drill bit (1) around the rotation axis (A₁) thereof so as to deepen the borehole bottom, through, in subsequent rotations (ω₁) of the bit, simultaneous o erosion of the borehole bottom by the respective abrasive jets (201,202) of the stream (200), impinging the borehole bottom ahead of the cutters, and o excavation of the borehole bottom by the cutters. 12. Method according to claim 11, wherein the extent of the erosion and the excavation of the borehole bottom are each substantially continuous over each rotation (ω₁) of the bit. 13. Method according to claim 11, wherein the extent of the erosion and the excavation of the borehole bottom are not continuous over each rotation of the bit, wherein the deepening of the borehole bottom is achieved through, in subsequent rotations of the bit, o a higher extent of erosion in respective zones (Z₂₀₁,Z₂₀₂) of the borehole bottom angularly extending continuously over respective opposing azimuthal ranges (α₂₀₁,α₂₀₂) by the respective abrasive jets (201,202) of the stream (200) and o a lower extent of erosion outside the respective zones (Z₂₀₁,Z₂₀₂), such that said deepening of the borehole bottom provides a directional effect over subsequent rotations (ω1) of the drill bit by differential hole making, e.g. wherein the drill bit (1) is a drill bit according to any one or more of claims 1-9. 14. Method according to claim 13, wherein the extent of the erosion outside of the zones (Z201,Z202) is such that there is at least predominant, e.g. substantially only, excavation by the cutters outside of these zones (Z201,Z202). 15. Method according to claim 13 or 14, wherein the extent of the erosion in the respective zones (Z201,Z202) of the borehole bottom is such that the cutters do substantially not excavate the borehole bottom in these zones. 16. Method according to claim 14 and optionally claim 15, wherein the abrasive jets (201,202) erode the zones (Z201,Z202) only, and do not provide erosion of the borehole bottom outside of these zones. 17. Method according to claim 16, wherein the supply of the stream (200) is such that stream portions are intermittently fed to the abrasive jet nozzles in time intervals which correspond to the nozzles facing the respective zones (Z201,Z202) during jetting of these stream portions in subsequent rotations (ω1) of the drill bit, no stream portions being fed to the nozzles in time intervals which correspond to the nozzles facing the borehole bottom outside the respective zones (Z201,Z202). 18. Method according to claim 13, 14 or 15, wherein the supply of the stream (200) is such that stream portions with a high concentration of abrasive particles (204) are alternated by stream portions with a low concentration of abrasive particles, the respective stream portions being fed to the abrasive jet nozzles in time intervals which respectively correspond to the nozzles facing the respective zones (Z₂₀₁,Z₂₀₂) during jetting of these stream portions in subsequent rotations (ω₁) of the drill bit. 19. Method according to any one or more of the claims 11-18, wherein the abrasive particles are substantially spherical, steel particles having a diameter of 0.5-1.2 mm, e.g. predominantly of 0.8 to 1.0 mm. 20. Method according to any one or more of the claims 11-19, wherein the zones (Z₂₀₁,Z₂₀₂) each have an angular range of 160-200°, preferably 170-190°, most preferably around 180°. 21. System (30) for directional drilling of a subterranean earth formation (100) simultaneously by abrasive jet drilling and mechanical cutting, the system comprising ^ the drill bit (1) according to claim 2, ^ a steering sub (32), fixed or fixable at a borehole bottom directed axial side thereof to the drill bit, and fixable at the other axial side thereof to a drill string (33), for via the steering sub (32) rotating the drill bit (1) around its rotation axis (A₁), wherein the steering sub (32) comprises o a sub fluid inlet port configured for by the connection to the drill string receiving from the drill string a stream (200) of drilling fluid (205) and abrasive particles (204), o a stream modulator configured for modulating the received stream (200), and o a sub fluid outlet port configured for by the connection to the drill bit discharging to the drill bit the modulated stream (200), via the fluid inlet port thereof, wherein the stream modulator is configured for modulating the stream (200) such, that the modulated stream (200) consists of stream portions succeeding one another in the flow direction thereof, wherein the stream portions are in synchronization with the rotations (ω1) of the drill bit around the rotation axis (A1) such that stream portions jetted towards the borehole bottom by the respective center and gauge nozzles only when facing the same, diametrically opposing, respective zones (Z201,Z202) of the borehole bottom, cause a higher extent of erosion in these zones (Z₂₀₁,Z₂₀₂) than outside these zones. 22. System according to claim 21, wherein the stream modulator is configured for modulating the stream (200) such, that the stream portions succeed one another such as to together form an intermittent modulated stream, the stream portions being dimensioned and spaced from one another such that that the stream portions are jetted towards the borehole bottom by the nozzles (21,22) only when facing the respective zones (Z₂₀₁,Z₂₀₂) of the borehole bottom, such as to cause erosion in the zones (Z₂₀₁,Z₂₀₂) only. 23. System (30) according to claim 21, wherein the stream modulator is configured for modulating the stream such, that the stream portions succeed one another such as to together form a continuous modulated stream of which the stream portions are alternatingly highly and lowly concentrated, and are dimensioned such that the highly concentrated stream portions being jetted towards the borehole bottom by the nozzles (21,22) when facing the respective zones (Z₂₀₁,Z₂₀₂) of the borehole bottom, and the lowly concentrated stream portions being jetted towards the borehole bottom by the nozzles (21,22) outside the zones. 24. System (30) according to any one or more of claims 21-23, wherein the stream modulator is configured for modulating the stream at least when the stream as fed to the stream modulator has a substantially homogeneous concentration of abrasive particles.