US3541854A

US3541854A - Device for sensing the product of the density and the square of the rate of circulation of a fluid

Info

Publication number: US3541854A
Application number: US742386A
Authority: US
Inventors: Marvin R Jones; Benton F Baugh
Original assignee: Cameron Iron Works Inc
Current assignee: Cooper Industries LLC
Priority date: 1966-12-30
Filing date: 1968-07-03
Publication date: 1970-11-24
Anticipated expiration: 1987-11-24

Description

NOV. 24, 1970 M, R, JONES ETAL 3,541,854

DEVICE FOR sENsING THE PRODUCT 0F THE DENSITY AND THE SQUARE 0F THE RATE 0F CIRCULATION CF A FLUIL Original Filed Dec. 30, 1966 3 Sheets-Sheet I Ik 44a/wn i. (fo/76u Nov. 24, 1970 M, R JONES ETAL 3,541,854

' DEVICE FOR SENSING THE PRODUCT OF THE DENSITY AND THE SQUARE OF THE RATE OF CIRCULATION OF A FLUID Original Filed Dec. 50, 1966 3 Sheets-*Sheet 2 l N VEN TORJ mh, .mq NE N mv.. Nw

nvm. Se mb S DSN 4 N i 5 Sheets-Sheet I5 M. R. JONES ETAI- Nov. 24, 1970 DEVICE FOR SENSING THE PRODUCT vOF THE DENSITY AND THE SQUARE OF THE RATE OF CIRCULATION OF A FLUID Original Filed Deo.

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United States Patent Olce 3,541,854 Patented Nov. 24, 1970 3,541,854 DEVICE FOR SENSIN G THE PRODUCT F THE DENSITY AND THE SQUARE 0F THE RATE OF CIRCULATION 0F A FLUID Marvin R. Jones and Benton F. Baugh, Houston, Tex., assignors to Cameron Iron Works, Inc., Houston, Tex. Original application Dec. 30, 1966, Ser. No. 606,312, now Patent No. V3,429,385. Divided and this application July 3, 1968, Ser. No. 742,386

Int. Cl. G01f l/06 U..S. Cl. 73-228 3 Claims ABSTRACT 0F 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 encountered 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 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 cooperate to cause the choke to respectively 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 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 iluid in such standpipe, and the predetermined pressure differential. The signal producing means includes a device 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. The device includes a conduit adapted to be connected in the drill string, a rotatable shaft extending through the side of the conduit, and an arm on the shaft within the conduit for rotation with the end extending longitudinally of the conduit. A sensing element is mounted and arranged on the end of the arm remote from the shaft for swinging out of a neutral position in proportion to MV2, wherein M equals the density and V the velocity of a fluid such as drilling mud flowing through the conduit. There is a means including a transmitter on the exterior of the conduitand responsive to loads of the arm due to swinging of the sensing element for returning the sensing element to its neutral position. The transmitter has means for producing asignal which is a mathematical function of the force necessary to so return the sensing element.

This application is a division of my copending application, Ser. No. 606,312, filed Dec. 30, 1966, for Well Control, now Pat. No. 3,429,385.

This invention relates to an improved device 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.

In systems for use in controlling the pressure of fluid Within the annulus between a well bore and a drill string extending into the bore, 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 a back pressure in the fluid diverted through the choke, which, together with the hydrostatic pressure of the mud, is sufficient to contain the pressure of uids within formations penetrated by the Well bore-ie., 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 t0 kill the well. More particularly, the choke is preferably adjustable s0 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 effort 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 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 circulating rate 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 string at the level it has reached at such circulating rate. This maintenance of a constant pressure in the standpipe continues until the kick is circulated out of the annulus.

The user then calculates the mud weight increase necessary to contain the formation fluid, and begins to pump the hea'vier 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.

The above-identified patent application is directed toward a system of this general type which is not only essen- -tially automatic in that it does not require manual adjustments to the choke but also enables the practice in a variety of methods in that it does not require the circulating rate to be maintained constant. Thus, it includes equipment which automatically senses certain conditions in the well in such a manner as to enable the circulating rate to vary in the use of the system. The primary object 3 of this invention is to provide a device which is particularly well suited for sensing one of these conditions, and more particularly for sensing the product of the density times the square of the circulating rate of the fluid circulating within the upper end of the drill string.

In the drawings, wherein like reference characters are used throughout to designate like parts:

FIG. 1 is a diagrammatic illustration of such a system including a sensing device 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 pneumatic system within the console of FIG. 2;

FIG. 4 is a diagrammatic illustration of a portion of 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 the 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. .21 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 0f 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 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 wellhead. 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. l, uid within the annulus 29 is 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.

The straight run, as Well as the upper and lower wings of the cross, is provided with valves of suitable construction for selectively opening or closing them. As shown in FIG. l, 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, howover, the well bore 21 penetrates a formation F or other strata bearing uid 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 fluid 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 and 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 pressure 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 fluid 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 fluid pressure. In some cases, however, when the choke has been of a positive type, 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.

It is also the practice to drill a well under pressure, in which case a rotating type of blowout 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 owline, and through the choke 32 for imposing a back pressure on the annulus. Ths 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. l includes a console 50 having computing means therein which determines and indicates circulating pressure loss, as will be described to follow. A front control panel of the console contains 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.

This system also has a transmitter 51 connected to the standpipe 28 and having a fluid line 51a leading therefrom for transmitting a signal proportional to standpipe 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, 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.

This system also 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 receives supply pressure through a fluid line 57 leading thereto from the console 50.

There is a dial 58 on the control panel for indicating the measured depth of the well in thousands of feed, and a dial 59 adjacent to the dial 58 for indicating the calibration factor entered into the computing means. The value of the depth which is measured and then entered into the computing means is adjustable by knob 58a, and the calibration factor is adjusted to its proper value by means of a knob 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 S1 and 5S is identical and receives supply uid from the same sourcenamely, line 54. The dial on each

gauge

52 and 56 has the same range, which may be, for example, -5,000 p.s.i., for indicating signals transmitted through the lines 51a and 55a in the range of O-SO p.s.i. Thus, the signals are in the same ratio to their respective measured pressure.

This system further 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 in connection with FIGS. 6 and 7, 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 thereby is transmitted by the transmitter 62 to computing means within the console for determining the circulating pressure loss in accordance with the formula described below. 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 control 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 54 leading to the console 50.

When the signal from this sensed product is entered into the computing means, along with the depth of the lwell and the proper calibration factor, such computing means is automatically operable to compute the circulating pressure loss in accordance with the formula:

dP=KMV2D wherein:

dPzCirculating 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 eect 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:

dPzKMV2 wherein:

dP=Circulating pressure loss K=Calibration factor Mf=Mud density V=Mud circulation rate.

As illustrated diagrammatically in FIG. l, the choke 32 includes a how-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. 5, the operator includes a piston sealably slidable within a cylinder and connected by a stem to the flow-restricting member. Thus, uid pressure on the left-hand side of the operator piston urges the member toward maximum flow-restricting position, while uid 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.

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 urges the How-restricting member of the choke 32 to the right and thus toward maximum How-restricting position. On the other hand, a signal transmitted from the computing means through the uid 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 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 system between standpipe and manifold control, by merely manipulating a lever 67 on the control panel. More particularly, 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 represents 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 is 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-hand 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 1s 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 58.

As show in FIG. 3, line 51a connects standpipe transmitter 51 with the gauge having dial 52, and line 55a connects the manifold transmitter 5S 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 fonm of a valve body 70 having a valve member 71 with passageways therein switchable by means of the lever 67 between the alternate posltlons on FIG. 3 and FIG. 4. In the position of FIG. 3, one endl of the left-hand passageway connects with the line 51a from transmitter 51, while in the position shown in FIG. 4, such passageway connects with the line 55a. The opposite end of the left-hand passageway of valve member 71 remains connected with a uid 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 urging the How-restricting member in the choke to the left and away from maximum flow-restricting position. Thus, switching of the level 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. 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 iluid 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 iiuid 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 y63 connecting with the transmitter 62 on sensing device 61 also leads to the force bridge 79 so as to transmit thereto a signal which is a mathematical function 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 80a 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 substracted 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 Y65 leading to the left side of the choke operator 40 for transmitting a signal thereto which urges the now-restricting member toward maximum flow-restricting position.

Thus, with the valve in the position shown in FIG. 3, 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 and indicated upon dial 60, and the previously measured static pressure in the standpipe plus the selected pressure, as indicated upon the dial 68. This signal may be termed a control signal. At the same time, and as previously mentioned, a signal is transmitted through the line v51a connected to lines 72 and `65 to urge the How-restricting member away from maximum Iflow-restricting position with a signal proportional to standpipe pressure. This signal may be termed a bias However, upon switching of the valve member 71 to the position of FIG. 4, the signal transmitted through

lines

84 and 66 originates` from line 82, and is thus proportional to static pressure, while the signal transmitted through

lines

72 and 66 originates from line 55a, and is thus proportional to manifold pressure. Both the standpipe and manifold transmitters are connected to supply line 54 by means of branch line 54h.

As will be understood by those skilled in the art, the above-mentioned safety margin or selected pressure represents a predetermined differential between the pressure of the formation nid and the pressure of the well fluid opposite the formation uid. This pressure dif- 8 ferential is a mathematical function of the standpipe pressure, the static pressure, and the circulating pressure loss in accordance with the equation:

pnzfQa-ps-m wherein:

pD is the pressure differential, p1 is the standpipe pressure,

pis is the static pressure, and

p1 is the circulating pressure loss.

Upon entering the console 50, fluid supply line 54 connects with a dryer 86a, a lter 86b and a pressure regu- Iator 87, all in series, and then continues for connection with both of the ampliers 73 and 85. Also, there are regulators 88 and 89 in each of the branch lines 54a and 54h. 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 elem-ent 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 ilowline and standpipe transmitters, respectively.

The secondary computer for determining the mud weight necessary to balance or underor 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 proportional to such depth. Also, the line 82, which transmits a signal from indicator 68 proportional to static pressure, has a branch 82b leading to relay 96, which adds a constant to this signal. The surnis then transmitted as a signal from relay 96 and through line 97 to the bridge 95. Control pressure from branch 54a is also connected to each of the bridge 95 and relay 96.

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 xed 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 actual 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

lines

65 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, Huid may be supplied from a suitable source through line 54 at 80-160 p.s.i. and then reduced in the regulator 87 upstream of4 amplifiers 73 and 85 to 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 95 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 l5 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 -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 scalecorresponding to 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 cornputed 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 scales on the

dials

60 and 68 for circulating pressure loss and static pressure, respectively, range from 04,000 p.s.i. and 05,000 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 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 ope-rator are, as previously mentioned, in the same ratio to the actual pressure values which they represent.

In preparing to control the well with this system, and 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. 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 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 member 7\1 to the right to the position of FIG. 3. Then, when a kick is encountered, the user picks the drill bit up off the bottom of the hole, shuts down the mud pumps, and closes the blowout preventer rams 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 of knob 68a to indicate the static standpipe pressure which he has read on dial 52 plus any desired safety margin for overbalance, and starts the mud pumps.

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 subtracts 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 7() and switchable Valve member 71. With the Valve mem ber 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 dow-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 ow-restricting member away from maximum oW- line-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 compensates for changes in the mud circulating rate.

As drilling mud is circulated through the Well, the choke 32 will automatically adjust for any deviation from the predetermined pressure differential so as to maintain 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 on 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-restricting member away from maximum dow-restricting 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 How-restricting position. Since it is a mathematical function of the Set static pressure, this signal is a constant so that the dow-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 lever 67 to the upper position of FIG. 2 for switching the system to drill string control. This, of course, switches the valve member 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 How-restricting member to flow-restricting position is similarly 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 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. 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 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 on 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 method above-described when he encounters a kickf That is, he picks the bit up off 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 56, and when it reaches zero he knows that the well should be dead. He then beings 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, the user may use this system in drilling under pressure, in which case he merely follows those procedures described in accordance with the irst 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 therein intersected by an inlet 102 to the chamber and an outlet 1103 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 member shown in FIG. 5, there is an annular opening between the inner end of the ow-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 member 105 moves to the left, this annular opening is, of course, enlarged so as to permit less restricted 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 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

12 member is guidably slidable within the small end of tting 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 member 105, and a stem 111 extends through the tting to connect the piston to a head on the flowrestricting member 105. Thus, reciprocation of the piston 110 of the operator will cause a corresponding reciprocation of the how-restricting member 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 11111 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 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 iitting is hollow to provide a skirt 115 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 the 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. 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 11'7 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 1:11 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 t0 atmospheric pressure acting on the cross sectional area of the telltale 11111, 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-liow-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. v5, the seat 104 comprises a removable ring which is cylindrical so as to be reversible end-for-end within an enlarged diameter portion 103:1 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 movement of the How-restricting member 105 into its extreme flow-restricting position. A seal ring 1.18 is received about a central portion of the outer diameter of the ring so as to sealably engage with the recessed portion 103:1 in either end-for-end position of the ring.

The hollow portion of flow-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 now-restricting member so as to slide with it closely within the skirt 115. 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 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 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 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. 5, cover 108 is similarly releasably secured to the cupshaped 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 small end of the fitting 106 so as to seal about the stern 111 connecting to the flow-restricting member 105.

As will be apparent from the foregoing, upon removal of the small end of the tting 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 endfor-end.

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 means, such as anges, 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 4the 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 midportion 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.

In order to reduce turbulence within the sensing device to a minimum, the arm 127 is of at, 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

14 shown in FIG. 6, and secured to the shaft 126 by means of 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 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. 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 opening 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 ow. 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 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 advantages which are obvious and which are inherent to the apparatus and method.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1. A sensing device, comprising a conduit for connection in a ilowline, a rotatable shaft extending within and through the side of the conduit, an arm mounted on the shaft within the conduit for rotation therewith and extending longitudinally of the conduit, a sensing element mounted and arranged on the end of the arm remote from the shaft for swinging out of a neutral position and thereby causing rotation of the arm and the shaft in proportion to MVZ, wherein M equals the density and V the velocity of a uid flowing through the conduit, and means including a transmitter on the exterior of the conduit responsive to rotation of the arm for returning the sensing element to its neutral position, said transmitter having means for producing a signal which is a mathematical function of the force necessary to so return the sensing element.

2. A sensing device of the character described in claim 1, wherein said returning means includes an arm mounted on the shaft for rotation therewith exteriorly of the conduit, said arm has a transmitter actuating part on the end thereof remote from the shaft, and said transmitter is of a null balance type and supported with a signal 1 5/1968 Gelinas 73-228 12/1959' Morse 73-228 RICHARD C. QUEISSER, Primary Examiner 0 M. SMOLLAR, Assistant Examiner U.S. C1. X.R.