US3429385A - Apparatus for controlling the pressure in a well - Google Patents

Description

Feb. 1969 M. R. JONES ETAL Sheec L of 3 Filed Des.

Feb. 25, 1969 M. R. JONES ETAL 3429,385

APPARATUS FOR CONTROLLING THE PRESSURE IN A WELL Filed Beo. so, 1966 Sheet 2 o1" I INVENTORS Feb. 25, 1969 APPARATUS FOR CONTROLLING THE PRESSURE IN A WELL Filed Dec. 30, 1966 M. R. JONES ETAL Sheet 3 CAI F Utiited States Patent O 3,429 ,385 APPARATUS FOR CONTROLLING THE PRESSURE IN A WELL Marvin R. Jones and Benton F. Baugh, Honston, Tex., assignors to Cameron Iran Works, Inc. Houston, Tex.

--;-Filed Dec. 30, 1966, Sex. N0. 606,312 U.S. 'Cl. 175-25 10 Claims Int. Cl. E2lb 3/12, 21/00, 47/06 ABSTRACT OF THE DISCLOSURE A choke is connected to an outlet from the upper end of the annulus between a well bre penetrating an earth formation containing fluid under pressure and a drill string extending into the well bore. When a kick is encountered during drilling of the well, a blowout preventer at the wellhead about the o1'1tlet may be closed to divert drilling fluid circulating through the drill string and annulus through the choke. The choke is responsive to a bias and a control signal for regulating the pressure of the drilling fluid in order to maintain the differential between the bottom hole pressure of such drilling fluid and the pressure of the formation fluid at a predetermined value. Means are provided for producing a control signal and a bias which cooprate to cause the choke t0 respectively increase or decrease the formation fluid pressure within the outlet automatically in response to a deviation, negative 01' positive, from said predetermined pressure dilferential, whereby the outlet pressure approaches a value at Which such deviation is zero. The bias is a signal representing the pressure of the drilling fluid within a standpipe connected to the upper end of the drill string, and the control signal represents the sum of the:circulating pressure loss within the drill string, the static pressure of the drilling fluid in such standpipe, and the predetermined pressure Hilferential. The signal producing means includes a means for sensing the product of the density and the square of the rate of circulation of drilling fluid within the upper end of the drill string, which is useful in computing the circulating pressure loss within such string.

This invention relates to the control of the pressure of fluid wit hin the annulus between a well bete and a drill string;e'Xtending into the hre. In one of its aspects, it relates t'o such control upon entry of formation fluid into the d frilling mud within the annulus. In another of its aspebts,it relates to such control as the well is drilled unde'r p essure. More particularly, it relates to improvements in 'systems in which the well is controlled by means of a deisired back pressure imposed on the annulus at the head'ofthte well, In another of its aspects, it relates to novel equipment especially well suited for use in such systems and methods.

In systems of this type, it is the usual practice to provide a choke in a manifold connecting with the annulus beneath a blowout preventer closed about the drill string in order to establish and maintain this back pressure in the fluid diverted through the choke, which, together with the hydrostatic pressure of the mud, is sutficient to contain the pressure of fluids within formations penetrated by the well bore-i.e. prevent them from flowing into the well bore. In the case of a kick, the choke must continue to contain the formation fluid as heavier mud is circulated down the drill string and up the annulus to kill the well. More particularly, the choke is preferably adjustable so that, in controlling the well pressure, it may be so regulated as to avoid establishing excessive back pressure which might caus'e the drill string to stick, or damage a formation, the well casing, or the wellhead 3,429,385 Patenized Feb. 25, 1969 ice equipment. In these systems, as distinguished from systems employing conventional positive chokes, an effort is made to so regulate the choke as to maintain a constant bottom-hole pressure without having to change the circu lating rate.

In the use of one such system, when a kick is encountered, and With the preventer closed, the mud pumps are stopped, the choke is closed, and shut-in pressure is observed at the manifold upstream of the choke. The pump is then started slowly and the choke is gradually opened to maintain a back pressure at a level slightly above the observed shut-in pressure. When the desired cii'culatingrate is reached, it is held constant and the choke is continuously adjusted to maintain the pressure in a standpipe connected to the upper end of the drill str ing at the level it has reached at such circulating rate. This maintenan ce of a constant pressure in the standpipe continues until the kick is circulated out of the annulus.

The user thian calculates the mud weight increase necessary to containthe formation fluid, and begins to pump the heavier mud into the drill string while now adjusting the choke to maintain the annulus back pressure constant. When the heavier mud reaches bottom, the user begins to adjust the choke in order to again maintain the drill string pressure constant as such mud circulates up through the annulus. Thus, in effect, the user maintains a constant bottom-hole pressure by controlling the pressure in that portion of the well where the average density of the fluid in it is known more closely. This, of course, is the drill string during both circulation of the kick out of the annulus and circulation of heavier mud up the annulus, and the annulus when heavier mud is circulated down the drill string.

An object of this invention is to provide a system of this general type which is not only essentially automatic in that it does not require manual adjustments of the choke, but also enables the practiee of a variety of methods in that it does not require-"that the circulating rate be maintained constant.

Another object is to provide equipment for such a system which automatically senses certain conditions in the well in such a manner as to enable the citculating rate to vary in the use of the system, and also to permit the construction and Operation of other equipment for the system to be greatly simplified.

In the drawings, wherein like reference cha.racters are used throughout to designate like arts:

FIG. 1 is a diagrammatic illustration of a system constructed in accordance With the present invention and installed upon a typical well for controlling the pressure of same during drilling;

FIG. 2 is an enlarged perspective view of a console for the system, as seen from one corner thereof so as to illustrate its control panel;

FIG. 3 is a diagrammatic illustration of a pneumati system within the console of FIG. 2;

FIG. 4 is a diagrammatic illustration of a portion 01: the pneumatic system of FIG. 3, with a switch thereon moved to an alternate position;

FIG. 5 is an enlarged cross sectional view of a choke in the control system;

FIG. 6 is an enlarged longitudinal cross sectional view of a sensing device in the control system; and

FIG. 7 is another longitudinal sectional view of the sensing device, as seen along broken line 7-7 of FIG. 6.

With reference now to the details of the above-described drawings, the drilling control system illustrated in FIG. 1 is installed upon a well including a casing 20 lining a portion of a well bore 21 and a casing head 22 connected to the upper end of casing 20. A blowout preventer 23 connected above the casing head 22 has a bore 24 therethrough aligned with the bore in the casing head 3 4 and rams 25 mounted therein for reciprocation between It is also the practice to drill a well under pressure, in extended positions for closing the bore 24 and retracted which case a rotating type of blowout preventer is mainpositions for opening sarne. More particularly, as well tained closed about the drill string during at least a porknown in the art, the rams are so formed on their inner tion of the drilling of the well. In this case, of course, as ends as to seal about a drill string 26 extending through 5 in the case of shutting in the well upon entry of formathe preventer and into the Wf:ll bore 21, and thus close tion fluid, the drilling mud within the annulus would be When the signal from this sensed product is entered into the computing means, along with the depth of the well and the proper calibration factor, such computing means is automatically operable to compute the circulating pressure loss in accordance with the formula:

dP-=KMWD Wherein dP=Circulating pressure loss K=calibration factor M=mud density V=mud circulation rate D=depth of the well.

This computed circulating pressure loss, is as previously noted, indicated on the dial 60 on the control panel of the console 50.

It may be possible, in the use of this system, to ignore the effect of a change in well depth upon the circulating pressure loss. In this.case well depth need not be measured and entered into the corriputing means of the console. Thus, circulating pressure loss is calculated in accordance with the formula:

dP=KMV wherein dP=circulatin-g pressure loss K=ca libration factor M=mud density V=mud circulation rate As illustrated diagrammatically in FIG. 1, the choke 32 includes a flow-restricting member which is urged toward (to the right) and away from (to the left) maxirnum flowrestrictin-g position by means of an operator 40. As will be described more fully hereinafter in connection with FIG. 5, the operator includes a piston sealably slidable within a cylinder and connected by a stern to the fiowrestricting member. Thusfluid pressure on the left-band side of the operator piston urges the membe r toward maximum flow-restricting position, while fluid pressure 0n the opposite right-band side thereof urges such member away from maxi-mum flow-restricting position. For rea sons to be described to follow, in this embodiment 013 the choke there are equal pressure responsive areas on opposite sides of the operator piston.

The opposite sides 015 the operator 40 for the choke 32 are connected with fluid lines 65 and 66 leading to the console. More particularly, a signal transmitted from the computing means through the fluid line 65 urges the 110W- restricting member of the choke 32 to the right and thus toward maxi-mum flow-rest-ricting position. On the other band, a signal transmitted from the computing means through the fluid line 66, acts upon the right-band side of the operator 40 so as to urge the flow-restricting member to the left and away from maximum flow-restricting position. These two signals bear the same ratio to the pressure values they represent.

As will be described to follow, the user switches the systern between standpipe and manifold control, by merely manipulating a lever 67 on the control panel. More partieularly, the user is able to swing the lever between an up position to place the system on standpipe control, as dur= ing circulation of the kick out of the annulus and circulation of heavier mud upwardly within the annulus, and a down position to place the system on manifold control, as during circulation of the heavier mud dow n to the bottom of the hole. Thus, the user merely manipulates the lever from one position to another at the proper stage in the control of the well.

The console 50 also has a means for producing and entering into the computer a signal which is a mathmetical function of the sum of the static condition of the stand pipe pressure and a selected pressure which reprcsents a desired safety margin. This includes a knob 68a adjacent a dial 68 on the control panel for indicating such sum. This static pressure is observed by the user upon stopping the mud pumps and closing the blowout preventer rams about the drill string. The sum of static pressure and the selected pressure indicated on the panel and the signal entered into the computing means, which automatically adds such signal to the signal which is a mathematical function of the computed circulating pressure drop and transmits a signal proportional to their sum through the line 65 to the left-band side of the choke operator 40 as the kick is circulated out of the annulus.

The console 50 also includes a secondary computing means for determining the increase in mud weight necessary to contain the well formation and for indicating it on the dial 99 on the front panel of the console in pounds per gallon. More particularly, this secondary computing means is integrated With the primary computer in that it receives and properly combines the values entered into the primary computer for static pressure, as indicated on dial 68, and depth of the well, as indicated by dial 5-8.

As shown in FIG. 3 line 51a connects standpipe trans- -mitter 51 with the gauge having dial 52, and line 55a Con nects the manifold transrnitter 55 with the gauge having dial 56. As also shown in FIG. 3, the transmitter lineS 51a and 55a continue beyond the gauges for connection with switch means in the form of a valve body having a valve member 71 with passageways therein switchable by means of the lever 67 between the alternate positions on FIG. 3 and FIG. 4. In the position of FIG. 3, one end of the left-band passageway connects with the line 51a from transmitter 51, while in the position shown in F IG. 4, such passageway connects -with the line 55a. The opposite end of the left-band passageway of valve member 71 remains connected with a fluid line 72 connecting with amplifier 73 for transmitting an amplified signal from line 72 to line 66 leading to the operator 40 of the choke for urgin-g the flow-restricting member in the choke to the left and away from maximu-m flow-restricting position. Thus, switching of the lever 67 between its alternate positions transtnits Signals to the right side of the choke operator 40 proportional to standpipe pressure or manifold pressure, as desired.

As also shown in FIG. 3, a fluid line 75 connecting with the indicator 58 for the depth of the well leads to a force bridge 76 for transmitting a signal thereto which is a mathematical function of such depth. Another fluid line 77 connecting with the indicator 59 for the calibration factor also leads to the force bridge 76 for transmitting a signal thereto which is a mathematical function of such calibration factor. More particularly, these fluid lines are connected with regulators 91 and 92 which are connected with a branch 54a of supply fluid line 54 for transmitting signals in a desired range. This branch supply line also connects with the bridge through line 76a. In the force bridge, the two signals are multiplied by one another, and the product is transmitted through fluid line 78 to a second force bridge 79.

The fluid line 63 connecting with the transmitter 62 on sensing device 61 also lgads to the force bridge 79 so as to transmit thereto a signal which is -a mathematical to transmit thereto the signal which 'is a mathematical function of the circulating pressure loss. A signal which is a mathematical function of the static pressure indicated on dial 68 is also transmitted to the relay 81 by means of fluid lines 82 and 82a leading from A branch 80a of the fluid line 80 leads to a relay 81 such iudicator. A line 68a also conuects line 82 with a regulator 90 which, like regulators 91 and 92, is counected to brauch supply line 54a. In the relay 81, the siguals are added, a coustant is su-btracted from the sum, and the resulting signal is transrnitted through fluid line 83 leading to the valve casing 70. The fluid line 82 counecting With static pressure iudicator 68 also conuects with the valve casing 70 to one side of the counection therewith of fluid line 83.

Thus, Upon switchiug of the valve mernber 71 by meaus of lever 67, the right-haud passageway rnay be switched betweeu a position connectiug it with the line 82 and a position connectiug it with the line 83. The opposite and of the right-haud passageway is fixed for couuectiou to a line 84 leadiug to an arnplifier 85. The outlet from the amplificr couuects with line 65 leadiug to the left side of the choke operator 40 for transrnittiug a signal thereto which urges the flow-restricting member toward maximum flow-restricting position.

Thus, with the valve in the position shown in FIG. 3, the signal trausruittod through line 83 conuected to lines 84 and 65 to the left side of the Operator 40 is proportional to the sum of circulating pressure loss, as computed and iudicated upou dial 60, and the previously measured static pressure in the staudpipe plus the selectcd pressure, as iudicated upon the dial 68. This signal may be terrued a coutrol signal. At the same time, and as previously meutioned, a signal is transmitted through the line 51a couuected to liues 72 and 65 to urge the flow-restrictiug meruber away from maximuru flow-restricting position with a signal proportional to standpipe -pressure. T bis signal may be termcd a bias. However, upon switching of the valve member 71 to the position of FIG. 4 the signal transmitled through liues 84 and 66 originatcs from line 82, and is thus proportional to static pressure, while the signal transmitted through liues 72 and 66 originates from line 55a, and is thus proportional to mauifold pressure. Both the staudpipe and mauifold transmitters are conuectcd to supply line 54 by means of brauch line 54b.

As will be understood to those skilled in the art, the above-mentioned safety margin or selected pressure repre sents a predetermined differential betwecn the pressure of the formation fluid and the pressure of the well fluid opposite the formatiou fluid. This pressure differential is a mathematical fuuctiou of the staudpipe pressure, the static pressure, and the circulating pressure loss in accordance with the equation:

n=f( i s il wherein P is the pressure differential, P, is the standpipe pressure,

P is the static pressure, and

P is the circulating pressure loss.

Upon enteriug the cousole 50, fluid supply line 54 cou uects with a dryer 86a, a filter 86b and a pressure regulator 87, all in series, and theu continues for councction with both of the amplifiers 73 and 85. Also, there are regulators 88 and 89 in each of the brauch lines 54a and 54b. As previously noted, brauch line 54a leads to the force bridgcs 76 and 79, adding relay 81, line 64 conuecting with the transmitter 62, for sensiug element 61 and regulators 90, 91 and 92 conuecting, respectively, with the indicators for static prcssure, well depth, and the calibratiou factor. The other brauch line 54b is counected with each of liues 57 and 63 leading to the flOW' line and staudpipe transrnitters, respectively.

The secondary computer for determiuing the mud weight necessary to balauce or undcr or over balauce by a predeterrniued pressure the formatiou pressure comprises a force bridge 95 adapted to divide the static pressure times a constaut by the depth of the well. For this purpose, the line 75 leadiug from the iudicator 58 for well depth has a brauch line 75a conuecting with the bridge 95 for transrnitting a signal thereto proportional to such. depth.

Also, the line 82, which transmits a signal from indicator 68 proportional to static pressure, has a. brauch 82b leading to relay 96, which adds a constaut to this signal. The sum is then trausmitted as a signal from relay 96 and through line 97 to the bridge 95. Coutrol pressure from brauch 54a is also counected to each of the bridge 95 and relay 96.

The above-describecl siguals alternately trausmitted through line 65 to the left-haud side of operator 40 bear the same ratio to the iudicated pressures ou the coutrol pauel and, as previously mentioued, bear a fixed ratio to the ratio of the signals from trausmitters 51 and transrnitted through line 66 to the right side of the Operator to the actual pressure within the couduits on which they are mounted. More particularly, with a choke operator 40 having equal pressure responsive areas on its opposite sides, the pressure siguals trausmitted through liues and 66, respectively, bear the same ratio to the actual values of the measured, set or computed pressures they represent.

Thus, for example, in this system, fluid rnay be supplied from a suitable source through line 54 at -160 p.s.i. and then reduced in the regulator 87 upstrcarn of amplifiers 73 and to 70 p.s.i. Regulator 88 reduces the regulated supplied fluid in brauch 54a from 70 p.s.i. to 20 p.s.i., and regulator 89 reduces it in line 54b, which connect with lines 53 and 57, from 70 p.s.i. to 40 p.s.i.

As well known in the art, most pneumatic computer compoueuts, such as the force bridges 76, 79 and above-described, operate withiu a range of 3-15 p.s.i. Thus, in this system, the siguals to be eutered iuto the computers are in the same range. That is, each of the dials 58 indicatiug the depth of the well in feet, 59 indicatiug the calibratiou factor, and 69 indicating the seused prod" not of mud deusity times the square of its circulatiug rate is adapted to trausmit a signal of 3 p.s.i. at its minimum reading and a signal of 15 p.s.i. at its maximum reading. Also, the dial 60 is adapted to indicate minimum to maximum values for measured circulating pressure loss in rcsponse to signals from the computer 79 in the same operatiug range.

The dial 68 for indicating observed static pressure is, ou the other haud, adapted to trausrnit siguals in the rauge of 015 p.s.i. However, in the relay 96, 3 p.s.i. is added to the signal proportional to static PT6SSUI6, and a signal proportional to the sum and in the range of 318 p.s.i. is eutered iuto force bridge 95. The mud weight iucrease computed in force bridge 95 is iudicated on dial 99 on a scale corresponding to the 3-15 p.s.i. rauge.

In the relay 81, on the other band, this increment of 3 p.s.i. is taken from the signal relatcd to the sum of computed circulating pressure loss and standpipc pressure. The adjusted signal, which is transmitted through line 83 to the switching valve, is in the range of 0-20 p.s.i., and the scales on the dials 60 and 68 for circulatiug pressure loss and static pressure, respectively, rauge from 04,000 p.s.i. and 05000 p.s.i. Thus, the signal transrnitted through line 83 bears the same ratio to the sum of the values indicated on these scales as does the signal trausrnitted through line 82 to the value shown ou the static pressure scale until the sum reaches 20 p.s.i. as supplied to the relay. More particularly, the signal in line 72 is doubled in amplifier 73, while the signal in line 84 is quadrupled in amplifier 85, so that the resultiug signals ou opposite sides of the choke operator are, as previously rneutioued, in the same ratio t0 the actual pressure values which they represent.

In preparing to coutrol the well with this systeru, and while drilling with the well open, the user will, from time to tirne, adjust the knob 58a for correctiug the depth of well to be eutered in the computer. The mud density and circulating rate need not be chauged or adjusted since their product, in the above-meutioued formula, is automatically seused and eutered into the computer coutinuously duriug circulatiou of the mud. Thus, after ad justing the depth of the well setting on dial 58, the user need only compare the standpipe pressure indicated on dial 52 with the circulating pressure loss indicated on dial 60. If they are not in agreement, the user adjusts the knob 59a so as to change the calibrating factor in order to bring the circulating pressure loss into agreement with the standpipe pressure. When this is done, the user records the adjusted calibration factor which is now entered into the Computer. Alternatively, and as previously described, the change in well depth may be ignored.

The user further prepares for the kick by moving the lever 67 up to standpipe control, which in turn moves valve mernber 71 to the right to the position of FIG. 3. Then, when a kick is encountered, the user picks the drill bit'up oif the bottom of the hole, shuts down the mud umps, and closes the blowout preventer rams 25 about the drill string 26. After a short wait, he then reads the standpipe pressure on the dial 52 andthe manifold pressure on the dial 56 and records both of them. He then sets the dial 68 by means of knob 68a to indicate the static standpipe pressure which he has read on dial 52 plus any desired safety margin for over balance, and starte the mud umps.

As will be apparent from the foregoing description, the force bridges 76 and 79 automatically computes and produces the signal which is a mathematical function of the circulating pressure loss, and the relay 81 automatically adds this signal to the signal proportional to the setting on dial 68 and substracts 3 p.s.i. from the sum to produce a signal which is proportional to the sum of the pressure values represented. This latter signal is then transmitted through the line 83 to the switch means including the valve casing 70 and switchable valve member 71. With the valve mernber moved to the right, as shown in FIG. 3,

this signal is transmitted through lines 84 and 65 to the choke operator 40 for urging the flow-restricting member toward maxirnum flow-restricting position. At the same time, a signal proportional to the standpipe pressure is transmitted through line 51a, through valve 70, into line 72 and then through line 66 to choke operator 40 for urging the flow-restricting rnember away from maximum flowline-restricting position. Thus, the well is controlled through the drill string by maintaining a bottom hole pressure equal to the sum of the hydrostatic head of the mud and the sum of static standpipe pressure and the selected pressure, plus that part of circulating pressure loss occurring in the annulus. The circulating pressure loss is constantly being computed, and automatically cornpen= sates for changes in the mud circulating rate.

As drilling mud is circulated through the well, the choke 32 will automatically adjust for any deviation frorn the predetermined pressure difierential so as to main tain the standpipe pressure at the level required for maintaining the bottom hole pressure substantially constant.

When the kick has been circulated out of the well bore, level 67 is moved to its lower, manifold control position, and the heavier mud is circulated down through the drill string 26 to the bottom of the hole. The added mud weight necessary in order to provide an adequate hydrostatic pressure when such mud has reached the bottom of the hole has, of course, been computed in the manner described and indicated on a dial 99 011 the console 50.

Movement of the lever 67 switches the valve member 71 to the left-hand position shown in FIG. 4. In this shifted position of the valve member, a signal proportional to manifold pressure is transmitted by line 55a through the switch to line 72 and thus into the line 66. Thus, this signal is transmitted to the choke operator 40 for urging the flow-rcstricting member away from maximum flowrestricting position. At the same time, a signal proportional to the static pressure which was set on the dial 68 is transmitted through line 82 and the switching valve into line 84 where it is transmitted by amplifier 85 and through line 65 to the operator 40 of the choke. This latter signal urges the flow-restricting member toward maximum flow restricting position. Since it is a mathematical function of the set static pressure, this signal is a constant so that the flow-restricting member of the choke 32 autorhatically adjusts in such a manner that the opposing signal through line 66, which is proportional t0 the manifold pressure, rernains constant. This continues until the heavier mud is pumped to the bottom of the hole.

At this time, the user turns the knob 68a to change the reading on the static pressure dial 68 to zero, and moves the lever 67 to the upper position of FIG. 2 for switching the systern to drill string control. This, of course, switches the valve mernber 71 back to the right, as shown in FIG. 3. However, since the dial 68 for static pressure has been moved to zero, the sum which is transmitted from the relay 81 to the valve 70 by means of line 83 is proportional only to the circulating pressure loss so that the signal transmitted to the operator 40 for urging the flow-restricting mernber to flow-restricting position is sirnilarly a signal proportional only to the circulating pressure loss. This signal, of course, is opposed by a signal proportional to standpipe pressure transmitted through line 51a and the switching valve into line 72 to the operator 40 through line 66. Thus, during circulation of the heavicr mud upwardly through the annulus of the well, the choke automatically adjusts to maintain the standpipe pressure at a level equal to the computed circulating pressure. The user begins to weigh the mud returns as soon as the manifold pressure indicated on dial 56 reads zero. When the weight of the returns approaches that of the heavier mud, the user checks the hole to see if it runs over with the mud pump stopped. If it does not, he knows the well is killed.

In the event of a 'sevcre kick, or With expensive rig rates, the user may want to start killing the well at the same time he starts to circulate the kick out of the annulus. In doing sohe will reduce the amount of pressure built up on the annulus, and also reduces the amount of time the drill bit is inactive.

In this latter alternative method, he follows the same initial steps as in the other method above-described When he counters a kick. That is, he picks the bit up off the bottom of the hole, he shuts the mud pumps down, and closes the preventer rams a'b0ut the drill string. Furthermore, the reads and sets the static pressure in the standpipe upon the dial 68 after the well has been shut in for a short time. Normally, he Will add to this reading an overbalance and set the sum on the dial 68. He further reads and records the choke manifold and standpipe pressures, as indicated on dial 56. moves the lever 67 to standpipe control position, and resumes mud circulavon.

In this method, the user immediatcly begins to circulate the mud into the drill string at whatever rate he is able to mix the mud. He reads the dial 99 indicating mud weight increase and mixes his mud accordingly, knowing that this reading includes any overbalance he has adcled to the static pressure. The user determines how long it takes the new mud to get to the bit at the bottom of the drill string, and rcduces the static pressure gradually so that it reaches zero when the heavier mud arrives at the bit.

More particularly, as the heavier mud reaches the sens-= ing device 61, the user observes the change in circulating pressure loss reflected on the dial 60, and reduces the static pressure reading on the dial 68 a corresponcling amount by suitable adjustrnent of the knob 68a. He then continues to acljust this knob in order to continuously reduce the static prcssure, as adjusted, in proportion to the depth reached by the mud, until such pressure reading is zero. He also watches the manifold pressure dial 56, and when it reaches zero he knows that the well should be dead. He then begins to weigh mud returns, and when they are within a point or two of the heavier mud weight, he checks the hole to see if it will 1 1 run over. lt it does not, he knows that the well is dead.

Other methods may be advisable under these same or different conditions, and the use of such methods with this system are contemplated by the present invention. Also, of course, the user may use this system in drilling under pressure, in which case he merely follows these procedures described in accordance With the first method during the initial standpipe control of the well.

As shown in FIG. 5, in its preferred form, the choke 32 includes a body 100 having a chamber 101 (herein intersected by an inlet 102 to the chamber and an outlet 103 from the chamber. The inlet and outlet are formed at right angles to one another and the intersection of the inner end of the outlet 103 with the chamber 101 forms an annular seat 104 which is adapted to be substantially closed by an annular, flow-restricting member 105 which moves axially toward and away from the outlet. Thus, in the position of the flow-restricting rnember shown in FIG. 5, there is an annular opening between the inner end of the flow-restricting member and the inner end of the seat 104 through which fluid may pass from the inlet 102 to the outlet 103. As the mernber 105 rnoves to the left, this annular opening is, of course, enlarged so as to permit less restrlcted flow, in which case there is less back pressure on the annulus 29 of the well.

On the other hand, as the member 105 moves to the right, it further restricts the annular opening between its inner end and the inner end of seat 104, so as to thereby increase the back pressure in the annulus 29. In its extreme right-hand position, the inner end of member 105 moves a short distance into the inner end of the seat 104 so as to restrict flow through the choke to a maximum extent.

The operator 40 comprises a T-shaped fitting 106 having its small end removably mounted within an opening 107 in choke 100 to close same. This opening extends from the charnber to the outer end of the body in axial alignment with both the outlet 103 and the seat 104, and thus parallel to the direction of rnovement of rnember 105. Thus in a manner to be described hereafter, the member 105 is guidably slidable within the small end of fitting 106.

The opposite large end of the fitting 106 comprises a cylinder 109 formed between a cup-shaped opening covered by a plate 108 releasably secured to and sealably engaged With the inside of the cup. A piston 110 is sealably slidable within the cylinder for reciprocation along the axis of reciprocation of the mernber 105, and a stem 111 extends through the fitting to connect the piston to a head on the flow-restricting member 105. T hus, reciprocation of the piston 110 of the operator will cause a corresponding reciprocation of the flow-restricting mernber 105 between the positions previously described.

This reciprocation of the piston results from the transmittal to its opposite sides of the signals previously described in connection with each of the systems. Thus, there is a threaded port 112 in the plate 108 for connection with the line 65. Also, there is a port 112a through the cup for threaded connection with the line 66.

The stem 111 has a telltale 111a extending sealably through the plate 108 and of the same diameter as the portion thereof extending sealably through the fitting to connect piston 110 to flow-restricting member 105. Thus, the piston 110 is balanced in this preferred embodiment of the choke 32, which is of advantage in responding to the signals. The telltale 111a is visible through a slotted guard 114 mounted about it on the outer side of plate 108 to permit the the user to determine, by its movement, whether or not the choke is working properly.

The small end of the fitting is received closely within choke body opening 107 and is sealed with respect thereto by a seal ring 116. This end of the fitting is hollow t provide a skirt 115 which extends inwardly beyond 'opening 107 and into the chamber 101 to a position close the seat so as to support substantially the entire length of the flow-restricting member which, as previously noted, fits closely within the inner diameter of the skirt so as to be guidecl thereby during its reciprocation.

As can be seen from FIG. 5, the flow-restricting member 105 is hollow at its inner end opposite the passageway 101, and has a head 116 on its outer end for threaded connection to the end of the stem 111 of the operator. There are a series of ports 117 extending through the head of the member 105 to freely connect the hollow interior of the member 105, and thus the chamber 101, with the area between the head and the closed end of the fitting at the base of the skirt 115. In this way, pressure within the Choke 32 acts only over the cross sectional area of the -stem 111 to urge the flow-restricting member 105 to the left or away from flow-restricting position. Even this small force is opposed by a force due to atmospheric pressure acting on the cross sectional area 0f the telltale 111a, which, as previously mentioned, is of the same cross sectional area as the stem 111. Thus, there is a minimum of tendency for pressure Within the choke to urge the member 105 away from flow-restriction position, particularly due to pressure within outlet 103 when the member 105 is in its extreme position within seat 104.

As can be seen from FIG. 5, the seat 104 comprises a removable ring which is cylindrical so as to be reversible end-for-end within an enlarged diameter portion 103a of the outlet 103 of the choke. Thus, it is possible to increase the life of the seat by so reversing it when wear has taken place at the inner diameter of one end. The inner diameter of each end of the seat ring is chamfered to facilitate movernent of the flow-restricting rnember 105 into its extreme flow-restricting position. A seal ring 118 is received about a central portion of the outer diameter 0f the ring so as to sealably engage with the recessed portion 103a in either end-for-end position of the ring.

The hollow portion of flowwestricting member 105 is recessed about its open end to receive a removable sleeve 119, which is also cylindrical so as to be reversible endfor-end, similarly to the seat ring 104, on the hollow portion of such member. More particularly, the sleeve 119 forms a continuation of the outer diameter of the hollow portion of the flow-restricting member so as to slide with it closely within the skirt 115. The opposite ends of the outer diameter of the sleeve are charnfered for guiding into the oppositely facing end of the ring 104.

A snap ring 120 is carried within the oppositely facing grooves on the inner diameter of the ring 119 and outer diameter of the recessed portion of the member 105 so as to releasably retain the sleeve about such member body. Access is had to the snap ring 120 by means of a slot 121 extending from the end of the recessed portion of the member to accommodate a tool of any suitable type. By means of this tool, the ring may be held in a collapsed position to permit insertion and removal of the sleeve 119.

The inner corners of the seat 104 and tthe outer corners of the sleeve 119 are lined with a hard, wear-resistant material, preferably tungsten carbide. More particularly, each such annular lining extends from an intermediate point on each end of the seat ring or sleeve to an intermediate point on the inner and outer diameter thereof, respectively. Thus, the linings cover the portions of these parts which are most susceptible of wear. Furtherrnore, since the linings are over both corners of these parts, they serve this function regardless of how they are disposed end-for-end.

The small end of the fitting 106, including the annular skirt 115 thereof, is releasably mounted within the opening 107 of the choke body by means of snap ring 122 engaging in a groove in an outer end of opening 107. Thus, an annular shoulder about the small end of the fitting is positioned to be opposite the inner side 0f this groove when such end is inserted fully within the choke body opening and seal ring 116 is sealably engaged with such opening. As can be seen from FIG. 5, cover 108 13 is similarly releasably secured to the cup-shaped open end of the*fitting. As can also be seen from FIG. 5, suitable seals are provided about the openings in plate 108 and the srr1all end of the fitting 106 so as to seal about the stem 111 connecting the flow-restricting member 105.

As v vill be apparent from the foregoing, upon removal of the small end of the fitting from within opening 107, the seat ring 104 can be replaced or reversed end-for-end, therethrough. Also, of course, with the fitting removed, the sleeve 119 may also be replaced, or reversed end-forend.

As previously described, and as shown in FIGS. 6 and 7, the sensing device 61 comprises a tubular conduit 125 of the same inner diameter as the standpipe 28 and having me'ans, such as flanges, on its opposite ends for connection in the standpipe as a smooth continuation thereof. It also includes a shaft 126 extending diametn'cally through the opposite sides of the conduit for rotation therein, and an arm 127 mounted on the shaft within the conduit for rotation therewith and extension longitudinally of the conduit. There is a sensing element 128 in the shape of an airfoil or hydrofoil on the end of the arm 127 rernote frorn the shaft 126 and occupying in a neutral position, substantially the mid portion of the conduit. More particularly, the sensing element 128 is arranged to be urged up or down out of the neutral position in proportion to the product of mud density times the square of the mud circulation rate through the conduit. i

In Order to reduce turbulence within the sensing device to a minimum, the arm 127 is of flat, narrow construction, as seen along the plane shown in FIG. 6, and of convergent tapering construction from the shaft 126 to the sensing element 128, as seen in the plane of FIG. 7. More particularly, the end of the arm 127 which surrounds the shaft 126 includes a tear-drop portion 127a extending from one side to another of the conduit, as shown in FIG. 6, and secured to the shaft 126 by means 015 a Set screw 131.

As shown in FIG. 6, there is also an arm 129 mounted on one outer end of the shaft 126 for rotation therewith along the outer side of the conduit 125. The end of this exterior arm 129 remote from the shaft 126 has a head 130 thereon for engagement at its lower end With an oppositely facing part on the transmitter 62 which, as previously described, is of such construction as to transmit a signal through line 63 proportional to the force by which the flowing drilling mud urges the sensing element 128 out of its neutral position. This force is, of course, transmitted to the head 130 through the arm 127, shaft 126, and arm 129.

The transmitter 62 is of a so-called null balance type which is operable to return the head 130 and thus the arm 129 to its original position With a force to the signal which it transmits. A suitable device for this purpose is a Nullmatic force transmitter manufactured by Moore Products, Inc. Thus, in the operation of the sensing device 61, the flowing mud acts upon the element 129 to urge it out of the neutral position shown in FIG. 7 with a force proportional to the product of the mud density times the square of its circulating rate. This in turn is transmitted through the inner and outer arms to the transmitter 62, which in turn transmits a signal to the above-described product to the console 50.

As shown in FIG. 6 the opposite ends of the shaft 126 extend through openings 132 in sleeves 133 on opposite exterior sides of conduit 125. The inner end of each openi'ng 132 has a shoulder 134 against which a seal ring 135 is held by means of a ball bearing 136. The bearing is in turn held tightly against the seal ring by means of a gland nut 137 threadedly engaged with the outer threaded end of opening 132. Preferably, the seal ring 135 includes a thin disc of Teflon whose inner diameter is held tightly against the outer diameter of the shaft 126. By means of the gland nut 137 engaging against bearing 136, only the outer diameter of the Teflon ring is held against rotation, so that its inner diameter is free to rotate with the shaft 126 as the sensing element 128 moves in a small arc responsive to the drilling mud flow. Thus, there is a minimum of frictional resistance to the rotation of the shaft 126, even during its small are of rotation.

The transmitter 62 is releasably mounted upon a platform 138 suspended from the lower side of the conduit 125, as seen in FIG. 7.

From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other ad vantages which are obvious and which are inherent to the apparatus and method.

The invention having been described, what is claimed 1s:

1. A system for controlling the pressure of a fluid within the annulus between a well bore penetrating a formation containing fluid under pressure and a drill string extending into the well bore, wherein drilling fluid is circulated through the drill string and the annulus, and there is a pressure diflerential, positive or negative, by which the bottom hole pressure of such drilling fluid exceeds the formation pressure, including a choke for connection to the upper end of the annulus, said choke having a flow-restricting member movable toward and away from maximum flow-restricting position and a signal responsive operator for so moving the flowrestricting member, means for sensing the pressure of fluid within the upper end of the drill string and for producing a first signal which is a mathematical function of the pressure so sensed, means for transmitting the first signal to the choke operator for urging the flow-restricting member away from maximum flow-restricting position, means for sensing the product of the density and the square of the rate of circulation of fluid within the upper end of the drill string and producing a signal which is a mathematical function of such product, means for producing a signal which is a mathematical function of a selected calibration factor, means for combining the two last-mentioned Signals in accordance With the equation:

wherein dP=circulating pressure loss K=calibration factor M=density V=circulation rate and producing a second signal which is a mathematical function of the circulating pressure loss, means for producing a third signal which is a mathematical function of the sum cf static pressure of fluid sensed within the upper end of the drill string and a predetermined pressure dilferential, means for producing a fourth signal which is a mathematical function of the sum of the second and third signals, and means for transmitting the fourth signal to the choke operator to urge the flow-restricting member toward maxirnum flow-restricting position and cooperating with said first signal to cause the choke to increase or decrease the pressure in the upper end cf the annulus automatically in response to deviations from said predetermined pressure diiferential, and thereby maintain said bottom hole pressure substantially constant.

2. A system for controlling the.,pressure of a fluid within the annulus between a well bore penetrating a formation containing fluid under pressure and a drill string extending into the well bore, Wherein drilling fluid is circulated through the drill string and the annulus, and there is a pressure differential, positive or negative, by which the bottom hole pressure of such drilling fluid exceeds the formation pressure, including a choke for connection to the upper end of the annulus, said choke having a floW-restricting member movable toward and away frorn maximum flow-restricting position and a signal responsive operator for so moving the flow-restricting rnember, means for sensing the pressure of fluid within the upper end of the drill string and for producing a first signal which is a mathematical function of the pressure so sensed, means for transmitting the first signal to the choke Operator for urging the flow-restricting member away from maximum flow-restricting position, means for sensing the product of the density and the square of the rate of circulation of fluid within the upper end of the drill string and producing a signal which is a mathematica1 function of such product, means for producing a signal which is a mathematical function of a selected calibration factor, means for producing a signal which is a mathematical function f the depth of the well, means for combining the three last-mentioned signals in accordance with the equation:

dP=KMV wherein:

dP=circulating pressure loss K=calibration factor M=density V=circulation rate D=depth of the well and producing a second signal which is a mathematical function cf the circulating pressure loss, means for producing a third signal which is a mathematical function of the sum cf static pressure of fluid sensed within the upper end of the drill string and a predetermined pressure differential, means for producing a fourth signal which is a mathematical function of the sum of the second and third signals, and means for transmitting the fourth signal to the choke operator to urge the flow-restricting member toward maximum flow-restricting position and cooperating with said first signal to cause the choke to increase or decrease the pressure in the upper end of the annulus automatically in response to deviations from said predetermined pressure dil'ferential, and thereby maintain said bottom hole pressure substantially constant.

3. A system for controlling the pressure of a fluid within the annulus between a well bore penetrating a formation containing fluid under pressure and a drill string ex= tending into the well bore, wherein drilling fluid is circulated through the drill string and the annulus, and there is a pressure dilferential, positive or negative, by which the bottom hole pressure of such drilling fluid exceeds the formation pressure, including a choke for connection to the upper end of the annulus, said choke having a flowrestricting member moveable toward and away from maximum flow-restricting position and a signal respon sive operator for so moving the flow-restricting mernber, means for sensing the pressure of fluid within the upper end of the drill string and producing a first signal which is a mathematical function of the pressure so sensed, means for transrnitting said first signal to the choke operator to urge said flow-restricting mernber away from maximum flow-restricting position, means for producing a second signal which is a mathematical function of the circulating pressure loss 0f fluid circulating within the well bore, means for producing a third signal which is a mathematical function of the sum of a sensed static pressure of fluid within the upper end of the drill string and a predeterrnined pressure differential, means for producing a fourth signal which is a mathematical function of the sum of said second and third signals, means for transmitting each of said third and fourth signals to the choke operator for urging said flow-restricting member toward maximum floW-restricting position, means for sensing the pressure 0f fluid within the upper end of the annulus up stream of the choke and producing a fifth signal which is a mathematical function of the pressure so sensed, means for transrnitting said fifth signal to the choke operator to urge the flow-restricting member away from maximum flow-restricting position, means for interrupting the trans- 16 mission of one of said first and fifth signals to the choke operator while the other is being transmitted thereto, and rneans for interrupting the transmission of one 01 said third and fourth signals to the choke operator while the other is transmitted thereto.

4. Apparatus for use as part of a pressure control system for a drilling well, wherein the system includes a choke connected to the upper end of the annulus between the well bore and a drill string extending into the well bore, and the choke has a flow-restricting member rnoveable toward and away from flow-restricting position and a signal responsive operator for so moving the flowrestricting member; said apparatus comprising a console having a control panel, means in the console for automatically computing the circulating pressure loss of fluid circulating within the well by combining signals which are mathematical functions of certain characteristics 0f the well including a selected calibration factor, the density of the fluid within the well, and the circulation rate of said fluid, means for independently entering each of said signals into said computing means, means for receiving signals which are mathematical functions of the pressure of fluid sensed within the upper end 0f the drill string and the upper end of the annulus, respectively, means on the control panel for indicating the computed circulating pressure loss, the entered well characteristics, and the sensed fluid pressures within the upper ends of the drill string and annulus, means on the control panel for adjusting the calibration factor, means in the console for producing a signal which is a mathematical function of the sum of a selected pressure and sensed static pressure of fluid within the upper end of the drill string, means in the console for producing a signal which is a mathematical function of the computed circulating pressure loss, means in the console for automatically adding the last two mentioned signals, and means in the console for producing a Signal which is a mathematical function of the sum thereof.

5. Apparatus of the character defined in claim 4, including means for transrnitting to said choke operator each of said signals which are mathematical functions of the fluid pressure sensed within'the upper end cf the drill string and the upper end of the annulus, respectively; said signal which is a mathematical function of the sum of selected pressure and sensed static pressure, and said Signal which is a mathematical function of the sum of said last-mentioned Signal and said Signal which is a mathematical function of the circulating pressure loss.

6. Apparatus of the character defined in claim 5, wherein said signal transmitting means includes switch means for transmitting, in one position, the signals which are mathematical functions of the fluid sensed within the upper end of the drill string and of the sum of computed circulating pressure loss and the sum of selected pressure and sensed static pressure, and, in an alternate position, the signals which are mathematical functions of the fluid sensed within the upper end of the annulus and of the sum of selected pressure and sensed static pressure, and means for moving said switch means between said positions.

7., Apparatus for use as part of a pressure control system for a drilling well, wherein the system includes a choke connected to the upper end of the annulus between the well bore and a drill string extending into the well bore and a means for sensing and producing a Signal which is a mathematical function of the product of the density and the square of the rate of circulation of a fluid within the upper end 0f the drill string, and the choke has a flow-restricting member movable toward and away from flow-restricting position and a signal responsive operator for so moving the flow-restricting member; said apparatus comprising a console having a control panel, means in the console for receiving said signal and automatically computing the circulating pressure loss of fluid circulating within the well by combining it with other Signals which are mathematical functions of certain characteristics of the well includinga selected calibration factor, means for independently entering each of said lastmentioned signals into said computing means, means for receiving signals which are mathematical functions of the pressure of fluid sensed within the upper end of the drill string and the upper end of the nnulus, respectively, means on the control panel for intlicating the computed circulating pressure loss, the entered well characteristics, and the sensed fluid pressures within the upper ends of the drill string and annulus, means on the control panel for adju sting the calibration factor, means in the console for producing a signal which is a mathematical function of the sum of a selected pressure and sensed static pressure of fluid within the upper en'd of the drill string, means on the control panel for adjusting said last-mentioned signal and indicating said sum, and means in the console for producing additional signgals which are mathematical functions of the computed 'circulating pressure loss andthe sum of said last-meritipned signal and the signal which is a mathematical function of the sum of a selected pressure and sensed statie pressure, respectively.

8. For use in drilling a well into an ea rth formation containing fluid under pressure, wherein drilling fluid is circulatd through a drill string extefiding intoa wellboxe anii through the annulus therizbetween, said string and annulus having upper ends, one of which is an inlet and the other an outlet, there being a pressure ditferential, positive or negative, by which the bottom hole pressure of the drilling fluid exceeds the formation fluid pressure, and there being a deviation, positive or negative, by which said pressure diiferential exceeds a predetermined value thereof; apparatus for maintaining said pressure difler ential at the predetermined value thereof, comprising a choke for regulating the outlet fluid pressure in response to a bias and a control signal, means for producing a con-= trol signal and a bias which cooperate to cause the choke to increase or decrease the outlet fluid pressure automatica1ly in response to said deviation being respectively negative or positive, whereby the outlet pressure approaches a. value at which said deviation is zero, said last-mentioned means including means for sensing the product of the density and the square of the rate of circulation of the drilling fluid and producing a signal corresponding to the sensed product, and means for computing a signal representing the eirculating pressure loss of the drilling 18 fluid within the drill string by multiplying said produced signal by a signal representing each of certain well characteristics including a calibration factor.

9. Apparatus of the character described in claim 8, whleirein another well characteristic is the depth of the we 10. For use in controlling a well, a console having a control panel, means in the console for automatically computing the circulating pressure loss of fluid circulating within the well by combining Signals which are mathematical functions of certain characteristics of the well, including a selected calibration factor and the product of density of the fluid within the well and the square of the circulat ion rate of said fluid, means for independently entering said signals into said computing means, means for receiving signals which are mathematical functions of the pressur'e fluid sensed within the inlet and outlet, respectively, of the well, means on the control panel for indicating the computed circulating pressure loss, the entered well characteristics, and the sensed fluid pressures within the inlet and outlet, means on the control panel for adjusting the calibration factor, means in the console for producing a signal which is a mathematical function of the sum of a predetermined pressure diiferential and a sensed static pressure of the fluid within the well, and means for producing additional signals which are mathematical functions of the computed circulating pressure loss and the sum of said last-mentioned signal and the signal which is the mathematical function of the sum of the predetermined pressure diflterential and the sensed static pressure, respectively.

References Cited UNITED STATES PATENTS Re. 26,220 6/ 1967 Records 25 X 2786652 3/1957 Wells 4...-..- 17525 3268,017 8/ 1966 Yarborough 17525 3338,3 19 8/1967 Griflin 175--25 3362487 1/ 1968 Lindsey 166-91 X 3372761 3/1968 Van Gils 175-25 CHARLES E. OCONNELL, Primary Examiner I. A CALVERT, Assistant Examiner U.S. Cl. X.R.

UNITED STATES PATENT :0Fmc1a: CERTIFICATE OF CORRECTION Patent N0. 3 429 385 February 25 1969 Marvin R. Jones et a1 It is certified tha.t error appea.rs in the above identified patent and tha.t seid Letters Patent are hereby corrected as shown below:

In the drawings Sheet l Fig. 1 the reference character G shou1d be added to show the ground level. Column l line 27 cancel "formation". Column 3 line 9 "spring" should read string Column 9 line 25 "computes" shou1d read compute line 25 "produces" should read produce line 29 "substracts" should read subtracts Column 10, line 42 "counters" should read encounters line 45 "the", first occurrence, should read he Column 15 that portion of the formula reading KMV2 should read KMVZD.

Column 16 line 52 after "fluid" insert pressure line 56 after "fluid" insert pressure Column 18 line 17 "pressure fluid" shou1d read fluid pressure Signed and sealed this 16th day of June 1970 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E.- SCHUYLER, JR. Attest1ng Officer Commis.sioner of Patents

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