US3373823A

US3373823A - Well drilling control system

Info

Publication number: US3373823A
Application number: US488530A
Authority: US
Inventors: Jr Hal B Fullerton; Richard C Webb; Jon E Benner
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-09-20
Filing date: 1965-09-20
Publication date: 1968-03-19
Anticipated expiration: 1985-03-19
Also published as: GB1115977A; DE1296103B

Description

March 19, 1968 H. B. FULLERTON, JR., ET AL 3, v

WELL DRILLING CONTROL SYSTEM Filed Sept. 20, 1965 5 Sheets-Sheet 1 INVENTORS HAL B. FULLERTON, JR. RICHARD c. WEBB BYJON E. BENNER ATTORNEYS March 19, 1968 H. B. FULLERTON, JR. ET AL 3,

WELL DRILLING CONTROL SYSTEM Filed Sept. 20, 1965 5 Sheets-Sheet 2 i g l I I. i I a! I 1 1 l J l 1 I In 8| I? i i I.

| I. l 1 I @l l l 1 I L. J

INVENTORS HAL B FULLERTON, JR. RICHARD C. WEBB JON E BENNER WVM-Qi/ ATTORNEYS March 19, 1968 H. FULLERTON, JR., ET 3,373,323

WELL DRILLING CONTROL SYSTEM Filed Sept. 20, 1965 SSheets-Sheet a SWIA n .8"

INVENTORS HAL B. FULLERTON, JR. RICHARD c. WEBB YJON E. BENNER ATTORNEYS United States Patent F 3,373,823 WELL DRILLING CONTROL SYSTEM Hal B. Fullerton, In, Whittier, Calif., and Richard C. Webb, Broomfield, and Jon E. Benner, Denver, Colo., assignors, by direct and mesne assignments, to Hal B. Fullerton, Jr., and Betty Jane Fullerton, both of Whittier, Calif.

Filed Sept. 20, 1965, Ser. No. 488,530 15 Claims. (Cl. 1736) ABSTRACT OF THE DISCLOSURE This invention is an automatic control system for controlling the draw works of a rotary well drilling rig. The system comprises means for sensing the rotational speed of the well drilling bit and means for sensing the weight of the bit on the strata being penetrated. The signals relating to speed and pressure are combined to g nerate a signal related to the product of bit weight times rotational speed. This product is used to control the draw works of the Well drilling rig to maintain a constant pressure-rotary speed relation. In addition, means are provided for allowing only a maximum drill pressure regardless of rotary speed. Further, a means is provided for calibrating the system so that it can be utilized with various Well drilling rigs.

This invention relates to an automatic control system for a rotary well drilling rig and particularly to a system for controlling the pressure of the drill bit on the bottom of a hole in accordance with prescribed factors including the product of bit Weight and bit rotation speed.

In rotary drilling of Wells, an oil wells in particular, it is desirable to conduct the drilling operations with the application of a predetermined, controlled weight W -acting on the drill bit. It is desirable to be able to set a predetermined weight on the drill bit, to control automatically this exact weight and to read this weight from a control panel.

Accordingly, it is an object of this invention to provide an automatic rotary drilling rig control system for controlling the maximum weight applied to the drilling string and drill bit.

Another object of the invention is to provide a rotary drilling rig control system for controlling the pressure of the drill bit as it acts on the bottom of the hole being drilled in accordance with the product of the bit weight and the bit rotational speed.

Additional objects of the invention will become apparent from the following description, which is given primarily for purposes of illustration, and not limitation.

Stated in general terms, the objects of the invention are attained by providing an automatic control system for manipulating the draw works of a rotary well drilling rig for automatically controlling the pressure of the drill bit acting on the bottom of a hole being drilled in accordance withpredetermined, prescribed factors such as the product of bit weight and bit rotation speed, maximum rate of bit penetration, maximum bit pressure, and the like. The automatic control system comprises a master electronic control unit which includes means for accepting signals signifying the total Weight of the drill string being employed at a given time, such as from an anchor means, means for accepting signals signifying the rotational speed of the drill bit at a particular time, such as from a tachometer means, and means for calibrating the master electronic control unit in accordance with the prescribed, predetermined factors so that the accepted signals of total weight of drilling string, the bit weight acting on the bottom of the hole being drilled and the rotational speed of the drill bit are converted 3,373,823 Patented Mar. 19, 1968 by the master electronic control unit into suitable output control signals. An electronic power source is connected to the master electronic control unit to supply thereto operating power and a suitable control means, such as a hydraulic, pneumatic, electrical or mechanical control means, for example, is connected to the draw works of the rotary drilling rig and to the master electronic control unit to receive the output control signals from the master electronic control unit and to convert these signals into automatic manipulative control actions on the draw works.

In essence, applicants invention utilizes the product of signals representing drill bit pressure and rotational speed to control the draw works of a drilling system. The use of this combination of signals provides unique results not shown by the prior art because either the rotational speed or the pressure can vary in accordance with the strata being drilled; however, the product of drill bit pressure and rotational speed remains constant.

A more detailed description of a specific embodiment of the invention is given below with reference to the accompanying drawings, wherein:

FIGURE 1 is a schematic diagram showing a rotary drilling rig in combination with a master electronic ntrol unit of the invention;

FIGURE 2 is a schematic diagram showing a partial arrangement of the circuit of the master electronic control unit; and

FIGURE 3 is a schematic circuit diagram showing the circuit of the calibrate box of the master electronic control unit.

The drill control system comprises a block and tackle including crown block 9, traveling block 10 and cables or strings 11 terminating in draw works 12. Brake band 13 of draw works 12 is linked at 14 to brake handle 15 pivotally mounted at point 16. Brake handle 15, in the prior art, conventionally serves as a manual control means for release of cable through draw works 12 and block and tackle system 9, 10, 11. It is an important object of this invention to provide an automatic control system whereby brake handle 15 is manipulated through a servo control cylinder 17 and linkage 18 connecting the control cylinder to the brake handle 15.

Servo control cylinder 17 is internally springloaded to apply continuously a fail safe spring load upon brake handle 15 to insure continuous closure of brake drum 13 except when servo control cylinder 17 is actuated. Cylinder 17 is actuated through an electric actuator valve 19 which, when open, permits hydraulic or pneumatic pressure from source 20 to act upon servo control cylinder 17 to release brake 13 through handle -15 and link 14. Operation of actuator valve 19 is controlled by electrical signals from master electronic control unit 5 transmitted through electrical control line 21.

An indication of the drill bit pressure on the bottom of the hole is obtained in information conveyed from a line tension transducer 1 contained in anchor 2 terminating dead line 3. This information is conveyed in the form of hydraulic pressure produced in anchor 2 and transmitted through hydraulic line 4 to electronic control unit 5 where it is converted into an electrical signal. Alternatively, the hydraulic pressure can be converted to an electrical signal Within anchor 2 and transmitted to control unit 5 over a wire line instead of hydraulic line 4.

Tachome er 6 coupled with rotary table 7 generates an electrical signal which indicates the rotational speed R of the drill bit. This electrical signal is introduced into control unit 5 via line 8 wherein it is employed to obtain the desired product of rotational speed multiplied by bit weight per inch of bit diameter. Power for operation of control unit 5 is obtained from a general purpose power source (not shown) through line 22 after it is processed through an electrical power supply converter 23 which prepares the power for its use in unit 5.

The mechanism through which tension in dead line 3 is converted in electronic control unit into a signal representing actual pressure of the drill bit on the bottom of the hole being drilled, or bit Weight W, is described with reference to FIGURE 2. The method of obtaining calibrated bit weight from tension in dead line 3, as well as panel indication of bit weight, also will be described.

A pressure transducer 24 is employed in the circuit of electronic control unit 5 to convert the hydraulic pressure information conveyed from dead line tension transducer 1 in anchor 2 through hydraulic line 4 into rotary motion of the potentiometer arm 24A of the pressure trans ducer 24. The rotary motion thus produced in the potentiometer arm 24A in pressure transducer 24 causes the potentiometer arm to move along the winding of the potentiometer resistance from the lower or rest position representing zero hydraulic pressure and zero dead line tension toward the upper end representing an arbitrary maximum hydraulic pressure and dead line tension.

To obtain an electrical signal proportional to the position of the potentiometer arm 24A in pressure transducer 24, an electric current is passed through the potentiometer from a positive voltage source 25 to a negative voltage source 26. Voltage sources 25 and 26 are of essentially equal voltage but of opposite polarity. Resistors 27 and 28 connected to the voltage sources 25 and 26, respectively, are so proportioned as to cause zero potential, with repect to ground potential, to occur on the potentiometer arm 24A of pressure transducer 24 when the arm is in the middle of its range of rotational movement, Thus, the position of the potentiometer arm 24A in pressure transducer 24 corresponds to an electrical signal which is proportional to tension on dead line 3 and to the total net weight of all of the equipment hanging on the drill string bottom of the hole being drilled.

The means for obtaining an electrical signal corresponding solely to bit weight W will now be described. When the drill bit is completely disengaged from the bottom of the hole, the tension in dead line 3 corresponds to the total net weight of all of the equipment hanging on the drill string. When the drill bit is in engagement with the bottom of the hole, part of the total net weight is taken on the bottom of the hole and the tension 011 dead line 3 is reduced by the amount resting on the bit.

A triply-ganged potentiometer system including potentiometers 29, 30 and 31 is coupled with the potentiometer in pressure transducer 24 through a compulter type operational amplifier 47. Ganged potentiometers 29, 30 and 31 are driven from a common drive shaft 32, shown as a broken or dotted line, which is an integral part of the electro-mechanical servo system 33. Electromechanical servo system 33 causes common drive shaflt 32 to follow the rotational motion of the potentiometer arm 24A of the potentiometer in pressure transducer 24 which, as explained above, is positioned to correspond to the tension in dead line 3.

Calibration of electromechanical servo system 33 to cause the angular position of common drive shaft 32 to represent accurately bit weight W is accomplished by adjustment of

potentiometers

35 and 36 connected respectively to opposite sides of ganged potentiometer 29.

Potentiometers

35 and 36 are connected by a common shaft 34, shown as a broken or dotted line, which can be made adjustable by a knob connected thereto and mounted on a panel of electronic control unit 5. The operator calibrates the system, such as when connecting a section to the drill string, by viewing the indicalted bit weight meter 37 while the drill bit is lifted off the bottom of the hole. By manually adjusting the

calibration control potentiometers

35 and 36 through common shaft 34, the indicated bit weight on meter 37 is set to reference zero. Thus, the angular position of common drive shaft 32 of electromechanical system 33 Weight W.

In order to provide a panel meter indication of bit weight W on electronic control unit 5 and to establish system control of bit weight W, it is necessary to provide an electrical signal in control unit 5 that is proportional to bit weight W. This is accomplished by also converting the angular position of common drive shaft 32 into an electrical signal representing bit weight W by the use of ganged potentiometer 31, which is one of the tripleganged potentiometers 29, 30 and 31, driven from a common drive shaft 32, as described above.

Ganged potentiometer 31 is provided with an electrical tap point 39 located about one-third of the distance from the lower end of the potentiometer resistance element. Potentiometer 31 also is provided with a current from positive and negative voltage sources 25 and 26, respectively, as in the case of pressure transducer 24, described above. Thus, the voltage between the arm 38 of potentiometer 31 and ground voltage also is proportional to to the position of common drive shaft 32, and therefore, also is proportional to bit weight W. The value of this voltage between potentiometer arm 33 and ground becomes zero when arm 38 is exactly opposite grounded tap point 39 of potentiometer 31.

The voltage from arm 38 of potentiometer 31 is applied to computer type

operational amplifiers

40 and 41. Amplifier 40 serves to drive panel indicating bit weight meter 37 and is provided with a high-low sensitivity switch 42 to increase the sensitivity of meter 37 during the calibration operating described above. Amplifier 41 serves to compare the voltage from arm 38 of potentiometer 31 with a voltage from arm 44 of maximum bit weight W, reference potentiometer 43. Reference potentiometer 43 preferably is a precision ten-turn helical potentiometer fitted with a three-digit ten-turn dial. Settings of maximum bit weight W can be made on the dial of potentiometer 43 to a fraction of a percent of full scale.

The output of amplifier 41 is zero when its two input voltages from arms 38 and 44 of potentiometers 31 and 43, respectively, are exactly equal regardless of their absolute magnitudes. When the voltage of the bit weight W signal from arm 38 of potentiometer 31 exceeds the voltage of the signal from arm 44 of maximum bit Weight W reference potentiometer 43, the output of am plifier 41 is of such polarity to cause the overall servo control system 55, enclosed with a dashed enclosure in FIGURE 2, to reduce the bit pressure on the bottom of the hole being drilled.

In calibrating the value of the bottom hole or lbit pressure in terms of the angular position of common drive shaft 32, note is taken of the fact that

calibration potentiometers

35 and 36, whose respective potentiometer arms simultaneously move upwardly and downwardly under the ganged control of common shaft 34, as described above, supply a voltage signal to the terminals of triplyganged potentiometer 29, whose arm is common to common drive shaft 32 together with the respective arms of the other two triplyganged potentiometers 30 and 31. The dotted lines within calibrate box 46 show the essential connections in simplified form of triply-ganged potentiometer 29 with the calibrating circuit.

As described above, computer type operational amplifier 47 has an input which is the difference voltage between the potentiometer in pressure transducer 24 and arm 48 of triply-ganged potentiometer 29. Furthermore, the output of operational amplifier 47 is the error signal input to electromechanical servo system 33. The output of servo system 33, in turn, is the angular positioning signal of common drive shaft 32 from which arm '48 of triply-ganged potentiometer 29 takes its position. It is evident therefore that electromechanical servo system 33 operates to position potentiometer arm 48 to produce a null balance at the output of operational amplifier 47. Moreover, the exact voltage level, relative to ground voltservo represents bit age, of potentiometer arm 48 varies in accordance with variations in the tension in dead line 3 which, in the form of voltage relative to ground voltage, is brought into the system through the potentiometer arm of pressure transducer 24, as described above. Thus, whether the tension in dead line 3 is near the maximum, minimum or therebetween, electromechanical servo follower system 33, which receives the error signal from operational amplifier 47, serves to position potentiometer arm 48 accordingly.

Bearing in mind that triply ganged potentiometers 29, 30 and 31 are identical and travel on the common drive shaft 32, that tap point 39 on potentiometer 31 is set about one-third of the distance from the end of the potentiometer and that zero bi-t weight W corresponds to an angular setting of arm 38 of potentiometer 31 opposite tap point 39, it is seen that the effective potential furnished to the outer terminals of potentiometer 29 must be adjusted during the calibration operation by the proper setting of

potentiometers

35 and 36 to force electromechanical servo system 33 to find a null balance point with arm 48 of potentiometer 29 (as well as with arms 49 and 38 of potentiometers 30 and 31, respectively) positioned at a point opposite tap point 39 of potentiometer 31.

The purpose of calibrate box 46, which contains the circuit shown in FIGURE 3, is to serve as calibration means for electronic control unit 5 to various line tension transducers, such as line tension transducer 1 contained in anchor 2. A second purpose is to calibrate electronic control unit 5 to various numbers of lines strung on block and tackle assembly 9, 10, 11, such as 6, 8 or 10 lines, for example.

Calibrate box 46 operates as follows.

Potentiometers

35 and 36 connected to either side of calibrate box 46, as shown in FIGURE 2, are connected by common shaft 34, as described above. Potentiometer 29 is provided with wiper arm 48 and wiper arm 48 is, in turn, connected to electrical-mechanical servo-system common drive shaft 32, as described above. In FIGURE 3 switch sections SW2A, SW2B, SW2C and SW2D of switch SW2 are connected by a common shaft (not shown). Switch SW2, a front panel control on electronic control unit 5, permits switching in different line tension transducers, such as line tension transducer 1 of anchor 2. Switching SW2 from position D to E or E to D switches in a completely different set of resistors, which are selected to calibrate electronic control unit 5 t the particular line tension transducer being used. Switching SW2 to position D switches in resistors 64 through 75 and switches out resistors 76 through 87. Therefore, by switching SW2 to the D position and by proper selection of resistors 64 through 75, electronic control unit is calibrated to a particular type anchor. Also, when SW2 is in position D, resistors 76 through 87 are no longer connected into the circuit in a manner which would affect the operation or calibration of electronic control unit 5.

By switching SW2 to position E, the exact reverse is true; that is, electronic control unit 5 is now calibrated to a particular E type anchor because resistors 76 through 87 are now switched into the circuit and their values of resistance are such as to calibrate electronic control unit 5. Further, resistors 64 through 75 are now switched out of the circuit and they no longer affect the operation or calibration of electronic control unit 5.

Switch sections SWlA, SWIB, SWlC, SWlD, SWlE, SWlF, SWIG, and SWlH of switch SW1 are connected to a common shaft (not shown). Switch SW1, a front panel control switch of electronic control unit 5, permits switching in different numbers of lines strung on block and tackle assembly 9, 10, 11. For example, in this

description

6, 8 and 10 lines strung will be used. By proper selection of resistors 64 through 87 different numbers of lines strung can be selected to calibrate electronic control unit 5 to the number of lines strung.

6 Of course, these interact closely with the line tension transducer 1, selected through switching of SW2.

An example of the switching arrangement is as follows. Let there be 6 lines strung with a particular D type anchor 2 being used. Switch SW2 will be switched to position D, switching in resistors 64-75 and switching out resistors 76-87, and switch SW1 will be switched to the 6 lines strung position. From FIGURE 3, it is seen that

resistors

64, 65 and 66 are all in the circuit. Resistor 67 is in, but resistors 68 and 69 are switched out. Resistor 70 is in, but

resistors

71 and 72 are out, and

resistors

73, 74, and 75 are in the circuit. By proper selection of

resistors

64, 65, 66, 67, 70, 73, 74 and 75, electronic control unit 5 is calibrated for 6 lines strung when using a particular D type anchor 2.

From FIGURE 3 it is seen that the resistors are blocked into four basic blocks of resistors. Each block of resistors serves a specific function. The block consisting of

resistors

67, 68, 69, 79, and 81 serves as the means for permitting the proper potential to appear at the top of potentiometer 29, as viewed in FIG. 2, at all times and under any conditions. A second block of resistors consisting of

resistors

70, 71, 72, 82, 83, and 84 serves as the means for permitting the proper potential to appear at the bottom of potentiometer 29 at all times and under any conditions. A third block of resistors consisting of

resistors

64, 65, 66, 76, 77 and 78 serves the purpose of permitting the proper potentials to appear at the top and bottom of potentiometer 29 at the same time. The last block of resistors, consisting of

resistors

73, 74, 75, 85, 86 and 87, permits the impedance looking into calibrate box 46 from switch point SW2A to be a constant under any and all conditions obtained by switching switches SW1 and SW2 to any position. In this manner the control system is brought into calibration in terms of bit weight W. The means by which the product of bit weight W (per inch of bit diameter) times rotational speed R of the rotary table 7 is accomplished will now be described.

The method used toobtain this product is well established in the analog computer art. It consists of introducing one of the variables W or R as angular position of potentiometer arm, in this case arm 49 of potentiometer 30, while the other variable is introduced as voltage across the terminals of the potentiometer 30. The value of the product W and R of the two variables is obtained as a voltage from arm 49 of potentiometer 30 to ground. It will be noted that potentiometer 30 is furnished with a tap point 50, which is at an identical position to tap point 39 on potentiometer 31. Thus, when the electrical signal from tachometer 6 is applied from the top of potentiometer 30 to tap point 50, the potential with respect to ground taken from arm 49 of potentiometer 30 is representative of the product of bit weight W times rotational speed R of table 7. This voltage is taken as one of the two input voltages applied to operational amplifier 51. The second voltage is obtained from arm 52 of the WXR reference potentiometer 53. Potentiometer 53 preferably is a tenturn helical potentiometer fitted with a three-digit, tenturn dial for setting in desired values of the product W R.

Operational amplifier 51 furnishes the W R error signal input to the general drilling rig servo controller system 55 through AND gate 45.

Since the W R product that is to be taken is preferably that of bit weight per inch of bit diameter times drill rotation speed R, a means for calibrating for bit diameter is required. This is accomplished by rheostat 54, which serves to adjust the current in potentiometer 53 and therefore adjusts the valve of the voltage with respect to ground taken from arm 52 of the potentiometer 53. To accommodate a range of bit diameters from 6 inches to 20 inches, the variation in current through potentiometer 53 must be from 6 to 20 times under control of calibration rheostat 54.

Referring now to AND gate 45 of the main servo controller system 55, it is seen that there are four inputs to this gate; namely at 56, 57, 58 and 59. Of this group, the inputs at 56 and 57 have already been explained, since they refer to bit weight and the product W R, respectively.

Servo controller system 55 furnishes a series of electrical inpulses to actuator valve 19 which in turn Opens actuator valve 19 more or less briefly, allowing hydraulic or pneumatic pressure to pass through actuator valve 19 to control cylinder 17 to FIGURE 1, thereby lifting off the preset braking load spring on brake handle 15 and allowing the line to be released by drawworks 12.

It is common practice in a servo controller such as 55 to introduce the control action as a series of short impulses, and it is generally desirable to make these impulses adjustable in duration as well as in repetition frequency. These electrical impulses, therefore, are furnished by a variable repetition rate pulse generator 60, FIGURE 2, which is fitted with a variable pulse width control 61. The net efifect of these two devices is introduced through AND gate 45 on its input terminal 58.

For AND gate 45 to furnish an impulse to valve actuator 19, it is necessary that all four of its inputs be in the on condition. This represents the condition within the servo system where action is called for and authorized. The word authorized is used here because under certain conditions the bit weight W may exceed some desired preset maximum which has been set up on potentiometer 43. Under this condition, if the electronic control unit Were attempting to increase bit weight through its W R product control section, and attempted to employ a bit weight which exceeded the maximum limit set on potentiometer 43, input terminal 56 of AND gate 45 would not authorize further transmission of electrical impulses to the valve actuator, and thus no further weight would be applied. The input to the gate applied to terminal 56 would, in this case, be off."

It is evident that W R product control of bit weight may be accomplished only as long as the bit weight W is smaller than the maximum value set in on potentiometer 43, thus leaving input terminal 56 to AND gate 45 in the on condition. Input terminal 57 to AND gate 45 will cycle from on to off as the conditions for satisfying the W R product requirement set on potentiometer 53 are met. This cycling or hunting procedure is common in all servo null-seeking systems of this class.

One additional feature of the control system is brought into AND gate 45 through input terminal 59. Input terminal 59 normally is furnished with an on signal. Loss of this on condition on terminal 59, however, prevents transmission of impulses to valve actuator 19. Such an interruption of on signal at terminal 59 may be brought about by any sudden change in the error signal furnished to the electromechanical servo system 33 by operational amplifier 47. Such a change in error signal would generally correspond to a variation in dead line tension and is detected by the sudden weight change override circuit 62, which serves to withhold further release of line from drawworks 12 until such time as the error signal steadies. This override feature is equally sensitive to increase and decrease in line tension and the time constant of this circuit can be adjusted in a manner appropriate to the installation.

Thus, the well drilling control system of the invention permits one to conduct the drilling operation with the application of a predetermined, controlled weight W acting on the drill bit while reading this weight from a control panel. The control system of the invention controls brake handle 15 of drawworks 1-2 of the rotary drilling rig. It enables the driller to maintain the product of the drilling variable of bit weight and rotation speed W R at predetermined, programmed values. Limitation of maximum bit weight as well as control of sudden variations due to changes in formation resistance to penetration,

8 brought about by cavities, hard streaks, and the like, are automatically accommodated by the use of the control system of the invention.

The use of the control system of the invention enables the driller to optimize drilling programs and to establish the inter-relationships of bit weight, rotational speed, mud pump input horsepower, and bit hydraulic horsepower or impact, which results in producing the maximum drill bit footage at minimum cost per foot with specific drilling equipment, formation drillability characteristics and drilling fluid environment.

The drilling control system of the invention also samples the bit weight and sometimes overrides itself during the process of releasing line from the draw works. This results in a remarkably accurate application of weight and a smoothing out of the drilling operation because it is detecting very small differences in the hardness of rock being penetrated by the bit. Since the W R product is a constant, changes in weight on the bit will occur as the rotary table speed is varied. Thus, as the table speed decreases, the weight on the bit will increase and, conversely, as the table speed increases the bit weight decreases. It will therefore be readily apparent that the drilling control system of this invention provides safe, accurate and automatic control of bit weight which permits the driller to make a hole as fast, eflicient, and safely as possible.

Designed to operate under the most adverse temperature and field conditions, the master electronic control unit 5 is housed in two weatherproof containers approximately 18 x 10 x 12 inches, each weighing about 20 pounds. Obviously, many modifications and variations of the well drilling control system of the present invention are possible in the light of the teachings given hereinabove. It is, therefore, to be understood that, within the scope of the appended claims, the invention can be practiced otherwise than as specifically described.

What is claimed is:

1. An automatic control system for manipulating the draw works of a rotary well drilling rig for automatically controlling the pressure and rotational speed of a drill bit acting on the bottom of a hole which comprises: an electronic control unit which includes pressure transducer means for generating a line tension signal fed thereto into a corresponding output electrical signal, three triplyganged potentiometer means driven by a common drive shaft, an electro-mechanical servo system containing as an integral part thereof the common drive shaft of the triply-ganged potentiometer means for causing the common drive shaft to seek an angular position corresponding to the output electrical signal of the pressure transducer means, calibrate means coupled with the first of said three triply-ganged potentiometer means for causing the angular position of said common drive shaft accurately to represent drill bit weight acting on the bottom of a hole, maximum drill bit weight reference potentiometer means coupled with the second of said three triplyganged potentiometer means, comparison operational amplifier means connected to said second triply-ganged potentiometer means and said maximum drill bit weight reference potentiometer means for receiving output voltages from said two potentiometer means and converting them by comparison and amplification and producing an electrical signal representing a conversion of the angular position of said common drive shaft of the triply-ganged potentiometer means and the drill bit weight into a corresponding electrical signal, a second operational amplifier means connected to said pressure transducer means and said first triply-ganged potentiometer means for receiving output voltages therefrom as a difference voltage therebetween and producing an amplified error signal output, said second operational amplifier means being connected to said electromechanical servo system for introducing the amplified error signal output of said second operational amplifier means as an input into said electromechanical servo system to cause more accurately said common drive shaft of the triply-ganged potentiometer means to seek an angular position corresponding to the output electrical signal of said pressure transducer means, a bit weight multiplied by bit rotational speed reference potentiometer means coupled with said third triply-ganged potentiometer means and a bit rotational speed input connected to said third triply-ganged potentiometer means for feeding an electrical signal thereto from a tachometer means and producing an electrical signal from the third triply-ganged potentiometer means representing the product of bit weight and bit rotational speed; a power source connected to the electronic control unit for supplying operating power thereto; a rotary well drilling rig draw works; and control means coupled with the draw works and the electronic control unit for receiving output control signals from the electronic control unit and converting the signals into automatic manipulative control actions on the draw works.

2. An automatic control system according to claim 1, wherein a general drilling rig servo control system is included in said electronic control unit and comprises: a third operational amplifier means connected to said second triply-ganged potentiometer means and said bit weight multiplied by bit rotational speed reference potentiometer means and producing amplified error signals of the product of bit weight and bit rotational speed, AND gate means connected to said third operational amplifier means for receiving said error signals therefrom, said AND gate means also being connected to said comparison operational amplifier means, said AND gate means being connected to said control means coupled with said draw Works, a variable repetition rate pulse generator, a variable pulse width control connected to the variable repetition rate pulse generator and to the AND gate means and a sudden weight change override circuit means connected to the output of said second operational amplifier means and to said AND gate means.

3. An. automatic control system according to claim 1 wherein said calibrate means is adapted for calibration of said electronic control unit to various line tension transducer means D and E and also various numbers of lines strung on block and tackle means used in the rotary well drilling rig employed.

4. An automatic control system according to claim 1, wherein said control means coupled with the draw works and said electronic control unit includes a fluid actuator valve means connected to the electronic control unit for receiving electrical control signals therefrom, a source of fluid actuating pressure connected to the fluid actuator valve means, a fluid pressure actuated control cylinder means connected to the fluid actuator valve means, and linkage means operatively linking the control cylinder means to a brake handle of said draw works for control of the draw works.

5. An automatic control system for the draw works of a rotary well-drilling rig for automatically controlling the pressure and rotational speed of a drill bit acting on the bottom of a drill hole, said system comprising an electronic control unit having first means for generating a first signal corresponding to the pressure of the drill bit on the bottom of a hole, second means for generating a second signal corresponding to the rotational speed of said bit, control means responsive to the product of said first and second signals to control said draw works, and third means for generating a third signal, said third signal being dependent on the diiference between the bit pressure and a reference maximum pressure for influencing said control means. I

6. A system according to claim 5 wherein said first signal-generating means comprises a difference signal amplifier connected to receive a signal from a pressure transducer responsive to tension in a drill rig cable supporting the drill bit, and a signal from a first potentiometer which is movable in response to the amplified difference signal in a sense to reduce the difference signal to 0, and calibrating means for varying the voltage across said first potentiometer.

7. A system according to claim 6 wherein said second signal-generating means comprises a second potentiometer ganged with the first potentiometer and connected to a voltage source which is dependent upon the speed of rotation of the drill, a second difference signal amplifier connected to receive a signal from the second potentiometer and from a reference potentiometer indicative of a reference value of bit pressure multiplied by bit rotational speed.

8. A system according to claim 7 wherein said third signal-generating means comprises a third potentiometer ganged to the first potentiometer, and a third difference signal amplifier connected to receive a signal from a third potentiometer and from a reference potentiometer indicative of a reference value of maximum-allowable bit pressure.

9. A system according to claim 6 wherein said calibrating means is adapted to calibrate the electronic control unit to various cable-tension transducers.

10. A system according to claim 7 wherein said control means comprises AND gate means connected toreceive the signals from said diiference signal amplifiers and a repetition rate pulse generator elfective to feed pulses to said AND gate means.

11. A system according to claim 10' wherein said control means further comprises means connected to the output of the first difference signal amplifier for supplying a signal to the AND gate means in response to sudden change of tension in the drill cable.

12. A system according to claim 5 wherein said control means further comprises a fluid actuator operatively connected to a brake handle of the draw works and responsive to said signals.

13. An automatic control system for controlling the draw works of a rotary well drilling rig comprising:

speed means for sensing the rotational speed of a bit and for generating a signal related to said speed; weight means for sensing the weight of said bit and for generating a'signal related to said weight;

combining means connected to said speed means and said weight means for combining the signals related to said speed and weight and for generating a control signal related to the product of said speed and weight; and

control means connected to said combining means for controlling the draw works of a rotary well drilling mg.

14. A system as claimed in claim 13- including further:

means connected to said weight means for generating a signal related to the weight of said bit and for applying said signal to said control means whereby said control means also controls said draw works in accordance with the weight signal generated by said further means.

15. A system as claimed in claim 14 wherein said further means includes maximum weight control means for controlling the maximum weight of said bit.

References Cited UNITED STATES PATENTS 1,913,752 6/1933 Goldman 173-6 2,005,889 6 /1935 Dillon et a1. 173-6 X 2,032,155 2/1936 Staege 1736 2,298,222 lO/194-2 McShane 1736 X 2,609,181 9/1952 Jaescjke 1734 X 2,651,198 9/1953 Hayward 17320 X FRED C. MA'I'IERN, JR., Primary Examiner.

L. P. KESSLER, Assistant Examiner.