NO168436B - BORE KRONE MOTOR - Google Patents

Abstract

A downhole screw motor is intended for drilling oil and gas wells. The downhole screw motor comprises a stator (3) and a hollow rotor (4) in the axial channel (5) of which is mounted a flow regulator (6) with a nozzle (16). The surface of the nozzle (16), arround which the working liquid flows, is formed by two consecutively located chambers: a receiving one (A) and a discharging one (B), the surfaces (19, 20) of which are conjugated along a break line (21). The part (22) of the receiving chamber (A) which adjoins the break line (21) has a convex form in the direction of flow of the working liquid, whereas the cross-sectional area of the receiving chamber (A) at its outlet is smaller than at its inlet.

Description

The invention relates to a drill bit motor including a spindle section and a motor section with working elements in the form of a stator and a hollow rotor with an axial passage which is connected to a working fluid high-pressure zone, and with a regulator for the working fluid flow, with a nozzle mounted in the axial passage

Today, two radically different methods are used for drilling wells. One method is a rotary drill. A rock-breaking tool - a drill bit - is placed against the ground, and the drill bit is rotated using a drill string. The second method involves using in-hole hydraulic machines that are placed directly above the drill bit. In this case, the drill string is kept stationary. This second method has several obvious advantages: There is no loss of energy in connection with the rotation of the drill pipe string and the load on the drill pipes is reduced. This reduces the risk of emergency situations in the well.

Drill bit motors are today the most used type among all the in-hole motors used during drilling operations. These engines are distinguished by simple operation and simple maintenance. They are compact and they enable the use of drilling muds of widely varying density and viscosity (see Gusman M.T. , Baldenko D.F, et al. Downhole Screw Motor for Well Drilling. M.„ Nedra Publishing House, Moscow, 1981). Such hydraulic motors include a housing, an output shaft with radial bearings and thrust bearings, and working elements consisting of two parts, namely an outer rubber-coated sleeve or stator with internal helical teeth and a rotor and shaft with external helical teeth and engaged in the stator. The number of teeth in the sleeve is greater than the number of teeth on the shaft, so that the inner space in the working elements is divided into high-pressure chambers and low-pressure chambers as a result of the interaction when a liquid is pumped through the working elements. The rotor will start to move relative to the stator as a result of the resulting pressure difference. The rotor axis will describe a circle about the stator axis. This rotation is transferred to the rotor's output shaft. Usually, a liquid flow is used as the energy source for operating the motor, but the hydraulic motor can also work using an air-mixed liquid or compressed air.

In the drill bit motors used today, which are used for drilling wells, the entire fluid flow goes through and between the rotor and stator.

One of the main disadvantages of such motors is that their power parameters are dependent on the inlet flow of the working fluid. The requirements during drilling of wells are often not in accordance with the energy capacity of drill bit motors and the motors are therefore often used under unfavorable conditions, with too high speeds and pressure differences, with associated early failure of parts and connections in the motor.

To avoid this, conical nozzles have been placed in the axial passage of the rotor (USSR inventor's certificate no. 436595, class E 21.B 4/00, 1972), as the flow of working fluid is throttled in these nozzles.

Such motors have a falling characteristic, i.e. that the speed of the output shaft; decreases much faster? with increasing load torque than is the case in hydraulic motors without such,1 nozzles. When the load increases, this will result in a sharp speed reduction, until the motor's output shaft stops. At low load torques, a lower output torque and a lower drilling efficiency are achieved.

The invention takes its starting point from the desire to provide a drill bit motor with a working fluid flow regulator designed in such a way that an increase in the output working torque can be achieved and a increasing the speed of the output shaft, while the output shaft speed remains practically unchanged under zero load.

This problem is solved in that the nozzle in a drill bit motor, which includes a spindle section and a motor section with working elements - a stator and a hollow rotor with an axial passage communicating with a working fluid high-pressure zone, and having a flow regulator with a nozzle, is made with two chambers arranged in series in the working fluid flow direction. This concerns an inlet chamber and a delivery chamber. The chamber surfaces that are touched by the working fluid conjugate along a break line, the annular part of the inlet chamber adjacent to the break line being concave in relation to the working fluid flow direction, and the cross-sectional area of the inlet chamber at its outlet is smaller than the cross-sectional area at its inlet.

The invention makes it possible to increase the torque and the speed of the motor's output shaft, with a corresponding improvement in the well drilling efficiency. When working fluid enters the nozzle, a strong vortex will form at the break line in the inlet chamber. The vortex energy will increase with increasing pressure difference and the result is an increase in the nozzle's hydraulic resistance with a corresponding increase in the fluid flow that goes between rotor and stator.

The regulator according to the invention is very compact and can be easily mounted in any engine. It can also be replaced without the need to dismantle the hydraulic motor.

In one embodiment, the nozzle is made up of two parts, namely a sleeve and a core part mounted inside the sleeve, the inlet and delivery chambers being formed between the sleeve and the core part and having an annular shape.

In another embodiment, the core part is a cylindrical rod, while the sleeve is internally provided with an annular projection which forms the concave part of the inlet chamber wall.

In another embodiment of the invention, the sleeve is cylindrical while the core part is provided with an annular projection which forms the concave part of the inlet chamber wall.

In another embodiment of the invention, both the sleeve and the core part have ring-shaped projections, each projection forming a convex part of the inlet chamber wall.

All embodiments of the invention make it possible to achieve improved stability for the engine characteristic, i.e.

to reduce the dependence of the engine speed on the load on the output shaft. This is achieved because the liquid flows which run along the curved wall of the inlet chamber will be slowed down at the breaking line so that an area with an intensive vertical flow appears there. The higher the pressure difference in the working elements (rotor and stator), the more intensive the liquid mixture will be in the nozzle and the higher the nozzle resistance will be and the larger the amount of liquid that passes through, outside the regulator. The invention does. it is therefore possible to get a larger quantity of liquid to go: through the rotor and stator than when using conical nozzles.-

This result, i.e. an increase in the fluid flow through the screw passage between the rotor and the stator by an increase in the load on the output shaft, can also be achieved by using other constructive means, but the main inventive idea will remain the same.

In order to lower the specific load at the nozzle, several nozzles can advantageously be arranged in the axial passage of the rotor. Such an engine will work in the same way.

The invention shall be explained in more detail with reference to the drawings, where: Fig. 1 shows a longitudinal section of a drill bit motor with an embodiment of a nozzle in a regulator mounted in the rotor's axial

passage,

fig. 2 shows a section through a flow regulator with a nozzle, on a larger scale,

fig. 3 shows how liquid passes through the nozzle,

fig. 4,5 and 6 show different constructive designs of the nozzle, and

fig. 7 and 8 show experimental data recorded for respectively

prior art and the present invention.

A drill bit motor (fig. 1) includes a motor section 1 and a spindle section 2. The motor section 1 has as working elements a stator 3 and a hollow rotor 4 mounted in the stator. The rotor 4 has an axial passage 5. This axial passage is in connection with a liquid high-pressure zone. A flow regulator 6 is mounted in the passage. The rotor 4 is connected in its lower part to a cardan shaft 7 which in turn is connected to an output shaft 8 in the spindle section 2. A radial bearing 9 and a thrust bearing 10 for the shaft 8 are mounted in a housing 11 in the spindle section 2, between a nipple 12 and a splicing sleeve 13. A splicing sleeve 14 is arranged at the upper end of the motor, intended for connection to a drill pipe string. A rock-breaking tool, not shown, is connected to the lower end of the output shaft 8.

The flow regulator 6 (Fig. 2) includes a removable housing 15 in which a nozzle 16 made, for example, of a ceramic material is mounted. Sealing rings 17 and 18, for example made of rubber, are inserted between the housing 15 and the rotor 4 and also between the nozzle 16 and the housing 15.

The nozzle 16 consists of two chambers which are arranged in series in the working fluid flow direction, namely an inlet chamber A and a delivery chamber B. The walls 19 and 20 of respectively the inlet chamber A and the delivery chamber B meet along a break line 21. An annular section 22 of the inlet chamber A, at the break line 21, is concave in the flow direction of the working fluid. The diameter D at the inlet section of the chamber A is larger than the diameter d in the outlet section of the chamber A. In other words, the cross-sectional area in the inlet chamber A at the inlet of the chamber is greater than the cross-sectional area at the outlet A of the same chamber.

The wall 20 in the delivery chamber B can have any suitable design. However, it is preferred that the chamber B is designed in such a way that. it will provide the maximum possible resistance to the flow of working fluid passing through the nozzle 16. The wall 20 in the chamber B is designed in the same way as the wall 19 in the chamber A, i.e. is described by a curve that rotates about the axis 0-0, with divergence in the flow direction.

Both curves which form the generatrices for the chambers A and B cross each other in the longitudinal section of the nozzle 16 at a place which gives a breaking point. Together, these points form an intersection line 21 which corresponds to the break line,

The engine works in the following way. When the drilling pumps on the surface are put in:, drilling mud is supplied through a string of drill pipe to the working elements in engine section 1 (see fig. 1). The current is divided on the upstream side of the working elements into a main current that will go between stator 3 and rotor 4 to thereby set the rotor in motion, and a second, smaller current that will go through the passage 5 in the rotor 4 and through the flow regulator 6 mounted therein. After having passed through the working elements, the two streams are collected again into a single stream which passes through the bore in the shafts 8 in the spindle section 2 and then up to the surface.

The torque produced in the motor section 1 is transferred from the rotor 4 via the cardan shaft 7 to the shaft 8 and from there to the rock-breaking tool (drill bit).

The resistance torque that the motor must overcome will depend on the interaction between the drill bit and the rock being broken. During the operation of the motor, the motor torque as well as the load or resistance torque will change.

The torque in engines of this type is proportional to the pressure difference at the working elements at a constant flow of a working fluid. In the previously known motors, when the motor is loaded by an external resistance moment as a result of the rotation of the drill bit, the amount of liquid that passes between the rotor and the stator will decrease proportionally with <y>/ P, where P is the pressure difference in the motor. This means that the motor characteristic falls and that the speed of the output shaft 8 drops significantly.

In the engine according to the invention, there are two fluid streams in the inlet chamber A (fig. 3). In the axis 0-0 in the nozzle 16, there will be a current that will go from the chamber A and out through its outlet section, with the diameter d, corresponding to the diameter of the breaking line 21. Another, peripheral current will go along the wall 19 in the chamber A. At breaking line 21, this peripheral current will be slowed down and will mix intensely with the central current. The peripheral current can henceforth be described as a resistance current.

The intensive mixing of the center flow and the resistance flow leads to a reduction in the flow energy that goes to chamber B. The greater the pressure difference at the working elements - stator 3 and rotor 4, respectively at the nozzle '6, the stronger the liquid flows will be mixed and the smaller the amount of liquid that goes from chamber A to chamber B be, i.e. that you get an even greater amount of liquid that goes to the working elements.

As shown in fig. 4, the nozzle 16 is made of two parts, namely a sleeve 23 and a cylindrical rod 24. These two parts are connected to each other by means of bridges 25. As in the aforementioned nozzle design, there are also two, in this case annular chambers which lie one behind the other in the axial direction, namely an inlet chamber A and a delivery chamber B, whose walls 19 and 20 are coated with the working liquid. The chambers A and B are limited by the wall surfaces in the sleeve 23 and on the rod 24. The wall in the sleeve 23 is produced by rotation about the axis 0-0 of a generatrix which is convex in relation to a generatrix for a cylinder with a radius R, where R is the smallest distance from the 0-0 axis of the nozzle 16 and to a line corresponding to the breaking line 21. The breaking line 21 is formed at the intersection of the wall 19 in the chamber A with the wall 20 in the chamber B. As before, here the wall 20 in the chamber B is formed by rotation of a generatrix about the axis 0-0.

Inside the sleeve 23 there is an annular projection which forms the concave part 22 in the inlet chamber A.

When using this regulator, the same result is achieved as with the device in fig. 3. The difference is that the resistance flow, which moves outwards from the cylinder surface of the rod 24, is reflected back to the inlet chamber A circumference for renewed mixing with the center flow (secondary mixing;).

Fig. 5 shows a nozzle 16 which is built up with a sleeve. 2.3<;> and a core 24 so that two chambers appear, namely an inlet chamber A and a delivery chamber B. In this embodiment of the nozzle 16, the sleeve 23 is cylindrical. The core 24 is designed with an annular projection 27 which forms the concave part 22 of the wall 19 of the inlet chamber A. The surface in the sleeve 23 which is in contact with the working fluid is cylindrical, and the wall of the core part 24 in the chamber B is formed by rotation about the axis 0-0 of a generatrix which is convex in relation to a generatrix for a cylinder with a radius R, where R is the smallest possible distance between the axis 0-0 in the nozzle 16 and the line 21 which corresponds to a breaking line that appears in the intersection between the wall surfaces of the rod 24 in chamber A and chamber B respectively.

Unlike the engine in fig. 3, the resistance flow, which moves along a curved surface away from the center of the nozzle and towards its circumference, will be reflected from the inner wall of the sleeve 23 and into the center again, but with a lower energy, and will mix with the center flow.

The nozzle 16 in fig. 6, as in the two previously described embodiments, has two parts, namely the sleeve 23 and the core 24, connected to each other by means of bridges 25. Here, too, the two chambers are arranged one behind the other in the axial direction and one thus has an inlet chamber A and a delivery chamber B with respective walls 19,20 which are coated with the working fluid. The sleeve 23 has an annular projection 28 and the core 24 has an annular projection 29. Each of these projections 28, 29 defines a concave part 22 in the wall 19 of the inlet chamber A. The wall surfaces of the sleeve 23 and the core 24 in the chamber A are produced by rotation about the axis 0-0 of a generatrix which is convex in relation to a generatrix for a cylinder with a radius R, where R is the smallest possible distance between the axis 0-0 of the nozzle 16 and a respective line corresponding to the breaking line 21.

This flow regulator works in such a way that two resistance currents appear here, one which moves along the curved wall surface of the sleeve 23, i from the circumference and inwards towards the center of the nozzle, and a second resistance current which moves along the curved wall surface of the core 24, out from the center of the nozzle 16 and towards its circumference. These streams will cross each other within a ring as determined by the two radii R and R', and this contributes to a further mixing of the liquid streams.

In the embodiment examples described above, you will therefore have two parallel flows. In one, a resistance current is formed which increases with an increase in the pressure difference, i.e. when the motor is loaded with an external torque. The interdependence between the amount of liquid that passes through the working elements and through the nozzle 16 when the engine is loaded is of a complicated nature, but it can be shown that by using the flow regulator with the nozzle design described here, a more stable engine characteristic will be obtained with an increase in the engine's load capacity and very little reduction in the speed of the engine's output shaft.

Fig. 7 and 8 show energy characteristics, i.e. the relationship between the relative pressure difference values AP and the rotation frequency n for the output shaft 8, and the relative torque value M for a previously known screw motor and a screw motor according to the invention, respectively.

A study of the curves in fig. 7 and 8 show that a zone Z, where the engine works stably, see fig. 8, is 18$ greater than a zone S with stable engine operation, see fig. 7, expressed by the torque. The speed reduction for the previously known motor is 57$ at the same point, and is 50% for a motor according to the invention. If you look at the speed reduction for both motors with the same external torque, the difference will be much greater. This is due to the fact that the engine with a flow regulator will have an increased fluid supply (compared to prior art) by increasing the pressure in the working elements, so that you not only get improved stability, but also get increased average values for working torque and speed.

The invention can be very advantageously used in drill bit motors with positive displacement, used as a propellant for a rock-breaking tool when drilling oil and gas wells. The invention can also be used in turbo drills.

Claims (5)

1. Drill bit motor including a spindle section (2) and a motor section (1) with working elements in the form of a stator (3) and a hollow rotor (4) with an axial passage (5) communicating with a working fluid high-pressure zone, and with a regulator (6) for the working fluid flow, with a nozzle (16) which is mounted in the axial passage, characterized in that the nozzle (16) has two chambers arranged one behind the other in the direction of flow of the working fluid, namely an inlet chamber (A) and a delivery chamber (B), whose walls (19,20) conjugate along a break line (21), in that an annular part (22) in the inlet chamber (A), at the break line (21), is concave in the direction of flow of the working fluid, and in that the cross-sectional area of the inlet chamber (A) at its outlet is smaller than the cross-sectional area of the same chamber at the inlet of the chamber. 2. Drill bit motor according to claim 1, characterized in that the nozzle (16) is made up of two parts, namely a sleeve (23) and a core part (24), which is mounted inside the sleeve with clearance, the inlet chamber (A) and the delivery chamber (B ) is limited by the wall surfaces in the sleeve (23) and on the core part (24). 3. Drill bit motor according to claim 2, characterized in that the core part is a cylindrical rod and that the sleeve (23) is internally provided with an annular projection (26) which forms the concave part (22) in the wall (19) of the inlet chamber (A). 4. Drill bit motor according to claim 2, characterized in that the sleeve (23) is cylindrical and that the core part (24) has an annular projection (27) which forms the concave part (22) in the inlet chamber (A). 5. Drill bit motor according to claim 2, characterized in that the sleeve (23) and the core part (24) both have annular projections (28,29), each such projection forming a concave part (22).