Well Monitoring Apparatus

Abstract

Method and apparatus for monitoring the operation of a well which is produced by a beam pumping unit. A load transducer is secured to the surface support structure of the beam pumping unit such that it generates a signal representative of load changes in the support structure as the walking beam is reciprocated. The transducer may take the form of an elongated bar which is secured to the support structure by longitudinally spaced rigid connections. The transducer bar as disclosed is mounted on the top of the walking beam.

Description

BACKGROUND OF THE INVENTION

This invention relates to the production of wells by means of beam pumping units and more particularly to processes and systems for monitoring the operation of wells produced by beam pumping units.

Beam pumping units are widely used in the petroleum industry in order to recover fluids from wells extending into subterranean formations. Such units are employed to reciprocate a sucker rod string which extends into the well to actuate a downhole pump. The sucker rod string is suspended at the surface of the well from a support structure which consists of a sampson post and a walking beam pivotallly mounted on the sampson post. The sucker rod string is connected to one end of the walking beam. The other end of the walking beam is connected to a prime mover through a suitable crank and pitman connection. Thus, the walking beam and the sucker rod string are driven in a reciprocal mode by the prime mover.

In order to analyze the performance of a well produced by means of a beam pumping unit, it is a conventional practice to measure the load on the rod string as the unit is in operation. Such load measurements normally are taken by means of a dynamometer which is attached to the sucker rod string (normally in the "polished rod" section thereof) to monitor variations in the stress in the sucker rod string. The output from the dynamometer may be recorded for future analysis or it may be used for realtime control of the pumping unit. For example, U.S. Pat. No. 3,359,791 to Pantages discloses a dynamometer which is mounted on the polished rod and which functions to generate an alarm or to initiate a control action such as shut down of the prime mover in response to abnormally high or low loads on the polished rod. Similar control measures can be taken through the action of a central control facility. For example, as described by Boggus, C. C., "Let's Weigh Those Wells Automatically," OIL AND GAS JOURNAL, Vol. 62, No. 5, Feb. 3, 1964, p. 78, the output from a large number of pump dynamometers can be applied to a central computer which is programmed to take appropriate control actions.

While sucker rod dynamometers have been most widely used for beam pumping analysis and/or control, various other techniques have been proposed. For example, in U.S. Pat. No. 3,192,336 to Lowery, there is disclosed a pump safety system which employs an inertial switch mounted on the walking beam. The switch is actuated in response to sudden movements of the walking beam, such as may result from a break in the sucker rod string, to cut off the prime mover. Another system employed for the analysis of beam pumping units is disclosed in U. S. Pat. No. 2,691,300 to Morris. In the Morris system, strain gage and sine function potentiometer units are mounted on the pitman. The outputs of these units together with the output from a d.c. generator driven proportionately to the crank arm are applied through a circuit to achieve a readout representative of the torque on the crank shaft.

SUMMARY OF THE INVENTION

The present invention provides a new and improved apparatus for monitoring the operation of a well produced by a downhole pump. The pump is actuated by a sucker rod string suspended from a surface support unit consisting of a walking beam pivotally mounted on a sampson post for reciprocal movement as described above. In accordance with the present invention, a load transducer is secured to the support unit on either the sampson post or the walking beam. This transducer functions to generate a signal representative of load changes in the support unit as the walking beam is reciprocated to operate the downhole pump. This signal then may be applied to a suitable utilization device such as a recorder or controller.

In a preferred embodiment of the invention, the transducer is secured to the top of the walking beam such that it responds to deformation in the beam resulting from tensile stresses induced by the sucker rod loading. In a further aspect of the invention, the transducer comprises an elongated bar which is secured to the beam by means of longitudinally spaced rigid connections and means responsive to deformation in the bar between such connections for generating the load signal.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a well and a beam pumping unit employing attendant equipment in accordance with the present invention.

FIG. 2 is an illustration showing a transducer bar attached to a walking beam in accordance with a preferred embodiment of the invention.

FIG. 3 is an illustration of a preferred form of transducer bar and strain gauge arrangement.

FIG. 4 is an illustration showing an electrical schematic of a circuit employed in the transducer.

DESCRIPTION OF SPECIFIC EMBODIMENTS

With reference to FIG. 1, there is illustrated the wellhead 10 of a well which extends from the earth's surface 12 into a subterranean oil producing formation (not shown). The wellhead comprises the upper portions of a casing string 14 and tubing string 16. The tubing string extends from the wellhead to a suitable depth within the well, e.g., adjacent the subterranean formation. Liquid from the well is produced through the tubing string 16 by means of a downhole pump (not shown) to the surface where it passes into a flowline 17.

The downhole pump is actuated by reciprocal movement of a sucker rod string 18. Rod string 18 is suspended in the well from a surface support unit 20 consisting of a sampson post 21 and a walking beam 22 which is pivotally mounted on the sampson post by a pin connection 23. The sucker rod string includes a polished rod section 18a which extends through a stuffing box (not shown) at the top of the tubing string and a section 18b formed of a flexible cable. The cable section 18b is connected to the walking beam 22 by means of a "horsehead" 24.

The walking beam is reciprocated by a prime mover 26 such as an electric motor. The prime mover drives the walking beam through a drive system which includes a belt drive 27, crank 28, crank arm 29, and a pitman 30 which is pivotally connected between the crank arm and walking beam by means of pin connections 32 and 33. The outer end of crank arm 29 is provided with a counterweight 35 which balances a portion of the load on the sucker rod string in order to provide for a fairly consistent load on the prime mover.

It will be recognized that the well structure and pumping equipment thus far described are conventional and merely exemplary, and that other suitable beam pumping units may be utilized in carrying out the present invention. For a more detailed description of such equipment, reference is made to Uren, L. C., PETROLEUM PRODUCTION ENGINEERING - OIL FIELD EXPLOITATION, Third Edition, McGraw-Hill Book Company, Inc., New York, Toronto, and London, 1953, and more particularly to the description of beam pumping units appearing in Chapter VI thereof.

As the pumping unit is operated, the loading on the sucker rod string varies greatly. By analyzing this variance in sucker rod loading, a determination can be made as to the efficiency and operating characteristics of the pumping unit. As noted previously, such analysis normally is carried out by measuring the stress in the sucker rod string by means of a dynamometer mounted thereon. In accordance with the present invention, there is provided a system for monitoring the operation of a pumping unit by measuring load changes induced in the surface support unit as the sucker rod string is reciprocated. This is accomplished by locating on the support unit a load transducer which generates a signal representative of load changes induced in the support unit during operation of the pump. While the support unit loading may not be directly proportional to the sucker rod loading during pumping operation, the relationship between the two loads is predictable. For example, when the transducer is mounted on the top of the walking beam, as is preferred, the beam loading is directly proportional to the sucker rod loading when the beam is horizontal and departs from such direct relationship by a predictable function as the beam moves from this mid position during an upstroke or downstroke.

Referring again to FIG. 1, there is illustrated a load transducer 40 mounted on the top of walking beam 22. The load transducer may be of any suitable type which generates a signal representative of the load changes in the walking beam as it is driven by prime mover 26. Preferably, the load transducer is mounted at the top of the walking beam 22, as shown, where only tension loading occurs. The signal output from transducer 40 is applied via a communications channel 41 to a utilization device 42 which performs suitable recording and/or control functions. For example, the utilization device may apply a readout to a strip chart recorder 44 via channel 45 and/or apply control functions via channel 46 to the prime mover, as discussed in greater detail hereinafter.

Preferably, the transducer is located on the front section of beam 22 between the pivotal connection 23 and the connection of sucker rod string to the walking beam. At this location little if any extraneous loading is induced in beam 22 and the load changes in the beam result for all practical purposes only from changes in the sucker rod loading.

The system described above is especially well suited for real-time control of the pumping unit. Because of its location on the sampson post or walking beam, there is little liklihood of damage to the transducer from normal maintenance operations such as are involved in repair or adjustment of the sucker rod string. Thus, the transducer can be left in place permanently to provide a continuous signal output for real-time control of the pumping unit.

In effecting control of the pumping unit, the utilization device 42 shown in FIG. 1 can be provided with one or more constraint functions for comparison with the signal from the transducer. Device 42 thus acts as a comparator which generates a utilization function such as actuating an alarm, shutting down the prime mover 26, or changing the speed of the prime mover, in response to the transducer signal matching the constraint function. Exemplary of the conditions for which constraint functions may be established are well pump-off, traveling valve obstruction in the downhole pump, and sucker rod breakage. For example, well pump-off, resulting from producing a well at a rate greater than the rate at which fluid flows into the well from the formation, is characterized by a gradual increase in minimum signal amplitude. Thus, device 42 may be programmed to generate a control function which reduces the speed of the prime mover when the transducer signal reaches the constraint function, that is, when the maximum signal amplitude undergoes a predetermined decrease in amplitude within a specified time interval. A break in the sucker rod string 18 will be characterized by a pronounced reduction in load. Accordingly, utilization device 42 may be programmed to actuate an alarm and/or shut down the prime mover 26 when the amplitude of the transducer signal reaches a specified low value. It will be recognized that the aforementioned control actions are exemplary only and that various other constraints may be established for comparison with the load signal from the transducer in order to generate appropriate control functions. Also, while FIG. 1 illustrates an arrangement for local control and analysis, such functions can of course be carried out remotely. Thus, the signal from transducer 40 can be applied to a remote facility such as a digital computer which is programmed to perform appropriate control and/or recording actions. This is advantageous where the invention is employed in a large number of wells within a field.

Turning now to FIG. 2, there is illustrated a preferred transducer system which includes an elongated bar rigidly secured to the support unit by longitudinally spaced connections and means for measuring the deformation in the bar between such connections. More particularly, and with reference to FIG. 2, there is illustrated an elongated bar 48 which is secured at its ends to the top flange 50 of a walking beam. The rigid connections may be provided by any suitable technique such as by welding or bolting the ends of the bar to the walking beam. Secured to bar 48 between the rigid connections is a deformation responsive means 52 such as a bonded strain gauge transducer. Means 52 measures the deformation in the bar 48 is induced by changes in the beam loading and applies an output signal through suitable circuitry (not shown) to an appropriate utilization device such as shown in FIG. 1.

By leaving the intermediate portion of the bar disconnected from the walking beam, the strain in the bar is representative of the average strain in the walking beam between the rigid connections. This greatly reduces the effect of small areas of abnormal strain such as may result from heterogeneities in the beam. It is preferred that the rigid connections be separated by a distance of at least 6 inches in order to avoid erroneous measurements due to small areas of abnormal strain.

Preferably, an intermediate portion of the bar between the rigid connections is offset from the contiguous portion of the walking beam surface. Thus, as illustrated in FIG. 2, spacer elements 53 and 54 may be interposed between the bar and the walking beam to provide an offset as indicated by reference numeral 56. This offset avoids frictional engagement between the bar and walking beam between the rigid connections and thus further ensures that the strain in bar 48 is representative of the average strain in the beam between the rigid connections.

As will be recognized by those skilled in the art, most commercially available pumping units employ a walking beam of an "I-beam" configuration. The present invention is particularly well suited for use with such units since the transducer bar can be attached to the top flange of the I-beam which will always be stressed in tension while the unit is in operation. The transducer bar can be connected either to the upper surface of the top flange as shown in FIG. 2 or to the underside thereof. In either case, the strain in the transducer bar will remain in tension during operation of the pumping unit, thus ensuring that the output signal from the transducer is unipolar.

In FIG. 3 there is illustrated another embodiment of the transducer which provides for amplification of changes in strain induced during operation of the pump, thus lessening the electronic amplification required for an output signal of a given amplitude. This unit, which preferably is mounted on the walking beam as described above with reference to FIG. 2, comprises an elongated bar 56 which has a gauge section 58 of reduced cross section. By way of example, the bar 56 may exhibit dimensions of 1 inch .times. 1 inch .times. 24 inches with a 1 inch section of the bar turned down to a diameter of approximately one-half inch to provide the gauge section. In addition, a hole 59 of a diameter of thirteen-sixtheenths inch is drilled along the center line of the bar to further reduce the cross-sectional area of the gauge section.

Mounted on gauge section 58 is a suitable means for measuring deformation of the bar. Preferably such means comprises a plurality of strain gauges connected to form the arms of a wheatstone bridge circuit and bonded to section 58 alternately in tension and poisson. Thus as illustrated in FIG. 3, opposed strain gauges 61 and 62 are bonded to the gauge section 58 in tension to measure longitudinal strain in the bar and opposed strain gauges 63 and 64 are bonded to section 58 in poisson to measure lateral strain in the bar.

FIG. 4 illustrates the local electronics associated with the transducer bar. This system includes an adjustable biasing means in the output circuit of the strain gauge bridge for imposing a bias on the output signal in order to balance the bridge at a given stress condition in the bar. Thus, the transducer bar can be prestressed in tension when it is welded or otherwise secured to the walking beam and the potentiometer adjusted to null out the initial imbalance in the bridge. This is particularly desirable since it avoids nonrepeatability of the bridge signal associated with low strain in the transducer bar. More particularly, and with reference to FIG. 4, tension strain gauges 61 and 62 and poisson strain gauges 63 and 64 are connected in the opposed arms of a wheatstone bridge circuit 66 such that resistance changes induced by longitudinal and lateral strain in the bar are cumulative in unbalancing the bridge.

The circuitry associated with the wheastone bridge 66 functions to convert the output signal from the bridge to an appropriate current level. Such circuitry includes a potentiometer 68 for imposing a bias as desired on the bridge signal. Thus, the wiper arm of the potentiometer can be adjusted as desired in order to compensate for initial imbalance of the bridge. The bridge output is then applied through series-connected operational amplifiers 70 and 72. Amplifier 72 is provided with a rheostat 72a in its feedback circuit which may be used to adjust the gain of the amplifier. The output from amplifier 72 is then applied through a Zener diode 73 to an emitter-follower circuit 74 which converts the amplifier output to a current signal for transmission to a utilization device. Power for the bridge circuit and amplifiers is supplied from a d.c. power source 75 through a voltage regulator circuit 76 which functions to stabilize the voltage supply. By way of example, the power supply may be 24 volts d.c. with the amplifiers 70 and 72 exhibiting a combined gain of 1,000 to amplify the bridge signal to a level within the range of 1 to 5 volts. The emitter-follower converts the amplifier output to a current signal within the range of 4 to 20, or optionally, within the range of 10 to 50 milliamps.

Claims

What is claimed is:

1. In a system for monitoring a well produced by a downhole pump, the combination comprising:

a surface support unit including a sampson post and a walking beam pivotally mounted on said sampson post for reciprocal movement by a prime mover,

a sucker rod string for operating said pump connected to said walking beam, and

transducer means secured to the top of said beam at a location between said pivotal mounting and the connection between said beam and said rod string for generating a signal representative of load changes in said beam as it is reciprocated.

2. In a system for monitoring a well produced by a downhole pump, the combination comprising:

a surface support unit including a sampson post and a walking beam pivotally mounted on said sampson post for reciprocal movement by a prime mover,

a sucker rod string for operating said pump connected to said walking beam, and

transducer means secured to said beam for generating a signal representative of load changes in said beam as it is reciprocated, said transducer means comprising an elongated bar secured to a surface of said beam by longitudinally spaced rigid connections and means responsive to deformation in said bar between said connections for generating said signal.

3. The system of claim 2 wherein said bar is secured to the top of said beam.

4. The system of claim 3 wherein said bar is prestressed in tension with respect to said beam.

5. The system of claim 2 wherein at least a portion of said bar intermediate said rigid connections is offset from said surface of said beam.

6. The system of claim 2 wherein said rigid connections are spaced by a distance of at least 6 inches.

7. In a system for monitoring a well produced by a downhole pump, the combination comprising:

a surface support unit including a sampson post and an I-shaped walking beam pivotally mounted on said sampson post for reciprocal movement by a prime mover,

a sucker rod string for operating said pump connected to said walking beam,

an elongated transducer bar secured to the top flange of said walking beam by longitudinally spaced rigid connections, and

means responsive to deformation in said bar between said connections for generating a signal representative of load changes in said beam as it is reciprocated.

8. The system of claim 7 wherein at least a portion of said bar intermediate said rigid connections is offset from said flange.

9. The system of claim 8 wherein said rigid connections are spaced by a distance of at least 6 inches.

10. The system of claim 9 wherein said bar includes a section of reduced cross section intermediate said rigid connections and said deformation responsive means is located on said section.

11. The system of claim 9 wherein said deformation responsive means comprises a plurality of strain gauges connected to form the arms of a wheatstone bridge and bonded to said bar alternately in tension and poisson.

12. The system of claim 11 further comprising an output circuit for said bridge including means for imposing an adjustable bias on the output signal from said bridge.

13. An apparatus for monitoring the strain level in a well pumping rod string comprising:

a pumping unit for actuating said rod string, said pumping unit including an oscillating beam and means pivotally supporting said beam and

deformation responsive transducer means secured to said beam for generating a signal representative of load changes in said beam as it oscillates.