US2455917A

US2455917A - Drilling control system

Info

Publication number: US2455917A
Authority: US
Inventors: Wilfred S Crake
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1946-02-09
Filing date: 1946-02-09
Publication date: 1948-12-14
Anticipated expiration: 1965-12-14

Description

W. S. CRAKE DRILLING CONTROL SYSTEM Dec. 14, 1948.

2 Sheets-Sheet l Filed Feb. 9, 1946.

o Pulley Pressure Fluid ourcz Prune Mover Speed Muli'piier- /9 DRILLING CONTROL SYSTEM Filed Feb. 9, 1946 2 sheets-sheet 2 /85 From Tachomahr 1 Speed 3 weighf Indicador /7 4 lndicaor- 5a Fr'om Pnssure. 35 From Pyjessu'n Fluid Sourc f Fluid Ssu'req, f

Speed Con-trailer FIG. 3

K-D To Wegh+ To Pressure Fluid Source lnverorl Patented Dec. 14, 1948 UNITED STATES PATENT OFFICE DRILLING CONTROL SYSTEM Wilfred S. Crake, Houston, Tex., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application February 9, 1946, Serial No. 646,551

(Cl. Z55-19) 1 Claim.

This invention relates to the drilling of boreholes, such for example as oil and gas wells, and refers in particular to an automatic control system for maintaining the rate of feed of the drill bit, and the load or weight applied to the bit, at predetermined values.

The rate of penetration of the drill bit into the ground depends generally on the hardness of the ground formation. The rate of feed of lthe drill bit, or in other words the rate at which the cable supporting the drill string is permitted to unwind from the cable drum, must be adjusted to conform to the rate of penetration. By properly adjusting the feed rate with regard to the penetration rate, load or weight applied to the bit, that is, the force exerted by the bit against the bottom of the borehole, may be controlled between desired limits,

and may be maintained at a desired or optimum value.

The feed rate is usually controlled by ythe oper- -ator by means of a brake applied to the cable drum in accordance with the indicati-ons of gages showing, for any given instant, the feed rate (for example, in feet per hour), and the weight on the drill bit (for example, in points or thousands of pounds).

This method of control, involving the human element, leaves much to be desired, especially in view of abrupt changes in the rate of penetration likely to occur during drilling. These changes, as to which lthe operator receives no direct indications, may occur, for example, when the bit passes from a soft to :a hard formation, or encounters a cavity, or is subject to rapid wearing out in a hard formation, etc.

If, under these conditions, the feed rate becomes too high with regard to the penetration rate, there occurs a slack in the supporting cable and the weight on the bit rises to an excessive value, causing a premature dulling of the bit, a deviation of the drill bit from the vertical, a slowing down of the rotary speed of the drill string, etc., and in general a lowering of the drilling efficiency and a loss of drilling time.

If, on the other hand, the feed rate is too low with regard to the penetra-tion rate, the load applied to the drill bit decreases to a value below that of good drilling practice, thus again slowing the drilling operations, causing crooked boreholes, and bringing other undesirable effects.

It is therefore an object of this invention to provide a drilling control system whereby the drill bit or cable feed rate, and the weight applied to the drill bit may be automatically controlled .to con- 2 form With the .actual penetration rate of the drill bit.

It is also an object of this invention to provide Aa control system whereby the drill bit feed rate and the weight appliedto the bit may be preset and maintained at desired predetermined values, and are not permitted to exceed predetermined maximum values. 1

It is also an object of this invention to provide a system comprising a speed or feed rate controller and a weight controller operating jointly to maintain the cable drum feed at a 4proper rate, each of said controllers being however capable of assuming sole and independent control of said cable drum feed rate when the limi-ting maximum value to which said controller has been pre-set is reached.

It is also an object of this invention to provide a system wherein the control of the cable feed rate and of the weight on the drill bit is effected by pressure fluid, pneumatic, mechanical or electrical means, or by a combination of said means.

It is also an object of this invention to provide an automatic drilling control system provided with safety means for stopping the feed or preventing the drop of the drill string in case of the failure of the medium, such as pressure fluid or electric power, used for control purposes.

These and other lobjects of this invention will be understood from the following description taken with reference to the attached drawings wherein:

Fig. 1 is a diagram schematically showing the general arrangement of the component parts of the present automatic control system.

Fig. 2 is a diagram illustrating the weight responsive controller of Fig. 1.

Fig. 3 is a diag-ram illustrating the speed or feed rate responsive controller of Fig. 1.

Fig. 4 shows a modification of a part of the diagram of Fig. l.

Referring to Fig. l, a drill bit I and drill string 2 are supported in a borehole by means yof a cable 4 passing over a block or pulley arrangement 5 attached to the top of a derrick, not shown.

The dead end 4A of the cable is attached to a fixed point 'l of the derrick structure, while the other end is wound on a cable drum 8 rotating `on a shaft 9. The cable drum may be wound up, for example, by means of a chain drive I0 and any desired prime-mover Il, provided with a clutch I3, which is released when it is desired to unwind the cable drum, said unwinding or feed action being thus effec-ted solely by the pull of the drill string 2 lon. the cable 4.

The shaft is connected to a speed multiplier i4, whose high speed shaft l5 carries a 4brake drum i1. Due to the extremely high ratio be tween the speeds of the shafts i6 and 9, for example ve hundred or more to one, a relatively small force applied to the brake drum I1 is sufricient to restrain the rotation of the cable drum 8 against the relatively very high force or pull exerted by the drill string 2.

A restraining force is applied to the brake drum l1 in any suitable manner, for example by means of shoe, band or disk brakes, as diagrammatically indicated in the drawing by brake means i9 and H9.

The brake means l5 and ||9 are urged against the brake drum I1 by means of powerful springs 2D and |20, capable of applying suflicient pressure to stop the rotation of the drum 8. The brakes are released against the action of the lsprings by means of a le-ver arrangement diagrammatically shown at 22 and |22.

The lever 22 is controlled by an arrangement involving a motor valve or diaphragm mechanism 28, responsive to a weight controller 3|, and the lever |22 is controlled by a fluid motor or diaphragm mechanism 29, responsive to a speed or cable feed controller 32.

A tachometer 25 is actuated by the high speed shaft i6 or another suitable element of the speed multiplier, and may be made, for example, as a small generator adapted to produce a current proportional to the rotating speed of the shaft l5 and therefore of the cable drum 8.

The tachometer 25 is electrically connected by leads 34 to the speed controller 32.

Connected to the cable 4, and preferably to the dead-end 4A thereof is a weight-indicating device 36 'connected by means of a conduit 35 to the weight controller 3|.

Referring to Fig. 2, the weight indicator may be of any desired type and is shown for purposes of illustration to comprise a housing 36 clamped to the cable 4A by means of members 31. A piston 39, positioned intermediate the clamps 31, extends through the walls of the housing and is attached to a fluid-tight diaphragm 38 xedly stretched' within the housing 34. The resiliency of the diaphragm causes the piston to press against'the cable 4A, causing a bend in said cable. rllheY housing 36 and the conduit 35 are filled with any desired fluid.

The conduit or pipe 35 extends to the controller 3 l, which may likewise be of any desired type and is shown for purposes of illustration to comprise a Bourdon type `tube 4|] and an indicating or recording gage 4|, both in communication with the conduit 35.

The end of the Bourdon tube is pivotally conected, for example, by means of a stem 43, to a plate 44, which is likewise pivotally attached to some xed point 46. The control mechanism comprises further a housing '41, in communication by means of a conduit or pipe 49 with a source of pressure fluid or air 52, and by means of a conduit 5| with the fluid motor 28, as shown in Fig. l.

Passing through the housing 41 is a stem 53 provided with an internal channel 55. The stem 53 has external screw-threads 56 and an adjusting micrometric screw-knob 51, whereby the stem may be laterally moved with regard to the housn ing 41, and the distance between the outer end of the channel 55 and the plate element 44 may be accurately adjusted as desired to control the amount of air or pressure fluid escaping through Channel 55.

The speed or feed controller 32 may likewise be of any desired type and is shown for simplicity in Fig. 3 as similar to the weight controller of Fig. 2.

The tachometer 25 of Fig. l is connected, through wires 34 and 58 to an indicator 59, which may be calibrated in any desired units, to give the feed rate of the cable drum 8 in revolutions per minute, or the cable or bit feed in terms of feet per hour.

A relay or solenoid coil 6| is connected to the wires 34 and serves to actuate, against the action of a spring |45, a stem |43 and a pivoted plate element |44, similar to

elements

43 and 44 of Fig. 2. Likewise similar to corresponding elements of Fig. 2 are the pressure housing |41 and the channeled and screw-threaded stem |53 adjustable by means of a knob |51, and having a channel |55.

The housing |41 is in communication, through pipes 54 and'49 with the pressure fluid source 52, and through pipe 65 with the motor valve 29.

The weight controller of the present system should preferably be adapted to handle and to record any weight between zero and 50,000 lbs. on the bit, or between zero and 400,000 lbs. on the hook or cable and the speed recorder any feed rate between Zero and feet per hour of vertical drill bit displacement.

The control of the drilling operations by means of the above system is effected as follows:

Assume that at the beginning of the process the drill string 2 is suspended within the borehole with the drill bit at some distance above the bottom thereof. The cable drum is held stationary by the action of the springs 2l) and |20 engaging the brake I9 and H9 against the brake drum l1.

The pressure fluid or compressed air, which may be admitted to the weight controller 3| by opening a valve 63, enters the housing 41 (Fig. 2) and is permitted to vent or escape through channel Y55. By rotating the adjusting knob 51, the stem is made to advance towards plate 44 and prevent the pressure fluid from escaping through channel 55. The pressure fluid thereupon passes through pipe 5| to the upper side of diaphragm 21 of the fluid motor 28, thus forcing said diaphragm and the rod 2| downwards and causing lever 22 to pivot and release the brake yI9 from the brake drum |1 against the action of spring 20.

The brake drum is then held stationary by brake shoe I I9 of the speed controller,

The pressure uid or compressed air, which has been admitted to the speed controller 32 by opening Valve 63, enters the housing |41 and is permitted to vent or escape through the channel |55. By rotating the adjusting knob 51, the stem |53 is made to advance against the plate |44, thus gradually shutting olf the escape of the pressure fluid through channel |55. The pressure fluid thereupon passes through pipe 65 to the lower side of diaphragm |5 of the motor valve 29, forcing said diaphragm and the rod |2| connected thereto upwards, and thus causing the pivoted lever |22 to release ,the brake ||9 from the brake drum |1A against the action ofthe spring |20.

.As the cable drum thus starts to unwind under the effect of the pull exerted by the drill string, the tachometer 25 and indicator or recorder 59 indicate the rate of feed 0f the drill bit. When some desired value, such for example as l0 feet per hour is reached, the further adjustment of the controller 32 by means of the screw |51 is discontinued, `and the drill string is lowered until the drill bit reaches the bottom.

Assume that the weight of the drill string and bit is 100,000 lbs. and that it is desired that the bit carry a load of 10,000 lbs., that is, a pressure of 10,000 lbs, be exerted by the bit against the bottom of lthe borehole.

In such case, the cable must support 100,000 lbs. so long as the drill string is completely suspended without touching the formation, and 90,000 lbs. when the drill bit rests against the formation to the whole extent of the load desired, that is, 10,000 lbs.

As the drill bit descends towards the bottom of the borehole, the whole weight of 100,000 lbs. is carried by the cable, and this value is registered or recorded by means of the weight indicating device 36 and gage 4I, this gage being suitably calibrated for any multiple line arrangement used for block 5, and preferably for indicating or recording the weight on the drill bit rather than the weight on the cable.

The whole weight of the drill string being at this time supported by the cable, the cable exerts a maximum force on the piston 39 of the weight indicating device 36 of Fig. 2, thus applying pressure to the fluid in said device and in conduit 35.

Under the effect of this pressure, the Bourdon tube 40 expands in well known manner, forcing, through stem 43, the plate 44 against the orifice of channel 55. The stem 53 is withdrawn at this time, by manipulating the knob 51 as far back as necessary to permit a full expansion of the tube 40 without allowing the pressure uid to escape through channel 55.

As the bit touches the bottom and the continued feeding of the cable causes said bit to rest on the :s

ground with an increasing force, for example, 2,000, 4,000, 6,000, 8,000 and 10,000 lbs. in succession, which weight is indicated or recorded by gage 4l, the weight on the cable correspondingly decreases from 100,000 lbs. to 90,000 lbs.

The decreasing pressure of the fluid within tube 35 causes the Bourdon tube to contract, thus pulling the plate 44 away from the orifice of channel 55. The stem 53 is however advanced at this time against the receding plate 44 so as not to permit any escape of the pressure fluid until the gage 4| reads the desired weight on the bit, that is 10,000 lbs., at which time the further adjustment of the stem 53 is discontinued.

The present system is now properly adjusted for control operations, and the drilling may be started in the normal manner, involving the use of the rotary table, drilling fluid, etc., with the bit feed rate and the weight on the bit being maintained at predetermined values and without being permitted to exceed the pre-set maximum values selected as described above, the drill bit feed rate being automatically made to adjust itself tc the actual drill bit penetration rate.

This automatic method of control can be best illustrated by the following example:

Assume as above that the maximum feed rate is set at 10 feet per hour and the maximum Weight on the drill bit at 10,000 lbs., a soft layer having been drilled through under these conditions.

Upon the drill bit encountering thereafter a hard layer where the penetration rate is for example only 4 feet per hour, the feed rate is in excess of the penetration rate, resulting immediately in a slack in the cable and a corresponding increase of the weight on the bit to a Value in excess of 10,000 lbs., thus causing an undesirable condition.

The slack on the cable, however, results in a contraction of the Bourdon tube of the Weight controllenwhich permits the pressure iiuid to escape through channel 55, thereby relieving the pressure on the diaphragm 21 of fluid motor 28, and applying the brake I9 to slow down the bit feed rate until said feed rate is reduced sufciently to take off the slack in the cable, whereafter the drilling proceeds as before with the bit feed rate automatically adjusted to the value of the new penetration rate, that is, 4 feet per hour.

If, after passing through the hard layer, the bit encounters an extremely soft formation, or even a cavity in the ground, all weight is momentarily removed from the bit and is carried in the cable. The weight controller acts in this case to disengage the brake i9, and the drum 8, undery the effect of the heavy weight of the drill string, has a tendency to unwind at a very high rate, thus dropping the drill string to the bottom.

The instantaneous increase of the drum speed, however, as transmitted by the tachometer 25 to speed controller 32, results in the solenoid -or relay coil Bl of Fig. 3 pulling in the plate |44, releasing the pressure on the diaphragm l5 of motor valve 29 and thus applying the brake II9 so as not Vto exceed the pre-set rate of the controller 32.

t will be seen therefore that the two controllers of the present system cooperate with each other in such a manner as to maintain the drill bit feed rate at a Value corresponding to that of the drill bit penetration rate, but below pre-set maximum values of weight carried by the bit and of feed rate of said bit, each of said controllers being adapted to take control over the system independently of the other controller as soon as the maximum value, weight or feed rate, to which said controller is pre-set, is exceeded, thereby bringing the system back to operation within normal limits.

It is understood that the particular structure of the weight or speed indicators, motor valves or diaphragme, weight indicators, etc., which have been described above to define clearly the operation of the control system as a whole, forms no part of this invention, and that any desired types of these devices, whereby the application of the brakes may be effected in response to increase or decrease of the weight of the cable, increase or decrease of fluid pressure on diaphragms, etc., may be equally well used. It is also understood that instead of eecting drilling control according to the present invention by pneumatic or electro-pneumatic ways, as described above for purposes of illustration, such control may be effected by mechanical or electrical means.

Fig. 4 shows a portion of the drilling organization of Fig. 1, wherein the brake drum Il is engaged by a brake 89 in response to an increase of fluid pressure on the diaphragm 8l of a motor valve 88 transmitted by the weight controller upon an excessive weight being applied tc the bit.

Instead of a pneumatic speed controller, there is used however in this embodiment a mechanical speed controller comprising a micrometric screw 84 connected by means of a Wire 85, passing over a pulley 83, to the lever 82 actuating the brake. The tachometer 25 and the speed or feed indicator 59 are the same as in Fig. l.

In adjusting the speed controller of Fig. 4 for operation, the drill string is permitted to descend in the borehole above the bottom thereof at a varying rate by varying the adjustment of the micrometric screw 84 and thus the engagement of the brake 89 with the brake drum l1. As there is no weight on the bit, there is no pressure in einem?? the Weight-responsive motor valve 88 and this valve exerts a-t1 this time noI controlling action. When the gage'v 59 indicatesA the@ desired maxi,- mumy speed, for example; 101feetv per hour, the further adjustment orv the micrometric screw 813 is discontinued, and the weight controlleris then adjusted for a desired maximum weight insub stantially the same manner as describedwith regard toAFig. 1.`

The operationof thesystem; of- Figf.. Lisv similar to tlatofiFig. 1 as Will-be seen fromthefollowing example-z Assuming, as before, tl'iatv the-drillbit reaches a cavity, the removal of pressure on` the bit will cause a removal of iiuid press-ure in thev motor valve 88 anda disengagement ofthe brake 89, the drill string tending to fallv` down` throughA the cavity: Since, however, the micrometric screw 81% r lias= been adjusted toA hold; theA brake inA such engagement withthe brake drum that no feed rateeiniexcess of for example 10'v feetper houris permitted, the drillbit will bemoved' through the cavity.l atv that maximum speed untill itI touches hard? ground again, whereupon the weight controllen will again assume controlto` maintain the weight on the bit below the pre-set maximum value;`

A safety brakey 99', operated by a lever 52 and motor valve 98, connectedto the source ofpressureA fluid, against thev action of a spring 98, may be used with. the system as additional protection in case-of a failnreoty the pressure uid or a--mechani'cal failure of the speed`- controller;

Iclaim as my invention.:

Anvautornati-c control system fior a` rotary; drilling installation@ comprising a drill stringv supported on'Y a cable: and a cabledrum rotatingl to -unwindtbe cableasftne drillistring-'descends, said systemvr comprising aI high-ratiov speed multiplier drivenl bythe cablel drum, said speed multiplier having a` high-speed shaft, brakemeansf on said shaft, first andi second fluid motormeans, leverage means connected to said uid motor means andsaid brake means for-applying the' restraining 8. force, of: said; brakeA means to said: high.,speed sliafit',V means for supplying4 to said fluidi motor means an actuating pressure uidg, said= means comprising-1 a` source. of fluid pressure, av weight controller and first conduit means; connecting saidi weight controller to said source and; the first uid motor'meansV a speed controller and second conduit meansy connecting. said speed controller to-4 saidi source and the. secondi fluid'r motor means, adjustaliole means on the weight' controller for pre-setting the fluid pressure transmitted thereby to the first fluid motor to; a value corresponding to a predetermined Weight supported-1 by the.- cable, adjustable meansy onthe: speed controller for pre-setting the ilud pressuretransmitted-` thereby to the second, motor. fluid' to a valuey corresponding to: a predetermined speed of said' multiplier shaft, a Weight indicator connected to the cable for registering the weight supported therei by, a speed indicator corlnectedito` the multiplier shaft for"v registering the speedv thereof, means responsively' connecting the weight' indicator to the-adjustable means on the Weight controller forI Varying-'the setting of said adjustable means inA proportion to thechanges of the Weight supported by: the cable, and meanslresponsively connecting the speed' indicator tof the adjustable means on the speed controller. for Varying the settingof' said adjustablemeans in proportion to the ehangesof the-speed of.' the multiplier shaft, whereby tbe fluid pressure transmitted to said fluid? motorsr` i'sindependently varied in. proportion to said Weight changes and to saidspeed changes.

WILFRED REFERENGES CITED' The following references are of record in the diev of this patent:

UNITED STATES PATENTS.

Number Name Date 1",9'l3"752y Goldman June 13i 1933 2,080,804 Brantly May 18?, 1937 2111110781 Brauer May 10,- 1938