NO168546B - PROCEDURE FOR PERFORMING MEASUREMENTS IN A DRILL. - Google Patents

Description

Many attempts have been made to provide a satisfactory monitoring of the condition of a borehole during drilling as known, for example, from U.S. Patent No. 2,096,279 where electrical conductors are used inside the drill stem, U.S. Patent No. 3,825. 078 where retractable loops of wire inside the drill stem are used, U.S. Patent No. 2,354,887 where inductive coupling of a coil or coils with the drill stem near the drill bit is used with measurement of induced electrical voltage at the earth's surface, U.S. Patent No. 2,787. 759 and U.S. Patent No. 3,488,629 using pulsed chokes in the drilling fluid flow that provide pressure pulse signals to the earth's surface, and U.S. 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 another disadvantage 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.

After jet drill bits have become common and very large mud volumes with high mud pressure are used, monitoring has also become unreliable and prone to rapid degradation. The use of controlled throttling in very powerful 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 drill 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 extended periods of time without adjustment and with a continuous source of electrical energy. Also, the signal transmission equipment must be capable of sending 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 bit pulsation for signal transmission are considered to be the most practical because the drilling in that case is 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 which requires a lot of energy to vary the throttling when the drilling mud flow exceeds 2270 liters per minute and the pump pressure exceeds 210 kg/cm 2.

More specifically, this invention relates in one of its aspects to a method for carrying out measurements in a borehole during drilling using a liquid circulation system and a liquid pump on the surface of the earth to circulate the liquid, the pump generating disturbing and repetitive pressure variations in the system. Furthermore, the invention includes a signal derivation apparatus for carrying out such measurements. Other aspects as well as new and distinctive features according to the invention will appear from the following description or from the patent claims.

In the following, the invention will be explained in more detail with reference to the drawings, where: Fig. 1 schematically shows a conventional rotary drilling rig where the present invention is used. Fig. 2a shows a block diagram for a radioactive sensor with associated instrumentation. Fig. 2b shows a block diagram for a temperature sensor with associated instrumentation. Fig. 3 shows a block diagram for instrumentation for controlling the valve in a 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. Fig. 5 shows graphically and in an idealized form certain curve shapes, pulses and time relationships to explain the signal output part 102 in fig. 4. Fig. 6 shows a block diagram of the component 105 in the signal output part 102 of Fig. 4. Fig. 7 shows a block diagram of the component 107 in the signal output part 102 of Fig. 4. Fig. 8 schematically shows another embodiment of the equipment on the earth's surface. Fig. 9 schematically shows another embodiment of the equipment on the ground surface.

Fig. 10 shows a block diagram of an alternative embodiment

of the timing pulse generator.

Fig. 11 shows a block diagram for yet another embodiment of the equipment on the ground surface.

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 here be denoted gE, 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 compacted drilling mud may have a somewhat elastic modulus. higher than 400,000, (b) there is some waveguide effect due to the drill stem which causes the signal to travel much more advantageously than it would in a large tank of the same volume, and (c) a sudden opening of a valve at the bottom of the borehole results in a higher ^ than in the case of a large tank due to the elasticity of the drilling 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. 33.5 m when a mud pump pressure of 210 kg/cm 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 becomes 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 collar and the circumference and closed in accordance with a controlled sequence. The pressure above the valve was 112 kg/cm 2 and the withdrawal was calculated at approx. 0.9 5 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 2pr. 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 shown 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 that has a very large pressure change rate, i.e. large on 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 has-_

tightness. The withdrawal speed through the valve should also be fast, but there is an upper limit above which a faster withdrawal is not advantageous. 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 wellbore and a long length of conventional drill 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 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 transducer 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.

An 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 which can be used in connection with the invention are given as an example... Fig. 2A shows a sensor for natural gamma rays and belongs to equipment which in this example is of an analogous nature. Fig.2B 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 instrument ring as shown in fig. 3 to be described below.

Fig. 2A shows a Geiger counter 168 which normally supplies a high voltage +HV. 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.2B shows the temperature sensor which is equipped with a temperature-dependent resistor 173 which supplies a DC voltage which is proportional to the temperature. An amplifier 174 amplifies the DC voltage and supplies it 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 is used for energizing the windings that operate the valve body. When the winding 55 is energized, an associated armature will be moved upwards so that a rod influences the valve to open. When the winding 59; is energized,,.the armature will move downwards and thus set the valve in 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. 3 shows how each individual pulse in this code moves the valve body• In fig. 3 represents 177 such a pulse which is very short in time, only a few microseconds. This pulse 177 is applied to the block 178 which contains 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 t1 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. 3, a constant t^= 500 milliseconds and tj= 20 milliseconds has been chosen. 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 opens for 500 milliseconds without requiring energy during this period. Energy is only required for the short 20 milliseconds needed to switch the valve to the open or 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.

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 negatives

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.

The pure information signal 1 from the signal emitter 102

takes the form of pulses originating from the operation of the valve body

36. Relevant information is obtained by dividing the pulses into time intervals. A time-amplitude converter 115 is connected to the signal emitter output 108 and converts these pulses originating from the operation of the valve body 36 into signals with amplitudes representing the intervals between the pulses.

The signals from the converter 115 are supplied to the input terminal

109 in a reciprocating circuit 118 which supplies output voltages which are the reciprocal of the input voltages. If a voltage of amplitude M is applied to the circuit 118, the output voltage will have an amplitude l/M. These signals with the amplitude l/M recorded

nes on a recording carrier in a recording device 120. Record- . the drawing carrier is moved in accordance with a change in the drilling depth by means of a sensor 30 in a depth sensing device 121.

To more clearly highlight the benefits of the signal extractor

102 below, various signals that come into play will be analyzed with reference to fig. 5. If

where S(t) is the desired information signal resulting from negative mud pressure pulses P , l»2, and P^ plotted on the time axis t as shown in fig. 5A. The times of appearance of these pulses which

correspond to the times for operating the valve body 36 are t^, t2resp. t3- The time intervals that separate these pulses are Xx= t2<-><t>1<#>A2=t3-t2,X3= t4- t3, etc. and indicate the strength of the measured radiation. If these time intervals are long, the strength is relatively small and vice versa. If the intervals are small, the strength is relatively large. The interfering signal produced by the sludge pump 12 is shown in fig. 5A shown as a periodic, but not necessarily sinusoidal function N(t) with a period T. The length of the period corresponds to the rotational speed of the pump.

To facilitate the explanation, the scales have been mutually distorted in fig. 5. In practice, there will be from 50 to 80 fluctuations in N(t) between the times for the occurrence of the pulses P^^ and P2. Thus, X1 and \2 will vary from 50T to 80T. In fig. 5A, however, only a few oscillations of M(t) are shown between P^ and P2« Furthermore, the negative mud pressure pulses P^, P2, P3 are not purely rectangular as shown in fig. 5A and much smaller than those shown. In reality, the size of P^, P2 or P3 is ca. 0.1 or 0.01 times the maximum amplitude of the oscillations N(t).

In fig. 5, the curves A to E are placed below each other so that the signals can be compared in terms of time, so that one can follow the different stages of the process in the signal extractor 102, namely:

Step 1. The input signal F(t) is shifted T to obtain

where S(t - T) and N(t - T) are the shifted desired signal and the shifted interfering signal, respectively. Both signals are shown in fig. 5B. The signal S(t - T) is represented by the pulses P^a^, P2^ and P3^ which are obtained by a displacement T of the pulses P.^, P2 and P3 in fig. 5A. The signal N(t - T) in fig. 5B is synchronous with the signal N(t) in fig. 5A. This is due to the periodicity of the signal so that:

Step 2. By subtracting the input signal F(t - T) from the rising input signal F(t), one gets:

On the basis of expressions (1), (2) and (3) one gets:

The interfering signal is thus eliminated and does not appear in M(t). This is also evident from fig. 5A and B.

As shown in f.g. 5C, M(t) consists of pulses occurring in pairs. Each pair contains a negative and a positive pulse which are separated from each other by a time interval T. Thus a pair P^^ ^ appears and which is followed by a pair Pp ^ and P_ ^ and which is again followed by a pair P_ ^ and (c) ■ 7

P3 and so on.

Step 3. By shifting M(t) by a time T, you get M(t. - T). The entire sequence of pulses in fig. 5C is in fig. 5D shifted by time a T, but the pulse pairs are retained with a new designation P^ ( c' ) and<p>j_<le>) etc.

Step 4. By comparing the shifted pulses in fig. 5D in relation to fig. 5C shows that two pulses in the same pair appear simultaneously. The timing of simultaneous occurrence is in fig'5E"~bét"suitable Pl(<d>,#P (<d>) oy P3(<d>), so_that

P^' simultaneously with P^^. cgP±{c)

P2(d) simultaneously with P2i^_ and P2(c)

<P>3(<d>) simultaneously with P3(<b>) and P3(<c>)

The timing of the pulses P]L^d^/. ?2 ^ and P3 ^ are fcl+ T/ t2+ T and t3+ T.

The pulses P^^, P2(<d*>and P3^<d>) correspond to the pulses P^ P2 and P3 shown in fig. 5A. The pulses in fig. 5E thus represents the useful signal S(t - T) because it is only shifted by time T. Clearly, the "pulses of Fig. 5E provide the information that is desired. The time interval between P^<d>^ and P2 ^ is X^and the time interval between P ^ and P3 ^ is X2 etc. The quantities X^ X2 etc. represent the measured radiation by means of the gamma detector.

The above-mentioned step must now be considered on the basis of the effect of the signal emitter 102 which consists of the components 105 and 107 in fig. 4 and which is shown in detail in fig. 6 or 7.

The component 105 receives on the input terminal 101 which is the same as the input terminal for the signal emitter 102 in fig. 1, the signal F(t). This signal is amplified in an amplifier 130 and supplied to the input 131 of a delay network 132. The delay network delays the signal F(t) by the time T and delivers the signal F(t - T) at the output 134. This signal is a sum of two component signals S(t - T) and N(t - T) which are shown in fig. 5B.

The signal F(t - T) is supplied to an input 134 in a subtraction circuit 135. The other input 136 directly receives the signal

F(t) from the input 101 via a line 137. In the output 106 from the subtraction circuit 135, the difference signal M8t) = F(t) - F(t-T) appears in fig. 5C.

The delay network 132 is provided with a control input 113 which receives a signal for controlling the delay time T. It is important that the length of the delay T is the same as the period of the mud pressure fluctuation which can be caused by the mud pump 12.

The length of the delay time T is controlled by time pulses derived from the pulse generator 111 which is shown in fig. 4 and supplied via a line 110 to the control input 113.

It is assumed that the pump makes 12 changes per stroke. second, so that T = 1/N^. The pulse generator ;.ll delivers time pulses with a relatively high rate N2 which is a multiple of N^. N2 is equal to KN^, where K is a constant that can be chosen equal to 512. If the pump strokes are one per second, the signal generator must deliver 512 pulses per second. It is clear that the rate of the pump strokes varies with time and consequently N2 will vary so as to ensure that the delay produced by the delay network 132 will always be equal to one period of the mud pressure fluctuations caused by the mud pump 12.

The above-mentioned steps 1 and 2 which apply to the component 105 and the signal emitter 102, and the input signal F(t) as shown in fig. 5A is converted into an output signal M(t) which appears in a series of pulse pairs as shown in fig. 5C. The two further steps are performed by the component 107 and signal emitters 102 as shown in fig. 7.

The signal M(t) is supplied via line 140 to a delay network 141 which is identical to the delay network 132 in fig. 6. The control input 114 receives the same control signal that was supplied to the control input 113 in the delay network 132. Consequently, the delay produced by the network 141 will be T and the signal appearing at the output of the delay network 141 is M(t - T) as shown in fig. 5D. This output signal is supplied via an amplifier 143 to one input 145 in an AND gate circuit 146. At the same time, the undelayed signal M(t) via line 147 via the amplifier 148 is supplied to the other input 149 in the AND gate circuit 146. These two input signals M( t) and M(t - T) supplied to the AND gate circuit 146 is shown in FIG. 5A or D. As previously mentioned, some pulses appear on fig. 5C simultaneously with pulses in fig. 5D. These pulses which appear simultaneously in the output of the AND gate circuit 146 are P, ^, P_^ (d) . 12

and P^ in fig. 5E. These simultaneous pulses are the output pulses from the component 107 and consequently from the signal emitter 102..

It is thus clear that by means of the component 107

steps 3 and 4 are done. The signal M(t) in fig. 5C is thus converted into a signal S(t - T) as shown in fig. 5E. The last-mentioned signal contains the sizes X^, X^, X^, etc. which represents the desired information. It should be noted that the signal S(t - T) represents a series of pulses as shown in fig. 5E.

These pulses are supplied to a time-to-amplitude converter 115 whose output supplies the various quantities such as X^, X^, X^ etc. which represent the time intervals between the occurrence of pulses. These signals are supplied in turn to and transformed by the reciprocating circuit 118 in fig. 4 to other reciprocal signals with the size 1/X^, 1/^2' which are recorded by a recording device 120 in fig. 4. It is clear that the quantities 1/X^, 1/X and 1/X^ represent the strength of the radioactivity in the soil formations sensed by the sensor 30 at different depths in the borehole.

There is equipment described above for performing the logical steps leading from the signal F(t) to the signal S(t - T). These steps are performed in analog form. If desired, the whole can alternatively be carried out in digital form as shown in fig. 8 when the output signal from the pressure converter 100 is supplied to an analog-to-digital converter 103 whose output signal is supplied to a digital data processing device 104 which contains the elements 122, 123, 124,

125 and 126. Time signals from the pulse generator 111 or 140 are introduced into the processing device 104 to control delays in accordance with the pump speed. The output signal from the processing device 104 is supplied to a digital-to-analog converter 127 whose output signal is supplied to the recording device 120.

Fig. 9 shows a device similar to the device in fig. 4, but where data is derived and recorded is the temperature sensed by the sensor 30 in fig. 1. Data supplied to the signal emitter 102 is in digital form as shown in fig. 3D. The signal emitter 102 in fig. 9 is identical to that in fig. 4, but the time-amplitude converter 115 and reciprocating circuit 118 of FIG. 4 is replaced with a digital-to-analog converter 141. The output signals from a suitable pulse generator are supplied to the control input 110 in the signal emitter 102.

It is not always easy to provide a mechanical connection to a mud pump 12 as shown with chain pull 112 in fig. 4 and an alternative solution for producing the necessary pulses for the signal emitter may be desirable. The control input 110 in the signal emitter 102 in fig. 4, pulses are supplied with a rate of 512 pulses for each full pump stroke. It is clear that this beat must be carefully synchronized with the pump strokes. All the times shown T, t^ t2, etc. on fig. 5 are not exact times, but are directly derived from the speed of the sludge pump 12 so that they should not be expressed in seconds or minutes, but in liters of sludge. When the input 110 in fig. 4, 512 pulses per pump stroke, it means that there are voltage pulses at the input with a frequency equal to the 512th harmonic of the pump stroke frequency. Fig. 10 shows how this can be achieved without a mechanical connection to the pump shaft.

In fig. 10, a voltage-controlled oscillator 145 is arranged whose output 110 supplies electrical pulses with a frequency controlled by a direct voltage applied to an input 108. The component 150 is a binary divider that divides the frequency of the pulses applied to the input 116 and produces output pulses at the output 117 with a frequency equal to 1/512 of the frequency of the input pulse. The component 119 is a phase comparison device which compares two input signals, one from the output terminal 117 and one from the output terminal 130 and delivers at the output 128 a voltage which is zero volts when the two input signals have exactly the same phase, and delivers a positive voltage when the input signal of 117 has a lead on the input 130, and a negative voltage when the input signal of 117 lags behind the input signal of 130. A battery 129 supplies bias voltage to the oscillator 145. The device 151 forms a phase-locked loop. The way it works is as follows: It is assumed that the pump stroke frequency is 1 Hz and the oscillator 14 5 delivers a frequency of 512 Hz. The output signal from the dividing circuit 150 will then be 1 Hz and the output signal from the pressure converter 100 will be 1 Hz and when these have the same frequency and phase, there will be zero volts in the output 128 from the comparison circuit and the oscillator 145 will, with the correct voltage from the battery 129, produce exactly 512 pulses per pump stroke.

If it is then assumed that the pump speed is increased, the frequency of the line 130 will be somewhat greater than 1 Hz, e.g. 1 + A^Hz. The comparison device 119 will then deliver an output signal at the output 128 which is no longer zero volts, but e.g. + A2V and this voltage is supplied to the oscillator 145 on the terminal 108 and increases the frequency until the number of pulses per second is increased by a value f so that f/512 = 1 + A^.

The frequency of the clamp 110 will always exactly follow the frequency of the mud pump 12 and will always be the 512th multiple.

A third solution for producing such time pulses is shown in fig. 11 where the input 154 of a correlation device 152 is fed from the output of the pressure converter 100 and receives the signal F(t) which contains the periodic signal N(t) and S(t). The output signal from the pressure converter 100 is also supplied to the input 101 in the signal emitter 102. The correlation circuit 152 delivers at its output the correlation of F(t), which is:

where the line above the expression indicates the average value of a specific time period. The expression ^^(t) can be expressed where and and (J>sg (t) becomes zero at a value of t =TQ and beyond tq becomes

Since 4»nn(T) is periodic, the expression <j>ff(x) is also periodic and has the period x. This expression delivered by the output of the correlation circuit 152 is fed to a pulse multiplier 153 which delivers a series of time pulses similar to those delivered by the pulse generator 111 in fig. 4 and which is supplied to the terminal 110 in the signal emitter 102. The pulse multiplier 153 multiplies the frequency of the input pulses by means of the phase-locked loop similar to the one in fig. 10 or in another usual way. The subsequent elements in fig. 11 are the same as in fig. 4 with the exception that the pulse generator 111 and the chain drive 112 are looped.

It is clear that within the scope of the invention, various changes and modifications are possible. For example 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.

In an example with three pumps, the periodic pressure curve in fig. 5A in practice not be a single periodic function N(t), but be the sum of three components, each of which is periodic and has its own specific period.

By using three delay systems as shown in fig.

6 each synchronizing its own pump, each will periodically

component of the interfering sludge pulse pressure signal be brought to zero individually. This will give a signal where interfering mud pump pressure signals are eliminated.

Claims (11)

1. Remote sensing method for use in connection with drilling operations in a borehole, for the transmission of information in the form of data signals (Fig. 5: A Pl) and when using a fluid circulation system (Fig. 1: 14, 16, 18, 22, 29) comprising a mud pump device (Fig. 1: 12), where the pump produces disturbing signals (Fig. 5: A N(t)) with distinct characteristics (Fig. 5: N(t)), which distinct characteristics are the result of pressure changes (N(t)) which is caused in the fluid in the circulation system during the drilling operations, and is repetitive (Fig. 5) according to an identifiable pattern (N(t)), and where the circulation system at least partially constitutes a communication channel (Fig. 1 : 22) between a transmitter device at a location down the borehole (Fig. 1: 24) for the transmission of data signals representing said information, and a signal receiver device (Fig. 1: 100) at the earth's surface (Fig. 1: 34), which signal receiving device serves to receive a mixture (Fig. 5) of the aforementioned data signals and the aforementioned disturbing signals, to produce electrical mixed signals (Fig. 5: A) which represents the aforementioned mixture, characterized in that a single pressure transducer (100) is used as a signal receiving device, to generate electrical signals that represent the aforementioned data signals and the pump-generated disturbing signals, that electrical control signals are derived (Fig. 4 : 111) which represents the action of the pump device (12), that the electrical mixed signals are time-shifted by one or a whole number of pump periods depending on the electrical control signals and thus produce time-shifted signals, that the time-shifted signals and the mixed signals are superimposed on a signal - diversion device (Fig. 4: 102) which is controlled by the electrical control signals (Fig. 4: 110) to produce processed signals (Fig. 4: 108) in which the pump-generated disturbing signals are reduced, and derivation of said information from said processed signals (Fig. 4: 120). ABC260891NOP49699 2. Device for remote measurement for use in connection with drilling operations in a borehole, for the transmission of information in the form of data signals (Fig. 5: A Pl) and using a fluid circulation system (14, 16, 18, 22, 29) comprising a sludge pump device (Fig.1: 12), where the pump produces disturbing signals (Fig. 5 A N(t)) with distinct characteristics (N(t)), which distinct characteristics are the result of pressure changes (N(t)) that are caused in the fluid in the circulation system during the drilling operations, and is repetitive according to an identifiable pattern (N(t)), and where the circulation system at least partially constitutes a communication channel (22) between a transmitter device at a location downhole for the transmission of data signals which represents said information, and a signal receiver device (100) at the earth's surface, which signal receiver device (100) serves to receive a mixture of said data signals and said disturbing signals (Fig. 5 A), to produce electrical mixed signals (Fig. 5 A) which represents the said mixture, characterized by the only pressure transducer (100) which constitutes the signal receiving device, and produces electrical mixed signals which represent a mixture of the said data signals and the pump-produced disturbing signals, a device for the derivation of electrical control signals (Fig . 4: 11) which represents the effect of the pumping device (12), a device for time-shifting the electrical mixed signals by one or a whole number of pumping periods depending on the electrical control signals and thereby producing time-shifted signals, a signal derivation device (Fig. 4: 102 ) which is controlled by the electrical control signals to combine the time-shifted signals with the electrical mixed signals to produce processed signals (Fig. 4: 108) in which the pump-generated interfering signals are reduced, and a device for deriving said information from the aforementioned processed signals. ABC260891NOP49699 3. Device according to claim 2, characterized in that the device for time shift (Fig. 6: 132) is arranged to shift the electrical mixed signals by a variable time interval (controlled by 113 in Fig. 6). 4. Device according to claim 2, characterized in that the repetitive signals comprise more than one repetitive component (the last 3 paragraphs of the description and Fig. 6) and the processing apparatus is arranged to work in accordance with the periodicity of each of the aforementioned components. 5. Device according to claim 2, characterized in that the device (Fig. 11: 152 and 153) for generating the electrical control signals comprises a device for deriving the electrical control signals from the aforementioned electrical mixed signals. 6. Device according to claim 2, characterized in that the device for producing the electrical control signals comprises means for forming the average of the electrical mixed signals (Fig. 11: 152). 7. Device according to claim 2, characterized in that the device for deriving electrical control signals comprises a correlator (Fig. 11: 152) to produce an autocorrelation of the electrical mixed signals. 8. Device according to claim 2, characterized in that the device for deriving the electrical control signals comprises a phase-locked loop (Fig. 10: 151). 9. Device according to claim 2, characterized in that the device for producing electric control signals is an electric generator connected (Fig. 4: 112) to the pump device. 10. Device according to claim 9, characterized in that the pump device pumps drilling fluid using a sequence of pump strokes caused by revolutions of the pump device and that the pulse generator produces a plurality of pulses (Fig. 4: 111) during the time interval corresponding to a single revolution of the pump device. 11. Device according to claim 2, characterized in that the pump device pumps drilling fluid by means of a sequence of pumping strokes of reciprocating pistons driven by a rotating part (Fig. 4: 12) in the pump device, and that the electrical control signals are generated in dependence on successive angular positions (Fig. 4: 112) of the rotating part during each of the pump strokes.