US2667626A

US2667626A - Telemetering system for wells

Info

Publication number: US2667626A
Application number: US140128A
Authority: US
Inventors: Donald W Blancher
Original assignee: Bendix Aviation Corp
Current assignee: Bendix Aviation Corp
Priority date: 1950-01-23
Filing date: 1950-01-23
Publication date: 1954-01-26
Anticipated expiration: 1971-01-26

Description

S L m Rw Em. ww Nm Aw .mms .m WI m um m E T 3 Sheets-Sheet l Filed Jan. 25, 1950 4 ELEMENT RECORDING RECEIVER m U S m 1,50A l E MR TM me VN NA lL B w D.

ATTORNEY Jan. 26, 1954 D'. w. BLANCHER TELEMETERING SYSTEM FOR lWELLS 5 Sheets-Sheet 2 Filed Jan. 23. 1950 672 Q 0V@ 066.? 5?*43 a. Q LM/@ M i@ a i A INVENTOR D.W.BLANCHER ATTORNEY Jan. 26, i954 Q W, BLANCHg@ 2,579 TELEMETERING SYSTEM FORA WELLS Filed Jan. 23, 1950 3 Sheets-Sheet 3 ha B.P. AMP. -2oo-22oo- OUTPUT /O SATURATION LEVEL OF TUBE {CUTOFF LEVEL oF TUBE .nlllllllmll 4 F G H VNU ATTORNEY Patented Jan. 26, 1954 UHTD 2,667,626 TELEMETERING SYSTEM FOR WELLS Donald W. Blancher, signor to Bendix North Hollywood, Calif., as- Aviation Corporation, South Bend, Ind., a corporation of Delaware Application January 23, 1950,` Serial No. 140,128

' 2 Claims.

This invention relates broadly to the art of telemetering and specifically, in part, to the telemetering up a well bore of data on the operating characteristics of a pump in the well, particularly data on the stress in and the motion of the pump rod at the pump.

Pumps in deep wells, usually oil wells, are cornmonly reciprocated by a sucker rod extending up through the well to a pumping jack at the surface. In deep wells the long sucker rod has considerable stretch and distributed inertia. Because of this, its motion at the pump end may be radically different from that imparted to it at the upper end, and may be quite unpredictable, particularly at high pumping speeds. it is desirable to be able to ascertain just what stresses and motion are induced at the lower end of the sucker rod and their relation to the stresses and motion at the upper end.

A general object of the invention is to provide a practicable and accurate system for continuously telemetering operating data from the bottom of a well to the surface.

Another object is to provide a satisfactory electrical communication channel through a well, utilizing existing elements therein as conducting elements, whereby special wires or cables are rendered unnecessary.

Other more specific objects and features of the invention will become apparent from the description to follow.

Broadly, in accordance with the invention, the stress in and motion of a pump rod in a well are translated into electrical values which are transmitted up the Well to the surface and there converted into readings, the time delay between subsurface and surface data being negligible.

More specifically, a first carrier wave is generated in the well and frequency modulated in accordance with the stroke of the pump, and a second carrier wave is generated in the well and frequency modulated in accordance with the stresses developed in the pump rod. These two frequency modulated carrier Waves are transmitted to the surface over a coaxial line consisting of a pair of existing elements in the well,

such as the production tube and the sucker rod therewithin, or the well casing and the production tubing therewithin. The inner of whatever pair of elements is used is insulated from the outer element by insulating spacers distributed therealong.

At the surface, the two carrier waves are separated by two filter circuits, and separately detected to produce direct currents of magnitude varying in accordance with the frequency modulations but independent of any variation in amplitude resulting from attenuation during transmission. These direct currents are preferably fed into a recording oscillograph. It is desirable to simultaneously record along with subsurface data the stresses and motion at the surface end of the sucker rod, but since equipment for doing this is in existence and does not require the use of the present invention, it will not be described in detail.

A complete understanding of the invention may be had from the following detailed description, with reference to the drawings, in which:

Fig. 1 is a schematic diagram showing the general arrangement of apparatus in a system in accordance with the invention;

Fig. 2 isa vertical sectional view showing the portion of the apparatus of the invention that is located in the well;

Fig. 3 is a vertical sectional view showing a portion of the apparatus of Fig. 2 drawn to larger scale;

Fig. 4 is a schematic circuit diagram of the transmitter of the system;

Fig. 5 is a schematic diagram showing a modification of the apparatus of Fig. 1, utilizing the production tubing and the casing as a coaxial electrical transmission line;

Fig. 6 is a schematic diagram of the receiver circuit;

Fig. 7 is a set of curves illustrating the operation of the receiver circuit shown in Fig. 6; and

Fig. S is a graph illustrating the operation of the frequency discriminator in the circuit of Fig. 7.

Referring rst to Fig. 1, there is shown a well having the usual well casing lll extending from the surface of the bottom thereof. Positioned within the well casing ID is the usual production tubing l! having the usual pump barrel I2 at the lower end thereof. The pump barrel l2 contains the usual standing valve lil and a plunger i4 containing the usual traveling valve i5. The plunger lli is actuated by the usual pump rod i6 which is connected by a strain rod 33 (Fig. 2) to the usual sucker rod l'! that ex.. tends up through the production tubing to the surface and is connected at its upper end (within the production tubing) by a coupling I9 to the usual polished rod I8 which extends through a packing joint in the well head to any desired reciprocating mechanism, which in this instance is shown as a pumping beam 20, the polished rod being shown connected to the beam by a cable 2l 4-lowerendr of the, sucker rod`- llqis ;-.a;s.crew coupling .2B

enclosed Y'with insulatingi `material 39, 'i such as v.1"1bre; glass to electrically v insulate it,v fromthe housing top29. .-TheheadZ-'laeissecured-to. .the

. resilient dielectric member therebetween The condenser *plates'lI 35:- and-3'! a-rev pressed'together-byfa pair vof insulating blocks t {39; and 4E! positioned on :opposite sides thereof and having centralY apertures: slideably Mfitting Ithe strain rod 33. .Theflowerfinsulating block 39 I rests on a clarnpcll that -is rigidlyclampedA as `by .boltsr42- to the strain rod ,3.3. have, an annular groove Ain'its inner"periphery 3 With the exception of the strain rod 33, the apparatus so far described is in accordance with the usual practice. The present invention resides in the addition to the usual apparatus of equipment responsive to the motion and stresses at the s upper end of this pump rod to produce frequency modulation of alternating currents, and transmit them to the surface 'where they are' detectedin aA receiver m1 and recorded byan oscillograph 81.

Apparatus in the well The apparatus in the well is, in part, contained in a uid-tight housing 22 and-comprises-additional elements including a torque :tube23.,a-nd

4 Resting on the top of the upper insulating block 40 is a pressure plate 45 which has an upwardly extending, externally threaded, neck 45a which is screwed into the lower end of a sleeve 4S. The sleeve is locked to the strain rod by a split clamp 41 and a snap ring 48 which engages grooves in the strain rod and split clamp urespectively. The split. clam-p '41.'istted in a counterbore in the upperiendof thesleeve 46 and l is locked in place by a lock nut 49, to force the :sleeve 46 to move with the strain rod. The con- A,structiondescribed causes the insulating blocks *"39and40 tomove apart, in response to elongationsofathefstrai-n; rod 33, thereby permitting the a helix tube 24 positionedrbelow.tha-housing.22ifls'fresilienta dielectricz38 to separate the condenser and above the pump barrel I2, the'fhelix-.tube 2t being mounted on the pump barreljZ. For reasons which will appear later; the 'pump rodl must not rotate with respect to the pum-@barrel l2 and the helix tube ,24, and for that reason 2g itis preferably offnon-circular..,cross section A,(.hexagonali as shown in .thedrawings 'F.ig.2 )z `and passes througha similar, .non.circular. opening Yin Vthealpper end of. the pumfip.,barrel.

.platesfiSSiandBl,-1and forces the plates together, compressing. .thedielectric 33, when the strain rod contracts. "The condenser 25 constitutes one of .thezfrequency determining elements of an oscillating circuit of an electronic unit, which will be described later.

-nadditionto performing the mechanical fune- .tion-of. causing the vplates 5S and` 3l to. follow .the movements: offfthe blocks Stand t0, lthe.. re-

.As previously1 indicated, the 4readings to beI25.isilientdielectricfperforms the important y.funcwhich this condenser is mechanically .inserted ...in the system/,will .now Sbe described rwith reference t0 lFlies-,1, 2 and 3.

Referring. rstato. Figfl as there shown,` the to.; a couplingifmember 21 (Fig. 2) which-,consists-zofia head. 2.lc1,f on-the .lower t.endzoraxstem.4 2b.the .ppeeriend of'fwhich fl-stem fis; .threadednto .the coupling-1 2 6. Therhead tion of increasing thev capacity-betweentheplates 36 .and.3'. .Suitable rubberlike materials .having a dielectricconstantfef Aabout-5 areavailable. for .this luse.

For convenience v.-in illustration, ,-in` Fig. Zsthe electronic unit is indicatedas .located .within van .annular container- 5) withinthe housing. 22h-and the leads fromtheoondenser 25rare-shown entering .this container. v,.lictually, theelementsfof the connected byzz electronic unitcare, physically vdistributed within :the housingv 22because ofsthe -limitedspacetherewithin.

The. resilient` dielectric: 38 ot the;v condenser is preloadedvtda.desiredvaluefso that undertthe 21al is secured to the uppereend;membereZlso .in "greatest/.elongationof-ithez-strainrod-:SSthe di- Ithe; -housing.-f22. vThe-,sucker rod is used inrcombination- .with the Vproduction tubing; as. a. coaxial electrical transmission line, and is electrically 'insulated` from .the housing .22. To this end; the head 21a and lower -portien of the stern- 21baare housing top 29 by a screw vcapr32,whiclr1.is.thread- ;edonto.thetopfZQ. ,Inxthiseway the insulating. 1.)

material 3G has only to resist compressive'forces` The/housing. top- 29 has threadedinto its/lower tube 24.

andgisf secu-red;v to ,f

velectric 138" will' stilllfiaver an f expansive force :to separatethe condenserplates. mThis-.preloading adjustment is madeibylooseningft avleclr 'nut-:45h on the. stem a.. and rotating the .pressure` Plate L f 45.With:respect to. .thesleeve-146: until the desired .pressureis. obtained, afterwhich .the lock nut' 45h ...is tightened.

The stroke-measuring portion' of Vvthe appafratus-:will next bedescribed. .Thegstrokeizo an J `.Loilrwell pumpis relatively/ great; Y varying.,g.from 3 feet to 20 feet, and it is desirable torapplycrza lshortermovement. to the electrical pick-up unit l:which effects the modulationsof'.thezelectricur- .f rent. .This streke'reduction-is effected -byzmeans `-fof the .helix tube 24 :andythe torque tube?. 23 in -,-conjunction with a traveller 5 l y which isthreaded on the upperendvof the torque-tube 23. :As clearly shown :Figg v2,:'the helix tube '24"isfs`ecured tias-byfscrews 24av to al necliJZa onthe .upperi end .'Referringnow to-` Fguthe Condenser-25 COD- i ma of thepump barrel, and` extendsv upwardly Athere-- yshape lwhich-.are separated ironie-each otherv 'byi a 38- w-hichi is positioned .engagingfafsnap ring.44 `which isA alse-V engaged ginanzanularggroove inthe outer surface ofthe y...strain rod 33,; the .objectbeing tdx thelanip i -rodf lato thestrainrod, foi-increment therewith. H275 rod :3311s recprocatedr; the acamifollower 54am( lfrom. .The helix-tuba24:.containsxatcontinuous f helical; groove. formed Vin two.;:sections 152 and. 53. The vtwo sections'Y are of; ,differentzpitcm thetupper ysection-52 beingof: rela-tively? high pitch `whereas the f bottomz section;y 53 Viis yiofi: muchr lower fpitch. The ltorque tube 23v which extendsdown into'. the helixrtubelf: has a-cam.follow.er' 54,;in the'form ci a roller', which extends radially therefrominto .The clamp-tney fm, portedI on the strain rod-33 for vertical movement therewith but for .free frotation .therearound To this end, it is shown secured between "twc thrust. collars..5i-. and El :whichfarelocked'to1.thf .LstraincrodL any;,.desiredr.nianner. .As .theistrair the helical groove into which it extends force rotation of the torque tube. When the cam follower 54 is in the upper section 52 of the helical groove, the rotation of the torque tube in response to vertical movement of the strain rod is relatively small, whereas it is much more rapid during movement of the cam follower 54 through the groove 53 of lower pitch. The purpose of this will be described later.

The rotation of the torque tube 23 in response to vertical movement of the strain rod produces a lesser vertical movement of the traveller 5|, because the threads 23a on the torque tube 23 and the cooperating threads on the traveller 5| are of very low pitch as compared to that of the

grooves

52 and 53. The traveller 5| is restrained from rotation by tongues 5|a thereon which register with vertical grooves 60 in a downwardly extending skirt 22c on the housing 22.

The traveller 5| actuates the core or plunger 6| of a variable inductance element 62, and also a rod 66 that actuates a switch 64 for energizing and de-energizing the electronic unit.

The plunger 6| is fixed rigidly to the traveller 5| so that it is always moved thereby. However, the inductance element 62 is only utilized during that portion of the stroke of the strain rod corresponding to movement of the cam 54 in the high pitch groove 52. The switch 64, on the other hand, is intended to be actuated only in response to movement of the strain rod near its lower limit and below the normal lower limit of the stroke during a pumping operation. It is to insure sufcient movement of the traveller 5| to engage the head 65 on the lower end of the switch-actuating rod 66 in response to a relatively limited movement of the strain rod below the lowermost pumping stroke limit that the low pitch groove 53 is employed. This causes a relatively large downward movement of the traveller 5| after the cam 54 gets into the low pitch groove 53.

The push rod 66 for actuating the switch 64 extends through the end wall 22a of the housing 22 with a seal t, the seal being indicated at 61 in Fig. 3, since the interior of the housing 22 is maintained at atmospheric pressure and must be maintained dry because of the equipment it contains. The plunger 6| associated with the inductance element 62 is surrounded by a closedtop sleeve 69 of non-magnetic material which extends into the inductance element 62 and is fluid tight. Where this sleeve |59 extends through the -lower end wall 22a of the housing 22 it is sealed with a conventional seal 2217. The sleeve '69 is preferably of non-magnetic non-conductive material, such as plastic, its sole purpose being to provide for free motion of the plunger 6| into and out of the inductance winding 62 while preventing entrance of pressure fluid into the housing 22.

The switch 64 is of a common type which opens in response to one actuation and closes in response to the next actuation. Downward movement of the traveller 5| suicient to engage the head 65, withdraws the push rod 66 and permits the switch button 64a, to move outwardly by virtue of a spring within the switch 64. On the next upward movement of the traveller 5|, the push rod 66 is forced upwardly by the oil pressure in the production tubing and the switch is reset, i. e. if it was in open position before, it is closed, and if it was in closed position before, it is opened. The result is that the apparatus can be lowered into the well with the switch in open position, and the switch then actuated by rst lowering the sucker rod all the way until the cam 54 is in the lower end of the helical groove 53, and then lifting the sucker rod to carry the cam 54 upwardly through the cam section 53. In an actual apparatus in which the useful stroke of the pump is 10 feet, the distance travelled by the cam 54 while traversing the lower groove section 53 may be only 3 feet. However, because of the difference in pitch of the helical groove section 53 as compared to that of the groove section 52, the traveller 5| will move a sufiicient distance to insure positive actuation of the switch 64 despite the fact that the vertical movement of the strain rod 33 that is utilized to produce the switching action is relatively short as compared to the normal pumping stroke.

A plurality of brush elements 10 are preferably provided on the upper end of the helix tube 24 for ibearing against the production tube and insuring goed electric contact therewith to complete the electrical return circuit from the electronic equipment, since the production tubing is used as one element of the coaxial line over which the electrical currents are transmitted to the surface. A ywiper or brush 1| is also provided on the upper end of the neck i|2a of the pump to bear against the pump rod 6 and insure good electrical -contact therewith. The circuit from the electronic unit 55 to the production tubing may be trace-d in Fig. 2 from the electronic unit 56 to the strain rod by means of a bonding clamp 12, down the strain rod through the coupling 34 to the pump rod I6, from the pump rod i5 through the wiper 1| to the pump head |2a, thence through the helix tube 24, which is directly secured to the pump neck, and thence through the brush 10 to the production tubing Connection from the electronic unit 5|?k to the sucker rod may be traced over a conductor 14 to a slip ring 15 su-pported on an insulating Ipartition 15a, thence through a brush 16, whichl is insulated from the housing top 29 by an insulator 11, and thence -over an insulated conductor 18 to a projection 19 on the head 21, which in turn is connected through the coupler 26 to the sucker rod.

The conductor 'I6 is in fluid sealing relation with the housing top 29 so as to prevent the entry of pressure uid from the well into the housing `22.

Referring to Fig. 1, the sucker rod |1 which extends up through the well must be maintained in spaced relation with the yproduction tube to prevent i-t from being electrically shorted thereagainst. To this end, spacing and insulating elements of rubber or the like, are distributed along the sucker rod at suciently close intervals to insure against contact between the sucker rod and the production tubing.

At the -well head, the polished rod I8, which constitutes a Icontinuation of the sucker rod |1. passes through an insulating bushing 8| to maintain it insulated from the production tubing, and the upper end of the polished rod I8 is mechanically connected to the hanger cable 2| by an insulating connector 82.

In practice, it is highly desirable, in order to utilize the present invention to its fullest extent, to simultaneously record the stroke motion and stress in the sucker rod. at the surface, so that these values can be compared with the stroke and stress at the bottom of the well. To this end, the polished rod I8 would ordinarily be equipped with a strain gauge 84 of any known design, and a stroke-measuring device B5 would be connected to the polished rod, the Vde vicesnild l.and .85 .being shown connected to the recording vges cillograph i|31 into .which :the readings lfrom the ibottom `of V'the :well :are also fed, Vlso `.that all :four .readings lcan be `recorded :simultaneously with respect ato time. As previously sindicatedthe stroke at the bot- :tom vof the rwell is converted 'into an electrical value by means of the variable inductance 62 having vthe movable plunger A6| Amoving in -synchronism with .and proportional yto the pump plunger. This causes the ,inductance of :the element 62 to vary 5in accordance with the move- :ment of the pump rod. It has also Ibeen pointed .out that the stress applied :to v'the lpump rod in -the-:well is measured :by the variations in capacity of the condenser 25 shown in Fig. y3, the capacity varying vin Aaccordance with Vthe stretch of the strain-rod 33 :between the rings -4'4 and 5.48.

.Referring now toFig. 4, which indicates schematically the circuit .of the electronic equipment located inthe well and Apreviously .identifiedwith the container 50, the condenser 25 is shown .con- .nected to an inductance `element 90 and forming therewith the .frequency determining circuit of an oscillator tube 9|. stabilizing capacitors 02 and '93 are connected between the cathode and anode, vand between the cathode and control grid of the -tube 9| to stabilize its operation, and a blocking Icondenser 94 is connected ,between the .cathode ,and the center tap ofthe inductance 90. The oscillator 9| oscillates continuously whenever it is .energized fby closure of the switch 64 to the filament ,energizing battery .95. The anode of vtube 8| is coupled thro-ugh a condenser 91 to the control grid Vof an amplifier v.tube A08, the

anode of which is coupled .by ian .output transformer 9? to :the coaxial line consisting of the .sucker rod and vthe production tubing for transmission to the surface.

The inductance element -62 having the Ymovable 'core 16| constitutes', with a'pair of-condensers |00 and the Afrequency controlling circuit of a .second oscillator tube |02, the anode of which is coupled through a coupling condenser |03 with v.the grid .of an amplifier tube |04, the anode .of which is connected, in :parallel with the anode of ltube t8, to the output 'transformer 99.

`I 'find it desirable in practice to so 'choose the constants of 'the circuit associated 'with vthe tube 8| that its :normal oscillating frequency is about 50 and Aso choose Vthe constants of .the ,frefquency determining circuit of the -ftube |02 that its fnorrnal operating frequency is .about 10 kc., Athese two frequencies being transmitted simultaneously up .the well to the surface. The variations in -capacity of the condenser l25 Vproduced by 1variations in stress applied to the pump plunger produce a total frequency variationvof about 2 kc. Likewise, the variations in the inductance of the inductance elements y52 .produced by movement of the plunger 6| in response to the stroke movevment of the pump plunger produce a frequency variation of about 2 kc.

At the surface, the Atwo frequency-modulated waves transmitted over the :coaxial line consisting of the sucker rod and production tubing are applied over conductors and |06 to the receiver |01 where A'they are separately detected and applied to the recording oscillograph to produce curves showing the stress in, and the stroke of, the .pump rod.

The characteristic, or surge, impedance of a coaxial line consisting of the production tubing and Ysucker rod of' a well, is yabout 50 ohms, and theoutputtransformer 991matches the relative ly high .impedance :of the tubes 9.8 and |10L4rtoathe relatively low impedance of ,the line.

Receiver at the surface Referring to Fig. 6, the composite signal .received .from the bottom of the well is applied to Athe Iinput terminals A of the receiver |91. A graphical representation .of the composite wave form is shown by curve A in Fig. '7. The 'composite wave A is applied to Vtwo band pass amplifiers Y| il? and Hua. The band pass .amplifier |10 will pass only the low frequency component which may vary in frequency from 8 .to 10 kc. The other band pass amplifier v|.| 8a vwill pass only the .high frequency component that may vary in frequency from 47 to 49 kc. At points B and :Ba the resultant separated waves are shown .in curves Band Ba. In practice, Ithe waves are approximately sinusoidal andthe wave B is .shown as increasing in frequency with time, whereas the wave Ba is shown as decreasing in frequency with time. From amplifier l0, the varying frequency wave B is passed into a converter whose .1ocal oscillator frequency is so chosen as to produce a 200 cycle per second beat Ynote at the lowest frcquency (8 kc.) to be used. The converter also contains a low pass filter to enable a frequency varying from 200 cycles per second to 2200 cycles per second to be passed with negligible attenuation. The wave at point C is approximately sinusoidal, varying in .frequency from 20,0 to.2200 cycles per second, depending upon the ,frequency of the received signal, and Visillustrated by curve C in Fig. l which is, along with the other curves, exaggerated to illustrate the point. Wave VC is fed into a clipper |3| consisting of Ya Ycondenser |15 in series with resistors 3 and l5 and a tube i i2 the control grid of which vis .connected tothe juncture of resistors 4H3 and I5. .On positive excursions, the grid draws current, producing a voltage drop across resistor |13 that limits its .potential and clips the positive .half waves. On negative excursions, the grid Vpotential is swung past the cut-off point of the tube, so that the wave at point D is substantially square topped, .and of constant amplitude as illustrated by curve D in Fig. '7. The condenser I4 is of such size as to -pass all frequencies within vthe band 20G-,2200 cycles with negligible distortion. A load ^resistor H5 in the anode circuit of the tube ||2 is chosen Irelatively large to accentuate the clipping action.

The square-'topped pulses of curve D- vary in width inversely with the frequency. They are shaped into pulses of constantwidth independent of the frequency by differentiating the wave form of curve D in a differentiating network |32, `and shaping it in a shaping amplier stage |33.

The differentiating network |32 comprises a condenser ||1 in series with a resistor H8, the junction of which is connected to the control grid of a vacuum tube ||9 in the shaping ampliiier stage |33. The time constant of the RC circuit consisting of the condenser lil and the resistor I8 is small compared to the time duration ofthe shortest pulses (curve D) applied thereto. The potential developed at the juncture of the condenser and the resistor |38 is represented by curve E of Fig. '7. It will be observed that this curve consists of a train of alternately positive and negative pips, the amplitude of which is llarge as compared to the positive and negative ypotentials required to drive the tube H9. Thus, as shown by the dotted lines in curve E, the positive pips drive the tube ||9 Well beyond saturation, thereby causing severe clipping in the-'plate circuit. The negative pips drive the tube He well beyond the cut-01T level of the tube, resulting in severe clipping of the negative pips. The resultant wave in the output circuit of the tube |9 is shaped as shown in curve F which consists of a train of pulses of constant amplitude and constant width, regardless of variations in the frequency, the latter simply affecting the dis tance between successive pips. In curve F the positive pips are of greater magnitude than the negative pips because of the aero bias point se lected for the grid of vacuum tube H9 to operate about. However, as will appeai` later, the relative magnitudes of the positive and negative pips is immaterial, only the positive pips producing an effect on the final current.

The anode load resistor |2'Ll of tube ||9 is of such size as to accentuate the steep sides of the pulses.

The output of the Shaper ampli'ler stage |33 at point F is coupled to the input of a power-aniplifying frequency discriminating and rectifying stage |313, which produces a direct current the amplitude of which varies with the frequency oi? recurrence of the positive pips in curve F. Stage |311 includes vacuum tube |2| having its anode connected directly to the B supply, and having an output inductance element i2-t in its cathode circuit, so that it functions as a cathode follower. The control grid of the tube i2| is connected to the juncture of a series connected condenser |23 and resistor |22 to which the pips of curve F are applied from the preceding stage i. The conh denser |23 and resistor |22 are of such value as to provide grid leak bias of the grid of tube |2| by virtue of rectied grid current. The output inductance element |2 is shunted by a rectier |40 so poled as to bypass negative impulses from the cathode of tube |2| past the inductaiice element |24. On the other hand, positive pulses applied from the cathode to the upper end of the inductance element Zii are conducted through a rectifier I4! to a lter consisting of a series inductance element |26, a shunt condenser l2?, a series resistor |28, and a potentiometer |29. The

movable contact of the potentiometer 29 is connected to one output terminal, and the lower end of the potentiometer |29 is connected by a biasing battery |30 to the other output terminal.

The action of stage |34 will be explained with reference to the diagram of Fig. 8 which shows a curve |43 representing the variation of cathode current in the tube |2| with variations in grid voltage, the latter being plotted horizontally, and the cathode current vertically. The pips of curve F are applied to the grid of the tube, and

a train of such pips is shown as including positive pips |44 and |45 equally spaced apart, and pips |46, |41, |48, |49, |50, and |52 spaced progressively closer together. Corresponding intervening negative pips are identified by the same reference numerals with the sux As has been previously explained, all of the pips applied to thestage |34 are of equal magnitude, but differ only in their spacing. Each positive pip applied to the grid of tube |2| causes the latter to draw current and charge the condenser l23, thereby applying a negative bias to the grid. This negative bias gradually leaks oil` through the resistor |22, but so long as the positive pips applied to the tube are equally spaced apart, the average bias of the grid will remain constant. However, if the pips come at closer intervals, the negative bias on the grid will increase, and its value will be a measure of the frequency of recurrence of the pips. Thus, referring to Fig. 8, let it be assumed that the pips |44 and |45 are uniformly spaced apart the same as the preceding pips, and that this spacing Was such as to produce a grid bias represented by the upper end portion or the dotted line lii. 'l'he positive pip |44 will drive the tube beyond saturation, and produce a current pip lesb in the cathode circuit or the tube izi. 'i he succeeding negative pip iena applied to the grid or the tube reduces the conductance o1 the tube and produces a negative cui-rent pip mac in the cathode circuit. 'lne positive and negative pips in the output circuit oi the tube remain constant so long as successive pips applied to the input circuit are unlioinily spaced. However, it will be noticed that the positive pip me in rig. 8 ioliows the pip ma more closely than the latter followed pip m4, this indicating an increase in frequency oi the original Wave. iecause or' the reduced lapse of time, less oi' the charge imposed on the condenser |23 can leal: oir between pulses, and the grid bias as represented by the dotted line itu in r'ig. increases to a more negative value. The result is that the positive current pip mail; in the output circuit starts ironi a lower base and is therefore larger. pips become shorter, but this is or no moment because the negative pips are blocked by the iectinei Isl and snorted across inductance |213 by rectifier I and do not appear in the iinal output.

ln Fig. 8 the pips from |46 to |52 inclusive recur at increasingly more frequent intervals, so that the potential on the grid of tube |2i becomes progressively more negative, as shown by line |60, the output positive current pips become progressively larger, and the unused negative pips become progressively smaller.

Referring to curve G of Fig. 7 which shows the potential developed across the inductance element |24, it will be observed that the pulses (positive) developed across this inductance element in response to the positive pulses applied to the grid not only recur at shorter intervals with increasing frequency, but are also of increasing magnitude. When integrated by the filter, consisting of the elements |26, |27 and |28, they become a direct current of increasing magnitude as shown in curve H.

The circuit associated with the tube i2| has several unique characteristics. In the rst place. whereas it is customary to employ a resistor as the output impedance element of a cathode follower pulse counter, the present circuit employs the inductance element the latter. It is therefore of the circuit.

The rectifier an essential element |40 is desirable because it pre- '.L'he corresponding negative Vproviding the biasing The biasing battery makes possible the delivery to the output terminals of a direct current varying strictly inV accordanoewith thefrequency variations` received. It has been previously indicated that the lowest frequency employed is 200 cycles per second, and this would represent a zero value of data transmitted. Since a frequency of 200 cycles per second would produce a current in the output circuit of the filter stage |34, there wouldl be no. null reading., By

battery ISI)l and theV adjustable potentiometer, the output potential ap.- plied to the oscillograph can be adjusted, tozero when the minimum frequency of 200 cycles per second is applied.

The time constant of the CR circuitconsisting o f thev condenser |23 and the resistor |22 isA large compared to the time interval betweenthe pulses applied thereto at the minimum frequency of 200 cycles per second, but it must notA be solarge as to damp out the most rapid `frequency Variations that may occur. For the telemetering function described, the circuit must pass a maximum pulse recurrence rate of 50 cycles per second.

The lower channel inKFig. 6.V beyond the fre-l quency convertingY unit I I Iav is identical withthe upper channel, the correspondingelenients being represented by blocks bearingY the same refer# ence numerals with the suffix a. In Fig. '7 the curves C@ to Ha are shown asdecreasingV in fre#Y quency instead of increasing. YOtherwise/they are similar to curves C to H. yThey would be the same as curves C to I-I if similar frequency modulations were applied to both the 1'0 kc. and the 50 kc. carriers in the well. Actually they 'would never be the same because the curve H repre'-l sents the position of the pump plunger, whereas the curve Ha represents the stress'in the pump rod. i

The output currents of the units |34 and |34a may be applied to two elements of the recording oscillograph 87 of Fig. I, and theoutputs of the surface stroke measuring device and the'surface stress measuring device 84 may be applied to the other two elements so that four curves may be recorded simultaneously to show the relation between the stroke and stresses of the sucker rod at the top and bottom respectively.

The method of transmitting signal currents through a well over a coaxial line constituted by existing elements in the well is not limited to the particular arrangement of Fig. 1, in which the sucker rod is the inner conductor andthe production tubing is the outer conductor. Any pair of concentric elements that can be insulated from each other can be used. Thus one alternative arrangement using the production tubing as the inner conductor and the well casing as the outer conductor is illustrated in Fig. 5.

In Fig. 5 there is shown schematically a well having a casing |10, and production tubingl |1-I, within the casing. At the lower end of the production tubing is a pump |12 having the usual sucker rod |13 extending therefrom up through the production tubing, and supported by anv insulating coupling |14 on an anchor |15 which engages the casing. A signal-current generating unit |16 is shown mounted on the pump and electrically connected by a lead |11 to the casing, and by a lead |18 to the pump, which is in turn directly connected to the production tubing. 'I'o prevent short-circuiting of the production tubing against the casing, insulating rings or collars |19 are mounted on the production tubing |1| at intervals therealong. At the surface, the casing head through which the production tubing extends is insulated from the casing |10 by an insulating bushing |8I, the production tubing is insulated from the lovl line I by an insulating coupling |83, and the polished rod |84 is in-v sulated from the lifting cable |85 by an insulating connector |36. Leads |81 and |88 from the cas.- ing |10 and the casing head |80 serve to complete electrical connection from the upper end of the coaxial line to receiving apparatus (not shown).

The transmitter |15 may generate frequency modulated currents representing any data to be transmitted, such as the pressure or temperature in the Well.

In Fig. 5 the sucker rod is not insulated from the production tubing, and it forms a part of the inner conductor of the coaxial line. The arrangement has the advantage over that of Fig. l in that there is no pumping motion between the insulators |18 and the casing |11! as there is between the sucker rod insulators 8S) and the production tubing II in Fig. l. On the other hand, with the particular telemetering transmitting system disclosed in Figs. 2 and 3 in which the electrical equipment is mounted on the sucker rod for movement therewith, it is simpler to use the sucker rod and production tubing as the coaxial line than to use the production tubing and casing.

The transmission losses, or attenuation, of a coaxial line defined by existing well elements,y examples of which are shown in Figs. l and 5, will vary according to the nature of the fluid between the inner and outer conductors and by variations from concentricity of the inner con# ductor with respect to the outer conductor, but such variations will no't aect the accuracy of the system described in which the output ofthe receiver is dependent only on frequency modulations andA is independent ofthe amplitude ofthe waves received at the'surface.

Although for the purpose of explaining the invention, a particular embodiment thereof has been shown and described, obvious modifications will occur to a person skilled in the art, and I- do not desire tobe limited to the exact details shown and described.

I claim:

1. In combination withra Well containing a pair of continuous metallic Velements extending therethrough, one at leastof which is hollow andthe other of which extends through the hollow element: aplurality of annular insulating elements between said elements spaced atintervals therealong for spacingsaid other element in ,appoxifmately coaxial relation to said one elementand forming` therewith a coaxial electrical trans-94.15. sion line; insulating means for. electricallyv isolating the end portions of said' other element from said one element; electrical means conf nected to said elements at one end fcrapplying alternating signal current tl'iereto,y and electrical means connected to said elements at the other end for receiving said signallingvcurrent therefrom.

2. In combination with a Well containing a pump connected to the surface by production tubing and a sucker rod Within the tubing for actuating the pump: insulating blocks attached at spaced intervals to said sucker rod to center and insulate it with respect to said tubing, means insulatingly connecting said sucker rod to said pump; test means in said Well electrically connected to said sucker rod and tubing for producing an alternating current modulated in accordance with test data to be transmittted to the surface; and receiving means electrically connected to said sucker rod and tubing at the surface end of the Well.

DONALD W. BLANCHER.

References Cited in the le of this patent Number UNITED STATES PATENTS