|Publication number||US3398794 A|
|Publication date||Aug 27, 1968|
|Filing date||Oct 3, 1966|
|Priority date||Oct 3, 1966|
|Publication number||US 3398794 A, US 3398794A, US-A-3398794, US3398794 A, US3398794A|
|Inventors||Fox Jr James E|
|Original Assignee||Pan American Petroleum Corp|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (9), Referenced by (8), Classifications (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Aug. 27, 1968 J. E. FOX, JR
APPARATUS FOR RUNNING LARGE DIAMETER CASING 2 Sheets-Sheet 1 Filed Oct. 5, 1966 AlR COMPRESSOR WATER PuMP\ v w v v M v E w v w N M .v H l L v w m a 2 w m m 2 v\\ H V k/;v 4 J 1 4 F 7 K/ r /v P U m i O 6- 2 2 5 /A///// & 22:51:: :s
SQWDA FIG I ATTORNEY Aug. 27, 1968 J. E. FOX, JR
APPARATUS FOR RUNNING LARGE DIAMETER CASING Filed Oct. 5, 1966 2 Sheets-Sheet 2 wags F 2W \K N f s 1 IO RELIEF VALVE 6O 2 2 50 42 I? E 5|- Ill! a 49 I a v Q 0 4 :Q48 RELIEF VALVE 58 I; 5
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JAMES E. FOX JR.
ATTORNEY United States Patent "ice 3,398,794 APPARATUS FOR RUNNING LARGE DIAMETER CASING James E. Fox, Jr., Fort Worth, Tex., assignor to Pan American Petroleum Corporation, Tulsa, Okla., a corporation of Delaware Filed Oct. 3, 1966, Ser. No. 583,537 4 Claims. (Cl. 16667) ABSTRACT OF THE DISCLOSURE This invention concerns the lowering of a large diameter easing into a water containing borehole drilled into the earth. In casing having diameters of 48 inches or larger, the weight of the casing is many time-s that of the smaller casings so it is desired to float the larger casing. However, the walls have lower collapse pressure than smaller casing for the same wall thickness. Means are provided to construct chambers within the casing and to maintain sufficient pressure therein to prevent collapse of the casing as it is lowered through a 'hole of water. As the casing is lowered into the hole, fluid in the compartment is maintained at a pressure at least as great as the difference between the rupture pressure of the casing and the pressure of fluid in the borehole exterior of the casing. Two lines run from the compartment to the surface so that the pressure and the type fluid therein can be controlled.
This invention concerns the running or lowering of a casing into a borehole drilled into the earth. It especially relates to apparatus for running large diameter casing into such borehole so that the lifting rig used in lowering the casing does not have to support the full weight of the string of casing.
My invention especially relates to a system wherein the interior of the casing is sealed into one or more fluid-tight compartments. Each compartment is filled with a fluid having a lesser density than that of the liquid in the borehole so as to impart buoyancy to the casing. This reduces the weight on the lifting rig. This aids one problem, but there remains the matter of preventing collapse of the casing. Therefore, means are provided so that pressure can be maintained in each compartment at least as great as the difference between the rupture pressure of the walls of the casing and the external pressure of the fluid in the well bore at the level of the compartment. This is to prevent collapse of the casing.
In the drilling of boreholes in the earth such as for the production of oil and gas, it is normal practice to run a string of casing into the borehole so as to line the borehole. This primarily is to prevent caving of the borehole walls, and to prevent fluid in formations other than the productive formation from entering a string of casing, and to form a vertical passage through which to produce the desired fluid. Normally this casing, in the production of oil and gas, is not over about 8 or 10 inches in diameter. For this size casing, the walls can be made relatively thick to withstand very high pressures, yet the weight can be carried by derricks. Recently, however, there have been an increasing number of large diameter holes drilled. By large, it is meant, for example, 48 inches and up.
The problems and environment encountered can be considerably different from those encountered in the drilling of the more conventional holes in oil and gas production. For example, the size of the casing in large diameter holes makes for a weight many times that of the smaller casing, the walls have lower collapse pressure than smaller casing for the same wall thickness largely because of hoop stress in the larger diameter casing. Frequently the large diameter wells are drilled through formations which are nearly free of fluid. One place where large diameter holes have 3,398,794 Patented Aug. 27, 1968 been drilled is at Mercury, Nevada, where the holes were drilled by the Atomic Energy Commission for various test sites. A major problem at such test sites is how to run large diameter casing of 48 inches in diameter, for example, to depths of over 4,000 feet. The use of hydraulic jacks large enough to handle the great weight of 4,000 feet of 48-inch casing is impractical. It is also impractical in some cases to seal off the lower end of the casing and float the string in for several reasons. For example, the 48-inch casing, if not over 2 inches in thickness, has a relatively low collapse strength of less than 2,000 p.s.i., for example. If there is 4,000 feet head of water in the hole, it is seen that the casing will probably collapse. If the thickness of the wall is increased to increase the collapse strength, then the weight of the already exceedingly heavy casing is again increased, requiring extra large jacks or lifting means at the surface. As mentioned, I propose to reduce this problem by a novel way of floating in the heavy casing string. From the above brief discussion of the problem, it is seen that there is certainly an immediate need for a solution.
Briefly, in a preferred embodiment, my invention includes the forming of one or more fluid-tight compartments, preferably in the lower end of the casing. Then as the casing is lowered into the hole, fluid in the compartment is maintained at a pressure at least as great as the difference between the rupture pressure of the casing and the pressure of fluid in the borehole exterior of the casing. One system of obtaining this is by running one or more conduits from each compartment to the surface. Air is injected through one of the conduits into the compartment at a pressure which will prevent collapse. The air, being of lighter density than the water in the surrounding borehole, will add buoyancy to the casing. If a negative buoyancy is neede, i.e., if the buoyancy should be reduced to permit the casing to sink, water is injected through the same, or a second conduit, into the compartment to effect such change in buoyancy. The proper pres sure is maintained in each of the compartments, if a plurality of compartments is used, as additional compartments are submerged in the water in the borehole. When the casing has been run to its total depth, the fluid is removed from the compartments and the partitions removed as by drilling, for example.
In a modification of the preferred embodiment, an upper compartment and a lower compartment are formed in the lower end of a string of casing by the use of first packer means and second packer means. Pressure means are provided to maintain fluid pressure within the compartments at a pres-sure at least as great as the difference between the rupture pressure of the casing and the pressure of fluid in the well bore exterior the string of easing. These pressure means include inner and outer concentric conduits suspended within the string of casing. The inner conduit extends to within the lower compartment, and the annulus between the concentric conduits terminates in fluid communication with the upper compartment. Relief valve means are provided between the lower and the upper compartments.
Various objects and a better understanding of the invention can be had from the following description taken in conjunction with the drawings in which:
FIGURE 1 illustrates one embodiment of the invention in which a casing is divided into a plurality of compartments and in which dual macaroni stringers are run from each compartment to the surface; and
FIGURE 2 illustrates another embodiment of the invention using a different arrangement of conduits from the compartments to the surface.
Reference is first made to FIGURE 1 which illustrates a borehole 10 having a string of casing 12 suspended therein. The lower end of the string of casing is enclosed 3 by a drillable shoe 14. By drillable, it is meant that the material can be readily removed by the use of ordinary drilling equipment, and such material includes aluminum, cement, cast iron, magnesium and/ or plastic, for example.
A lower packer 16 and an upper packer 24 make lower and upper compartments 18 and 26. The interior of compartment 18 is connected to the surface by a first conduit 20 and, if desired, a second conduit 22. Conduit 20 is connected to an air compressor 34 and through valve 40 to the atmosphere. Conduit 22 connects compartment 18 to a Water pump 36 and through valve 38 to the atmosphere or storage.
Compartment 26 is similarly connected through conduits 28 and 30 to the surface. Suitable water pumps and air compressors can also be connected to these conduits. Although only two compartments 18 and 26 are shown, it is to be understood that any desirable number can be made.
Frequently the hole will be essentially free of liquid. Then, in order to float the casing in, one must inject Water 32 into the borehole. The amount of water injected need not be enough to fill the borehole, but must be high enough to add the proper buoyancy effect to the string of casing.
When it is desired to run casing 12, packers 16 and 24 are set in the casing as it is made up and the conduits 20 and 22, 28 and 30 extend through the packers as necessary to the surface. Conduits 20 and 22 may contain retrievable valves 21 located near packers 16, and conduits 28 and 30 may contain such valves adjacent packer 24. A suitable valve can be an Otis wireline remote-controlled, subsurface, safety valve such as advertised on page 3841 of the Composite Catalogue of Oil Field Equipment and Services for 1966-1967, and published by World Oil, PO. Box 2608, Houston, Tex. As will be seen, these valves 21 aid in maintaining pressure in compartment 18- when adding joints of conduits and casing as the assembly is lowered.
As the casing 12 is lowered into the borehole and the lower end enters the water 32, buoyancy is quickly added to the casing as the compartment 18 contains air. The air is obtained from air compressor 34 and injected through conduit 20 to maintain the pressure within compartment 18 at the required level. A pressure gauge 41 is provided at the surface on air conduit 20 when in the hole in an assembled position as illustrated. Of course, the pressure of the air within compartment 18 will be low enough so that it will not rupture the casing outwardly and high enough to prevent collapse at various hydrostatic water levels outside. The distance between packer 16 and shoe 14 is kept sufficiently small so that the difference in head at the level of the packer and at the level of the shoe 14 will not be greater than the rupture pressure of the casing. This is because the pressure of the gas within compartment 18 is substantially the same at the top and bottom and I am merely controlling the differential pressure between the interior compartment 18 and the exterior of the casing, both at the level of packer 16 and shoe 14, so that the differential pressure will be within the safety limits.
As mentioned, the remote-controlled valves 21 aids in making up the various strings of conduits. For example, compartment 18 can be pressured as desired, then by closing valves 21, the conduit 22 or 20 can be broken or parted and additional joints of conduit added as the assembly is lowered into the Well bore; yet the pressure of the air in compartment 18 maintained.
Depending upon the thickness of the wall and the density of the wall material, it may occasionally be that one will have to reduce the buoyant effect of the compartments 18 and 26. This can be accomplished by opening valves 21 in conduits 20 and 22 and then pumping water down conduit 22 and exhausting air through conduit 20 through valve 40 to the atmosphere so that the proper buoyancy is obtained. Alternatively, as will be seen in FIGURE 2, the air can be evacuated to compartment 26 4 by use of a relief valvesThe desired buoyancy can be determined fairly easily by knowing the density of the fluid 32, the density and thickness of the walls of casing 12 and the strength of the lifting jacks for raising and lowering the casing 12 and the density of liquid 32 and its level. If too great a buoyancy is obtained, casing 12 floats and does not sink to the bottom of the hole 10 as desired. However, by injecting the proper amount of water into compartments 18 and 26, the desired buoyant eifect is readily obtained from the casing 12 so that it can be lowered to the bottom of the well bore. The proper amount of water injected into the compartments can be determined by merely observing the weight of the casing on the supporting derrick and adding or removing water from such compartments to maintain the desired weight.
' One of the conduits such as 22 can extend to the lower end of compartment 18 to facilitate removal of water by injecting air through conduit 22.
If desired, a relief valve 44 can be placed in the bottom 14. The relief valve can be set at the maximum desired differential pressure. Then when the pressure of the fluid in the borehole exceeds the pressure in chamber 18 by a given amount, valve 44 opens, permitting water or other fluid in the well bore to enter chamber 18. If rather close control of the buoyancy is desired, one can omit relief valve 44.
In normal operation, casing 12 is lowered to and against the bottom of borehole 10 which then supports the excess weight over that for which the lifting equipment at the surface is designed to lift. At this point in the operation, the casing then normally contains water so that there is no differential pressure between the interior and exterior of the casing. Conduits 20, 22, 28 and 30 can then be removed. If the hole is not full of water, water is normally added only to a height in the casing so that the water level in the interior of the casing is the same as that in the annulus. The casing is then cemented such as by using several tubing strings supported on the outside of the big casing 12, such as indicated at 13. Such cement tubing strings can be fastened to the casing 12 by means 13A. Another way of cementing large diameter casing is shown in United States Patent 3,202,213, issued Aug. 24, 1965, in the name of George C. Howard.
After cement is set in the annulus between casing 12 and the borehole wall, the pressure inside the casing 12 can be relieved. The cement either increases the collapse strength or removes the cause of collapse after the casing is in place. After the cement is set, the pressure in compartments 18 and 26 can be reduced by removing the water, if desired. These packers can be removed if they are the retrievable type, or if they are the drillable type, they can be drilled through. After the packers 16 and 24, conduits 20, 22, 28 and 30, and the water, if any, in casing 12, are removed, casing 12 is free of obstructions and equipment and personnel can be raised and lowered through the casing in a conventional and normal manner, or drilling can be resumed to the next casing point.
Casing 12 can serve several possible uses. It can be a liner for a mineshaft type operation, to case off a trouble zone for deeper drill, or to hold the cement placed behind all large casing strings from top to bottom.
The areas for big hole drilling can vary such that in some areas the borehole may be dry to total depth, or have an intermediate fluid level which rises to about 2,500 feet below the surface, as in certain areas of Nevada, or to a hole completely full of water, such as in most areas in Mississippi. The system of using the buoyancy for reducing the weight of the casing string will work in a hole having fluid naturally occurring therein, or in a hole not having fluid but one which can be loaded with liquid, such as water. For example, if hole 10 is dry but has walls capable of holding water, water 32 is added to the desired level. The desired level is that necessary to obtain the required buoyancy for the system. The use of this invention for preventing collapse of the casing as described herein can be used, for example, for any of the following:
(a) for thin wall casing in a dry hole where water is first added and then later removed, (b) for use with a thin wall casing string to which some material is-added later for example, the addition of cement to the annulus between the casing string and the borehole wall that will increase the collapse as noted above or remove the cause of collapse after the casing is in place, and (c) for an increased safety factor while running large diameter casing, even though such safety factor may not be required after reaching total depth where the casing is cemented in place. It is to be noted that there can be pressure surges in well bore fluid when a casing is run therein.
Attention is next directed to FIGURE 2 which illustrates concentric tubings 46 and 48; both of which are run through upper packing 50. The inner tubing 48 is run through packer 52 which is set beneath packer 50. Packers 50 and 52 are set in casing and together form therewith a lower chamber 54 and an upper chamber 56. The running of concentric tubing through casing is a wellknown oil field practice. In FIGURE 2, then, an independent communication is obtained between the surface and each compartment. If it were desired to add water to compartment 54 in FIGURE 2, and relieve the air pressure, this can be accomplished by the use of a relief valve 58 which relieves the pressure from compartment 54 into compartment 56 as water is injected through conduit 48 into lower compartment 54. For purposes of illustration, it will be assumed that compartment 54 has been pressured with air to the desired pressure. However, it may be desired to decrease the buoyancy of the system. This is conveniently done by adding water through inner conduit or tubing 48. If water were added to compartment 54 and no air removed, the pressure therein might become excessive. This can be controlled by use of relief valve 58 in upper packer and which is set at a selected pressure to prevent such over-pressurizing. Then as water enters compartment 54 and a given pressure is reached, such pressure is relieved through relief valve 58. Upper packer 50 can also conveniently contain a relief valve 60 which serves essentially the same function as relief valve 58.
In running or lowering the device of FIGURE 2 into a borehole, packer 52 with conduit 48 is first set, forming compartment 54. Casing 10 and extensions of conduit 48 are then run to a depth where it is necessary to pressurize compartment 54. This is done by injecting air under pressure through conduit 48. A remotely operated valve 49 can be provided in conduit 48. Then when additional strings of tubing 48 are added at the surface, as casing 10 is lowered, the pressure in compartment 54 will not bleed off; however, the valve can be opened to permit air to be added or removed. The annulus 51 between inner tubing string 48 and outer string 46 is in communication with compartment 56. It is through annulus 51 that compart ment 56 has fluid communication with the surface. The use of concentric tubing as illustrated in FIGURE 2 facilitates the running of such tubing during drilling operations, and is normally preferred as it is easier to install than the system shown in FIGURE 1 which, for example, uses the common dual completion techniques in running the dual strings of tubing. It is contemplated that it will not always be necessary to have compartment 54 in fluid communication with the surface. For example, if only one pressure is needed in compartment 54 for existing conditions, it can be pressurized at the surface and sealed until such time as it is desired to lower the pressure.
While there are disclosed above the limited number of specific embodiments of this invention, various modifications can be made thereto without departing from the spirit or scope of my invention.
1. An apparatus for use in lining a borehole which comprises: I
a string of casing in which at least one fluid-tight compartment has been formed in the lower end portion thereof, the wall of said lower end portion forming a part of said fluid-tight compartment;
pressure means to maintain fluid pressure within said compartment at a pressure at least as great as the difference of the rupture pressure of said casing and the pressure of fluid in said borehole exterior of said string of easing;
said pressure means including a first fluid conduit and a second fluid conduit extending from the interior of said first compartment through the wall thereof and to the surface above said well bore.
2. An apparatus as defined in claim 1 including a second compartment above and adjacent said first compartment and a third and a fourth conduit extending from the interior of said second compartment through the wall thereof to the surface.
3. An apparatus for use in lining a borehole which comprises:
a string of casing closed at the lower end;
a first packer means and a second packer means set in the interior of said casing to form an upper compartment and a lower compartment in the lower end of said string of casing, a circumferential portion of the wall of said casing forming a part of the wall of said compartments;
pressure means to maintain fluid pressure within said compartments at a pressure at least as great as the difference of the rupture pressure of said casing and the pressure of fluid in said borehole exterior of said string of casing, said pressure means including inner and outer concentric conduits suspended within said string of casing, said inner conduit extending to within said lower compartment and the annulus between such concentric conduits terminating in fluid communication with said upper compartment and relief valve means between said lower and said upper compartments.
4. An apparatus as defined in claim 3 including a relief valve in the wall of said lower compartment such that when the pressure in the fluid exterior of said compartment is a selected value greater than the pressure within said lower compartment, said relief valve opens permitting the fluid to enter said lower compartment.
Oil Field Development, N.Y., McGraW-Hill, 4th ed., 1956, pp. 428-430.
CHARLES E. OCONNELL, Primary Examiner. I. A. CALVERT, Assistant Examiner.
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|U.S. Classification||166/67, 166/381|
|International Classification||E21B43/10, E21B43/02|