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Publication numberUS3583500 A
Publication typeGrant
Publication dateJun 8, 1971
Filing dateApr 1, 1969
Priority dateApr 1, 1969
Publication numberUS 3583500 A, US 3583500A, US-A-3583500, US3583500 A, US3583500A
InventorsBilly V Randall, Renic P Vincent
Original AssigneePan American Petroleum Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Control system for high pressure control fluid
US 3583500 A
Images(1)
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Description  (OCR text may contain errors)

0 United States Patent 111 3,583,500

[72] Inventors Billy V.Randall; 3,429,385 2/1969 Jones etal l75/38X Renic i. Vincent, both of Tulsa, Okla. P E M A Ch A I No H7107) xamnterarvin amplon fg p 1 1969 Assistant Exammer-R|chard E. Favreau pmemed June 8 Attorneys-Paul F. l-lawley and John D. Gassett [73] Assignee Pan American Petroleum Corporation Tulsa, Okla.

Continuation-impart of application Ser. No. 628,748, May 5, i967, now abandoned.

[54] CONTROL SYSTEM FOR HIGH PRESSURE ABSTRACT: A pressure multiplying apparatus for supplying, at a regulated pressure, a control fluid in a closed system to control a device such as a hydraulically operated valve. The system is used to control either 1; automatic blowout control devices around a drilling well or 2; to use such control equipment to control the pressure on the drill string used to drill the well. Such system includes a pump for supplying the control liquid to the valve being controlled at a pressure which is a constant factor greater than the pressure of the gas used to power the pump. Valve means are provided to bleed the pressure of the control fluid proportionally to the lowering of the pressure of the power gas. This includes a differential piston exposed on one side to the pressure of the power air and on the other side to the pressure of the control fluid from the pump, The two areas of the differential piston have approxi' mately the same ratio as the multiplying pressure factor of the pump. Means are further provided so that a constant drill pipe pressure can be maintained by using the pressure of the fluid in the drill pipe to regulate the control fluid.

190 30 Q as I02 loo 92 62 I03 96 94 32 97 98 as as 1 RESERVOIR 26 5 24 AIR SOURCE CONTROL SYSTEM FOR HIGH PRESSURE CONTROL FLUID CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application S.N. 628,748, filed Apr. 5, I967, and now abandoned Billy V. Randall and Renic P. Vincent, inventors.

SUMMARY OF THE INVENTION This invention relates to a system for supplying control fluid under regulated pressure to a fluid controlled device. It relates especially to a system utilizing a relatively low pressure driving fluid to operate a pump having an output control fluid at a pressure much greater than that of the driving fluid. It relates especially to control equipment for use in controlling back pressure on a well being drilled in the earth by the rotary drilling method or for maintaining a selected pressure on the fluid in the drill string used in drilling the well.

BACKGROUND OF THE INVENTION When drilling oil and gas wells by the rotary drilling method, a bit is attached to the lower end of a string of hollow drill pipe and the bit obtains its rotation by rotation of the drill pipe at the surface.

Drilling fluid is circulated down the drill pipe, through the bit and up the annulus between the drill pipe and the borehole wall. The drilling fluid is used primarily to remove cuttings made by the bit and also to lubricate and cool the bit. When a liquid is used as the drilling fluid, the hydrostatic head of this liquid outside the drill pipe imposes a pressure on the formation which is highest at the bottom of the well. In some cases the drilling formation contains a gas, a liquid or a mixture of gas and liquid at a pressure greater than this hydrostatic head. When the bit reaches such a formation, the high pressure fluid enters the well and flows toward the surface with the drilling fluid outside the drill pipe. The fluid entering the well may be salt water, oil or natural gas. Oil and gas are almost always less dense than the circulated liquid drilling fluid. If the circulated drilling fluid has been weighted with the addition of suspended particles, as is usually the case, even salt water is less dense than such drilling fluid. If these less dense fluids dilute the heavier drilling fluid, the hydrostatic pressure is reduced and still more fluids enter the well bore from the formation. This process can continue until the well is flowing out of control.

In order to regain control of the well, a blowout preventer, which is a means of closing the upper end of the casing, may be closed. Normally, this means sealing the annular space between the drill pipe and the casing. The blowout preventer may be closed while a more highly weighted drilling fluid is circulated down the drill pipe. In order to fill the annular space between the drill string and the well wall with this heavier liquid, it is necessary to allow some flow from the well below the blowout preventers. It is customary to provide a choke valve on a line from the casing below the blowout preventer. Fluids can be bled off through this choke permitting the more highly weighted drilling fluid to be circulated up the well outside the drill pipe. The choke valve must hold back pressure on the top of the well to restrict flow of the high pressure formation fluids into the well.

Instead of using a choke valve, it has lately become desirable in many cases to use automatic blowout control devices such as the ABC valve sold by Regan Forge and Engineering Company, San Pedro, California, and described in their Bulletin ABC-366. Other hydraulically operated control valves can be used. In such valve, a control fluid is required to be provided a the pressure at which it is desired to hold on the well. However, there is not ordinarily fluid readily available at pressure that high at a drilling unit. However, there is nearly always air or gas available at a lower pressure, e.g., 100 p.s.i. There is a need for a pump means for supplying control fluid to control valves such as the ABC valve at any selected pressure up to 5,000 lbs., for example, and in which the selected pressure may be changed nearly instantaneously. The control fluid is in a closed system; thus, there is also a need for relieving the pressure in the control fluid if a lower pressure is desired. It is further desired that these requirements be accomplished by the moving of one lever because in controlling a well that is about to blow out or is building up pressure too rapidly, it is sometimes desirable to change the back pressure setting as rapidly and as simply as possible. We have also found that it is sometimes desirable and important to have means for controlling the pressure of the fluid in the drill string. The present invention fills these needs.

BRIEF DESCRIPTION OF THE INVENTION This invention concerns a pressure multiplying apparatus for supplying, at a regulated pressure, a control fluid in a closed control fluid system to a hydraulically operated valve especially adapted for use in controlling either the back pressure on a well being drilled or the pressure on a drill string used to drill such well. It includes a pump means receiving its power from a first fluid source. The pump means provides at its output, a second fluid which can for convenience be called the control fluid; the pressure of this control fluid is a constant factor of the pressure of the power fluid provided the pumps. A control fluid conduit connects the output of the pump means to the device, such as a hydraulically operated pressure control valve, to be controlled. It includes special control bleed means connected into the control fluid conduit to bleed off fluid or lower the pressure in the control fluid conduit only when the power input fluid pressure is reduced. The power input fluid pressure is regulated to meet changing conditions. The control bleed means is thus responsive to the pressure of the input power fluid and is further of a character to permit bleeding of control fluid only when the pressure of the control fluid is greater than the factor of the pump means times the pressure of the newly adjusted power fluid. It is thus seen that the changing of the pressure of the power fluid to the pump does two things nearly simultaneously: (1) changes the pressure of the control fluid at the outlet of the pump, and (2) bleeds fluid from the closed control fluid system when the pressure is to be lowered. This is done by merely moving one control point on the regulator. Means are also provided so that the pressure of the fluid in the drill string can be maintained constant at a set pressure.

Various other objects and a better understanding of the invention can be had from the following descriptions taken in conjunction with the drawings in which:

FIG. 1 illustrates schematically, and partly in section, a hydraulic pressure multiplier system for high pressure control in combination with a well control device and drill pipe pressure controller;

FIG. 2 illustrates a modification of the differential piston of FIG. 1; and

FIG. 3 illustrates position 2 of the three-way valve of FIG. 1.

We will first describe that first part of the embodiment of FIG. 1 which is used primarily to maintain a constant back pressure on the outlet mud return line. We will later discuss that part which cooperates with this first part to control the pressure of the drilling fluid in the drill string.

Shown in the drawing is a source 10 for providing high-pressure power fluid. This source is connected to three-way valve 81 which, when in the position of FIG. 1, connects the power fluid to regulator 24. This power supply can be high-pressure air or gas which is ordinarily available on conventional drilling units. On the other side of the drawing is a device 12 which is to be controlled by a control fluid within control conduit 14. Device 12 is connected to the annulus 11A of casing 11 and drill string 13 used to drill the well. As will be explained more fully, device 12 is used to control the flow of fluid from annulus 11A. Control fluid conduit 14 is connected to the fluid control output of pump I6. Conduit 14 is provided with gauge 15. Pump 16 also has a fluid control supply input 20 and a power or drive input 22.

Pump 16 is a type which has an output pressure at output 18 which is a constant factor of the pressure of the power fluid supplied to drive input 22. A suitable pump is commercially available from several sources, including Sprague Engineering Corporation of Gardena, California, and is identified as their Model 2l6-C60. If pump 16 has a multiplying factor 60, for example, a p.s.i. supply of power fluid at input 22 provicles a 600 p.s.i. output pressure of control fluid at output 18. Thus, by controlling the pressure of the input fluid to power or drive conduit 22, one can control the pressure of the control fluid at output 18. A regulator 24 is provided in the conduit 26 from power source 10 to power input 22 of pump 16. By manipulating the setting of regulator 24, the output at 18 can be controlled. However, as conduit 14 is connected to a closed system, as illustrated in the drawing, means must be provided to relieve fluid from conduit 14 when it is desired to lower the pressure therein. Means for relieving this pressure will now be discussed. This includes differential area piston means 28 which is connected at its top through conduit 30, having pressure gauge 31, to the downstream side of regulator 24. Differential area piston means 28 includes an upper cylinder portion 32 and a lower cylinder portion 34. The cross-sectional area of cylinder 32 and cylinder 34 has approximately the same ratio as those of the pressure of the drive fluid provided power input 22 and the pressure of the fluid control fluid at output 18 of pump 16. An upper piston portion 36 having seals 38, sealingly and slidingly fits with cylinder portion 32. A piston extension 40 extends downwardly from piston portion 36 and slidingly fits within cylinder portion 34. A spring 44 is provided above piston portion 36 to provide proper bias to permit adjustment of the control range, i.e., the amount of pressure change required to activate the system. In practice a spring 44 is used as a bias to cause the upward movement of the piston to be delayed until the pressure exceeds the desired pressure by some small, but finite amount. This prevents constant bleeding of the system with infinitesimal changes in control pressure. A bleed conduit 46 connects port 48 in the wall of cylinder portion 34 to reservoir 50. Reservoir 50 is connected by supply conduit 52 to the control fluid input of pump 16. Pressure will not build up under piston 36 within cylinder 32 as the cylinder is provided with port 42 to the atmosphere. Fluid, if any, under cylinder 36 can thus escape.

Cylinder extension 34 is provided with a circumferential passage 53. This passage is in fluid communication with conduit 46. In the position shown, there is no escape of fluid from conduit 14 through bleed conduit 46. However, if the pressure differential below piston extension 40 compared to that above piston portion 36 exceeds the ratio of the area, then the stepped piston will be forced upwardly, causing piston extension 40 to clear port 48. This permits bleeding of fluid from conduit 14 through conduit 46 to reservoir 50, thus reducing the pressure within conduit 14. In this embodiment there is a constant cross-sectional area on piston extension 50 as the valve opens.

As illustrated, conduit 14 is connected to automatic blowout control valve, such as an ABC valve, as may be used on a return mud flow line 21 from a drilling well having a casing 11 closed at the top and a drill string 13 extending therebetween in a known manner. Line 21 is provided with internal cylinder 62 and a rubber diaphragm 64. The control of fluid pressure within space 66 of diaphragm 64 then is seen to control the pressure P, upstream of the rubber diaphragm 64. When pressure P, exceeds the pressure within diaphragm 64, the diaphragm is pushed back or deformed and fluid flows through. An ABC valve, illustrated as numeral 12, is commercially available from Regan Forge and Engineering Company of San Pedro, California, illustrated in their Bulletin ABC-366.

We will now discuss the operation of that part of the apparatus of the drawing just described when used to control the back pressure on return mud flow line 21. (When three-way valve 81 is in the position shown in FIG. 1, regulator 80, to which the other outlet of three-way valve 81 is connected, is ineffective. Its operation will be discussed later.) Reservoir 50 is filled with a fluid, preferably a hydraulic fluid such as brake fluid used in hydraulic brakes for automobiles, or a good grade motor oil, for example. An air supply 10 is connected to regulator 24. If the maximum pressure of the power air supply is 100 p.s.i. and pump 16 has an air to oil ratio of 60/1, then the output pressure in pump 16 can vary from zero to as high as 6,000 p.s.i. This permits control fluid of much higher pressure than the pressure of most fluids or gases connected with a drilling rig. Regualtor 24 is then adjusted to obtain the desired back pressure P, in line 21. For example, if it is desired to control P, at 3,000 p.s.i., then regulator 24 is set to have an output pressure of 50 lbs. Regulator 24 can have a dual range calibration thereon, wherein one range indicates the true air pressure downstream of the regulator and the other is 60 times this to indicate the pressure of the fluid in conduit 14 which in turn controls or is equal to pressure P,. If the pressure output of regulator 24 is 50 p.s.i. then the downward force on piston extension 40 is 3,000 times A As A, is 60 times A,, then there is equal force exerted on the differential piston by the air in conduit 30 and the control fluid on conduit 14. Thus, no movement of the differential piston. If it is desired to increase the pressure P,, all that is necessary to do is to increase the setting on regulator 24 the correct amount. This increases the output pressure of the control fluid from pump 16 which increases the upward force on differential piston. However, this is offset by the increased pressure acting downwardly on area If it is desired to reduce pressure P,, then all that is necessary for an operator to do is to lower the setting on regulator 24. This lowers the pressure on A,. However, the pressure in conduit 14 is not now affected by the output of regulator 24 as conduit 14 is a closed system. To lower the pressure in conduit 14, part of the fluid must be bled. As the pressure in conduit 14 times the area A, is greater than the pressure in conduit 30 times A,, the differential piston will start to rise. As soon as this total upward force exceeds the downward force by an amount equal to the resistance of spring 44, the differential piston will move upward. This movement continues until piston extension 40 clears port 48, thus opening it. The instant this occurs, the fluid will flow through port 48 and conduit 46 to reservoir 50. This permits a rapid reduction in pressure in conduit 14. This is especially rapid if the fluid in conduit 14 has a low compressibility factor because then a bleeding off of a small volume gives a large decrease in pressure.

As seen as the pressure in conduit 14 reduces to the point where the upward force is equal to the downward force, the differential piston moves downwardly to the position where piston extension 40 acts as a valve closing port 48. At this time the pressure in conduit 14 is approximately 60 times the pressure in conduit 30. Thus, there is a quick response to controlling pressure P, by merely operating one regulator, namely regulator 24. This regulation can act to either increase, decrease or maintain constant the pressure P,.

That part of the drawing will now be described which shows means available for controlling the pressure on the drill pipe. This includes three-way valve 81 and second regulator 80. Three-way valve 81 which is between the power source 10 and regulator 24 is turned to position 2 as shown in FIG. 3. When in this position the outlet of air source 10 is connected to regulator which is controlled by the drill pipe pressure. This regulator 80 includes a power air inlet 84, a power outlet 82, and control fluid inlet 97. Inlet 84 is connected through conduit 88 to three-way valve 81 to obtain power fluid. Outlet 82 is connected through conduit 86 to conduit 30 which is connected to the upper side of differential piston 28 to bleed type regulator 24 and to pump 16. Regulator 80 has an internal cylinder portion 99 which connects with an inlet 84 and outlet 82. Mounted within cylinder 99 is a piston valve assembly including a first piston head 98 and a second piston head 100 connected by rod 102. The left end of cylinder 99 or the end adjacent piston 98 is connected through conduit to a pressure source indicative of the pressure in drill pipe 13.,Thus, power fluid or other power means representative of the pressure of fluid in the drill pipe urges the piston assembly to the right. Details of such power means are not shown as they are well known. This movement to the right is resisted by a spring 92 in chamber 103 whose set compression is adjustable by means 94. A port 96 is provided in the chamber 103.

When the drill pipe pressure in conduit 90 is less than the setting on spring 92, the piston valves are in the position shown in the drawing and high pressure air from source flows through regulator 82 through conduit 86. This causes the pressure in line 14 to build up. By controlling the pressure in pipe 12 one can control the drill pipe pressure. Pipe 12 is connected to the annulus between drill pipe 13 and casing 11a. This annulus and the drill pipe is like a manometer and has a U-tube effect. lf the pressure is built up in the control conduit 14, the annulus around pipe 12 is closed off. Then the pressure in the drill pipe builds up. When sufficient pressure buildup in the drill pipe occurs, piston valves 98 and 100 are shoved to the right so that the power air in conduit 88 is shut off. When valve 100 moves sufficiently to the right, the pressure in conduit 83 is vented through chamber 103 and vent port 96. This causes differential piston stem 40 to rise and relieve the pressure on conduit 14. This also stops pump 16. The combination of stopping pump 16 and relieving pressure in conduit 14 opens the valves 64 which reduces the pressure in conduit 21. This in turn reduces the pressure on the drill pipe which is what is desired in such instances.

0n the other hand, if the pressure in drill pipe 13 drops too low, spring 92 shoves the valve assembly, including the piston heads 98 and 100, to the left sufficiently so that conduit 88 is in fluid communication with conduit 86. This permits the high power fluid from source 10 to act directly upon pump 16 and upon regulator 28. This causes the pressure in conduit 14 to rise, thus increasing the pressure holding valve 64 closed in pipe 21. Thus the lower the drill pipe pressure drops, the more the system wants to build up the pressure in control conduit 13. This can be dangerous as the pressure might exceed the rupture pressure of casing 11. However, we provide a safeguard for this. It is to be noted that even when three-way valve 81 is in position shown in HO. 3, the outlet of regulator 24 is connected to the input of pump 16 and to the top side of differential piston 28. lt will be recalled that we specified that regulator 24 is a bleed type, e.g., if the regulator is set for lOO lbs. and the pressure in conduit 26 is greater than 100 lbs., regulator 24 will bleed off sufficient air through bleed vent 25 so that the pressure in conduit 26 drops to 100 lbs. Thus, by proper setting of regulator 24 we can keep the pressure from building up in line 14 to the point where it would rupture casing 11 although the pressure of the drill pipe 13 remains low.

FIG. 2 illustrates a modification of the differential piston illustrated in H0. 1. There are two main modifications: (1) the connection between upper cylinder portion 36A and lower extension 40A, and (2) passage means within extension 40A. Piston extension 40A is connected to large piston portion 36A by a pin 70 which fits within holes 72 and 74 of large piston 36A and extension 40A, respectively. The upper end of pin 70 is rounded as is hole 72. Hole 72 is slightly larger than pin 70. This arrangement lessens the strictness of alignment of the piston, piston extension and the cylinders. This manner of connecting extension 40A to large piston portion 36A can readily be used in the embodiment of FIG. 1.

FIG. 2 shows a further modification from FIG. 1. This includes a passage 75 within piston extension 40A. One end of passage 75 opens into conduit 14 and the other end opens into circumferential groove 76 which is cut into the exterior wall of piston extension 40A. The differential piston of FIG. 2 operates in substantially the same manner as that of FIG. 1 and can be substituted into the system of FIG. 1. For example, if pressure in conduit 14 exceeds a given pressure, it forces piston extension 40A upwardly until groove 76 is aligned with port 48 to relieve the pressure in conduit 14. Upon the proper relief of pressure, the piston valve on extension 40A is driven downwardly, closing off port 48.

While the above embodiment has been described with a great deal of detail, it is possible to produce modifications thereof without departing from the spirit or scope of the invention.

We claim:

1. An apparatus for supplying a control fluid for use with a well being drilled in the earth with the drill bit attached to the lower end of a drill pipe through which drilling fluid is circulated which comprises:

a power fluid source;

a first regulator means having an inlet and an outlet and including vent means to bleed fluid from said outlet when the pressure in said outlet exceeds the setting of said regulator means;

a second regulator means having a power fluid inlet, a power fluid outlet, and a pressure control fluid inlet for admitting control fluid to control the opening and closing of said power fluid inlet;

means for selectively connecting said power fluid source to said first regulator means and to the power fluid inlet of said second regulator means;

a pump means having an inlet and an outlet for control fluid and a power fluid inlet, said pump means being of a character to have an output pressure a constant factor of the pressure of the power fluid;

control fluid conduit means connecting the outlet of said pump means to the device being controlled;

means connecting the outlet of said first regulator means and the outlet of said second regulator means to said power fluid inlet of said pump means;

control bleed means operable to lower the pressure in said control fluid conduit when the pressure of the fluid therein exceeds the power input fluid pressure to said pump means by the same said given factor of said pump means and otherwise to be closed;

pressure sensing means for controlling said second regulator means responsive to the pressure of fluid in said drill pipe.

2. An apparatus as defined in claim 1 in which said control bleed means includes a differential area piston in a stepped cylinder in which space on one side of said piston is connected to the power fluid input conduit from said first and second regulator means and the space on the other side of said differential piston being in pressure communication with said control fluid conduit, said control means further including bleed conduit means having valve means therein operable by movement of said differential piston to open and close, the differential areas of said piston having a ratio the same as the factor of said pump means.

3. An apparatus as defined in claim 1 wherein said control bleed means includes a vertical stepped cylinder comprising two axially aligned cylinders of different diameters, there being a large portion and a small portion thereof, the crosssectional area of one cylinder portion to the other being the same as the power multiplication factor of said pump means;

a first piston portion sealing and reciprocally fitting within the large portion of said cylinder; and

an extension from said piston portion, said extension sealing and reciprocally fitting within said small portion of said cylinder, said extension having a passage extending from its end opposite said first piston portion to a lateral open ing in said extension;

a bleed conduit connected to a port in the wall of said small portion of said cylinder to register with the lateral opening in said extension when said extension is in one position and to otherwise be in nonregister.

4. An apparatus as defined in claim 3 in which said first piston portion is urged by a spring in a direction toward said extension.

5. An apparatus as defined in claim 3 in which said bleed conduit is connected to a reservoir and including means connecting said reservoir to the inlet of said pump means.

6. An apparatus as defined in claim 5 in which said power fluid source is a source for air under pressure and the fluid in said control fluid conduit means and said bleed means and said reservoir is a liquid.

7. An apparatus as defined in claim 3 in which said extension from said piston portion is provided with a circumferential groove in fluid communication with said passage of said extension.

8. An apparatus as defined in claim 3 in which the said extension having an axially aligned hole in one end thereof and said large piston portion having an axially aligned hole in one side thereof; said holes being adjacent each other; a pin within said holes to align said large piston portion and said piston extension within said stepped cylinder, said pin being smaller in diameter than said hole in said large piston portion.

9. An apparatus as defined in claim 3 in which said large portion of said cylinder is provided with a port beneath said first piston portion and said port opening into the exterior thereof.

10. An apparatus as defined in claim 9 in which said smaller cylinder portion is provided with a circumferential passage in communication with said port in the wall of said smaller portion.

11. An apparatus for supplying a control fluid in the closed system at a regulated pressure to a device to be controlled for use with a well being drilled in the earth with a drill bit attached to the lower end of a drill pipe through which drilling fluid is circulated which comprises:

a power fluid source;

a first regulator means connected to said power fluid source;

a second regulator means connected to said power fluid source;

a pump means having an input and an output for control fluid and a power fluid input, said pump means being of a character to have an output pressure a considerable factor of the pressure of the power fluid;

control fluid conduit means connecting the output of said pump means to the device being controlled;

means for selectively connecting said power fluid source to said first regulator means and to said second regulator means;

conduit means connecting the first regulator means and the second regulator means to said power fluid inlet of said pump means;

control bleed means operable to lower the pressure in said control fluid conduit when the pressure of the fluid therein exceeds the power fluid pressure to said pump means by the same given factor of said pump means and otherwise to be closed;

pressure sensing means for controlling said second regulator means responsive to the pressure of fluid in said drill pipe.

12. An apparatus as defined in claim 11 in which said control bleed means includes a differential area piston in a stepped cylinder in which space on one side of said piston is connected to the power fluid input conduit from said first and second regulator means and the space on the other side of said differential piston being in pressure communication with said control fluid conduit, said control means further including bleed conduit means having valve means therein operable by movement of said differential piston to open and close the differential area of said piston having a ratio the same as the factor of said pump means.

13. An apparatus as defined in claim 11 wherein said control bleed means includes a vertical stepped cylinder comprising two axially aligned cylinders of different diameters, there being a large portion and a small portion thereof, the crosssectional area of one cylinder portion to the other being the same as the power multiplication factor of said pump means;

a first piston portion sealing and reciprocally fitting within the large portion of said cylinder; and

an extension from said piston portion, said extension sealing and reciprocally fitting within said small portion of said cylinder, said extension having a passage extending from its end opposite said first piston portion to a lateral opening in said extension;

a bleed conduit connected to a port in the wall of said small portion of said cylinder to register with the lateral opening in said extension when said extension is in one position and to otherwise be in nonregister.

M. An apparatus as defined in claim 13 in which said bleed conduit is connected to a reservoir and including means connecting said reservoir to the inlet of said pump means.

115. An apparatus as defined in claim 13 in which said extension from said piston portion is provided with a circumferential groove in fluid communication with said passage of said extension.

16. An apparatus as defined in claim 13 in which the said extension having an axially aligned hole in one end thereof and said large piston portion having an axially aligned hole in one side thereof; said holes being adjacent each other; a pin within said holes to align said large piston portion and said piston extension within said stepped cylinder, said pin being smaller in diameter than said hole in said large piston portion.

mg? UNITED STATES PA'IENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,581,500 Dated June 1971 Inventor) Billy V. Randall and Renic P. Vincent It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' I In the abstract, line should read line 5, should read Column 1, line 71, after 'hell." Insert "Sometimes it is desired to hold up to 5000 to 6000 psi backpressure 0n the well.-.

Column 3, line 5 "50" should read "no".

Column line +6, "seen" should read --soon--.

Signed and sealed this 16th day of November 1 971 (SEAL) Attest:

EDWARD M.FLETGHER,JR. ROBERT GOTTSCHALK Attoating Officer Acting Commissioner of Patents

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3338319 *Jul 29, 1965Aug 29, 1967Bass Brothers Entpr IncApparatus for maintaining balanced mud circulation to prevent blowouts
US3362487 *May 3, 1966Jan 9, 1968Swaco IncControl for a hydraulically actuated choke in a drilling mud flow line
US3385376 *Jul 28, 1966May 28, 1968Henry HobhouseDrilling apparatus with means for controlling the feed and supply of drill fluid to the drill
US3429385 *Dec 30, 1966Feb 25, 1969Cameron Iron Works IncApparatus for controlling the pressure in a well
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US6719071Feb 25, 2000Apr 13, 2004Weatherford/Lamb, Inc.Apparatus and methods for drilling
US6968911Apr 12, 2004Nov 29, 2005Weatherford/Lamb, Inc.Apparatus and methods for drilling
US7111692Oct 5, 2004Sep 26, 2006Weatherford/Lamb, IncApparatus and method to reduce fluid pressure in a wellbore
US7395877Sep 26, 2006Jul 8, 2008Weatherford/Lamb, Inc.Apparatus and method to reduce fluid pressure in a wellbore
WO2000050731A1 *Feb 25, 2000Aug 31, 2000Peter Barnes MoyesDrilling method
Classifications
U.S. Classification175/38
International ClassificationE21B21/08, F15B11/032, E21B33/06, E21B21/00, F15B11/00, F15B11/072, E21B33/03
Cooperative ClassificationF15B11/0725, F15B11/032, F15B2211/5151, F15B2211/55, F15B2211/30525, F15B2211/528, E21B33/06, E21B21/08, F15B2211/565, F15B2211/7052, F15B2211/6051, F15B2211/20538, F15B2211/50554, F15B2211/25, F15B2211/50536, F15B2211/214
European ClassificationF15B11/032, E21B33/06, E21B21/08, F15B11/072B