US2677272A - Stress indicating apparatus - Google Patents

Description

May 4, 1954 D. w. BLANCHER STRESS I NDICATING APPARATUS 2 Sheets-Sheet 1 Original Filed Jan. 23, 1950 4 ELF. RECORDING OSCILLOGRAPH RECEIVER INSULATION INVENTOR D. W Blancher A TORNEY D a a. 0 6544 7 6 5 WWW. a %Mw4266 56 6 w H w M a 6 2 a a :hmr i..: q I 3 2 M a. a. Q. a. a 0 4. 4 4 3 iawwwflm/ fim flwwflw w w 6 2 5 35M Mum May 4, 1954 D. w. BLANCHER STRESS INDICATING APPARATUS 2 Sheets-Sheet 2 Original Filed Jan. 23, 1950 u NW hm R 4m QR INVENTOR D. 14 5/0/7C/76l" ATTORNEY 1 lllllllllllllllllllll L nm+H I Q0: muxODw OP QZ m O 20:250.! Ch

Patented May 4, 1954 UNITED STATES PATENT QFFICE signor to Bendix Aviation Corporation, South Bend lea co po of B ar Original application January 23, 1950, Serial No. 140,128. Divided and this application March 19, 1951, Serial-N0. 216,430

2tC laims. 1

This invention relates broadly to .the artof telemetering and specifically, in part, .to thetelemetering up a well bore ofdata 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,.usua1ly oil wells,.are commonly reciprocated by a sucker .rod extending up through the well to a pumping jack at the surface. ln deep wells the long sucker rod has considerable stretch .and distributed inertia. Because of this, its motion at the pump .endmay be radically different from that imparted to it at the upper end, and may be quite unpredictable, particularly at high pumping speeds. It isdesirable 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.

Anotherobjectis to provide asimple andeffective apparatus for translating thestress .applied -to a pump plungerin a well into anelectricalvalue that'can be transmitted to thesurface.

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

This is a division ofmy application Serial No. 140,128 filed January 23, 1950 for Telemetering System for Wells, now-Patent 2,596,361, to which reference is made.

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 thewell to the surface and there converted into readings, the-time delay between subsurface and surface data being negligible.

-More specifically, a first carrier waveisgenerated in the Welland frequency modulated .in accordance with the stroke of the pump, and

a second carrier wave is generated in the well outer element by insulating spacers distributed therealong.

At the surface, the two carrier waves areseparated by two filter circuits, and separately detected to producedirect currents of magn varying in accordance \withthe frequency nodulations butindependent of any variation inarnplitude 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 stressesand motion at the surfaceend of the sucker rod, butsinceequipment for doing this is in existence and not require the use of the present invention, it will not be described indetail.

A complete understanding of the invention may be had from the f oll owill detailed description, with reference to thedrawingi ,in which:

Fig. 1 is a schematic diagram showing the general arrangementof apparatus in asystem in accordance with the invention;

Fig. .2 is a 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; and

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

Referring first to ,Fig. 1, there is shown awell having the usual well casing It extendingfrom the surface to the bottom thereof. Positioned within the Well casing It is the usual production tubing I! having the usual pump barrel 5 l2 at the lower end thereof. The pumpbarrel .52 contains the .usual standing valve 13 and a plunger licontainingthe usual traveling valve 45. The plunger i4 is actuated by the usual pump rod 16 whichis connected by a strain rod 33 (Fig. 2) to the usual sucker rod ll that cg;- tends up through the production tubing to the surface and is connected, at its upper end (within theproduction tubing) by a coupling 19 to the usual polished rod 18 which extends through a packing joint in the well headto any desired reciprocating mechanismwhich in this instance is shown asa pumpingbeam 29, the polished rod being shown connected to the beam ,by,a cable 2!.

-With the exception of the strain rod 33, the apparatus soiar described is in accordance with the usual practice. The present invention resides in the addition to the usual apparatus pf equipment responsive to-the motion and stresses at the pump rod to produce frequency modulation of alternating currents, and transmit them to thesurface where they aredetectedin auii 3 ceiver ml and recorded by an oscillograph 81.

The apparatus in the well is, in part, contained in a fluid-tight housing 22 and comprises additional elements including a torque tube 23 and a helix tube 23 positioned below the housing 22 and above the pump barrel I2, the helix tube 2 being mounted on the pump barrel [2. For reasons which will appear later, the pump rcd it must not rotate with respect to the pump barrel [2 and the helix tube 24, and for that reason it is preferably of non-circular cross section (hexagonal as shown in the drawing, Fig. 2) and passes through a similar non-circular opening in the upper end of the pump barrel.

As previously indicated, the readings to be transmitted to the surface are the stroke and the stress at the pump rod 16. The stress is measured by means of a condenser 25 (Figs. 2 and 3) the capacitance of which varies with stretch in a short section of the strain rod The way in which this condenser 25 is mechanically inserted in the system will now be described with reference to Figs. 1, 2 and 3.

Referring first to Fig. l, as there shown, the lower end of the sucker rod ii is connected by a screw coupling 26 to a coupling member 2l' (Fig. 2) which consists of a head 21a on the lower end of a stem 27b, the upper end of which stem is threaded into the coupling 2 The head 27a is secured to the upper end member 29 of the housing 22. The sucker rod is used in combination with the production tubing as a coaxial electrical transmission line, and is electrically insulated from the housing 22. To this end, the head 2la and lower portion of the stem 21b are enclosed with insulating material 30, such as fibre glass, to electrically insulate it from the hous ing top 29. The head 21a is secured to the housing top 23 by a screw cap 32 which is threaded onto the top 29. In this way the insulating inaterial has only to resist compressive forces.

The housing top 29 has threaded into its lower end the upper end of the strain rod 33 which extends down through the housing 22, and through the torque tube 23, and is secured to the upper end of the pump rod [6 by a coupling 34 which also functions as a centering device for centering the strain rod with respect to the helix tube 24.

Referring now to Fig. 3, the condenser 25 consists of a pair of plates 36 and 31 of flat annular shape which are separated from each other by a resilient dielectric member 38 which is positioned therebetween. The condenser plates 36 and 3'! are pressed together by a pair of insulating blocks 39 and 49 positioned on opposite sides thereof and having central apertures slideably fitting the strain rod 33. The lower insulating block 39 rests on a clamp 4| that is rigidly clamped as by bolts 42 to the strain rod 33. The clamp may have an annular groove in its inner periphery engaging a snap ring 44 which is also engaged in an annular groove in the outer surface of the strain rod 33, the object being to fix the clamp rod 4'5 to the strain rod for movement therewith. 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 sleeve 45 to move with the strain rod. The corn struction described causes the insulating blocks 33 and E0 to move apart, in response to elongation of the strain rod 33, thereby permitting the resilient dielectric 38 to separate the condenser plates 38 and 37, and forces the plates together, compressing the dielectric 38, when the strain rod contracts. The condenser 25 constitutes one of the frequency determining elements of an oscillating circuit of an electronic unit, which will be described later.

In addition to performing the mechanical function of causing the plates 35 and 31 to follow the movements of the blocks 39 and 43, the resilient dielectric 38 performs the important function of increasing the capacity betwee the plates 36 and 31. Suitable rubber-like materials having a dielectric constant or" about 5 are available for this use.

For convenience in illustration, in Fig. 2 the electronic unit is indicated as located within an annular container 50 within the housing 22, and the leads from the condenser 25 are shown entering this container. Actually, the elements of the electronic unit are physically distributed within the housing 22 because of the limited space therewithin.

The resilient dielectric 38 of the condenser 25 is preloaded to a desired value so that under the greatest elongation of the strain rod 33, the dielectric 38 will still have an expansive force to separate the condenser plates. This preloading adjustment is made by loosening a lock nut 45b on the stem 45a and rotating the pressure plate 55 with respect to the sleeve 46 until the desired pressure is obtained, after which the lock nut 45b is tightened.

The stroke-measuring portion of th apparatus will next be described. The stroke of an oil well pump is relatively great, varying from 3 feet to 20 feet, and it is desirable to apply a shorter movement to the electrical pick-up unit which efiects the modulation of the electric current. This stroke reduction is eifected by means of the helix tube 24 and the torque tube 23 in conjunction with a traveller 5! which is threaded on the upper end of the torque tube 23. As clearly shown in Fig. 2, the helix tube 24 is secured as by screws 24a to a neck l2a on the upper end of the pump barrel, and extends upwardly therefrom. The helix tube 24 contains a continuous helical groove formed in two sections 52 and 53. The two sections are of different pitch, the upper section 52 being of relatively high pitch whereas the bottom section 53 is of much lower pitch. The torqu tube 23 which extends down into the helix tube 24 has a cam follower 54, in the form of a roller, which extends radially therefrom into the helical groove. The torque tube 23 is supported on the strain rod 33 for vertical movement therewith but for free rotation therearound. To this end, it is shown secured between two thrust collars 5'5 and 51 which are locked to the strain rod in any desired manner. As the strain rod 33 is reciprocated, the cam follower 54 and the helical groove into which it extends force rotation of the torque tube. When the cam follower 5 2 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 en rave to'vertical movement of the strain rod produces a lesser vertical movement of thetraveller 551., because the threads 23a on the torque .tube '23 andthe cooperating threads on the traveller 5| are of very low pitch ascompared to that of the groovesfiii and E3. The traveller 5| is restrained from rotation by tongues 5m thereon which register with vertical grooves (iii in a downwardly extending skirt 220 on the housing v22.

The traveller 5i actuates the .core or plunger 610i a variable inductance element 62, and also asrod 5t; thatactuates a switch 64 for energizing and .de-energizing the electronic .unit.

The plunger ti is fixed rigidly to the traveller 5| so that it is always moved thereby. However, the inductance element 62 is only utilizedduring that'portion of the stroke of the strain rod corresponding to movement of the cam 54 in the high pitch groove 52. The switch 84, on the other hand, .is intended to be actuated only in response tomovement 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 sufficient movement of the traveller 5| to engage the head 65 on the lower end of the switchactuating rod 66 in response to a relatively limited movement of the strain rod below the lowermost pumping strok limit that the low pitch groove. 53 is employed. This causes a relatively large down- .wardmovement of the traveller 5! after the cam {i l-gets into the low pitch groove 53.

The push rod St for actuating the switch 64 extends through the end wall 22a of the housing 22 zwitha seal fit, the seal being indicated at E7 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 closed top sleeve 69 of non-rnagnetic material which extends into the inductance element t2 and is fluid tight. Where this sleeve 69 extends through the lowerend wall 22a of the housing 22 it is sealed with a conventional seal 22b. The sleeve .69 is preferably of non-magnetic non-conductive material, such as plastic, its sole purpose being to provide for free motion or" the plunger 6! into and out of theinductance windingtZ while preventing entrance of pressure fluid into the housing 22.

Th switch 5% is of a common type which opens in response to one actuation and closes in response to the next actuation. Downward move- .ment of the traveller 5! sufficient to engage the head 65, withdraws the push rod 66 and permits the switch button Bid to move outwardly by virtue of a. spring within the switch 6 1. On the next upward movement of the traveller 5!, the push rod 56 is forced upwardly by the oil pressure in the production tubing ii andthe 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 first lowering the sucker rod all the way until the cam 55 is in the lower end of the helical groove 53, and then lifting the sucker rod to carry the cam 56 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 difierence in pitch of the helical groove section 53 as compared to that of the groove section 52, the traveller 5| will move a sufficient 6 distance to insure positiveactuation of the switch ii ldespite 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 .theznormal pumping stroke.

.A plurality of brush elements it are preferably providedon the upper end of the helix tube. for bearing against the production tube ll and insuring good electric contact-therewith to .complete the electrical return circuit from the electronic :equipment, since the production tubing isused as one element of the coaxial line ,over which the electrical currents. are transmitted to the-surface. .A wiper or brush H .is also .provided on the upper end of ithe'neck 12a .ofthe pump to :bear against the pump rod is andinsure .goodlelectrical contact therewith. The :circuit from the electronic unit 59 to the production tubing H may be traced in Fig.2 from1the electronicunitueil to the strain red by means of a bondingclamp i2, downthe strain .rod through the coupling 3:3 to the pump rod It, fromn-the pump rod isthroug-h the wiper ii to the pump head li2a thence throughthe helix tube, E i, which is directly secured-to th pump neck, andthence throughthe brush it tot-he production tubing LL Connection from the electronic unit 5%] to the sucker :rod may be traced over .a conductor 14 to a slip rin iii supported on an insulatingpartition -lira,thence througha brush it, which is insulated from the housing top 29 by aninsul-ator .11, and thence over an insulated conductor 18 to a projection id on the head 2?, which turn is connected throughthecoupler Ziito the sucker rod.

The conductor fit; is in fluid sealingrelation with the housing top 29 soas to prevent theentry of pressure fluid from the well into the housing :22.

Referring to Fig. 1, the sucker rod I! which extendsu-p through the Well must be maintainedin spaced relation with the production tube H .to prevent it from being electrically .shorted thereagain. To this end, spacing and insulating elementsilil of rubber or the like, are distributed along the sucker rod at sufficiently 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 continuation of the sucker red I], passes through an insulating bushing 3 l to maintain it insulated from the production tubing, and the upper end of the polished rod iflis mechanically-connected to the hanger cable M by an insulatingconnector 82.

Inpractice, it is highly desirable, in order to utilize the-present invention to its fullest, extent, to:simultaneously recordthe 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 It would ordinarily be equipped with a strain gauge 8d of any known design, and a stroke-measuring device as would be connected to the polished rod, the devices 84 and 85 being shown connected to the recording oscillograph 81 into which the readings from the bottom of the well ar also fed, so that all four readings can be recorded simultaneously with respect to time.

As previously indicated, the stroke at the bottom of the Well is converted into an electrical value by means of the variable inductance 62 having the movable plunger 61 moving in synchronism with and proportional to the pump plunger. Thi causes the inductance of the element; 62 to vary in accordance with the movement of the pump rod. It has also been pointed out that the stress applied to the pump rod in the well is measured by the variations in capacity of the condenser 25 shown in Fig. 3, the capacity varying in accordance with the stretch of the strain rod 33 between the rings 44 and 48.

Referring now to Fig. 4, which indicates schematically the circuit of the electronic equipment located in the well and previously identified with the container 50, the condenser 25 is shown connected to an inductance element 90 and forming therewith the frequency determining circuit of an oscillator tube 9|. Stabilizing capacitors 92 and 93 are connected between the cathode and anode, and between the cathode and control grid of the tube 91 to stabilize its operation, and a blocking condenser s4 is connected between the cathode and the center tap of the inductance S0. The oscillator 55 oscillates continuously whenever it is energized by closure of the switch 64 to the filament energizing battery 95. The anode of tube BI is coupled through a condenser 97 to the control grid of an amplifier tube 98, the anode of which is coupled by an output transformer 99 to the coaxial line consisting of the sucker rod and the production tubing for transmission to the surface.

The inductance element 52 having the movable core Bl constitutes, with a pair of condensers I96 and IE1, the frequency controlling circuit of a second oscillator tube I02, the anode of which is coupled through a coupling condenser 103 with the grid of an amplifier tube [G4, the anode of which is connected, in parallel with the anode of tube 98, to. the output transformer 99.

I find it desirable in practice to so choose the constants of the circuit associated with the tube 9| that its normal oscillating frequency is about 50 kc. and so choose the constants of the frequency determining circuit of the tube 82 that its normal operating frequency is about kc., these two frequencies being transmitted simultaneously up the well to the surface. The variations in capacity of the condenser produced by variations in stress applied to the pump plunger produce a total frequency variation of about 2 kc. Likewise, the variations in the inductance of the inductance elements 52 produced by movement of the plunger 6! in response to the stroke movement of the pump plunger produce a frequency variation of about 2 kc.

At the surface, the two frequency-modulated waves transmitted over the coaxial line consisting of the sucker rod and production tubing are applied over conductors i s and [06 to the receiver l0! where 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 sucker rod of a well, is about 50 ohms, and the output transformer 99 matches the relatively high impedance of the tubes 98 and I84 to the relatively low impedance of the line.

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 to be limited to the exact details shown and described.

I claim:

1. Apparatus for measuring variations in strain in a rod comprising: a condenser having annular electrically conductive plates encompassing and normal to said rod and having a yieldable dielectric interposed between said plates, at least one of said annular plates being oi larger internal diameter t said red and spaced therefrom; a pair of pressure members on opposite sides of said plates for variably compressing dielectric and thereby varying the capacity of the condenser; means for securing said respective pressure members rigidly to said rod at spaced points thereon; at least that pressure member adjacent said one plate comprising a rigid insulating element interposed between one plate and said rod and electrically insulating them from each other; and means for indicating variations in capacity of said condenser, said yieldable dielectric having a high dielectric constant and having negligible resistance to compression relative to that of said rod.

2. Apparatus according to claim 1 including: means locking one of said pressure members directly to said rod for movement with the portion of the rod it encompasses, the other pressure member being slideable on said rod, and means mechanically connecting said other pressure member to said rod at a point longitudinally displaced from said first member a distance greater than the spacing between said members.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,183,078 Kemler Dec. 12, 1939 2,368,278 Warshaw Jan. 30, 1945 2,409,876 Martin et al Oct. 22, 1946 2,422,806 Silverman et al. June 24, 1947 2,476,410 Gardiner July 19, 1949 2,564,784 Jones Aug. 21, 1951 FOREIGN PATENTS Number Country Date 343,162 Italy Sept, 16, 1936

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