GB2226583A

GB2226583A - Method of placing a pipe string in a borehole and pipe section for use in the method

Info

Publication number: GB2226583A
Application number: GB8829843A
Authority: GB
Inventors: Robert Nicholas Worrall; Rudolph Wilhelmina Jo Driessen; Anthony Philip King
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1988-12-30
Filing date: 1988-12-30
Publication date: 1990-07-04
Also published as: GB8829843D0

Abstract

A casing 1 or other pipe string is placed in a borehole by providing its inner surface with removable buoyancy means 2, such as an annular foam lining or buoyancy chamber, in which a longitudinal fluid passage 3 is present via which a hydraulic cement or other fluids can flow during installation of the pipe string in the borehole. After completion of the installation operations the buoyancy means 2 are removed from the pipe string using a mill or fishing tool. <IMAGE>

Description

METHOD OF PLACING A PIPE STRING IN A BOREHOLE AND PIPE SECTION FOR USE IN THE METHOD The invention pertains to a method of placing a pipe string in a borehole and to a pipe section for use in the method.

In highly deviated or horizontal boreholes is often difficult to lower a string of casing pipes through the hole and to subsequently cement the casing in place as the casing string is deflected by its own weight towards the lower side of the deviated hole section thereby causing a non-uniform distribution of cement slurry around the casing and a poor bond between the casing and surrounding formation.

Numerous attempts have been made to solve the problem of placing casings, liners, or other pipe strings in both deviated and vertical wells. The known solutions generally boil down to giving buoyancy to the casing or other pipe string by filling it with a gas or low density fluid. US patent Nos. 3,526,280, 3,398,794 and 4,383,616 disclose such methods where a casing string is at least partly filled with gas to provide a buoyancy chamber during placement of the casing in a borehole. A difficulty encountered with the known installation methods is that the gas filled section of the casing is plugged by seals so that circulation of fluids, such as a cement slurry or cleaning fluid, via the casing interior into or from the surrounding annular space is impossible.US patent No. 3,398,794 teaches to solve this problem by securing a cement injection tube to the outer surface of the casing, whereas US patent No. 3,526,280 teaches to place a delayed setting type cement in the borehole before the casing is run. US patent No. 4,384,616, on the other hand, discloses to remove the sealing plugs above and below the buoyancy chamber after running the casing, but before placing the cement slurry in the borehole. A disadvantage of the latter known method is that in a deviated borehole the removal of the buoyancy chamber will cause the casing to deflect again towards the lower side of the borehole thereby causing a non-uniform cement distribution around the casing and a poor casing bond.

It is a primary object of the present invention to provide a method for placing a buoyant casing or other pipe string in a borehole wherein at any time fluid can be circulated through and around the string during the steps of running the string and cementing it in place. Further objects of the invention are to enable an influx of oil, gas or water to be circulated out while running the casing or other string, and to enable cement to be pumped in a controlled manner therethrough by eliminating the free fall effect that will occur if the cement or another high density fluid is pumped down through a large diameter pipe.

The method according to the invention comprises the steps of: providing at least one pipe section having attached at its interior side buoyancy means, said buoyancy means having a longitudinal opening which forms a fluid passage for passing fluid in longitudinal direction through the pipe section; securing said pipe section to other pipe sections; lowering the string of interconnected pipe sections into a borehole until the pipe string has reached a location where it is to be placed; inducing a fluid to flow through said longitudinal opening and through the interior of said other pipe sections; and securing the pipe string inside the borehole.

Preferably the fluid comprises a slug of hydraulic cement which is pumped down through said longitudinal opening of said buoyancy means and through the interior of the other pipe sections and up through an annular space surrounding the pipe string, whereupon the cement slug is allowed to set in said annular space so as to secure the pipe string inside the borehole.

It is furthermore preferred that during the step of lowering the pipe string the string is rotated about its longitudinal axis in order to reduce axial frictional forces. It is an important aspect of the present invention that after setting of the cement the buoyancy means are detached from the inner surface of the pipe section or sections and subsequently removed. This may be accomplished either by removing the buoyancy means by a fishing tool or by crushing, grinding, or shearing them with a drill bit and by subsequently flushing away the crushed parts by a drilling fluid passing through the bit.

In accordance with another aspect of the present invention there is provided a pipe section for use in the method. The pipe section according to the invention is equipped with buoyancy means that are removably attached to the interior side of the pipe section. Furthermore, a longitudinal opening is present in the buoyancy means so as to form a fluid passage for passing fluid in longitudinal direction through the pipe section.

Preferably the buoyancy means include an annular body of a syntactic foam in which a tubular plastic coating may be present.

The plastic coating may have near one end of the pipe section a widened terminal section of which the internal diameter is substantially equal to the external diameter of the rest of the coating.

Alternatively the buoyancy means may be formed by an annular space filled with a low density fluid. This annular space extends alongside the inner surface of the pipe section between a pair of ring-shaped seals near the ends of the pipe section and a tube which is co-axially arranged in the pipe section and which passes through the seals.

These and other features, objects and advantages of the present invention will be described in more detail with reference to the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of a pipe section provided with buoyancy according to the invention; Figure 2 shows schematically how the removal of the buoyancy means by drilling them away from the pipe section of Figure 1; Figure 3 is a longitudinal sectional view of a pipe string where the inner surface of a foam lining is provided with a plastic coating; Figure 4 is a longitudinal sectional view of a pipe string where a foam lining is secured to each pipe section by shear pins; Figure 5 shows at an enlarged scale detail A of Figure 4 while a foam lining is being removed by a fishing tool; and Figure 6 is a longitudinal sectional view of an embodiment of the invention where a pipe section contains an annular buoyancy chamber.

Referring now to Figure 1 there is shown a buoyant pipe section 1 according to the invention. The pipe section 1 is at its inner surface coated with a lining 2 of a buoyancy material, such as a syntactic foam consisting of a polymeric matrix material cqntaining glass microspheres.

A central opening 13 extends through the lining 3 in such a manner that the opening 3 is located either concentrically or excentrically relative to a central axis I of the pipe section 1.

The opening 3 serves to allow passage of a cement slurry or other fluids through the pipe section 1 during the steps of lowering a pipe string which includes the pipe section 1, into a borehole and cementing it in place.

In the embodiment shown in Figure 1 the pipe section is a casing section which is at its ends equipped with external screw threads 4 which cooperate in use with internal screw threads 5 of box-type pipe couplings 6. The box-type pipe couplings 6 are not equipped with foam linings and they are intended to interconnect various casing sections to an elongate casing string which serves to encase a borehole penetrating through subsurface earth formations. During installation of the casing string the casing sections are screwed together by means of the pipe couplings 6 while the casing is gradually lowered into a borehole (not shown).

The borehole is filled with a liquid and at least one casing section 1 is provided with a foam lining 2 which provides buoyancy but which at the same time allows fluid to flow through the interior of the casing string so as to avoid a plunger effect when the casing string is moved up or down through the borehole.

Preferably, the casing is rotated about its longitudinal axis I during running of the casing through the borehole to decrease axial frictional force. The casing may be centralized in the hole using casing centralizers. These are known in the art, and are not therefore described.

When the casing string has reached the depth where it is to be installed it is cemented in place by pumping a hydraulic cement down through the interior of the string and up through the annular space between the outer surface of the casing string and the borehole wall whereupon the cement is allowed to set.

As after placement of the casing string tubings or other casing strings may be installed in its interior it is generally desirable that the foam lining is removed after completion of the installation procedure. Figure 2 shows how the foam lining 2 can be removed from the interior of the casing or other pipe section 1 by a rotary drill bit 8. The bit 8 is carried by a rotary drill string 9 and comprises a pilot bit section 10 and a mill section 11.

The mill section 11 comprises a series of hard facing ribs which centralize the bit in the pipe sections 1 without causing damage of the inner surface of the sections. The crushed foam segments are flushed away by a drilling fluid that circulates through the drilling assembly in the direction of the arrows.

Figure 3 shows an alternative embodiment of a buoyant pipe strings according to the invention. In this embodiment the various pipe sections 30 of a casing string are provided with an annular foam lining 31 in which a tubular internal coating 32 is arranged.

The coating 32 is made of fiber glass, polyvinylchloride (PVC), or other drillable material. The inner surface of each pipe section 30 is along the majority of its length covered by the foam lining 31, which extends at one end of the section 30 about halfway into a pipe coupling 33 interconnecting adjacent sections.

At the location where the foam lining 31 extends outside the pipe section into the pipe coupling 33 the coating 32 comprises a widened terminal section 35 of which the internal diameter is substantially equal to the external diameter of the rest of the coating 32. In use said terminal section 35 fits co-axially around a bottom section 36 of a coating 32 of an adjacent pipe section 30 in the manner illustrated in Figure 3. The tubular coatings 32 thereby form a continuous tube inside the casing string by means of which fluids can be circulated through the tubing. The tubular coatings 32 thereby protect the foam lining from direct contact with the fluids that are circulated through the casing string.

After installation of the casing string and cementing it in place the foam lining 31 and internal coating may be drilled away by a drill bit as shown in Figure 2.

Alternatively the foam lining and coating may be retrieved by a fishing tool.

Figure 4 shows a casing string where in each pipe section 40 an annular foam lining 41 is loosely inserted so that it can easily be retrieved by a fishing tool. Each foam lining is secured to the casing string by means of a shear pin 44 which is mounted inside a pipe coupling 45. Other methods of axially locating the foam lining in the casing pipe are possible and will be known to those skilled in the art.

After placement of the casing string in a borehole the foam linings 41 may be retrieved one by one by a collet or slip type fishing tool 46. In use the lower end of the fishing tool 46 is lowered into the upper end of a foam lining 41.

As illustrated in Fig. 5 collet 48 of the fishing tool 46 is expanded inside a recess 49 at the inner surface of the foam lining 41 as soon as the tool 46 has been manouvred into the top of the uppermost foam lining 41 in the string. Subsequently, the tool 46 is pulled in the direction of the arrow so that the shear pin 44 is broken and the foam lining 41 is retrieved to the surface. By repeating the cycle of gripping an uppermost foam lining 41 with the tool 46 and retrieving it to surface all foam linings 41 can be retrieved to the surface.

Figure 6 shows an embodiment of the invention where at least one pipe section 60 of a casing string contains an annular buoyancy chamber 61. This chamber 61 is formed between the inner surface of the pipe section 60, a pair of ring-shaped seals 62 and a tube 63 which is arranged co-axially within the pipe section 60. The tube 63 is made of plastic or another drillable material.

The seals 62 may be formed by a pair of foam disks which sealingly engage the inner surface of the pipe section 60 and the outer surface of the tube 63. One seal 62 is equipped with a pressure valve 64 via which the annular chamber 61 may be filled with a pressurized gas, such as nitrogen, before the pipe section 60 is lowered into a borehole so as to prevent collapse of the pipe section 60 downhole under the hydrostatic pressure of the borehole fluids.

During installation of the casing string fluid can flow through the interior of the tube 63 and after completion of the installation the tube 63 and seals 62 can be retrieved by drilling them away using a drill bit shown in Figure 2 or a fishing tool as shown in Figure 5. It will be understood that the annular chamber shown in Figure 6 may be filled with any low density fluid such as a gas, a foam, a low density liquid or a mixture of for example a gel and gas-filled glass or plastic balls.

The principle advantages of the buoyant casing concept and the method of installing it can be summarized as follows.

It reduces the buoyant weight of the casing when immersed in drilling fluid. It thereby reduces tension in the upper part of the casing string and in the hoisting cables of the rig from which the casing is suspended during installation.

Furthermore it reduces in particular in deviated or horizontal boreholes frictional and other contact forces between the casing and borehole wall and it thereby enables the casing to be run under its own weight in more deviated boreholes.

Moreover, the presence of the longitudinal opening inside the buoyant casing enables the casing to be run in the hole while circulating drilling fluid through the string so that an influx of oil, gas or water into the borehole can be circulated out while running the casing. In some special cases the longitudinal opening may be temporarily plugged during the installation procedure.

The small width of the opening in comparison to the internal width of the casing string itself moreover allows a controlled pumping of hydraulic cement down via the casing and subsequently up into the annulus surrounding it due to the suppressing of the free fall effect. A final advantage of the method and pipe system according to the invention is the removable arrangement of the foam lining or other buoyancy means. This enables that after completion of the installation operations the string can be utilized over its total internal width so that utilization of an oversized casing and borehole is avoided.

It will be understood that instead of using the present invention in a casing installation procedure it may be used in other well pipe installation procedures as well. For example it may also be used for installing a liner in a well. Furthermore, instead of cementing the casing in place it may also be secured inside the borehole by using external casing packers or by cold forming the casing against the formation.

It will further be understood that the buoyancy means may consist of a cylindrical body of buoyancy material and that the longitudinal opening may be formed by a straight or helical groove in the cylindrical surface of the body. Alternatively the buoyancy means may consist of a series of printmatic or rectangular blocks, in which case the longitudinal opening is formed by the space left between the outer surface of the blocks and the inner pipe wall.

From these examples it will become apparent to those skilled in the art that there are numerous possible implementations and configurations of the present invention. Accordingly it should be clearly understood that the embodiments of the invention depicted in the accompanying drawings are illustrative only.

Claims

1. A method of placing a pipe string in a borehole, the method comprising: - providing at least one pipe section having attached at its interior side buoyancy means, said buoyancy means having a longitudinal opening which forms a fluid passage for passing fluid in longitudinal direction through the pipe section; - securing said pipe section to other pipe sections; - lowering the string of interconnected pipe sections into a borehole until the pipe string has reached a location where it is to be placed; - inducing a fluid to flow through said longitudinal opening and through the interior of said other pipe sections; and - securing the pipe string inside the borehole.

2. The method of claim 1, wherein the fluid comprises a slug of hydraulic cement which is pumped down through said longitudinal opening of said buoyancy means and through the interior of the other pipe sections and up through an annular space surrounding the pipe string, whereupon the cement slug is allowed to set in said annular space so as to secure the pipe string inside the borehole.

3. The method of claim 2, wherein after setting of the cement the buoyancy means are detached from said pipe section and subsequently removed from the pipe string.

4. The method of claim 3, wherein the buoyancy means are detached and removed from the pipe string by a fishing tool.

5. The method of claim 3, wherein the buoyancy means are detached and removed from the pipe string by crushing, grinding, or shearing the buoyancy means by a rotary drill bit and by subsequently flushing away the crushed parts of the buoyancy means by a drilling fluid passing through the bit.

6. The method of any preceding claim, wherein a plurality of pipe sections are provided with buoyancy means, said pipe sections being interconnected in such a manner that the longitudinal openings of said buoyancy means form a continuous fluid passage for passing fluid through the interior of the pipe string.

7. The method of any preceding claim, wherein during the step of lowering the pipe string into the borehole the string is rotated about a longitudinal axis thereof.

8. A pipe section for use in the method according to claim 1, the pipe section having removably attached at its interior side buoyancy means, said buoyancy means having a longitudinal opening which forms a fluid passage for passing fluid in longitudinal direction through the pipe section.

9. The pipe section of claim 8, wherein the buoyancy means comprise an annular body of foam which is co-axially arranged within the pipe section.

10. The pipe section of claim 9, wherein the foam is a syntactic foam.

11. The pipe section of claim 9 or 10, wherein annular body of foam is at its inner side provided with a tubular plastic coating, the coating having near one end of the pipe section a widened terminal section of which the internal diameter is substantially equal to the external diameter of the rest of the coating.

12. The pipe section of any one of claims 9-11, wherein the buoyancy means is formed by an annular buoyancy chamber which is filled with a low density fluid, said chamber extending alongside the inner surface of the pipe section between a pair of ring-shaped seals near the ends of the pipe section and a tube which is co-axially arranged in the pipe section and which passes through the seals.

13. The pipe section of claim 11, wherein said low density fluid is a gas.

14. The pipe section of claim 11, wherein said low density fluid contains gas filled balls.

15. A method according to claim 1 substantially as described with reference to the accompanying drawings.

16. A pipe section according to claim 8 substantially as described with reference to the accompanying drawings.