US3486555A - Small diameter riser pipe system - Google Patents

Description

Dec. 30, 1969 y R. P. VINCENT 3,486,555

` SMALL DIAMETER RISER PIPE SYSTEM Filed June 25, 1968 2 Sheets-Sheet 1 ATTORNEY Dec. 3o, 1969 Filed June 25, 1968 SR. P. VINCENT 3,486,555

SMALL DIAMETERRISER PIPE SYSTEM 2 Sheets-Sheet 2 f RENC R VINCEN mvmon.

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ATTORNEY United States Patent O 3,486,555 SMALL DIAMETER RISER PIPE SYSTEM Renic P. Vincent, Tulsa, Okla., assignor to Pau American Petroleum Corporation, Tulsa, Okla., a corporation of Delaware Filed June 25, 1968, Ser. No. 739,723 Int. Cl. E21b 33/035, 7/12, 43/01 U.S. Cl. 166-.5 8 Claims ABSTRACT OF THE DISCLOSURE This describes Ithe use of a riser pipe which has an inside diameter only about one-half to one inch larger than the outside diameter of the drill collar and drill pipe which must pass therethrough. The riser pipe, when being raised or lowered, is supported by a special sub or enlarged section of drill pipe which is connected to the lower end of the drill string just above the bit. Buckling of the riser pipe is resisted by the stiffness of the drill pipe in tension. Means are provided to guide the lower end of the riser pipe into sealing engagement with the wellhead. Thus, no tensioning device is required on the vessel. By using this system, the weight of the riser system is reduced by a factor of between 10 and 20.

This invention relates to drilling in earth formations located beneath a body of water, such as in the Gulf of Mexico, in which the drilling operations are conducted from a floating vessel. More specifically, this invention relates to a method and apparatus involving a riser pipe which extends from the ocean oor to the floating vessel located at the surface of the body of water. It relates to a riser pipe which is only slightly larger than the drill pipe it passes through such that the weight of the riser pipe system is reduced, for example, by a factor of l to 20 over that of the conventional riser pipe.

Background In recent years it has become desirable to use a oating vessel from which to drill wells in marine locations. In such operations the floating -vessel is sometimes connected to a submarine well bore by a long tubular member through which drill pipe, drilling uids, etc., pass between the vessel and the well bore. This long tubular member is commonly referred to as a riser pipe.

A submerged well head usually includes a blowout preventer and other control equipment. The control equipment is usually operated by hydraulic lines which extend from the equipment to the Vessel. However, sonic instruments can be used for operating the control equipment. In one embodiment of the commonly used systems, the upper part of the well head assembly includes a ball connector which provides a flexible connection between the well head assembly and the riser pipe. The lower end of the riser pipe is connected to the ball joint and is free to pivot thereabout. This is commonly called a flex joint. The purpose of this is to permit relative pivotal movement between the riser pipe which is subject to forces such as the ocean current and the well head assembly which is secured to the earth. Other types of flex joints are commercially available; however, the ball and socket joint is enjoying increasing popularity. Although a vessel is anchored, it normally has some vertical movement and it can rise and fall from a few feet up to 20-30 feet or more. To compensate for this vertical movement, a slip or telescopic joint is provided in the riser pipe.

In conventional riser pipes which are supported solely at the lower end, its own effective weight, that is, weight in water, causes it to be in a state of axial compression increasing from zero at the top to a maximum at the Patented Dec. 30, 1969 bottom support. When drilling in deep water, the compressive stress in the wall of the riser pipe from this source alone is sometimes sufficient to buckle the riser pipe, that is, to cause it to bend. To counteract this buckling effect it has become a practice to apply a tensile force to the top of the riser pipe. Special tensioning devices are mounted on the ship and have their cables attached to the upper end of the riser pipe but below the slip joint. These tensioning devices are commonly referred to as constant tensioning devices so that they can maintain a constant tension on the riser pipe although the ship may rise and fall with respect to the riser pipe. These constant tensioning devices are helpful but are also' costly and must be maintained. A failure of the tensioning device can be catastrophic.

In ordinary drilling using conventional riser pipe systems, the riser pipe may commonly -be about 20 inches in diameter and the drill string which passes therethrough is commonly about 41/2 inches in diameter. The relatively larger diameter of the riser pipe is provided so that the drill bit, etc., at the lower end of the drill string can pass readily through the riser pipe. In ordinary operations the drilling fluid circulates down through the drill pipe, out the bit at the lower end where the hole is being made, up the annulus, first between the drill string and the earth, and then between the drill string and the riser pipe. The bigger the riser pipe, the greater the stresses due to buckling, thus the greater the tensioning force which must be applied to keep it from buckling.

Brief description of the invention Briefly, this invention concerns an improved riser pipe in which the riser pipe is only slightly larger than the diameter of the drill string. The lower end of the riser pipe sealingly tits and mates into an upwardly facing conical surface on the subsea well head. A drill string extends through the riser pipe and has an operational sub of a diameter larger than the drill string attached thereto. The sub has an outer diameter larger than the inner diameter of the riser pipe and supports the riser pipe when the riser pipe is being run into or removed from its operating position. Buckling of the riser pipe is prevented lby having either heavy drill collars extending therethrough or when the drill pipe is in operation, the tension is the drill pipe imputes stiffness to the riser pipe. In this system, therefore, no tensioning device is required for the riser pipe.

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 a preferred embodiment showing the riser pipe seated in the well head and extending to a drilling vessel at the surface;

FIGURE 2 illustrates several stands of drill collars attached to a special sub and bit and positioned inside small diameter riser pipe section;

FIGURE 3 illustrates the next stand, after that of FIG- URE 2, of collars and riser assembled as used when running into the position of FIGURE 1.

Attention is first directed to FIGURE 1 of the drawing which illustrates a conventional subsea well head including a blowout preventer stack 10 having a vertical passage therethrough. The blowout preventer stack is supported by a casing 14 which is set in larger surface casing 16. A guide base plate 18 is supported by casing 16. A long spool 12 is attached to the upper end of the blowout preventer stack. Long spool 12 is somewhat greater in length than the maximum Vertical displacement of the vessel due to wave and tides. The purpose of this will be explained hereinafter. Ihe upper end of long spool 12 is provided with an upwardly facing conical surface 20.

Show in the drawing is a riser pipe 22 which has a lower enlarged portion 24. Attached to the lower end of the riser by clamp 25 is guide arm 40 and an inverted guide funnel 26 which has a lower sealing surface 28. The guide arms 40 are loosely mounted on guide posts 39 to which guide lines 38 are connected and extend to the floating vessel 41. The purpose of the funnel 26 is to aid in centering the surface 28 on the conical surface 20 of the long spool 12. A seal 30 is carried by sealing surface 28 of the riser pipe 22. It will be noted that the mating surface 28 of the riser pipe and the upwardly facing surface 20 of the spool 12vare spherical in shape so that they can pivot with respect to each other without losing their seal. Thus, they make up what can be called a ex joint. This permits the upper end of the riser pipe to move laterally with the tide without breaking contact with the spool.

Mounted within riser pipe 22 is a drill string 32. The clearance between drill string 32 and riser pipe 22 is very small, being not over about one inch, for example. This clearance is kept small so that the stiffness of drill pipe 32 will be imputed into riser pipe 22 and prevent it from buckling. The upper end of riser pipe 22 is supported at the upper end from ship 41 by lines 23 and a conventional slip joint 27 of suitable size. No special tensioning means need be connected to lines 23. It has been determined that the stiffness of the drill pipe 32 held in tension by the weight of pipe and drill collars suspended below the riser is sucient to prevent buckling of the riser. The inherent stiffness of the drill collars is suicient to prevent buckling of the riser as it is lowered in the well.

I will now consider the manner of supporting the riser by the drill string 32 when the riser pipe is either being run or removed. This is accomplished by having a special sub 34 attached to the lower end of drill pipe 32 just above bit 36. Sub 34 is of a larger outside diameter than the inside diameter of riser 22. Sub 34 has an upwardly facing shoulder 33 which mates with or engages the downwardly facing shoulder 21 at the lower end of riser 22.

The length of spool 12 should be somewhat greater than maximum vertical displacement of the vessel due to wave and tide. It will be noted that the weight of the riser pipe 22 forces the surface 28 of funnel 26 downwardly against upwardly facing surface 20 to form a good seal. This seal is broken when sub 34 forces the riser pipe upwardly. Thus, by making the length of the spool greater than the maximum vertical displacement of the vessel, the blowout preventer 10 can be closed before the riser connection is broken. This is when pulling pipe. It also functions to permit the blowout preventers to remain closed until the seal is made between the riser and the spool.

FIGURE 2 is a view of the riser pipe assembly including drill collars. Shown thereon are a plurality of drill collars 22A having enlarged sub 34 just above bit 44. The drill collars 22A are held in place by slips 46 in rotary table 48. A safety clamp 50 has been positioned about the drill collars just above the slip. A pickup sub 52 is connected to the top of the top of the drill collars 22A. Mounted about the drill collars are a plurality of stands of riser pipes 54a, 54b and 54e. These stands of riser pipes are connected by suitable riser connectors 56. The lower stand 54a of the riser pipe is enlarged at the bottom similarly as shown in FIGURE l to provide an enlarged portion 24 having guide arm 40 and guide funnel 26 connected thereto.

FIGURE 3 illustrates a string of drill pipe or drill collars 22B closely surrounded by three stands of riser pipes 58a, SSb and 58e connected by suitable riser connectors. A safety clamp 60 is placed about drill collar string 22B just below the stand of riser pipe 52a.

When it is desired to run the riser pipe into the hole, the rst step is to place several stands of riser pipe such as 52a having enlargement 24 at the lower end about the string of pipe just above sub 34. The various stands of riser pipe are connected as by clamps 56. The riser pipe is stripped down over the drill string while the pipe is still in the derrick supported above the working deck. The whole device is then picked up by the hoisting means on rig 60 and lowered down through slips 46 which are in their open position. As soon as the lower end of riser pipe section 54a is clear below the rotary table, guide arms 40 and guide funnel 26 are connected thereto by clamp 25. The whole assembly is lowered to the position shown in FIGURE 2. The slips are then set as illustrated.

At this time another set of `drill collars 22B such as shown in FIGURE 3 mounted in riser section 58a, 5817 and 58C is supported in the derrick 60. Safety clamp 62 mounted on drill collar 22B some distance suicient to allow tongs to be used on the drill collar below the clamps prevents the riser pipe 58a from falling down over the lower end of drill collar 26B of FIGURE 3. The drill collar is picked up by pickup sub 52 which is now on the top of drill collar section 22B. The drill collar and riser of FIGURE 3 are then lowered and the threads 68 of drill collar 22B are connected into the threads of the upper section of the drill collars of FIGURE 2. At this point the riser section 58a, etc., is picked up by a catline or other auxiliary means, not specifically shown, and supported from derrick 60. Safety clamp 62 is removed and the riser section is lowered so that riser section 58a can be clamped or connected to the upper end of previously installed riser pipe section 54C. Additional stands of riser pipe and drill collars are added until the riser pipe has reached the desired length so that it can rest and seat on seat 20.

A brief discussion of the procedure of removing the riser pipe assembly will now be made. The drill pipe is removed by the use of derrick 60 in a conventional manner until the sub 34 is raised to the position illustrated in FIGURE 2. Pickup sub 52 is placed on the upper en d of the drill collars, the slips 46 released and the entire assembly of FIGURE 2 below the table 48 is raised by the raising of the drill collars. When the drill collars have been raised their maximum distance, such as 2 or 3 joints, the upper two or three stands of riser pipes are disconnected from the lower stands of riser pipe. An auxiliary hoist lifts the riser stand up suiciently so that a safety clamp can be placed about the drill collars just below the lower end of the disconnected riser pipe section, such as safety clamp 62 of FIGURE 3. Then the auxiliary means for lifting the riser pipe is removed and the upper section of drill collars such as 22B is disconnected from the upper portion 22A after portion 22A is firmly supported by the slips. The safety clamp 62 is used to support the riser pipe assembly on the stand of drill collars. The remaining drill collars are now lowered so that the remaining riser pipe joints are below table 48. The slips 46 are now set on the drill collars so that the drill collar joint immediately above the table can be broken out. Then we have a section broken out as shown in FIG- URE 3. This can be stored on the deck. Ideally, the sub 52 is of sufficient length to give greater length to the string of drill collars for manipulating the riser pipe sections thereabout. This process is repeated until all the riser pipe assembly as desired is pulled from the hole.

While the above embodiments of the 'invention have been described with considerable detail, it is to be understood that various modifications of the device can be made without departing from the scope or spirit of the invention.

I claim:

1. A riser pipe system for use with a well in the floor of a body of water which comprises:

a well head having an upwardly facing surface and a vertical passage therethrough; a drill string having a hollow sub member connected into the lower end portion thereof, said sub being insertable in the vertical passage of said well head, said sub member having a larger diameter than the other part of said drill string;

a riser pipe surrounding said drill string, the internal diameter of said riser pipe being less than the diameter of said sub member, the lower end of said riser pipe having a downwardly facing surface for mating and sealing with the upwardly facing surface of said well head.

2. An apparatus as defined in claim 1, including guide means to guide said riser pipe and drill string downwardly to engagement with said well head.

3. An apparatus as defined in claim 1 in which the outside diameter of said drill string is not over about one inch less than the inside diameter of said inside diameter of said riser pipe.

4. An apparatus as defined in claim 2, including a downwardly opening funnel secured to the lower end of said riser pipe for guiding the riser pipe into engagement with the upwardly facing surface of said well head.

5. A riser pipe system as defined in claim 1 for use in a floating vessel having a vertical movement due to waves and tide which comprises:

said well head including a hollow spool of a vertical length greater than the vertical movement of the oating vessel, said well head further including a blowout preventer connected to the lower end of said spool.

6. A riser pipe assembly as defined in claim 1 in which the downwardly facing surface of the riser pipe and the upwardly facing surface of the well head are spherical.

7. A method of removing a riser from engagement with a well head in which the riser is made up of at least two joints clamped together, a drill string inside said riser and having a sub of larger diameter than the inner diameter of said riser pipe, which comprises:

pulling up on said drill string until said sub engages the lower end of said riser pipe, continue pulling on said drill string until at least one joint of said riser pipe has cleared the work deck on said ship;

disconnecting the said first joint from said second joint;

securing the disconnected joint of the riser pipe;

lower the drill pipe and the lower section of riser pipe so that the top of the lower section of riser pipe is below the work deck;

then secure the drill collar to the work deck;

disconnect the joint of drill pipe above where it is secured;

store the disconnected joint of drill pipe and riser pipe. 8. A method of running riser pipe from engagement with the Well head in which the riser is made up of at least two joints clamped together, drill string inside said riser and having a hollow sub at the lower end thereof of larger diameter than the inner diameter of said riser pipe which comprises:

stripping at least one joint of riser pipe down over a section of drill string until the lower end of the riser pipe presses on said sub; lowering the drill pipe and riser down through the rotary table; placing another section of riser pipe over another section of drill string; placing a safety clamp about the lower end of said second section of drill pipe to support the riser pipe section; connecting the second section of drill pipe to the first section supported in said rotary table; lifting up on said second section of drill pipe; independently lift up on said second section of riser pipe until the weight is removed from said clamp on said second section of drill pipe; removing said safety clamp; independently lowering said second section of riser pipe; clamping said second section of riser pipe to said first section; thereafter lowering said connected sections of drill pipe and said connected sections of said riser pipe; repeating the above steps until said riser pipe engages said well head.

References Cited UNITED STATES PATENTS 3,145,775 9/ 1964 McCarty 166-.5 3,247,914 4/1966 Slack 166-.5 X 3,319,726 5/1967 Brown 166-.5 X 3,338,303 8/1967 Hoch et al 166-.5 3,340,928 9/1967 Brown 166-.5 3,369,599 2/1968 Evans 166-.5 3,422,889 1/ 1969 Yost 166-.5

JAMES A. LEPPINK, Primary Examiner R. E. FAVREAU, Assistant-Examiner U.S. Cl. X.R. -7

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