GB2140599A - Detection means for mud pulse telemetry system - Google Patents

Abstract

Information is conveyed from a downhole location within wellbore being drilled by producing pressure and velocity of flow variations from the steady state drilling fluid pressure and velocity of flow so as to get up transient acoustic waves that propagate to the surface through the drilling fluid within the drill string, and a simple and reliable method of recovering the propagated information is to monitor at 88 the pressure of the gas filled side 70 of the accumulator or dessurger device that is coupled to the drilling fluid line adjacent the pump. Alternatively the height variations of fluid in a stand pipe may be used to recover the information. <IMAGE>

Description

SPECIFICATION Detection means for mud pulse telemetry system This invention relatesto detectingthefluid particle velocity of flow variations that are produced in a column of drilling fluid, i.e., drilling mud, by downhole signaling apparatusthatis located in the region of a drill bitthat is engaged in drilling a borehole in the earth.

During drilling of a well, it is desirable to provide information to the driller as to conditions that exist at the bottom of the well. For example, the inclination of the lower portion of the drill string with respect two a vertical reference axis and the azimuthal direction of that inclination are quite important, particularly in directional drilling, in order to assure that the borehole is drilled along an intended path. Similarly, it may be desirable to convey to the surface ofthe earth information relative to temperature and pressure conditionsatthe bottomofthehole,theweightthatis applied to the bit at a particular instant, and other parameters that are importanttothe satisfactory completion ofthe drilling operation.

In the past, much ofthis downhole information has been obtained by parameter measuring instruments that wee lowered into the drill sting on a wire line. In many applications it is desirable to avoid the use of a wire line, if at all possible. Accordingly, systems have been devised for conveying information from a downhole location to the surface of the earth by employing pressure pulses, ortrnnsient acoustic waves, in the drilling fluid. These pressure pulses propagate upwardly th rough the column of drilling fluid to the surface wherethey are detected by a pressure responsive transducer. In some instances, a negative pressure pulse is produced by momentarily bypassing some of the circulating fluid from the interior of the drill string to its exterior.In other types ofsignalling equipment a positive pressure pulse is produced by closing or restricting a downholevalve through which drilling fluid flows toward the bit. In either case, the surface equipment responds to the momentary variation in drilling fluid pressure that resultsfrom actuation of a valve atthe downhole location.

One reason thatthe detection of signaling fluid pressure pulses on the surface has been less success furl than hoped is because the drilling fluid line at a well site includes an accumulatorordesurgerdevice whose function is to smooth out the pressure surges in the line caused bythe piston strokes ofthe pump.

Not only does the accumulator attenuate the pump pressure pulses, but it also attenuates the signaling pressure pulses that are produced downhole. I have found thatthe sensing method and apparatus of my invention results in optimum detection of signaling pulses in the drilling fluid and completely obviates the problem that limits the usefulness of prior art mud pulse pressure sensing.

In accordance with the presently preferred embodi mentofmyinvention, Imonitorthe pressure in the gas filled portion of an accumulator device that is connected on the downhole side ofthe drilling fluid (mud) pump. As a valve in the downhole signaling apparatus opens and closes, in rapid succession,the restriction to the flow ofthe mud in the drill string correspondingly decreases and increases, assuming thatthevalve is a bypass valve. This action creates a transient acoustic wavethat propagates upthe mud column to the surface. The momemtary reduction in the mud flow restriction is accompanied by a momentary increase in flowvelocity, and in a momentarily increased volumeofflow.It also is accompanied byan increased quantity of drilling fluid flowfrom the accumulator, thereby causing the gas filled portion thereof to expand. The expansion of the volume of the gas filled portion of the accumulator causes the gas pressure thereofto decrease. A pressuretransducerthat monitors the gas pressure ofthe accumulatorthus is a simple and effective detector of the variation offluid particle flow in the mud column. In effect the accumulator and pressure monitor connected thereto are functioning as a transducer that converts drilling fluid acoustic particle velocity changes to pressure changes.

The invention will be described in connection with the accompanying drawings wherein: Fig. lisa simplified illustration of a well drilling rig provided with telemetry apparatus constructed and arranged in accordance with the present invention; Fig. 2 is a simplified illustration of a downhole tool of a type used in a measuring while drilling operation; Fig. 3 is a simplified illustration of an accumulator device that is used in the apparatus of Fig. 1; Fig. 4is a simplified illustration of an alternative type ofaccumulatorthat may be used in the apparatus of Fig.1; Fig. 5 is a simplified diagram of an experimental test system that demonstrated the principle of my invention, and Fig. 6 and 7 are illustrations of waveforms of signals obtained from the pressure transducers of Fig. 5.

In the simplified illustration of Fig. 1, a well drilling rig, which is conventional in most respects, includes the usual upwardly projecting derrick our mast 11 from which a drill string 12 is suspended by a block and tackle assembly 13 which includes a crown block 14 and a traveling block 15 suspended from the crown block by a line 16. Drawworks 17 actuates line 16to movethetraveling block and drill string upwardly and downwardly along vertical axis 18. The drill string is formed of a series oftubular pipe sections 19 th readedly interconnected at joints 20.For purposes ofthe present invention the drilling apparatus may be of a type in which the entire string is rotated by a rotary table 21 mounted on the rig floor 22, or of a type in which the string is stationary and only the drill bit 23 at its lower end rotates. Fig. 1 is intended to illustrate that latter arrangement, with the lowermost section 24 of the drill string containing a motor 25 of known type adapted to be driven bythe drilling fluid circulating downwardlythroughthe drill string to turn bit 23 about vertical axis 18. Connected into the string above the bottom motor section 24 is an instrument section 27 that develops and transmits the monitored downhole information to the surface of the earth.

The drilling fluid, or mud, is delivered under pressure by a pump 28 through a line and flexible hose 29 to the upper end ofthe drill string 1 9.The mud then flows downwardlyth rough the interior ofthe drill string to bit 23. The fluid isdischargedthrough restricted passages in the bit to the outside of the string, and then returns to the surface th rough the annulus 30 between the drill string and the borehole.

Atthe upper end ofthe well the returning fluid received from annulus 30 is confined within a structure 31 and is discharged through a line 32 to a collection sump 33. Pump 28 takes suction through a line 34 for recirculation ofthe mud to the drill string.

Before recirculation ofthe mud, cuttings and other unwanted materials are separated out by a screen, filter or other separation system represented diagram matically at 35.

Pump 28 is a conventional mud pump of the positive displacement type, typically including one or more piston and cylinder mechanisms. The pump is driven by a motor 37 at a rate which can be varied by control means 38.

Fig.2 is a simplified illustration of the downhole tool. Itforms no part of my invention but is illustrated in simplified form herein to assure a complete understanding ofthe background of my invenion.The instrument or tool section 27 ofthe drill string has a rigid tubular body 39 centered about axis 18 of the string and its upper end is threadedly connected at40 to the next upper section 19 of the string. Its lower end is threadedly connected at 41 to the lowermost section 24 of the string that carries the mud motor. Drilling fluid flows downwardlyfrom a passage 42 formed in the string above instrument section 27 into an axial passage 43 formed in body 39. From the lower end of passage 43 the fluid flows into a passage 44 in bottom section 24to drive motor 25.The fluid then is discharged into annulus 30 through a passage represented at 45.

The active elements of instrument section 27 ofthe string are illustrated within cavities formed in the relativelythick sidewall of body 39 of section 27 and may include an instrument46 adapted to sense a condition or conditions in the well, battery pack 47 for energizing the instrument and other related parts, an electronic circuit 48, and an electrically operated device 49 for actuating a valve 50 between open and closed positions. Valve 50 acts to control flow ofthe circulating drilling mud from passage 43 through a passage 51 in the sidewall of body 39 to the exterior of that body.The valve 50 may be a gate valve which is actuablevertically between its closed and open positions in which it blocks flow of drilling mud laterally from passage 43, or permits the fluid to bypass laterallythrough passage 51 to the annul us 30 about body39withoutflowthrough motor 25 and the bit. The actuator 49 for valve 50 may be a solenoid which opens the valve when energized and permits closure ofthe valve by a spring represented at 52 when the solenoid is deenergized. Other arrange- ments of instrument sections are known and may be used.

Each time valve 50 is opened in response to coded information signals the bypassing of drilling mud through passage 51 from the interior of body 39to its exterior reduces the restriction to flow of the mud down the drill string,thereby allowing the drilling mud to flow down the string at a greater velocity and with an accompanying reduction in fluid pressure in the mud column.These arethe so called "mud pulses" that are detected at the surface to recover the transmitted information. In fact, the mud pulses are transient acoustic waves that propagate through the mud column in the drill string.

A number of different methods and apparatus have been proposed for detecting the mud pulses. For example, it is known to mount a pressure transducer 102 on the pipe 72 that connects the mud pump and accumulatorto the drill string.Additionally, in U.S.

patent application S.N. 330,836 entitled Well Information Telemetry, filed Decemeber 15,1981, by H. Moll, and assignedto applicant's assignee, a telemetry system is disclosed in which optical, ultrasonic or mechanical means are utilized atthesurfaceto monitorthe velocity orflowrate ofthe drilling fluid in order to detectthe information pulses produced down hole in the instrumentsection 27. That system is attractive, butthe information receiving means of my invention is simplerto construct and produces better quality information at the surface.

The implementation of my invention is illustrated in simplified form in Figs. 1 and 3 wherein the accumula tor70thatis commonly employed in a mud circulating system is illustrated as coupled to pipe 72that in turn is connected to the output port of mud pump 28. As is well understood, the accumulator functions to smooth outthe pressure pulses in the mud linethatare caused by the piston strokes ofthe mud pump. The accumulatorsometimes is called a desurger.

Accordingly, a relatively more steady state pressure and velocity offlow are established in the drilling fluid line. As illustrated in simplified form in Fig. 3, accumulator 70 is connected to pipe 72 by means of a short vertical section of pipe 74. Accumulator 70 has an enclosed body 78 that is hollow except for a flexible diaphram or septum 80 secured within the body of the accumulatorto provide two isolated interior regions or portions. The first region 82 is coupled to pipe 72, and mud under pressure from pump 28 flows into this first region. The other region 84 on the opposite side of the diaphram 80 is filled with a given quantity of inert gas such as nitrogen.Diaphram 80 is flexible and gas impervious so that itwill moveto either side of an equilibrium position in response to the quantity of mud within region 82 ofthe accumulator. As more mud is introduced into the accumulator, diaphram 80 is displaced upwardly and the gas in upper portion 82 is correspondingly compressed. On the other hand, when a quantity of mud flows out of accumulator70 theforce ofthe mud on diaphram 80 is reduced and the gas expands within portion 84to force the diaphram 80 downwardly to maintain contact with the mud. The gas is bound within the second portion 84 of the accumulator so that its pressure varies as a function of the amount of mud in the first section 82. In terms of its acoustic properties, diaphram 80 is an acoustically complaint medium.

As previously stated, when mud porting or venting valve 50, Fig. 2, is open to divert mud from within the drill string,the resistance to flow of mud within that string is decreased and the velocity of flow ofthe mud in the drill string increases. Because mud pump 28 may be consideredto beaconstantvolume pump, during the time signals are produced downhole,the increased velocity of flow of mud particles in the drill string results in at least a portion ofthe mud within the first portion 82 of accumulator 70 flowing into the pipe 72 that leads to the drill string. This flow of mud out of the accumulator permits the gas in the second portion 84to expand with an accompanying decrease in its pressure.Pressure transducer 88 is mounted on accumulator so as to be in contact with the second portion 84 ofthe accumulatorfor monitoring the gas pressure therein. In this mannerthe pressure transducer 88 that monitors the pressure on the gas side of diaphram 80 will produce output signals corresponding to the flow of mud into and out of the other side of the accumulator in response to the changing velocity offlow in the drill pipe that is produced by the signaling pulses. It should be understood that the mud pulsing that is produced in instrument section 27 may be negative pulses as described, orthey could be positive pressure pulsesthat resultfrom a different valve arrangement in the instrument section. Both systemsarewell known and need nowt be further described.In a strict sense, what is being measured is thevariationfrom steady state in the acoustic wave fluid particle velocity of flow ofthe mud into and out of accumulator70 resultingfrom the signal pulses produced downhole.

It is thus seen that by the simple expedient of placing a readily available pressure transducer on the gas filled side of the accumulator a reliable signal is obtainedthat is indicative ofthe variation in the acoustic wave fluid particle velocity in the mud flow in the drill string.

As illustrated in Fig. 1, the electrical output signal of pressure transducer 88 may be coupled over lead 90 to an amplifier device 92, and then through a signal conditioning means 94to an appropriate readout and display device 96. This readout and display device 96 is available to the driller to guide him in his drilling operation. If desired, additional information may be obtained from a pressure transducer 102 that is coupled directlyto pipe 72 on the downstream side of accumulator 70. This additional information is coupled over a lead 106 to an amplifier 108 and may be utilized in an appropriate manner.

The type of accumulator illustrated in Fig. and described above is one example of a transducerthat can be used in accordance with the teachings of this invention. Accumulators having other types of construction are known and could be used in practicing this invention. In Fig. 4,for example, the accumulator 70 could beaclosedcylindrical member 90 that is connected to pipe 72 by means of the short vertical section of pipe 74. Mud from the pump (not illustrated) enters vertical pipe 74 and the bottom portion of cylindrical body 90 and exerts a force against a piston member 92. Piston member 92 moves upwardly within cylindrical member 90 in response to a force from the mud on one side, and moves downwardly in response to a spring member 94 on the opposite side.

Piston member 92 will be at some intermediate position within cylindrical member 90 under the normal steady state pressure and velocity flow in mud line 72. Asthe velocity of flow of mud into and out of the cylindrical member 90 changes in response to changes in the velocity of mud flow in the drill string, as described above, piston member92will raise and fall to cause the upper gas filled region 96 ofthe cylindrical member to become larger or smaller. This causes the pressure of the gas within the upper portion 96to increase or decrease in response to the signal pulses in the mud line. Pressure sensor 88 is in communication with the gas filled region 96 of cylindrical member 90 and produces an output signal that is a function of the gas pressure and of the flow velocity variation of mud in the drill string.

Instead of measuring the gas pressure inthetop portion 96 of accumulator70', means such as a strain gauge may be provided for measuring the strain in the spring means 94to provide an indication ofthefluid particlevelocity of mud flow. Similarly, in Fig. 3, although not presently preferred, strain gauges could be secured to diaphram 80 to provide the desired outputsignal in place of the use of a gas pressure gauge 88.

Asan alternative to the conventional accumulator, a simple standpipe that is at least partially filled with mud also could be used asthetransducer. Means could be provided for determining the height of the mud in the column, thereby providing a transducer whose output signal contain pulses corresponding to the mud pulsing produced bytheinstrumentsection ofthe downhole tool. This points out another feature that would be possible with the embodiments of Figs.

3and 4. That is, aseparate diaphragm 80 or piston 92 would not be absolutely necessary. The gas pressure will act directly against the mud in the round body members 78 and 90, and vice versa. However, at the presenttime a separate diaphragm or piston is preferred.

As a further alternative to the diaphram 80 and pressure transducer 88 of Fig. 3, an ultrasonic transducer and associated circuitry for ultrasonic pulse echo ranging could be mounted at the top of the accumulator illustrated in Fig. 3 as a means for detecting the level ofthe mud in the device. Furthermore, appropriate mechanical means such as float level detectors could be used as an indication ofthe level of mud within the accumulator. The position of the float level detector would be correlated to mud acoustic particle velocity flow and/or pressure of mud in the drill string.

The improved performance that is achievable with mud pulsing telemetry system ofthis invention was confirmed in an arrangement that is illustrated in simplified form in Fig. 5. Two inch diametertubing was connected in aclosed loop 100 for circulating drilling fluid from collection sump33' around the loop.

The drilling fluid that was used included a commonly available drilling mud that had a density of 9.5 pounds per gallon and a viscosity of 17 CPS. Pump 28' was a model P323,triplex plunger pump, manufactured by Wheatley Division of Geosource Incorporated, Tulsa, Oklahoma. The pump was operated at 330 revolutions per minute and had a flow rate of 54 gallons per minute. Accumulator70wasa model number NS 2373 10-51, a product of Greer Hydraulics Inc. Atthetop of loopi00ofFig. 5,thefluidpath divides into parallel paths 103 and 104. Path 103 includes a throttle valve 105 that helps to establish the steady state flowwithin loop 100.Path 104 includes a valve 106that is actuated by motor 112 to continuously open and close at a fixed rate. Valve 106 was operated at a rate of approximate- liy two cycles per second, and at a 50% duty cycle to produce 25 psi negative pressure pulses when the valvewas opened. Accumulator70' includes aflexi- ble, gas impervious diaphram 80' that provides a mud filled portion atthe bottom of the accumulator and a gas filled portion at the top thereof. Pressure transducer 88' measures the gas pressure in the top portion of accumulator70' and produces an electrical output signal that is coupled through switching means 120 to an oscillocope 124.

Afind pressure transducer 102' is coupled directly tote loop 100 and monitorsthe pressureofthe mud within the loop. The electrical output on pressure transducer 102' may be selectively coupled to oscilloscope 124through the switching means 120.

With the mud pulsing valve 106 operating as described above, the output signal from pressure transducer88' on the gas filled side of accumulator 70' is illustrated in the oscilloscope trace of Fig. 6a. This trace shows a very regular sawtooth waveform having a tvvo Hz repetition frequency. The 16.5 Hzsignal representing the pressure variations from the triplex mud pump28' is bearly discernable on-the sawtooth waveform.On the other hand, the output signal from pressure transducer 102' that is directly monitoring the mud pressure within loop 100 is illustrated in the oscilloscope trace of Fig. 6b. In this waveform, the two Hz pressure pulses produced by mud pulsing valve 106 are bearly discernable and are manifested only as a small spike at each valve opening and a slight undulation ofwaveform.

Fig. 7a is an oscilloscope trace ofthe output of pressuretransducer88' on accumulator70' when the output ofthetransducer has been differentiated prior to coupling to the oscilloscope. The 50% duty cycle square wave pulses are clearly discernable, and the higherfrequency piston strokes of pump 28 are clearly discernable on the waveform. The waveform of Fig. 7a may be filtered to remove the higherfrequency pump piston strokesignals andto leave onlythe 50% duty cycle square wave resulting from mud pulsing valve 106, as illustrated in Fig. 76.

Reasons why difficulties have been encountered in the past in receiving good and reliable mud pulsing signals at the surface, and the reasons why the present invention is successful, may become evident to some by analyzing the drilling fluid columnMfrom pump 28to the drill bit 23, Fig. 1, as an acoustictransmission line.

The mud pump 28 hasthecharacteristicsofan open circuit at the end of the transmission line, and accumulator 70 may be considered to be analogous to a Helmholzresonator,thatis,a means that manifests acoustic compliance. The purpose of the accumulator 70 is to smooth out the pressure surges caused by the piston strokes ofthe pump. The accumulator does its job bestwhen its resonancefrequency is equal to the frequency of the piston strokes of motor 28, which in practice might rangefrom 1 to 9 Hz, as an example.

The resonant rccumulator may be considered as a short circuit across the end ofthe transmission line or, more realistically, as avery low impedance, relative to the characteristic impedance of the acoustictransmis- sion line.

In transmission line theory, pressure pulses in an acoustictransmission line are analogous to voltage pulse in an electromagnetic transmission line, and acoustic particle velocity fluctuation around the steady velocity ofdrilling fluid resulting from the pressure pulsing isanalogous to current pulses in the electromagnetictransmission line. The accumulator is analogous to a series resonant RLC circuit.Consequently, the very low impedance presented by the accumulator at resonance meansthatthere is a very low pressure present at the end ofthetransmission line. (Because the frequency of the piston strokes of the mud pump and thefrequencyofthe mud pulsing signals from downhole both areexremely'low and the wavelengths are extremely long, aefrraEsepara- tions between the mud pump arsd theaccumulator, and between the mud pump and drill stringatthetop ofthe borehole, are extremely small fractionsofthe acoustic wavelength and for practical purposes can be considered to be at the end ofthe transmission line).

With the above explanation it is seen that any mud pulse signaling rate near the resonantfrequency ofthe accumulator inherently will produce low magnitude pressure pulses atthe surface. On the other hand, in the present invention, the mud particle velocity fluctuation atthe end ofthetransmission line will be optimum since it corresponds to electrical current at a short circuited transmission line.

The acoustic characeristics of accumulator 70, the properties of the acoustic transmission line comprised ofthe drilling fluid line and drill string, and the mud pulse repetition rate must be proportioned according to thetheory of resonance,transmission line theory, and the equivalentstructures presentto selectthe optimum type of accumulator mostadvan- tageous repetition rate. Inasmuch as accumulator 70 is performing a dual function of a pressure pulse smoother and as an acoustic signal transducer, it is possible, and may even be advantageous, to use two instead of one accumulators connected to fluid line 72.

In this instance, the first accumulator may have charactertics that optimize its performance as a pressure pulse smoother orsurge preventer, and the second accumulator may have characteristics that optimize its performance as an acoustic signal trans- ducer.

In its broader aspects, this invention is not limited to the specfic embodiment illustrated and described.

Various changes and modifications may be made without departing from the inventive principles herein disclosed.

Claims (12)

1. A method for detecting information signals that are produced down hole in a well bore by creating variations in the acousticwavefluid pressure and particlevelocity of drilling fluid within the driltstring and in a fluid linethat connects the drill string to a fluid pump on the surface, said method comprising, connecting to said fluid line an acoustically compliant means having a characteristicthat changes as a function ofthe acoustic wave fluid pressure and particle velocity of drilling fluid in the fluid line, and producing a signal that is a function ofthe change in said characteristic of the medium.

2. Amethodfordetecting information signals that are produced in a well bore by creating variations in the acoustic wave fluid particle velocity of drilling fluid within the drill string and in a drilling fluid line that connects the drill string to a drilling fluid pump on the surface, wherein an accumulator is connected to said fluid line on the downstream side of the pump to smooth outpump induced pressure variation in the line and drill string, and wherein said accumulator includes a compliant medium having a characteristic that changes as a function ofthe change in the drilling fluid present in a portion ofthe accumulator, said method comprising measuring said characteristic of the compliant medium, and producing an output signal having a characteristic that varies as a function ofthe variation in the measured characteristicofthe medium.

3. A method for receiving on the surface signals in theform of drilling fluid pressure and velocity variations from adownhole location in awell bore, wherein a pump on the surface circulates drilling fluid understeadystateflowconditionsfrom a line on the surfacetoa drill string in the well bore,said method comprising connecting to said drilling fluid line onthe surface means for receiving drilling fluid from the line when the drilling fluid particle velocity of flow decreases in said line from a steady state velocity offlow andfor transmitting drilling fluid therefrom into the line when the drilling fluid particle velocity of flow increases in said linefrom a steady state velocity of flow, and providing an output signal in response to said movement of drilling fluid into and out of said means.

4. Amethodfor receiving onthe surface signals in theform of drilling fluid pressure and velocity variations from a downhole location in a well bore, wherein a pump on the surface circulates drilling fluid under steady state flow conditions from a line on the surface to a drill string in the well bore, said method comprising connecting to said drilling fluid line on the surface means for receiving drilling fluid from the line when the drilling fluid pressure increases in said line from its steady state pressure and fortransmitting drilling fluid therefrom into the line when the drilling fluid pressure in said line decreasesfrom its steady state condition, and providing an output signal in response to said movement of drilling fluid into and out of said means.

5. A method for detecting information signals that are produced downhole in a well bore by creating variations in the acoustic wave fluid pressure and particle velocity of drilling fluid within the drill string, wherein a pump and a drilling fluid line on the surface are connected to the drill string to provide drilling fluid thereto, said method comprising connectingto said drilling fluid line on the surface a means for receiving drilling fluid from the line when the drilling fluid acoustic wave particlevelocity decreases in the line due to said information signals and for transmitting drilling fluid therefrom into the line when the drilling fluid acoustic wave particle velocity increases in said line dueto said information signals,and producing an output signal that has a characteristic that changes as a function of said movement of drilling fluid into and out of said means for receiving drilling fluid.

6. Amethodfordetecting information signals that are produced downhole in a well bore by creating variations in the acoustic wave fluid particle velocity of drilling fluid within the drill string and in a drilling fluid linethat connects the drill string to a drillingfluid pump on the surface, wherein an accumulator is connected to said fluid line on the downstream side of the pump to smooth out pump induced pressure variation in the line and drill string, and wherein said accumulator includes a first portion containing a compressible medium whose volume and pressure change as afunction ofthe amountofdrilling fluid present in a second portion of the accumulator, said method comprising measuring the pressure in said first portion of the accumulator, and producing an output signal having a characteristic thatvaries as a function ofthe pressure measured in said first portion ofthe accumulator.

7. In atelemetry system fortransmitting signals in the form of drilling fluid pressure pulses from a downhole location in a well bore to a pulse receiving location on the surface, wherein a pump an the surface circulates drilling fluid from a fluid line on the surfaceto a drill string in the well bore, improved means on the surface for detecting said signals, comprising accumulator means connected in said fluid line on the surface for minimizing pump pressure pulses in the drilling fluid, said accumulator including a gas filled portion whose volume is changed as a function of the change in fluid particle velocity of the drilling fluid in said line, and means connected to the gas filled portion of the accumulatorfor producing a signal having a characteristicthat is a function ofthe gas pressure in said accumulator.

8. Inatelemetrysystemfortransmitting signals in the form of drilling fluid pressure pulses from a downhole location in a well bore to a pulse receiving location on the surface, wherein a pump on the surface circulates drilling fluid from a fluid line on the surface to a drill string in the well bore, improved means on the surface for detecting said signals, comprising means connected to said drilling fluid line on the surface at the downstream side of said pump for receiving drilling fluidfrom the line when the drilling fluid particle velocity of flow decreases in said line and fortransmitting drilling fluid therefrom into the line when the drilling fluid particle velocity of flow increases in said line, and means responsive to the movement of drilling fluid into and out of said means for providing an output signal corresponding thereto.

9. The combination claimed in claim 8wherein said means connected to the drilling fluid line includes means that include a compliant medium that has a characteristic that changes with a variation in velocity of flow of drilling fluidcaused byfluid pressure pulses produced downhole in the well bore.

10. Inatelemetrysystemfortransmitting signals in the form of drilling fluid pressure pulses from a downhole location in a well bore to a pulse receiving location on the surface, wherein a pump on the surface circulates drilling fluid from a fluid line on the surface to a drill string in the well bore, and wherein accumulator means are connected in said fluid line on the surface for smoothing pump pressure pulses in the drilling fluid and the accumulator includes a gas filled portion whose volume is changed as a function ofthe change in fluid particle velocity of the drilling fluid in said line, improved means on the surfacefor detecting said signals, comprising means connected to the gas filled portion ofthe accumulatorfor producing a signal having a charac teristicthat is afunction ofthe gas pressure in said accumulator.

11. A method for detecting information signals as described in Clain 1 substantially as disclosed herein.

12. Atelemetry system as claimed-in Claim-7 and substantially as described with reference to the accompanying drawings