US3443643A - Apparatus for controlling the pressure in a well - Google Patents

Description

May 13, 1969 M. R. JONES APPARATUS FOR CONTROLLING THE PRESSURE IN A WELL l of 4 Sheet Filed Dec.

INVENTOR.

ATTORNEVJ May 13, 1969 M. R. JONES APPARATUS FOR CONTROLLING THE PRESSURE IN A WELL Sheet 2, 014

Filed Dec. 30. 1966 Mar wn /?f (fa/7e;

Q Q \Q Q R R w% mm, -w Q. NM...

N A WELL M. R. JONES May 113, M6

APPARATUS FOR CONTROLLING THE PRESSURE l Sheet Filed Dec.

A 770/?NE VJ M. R. JONES APPARATUS FOR CONTROLLING THE PRESSURE IN A WELL Sheet Filed Dec.

/lia INVENTUR.

3,443,643 APPARATUS FOR coNaRoLLING THE PRESSURE ABSTRACT OF THE DISCLOSURE A choke is connected to an outlet from the upper end of the annulus between .a well bore penetrating an earth formation containing fluid under pressure and a drill string extending into the well bore. When a kick is en countered during drilling of the well, a blowout preventer at the wellhead about the outlet may be closed to divert drilling :fluid circulating through the drill string and an nulus through the choke. The choke is responsive to a bias and a control signal so as to regulate the pressure of the drilling fluid in order to maintain the differential be= tween 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 cooperate to cause the choke to respec tively increase or decrease the formation fluid pressure within the outlet automatically in response to a deviation, negative or positive, from said predetermined pressure differential, whereby the outlet pressure approaches a value at which such deviation is zero. The bias is a signal representing the pressurejof 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 predeter mined pressure differential.

This invention relates to the control of the pressure of fluid within the annulus between a well bore and a drill string extending into the'bore. In one of its aspects, it relates to such control upon entry of formation fluid into the drilling mudwithin the annulus. In another of its aspects, it relates to such control as the well is drilled under pressure. More part'icularly, it relates to improve= ments in systems in which the well is controlled by means of a desired back pressure imposed on the annulus at the head of the well. In another of its aspects, it relates to novel equipment especially well suited for use in such systems.

In systems and methods of this type, it is the usual prac tice 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 suf-= ficient to contain the pressure of fluids within formations penetrated by the well borei.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 cause the drill string to stick, or damage a formation, the well casing, or the wellhead equipment. In these systems, as distinguished from systems employing conventional positive chokes, an eflort is made to so regulate the choke as to maintain a constant bottom-hole pressure without having to change the circulating rate.

In the use of one such system, when a kick is encoun:

iifl ikd tii Patented May 13, 1959 tered, and with the preventer closed, the mud pumps are stopped, the choke is closed, and shut-in pressure is ob served at the manifold upstream of the choke. The pump is then started slowly and the choke is gradually opened tomaintain a back pressure at a level slightly above the observed shut-in pressure. When the desired circulating rate is reached, it is held constant and the choke is con= tinuously adjusted to maintain the pressure in a standpipe connected to the upper end of the drill string at the level it has reached at such circulating rate. This maintenance of a constant pressure in the standpipe continues until the kickis circulated out of the annulus.

The user then calculates the mud weight increase neces sary to contain the 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 at the value it reaches after the kick has been'cin culated out of the annulus. When the heavier mud reaches bottQrn, the user begins to adjust the chokein order to again maintain the drill string pressure constant as such mud circulates up through the annulus. Thus, in effect, the user maintains a substantially constant bottom-hole pressure by controlling the pressure in that portion of the well-:where the average density of the fluid injt is known more closely. This, of course, is the drill string during both circulation of the kick out of the annulus and cir culation of heavier mud up the annulus, and the annulus wher rheavier mud is circulated down the drill string.

-An' object of this invention is to provide a system of this general type which is more automatic thanprior sys terns in that it requires at most a minimum of manual adjustment of the choke.

- A further object is to provide a system having equip ment. which enables an unskilled operator to control the well with a minimum of time and effort.

A' still further object is to provide a console having a control panel from which the operator can obtain informationl required in controlling the well and *parts thereon by means of which the operator can perform the manipulations necessary to such control, and a computer therein for automatically determining and transmitting to the choke signals responsive to the computed control pressures.

- Inthe drawings, wherein like reference characters are used throughout to designate like parts:

FIG. 1 is a diagrammatic illustration of a system construe't ed in accordance with one embodiment of 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 forthe system, as seen from one corner thereof so as to illustrate its control panel;

FIG. 3 is a diagrammatic illustration of another sys tem constructed in accordance with the present invention and, similarly to the system of FIG. 1, installed upon a well for controlling of same;

FIG. 4 is an enlarged perspective view of the console for the system shown in FIG. 3, also seen from one corner thereof to illustrate its control panel;

FIG. 5 is a diagrammatic illustration of a pneumatic system within the console of FIG. 4;

FIG. 5A is a diagrammatic illustration of a portion of the pneumatic system of FIG. 5, with a switch thereon moved to an alternate position;

FIG. 6 is an enlarged cross sectignal view of a choke in both the control system of FIG. 1 and the control system of FIG. 3;

FIG. 6A is a longitudinal sectional view of replaceable parts for the choke;

FIG. 7 is an enlarged longitudinal cross sectional view of a sensing device in the control system of FIG. 3; and

FIG. 8 is another longitudinal sectionalview of the sensing device, as seen along broken line 88 of FIG. 7.

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 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 there-- through aligned with the bore in the casing head and rams 25 mounted therein for reciprocation between extended positions for closing the bore 24 and retracted positions for opening same. More particularly, as well known in the art, the rams are so formed on their inner ends as to seal about a drill string 26 extending through the preventer and into the well bore 21, and thus close the annular space between the drill string and preventer bore in order to shut the well in.

There is a bit 27 at the lower end of the drill string 26 for drilling the well bore 21 as the string is rotated by suitable well known apparatus located at the well-head. A standpipe 28 is connected to the upper end of the drill string 26 above blowout preventer 23, and drilling mud is circulated through the standpipe downwardly through the drill string 26 to the bit 27, and upwardly within the annulus 29 between the drill string and the casing 20 and uncased well bore 21.

A side outlet 30 connects with the bore of the casing head 22 beneath the preventer 23 and above ground level G. Thus, upon closing of the blowout preventer rams 25 about the drill string, as shown in FIG. 1, fiuid within the annulus 29is diverted into the outlet 30. Manifolding in the form of a cross 31 connecting with the outlet 30 provides a straight run forming a continuation of the outlet and upper and lower wings to which chokes 32 are connected. In the present case, as will be described to follow, these chokes are of special construction and com prise a part of the novel control system of the present invention.

The straight run as well as the upper and lower Wings of the cross are provided with valves of suitable con struction for selectively opening or closing themflAs shown in FIG. 1, a valve in the straight run and a valve in the lower wing are closed to divert flow through the choke 32 in the upper wing. In this way, the system is ready for use on the well. Alternatively. the valve in the upper wing could be closed and the valve in the lower wing opened to put the lower choke in operation. Or, when the system is not needed, the valve in the straight run can be opened and the wing valves closed.

As well known in the art, during the ordinary drilling of the well, the preventer rams 25 are open so that drilling mud circulated downwardly through the drill string 26 and upwardly through annulus 29 passes out the upper end of the blowout preventer 23 for collection and subsequent recirculation through the drill string. When. however, the well bore 21 penetrates a formation F or other strata bearing lluid of a higher pressure than the hydrostatic pressure of the drilling mud at an adjacent level, it has been the practice to close the preventer rams 25 about the drill string to prevent the blowout of the well due to the entry of higher pressure formation fiuid into the annulus. Then, as preparations are made to replace the existing drilling mud with denser mud for increasing the hydrostatic pressure in the well bore, the mud containing the formation fluid is diverted by the closed rams into the outlet 30 through a choke.

It will be understood that bottom hole pressure means the pressure within the well bore at the bottom of the drill string regardless of the position of the drill string in the well bore. It will also be understood that formation pres sure, at least when the drill string is not at the bottom of. the well bore, is adjusted to the actual position of the lower end of the drill string by reducing it by the amount of pressure due to the head of fiuid between the formation and the bottom of the drill string.

As previously described, this establishes a back pressure in the annulus 29 for containing formation fiuidpressure. In some c ses, however, when the choke has b n of a positive ty e, it created a back pressure which tended either to break down a formation or to damage the casing. Even when attempts have been made to adjust the choke, the apparatus and systems for doing so have had many shortcomings. In accordance with the present invention, these and other problems areovercome by the improved system of this invention including a choke 32 having a novel construction to be described.

It is also the practice to drill a well under pressure, in which case a rotating type ofblowout preventer is maintained closed about the drill string during at least a portion of the drilling of the well. In this case, of course, as in the case of shutting in the well upon entry of formation fluid, the drilling mud within the annulus would be diverted into the flowline, and through the choke 32 for imposing a back pressure on the annulus. This enables the operator to drill the well with at least somewhat lighter drilling mud.

In addition to the choke 32, the system shown in FIG. 1 includes a console 33 having a computing means therein adapted to receive information regarding certain conditions of the well, including its depth, the rate at which the drilling mud is circulated therethrough, and the density of the drilling mud. These conditions are measured in a well-known manner and are indicated on a control panel of the console, which automatically enters them into the computing means. The computing means also includes a means for receiving a calibration factor which is entered into it by a suitable control knob on the front panel. Upon entry of this calibration factor, together with the other values representing well conditions, the computer automatically calculates the circu lating pressure loss in the well in accordance with the formula:

dP=KMV D 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 indicated on the panel of the console for the information of the user in using the system, in a manner to be described.

The console also includes means for receiving signals proportional to and indicating the measured pressure within the standpipe 28 as well as within the manifold upstream of the choke 32. For this purpose, there is a pres sure transmitter 34 mounted on the standpipe 28 and a similar transmitter 35 mounted on the side outlet 30. Each such transmitter may be of conventional construc tion, such as the Type J illustrated and described on pages 1196-97 of the 1966-67 edition of the Composite Catalog of Oil Field Equipment and Servicesv Thus, it includes a diaphragm. which is exposed to the lluid pressure to be measured on one side and a signal pressure on the other side, and means including a supply pressure for maintaining a fixed ratio between the measured pressure and the signal pressure. This then produces a signal which is proportional to the measured pressure and transmitted in the manner to be described.

Thus, as shown in FIG. I, there is a branch 360 from a pressure supply line 36 leading to the transmitter 34 on the standpipe 28 and a transmitting line 34a extending from the transmitter for connection with a branch line 341; leading to pressure gauge 37 on the panel of the console 33. As also shown in FIG. 1, branch 360 of the supply line connects with the transmitter 35 on side outlet 30, from which a transmitting line 35a extends to connection with gauge 38 on the panel of the console 33.

As illustrated diagrammatically in FIG. I, the choke 32 includes a flow-restricting member which is urged toward (to the right) and away from (to the left) maximum flow-restricting position by means of an operator 40. .As will be described more fully hereinafter in connection with FIG. 6, the operator includes a piston sealably slid able within a cylinder and connected by a stem to the flow-restricting member. Thus, fluid pressure on the left hand side of the operator piston urges the member toward maximum flow-restricting position, while fluid pressure on the opposite right-hand side thereof urges such member away from maximum flow-restricting position. For reasons to be described to follow, in this embodiment of the choke there are. equal pressure responsive areas on opposite sides of the operator piston.

As can be seen from FIG. 1, transmitting line 34a from transmitter 34 on the standpipe 28 is also connected by a branch 340 to the right-hand side of operator so as to transmit thereto the same signal that is transmitted to gauge 37, which signal may be termed a bias. As previously described, this signal is proportional to standpipe pressure. It urges the flow-restricting member to the left and thus away from maximum flow-restricting position.

The operator is urged in the opposite direction by means of a signal transmitted to the left-hand side thereof by means of a line 41 extending from the console 33, which signal may be termed a control signal. More par= ticularly, the line '41 is connected with branch 36b of supply line 36 leading into the console 33. A regulator is connected between the lines 36b and 41 so as to regulate the pressure in the line 41 and thus the signal trans mitted therethrough on the left-hand side of operator 40. There is a gauge 42, on the front panel of the console for indicating this regulated pressure, and a knob 43 on such panel which is manually operable for adjusting the regulator so as to thereby adjust the signal.

More particularly, this gauge bears the same relationship to the regulated signal pressure as does the gauge 37 for indicated measured standpipe pressure. Consequently, the signals transmitted to the equal pressure responsive areas on opposite sides of the operator piston bear the same ratio to the measured and indicated pressures they represent. Thus, in a manner to be described hereinafter, the user of this system can by means of the knob 43 adjust the choke and thus the amount of back pressure imposed on annulus 29.

The various factors which are entered into the com puting means for arriving at circulating pressure loss in the drilling mud are indicated upon dials along the upper portion of theffront panel of console 33. Thus, as indi= cated in FIG. 2; there is a dial 44 for indicating mud den sity in pounds per gallon, a dial 45 for indicating the cir-= culating rate of the drilling mud in gallons per minute, a dial 46 for indicating the depth of the well in thousands of feet, and a dial 47 for indicating the calibration factor. In this particular embodiment of the console, each of these values is set on its indicator and a signal proportional thereto is entered into the computer in response to manipulation of the knobs 44a, 45a, 46a and 47a just beneath their respective dials.

The computed circulating pressure loss of the drilling mud is indicated upon the circular dial 48 on the upper portion of the front panel and to the left of the above= described dials 44 to 47. Thus, when the signals propor tional to these well characteristics have been entered by means of the knobs 44a, 45a and 46a, and a proper calibration factor has been entered by the knob 47a, the computing means is automatically operable to determine the computed circulating loss and indicate it in pounds per square inch upon the dial 48. The details of this computing means are unimportant and may comprise any suitable means, such as a gear train of such design as to produce the computed circulating pressure loss in accordance with the above-described formula.

On the right-hand side of the upper portion of the front panel of console 33 are concentrically arranged dials for indicating a computed increase in mud density in points (one-tenth of a pound) per gallon necessary to contain formation pressure as well as the depth of the well in thousand feet increments and static standpipe pres sure in pounds per square inch. The necessary mud weight is automatically computed upon the entry of signals proportional to the respective measured values of Well depth and static standpipe pressure into arcomputer within the console by means of concentric knobs beneath the dials. The details of this computer are unimportant to the novel aspects of the present invention, although the use of the computed mud weight increase, and an indica tion thereof on one of the dials, by this or other means, is important to the user.

In contemplation of the need for operating the system, the user will continue to adjust the setting of the knob 47a and thus the calibration factor signal entered into the computing means. For this purpose, the user will from time to time weigh the drilling mud, check the depth of the well, check the circulating rate of the drilling mud, and then adjust the knobs 44a, 45a and 46a accordingly to reflect these values. He then observes the measured standpipe pressure indicated upon the gauge 37 in pounds per square inch. If this reading is different from the criculating pressure loss shown on the dial 48, the user adjusts the calibration knob 47a so as to bring the circulating pressure loss reading up to or down to the observed standpipe pressure reading. He then records the adjusted reading on the calibrating factor dial 47 for future reference.

All of these operations are, of course, done while the well is open during the normal drilling operations, their purpose being to determine the calibration factor at the proper value during different drilling conditions. Thus, it is known that with the well drilling normally and open, the circulating pressure loss should equal the standpipe pressure, so that if it doesnt, the calibration factor needs to be adjusted.

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

dP=KMV where:

dP=Circulating pressure loss K=Calibration factor M=Mud density V=Mud circulation rate When the user first encounters a kick, he shuts off the mud pumps to stop the circulation of drilling mud and picks the bit 27 up off the bottom of the well bore. Assuming that the well has been drilled open, he closes the rams 25 of the blowout preventer 23 about the string 26. After a short pause, he reads the measured standpipe pressure upon the gauge 37 and the measured manifold pressure on gauge 38 and makes a record of them. For this purpose, the console 33 may, as in the case of the console shown in FIG. 4, to be described, be provided with an additional dial upon which the user may make a record of the static pressure in the standpipe when the well is so shut in and mud circulation is stopped.

The user then adjusts the regulator knob 43 to bring the regulated pressure indicated on gauge 42 into agreement with the standpipe pressure reading on gauge 37. He then starts the mud pumps and gradually increases the regulator pressure by adjusting the knob 43 in such a manner as to keep the manifold pressure indicated on gauge 38 at a constant value. As soon as the user reaches the rate at which he desires to resume circulation of the drilling mud, he makes any required adjustment of the knobs for the dials 44 and 45, depending on such desired rate and density of mud which is to be used upon re circulation,

The user then adds the static pressure in the stand pipe, which he observed in a manner previously described, to the computed circulating pressure loss shown on the dial 48. After adding a safety margin of desired amount to this sum, he adjusts the regulator knob 43 so as to bring pressure indicated on the gauge 42 up to the adjusted sum. During this time, the manifold pressure indicated upon gauge 38 will vary, although normally it will not get high enough to injure the casing, as long as the user has detected the entry of formation fluid promptly.

As will be understood to those skilled in this art, the above-mentioned safety margin represents a predetermined ditferential between the pressure of the formation fluid and the pressure of the well fluid opposite the formation fluid. This pressure differential is a mathematical function of the standpipe pressure, the static pressure, and the circulating pressure loss in accordance withthe equation:

PD )(PrPs-P1) wherein:

p is the pressure differential p, is the standpipe pressure p, is the static pressure p, is the circulating pressure loss The effect of this is to transmit to the left-hand side of the choke operator 40 a signal proportional to at least the sum of the static standpipe pressure and computed circulated pressure loss. More particularly, the effective pressure areas on the opposite side of the piston within the operator are equal, so that the flow-restricting member of the choke will move first to the right toward flow-restricting position so as to impose a rather large back pressure on the annulus 29. As this back. pressure increases, it will, due to the U-tube effect of the drill string and well annulus, raise the pressure within the drill string. When this increase reaches that of the sum of static pressure and circulating pressure loss plus the desired safety margin, it will, through the signal transmitted through the fluid line 34a, back the flow-restricting member off. Thus, as the drilling mud is again circulated through the well, choke 32 will automatically adjust so as to maintain the standpipe pressure at this level. This, of course, contains the formation fluid as the kick" is circulated out of the annulus.

In the meantime, the user enters the depth of the well and observed static pressure into the aforementioned computing means of the console having the dials and knobs on the upper right-hand side of the panel for use in computing the mud weight increase necessary to contain the increased formation pressure, as indicated upon one of the dials. That is, as previously described, this entry of the static pressure and well depth into the secondary computer automatically determines and indicates such mud weight increase on one of the dials.

The user may add to this computed mud weight in-- crease whatever safety margin or overbalance he considers necessary. As the drilling mud is circulating the kick out of the annulus, the user mixes the heavier mud, so that, when the kick has been circulated out, the heavier mud is ready to be pumped into the drill string through the standpipe 28. Again due to the U tube effect of the drill string and annulus, the manifold pressure will increase as heavier mud is pumped through the drill string. The user watches this on gauge 38, and when it increases a desired amount over that originally observed, he adjusts the regulator knob 43 so as to adjust the regulator pressure to lower the manifold pressure to the value originally observed. The user then continues to adjust the knob 43 so as to maintain the manifold pressure indicated on the gauge 38 at the observed value as the new mud is pumped down to the bottom of the hole.

In the meantime, the user has set the new mud weight on the dial 44 by adjusting the knob 44a. This, of course, adjusts the circulating pressure loss shown on the dial 48 accordingly. Then, when the heavier mud hits bottom, the user adjusts the knob 43 so as to bring the regulated pressure indicated on dial 42 into agreement with the adjusted circulating pressure loss which has just been computed and is indicated on dial 48. He leaves the regulated pressure at this value as the heavier mud is pumped up the annulus 29, and watches the manifold pressure indicated on dial 38. As the heavier mud circulates up the annulus and the manifold pressure reaches zero, he begins to weigh the returns into the mud tanks. When the weight of the returns equals the weight of the heavier rnud being pumped into the drill string, the user knows that the well has probably been killed, and checks this by shutting down the mud pumps to see if the casing will flow. When he is assured that the well has been killed, he opens the blowout preventer rams 25 and resumes open drilling.

Thus, the only continuous control which the user has had to exert over the choke in using this system is the adjustment of the regulator knob 43 during manifold control as the heavier mud is pumped to the bottom of the hole. That is, he merely sets it during standpipe con trol in order to transmit a signal to the choke operator 40 equal to the sum of the static pressure and computed circulating pressure loss, plus the desired pressure, differential. Finally, when the user returns the system to standpipe control, as the heavier mud begins to flow upwardly in annulus 29, he again merely sets the knob 43 in order to transmit a signal to the left-hand side of operator 40 equal to the adjusted circulating pressure loss.

In the past, it has been the practice to drill under pressure by maintaining a constant back pressure in the annulus. However, as will be understood to those skilled in the art, the system above described remains on standpipe control as a well is drilled under pressure. Consequently, during its use, there is no need whatsoever for continuous supervision by the operator.

The system shown in FIG. 3 is, in many respects, similar to that shown and described in connection with FIG. 1. Thus, it is illustrated as being installed upon a typical well identical to the one shown in FIG. 1, and thus bearing identical reference characters. It also includes a choke 32 identical to the choke 32 of the system of FIG. 1, and connected, as in the choke 32 of FIG. 1, in the-manifold 31 on the wellhead.

The FIG. 3 system also includes a console 50 having computing means therein similar to that of FIG. 2, in that it determines and indicates circulating pressure loss, but in other respects it is an improvement thereon, as will be described to follow. This console 50, like the console 33 of the system in FIG. 1, has a front control panel containing various dials indicating measured and selected values entered into the computer and knobs for setting these values, as well as means manipulatable by the user in switching the system between standpipe and manifold control.

As in the system of FIG. 1, the system of FIG. 3 also has a transmitter 51 connected to the standpipe 28 and having a fluid line 51a leading therefrom for transmitting a signal proportional to sfandpipe pressure to the console 50, and particularly to a gauge 52 on the panel having a dial thereon for indicating such standpipe pressure in pounds per square inch. More particularly, as in the case of the transmitter 34 of FIG. 1, there is a fluid line 53 connecting with the transmitter 51 for delivering a supply pressure thereto from an external fluid source through a line 54 connecting with the console 50, and thus with the fluid line 53, by suitable means to be described.

The system of FIG. 3 is also similar to the system of FIG. 1 in that it includes a transmitter 55 connected to the side outlet 30 from the annulus 29 of the well, upstream of the choke 32. A fluid line 55a therefrom transmits a signal proportional to the manifold pressure to the console, and more particularly, to a gauge 56 on the panel of the console having a dial for indicating such manifold pressure in pounds per square inch. This transmitter also receives supply pressure from the abovementioned external source, in this case through a fluid line 57 leading thereto from the console 50. 1

Further similarities between the console Stl and the console 33 are dial 58 on the control panel for indicating the measured depth of the well in thousands" of feet, and dial 59 adjacent to the dial 58 for indicating 'a calibration factor entered. Setting of these dials enters a signal proportional to the indicated depth into the computing means, and a signal proportional to the calibration factor. These are adjusted by means of knobs 58a and 59a. Still further, there is a dial 60 on the control panel for indicating the computed circulating pressure loss of the drilling mud in pounds per square inch.

As indicated above, each transmitter 51 and 55 is identical and receives supply fluid from the same source namely, line 54. The dial on each gauge 52 and 56 has the same range, which may be, for example, -5000 psi, for indicating signals transmitted through the lines 51a and 55a in the range of 0-30 p.s.i. Thus, the signals are in the same ratio to their respective measured pressure.

In other respects, this console and the sy .em of which it forms a part differ from those of FIG. 1..-Th1ifs for example, this FIG. 3 system includes a device, ,,indicated in its entirety by reference character 61, for sensing the product of the mud density times the square of the circulating rate. As shown and described in detail inf'connec tion with FIGS. 7 and 8, this device comprises 'a conduit adapted to be connected in the standpipe and a transmitter 62 to one side of the conduit. A signal which is a mathematical function of the product sensed the'rebyjis transmitted by the transmitter 62 to computing fmea rj ts within the console for determining the circulatingipre s sure loss in accordance with the previously described formula. This transmitter, similarly to transmitters 51 and 55, is connected to a fluid line 63 leading to the console 50 and, more particularly, to a gauge having a dial 69 on the con-: trol panel of the console for indicating the product. This transmitter is also connected to the console by line 64 which in turn is connected with the supply line 4 leading to the console 50.

When the signal from this sensed product is eritered 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 circulgting pressure loss in accordance with the same formula used in the illustrated computing means of FIG. 1 system, namely:

dP=KM V D 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.

The opposite sides of 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 flowrestricting member of the choke 32 to the right and thus toward flow-restricting position. On the other hand, a signal transmitted from the computing means through the fluid line 66, acts upon the right-hand side of the operator 40 so as to urge the flow-restricting member to the left and away from flow-restricting position. These two signals bear the same ratio to the pressure values they represent.

As will be described to follow, the user swiches the system between stand'pipe and manifold control, by merely manipulating a lever 67 on the control panel. More par ticularly, the user is able to swing the lever between an up position to place the system on standpipe control, as during 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 down 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 mathematical function of the sum of the static condition of the standpipe pressure and a selected pressure which representsr'a desired safety margin or pressure differential. This includes a knob 68a adjacent a dial 68 on the control panel for indicating such sum. As in the case of the system of FIG. 1, this static pressure is observed by the user upon stopping the mud pumps and closing the blowout prevente r rams about the drill string. However, in this system of FIG. 3, the static pressure is not only observed, but the sum is actually 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 line65 to the left-hand side of the choke operator 40 as the ifkick 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 poii'tts per gallon. However, as distinguished from the secondary computer of the FIG. 1 system, this is integrated with the primary computer. Thus, it receives and properly combines the values entered into the primary computer for the sum of static pressure, and a selected pressure, as indicated on dial 68, and depth of the well, as indicated by dial 58.

As shown in FIG. 5, line 51a connects standpipe transmitter 51 with the gauge having dial 52, and line 55a connectes the manifold transmitter 55 with the gauge having dial 56. As also shown in FIG. 5, the transmitter lines 51a and 55a continue beyond the gauges for connection with switch means in the form of a valve body 70 having a valve member 71 with passageways .therein switchable by means of the lever 67 between the alternate positions of FIG. 5 and FIG. 5A. In the position of FIG. 5, one end of the left-hand passageway connects with. the line 51a from transmitter 51, while in the position shown in FIG. 5A, such passageway connects with the line 55a. The opposite end of the left-hand passageway of valve member 71 remains connected with a fluid line 72 connecting with amplifier 73 for transmitfing an amplified signal from line 72 to line 66 leading to the operator 40 of the choke for urging the flow-restricting member in the choke to the left and away from flow-restricting position. Thus, switching of the lever 67 between its alternate positions transmits signals to the right side of the choke operator 40 proportional to standpipe pressure or manifold pressure, as desired.

As also shown in FIG. 5, a fluid line 75 connecing 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 wifh 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 transmiiting 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 sec= ond force bridge 79.

The fluid line 63 connecting with the transmitter 62 on sensing device 61 also leads to the force bridge 79 so as ill to transmit thereto a signal which is a mathematical fune tion of the sensed product of mud density times the square of the mud circulating rate. Supply fluid is also entered into the bridge 79 through line 79a connecting with branch supply line 54a, and, in this bridge, the two signals transmitted through lines 78 and 63 are multiplied by one another. The product, a signal which is a mathematical function of the circulating pressure loss, according to the above-mentioned formula, is transmitted through fluid line 80 to the dial 60 for indicating such loss.

A branch 80:: of the fluid line 80 leads to a relay 81 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 such indicator. A line 68a also connects line 82 with a regulator 90 which, like regulators 91 and 92, is connected to branch supply line 54a. In the relay 81, the signals are added, a constant is subtracted from the sum, and the resulting signal is transmitted through fluid line 83 leading to the valve casing 70. The fluid line 82 connecting with static pressure indicator 68 also connects with the valve casing 70 to one side of the connection therewith of fluid line 83.

Thus, upon switching of the valve member 71 by means of lever 67, the right-hand passageway may be switched between a position connecting it with the line 82 and a position connecting it with the line 83. The opposite end of the right-hand passageway is fixed -for connection to a line 84 leading to an amplifier 85. The outlet from the amplifier connects with line 65 leading to the left side of the choke operator for transmitting a signal thereto which urges the flow-restricting member toward flow-restricting position.

Thus, with the valve in the position shown in FIG. 5, the signal transmitted through line 83 connected to lines 84 and 65 to the left side of the operator 40 is proportional to the sum of circulating pressure loss, as computed andindicated upon dial 60, and the sum of the previously measured static pressure in the standpipe, and a selected pressure representing the desired margin or pressure differential as indicated upon the dial 68. At the same time, and as previously mentioned, a signal is transmitted through the line 51a connected to lines 72 and 65 to urge the flow-restricting member away from flow-restricting position with a signal proportional to standpipe pressure. However, upon switching of the valve member 71 to the position of FIG. 5A, the signal transmitted through lines 84 and 66 originates from line 82, and is thus proportional to the sum of static pressure and the selected pressure, while the signal transmitted through lines 72 and 66 originates from line a, and is thus proportional to manifold pressure. Both the standpipe and manifold transmitters are connected to supply line 54 by means of branch line 54b.

Upon entering the console 50, fluid supply line 54 connects with a dryer 86a, a filter 86b and a pressure regulator 87, all in series, and then continues for connection with both of the amplifiers 73 and 85. Also, there are regulators 88 and 89 in each of the branch lines 54a and 54b. As previously noted, branch line 54a leads to the force bridges 76 and 79, adding relay 81, line 64 connecting with the transmitter 62, for sensing element 61 and regulators 90, 91 and 92 connecting, respectively, with the indicators for static pressure, well depth, and the calibration factor. The other branch line 54b is connected with each of lines 57 and 63 leading to the flow-line and standpipe transmitters, respectively.

The secondary computer for determining the mud weight necessary to balance or under or overbalance by a predetermined pressure the formation pressure comprises a force bridge 95 adapted to divide the static pressure times a constant by the depth of the well. For this purpose, the line 75 leading from the indicator 58 for well depth has a branch line 75a connecting with the bridge 95 for transmitting a signal thereto which is a mathematical function of such depth. Also, the line 82, which transmits a signal from indicator 68 proportional to static pressure, has a branch 82!) leading to relay 96, which adds a con stant to this signal. The sum is then transmitted as a signal from relay 96 and through line 97 to the bridge 95. Control pressure from branch 54:: is also connected to each of the bridge 95 and relay 96. I

The above-described signals alternately transmitted through line 65 to the left-hand side of operator 40 bear the same ratio to the indicated pressures on the control panel, and, as previously mentioned, bear a fixed ratio to the ratio of the signals from transmitters 51 and 55 transmitted through line 66 to the right side of the operator to the aiitual pressure within the conduits on which they are mounted. More particularly, with a choke operator 40 having equal pressure responsive areas on its opposite sides, the pressure signals transmitted through line 65 and 66, respectively, bear the same ratio to the actual values of the measured, set or computed pressures they represent.

Thus, forexample, in this system, fluid may be supplied from asuitable source through line 54 at -160 p.s.i. and then reduced in the regulator 87 upstream of amplifiers 73 andto 70 p.s.i. Regulator 88 reduces the regulated supplied fluid in 'branch 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 components,such-as the force bridges 76, 79 and abovedescribed, operate within a range of 3-15 p.s.i. Thus, in this system, the signals to be entered into the computers are in the same range. That is, each of the dials 58 indicating the depth of the well in feet, 59 indicating the calibration factor, and 69 indicating the sensed product of mud density times the square of its circulating rate is adapted to transmit 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 response to signals from the computer 79 in the same operating range.

The dial 68 for indicating observed static pressure is, on the other hand, adapted to transmit signals in the range of 0-15 p.s.i. However, in the relay 96, 3 p.s.i. is added to the signal proportional to static pressure, and a signal proportional to-the sum and in the range of 3-18 p.s.i. is entered into-force bridge 95. The mud weight increase computed in-force bridge 95 is indicated on dial 99 on a scale correspondingto the 3-15 p.s.i. range.

In the relay 81, on the other hand, this increment of 3 p.s.i. is taken from the signal related to the sum of computed circulating pressure loss and standpipe 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 scale on the dials 60 and 68 for circulating pressure loss and static pressure, respectively, range from 0-4000 p.s.i. and 0-5000 p.s.i. Thus, the signal transmitted through line 83 bears the same ratio to the sum of the values indicated on these scales as does the signal transmitted through line 82 to the value. shown on 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 resulting signals on opposite sides of the choke operator are, as previously mentioned, in the same ratio to the ,actual pressure values which they represent.

The user prepares for controlling the well with this system in much the same way that he prepares for its control in connectionwith the system of FIG. 1. Thus, while drilling with the well open, the user will, from time to time, adjust the knob 58a for correcting the depth of well to be entered in the computer. His job is simplified, however, with the system of FIG. 3, in that the mud density and circulating rate need not be changed or adjusted since their product, in the above-mentioned formula, is automatically sensed and entered into the computer continuously during circulation of the mud. Thus, after adjusting the depth of the well setting on dial 58,

the user need only compare the standpipe pressure indi cated on the dial 52 with the circulating pressure loss indicated on the 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 withthestandpipe pressure. When this is done, the userfrecords the adjusted calibration factor which is now entered into the computer, as in the case of the system shown in FIG. 1. Alternatively and as in the previously described system, 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 member 71 to the right to the position of FIG. 5. Then, when a kick is encountered, the user, as in the case of the system of FIG. 1, picks the drill bit up off the bottom of the hole, shuts down the mud pumps, 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 and the manifold pressure on the dial 56 and records both of them. He then sets the dial 68 by means ofknob 68a to indicate the static standpipe pressure which he has read on dial 52 plus any desired safety margin or pressure differential for overbalance, and starts the mud pumps, as previously described in connection with the system of FIG. 1.

As will be apparent from the foregoing description, the force bridges 76 and 79 automatically compute and produce thefsignal which is a mathematical function of the circulatinglpressure loss, and the relay 81 automatically adds this signal to the signal proportional to the setting on dial 68 and subtracts 3 psi. 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 member moy'ed to the right, as shown in FIG. 5, this signal is transmitted through lines 84 and 65 to the choke op erator for urging the flow-restricting member toward maximum 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 member away from maximum fiowline-restricting position. Thus, as in the case of the system of FIG. 1, 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. However, in this FIG. 3 system, the circulating pressure loss is constantly being computed, and automatically compensates for changes in the mud circulating rate.

When the kick has been circulated out of the well bore, lever 67 is moved to its low manifold control position, and the heavier mud is cifcu ated down through the drill string 26 to the bottom of the hole. The added mud weight necessary in order to provide an adequate hy-= drostatic pressure when such mud has reachedthe bottom of the hole has, of course, been computed in the manner described and indicated on a dial 99 on the console 50.

Movement of the lever 67 switches the valve member 71 to the left-hand position shown in FIG. 5A. In this shifted position of the valve member, a signal proportional to manifold pressure is transmitted by line 55a through the switch toline 72 and thus into the line 66. Thus, this signal is transmitted to the choke operator 40 for urging the flow-restricting member away from maximum flow-re-= stricting 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 automatically adjusts in such a manner that the opposing signal through line 66, which is proportional to the manifold pressure, remains 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 level 67 to the upper position of FIG. 4 for switching the system to drill string control. This, of course, switches the valve member 71 back to the right, as shown in FIG. 5. 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 member toward maximum flow-restricting position is similarly av signal proportional only to thecirculating pressure loss. This signal, of course, is opposedby asignahproportional to standpipe pressure plus the predetermined pressure differential transmitted through line 51a and the switching valve into line 72 to the operator 40 throii'gh line 66. Thus, during circulation of the heavier 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. As in the case of the system of FIG. 1, 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 punfp stopped. If it does not, he knows the well is killed.

The user has a choice of alternative methods in using such system, especially since the system in FIG. 3 includes equipment for continuously measuring those factors which affect the control pressure to be used in maintaining the bottom hole pressure, all in the manner previously described. For example, the user may not have facilities for mixing mud continuously at a rate to kill the well in one circulation. That is, it may be necessary for the user to do this in several steps.

In this event, the user first follows those procedures above-described through the steps of setting the proper static pressure on dial 68, placing the system on difill string control, and starting the mud pumps to circulate the kick out of the annulus. At this time, however, the user determines the length of time needed to fill the drill pipe attherate at which the mud is being circulated. He then determines how much mud weight is required'gto increase bottom hole pressure by a certain amount. For this purpose, he may set the static pressure dial at such amount long enough to read the amount of mud .wei'ht increase required on the dial 68.

He leaves the lever 67 on standpipe control, and continues to circulate the mud as he increases its weight at a rate not to exceed the amount he. has determined, as described above. He also reduces the static pressure reading on the dial 68 to correspond with the increase in mud weight, then when the dial 56 indicating manifold pres sure reads zero, he begins to weigh the mud. When the mud returns weigh within one or two points of the 'mud being circulated into the well, the user checks the hole to see if it will run over. If it does not, he knows that the well is dead.

In the event of -a severe 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 "so, he will reduce the amount of pressure built up in the annulus, and also reduce the amount of time the drill bit is inactive.

In this latter alternative method, he follows the same initial steps as in the other two methods above-described when he encounters a kick. That is, he picks the bit up 01f the bottom of the hole, he shuts the mud pumps down, and closes the preventer rams about the drill string.

Furthermore, he 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 circulation.

In this method, the user immediately 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 added 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 reduces 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 sensing 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 corresponding amount by suitable adjustment of the knob 68a. He then. continues to adjust this knob in order to continuously reduce the static pressure, as adjusted, in proportion to the depth reached by the mud, until such pressure reading is zero. He also watches the manifold pressure dial S6, 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 run over. If 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, as in the system of FIG. 1, the user may use the system of FIG, 3 in drilling under pressure, in which case he merely follows those procedures described in accordance with the first method during the initial drill string control of the well.

As shown in FIG. 6, in its preferred form, the choke 32 includes a body 100 having a chamber 101 therein 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 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 member shown in FIG. 6, there is an annular opening between the inner end of the flow-restricting member afid the inner end of the seat 104 through which fiuid may pass from the inlet 102 to the outlet 103. As the member [05 moves to the left, this annular opening is, of course, enlarged so as to permit less restricted flow, in which case there 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 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 chamber 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 movement of member 105. Thus, in a .manner to be described hereafter, the member 105 is guidably slidable within the small end of fitting 106.

The opposite larg 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 member 105, and a stem 111 extends through the fitting to connect the piston to a head on the flow-restricting member 105. Thus, reciprocation of the piston 110 of the operator will cause a corresponding reciprocation of the flow-restricting member between the positions previously described.

This reciprocation of the piston results from the transmittal to its opposite sides of the signals previously de scribed in connection ,with each of the systems. Thus, there is a threaded port 112 in the plate 108 for connection with the line 41 of the system of FIG. 1 or the line 65 of the piston system of FIG. 3. Also, there is a port 112a through the cup for threaded connection with either the line 34c of the system of FIG. 1 or the line 66 of the system of FIG. 3. V

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 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 user to determine, by its movement, whether or not the choke is working properly,

The small endof 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 to pro' vide a skirt 1 15 which extends inwardly beyond opening 107 and into the chamber 101 to a position close to the seat so as to support substantially the entire length of he flow-restricting member 105 which, as previously noted, fits closely within the inner diameter of the skirt 115 so as to be guided thereby during its reciprocation.

As can be seen from FIG. 6, 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 stern 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 of 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 maximum flow-restriction position, particularly due to pressure within outlet 103 when the member 105 is in its extreme position with in seat 104.

As can be seen from FIGS. 6 and 6A, 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 chocke. 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 movement of the flow-restricting member 105 into its maximum flow-restricting position. A. seal ring 118 is received about a central portion of the outer diameter of 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 the fiow-restricting member 105 is recessed about its open end to receive a removable sleeve 119, which is also cylindrical so as to be reversible end-for-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 1 15. The opposite ends of the outer diameter of the sleeve are chamfered 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 bad 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,

As shown in FIG. 6A, the inner corners of the seat 104 and the 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. Furthermore, 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 of 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. 6, cover 108 is similarly releasably secured to the cup-shaped open end of the fitting. As can also be seen from FIG. 6, suitable seals are provided about the openings in plate 108 and the small end of the fitting 106 so as to seal about the stem .111 connecting to the flow-restricting member 105.

As will 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 for-end.

As previously described, and as shown in FIGS. 7 and 8, the sensing device 61 comprises a tubular conduit 125 of the same inner diameter as the standpipe 28 and having means, such as flanges, on its opposite ends for connection in the standpipe as a smooth continuation thereof. It also includes a shaft 126 extending diametrically 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 remote from 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 circu lation rate throught the conduit,

In order to reduce turbulence within the sensing device to a minimum, the arm 127 is of fiat, narrow construction, as seen along the plane shown in FIG. 7, and of convergent tapering construction from the shaft 126 to the sensing element 128, as seen in the plane of FIG. 8. 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. 7, and secured to the shaft 126 by means of a set screw 131.

As shown in FIG. 7, 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 l26 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 proportional 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. 8 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 which is a mathematical function of the above-described product to the console 50.

As shown in FIG. 7, 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 opening 132 has a shoulder 134 against which a thin Teflon disc (not shown) is held by means of a metal ring 135. A ball bearing 136 is in turn held tightly against the metal ring by means of a gland nut 137 threadedly engaged with the outer threaded end of opening 132. The inner diameter of the Teflon disc is held tightly against the outer diameter of the shaft 126, and its inner annular portion (which may be in the order of 0.10") intermediate, the inner diameter of the metal ring and the outer diameter of the shaft, is free to rotate with the shaft 126 as the sensing element 128 moves in a small are 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 arc of rotation.

The transmitter 62 is releas-ably mounted upon a platform 138 suspended from the lower side of the conduit 125, as seen in FIG. 8.

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 advantages which are obvious and which are inherent to the apparatus and method.

The invention having been described, what is claimed is:

1. A system for controlling the pressure of a fluid within the annulus between a well bore penetrating an earth 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, comprising a choke for connection to the upper end of the annulus, said choke having a flow-restricting member moveable toward and away from maximum flow restricting position and a signal responsive operator for so moving the flow-restricting member, 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 transmitting said first signal to the choke operator to urge said flow-restricting member away from maximum flow-restricting position, means for producing a second signal which is a mathematical function of the circulating pressure loss of fluid circulating within the wellbore, 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 predetermined pressure differential, means for producing' a fourth signal which is a mathematical function of the sum of said second and third signals, and means for transmitting said fourth signal to the choke operator for urging said 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 pressure differential, and thereby maintain said bottom hole pressure substantially constant.

2. A system of the character defined in claim 1, in which said second signal producing means includes means for producing signals which are mathematical functions of the density of fluid within the well, the circulation rate of said fluid, and the depth of the well respectively, and means for producing said second signal by combining said last-mentioned signals in accordance with the equation:

dP:KMV D wherein:

dP=Circulating pressure loss K=Calibration factor M Density V=Cireulation rate D=Depth of the well 3. A system of the character defined in claim 1, in which said second signal producing means includes means for producing Signals which are mathematical functions of the density of fluid within the well and the circulating rate of said fluid, respectively, and means for producing said second signal by combining the signals in accordance with the equation:

dp=KMV wherein:

dP=Circulating pressure loss K calibration factor M=Density V=Circulation rate 4. A system of the character defined in claim 1, wherein said first signal transmitting means includes a transmitter for connection to said upper end of the drill string, means for connecting the transmitter to the choke operator to urge it away from flow-restricting position, a source of supply fluid, means connecting the supply fluid to the choke operator to urge it toward maximum flow-restricting position, and means for regulating the pressure of said supply fluid.

5. A system of the character defined in claim 1, including means for sensing the pressure of fluid within the upper end of the annulus upstream of the choke.

6. 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 movable toward and away from maximum 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 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, 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 of the drill string and the upper end of the annulus, respectively, means on the con trol 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, and means in the console 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 a mathematical function of the sum of a selected pressure and sensed static pressure, respectively.

7. Apparatus of the character defined in claim 6, wherein said means for producing the last three mentioned signals include means in the console to receive a regulated source of supply fluid.

8. Apparatus of the character defined in claim 6, including means for transmitting to said choke operator said signal which is the mathematical function of the fluid pressure sensed within the upper end of the drill string, 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.

9. For use in drilling a well into an earth formation containing fluid under pressure, wherein drilling fluid is circulated through a drill string extending into a wellbore and through the annulus therebetween, said string and annulus having upper ends, one of which is an inlet and the other an outlet, there being a pressure differential, 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 differential exceeds a predetermined value thereof; apparatus for maintaining said pressure differential at the predetermined value thereof, comprising a choke for regulating the outlet fluid pressure in response to a bias and a control signal, and means for producing a control signal and a bias which cooperate to cause the choke to increase or decrease the outlet fluid pressure automatically in response to said deviation being respectively negative or positive, whereby the outlet pressure approaches a value at which said deviation is zero.

10. Apparatus of the character described in claim 9, wherein said pressure differential is a mathematical function of the drilling fluid inlet pressure, the inlet static pressure when the well is shut-in, and the circulating pressure loss in the drill string in accordance with the equation:

D=f( i s 1) where:

P is the pressure differential P is the inlet pressure P is the static pressure P is the circulating pressure loss 11. Apparatus of the character defined in claim 10, including means for sensing the static pressure and circulating pressure loss, means for producing signals corresponding to said sensed pressures and to the pressure differential, means for combining said last-mentioned signals to provide said control signal, means for sensing the inlet pressure, and means for producing a signal corresponding to said sensed inlet pressure to provide said bias.

12. Apparatus of the character defined in claim 11, including means for sensing the outlet pressure, means for producing a signal corresponding to said outlet pressure, means for selectively rendering said choke responsive to said last-mentioned signal and said signal corresponding to static pressure so as to maintain said outlet pressure constant,

13. Apparatus as defined in claim 11', wherein said means for producing the signal corresponding to circulat ing pressure loss includes means for producing signals which are mathematical functions of certain well characteristics including the density of fluid within, the well, the circulation rate of said fluid, and the depth of the well, respectively, and means for combining said last mentioned signals in accordance with the equation;

dP=KMV D wherein:

dP=Circulating pressure loss K=Calibration factor M=Density V=Circulation rate D=Depth of the well 14. Apparatus as defined in claim 11, wherein said means for computing the circulating pressure loss includes means for producing signals which are mathematical functions of certain well characteristics including the density of the fluid within the well and the circulating rate of said fluid, respectively, and means for combining said signals in accordance with the equation:

dP=KMV D wherein:

dP=Circulating pressure loss K==Calibration factor M=Density V=Circulation rate 15, 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, includinga selected calibration factor, the density of the fluid Within the well, and the circulation rate of said fluid, means for independently entering said signals into said computing means, means for receiving signals which are mathematical functions of the pressure 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 char= acteristics, 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 differential and a sensed static pressure of the fluid within the well, and means for producing additional signals which are mathematical func= tions 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 predeter= mined pressure differential and the sensed static pressure, respectively,

16. Apparatus for controlling the pressure of a fluid within the annulus between a well bore penetrating a for= mation 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, comprising a choke for connection to the upper end of the annulus, said choke having a flow-restricting member moveable toward and away from maximum flow-restricting position and a signal responsive operator for so moving the flow-restricting member, 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 transmitting said first signal to the choke operator to urge said flow-restricting member away from maximum flow-restricting position, means for pro ducing a second signal which is a mathematical function of the sum of the circulating pressure loss of fluid cir= culating within the wellbore, a sensed static pressure of fluid within the upper end of the drill string, and a predetermined pressure ditfelrential, and means for transmit= ting said second signal t9 the choke operator for urging said flow-restricting member toward maximuin 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 pressure differential, and thereby maintain said bottom hole pressure substantially constant.

17. Apparatus of the character defined in claim 16, including means for producing signals which are mathematical functions of thedensity of fluid within the well, the circulation rate of said fluid, and the depth 'of the well respectively, and means for producing said second signal by combining said last-mentioned signals in accordance with the equation:

dP=KMV D wherein: v dP=Circulating pressure loss K=Calibration M=Density V-=Circulation rate D=Depth of the well 18. Apparatus of the character defined in claim 16, including means for producing signals which are mathematical functions of the density of fluid within the Well and the circulating rate of said fluid, respectively, and means for producing said second signal by combining the signals in accordance with the equation:

dP=KMV wherein:

dP=Circulating pressure loss K=Calibration factor M=Density V=Circulation rate References Cited UNITED 3FATES PATENTS CHARLES E. OCONIflELL, Primary Exam-flier, I. A. CALVERT, Assistant Examiner,

US. Cl, X.R,

Patent No. 3,143643 Dated y 3, 9 9

Inventor(s) Marvin H. Jones It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' Column 1, line 26, cancel "formation"; line 51, cancel "and methods". Column 7, line 3 L, U should be in quotes. Column 12, line 23 85 should be in bold face type; line 52, "scale" should be --sca1es--. Column 15, lines MI and 45, cancel "of the intersection". Column 16, line 62, "chocke" should be --choke--. Column 21, in claim 13, that portion of the formula reading KMVQD should read KMVQD;

in claim 14, that portion of the formula reading KMVQD should read KMV2.

SIGNED AND SEALED MAY 2 6 1970 (SEAL) Attest:

Edward M. Fletch I WILLIAM E. 'S-GHUYLER. JR-

Attesting Officer commissioner of Patents

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