NO831701L - DEVICE FOR BORING HOLE DURING DRILLING - Google Patents

Abstract

A radially unstable, solenoid-controlled valve in a channel that bypasses the pressure drop in the drilling fluid past a drill bit (34). at the lower end of a drill string (28) opens and closes depending on the conditions of a borehole, to form pressure pulses in the drilling fluid. The valve (166) is driven to the closed position by drilling fluid being punched through the drill string. A greater force is needed to open the valve rather than to keep it open.The current supplied to the solenoid (67.70) is then reduced to a value sufficient to keep the valve open.The solenoid is deactivated to close the valve.

Description

DEVICE FOR MEASURING IN BORE HOLE DURING DRILLING

Cross-reference to related applications.

This is a continuation-in-part of application no. 06/211501 filed on 28 November 1980, which is a continuation of application no. 06/021348

. filed 19 Mar 1979, now withdrawn.

The present origin concerns measurement in boreholes during drilling, and more specifically wireless telemetry of data relating to conditions down the hole.

It has long been practice to measure boreholes, i.e. to sense different conditions down the hole and to transmit the desired data to the surface using equipment of the wire or cable type. To carry out such measurement operations, drilling is stopped and the drill string is removed from the well. As it is expensive to stop the drilling operations, the benefits of measuring while drilling have long been recognized. However, the lack of an acceptable telemetry system has been a major obstacle to successful measurement while drilling.

Different systems have been proposed for measurement during drilling. E.g. it has been proposed to transfer data to the surface electrically. Such methods have not been possible, due to the necessity to equip the sections of the drill string with a specially insulated conductor and suitable connectors for the conductor at the joints in the drill string. Other proposed techniques include the transmission of acoustic signals through the drill string. Examples of such telemetry systems are shown in US-PS 3,015,801 and 3,205,477. In these systems, an acoustic signal is sent up through the drill string and is frequency modulated in accordance with an indicated condition in the hole.

Wireless systems have also been proposed that

uses low-frequency electromagnetic radiation through the drill string, casing and rocks in the earth's crust, up to the surface of the earth.

Other proposed procedures for telemetry for measurement during drilling use the drilling fluid in the well as a transmission medium. US-PS 2,925,251 and 3,964,556 describe systems

where the flow of drilling fluid through the drill string periodically

is limited to cause positive pressure pulses that are transmitted up through the column of drilling fluid to indicate the downhole condition. US-PS 2,887,298 and 4,078,620 describe systems that periodically release drilling fluid from the interior of the drill string into the annular space between the drill string and the borehole in the well, to send vacuum pulses to the surface in a coded sequence corresponding to a measured condition down in the hole. A similar system is described in The Oil and Gas Journal, June 12, 1978, page 71.

Of the many wireless transmission systems that have been considered so far, the most promising create negative pressure pulses in the drilling fluid that are circulated through the drill string, the drill bit and the annular space in the borehole. Negative pressure pulses are created by intermittently directing a relatively small part of the total flow of drilling fluid around the drill bit, by opening and closing a valve in a channel that connects the interior of the drill string with the annular space in the borehole.

A general problem with the use of pressure pulses in the drilling fluid

to send information is that the pulse generators have so far been large in scope, and therefore produce an unhelpful pressure drop

in the drilling fluid flowing through the drill string. The present invention involves a small pulse generator that reduces energy losses due to pressure drop in the drill string.

A particular problem with previous vacuum generator systems is that if the valve in the bypass flow channel fails in the open position, energy is lost in the drilling fluid, because part of the drilling fluid continuously flows outside the drill bit . Also, when the valve is locked in the open position, the abrasiveness of the drilling fluid can rapidly widen the bypass channel, with additional energy loss in the drilling fluid. What is even more serious is that a continuous, uncontrolled jet of drilling fluid at high velocity out the side of the drill string can wash out a cavity in the wellbore, which can cause the drill string to penetrate the cavity and become stuck. Uncontrolled past flow of drilling fluid also makes it difficult to place lost circulation material or the like in the desired position in the wellbore, when the volume of liquid that is passed through the drill bit must be precisely known.

Because of the disadvantages listed above, bypass valves have not generally been considered reliable in drilling operations in oil wells. The present invention provides a safe bypass valve for creating negative pressure pulses in a safe, efficient and reliable way.

Another problem with valves used to create pressure pulses in a circulating drilling fluid is that the valve seats and valve discs, which open and close the valves, tend to wear quickly due to the abrasive properties of the drilling fluid. Consequently, the valves usually have to be replaced much earlier and more often than the rest of the pulse-generating equipment in the drill string.

The present invention results in an adapted valve housing which can be quickly brought into and out of operational connection with other equipment, in the drill string, and provides an excellent valve action with a longer service life, because each valve seat and each valve disc can be adapted to a specific fit to ensure a perfect seal, which increases the service life of the valve.

The pulse generator according to this invention comprises a monostable valve in a channel which bypasses the pressure drop in the drilling fluid past a drill bit at the lower end of a drill string in a well. The valve opens and closes in a coded sequence depending on the conditions downhole, to form negative pressure pulses in the drilling fluid. The pulses can be generated and recorded during drilling.

Means are arranged to drive the valve from open to closed position, preferably by means of the pressure in the drilling fluid which is pumped through the drill string. A greater force is required to open the valve than to keep it open.

Preferably, the valve is actuated by a solenoid, which is first supplied with sufficient current to open the valve. The current to the solenoid is then reduced to a value that is just sufficient to keep the valve open, to reduce power consumption. The solenoid is de-energized to close the valve. Opening and closing the valve creates a negative pressure pulse in the drilling fluid, to indicate the condition downhole.

In one embodiment of the invention, the valve is driven to the closed position by a fluid barrier attached to a valve disk, which opens and closes the valve by being moved away from or in contact with a valve seat. Preferably, the fluid barrier is arranged on the low-pressure side of the valve seat.

In another embodiment of the invention, a spring presses the valve disc against the valve seat. Thus, when the flow of drilling fluid is stopped, or is relatively slow, the valve closes automatically, thereby preventing by-flow of drilling fluid around the drill bit during slow pumping operations, such as when lost circulation media is placed in a desired position.

In a preferred embodiment, the surface of the valve seat slopes inwards in the direction of the fluid flow at an angle of between approximately 5° and 40° with where the disc lies in the sealed position. The valve disk is undercut on the low pressure side to effect rapid opening of the valve caused by a slight movement of the disk away from the seat. The valve also includes a valve guide chamber on the high-pressure side of the seat.

A piston connected to the disc forms a sliding seal in the chamber, and a pressure compensating bore connects

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the interior of the valve guide chamber with the low pressure side of the valve close to where the valve disc rests against the valve seat. The effective area of the piston that is affected by drilling fluid on the high-pressure side when the valve is closed is slightly smaller than the area of the valve disc, so that a positive closing force acts on the disc when the valve is closed. Preferably, the pressure compensating bore protrudes through

a valve stem that connects the piston to the valve disk, to simplify the construction and reduce the size of the pulse generator.

The valve is preferably operated by a solenoid shaft which is mounted so that it is in contact with and raises the valve disc from the valve seat. A circuit supplies a relatively strong current to the solenoid to create a force large enough to open the valve. The force required to hold the valve open is significantly less than that required to open it. After the valve is open, the current to the solenoid is reduced to a value that produces a force just sufficient to overcome the closing force created by the flow of fluid through the valve. The solenoid is then de-activated, so that the fluid flow through the valve (and the spring, if used) pushes the valve to the closed position.

The solenoid is usually surrounded by a liquid, such as

oil or drilling fluid. In order for the solenoid to work faster, the front plate of the solenoid is equipped with shallow channels to facilitate the movement of fluid when the front plate moves towards and away from the solenoid core. Preferably, longitudinal bores project through the faceplate to further facilitate the flow of fluid when the solenoid is actuated.

In a preferred embodiment of the invention, the solenoid is arranged in a housing that is filled with oil, and the solenoid shaft projects from a solenoid armature in the housing I and out through a floating piston, which keeps the pressure in the oil in the solenoid housing equal to the pressure in the drilling fluid that surrounds the housing , so that the solenpid is not exposed to extreme pressure differences.<1>The end of the solenoid shaft that protrudes through it. floating piston from the solenoid is arranged to come into operative contact against a valve stem which is operatively connected to a valve disc. The valve stem, the valve disc. and the valve seat is preferably located in a adapted, valve housing that can be displaced in the longitudinal direction, in relation to, the drill string., so that the valve housing can be lowered into the drill string to the position of use, where the valve stem can. come into operative contact with the solenoid shaft. Means have been arranged for releasable blocking of the valve housing in the utility path. in the drill string. Thus, the adapted valve body can be quickly disassembled, removed and replaced by a similar valve body when the operating conditions require it. Moreover, a valve housing' is replaced by another without. to disrupt the solenoid array. Fig, 1 shows a system for simultaneous drilling and measurement in a well. Fig, 2 schematically shows a longitudinal section through an embodiment of the pulse generator placed in a drill string. Fig. 3 shows in perspective a front plate of the solenoid, modified according to the present invention. Fig, 4 shows schematically1 a circuit which is used to control the current through one or more solenoids for operation of the pulse generator. Fig. 5 schematically shows a longitudinal section, through part of a preferred embodiment of the pulse generator mounted in a drill string, so that the valve can be replaced without

. disrupt the solenoid device, and

Fig. 6 shows an enlargement of the area 6-6 in fig. 5, with the •valve disk at a distance from the valve seat in the first stage 'during opening of the valve.

In the preferred embodiments of the invention, as described in detail below, pressure pulses are transmitted through a drilling fluid to transmit information from near the drill bit on the lower end of a drill string in a well to the surface of the earth as the well is drilled.

At least one state down in the well is recorded, and

a signal, usually analog, is generated to represent the sensed state. The signal controls the flow of drilling fluid around the bit, to cause pressure pulses at the surface, in a coded sequence that represents the condition downhole.

With reference to fig. 1, a well 10 is drilled into the earth with a drilling rig 12 for rotary drilling, comprising the conventional derrick 14, a drill floor 16, a winch 18, a hook 20, a swivel 22, a kelly 24, a rotary table 26, and a drill string 28 formed by a drill pipe 30 attached to the lower end of the kelly joint 24 and to the upper end of a section of weight pipe 32, which holds a drill bit 34. Drilling fluid (commonly called drilling mud in the industry) is circulated from a mud reservoir 38, through a mud pump 38, a damper 40, a mud line 41 and into the swivel 22. The drilling mud flows down through the kelly joint, the drill string

and the weight tubes, and through nozzles (not shown) in the underside of the drill bit. The drilling mud flows back up through an annular space 42 between the outside of the drill string and the wellbore, to the surface, where it returns to the mud reservoir through a return line 43. The usual vibratory screen to separate drilled material from the drilling mud before it returns to the mud reservoir is not shown.

A converter 44 in the sludge line 41 registers variations

in the drilling mud pressure at the surface. The converter forms electrical signals depending on pressure variations in the drilling mud. These signals are transmitted by an electrical line 46 to an electronic signal processing system 48 on

the surface, such as that described in US-PS 4,078,620;

With reference to fig. 2, an elongated, vertical, cylindrical housing 50 comprises a pair of outwardly projecting fins or ribs 52 on diametrically opposite sides of the housing. The ribs center the housing inside the collar, and rest with their lower ends on inwardly projecting shoulders 54 formed on the inside of the collar. Drilling fluid flows down through an annular space 55 formed between the housing and the collar, past the ribs, and out of nozzles (not shown) in the bit,

where it is exposed to a pressure drop of 70 - 210 kp/cm<2> during a normal drilling operation.

A central bore 56 projects longitudinally through the housing. An externally threaded plug 58, screwed into an internally threaded portion 59 at the lower end of the central bore, closes the bottom of the housing. The plug seals against an O-ring seal 60 in a downward-facing, annular groove 61 in the underside of an inwardly projecting, annular shoulder 62 in the central bore 56, just above the threaded portion 59.

A first, or lower, solenoid 67 rests against the upper end of a cylindrical, lower solenoid spacer 68, which snugly fits into the lower end of a solenoid housing 69, which snugly fits into the housing. The lower end of the solenoid spacer and the solenoid housing rest against the upper side of an annular shoulder 6 2 on the lower end of the housing. Another, or upper, solenoid 70 rests against the upper end of a cylindrical, upper solenoid spacer 72, which has an inwardly projecting annular flange 74 which rests against the top of the lower solenoid. A pair of upwardly projecting alignment pins 76 on the top of the lower solenoid fit into vertical bores 78 in the inwardly projecting flange 74. Upwardly projecting alignment pins 110 on the top of the upper solenoid project into alignment holes 112 in the bottom of a cylindrical valve housing 113, which fits snugly into the house. The bottom of the valve housing 'lies against the upper end of the solenoid housing and the upper side of

the upper:isolenoid.

The two solenoids are identical, and may be conventional. Only the lower solenoid is shown in section. Each solenoid comprises a solenoid winding 116, which is supplied with electrical current to produce a strong magnetic field in an annular core 118, which has a relatively small central vertical bore 120 extending from the top to approximately the center of the core. The bore is then stepped outwards to the increased diameter, at 122, to form a downwardly facing internal shoulder 124. A cylindrical solenoid armature or faceplate 126 includes a central cylindrical core 127 which closely slides into the enlarged portion 122 of the bore. 120. Radially projecting channels 128 (Fig. 3) in the upper side of an outwardly projecting annular flange 129 on the lower end of the core of each front plate as well as bores 132 extending longitudinally through each core enable the front plate to be moved freely in oil (not shown) surrounding the two solenoids. Each face plate supports a central shaft 133 which projects longitudinally and projects above and below the face plate. The upper end of the solenoid shaft of the lower solenoid is against the lower end of the solenoid shaft of the upper solenoid. The solenoids are activated simultaneously, so that the solenoid front plates are driven upwards together when the valve according to the invention is to be opened. The two tandem-connected solenoids produce a large force with a relatively small diameter required for the solenoids, and thus enable the housing to be relatively small in diameter, to reduce the throttling of the flow of drilling fluid that flows past. When the solenoids are de-activated, the outwardly projecting annular flange 129 on the lower end of the core of the faceplate of the lower solenoid rests against an inwardly projecting limit switch 136 on the upper portion of the support sleeve 68 of the lower solenoid. The limit switch and its operation are described in more detail below, with reference to fig.'4..

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The upper end of the shaft of the upper solenoid is displaceable through an O-ring seal 138 in a central bore 144 in a floating piston 146, which has an outwardly projecting annular flange 148 with an inwardly displaceable annular O-ring seal 150 of a narrowed bore portion 152 in a central bore 153 through the housing of the valve device. An inwardly projecting C-ring 154 in an internal annular groove 156 just above the floating piston limits the upward movement of the piston, which forms the upper end of a solenoid chamber 157 which is filled with oil (not shown).

The lower end of a vertical valve stem 160 abuts the upper end of the shaft of the upper solenoid. The valve stem projects up through a bore 162 in a transverse partition wall 164 which projects across the central bore in the housing of the valve device. An opening 165 through the partition balances the fluid pressure on the two sides of the partition. The intermediate part of the valve stem has a thickening which forms an annular valve disc 166, which normally lies against an annular valve seat 167, formed in one with the inner wall of the housing for the valve device. The valve seat comprises an upwardly and outwardly beveled, conical wall forming an angle of between about 20° and about 30° with the centerline of the valve stem.

The valve disc comprises a downwardly and outwardly chamfered, upper, conical plate 168, with a lower edge that lies against the valve seat. The valve disc projects inwards and horizontally a small length from the contact line between the valve disc and the valve seat, and then projects downwards and inwards along another conical surface 169. This results in a sharp opening which opens quickly when the valve disc is slightly raised from the valve seat, thereby facilitating the movement of the drilling fluid around the edge of the valve disc after it has barely moved up from the seat. This effect reduces the force required to open the valve.

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A piston 170 on the upper end of the valve stem forms

a tight sliding fit within a downwardly open cylindrical valve guide chamber 172 on the underside of a cylindrical valve stem upper guide 174. The upper part of the valve control chamber 172 is stepped in a part 176

with a reduced diameter, for the introduction of the upper end of a compression spring 178, the lower end of which lies against the upper side of the piston on the valve stem.

A main locking ring 180 which is screwed down at the upper end

of the middle bore in the housing for the valve assembly holds an outwardly projecting flange 181 on the upper valve guide compressed against the upper end of the housing for the valve assembly. An annular O-ring seal 184 around the outside of the upper valve guide forms a fluid-tight seal against the interior of the housing of the valve device. An annular O-ring seal 185 on the upper end of the housing of the valve device forms a fluid-tight seal against the interior of the housing 50.

An annular O-ring seal 186 on the piston of the valve stem forms a fluid-tight sliding seal within the wall of the valve control chamber. A pressure compensating bore or channel 188 extends longitudinally through the piston and the upper portion of the valve stem, down to a point just below the valve disc 166. The lower end of the bore 188

is branched into two side bores or channels 190, both of which open into the central bore, in the housing for the valve device, just below the valve seat, so that pressure against the low pressure side of the valve disc when the valve is closed is transferred to the upper side of the piston on the valve stem. The effective area of the piston on the valve stem which is affected by the pressure in the drilling fluid in the valve is slightly smaller than the area of the valve disc, so a pressure difference occurs across the disc which forms a relatively small but stable force which seeks to hold the disc down against the valve seat. This force is equal to the pressure difference multiplied by the difference in effective cross-sectional area between the piston and the valve disc. When using the internal bore in the valve

stem, instead of channels through the housing or housing for the valve assembly, the diameter of the housing is determined by the diameters of the solenoids, which can be relatively small due to the two solenoids working together.

A lateral bore 192 through the wall of the valve assembly is arranged after a bore 194 through the wall of the housing, to form a valve inlet 196 for drilling fluid from the annular space 55 between the exterior of the housing and the interior of the casing. A strainer 198 above the valve inlet prevents the entry of large solid particles into the valve. Several upwardly and inwardly inclined bores 200 in the strainer reduce the ingress of solid particles into the valve.

An inner outlet nozzle 202 fits into collinear bores

204 and 206, respectively in the wall of the housing and in the wall of the housing for the valve device. The inner end of the inner nozzle lies against an annular shoulder 209 which is formed where the bore 206 is reduced in diameter. Preferably, the inner nozzle has a reduced diameter in the outward direction. An outer outlet nozzle 208 fits into a bore 210 in the wall of the weight tube which is collinear with a bore 211 through the rib on the left side of the housing 50 (as shown in Fig. 2). The bores 210 and 211 are collinear with and slightly larger than the bores 204 and 206, so that the inner end of the outer nozzle lies against a shoulder 212 at the transition between the bores 204 and 211.

Preferably, the outer outlet nozzle increases in diameter in the outward direction. A retaining ring 213 in an annular groove 214 at the outer end of the bore 210 holds the outlet nozzles in place. The outlet nozzles 202 and 208 form a valve outlet 216 for fluid when the valve is open. A check valve 217 in the nozzle 202 prevents the flow of fluid from the annular space in the wellbore into the valve, such as when the drilling fluid is subjected to reverse circulation.

An outwardly projecting fluid barrier 220 in the form of an annular

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ring with an inwardly and upwardly sloping surface 222, is fixed to the valve stem by means of a set screw 224 at about the same level as the upper part of the valve outlet. Alternatively, the fluid barrier can be designed in one with the valve stem.

An annular O-ring seal 230 in the bore 204 forms a fluid-tight seal around the inner outlet nozzle, and an annular O-ring seal 232 in the bore 210 forms a fluid-tight seal around the outer outlet nozzle.

An o-ring 233 in an annular groove 234 in the outer surface of the valve housing forms a fluid-tight seal against the inner surface of the wall 66 of the housing 50 above the upper end of the solenoid housing. An O-ring 235 in an annular groove 236 in the outer surface of the housing of the valve device forms a fluid-tight seal against the inner surface of the housing 50 between the valve inlet and outlet.

An upper end of the housing 50 is sealed by a lid 240 which is screwed into the housing. An annular O-ring 242 on the underside of the cap seals against the upper end of the housing 50 to form a fluid tight seal.

Upward open recesses 246 in the upper side of the main locking ring for the housing of the valve device enable the main locking ring to be screwed tightly in place or removed, as required. Similar recesses 248 in the upper side of the lid 240 make it possible for this to be mounted or removed, as required.

With the housing 50 mounted in the neck tube as shown in fig. 2, drilling fluid thus flows as indicated by arrows down into the annular space between the housing and the weight tubes, into the valve inlet, and, when the valve is open, out of the valve outlet, thereby bypassing some of the fluid flow around the drill bit on the lower end of the drill string. The drilling fluid that does not pass through the valve continues to flow down past the housing 50 and out through the drill bit.

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Although fig. 2 shows the valve inlet and valve outlet i

the same vertical plane, more than one inlet or outlet can be arranged, and these do not have to be in the same vertical plane. E.g. the housing for the valve arrangement can include two inlets (not shown) on opposite sides of the housing for the valve arrangement, a single valve outlet being located in the middle between the two inlets.

A power source (not shown in Fig. 2) such as a battery

or a generator (not shown) driven by a turbine (not shown) through which the drilling fluid flows may be mounted in the housing 50.

The valve opens and closes depending on electrical signals generated in the circuit shown in fig. 4. The circuit may be in a sealed chamber (not shown) inside the housing 50. For the sake of clarity, the electrical wiring between the power source, the electronic circuits and the solenoids is not shown

in fig. 2.

With reference to fig. 4 supplies a power source 300

current through a first wire 301 to solenoid winding

one 116 which is connected in series, and a diode rectifier 302 is connected in parallel with these. The solenoid windings 116

is grounded at 304 through an adjustable resistor 306 and a first transistor 310, the base of which is connected to the output of a pulse generator 314 by means of a wire 312. The input of a single pulse vibrator 316 is connected to the output of the pulse generator, and the output of the single pulse vibrator is connected to the base of another transistor

318, whose collector is connected to the end of the solenoid windings furthest from the current source. The emitter of the second transistor is grounded to provide a low resistance current path for the current through the solenoid windings. The R-C components (not shown) of the single-pulse vibrator are

via a wire 319 connected to a contact in the switch 136,

which is open when the valve is closed. A compression spring 320 closes the switch when the valve opens, thereby grounding

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The R-C components to interrupt the pulse from the single pulse vibrator.

A sensor 322 (usually mounted in the collar near the drill bit) detects a condition in the hole, such as the electrical resistance in the ground, the mud temperature, the mud pressure, the weight of the drill bit, natural radioactivity in the ground, the inclined direction of the drill hole, or the like. The pulse generator emits a coded sequence of pressure pulses depending on signals received from the sensor.

When the valve is to be opened and closed to cause a negative pressure pulse in the drilling fluid, the pulse generator gives a long pulse, e.g. of 500 milliseconds, to the input of the single pulse vibrator, and to the base of the first transistor. The single-pulse vibrator gives a short pulse to the base of the second transistor, causing it to conduct direct current from the power source, through the solenoid windings, and to ground.

The pulse from the single pulse vibrator lasts until the valve opens. At this time, the flange of the lower solenoid is moved away

from switch 136 which closes and turns off the single pulse vibrator, causing the second transistor to cease conducting. The switch may be of any suitable type, such as a limit switch, proximity detector, magnetic switch or the like. Alternatively, the switch can be omitted and the vibrator can be adjusted to give a pulse of a specific duration, e.g. 40 milliseconds, which is usually sufficient time for the valve to open. The duration of the short pulse is considerably less than that of the long pulse. E.g. is the duration of the short pulse between about 1% and about 50% of the duration of the long pulse.

The resistance in the circuit through the second transistor is low so that a relatively strong current of 4-5 A passes through the fluid windings, creating a sufficiently large force on the solenoid armatures that the solenoid shafts are driven upwards to raise the valve disk from its seat, so that drilling fluid

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thereby allowing flow from the annular space between the housing 50 and the casing, through the valve and into the annular space between the casing and the wellbore.

The diode which is connected in parallel with the solenoid windings enables a weak current to pass through them when the strong current drops to the low value. This results in extra power without taking energy from the power source, and helps to keep the valve open if it tends to go to the closed position.

After the second transistor ceases to conduct, current continues to flow through the resistor 306 and the first transistor 310 until the long pulse from the pulse generator ceases.

The variable resistor is set so that the current through the solenoid windings after the pulse from the single pulse vibrator has ceased is just sufficient to keep the valve open against the pressure exerted by the drilling fluid flowing through the valve towards the fluid barrier. When the solenoid is de-activated, the force exerted by the drilling fluid on the fluid barrier will drive the valve stem downwards so that the valve disc comes into contact with the valve seat, thereby preventing further flow of drilling fluid around the drill bit, and completes a negative pressure pulse, which can be detected on the surface .

Because the area of the piston on the valve stem is slightly smaller than the area of the valve disc, a relatively small,

but stable force on the upper side of the valve disc when the valve is closed. Usually the pressure drop across the drill bit is between approximately 70 and 310 kp/cm 2 , but with the pressure equalizing bore in the valve stem, the force on the valve disc in the closed position is only 1.3 to 2.3 kp, so that the valve can be opened with a relatively small force. It is held open with even less force. E.g. the current through the solenoid windings after another transistor ceases to conduct is substantially less than, and usually only about 10% of, that required to keep the valve open. Typically, the holding current is between about 1% and about 50% of the opening current.

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The amount of current required to hold the valve in the open position depends on the shape, size and location of the fluid barrier. In a valve where the diameter of the valve seat is approximately 19 millimeters and the largest diameter . until the detent is approximately 15 millimeters, the minimum holding flow is achieved when the detent is between approximately 6 millimeters and approximately 19 millimeters below the line where the valve disc is in contact with the valve seat.

The two solenoids acting in tandem and simultaneously in the same direction provide a large lifting force, and they are still smaller in diameter than a single solenoid which would provide the same force with the same current. Consequently, the housing can be made relatively small, in order to reduce the pressure drop in the drilling fluid when it flows down the drill string.

Another advantage of the two solenoids working together is

that the solenoid shafts and the valve stem are connected end to end, without the need for any complicated connections that could break, jam or enable incorrect alignment during use.

Also, the mohostable valve cannot move to a permanently open position, as can happen with a bistable valve. Therefore, the adapted force holding the valve closed may be less, resulting in less opening force. This naturally enables the use of smaller solenoids and requires less current during use.

The spring 178 which presses the valve disc to the closed position

is not essential to the operation of the valve, although it is useful in situations where the valve tends to stay open when flow is low. For example, if concrete is placed in the well by shifting downwards during slow operation of the drill pump, the accuracy of the placement is improved if the valve is closed so that no drilling fluid can flow outside the drill bit. In such a situation, the spring will ensure that the valve is closed,

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When used, the spring is selected so that it mainly

does not affect the force required to open the valve. The spring is not intended to supplement the force produced by the fluid barrier on the valve stem. It is only used to provide a stable minimum closing force under conditions with little or no flow of the drilling fluid.

The fluid barrier can be omitted if the valve disk is designed

and positioned so that the flow of drilling fluid through the open valve provides the desired closing force after the solenoids are de-activated.

The opening 165 enables the pressure in the drilling fluid to act against the top of the floating piston 146, so that the oil in the solenoid chamber remains under full pressure, to reduce any tendency for the drilling fluid to leak into the solenoid chamber.

The radial channels 130 and bores 132 in the face plate of the solenoids facilitate flow of the oil and free movement of the face plates of the solenoids when the solenoids are activated and de-activated.

The surfaces of the valve which are exposed to the abrasive action of the flowing drilling fluid are preferably made of a wear-resistant material, such as tungsten carbide or titanium carbide to ensure a long service life.

With reference to fig. 5, which shows the now preferred embodiment of the invention, an elongated, vertical, cylindrical housing 4 50 comprises a pair of elongated, outwardly projecting fins or ribs 452 on diametrically opposite sides of the housing. The ribs center the housing inside the neck tube 32, and rest with their lower ends on an inwardly projecting shoulder (not shown) formed inside the neck tube, as shown and described above with reference to fig. 7. Drilling fluid flows down into the annular space 55 between

the housing and collar, past the ribs and out through the nozzles in the drill bit (not shown), where it is exposed to a pressure drop

of 70 - 210 kp/cm 2 during a normal drilling operation.

A central bore 456 projects longitudinally through

the housing, and the lower end (not shown) of this is closed, as described above in connection with the housing shown in fig. 2.

The lower end of a solenoid housing 4 57 lies against the upper end of a housing 4 58 for a control circuit in the central bore in the housing. The housing 458 for the control circuit lies against the bottom cover of the housing 450, and will not be described in detail, because it does not form any part of the present invention.

A plug 4 59 closes the lower end of the solenoid housing, and is held in place by an externally threaded latch 460 which is screwed into the lower end of the solenoid housing. An O-ring 461, in an outwardly open, outer groove 462 around the circumference of the plug 459, forms a fluid tight seal between the plug and the inside of the lower end of the solenoid housing. Standard bushings 463 for the circuits are fitted sealingly through the plug 459 to control the operation of the solenoids, as described in detail above with reference to FIG. 2 and 4.

A first cylindrical spacer 464 lies against the upper end of the plug 459. A first, or lower, solenoid 467 in the solenoid housing lies against the upper end of the first spacer 464. Another, or upper, solenoid 470 lies against the upper end of another cylindrical spacer element 472, the lower end of which lies against the upper side of the lower solenoid.

The bottom of a cylindrical valve housing 474 is against the upper end of the solenoid housing.

As in the embodiment shown in fig. 2, the two solenoids may be identical, and they may be conventional. Each solenoid comprises an annular solenoid winding (not shown) through which electric current is passed to form a

magnetic field in an annular core (not shown in detail).

A cylindrical solenoid armature or face plate 526 comprises a central cylindrical core 527 which forms a sliding fit within the annular core of the solenoid. Each fixture or faceplate holds a solenoid shaft 533

which project longitudinally, and which project above and below the solenoid. The upper end of the solenoid shaft of the lower solenoid abuts the lower end of the solenoid shaft of the upper solenoid. The solenoids are activated simultaneously, so that the front plates of the solenoids are driven upwards together when the valve according to the invention is to be opened. The two solenoids which are connected in tandem provide a large force with a relatively small diameter for the solenoids, and thus enable the housing 450 to have a relatively small diameter, in order to reduce the constriction in the flow of drilling fluid past the housing. When the solenoids are de-activated, the protruding portion of the face plate of the lower solenoid contacts a limit switch (not shown), which operates as described in detail above in connection with fig. 4.

The upper end of the shaft of the upper solenoid has a

easy slip fit through a vertical bore 534 in a transverse wall 535 projecting transversely inside the solenoid housing.

The upper end of the shaft of the upper solenoid forms a sliding fit through an O-ring seal 538 in a central bore 544 in a floating piston 546, which has an outwardly open, annular groove 547 which holds an O-ring 550 forming a sliding seal against the inside of the upper part of the solenoid housing. The solenoid housing is filled. with oil from the plug 459 to the floating piston 546, which keeps the oil pressure equal to the pressure in the surrounding drilling fluid,

so that the solenoids work without accidental pressure differences.

An inwardly projecting C-ring 554 in an annular groove 556

which faces inwards just above the floating piston limit-

seeing the upward movement to this stamp..

IN

The lower end of a vertical valve stem 560 lies against

the upper end of the shaft of the upper solenoid. The valve stem projects upwards and forms a tight sliding fit through a central bore 562 in a transverse partition 564 above the bottom of a cylindrical lower spacer 566 in the valve body, which spacer lies on the upper side of an inwardly projecting annular flange 567 which forms the lower end of the valve housing 474 which is located on

the upper end of the solenoid housing.

The intermediate part of the valve stem is extended like this

that it forms an annular valve disc 568, which normally lies against an annular valve seat i.569, the lower end of which lies against the upper edge of the lower spacer element 566

in the valve housing. An O-ring 570 in an inward-facing, annular groove on the inside wall of the valve body forms a seal against the outer surface of the annular valve seat 569. The valve seat comprises an upwardly and outwardly beveled, conical wall 571 (forming an angle of between approximately 15° and approximately 25° with the center line of the valve stem) where the valve disc lies opposite when the valve is closed. The placement of the valve disc on the valve seat is described in more detail below, with reference to fig. 6. The valve seat also includes a conical wall 572, which is sloped downward and outward (at an angle of between about 15°

and approximately 25° with the center line of the valve stem) below where the valve disc rests against the seat when the valve is closed.

A piston 573 on the valve stem, on the upper end of

this, forms a tight sliding fit in a downwardly open cylindrical valve guide chamber 574 in the underside of an upper cylindrical guide 575 for the valve stem. The steering 575

is externally threaded, and is screwed into an internally threaded portion at the upper end of the valve body so that an annular shoulder 575A is flush with the upper end of the valve body. An annular boss 575B, integrally formed with the guide 575, is internally threaded for the insertion of a threaded handle (not shown), which can be used to pull

the valve housing and the associated elements out of the housing 450. The guide 575 lies against the upper end of an upper, cylindrical spacer element 575C in the valve housing, and the lower end of the spacer element lies against the upper end of the valve seat'569. The upper part of the valve control chamber 574

is tapered in a part 576 with a reduced diameter, for the introduction of the upper end of a compression spring 578, the lower end of which lies against the upper side of the piston on the valve stem.

A locking ring 580, which is screwed into the upper end of the housing 450, locks the valve housing, the solenoid housing and the housing 578 with the circuits firmly in the position of use in the neck tube, as shown in fig. 5.

An O-ring 581 in an outwardly open, annular groove around the outside of the cylindrical upper guide 574 forms fluid-

tight seal against the interior of the valve body.

A portion of the upper end of the valve body is reduced in diameter, for the insertion of a sleeve 582, which compresses an O-ring 583 which lies against an annular shoulder formed

where the part with reduced diameter ends. The lock ring 580 holds the sleeve 582 and the O-ring 583 compressed, to form a seal that prevents drilling mud from flowing into a conduit channel 584 in the longitudinal direction of the housing 450.

An annular O-ring seal 586 on the valve stem piston forms a fluid tight sliding seal against the inside wall of the valve control chamber.

A pressure compensating bore or channel 588 extends longitudinally through the piston and the upper portion of the valve stem down to a point just below the valve disc 568.

The lower end of the channel 588 branches into two side bores or channels 590, both of which open into a central bore in the valve body just below the valve seat so that the pressure on the low pressure side of the valve disc, when the valve is closed,

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is transferred to the upper side of the piston on the valve stem in chamber 574. The effective area of the piston on the valve stem which is affected by the pressure in the drilling fluid in the valve is slightly smaller than the area of the valve disc, in order to equalize the pressure above the disc so that a relatively small, but stable force that seeks to hold the valve disc down against the valve seat. This force is equal to the pressure difference multiplied by the difference in effective cross-sectional area of the piston and valve disc. When using the internal bore in the valve stem, instead of channels through housing 450 or the valve body, the diameter of housing 450 is determined by the diameters of the solenoids, which can be relatively small because the two solenoids work together.

A side bore 592 through the wall of the valve housing is arranged after a bore (not shown) through the wall of the housing 450, to form a valve housing inlet for drilling fluid from the annular space 55 between the outside of the housing 450 and the interior of the casing. A strainer (not shown) above the valve inlet prevents large solid particles from entering the valve. As for the inlet 196 described above in connection with the device shown in fig. 2, several upwardly and inwardly inclined bores (not shown) in the strainer above the inlet reduce the ingress of solid particles into the valve.

An internal outlet nozzle 602 fits into collinear and horizontally aligned bores 604 and 606 in the wall of the housing and the wall of the valve body. The inner end of the inner nozzle lies against an annular shoulder 609 designed where a bore 610 through the wall of the lower spacer in the valve housing is aligned with the bores 604 and 606.

The nozzle has a decreasing diameter in the outward direction. An outer diffuser 611 fits into a bore 612 through the wall of the neck tube and is collinear with a bore 613 through the rib on the left side of the housing (as shown in Fig. 5). O-rings 612 and 613 are collinear with bores 604 and 606. The inner end of the diffuser is against the outer end of the nozzle. The diffuser increases in diameter in the outward direction.

A locking ring 614 in an annular groove 615 at the outer

end of the bore 612 secures a lock ring 616 which is screwed into a threaded portion of the bore 612, to hold the diffuser and nozzle pressed against the annular shoulder 609 of the lower spacer in the valve body. Outlet nozzle 602

and the diffuser 611 forms a valve body outlet 618 for fluid when the valve is open.

An annular O-ring seal 630 in bore 604 forms a fluid-tight seal around the inner outlet nozzle.

An O-ring 635 in an annular groove 636 in the outer surface of the valve housing forms a fluid-tight seal against the inside of the housing between the valve housing inlet and outlet.

An O-ring 637, between the diffuser and the lock ring, and another O-ring 638, between the inner end of the diffuser and the outer end of the nozzle, prevent leakage of drilling fluid from the interior to the exterior of the drill string.

The upper end of the housing is closed by a lid (not shown)

in a similar way as described above in connection with the device shown in fig. 2.

Upward open recesses 646 enable the locking ring 580

can be screwed into place or removed, as required. Similar recesses (not shown) in the outer surface of the locking ring 616

at the outer end of the diffuser enables the ring 616

can be screwed in place or removed, as required. With the upper end of the housing open, the locking ring 580 can thus be removed, and so can the locking ring 614, the locking ring 616, the diffuser 611 and the nozzle 602. This means that the valve housing can be freely displaced in the longitudinal direction in relation to the drill string and out of the housing, so that the valve housing can quickly be removed and replaced with another if the valve is worn during use or defective for any reason. Also, removal of a valve housing for replacement can be done without disturbing the solenoid housing or equipment located below it.

With the housing mounted in the neck tube, as shown in fig. 5, drilling fluid, as indicated by the arrows, flows down into the annular space between the housing and the weight tubes, into the valve housing inlet, and, when the valve is open, out of the valve housing outlet,^ thereby bypassing some of the fluid around the drill bit around the lower end of the drill string. The drilling fluid that does not pass through the valve continues to flow down past the housing and out through the drill bit.

As with the device described in connection with fig. 2,

a power source (not shown in Fig. 5), such as a battery or a generator (not shown), driven by a turbine (not shown) through which drilling fluid flows, may be mounted in the housing.

The valve shown in fig. 5 opens and closes in response to electrical signals generated by the circuit shown in fig. 4. This is described above in connection with fig. 2 and 4, and shall not be repeated here. For simplicity, the electrical wiring between the power source, the electronic circuit and the solenoids is not shown in fig. 5.

In addition to the fact that it is mounted in a valve housing that is light

can be removed and replaced without disturbing the solenoid housing, the valve shown in fig. 5 and 6 from that shown in fig. 2 on another important point. With reference to fig. 6, which enlargedly shows the area 6-6 in fig. 5, the valve disc comprises a central, cylindrical part 700, where the disc has the largest diameter. The cylindrical part is parallel to the longitudinal axis of the valve stem, and ends at its lower end in an inwardly and downwardly projecting, first annular bevel surface 702, which ends in an annular contact area 702 on the valve disk which lies against the valve seat 567.

The width of the contact area is determined by the polishing process used to achieve a perfect fit between the surface 702 and the valve seat 571. Typically, it has a width in the range of 0.15 mm to 0.30 mm. The thicker part of the valve disc above the contact area provides strength, and provides space for

to process the contact area, as needed, and without changing

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the diameter of the valve disk where it lies against the valve seat Below the contact area, the valve disk comprises an annular, inwardly and downwardly projecting portion 704, which transitions into a gentle arc 706, which transitions into a third inwardly and downwardly projecting annular portion 708 that continues past the side bores 590 .

As shown in fig. 6, the first downwardly and inwardly projecting annular surface 702 is inclined at an angle of approximately 15° relative to the longitudinal axis of the valve stem. The annular contact area 702 forms an angle of approximately 30° with the longitudinal axis of the valve stem, so that it is parallel to the surface 571 of the valve seat. The third inclined area 704 forms an angle in the range of 50° to 60° with the longitudinal axis<1> of the valve stem. The fourth beveled portion 708 is beveled at an angle of approximately 30° relative to the longitudinal axis of the valve stem.

In that the side bores 590 open into the valve body on the low pressure side of the valve seat, advantages are achieved with regard to the inevitable fluid cavitation that occurs when the valve opens, i.e. with the valve disk and the valve seat approximately in the position shown in fig. 6. The relatively sharply undercut part of the valve disk below the contact area enables strong flow as soon as the valve disk has left the valve seat. Fluid flows so rapidly through the first formed opening between the valve disc and the seat that the streamlines separate from the valve disc and cause cavitation just below the contact area. (Cavitation is caused by a low pressure zone caused by the fluid not being able to stay on the surface of an object).

When the valve disc leaves the valve seat, the fluid forms with

high velocity a pressure zone below the contact ledge that is less than the low pressure that occurs in the annular space between the drill string and the wellbore. Thus the pressure on the top of the piston on the valve stem is momentarily reduced,

<q>g helps to reduce the force to keep the valve closed,

so that the solenoids can be moved maximally with less force. As the valve disc moves further from the valve seat, the cavitation decreases, but a smaller force is now required to keep the valve open, after the valve disc has left the seat. However, the valve disk is designed in such a way that when it is held in the open position, the fluid flow past the disk will try to keep it closed, but only with a relatively small force, which is easily counteracted by the solenoid force that keeps the valve open. When the solenoids are de-activated, the force of the fluid flow against the valve disc causes the valve to close almost instantaneously. Thus, the design of the valve is such that the forces due to the fluid velocity are moderated and used to enable solenoids with small forces to control the valve.

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As the dimensions are quite decisive for optimal operation of the valve shown in fig. 5 and 6, it may be an aid to understanding and practicing the invention to state some dimensions which have been found to be successful in practical use. For example, if the valve disc has a diameter of approximately 19.8 mm in the straight, cylindrical portion 700, „

where the valve disc has its largest dimension, and the contact area has a diameter of 19.2 mm, with a diameter for the compensation piston of 19.1 mm, good results have been achieved by using the design shown in fig. 6, where the side bore 590 begins approximately 4 mm from the contact area of the valve disc.

With the valve disk designed as shown in fig. 6, the contact area on the valve disc can be polished repeatedly, which may be necessary due to wear caused by the conditions during use, without the valve disc and seat having to be scrapped. In addition, the valve discs and seats can be easily replaced when necessary, without the entire valve housing having to be dismantled.

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Claims (29)

1. Apparatus for transmitting information to a surface detector for fluid pulse through a drilling fluid in a borehole which is drilled into the earth by a drill bit on the lower end of a drill string in the borehole, and through which the drilling fluid is circulated by a pump to flow through it interior of the drill string, past the drill bit, and into an annular space between the drill string and the wall of the borehole, comprising: a) means that define a channel for drilling fluid between the interior of the drill string and the annular space, for bypass flow around the drill bit, b) a valve arranged in the channel, to be held in a normally closed position by means of the pressure difference in the drilling fluid across the valve, c) which valve includes: (i) a valve housing with an inlet and an outlet, (ii) a valve seat in the housing, between the inlet and outlet, (iii) a valve disk arranged in the housing, on the inlet side of the seat, so that the disk is pressed against the seat by the pressure difference in the fluid between the valve inlet and outlet, which disk is designed so that it lies against the seat and closes the valve by blocking valve in- the run from the outlet, (iv) a valve control chamber in the housing, on the inlet side of the seat, (v) a piston which is fixed so as to move with the disc and is arranged to be displaced in the chamber, (vi) means connecting the interior of the chamber with the fluid on the outlet side of the seat when the valve is closed; (vii) means on the valve disc to drive the valve towards the closed position when fluid passes through it; so that the fluid exerts a resultant force on the valve disc in the direction of the seat, d) means for exerting an opening force to open the valve so that drilling fluid flows therethrough, and e) means for canceling the force on the valve so that it moves to the closed position, the opening and closing of the valve forming a pressure pulse in the drilling fluid. 2. Device as stated in claim 1, which includes means that are affected by the flow of drilling fluid through the valve, to operate it from open to closed position. 3. Device as stated in claim 1, which includes means to reduce the opening force to a holding force which is large enough to keep the valve open against the means which press the valve towards the closed position when drilling fluid flows through it. 4. Device as stated in claim 3, in which the valve comprises means for connecting the interior of the chamber with fluid in the vicinity of the valve seat when the valve is opened. 5. Device as stated in claim 1, in which the valve seat comprises a mainly conical surface which projects inwards in the direction of the fluid flow through the valve to where the valve seat comes into contact with the valve disc when the valve is closed. 6. Device as stated in claim 5, in which the valve seat surface is inclined at an angle of between about 5° and about 40° in relation to the direction of movement of the disk when the valve is activated. 7. Device as stated in claim 5, in which the valve disc comprises a mainly conical surface which projects outwards in the direction > of the fluid flow, to where the valve disc comes into contact with the valve seat. 8. Device as stated in claim 7, in which the valve disk comprises a mainly annular surface which projects mainly, essentially perpendicular to the direction of movement of the valve disk, from where the valve disk comes into contact with the valve seat when in the valve is closed. 9. Device as specified in claim 1, which comprises a fluid barrier attached to the valve disc and arranged inside the valve housing, on the downstream side of the valve seat. 10. Device as stated in claim 9, in which a valve stem is attached to the valve disk and projects through the valve seat when the valve is open, the fluid barrier being attached to the valve stem. 11. Device as stated in claim 9, in which the fluid barrier comprises a mainly conical surface which projects outwards in the direction of the fluid flow through the valve. 12. Device as stated in claim 10, and which includes means for adjusting the position of the fluid barrier on the valve stem in relation to the valve seat. 13. Device as stated in claim 4, and which comprises means for supplying pressure from the fluid on the downstream side of the valve seat to the interior of the valve control chamber. 14. Device as stated in claim 13, and which comprises a valve stem connecting the piston to the valve disc, the piston, valve stem and disc having a through channel to connect the interior of the valve control chamber with fluid pressure on the downstream side of the valve seat to reduce the force on the valve disc when the valve is closed. 15. Device as set forth in claim 1, and comprising a solenoid winding, a solenoid armature, a solenoid shaft attached to the armature and arranged to come into contact with the valve disk to move the disk from the valve seat to the open position, means for supplying a first strong current to the solenoid winding to produce a relatively large force to open the valve, means to decrease the current to the solenoid winding to produce a moderate force which holds the valve disc in the open position, and means to de-activate in the solenoid so that the valve disc returns to the valve seat and closes the valve. 16. - Device as specified in claim 15, and which comprises another solenoid winding, armature and shaft, the solenoid windings being connected for simultaneous supply of current, and the solenoid shafts are aligned one behind the other to exert a force simultaneously in the same direction. 17. Device as stated in claim 15, in which the solenoid winding and the armature are arranged in a chamber designed to be filled with fluid, the armature having through bores in the direction in which the armature is moved, to facilitate the movement of the armature in the fluid. 18. Device as stated in claim 17, in which the front end of the armature has outwardly projecting grooves to facilitate fluid flow past the armature when the solenoid windings are energized. 19. Device as stated in claim 18, in which the armature comprises continuous bores in the direction of movement of the armature. 20. Device as stated in claim 1, and which comprises a spring that presses the valve disc to the closed position when there is no flow of drilling fluid through the drill string. 21. Device as stated in claim 15, in which the duration of the opening current is significantly less than the holding current. 22. Device as set forth in claim 21, in which the duration of the opening current is between about 1% and about 50% of the holding current. 23. Device as stated in claim 15, in which the holding current is significantly less than the opening current. 24. Device as stated in claim 23, in which the value of the holding current is between approximately 1% and approximately 50% of the opening current. 25. Device for transmitting information to a surface detector for fluid pulse through a drilling fluid in a borehole which is drilled into the earth by a drill bit on the lower end of a drill string in the borehole, and through which the drilling fluid is circulated to flow through the interior of the drill string , past the drill bit and into an annular space between the drill string and the wall of the borehole, comprising: a) means that define a channel for drilling fluid between the interior of the drill string and the annular space, for bypassing the drill bit, b) a valve arranged in the channel, to be held in a normally closed position due to the pressure difference in the drilling fluid across the valve, c) which valve includes: (i) a valve housing with an inlet and an outlet, (ii) a valve seat in the housing between the inlet and the outlet, (ili) a valve disc arranged to the housing on the inlet side of the seat, so that the disc is pressed against the pressure difference in the fluid between the valve inlet and the outlet, as the disc is designed to lie against the seat and close the valve by blocking between the valve inlet and outlet, and the valve disc can be moved away from the seat to a position to open the valve, (iv) a valve control chamber in the housing, on the inlet side of the seat, (v) a piston fixed to move with the disk and arranged to be displaced in the chamber, (vi) means connecting the interior of the chamber with fluid on the outlet side of the seat when the valve is closed, and (vii) as the valve disc is designed and arranged in such a way that when the valve is in the open position, fluid passes through the valve and exerts a force on the valve disc in the direction of the seat, d) means for exerting an opening force on the valve disc to move the valve disc away from the seat: and for opening the valve so that drilling fluid flows through it, and e) means for canceling the force on the valve disc so that the flowing fluid moves the valve disc to the closed position, opening and closing of the valve forming a pressure pulse in the drilling fluid. 26. Device for transmitting information to a surface detector for fluid pulse through a drilling fluid in a borehole which is drilled into the earth by a bit on the lower end of a drill string in the borehole, and through which the drilling fluid is circulated to flow through the interior of the drill string , past the drill bit and into an annular space between the drill string and the wall of the borehole, comprising: a) means which define a channel for drilling fluid between the interior of the drill string and the annular space, for flow past the drill bit, b) a valve comprising a valve housing in the drill string, which valve housing has an inlet and an outlet, the inlet opening inside the drill string and the outlet opening into the annular space, c) a valve seat in the valve housing, between the inlet and the outlet, d) a valve disk arranged in the housing, on the inlet side of the seat, so that the disk is pressed against the pressure difference in the fluid between the inlet and the outlet of the valve housing, which disk is designed to lie opposite and to close the valve by blocking between the inlet to valve body and outlet, e) a valve stem which is operatively connected to the valve disc and projects away from the disc, - f) a solenoid housing arranged inside the drill string, IN g) a solenoid winding and a solenoid armature in the solenoid housing, h) a movable solenoid shaft which is operatively connected to the fitting and projects from the solenoid housing so that it can be operatively connected to the valve stem, i) as the valve housing is constructed and arranged in such a way that it can be displaced in relation to the drill string and moved into the drill string to the position of use, with the valve stem operatively connected to the solenoid shaft, and out of the drill string, without disturbing the solenoid housing, j) means for releasably locking the valve housing in the position of use in the drill string, k) means for energizing the solenoid winding to move the solenoid shaft and valve stem, to move the valve disc away from the valve seat and thereby open the valve; 1) which valve disk is designed and arranged so that when the valve is in the open position and fluid passes through the valve, the fluid exerts a closing force on the valve disk in the direction of the seat, which closing force is less than the force exerted on the valve stem by the solenoid shaft, and m) means to reduce the force exerted by the solenoid shaft, so that the force from the flowing fluid moves the valve disc towards the valve seat and closes the valve, the opening and closing of the valve forming a pressure pulse in the drilling fluid. 27. Device as stated in claim 26, in which the valve comprises ? a valve control chamber in the housing, on the inlet side of the seat, a piston fixed to move with the disk, and arranged to be displaced in the chamber, in and means connecting the interior of the chamber with the fluid on the outlet side of the seat when the valve is closed. 28. Device as stated in claim 27, and which comprises a valve stem which connects the piston to the valve disk, the piston and the valve stem having a continuous pressure equalization channel, to connect the indce of the valve-throwing chamber with the fluid pressure on the downstream side of the valve seat and in the vicinity of the valve seat, to reduce the force on the valve disc when the valve is closed, and to reduce the force required to move the disc from a slightly open position to a more fully open position. 29. Device as stated in claim 26, 27 or 28 in which the valve seat comprises an annular surface which converges in the direction of the fluid flow, and the valve disk comprises an annular contact surface which converges inwards in the direction of the fluid flow substantially at the same angle as the annular surface of the valve seat a first annular surface near and upstream from the contact surface, and a second annular surface near and downstream from the contact surface, the first annular surface converging in the direction of the fluid flow to a lesser extent than the contact surface, and the second annular surface converging to a greater extent than the contact surface .