US3306210A

US3306210A - Automatic oil well pump control

Info

Publication number: US3306210A
Application number: US482538A
Authority: US
Inventors: Harvey W Boyd; Joseph I Burleigh; Jessie L Roberson
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-08-25
Filing date: 1965-08-25
Publication date: 1967-02-28
Anticipated expiration: 1984-02-28

Description

Feb. 28, 1967 H. W. BOYD ETAL AUTOMATIC OIL WELL PUMP CONTROL Filed Aug. 25, 1965 NE MINUTE 30 MINUTES I :41

DRIVE TIMER 40 MOTOR #30 SWITCH .6; START f {1 STOP MOTOR CONTROL 22 cmcun INVENTORS HARVEY W. BOYD JOSEPH I. BURLEIGH JESSIE L. ROBERSON ATTORNEY S United States Patent Ofltice 3,305,210 Patented eb. 28, 1967 3,396,210 AUTGMATIC OIL WELL PUMP CONTROL Harvey W. Boyd, 4401 Anetta Drive; lioseph I. Eurleigh, 1205 Superior Lane; and Jessie L. Roberson, 2093 W. Indiana, all of Midland, Tex. 79701 Filed 25, 1965, Ser. No. 482,538 2 Claims. (Cl. 103-25) This invention relates to oil well pump controls and, more particularly, it relates to means for automatically starting and stopping an oil well pump responsive to the presence of fluid in the wellbore to thereby efliciently pump out wells which produce less than the capacity of the pump.

In many instances a producing oil well will have a maximum productive capacity which is less than the capacity of the pump installed in the well. For example, a small standard size pump has a flow pipe 1% inches in internal diameter. This pump will displace 40 to 50 barrels per day even when reciprocating at slow speeds. Many wells however operate in the production capacity range of to 20 barrels per day. In such wells it is more eflicient to run the pump intermittently only when the oil is present in the wellbore. It is significant that the loading on the pump is increased when pumping a dry well.

It is characteristic of oil bearing strata that oil may seep slowly into a wellbore over a relatively long period of time as compared with the pump out speed. Thus, a continually operating pump will tend to erratically pump and be subject to excessive wear when the store of oil in the wellbore is exhausted and it is pumping only the re sidual flow from the oil bearing strata into the wellbore. Although systems for automatic pump shutdown based upon presence of fluid flow from the pump are known,

these have not been efl'lcient or satisfactory because of the erratic conditions of sensing the partial flow as the stored oil in the wellbore nears the minimum pumping level and the pumping is dependent in part on the residual flow through the oil bearing strata.

Accordingly, it is an object of the invention to provide improved, automatic controls for starting and stoppin an oil well pump responsive to the conditions at the downhole pump which signal presence of fluid in the wellbore.

In accordance with the present invention therefore the loading of the pump is sensed to indicate an increased load on the doWnstroke which occurs when the wellbore is pumping dry. This loading is sensed by determining the weight or the load upon the pump rod string and determining when it changes as a result of pump out of the wellbore, and using this sensed control to automatically shut down the pumping until such time that enough residual oil has filtered back into the well to provide enough of a store in the wellbore for a further pump out operation.

A more detailed description of the invention and its mode of operation will be found in the following specification with reference made to the accompanying drawings, wherein:

FIGURE 1 is a diagrammatic view of an oil well pump; and

FIGURE 2 is a block control circuit diagram of an automatic pump shut down control mechanism.

In the typical oil well pump as shown in FIGURE 1, a pumping unit or a prime mover is mounted on a tower 4 which permits the rocking beam 5 to reciprocate the pump rod string 6 against the counterbalance 7 by action of an electric motor or engine unit (not shown). The sucker rod string is inserted down the hole inside the tubing 8 to terminate at a down hole pump 9 which is located inside the wellbore 10. Inside the wellbore a fluid level 11 is attained by oil trickling through the oil bearing strata 12.

In general, the pump operating mechanism comprises a first traveling valve 14 which is reciprocated with the rod string connected to the hollow plunger 15 and a second standing or stationary valve 16 positioned at the end of the pump 9. Thus in operation, the weight of the oil inside the tubing 8 will hold the traveling valve 14 closed on the pumping upstroke and permit the oil to be lifted up the tubing and out the flow pipe 17. During this operation the standing valve 16 will be lifted by pressure of the oil within the well casing 10, and the tubing is filled to a level substantially equal to that of the level of the oil 11 within the wellbore 10. Thus, upon the downstroke the standing valve 16 is closed when oil stands in the lower section of the pump 9 beneath the hollow plunger 15. This therefore opens the traveling valve 14 and permits the pump to attain its downward stroke while transferring the oil within the lower part of the pump 9 into the hollow plunger 15 of the pump for attaining a further pump out cycle on the pump upstroke.

In accordance with the present invention this pumping action is used directly to sense the conditions of the bottom of the bore and provide a signal for shut down of the pump when the level of the oil 11 in the wellbore 10 falls to such an extent that the loading on the pump is significantly increased. Consider in this respect the operation of the pump when the oil level is below that required to operate the standing valve 16. On the normal downstroke the fluid in the lower barrel causes the traveling valve 14 to open and transfers the fluid load or the weight of all the oil in the tubing 8 to the standing valve 16 which then closes. Thus, the weight of the rods or the load on the rods is less because of the loss of the weight of the oil in tubing 8 on the downstroke than weight on the upstroke when the fluid valve 14 is closed and the rods must pull the weight of the oil in the pipe upward within the tubing 8. This weight transfer occurs because the plunger 15 inside the pump 9 is essentially leak-proof containing a seal so that the entire fluid passage takes place through the valve 14.

However, if there is no fluid in the barrel as the downstroke begins, the traveling valve 14 does not open and the weight is not transferred to the standing valve 16. In a typical well installation with a l fii-inch pump installed inside a 2 /2-inch tubing and a wellbore diameter of 7 inches having the pump connected to the surface with 4-inch sucker rods, the weight of the rod string on the upstroke was 9000 pounds with a depth of 4500 feet. This dropped to 4500 pounds during the downstroke when the well was pumping fluid, but reverted to 9000 pounds when the well was pumped dry.

For the purpose of sensing this change of weight in the rods a hydraulic load indicator 20 manufactured by the I. M. Huber Corporation was installed in the rod string. This produced a hydraulic pressure signal of pounds per square inch for each 1000 pounds of rod weight. Such pressure is carried by hydraulic line 21 to a hydraulically operated pressure switch 22, for which the pressure shut down mechanism of the switch was adjustable. In a typical example the pressure switch was set at 800 pounds per square inch as a threshold pressure so that the pressure switch 22 would send an electric signal at its output leads which can be used for shut down whenever the pressure exceeds 800 pounds per square inch. It may be seen from the foregoing data that when the oil level 11 in the wellbore 10 falls below the necessary level that the loading during the downstroke will increase to 9000 pounds and give a pressure reading of 900 pounds per square inch thereby exceeding the pressure threshold level of switch 22 and sending a signal which will indicate that the pump should be shut down.

A typical control circuit for this sort of operation is shown in FIGURE 2 where a drive motor 30 is operated from a three phase electrical supply line, for example, by way of the motor control circuit 31 which provides for starting and stopping the drive motor. These and similar power control units are conventionally supplied with standard oil well rings. It is noted that in the control operation that the pressure only varies on the downstroke of the pump and is always attained at the high pressure on the upstroke of the pump. Accordingly, a magnetic proximity switch 32 is used in connection with the counterbalance mechanism 7 to indicate the downstroke position of the pump. Thus as shown in the motor control circuit, the two

switches

22 and 32 are used in series to provide a stop control for the motor control circuit when the pressure switch 22 indicates that the pressure is high on the downstroke and closes contact 22 at the same time that the contact 32 indicates the pump is on the downstroke. Then in the normal course of events when the pump is on the upstroke and contact 22 closes it will not effectuate a stopping of the drive motor through the motor control circuit stop lead.

It is thus seen that the pump mechanism may be stopped automatically by the actual critical level of fluid encountered at the bottom of the here. It may be readily seen that this mode of control significantly improves the efficiency in loading upon the pumping mechanism and provides for pump out of the maximum capacity of any well which has a capacity or a productive flow which is less than the full capacity of the pumping mechanism.

In order to make the system fully automatic, the start control for the drive motor is operated by means of a timer switch 40, which serves to provide a typical periodic on-otf cycle such as shown in Waveform 41 where the switch 42 is closed to start the drive motor and maintain it in operation for only one minute at a repetitive cycle of perhaps 30 minutes. This assures that the pump will be operating normally before automatic shut down control is eifectuated by means of the control switches 22' and 32' previously described. The timer switch 40 may be simply a clock motor with appropriate cam and switch set selected to close the switch during chosen intervals which can be set to correspond to the capacity of a particular well. For example, if the well has a capacity that requires pumping for 10 minutes before shutting down, the timer will permit the well to be held in shut down condition for 20 minutes while more fluid is accumulating in the wellbore by seepage through the oil bearing strata. Then the pump will be started for another automatic pumping cycle and in this manner the maximum capacity may be realized from the well by automatic cycling of the pump drive mechanism.

It may be recognized in accordance with the teachings of the present invention that the method of controlling the pump shut down is effectuated by conditions existing at the bottom of the well as indicated by the measure of the weight or the loading upon the pump rod assembly or the pumping mechanism itself which changes significantly during the downstroke during conditions when the fluid is present and when the fluid is absent. Therefore, in accordance with the teachings of the present invention various types of weight sensing devices and shut down control circuits could be used without departing from the spirit or the scope of the invention. For example, a strain gauge could be mounted upon the pump rods to indicate the difference in loading to replace the hydraulic senser. Those novel features believed descriptive of the scope and the nature of the invention are defined with particularity in the appended claims.

What is claimed is:

1. Control means for a motor driven reciprocating rod type of oil well pump which exhibits the property of increasing the load on the pump rod on the downstroke when the Well fluid is below pumping level comprising in combination, means for sensing an increase in the weight of the pump rod string, switch means operable by the sensing means at a threshold when the weight exhibited by the rod string on the downstroke increases to substantially that on the upstroke, and means shutting down the pump motor responsive to operation of said switch for a time period permitting fluid to enter the well and reach said pumping level.

2. Control means as defined by claim 1 wherein the switch means includes one switch actuated by position of the pump rod on the downstroke and another switch actuated responsive to said threshold, and wherein the control means includes a circuit connecting the two switches in series circuit with the means shutting down the pump motor.

References Cited by the Examiner UNITED STATES PATENTS 2,456,456 12/1948 Smith 103-25 2,661,697 12/1953 Long et al 10325 2,947,931 8/1960 Hubby 10325 X 3,225,697 12/1965 Brown 10325 ROBERT M. WALKER, Primary Examiner.