NO151907B - TELEMETRY DEVICE FOR GENERATING PRESSURE PULSES REPRESENTING ONE OR MORE PARAMETERS DOWN IN A DRILL - Google Patents

Description

This invention relates to a telemetry device for generation

of pressure pulses representing one or more downhole parameters during a drilling operation using a drilling rig with a tubular drill string and a drill bit at the lower end, a pump to push drilling fluid down through the interior of the drill string and the rig to flow back through an annular surrounding space, which drilling device entails a restriction on the flow of the drilling fluid so that a high-pressure zone and a low-pressure zone appear, and a device to detect the pressure pulses and give a measure of the size of each of the parameters. Such a device comprises a drilling fluid see-through means for forming fluid communication between the high-pressure zone and the low-pressure zone, which see-through means is formed in part by a valve seat, a valve body which is movable to and from the valve seat and constitutes a valve capable of operating rapidly for closing or opening of the cut-through, and a device for detecting the size of one or more parameters down the borehole and for generating electrical signals representing these sizes.

Many attempts have been made to provide satisfactory monitoring of the condition of a borehole during drilling, such as, for example. known from US patent document no. 2,096,279 where electrical conductors are used inside the drill stem, US patent document no. 3,825,078 where retractable loops of wire are used inside the drill stem, US patent document no. 2,354,887 where inductive coupling

of a coil or coils with the drill stem close to the drill bit with measurement of induced electrical voltage at the earth's surface, US patent document no. 2,787,759 and US patent document no. 3,488,629 where pulsed chokes are used in the drilling fluid flow which provides pressure-pulse signals to the earth surface, and US Patent Nos. 3,186,222, 3,315,224, 3,408,561, 3,732,728, 3,737,845, 3,949,354 and 4,001,774. Each of the above-mentioned proposals has one or the other drawback which

has meant that they have not come into common use, e.g. the inappropriate and time-consuming nature of a large number of connections of electrical conductors, that they can only be used for short drilling depths, and that the signal-to-noise ratio is such that it can hardly be used for larger drilling depths.

Finally, it can be mentioned that US patent 4,078,620 describes valve devices and associated maneuvering and switching devices

nings, for the transmission of information from a borehole.

After jet drill bits have become common and very large mud volumes with high mud pressure are used, the monitoring has also become unreliable and prone to rapid degradation. The use of controlled throttling in very strong mud flows requires large and powerful equipment that wears out quickly and requires a lot of energy.

The condition is very unfavorable at the bottom of a borehole where the bit can have vibrations of the order of 50 g. The temperature is often as much as 204°C. The pressure at the bottom of the borehole can be more than 1050 kg/cm 2. The drilling fluid that flows through the drill collar and drill bit is very abrasive. With today's drilling equipment with improved drill bits, continuous drilling time can be achieved with a particular drill bit in the order of 100 to 300 hours and sometimes longer before it is necessary to change the drill bit. Therefore, a device for sensing and sending signals for the conditions near the drill bit must be able to work unattended for a long time without adjustment and with a continuous source of electrical energy. Also, the signal transmission equipment must be able to send a continuous usable signal or signals to the ground surface after each jointing of the drill stem which usually occurs as the depth of the borehole increases.

In general, devices that use drill lamp pulsing for signal transmission are considered to be the most practical because the drilling is in that case the least disruptive. So far, however, the reliability achieved by such devices has not satisfied the requirements. The previously proposed application of introducing controlled throttling in the drilling mud flow is, however, complicated and requires powerful equipment down the borehole that requires a lot of energy to vary the throttling when the drilling mud flow exceeds 2270 liters per hour. minute and the pump pressure exceeds 210 kg/cm 2.

The purpose of the invention is therefore to provide a device of the nature mentioned at the outset with the aim of achieving a sufficiently strong pressure pulse to be effective for signaling states or conditions down in the borehole, while at the same time that the energy used to generate the pulse is kept at a sufficiently low value to be operative in the field.

The new and distinctive feature of the device according to the invention

stands in a passage in connection with the grinding means and provided with a movable compensating sealing means connected to

the valve body so that the fluid pressure exerts a first hydraulic force on the sealing member in the direction corresponding to opening the valve, and the fluid pressure exerts a second hydraulic force on the valve body in the direction corresponding to closing the valve, the net hydraulic force on the valve body being proportional to the difference between the mentioned first force and the second force, and a device which is actuable by the electrical signals to move the valve body for generating the pressure pulses in the drilling fluid.

The previously mentioned problems with known designs have been overcome with the solution indicated here, especially as a result of the rapid effect that has been achieved, and the reduction in the energy required to maneuver the valve.

Further distinctive features and advantages achieved by the invention will be apparent from the following description, where the invention will be explained in more detail with reference to the drawings.

Fig. 1 schematically shows a conventional rotary drilling rig equipped

with a device according to the invention.

Fig. 2A schematically shows a generator for generating a

negative drilling mud pressure pulse, with the valve in the open position.

Fig. 2B shows the valve in the closed position in the same way.

Fig. 3A schematically shows a longitudinal section through an embodiment of the pressure pulse generator in fig. 2A and 2B together with the sensing device and the instrumentation in the drill stem near the drill bit. Fig. 3B shows an axial section through a pulse generator according to

fig. 2A and 2B in a practical embodiment.

Fig. 3C shows a block diagram for a radioactive sensor with hearing instrumentation. Fig. 3D shows a block diagram for a temperature sensor with associated instrumentation.

Fig. 3E shows a block diagram of instrumentation for control

of the valve in the pressure pulse generator.

Fig. 4 schematically shows the equipment on the earth's surface in connection with a preferred embodiment of the invention for sensing a radioactive parameter down in the borehole.

Before a more detailed description of the invention, some basic factors will be explained below.

In a drill stem with a length of 3,050 m and a diameter of 11.5 cm, the drilling mud volume in the drill stem is of the order of 19,000 litres. If it is assumed that the modulus of elasticity for the compressed drilling mud is 400,000, a withdrawal of 1.9 liters of fluid will cause a pressure loss of 2.8 kg/cm 2. It can therefore be assumed that a withdrawal of drilling mud near the bottom of such a drill stem with a speed of

0.47 l/sec., will cause a signal of 0.7 kg/cm 2 per second on the earth's surface. The rate of change for the pressure shall be denoted here, which in the present case is equal to 10.

Three important experiments have been carried out:

1. The measurements were made in a test borehole at a depth of

549 m with moderate differential pressures of 70 kg/cm 2 over a valve at the bottom. 2. The measurements were made in a borehole in an oil field at a depth of 2440 m and low differential pressures of 28 kg/cm 2. 3. The measurements were made in a second borehole in the oil field in a

depth of 1525 m and with high differential pressures of 112 kg/cm 2.

All three series of experiments indicated that ^ for the pressure pulses received at the earth's surface when the valve was suddenly opened was substantially higher than calculated. The reasons for this are: (a) highly compressed drilling mud can have a modulus of elasticity somewhat higher than 400,000, (b) there is some wave-guiding effect due to the drill stem which causes the signal to travel much more advantageously than it would have in a large tank with the same volume, and (c) a sudden opening of a valve at the bottom of the borehole causes a higher ^ than in the case of a large tank due to the elasticity of the mud column above the valve.

In a drill stem with a length of 4575 m with a closed bottom and with a marker placed at the top of the mud column, the marker would fall approx. 3 3.5 m when a mud pump pressure of 210 kg/cm <2> is applied. It can therefore be assumed that the mud column is continuously compressed approx. 30.5

m and acts like a long spring in which a large amount of potential energy is stored. When the valve at the bottom of the drill stem is suddenly opened, this potential energy is released and causes a large negative mud pressure pulse, so that the mud pressure pulse is significantly greater than in the case where the mud was not compressible.

In the experiments carried out in a borehole of 1525 m

a narrow passage of 0.30 cm 2 was opened between the inside of the drill

ven and the perimeter and closed in accordance with a controlled sequence.

The pressure above the valve was 112 kg/cm 2 and the discharge was calculated

to approx. 0.95 l/sec. The mud volume inside the drill stem was approx. 9462

liters and with a modulus of elasticity for the sludge of 400,000, the pressure drop was calculated to be 2.8 kg/cm 2 per second. During the tests, the pressure drop on the soil surface was measured at over 7 kg/cm 2 per second or significantly more than expected from the simple calculation. The following conclusion was made: With high pressures (70 kg/cm 2 or more) above the drill bit, large sharp signals can be produced on the earth's surface by opening and closing a very small valve near the drill bit. Valves with an opening of 0.35 cm 2 can produce strong signals from a depth of 1525 m and the attenuation of the signal amplitude from depths between 762 and 1525 m has been found to be very small, indicating that signal attenuation is small.

The device according to the invention has several important advantages:

The fast dispensing with a rate of as little as 0.47 l/sec. will produce a sharp pulse, i.e. a pulse which has a very large pressure change rate, i.e. large ^ of e.g. 40. Furthermore, the rapid opening of the valve will also reduce wear for the following reasons: When the valve is closed, there is clearly no wear on the valve seat.

When the valve is open and the opening area is large compared to

the subsequent throttling, the valve will have a very low flow rate and consequently the wear will lie mainly in the subsequent throttling, which can be tolerated to be made of non-erodible material such as e.g. boron carbide. Wear occurs in the valve only during opening and closing, i.e. only when the flow rate in the valve seat is very high. The valve operation should therefore be as fast as possible for opening and closing and there are no limits to the desired speed. The rate of withdrawal through the valve should also be fast, but there is an upper limit above which one faster withdrawal is not beneficial. This is because there is a limit to the high-frequency transmission through the sludge. Frequencies higher than 100 Hz are strongly attenuated and are of little value for the build-up of a fast pulse on the earth's surface. To determine the maximum usable outflow rate, it is necessary to do full-scale experiments using a proper oil well and long length of a van-

lig boron stem. The experiments involved a particularly large valve followed by an adjustable opening.

Changes to the size of the opening can determine the flow rate in liters per second. It was determined that a flow rate greater than approx. 11.35 l/sec. meant little improvement of the signal. A comparison of signals from a depth of 1529 m with different aperture sizes was made with 1.3 cm diameter, 1.08 cm diameter and 0.68 cm diameter. It was determined that with an aperture diameter of 0.68 cm a signal was produced on the earth's surface which was approximately the same as that produced with an aperture diameter of 1.3 cm.

Fig. 1 shows a typical drilling rig 10 with a mud circulation pump 12, a pipe 14, a standpipe 16, a flexible rotatable high-pressure hose 18, a pivot joint 20 and a drill stem 22 comprising a drill collar 24 and a drill bit 26. A short distance above the drill bit 26 and mounted in the drill collar 24 is a negative mud pressure pulse generator 28, a sensing device and instrumentation 30. The pulse generator 28 is of special construction. It produces a series of programmed pulses, each of which consists of a short momentary reduction in mud pressure. In one embodiment, this is achieved by means of a valve which opens momentarily and provides a passage between the inside and outside of the drill collar 24, i.e. the valve controls a passage between the inside of the drill collar 24 and the annular space 29 between the drill collar and the borehole wall.

The equipment 32 on the ground surface is connected to a pressure converter 100 which in turn is connected to the stand pipe 16. Alternatively, the converter 100 can be connected to the stationary part of the rotatable joint 20.

Figs. 2A and 2B show the negative mud pressure pulse generator 28 schematically to facilitate the explanation of its function and operation. The pulse generator comprises a valve inlet chamber 42, a valve outlet chamber 44 and a compensation chamber 72. The inlet chamber 42

is hydraulically connected via an inlet 38 to the inside of the drill collar 24. This chamber 42 is also hydraulically connected with a passage

48 to the outlet chamber 44. The hydraulic flow through the passage 48 is controlled by cooperation between the valve body 36 and the valve seat 37. The outlet chamber 44 is hydraulically connected with an outlet 51 to the annular space 29. In the outlet 51, a first 52 and a second 53 compensation opening are arranged . The space 40 between the openings 52 and 53 is hydraulically connected through a pipe 74 to the compensating chamber 72. The inlet chamber 42 communicates with the compensating chamber 72 via a cylinder 49 which contains a movable sealing member in the form of a compensating piston 50 which is connected to the valve body 36 via a piston rod 46. The valve body 36 is also connected by means of a connecting rod 47 (fig. 3A and 3B) to an operating device 54.

Fig. 2B shows the valve body 36 in the closed position, where the shaded part indicates the high-pressure part and the non-shaded parts denote the low-pressure parts. High, low and medium pressures are relative, i.e. the difference between pressure at a certain location and the surrounding pressure which is here assumed to be zero, but the real pressure will be equal to this pressure plus the hydrostatic pressure which can be 700

2

kg/cm or more.

The effective area of the valve body 36 is made somewhat larger than the effective area of the piston 50 so that when the valve body 36

is closed or nearly closed, the force on the piston rod 46 will have the direction shown by the arrow in fig. 2B and may be approximately equal to 1000 X (a-a') where a is the effective area of the valve body 36 and a<1> is the effective area of the compensating piston 50 on the piston rod side.

Fig. 2A shows the valve body 36 in the open position, i.e. that the mud flow from the inlet chamber 42 can pass to the outlet chamber 44 via the passage 51 to the annular space 29. The first and second compensating openings 52 and 53 respectively provide a predetermined throttling of the mud flow and they effect both a pressure drop. Consequently, the pressure in the compensation chamber 72 will have any value between the maximum pressure in the chamber 44 and the minimum pressure in the outlet 51 which corresponds to the pressure in the annular space 29.

As mentioned above, the shaded part in fig. 2A as in fig. 2B denoting high pressure and the non-shaded part outside 51 denoting low pressure. During the opening of the valve, the sludge will pass through the openings 52 and 53 and as a result the pressure in the space 40 between the high pressure and the low pressure will be an average pressure which is indicated by dots as shown in fig. 2A. The average pressure in the space 40 between the openings 52 and 53 communicates via the line 74 with the compensating chamber 72. The pressure in the compensating chamber 72 can therefore be adjusted to any suitable value between high pressure and low pressure. The dimensioning of the openings 52 and 53 therefore determines the pressure in the compensating chamber 72 and consequently the force on the compensating piston 50. If the opening 52 had the same cross-sectional area as the opening 52, the pressure in the space 40 and consequently in the compensating chamber 72 would lie in the middle between high and low pressure. When the opening 53 is made larger than the opening 52, the pressure in the compensating chamber 72 will be less and when the opening 53 is made smaller than the opening 52, the pressure in the compensating chamber 72 will increase. E.g. if the opening 53 is small compared to the opening 52, the pressure in the compensating chamber 72 will be high and therefore the force on the piston 50 will be large and close the valve. On the other hand, if the opening 53 is large compared to the opening 52, the pressure in the compensating chamber 72 will be low so that the valve will remain open. It is therefore clear that the force on the piston 50 can be adjusted between wide limits and thereby control the action of the valve.

It is important that the force that closes the valve in fig. 2B

and opens the valve in fig. 2A is determined by a first and a second independent parameter, i.e. the force which closes the valve derives from the effective area difference between the valve body 36 and the side of the compensating piston 50 facing the piston rod, while the force which serves to open the valve is derived from the area- the difference between the openings 52 and 53. By suitable selection of these parameters, the valve can be made to open and close with the aid of a very small external mechanical force.

It is also important that the valve has a bistable effect, i.e. that the valve can swing from open to closed position or vice versa.

In other words, the first independent parameter is chosen so that when the valve is in the region of nearly closed to fully open position, a predetermined force is applied to the valve in the closing direction and is maintained, and the second independent parameter is chosen so that when the valve is in the area between almost open and fully open, a predetermined force is applied to the valve body to the open position and maintained.

It is thus clear that the negative mud pressure pulse generator

28 according to the invention utilizes the existing energy derived from the mud pressure in such a way that the degree of external energy required to operate the valve is significantly reduced and in

in addition, a bistable effect of the valve is achieved.

Fig. 3A shows a schematic design of the pulse generator 28 and associated equipment down in the drill hole mounted at the lower end of the drill stem. In fig. 3A has a drill stem part 58 an outer diameter of 17 cm and a length of 91 cm which occupies a housing 5 6 and is held by support means not shown. The housing 56 contains the pulse generator 28 and has at the lower end the instrumentation section 62, 66 and the feed section 64. Mud from the interior of the drill stem passes on the outside of the housing 56

in the direction of the arrows. A filter 60 prevents solid sludge particles from entering the housing. The valve body 36 is operated by an operating device 54. When the valve is open as shown in fig. 2A, some sludge will exit into the annular space 29. The bent arrows show the direction of the sludge flow. The pressure that forces the mud into the annular space 29 is the pressure above the drill bit 26. When the valve is closed, access to the 'annular space 29 is also closed.

The piston 76 separates the chamber 72 from the oil-filled chamber 78. The operating device 54 is mounted inside an oil-filled chamber 80. An equalizing passage 82 connects the chambers 78 and 80. By the cooperation between the piston 76 and the passage 74, the chambers 72, 78 and 80 are maintained on essentially same pressure as the chamber 40. The passage 82 is shown in broken lines in fig. 3A and is not shown in Fig. 3B, because it is in a different plane than in the cross-section shown.

The section 6 6 has a diameter of 6 cm and fits into a drill stem part with an outer diameter of 17 cm and an inner diameter of 8.25 cm. The parts 30 are provided with centralizing arms 70 which fit into the track stem part 69. The centralizing arms are intended to centralize the part 30, but to provide free passage for the sludge.

Fig. 3B shows a more detailed embodiment of the pulse generator

28 with an operating device 54 which comprises a pair of electrical energizing windings which are arranged opposite each other. The winding 55 is arranged at the top of the drawing and exerts an upward force on the armature 57, while the winding 59 at the bottom of the drawing exerts a downward force on the armature 61. The armatures 57 and 61 are loosely connected with a mechanical link 63 which is attached to the connecting rod 47 so that a hammer effect is achieved, i.e. when one of the energizing windings energizes, the armature is moved a short distance before it takes up the load of the rod 4 7 so that a hammer-like blow is achieved. This hammer action has a beneficial effect on the opening and closing of the valve body 36.

The openings 52 and 53 have a smaller area than the passage 48, as follows

that the speed of the mud flow past the valve body 36 and the seat 37 is significantly reduced compared to the speed of the mud flow through the openings 52 and 53, so that the wear is concentrated to the openings 52 and 53 which consist of wear-resistant material such as boron carbide and which can be easily replaced as indicated in fig. 3B. These small wear-resistant openings 52 and 53 mean that the pulse generator 28 becomes completely fail-safe, i.e. that it is the same as what happens with the valve body 36 as e.g. that it remains in the open position, the amount of mud that can flow through the openings 52 and 53 will not have any significant adverse effect on the drilling. A further advantage of making the openings 52 and 53 easily replaceable is that they can be adapted to varying weight and viscosity of the sludge.

As the pulse generator 28 is exposed to strong vibrational forces, stability of the valve body 36 must be ensured in both the open and closed position. This is ensured by a bistable effect of the valve body 36 as previously described.

The vertical acceleration due to drilling is stronger in the upward direction than in the downward direction. When the teeth of the bit 26 meet hard rock, the bit and collar 24 are pushed upwards, i.e. accelerated in an upward direction, but when the bit is moved upwards and out of contact with rock, there is little force other than the acceleration due to the force of gravity forcing the bit and collar downwards. Consequently, the upward acceleration can be several hundreds of g, while the downward acceleration is only of the order of 1 g. The valve body 36 must therefore be constructed so that when it is in the closed position, strong upward acceleration must keep the valve body closed and strong downward acceleration will open the valve. This is achieved by the construction shown in fig. 3A and 3B.

In various tests and experiments, it has been found that a force of approx. 15 kg is required to operate the valve body 36 when the first and second independent parameters as described above are selected so that a bistable effect is achieved to achieve sufficient stability of the valve body 36. With a good safety factor in addition, the required force is 30 to 45 kg . To exert force of this magnitude over the required path of movement of the valve body with electromagnetic windings of reasonable size, approx. 350 Watts or close to half a horsepower. With such a large amount of electrical energy required, it immediately appears that for a greater number of operations of the valve body 36, an electrical energy source is needed which is far above the capacity of a normal self-maintaining power source. This problem is overcome by means of the described pulse generator 28 which provides a very rapid movement of the valve body 36, i.e. that the valve body 36 can. opens or closes with 350 watts in just 20 milliseconds. The energy consumption for opening or closing the valve is therefore

There are currently available batteries of reasonable size to

be placed inside a drilling collar 24 and which can easily deliver 2000

watt hours. Such a battery can therefore, without recharging, supply enough energy to operate the valve body 36 approx. 1 million times. Assuming that the valve is operated 1 time every 4 seconds, a single battery may be able to operate the valve continuously for over 1 month. This is important for continuous drilling because the time that elapses between replacing the drill bit is approx. 100 to 300 hours so that 30 days should be more than sufficient.

The construction of the pulse generator 28 is a complex matter. Although careful calculations on the basis of hydrodynamic theories have been made, many parameters must be determined empirically. An important point here is that the viscosity of the drilling mud is thixotropic and the dynamic process is very different from liquids with so-called Newtonian viscosity. Specific gravity of the drilling mud gram per cubic centimeters and viscosity vary over a large range and specific gravity usually varies over a much smaller range than viscosity. Drilling mud usually contains not only colloidal particles in solution, but also larger sand grains and other particles.

Determination of the minimum area for the openings 52 and 53 which determines the rate of discharge of the liquid in the annular space 29

is done experimentally. A large servo valve with a diameter of 25 mm and smaller replaceable openings was then used. The experiments

was carried out in boreholes with a depth of 2440 and 1525 m by careful measurements of the size of the negative mud pressure pulse at the soil surface as a function of the size of the openings. When the apertures were reduced, the size of the pulse at the earth's surface was approximated

regardless of the area of the openings up to a surprisingly small area of 0.35 mm, after which a small decrease in the pulse size was observed. This was certainly unexpected, but was later understood after careful consideration of the elastic properties of the mud column and the stored potential energy as described above. This discovery led to the result that a small pulse generator can deliver

a usable signal at the earth's surface. Calculations were then made and it was decided that the servo principle for the valve action was not necessary and that the servo valve was therefore omitted. The direct fast-acting pulse generator described here was then constructed and has proven to be suitable.

A negative mud pressure pulse generator 28 with the following dimensions has proven suitable: The opening 52 has a diameter of 1.27 cm, the opening 53 has a diameter of 0.78 cm, the working stroke of the valve body 36. is 0.3 cm, the diameter of the piston 50 is 0.97 cm, the diameter of the valve body 36 in the seat surface is 1.1 cm, the angle of the seat 37 in relation to the axis of the valve body is 60°, the diameter of the opening in the seat 37 or the passage 48 is 0.95 cm, and the diameter of the piston rods 46 and 47 is 0.475 cm.

Another important aspect of the invention is that the length of time in which the valve is open has no connection with the amount of energy that is required. The only energy that is necessary is that which brings the valve to the open position. The importance of this is clear from the following consideration.

Experiments have shown that in order to obtain a strong signal from a depth of 3050 m to 6100 m, the valve must be kept open for approx. for up to 1 second and any electromechanical device that works for such a long time will not only require a lot of energy, but will also overheat and under special conditions burn up as a result of the heat developed.

As mentioned above, two typical sensors that can be used in connection with the invention are indicated as examples. Fig. 3C shows a sensor for natural gamma rays and belongs to equipment which in this example is of an analogue nature. Fig. 3D shows a temperature sensor and in this example this is of a digital nature. One or the other of these sensors can be connected to the input terminal in the instrumentation as shown in fig. 3E to be described below.

Fig. 3C shows a Geiger counter 168 which supplies a high voltage +HV in the usual way. The Geiger counter produces pulses which via a capacitor 169 are supplied to an amplifier 171 which produces pulses in the output corresponding to the Geiger counter's pulses. These pulses are supplied to a circuit 172 which produces an output pulse for every 1024 Geiger counter pulses and these output pulses have a time interval t^.

The stronger the gamma radiation, the greater the pulse frequency from the circuit 172 and the shorter the time t^ will be.

Fig. 3D shows the temperature sensor which is equipped with a temperature-dependent resistor 173 which supplies a direct voltage which is proportional to the temperature. An amplifier 174 amplifies the direct voltage and supplies this to an analog-to-digital converter 175 which delivers a series of bit groups, one after the other, each representing a number proportional to the sensed temperature. The output signals from the power amplifiers 185, 186 are used to energize the windings that operate the valve body 36. When the winding 55 is energized, the armature 57 in fig. 3B is moved upwards so that the rod 47 operates the valve body 36 so that it opens. When the winding 59 is energized, the armature 61 will be moved downwards and thus the rod 47 which operates the valve body 36 to the closed position.

With the sensors used here, the size of the parameters down in the borehole is represented by electrical pulses. The series of pulses

represents a code (binary or other) and the array represents the size of the parameter. Fig. 3E shows how each individual pulse in this code operates the valve body 36. In fig. 3E represents 177 such a pulse which is very short in time, only a few

microseconds. This pulse 177 is applied to the block 178 containing a monostable multivibrator and preferably inverting rectifier circuits which respond to a single input pulse and deliver two output pulses which are separated in time by small t^, of which the first occurs simultaneously with the input pulse and the second occurs with a delay of t^ as shown with the pulses 179 and 180. These pulses 179 and 180 are each applied to blocks 181, 182 which are identical and extend the pulses. Each input pulse is extended to a pulse 183 or 184 respectively and applied to a "Darlington" amplifier 185 or 186 respectively.

In a practical embodiment of fig. 3E a constant has been chosen

t^ = 500 milliseconds and t2 = 20 milliseconds. When a single pulse 177 is applied to the wire 167, the Darlington amplifier 185 is switched on for 20 milliseconds and then switched off. 500 milliseconds later, the Darlington amplifier 186 is switched on for 20 milliseconds and then switched off. The valve body 36 is opened for 500 milliseconds without energy being required during this period. Energy is required only for the short 20 milliseconds necessary to operate the valve body 36 to the open or to the closed position. With the fast bistable effect, high pressures and volumes are exerted in the sludge without the need to use large amounts of energy, but on the other hand small energy from batteries that can operate the valve body approx. 1 million times.

In an embodiment of the device according to the invention, the weight of the entire mechanism, including the valve body 36, the armature 54, the rod 46 and the piston 50, is approx. 255 g. The valve body 36 is designed for a differential pressure of 112 kg/cm 2 which includes the force necessary to open and close the valve body 36 and must exceed forces due to vertical acceleration of the entire device near the bit 26. If it is assumed a vibration of 60 g and a weight of 255

g, the maximum vertical force on the valve body 36 due to vibration of the device 56 is approx. 15.5 kg. To be sure that the valve body 36 will not open unintentionally, the force holding the valve body closed in FIG. 2B and the force that opens the valve on

fig. 2A both exceed approx. 15.5 kg. By suitable selection of the first and second independent parameters, a balanced state can be achieved. Balanced means here that the force required to open the valve is equal to the force required to close it.

The equipment on the ground surface that is used in connection with the device down in the borehole must eliminate the interference effect that occurs in the pressure converter 100 and which can take different forms.

Fig. 4 shows the equipment on the earth's surface for monitoring radioactivity for soil formations that the drill passes during drilling. The pressure converter 100 is connected to the standpipe 16 and converts variations in the mud pressure in the standpipe into electrical voltage. This voltage represents a mixture of two component signals, namely the useful information signal and interference signal. The information signal is a series of short negative mud pressure pulses that are formed by rapid opening and closing of the valve. The interference signal takes the form of relatively slow and periodic pressure variations which are produced by the strokes in the mud pump 12. These mud pump signals mask or make the information signals

indistinct.

An important function in this connection is to derive a clean, desired information signal from the disturbed signal delivered by the converter 100. This is achieved by means of a signal emitter 102 which is connected to the output terminal 101 of the pressure converter 100. The signal emitter eliminates the interfering effect and delivers at the output 108 a series of pulses from which the information regarding the parameter down in the borehole can be easily derived. ^It is clear that within the scope of the invention various changes and modifications are possible. E.g. sensors for more than two parameters can be placed down in the borehole. It is also clear that sensors for several parameters can be used simultaneously and in this case known techniques such as e.g. time division, multiplexing and the like for processing data representing the various parameters.

It is also clear that the drill stem 31 in fig. 1 does not need to be rotated by means of a rotating body on the ground surface, but the drill bit 26 can be rotated by means of a mud motor which is arranged immediately above the drill bit 26 in the drill stem. When such a mud motor is used, a large pressure drop will occur across it because it is driven by the mud flow. This large pressure drop can be used to achieve a pressure difference between the inside of the drill stem and the annular space between the drill stem and the borehole wall, and in such a case a jet-type drill bit does not need to be used.

The presence of the pressure drop above the mud motor supports the operation of the device according to the invention as long as the negative mud pressure pulse generator is located above the mud motor.

The aforementioned throttling applies to either a jet-type drill bit or a mud motor or both. The term high pressure zone applies to the upper side of the throat and low pressure zone applies to the lower side of the throat.

It is clear that in some cases several mud pumps can be used in a single drilling rig and these pumps must necessarily work synchronously.

Claims (21)

1. Telemetry device for generating pressure pulses representing one or more downhole parameters during a drilling operation using a drilling rig with a tubular drill string and a drill bit at the lower end, a pump to push drilling fluid down through the interior of the drill string and the drill rig to flow back through an annular surrounding space, which drilling device entails a restriction on the flow of the drilling fluid so that a high pressure zone and a low pressure zone appear, and a device for detecting the pressure pulses and giving a measure of the magnitude of each of the parameters, and comprising a drilling fluid - grinding means (4 2) to form fluid communication between the high pressure zone and the low pressure zone, which grinding means (42) is partially formed by a valve seat (37), a valve body (36) which is movable to and away from the valve seat and constitutes a valve capable of to work quickly for closing or opening the through grinding, and a device (6 4) to detect the magnitude of one or more parameters down the borehole and to generate electrical signals representing these magnitudes, characterized by a passage (49) in connection with the grinding means and provided with a movable compensating sealing means (50) connected to the valve body ( 36) so that the fluid pressure exerts a first hydraulic force on the sealing member in the direction corresponding to opening the valve, and the fluid pressure exerts another hydraulic force on the valve body (36) in the direction corresponding to closing the valve, the net hydraulic force on the valve body being (36) is proportional to the difference between the mentioned first force and the second force, and a device (54) which can be influenced by the electrical signals to move the valve body for generating the pressure pulses in the drilling fluid. 2. Device according to claim 1, characterized in that the movable sealing member (50) is a piston and the passage (49) is a cylinder. 3. Device according to claim 1 or 2, characterized in that the valve is arranged to be energized electrically and is capable of working quickly for closing and opening the through-hole, and comprises an electrical energy source (181) which can be influenced by the aforementioned electrical signals to supply a relatively large amount of electrical power to initiate opening of the valve, respectively significantly less power when the valve is open or closed, to generate the pressure pulses in the drilling fluid. 4. Device according to one of claims 1-2, characterized in that the device which can be influenced by the electrical signals is arranged to generate a first voltage change (183) to open the valve and a second voltage change (184) to close the valve . 5. Device according to one of claims 1 - 4, characterized in that part of the grinding member (42) has a longitudinal axis and has the aforementioned valve seat (37) in it, and that the valve body (36) is movable in a linear path that coincides with the axis through the valve seat, and that the electromagnet device (55) exerts a force which axially coincides with the valve body, to reset the valve. 6. Device according to one of the claims 1-5, characterized by a device (181, 182) for delivering electrical current signals for adjustment of the valve and depending on the mentioned size representing electrical signals, and a device (50), which reaches the valve is held in the open or closed position, uses electrical currents that are lower than the electrical current magnitudes originally applied to open or close the valve. 7. Device according to one of claims 1-6, characterized in that the valve is designed so that it changes from a closed to an open position in a time that is shorter than 20 milliseconds. 8. Device according to one of claims 1-7, characterized in that the valve (36) is dimensioned to produce a flow rate for drilling fluid through the grinding member of at least 0.4 7 1 per seconds when the valve is in the open position. 9. Device according to one of the claims 1-8, characterized in that the valve is dimensioned to be able to produce an increase rate in drilling fluid flow through the grinding means when the valve is brought to open, of at least 23.8 1 per second per second, thereby producing sharp pressure pulses in the drilling fluid. 10. Device according to one of claims 1-9, characterized by a device (131, 182) for the derivation of valve influence signals from the aforementioned size representing electrical signals (175) and a device (50) for keeping the valve in an open or closed position in the absence of an impact signal. 11. Device according to one of claims 1-10, characterized in that the device (50) for holding the valve in the open or closed position is based on hydraulically generated forces. 12. Device according to one of claims 1 - 11, characterized in that the valve, after being moved to the open position, is pressed to the closed position by the force of drilling fluid flow through the grinding member (42). 13. Device according to one of claims 1 - 12, characterized in that the valve body (36) is connected to the movable, compensating sealing member with fluid connection with the grinding member (42) in order to create a pressure difference across this so that a force is generated in the opposite direction of the force generated by the fluid pressure on the valve body (36), thereby reducing the force required to open the valve. 14. Device according to one of claims 1-13, characterized in that an electromagnet device (55, 59) serves to apply a force in a first direction to open the valve and to apply a force in another direction to close the valve. 15. Device according to one of claims 1 - 14, characterized by an electromagnet device (55, 59) comprising two windings which are arranged so that when one winding is energized it exerts a force in the aforementioned first direction to open the valve, and when the second winding is energized it exerts a force in the other direction to close the valve. 16. Device according to one of claims 1-15, characterized in that the liquid grinding means (42) has an inlet (38) for drilling fluid and a liquid filter device (60) is arranged in the grinding means between the inlet and the valve. 17. Device according to one of claims 1-16, characterized in that the valve body (36) is located above the valve seat (40) so that upward acceleration of the valve seat (40) pushes the valve towards the closed position. 18. Device according to one of the claims 1-17, characterized by a device (74) for applying the pressure downstream of the valve, on the side of the compensation member (50) which is opposite the valve (36). 19. Device according to one of claims 1-18, characterized in that the grinding member (42) has an outlet (53) for drilling fluid and an opening (52) located between the valve seat and the outlet, in order - when the valve is open - to produce eh intermediate pressure zone (40), and comprising a device (74) for connecting the intermediate pressure zone (40) to the side of the compensating sealing member (50) which is opposite to the valve body, where the effective area differences between the valve body (36) and said member (50), as well as the relative dimensions of the opening (52) are chosen so that the valve body (36) can be changed to an open or closed position by the application of forces that have reduced magnitudes. 20. Device according to one of the claims 1 - > 1 9 , characterized by a device (181, 182) which delivers current signals for influencing the electromagnet in dependence on the mentioned quantity representing electrical signals (175), and a device (178 ) which, when the valve body (36) is held in the open or closed position, uses electrical currents whose magnitudes are lower than the electrical current magnitudes that were originally applied to reset the valve body. 21. Device according to claim 3 and one of claims 4-20, characterized in that essentially less effect includes essentially no effect.