AU2012101304A4 - A threaded bore casing - Google Patents

Abstract

A bore casing for use in the oil and gas industry, the casing having a box end with an internal thread and a pin end with an external end, the casing adapted to be threadingly connected to other said casings to form part of a casing string, the thread having a pitch of larger than 0.20 inches. .124+00 .126 +M .00.001 .020 --. 002 DETAIL B SECTION A-A FIG 1 THE INTERNAL BOX THREAD 126+ .124+.M _ .0 .001 1."23 R.010+.0 R.010+.0 |Pikh Lim- R.G20+.D 13*0-.0 .250 - .2 +.00213 .020 .125125.O D .040 O .001 - - Pvtch Lim- 4 TPI Taper =.A8 in. per ft or 0.04 in/ per in. an Diameter 1/24 FIG 2 CLOSE UP OF INTERNAL BOX THREAD

Description

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION Innovation Patent A THREADED BORE CASING The following statement is a description of the invention: 1 A THREADED BORE CASING TECHNICAL FIELD 5 The present invention is directed to a threaded bore casing for use in the oil and gas industry and which has a special thread design to enable casings to be threaded together. BACKGROUND 10 Bore casings are pipes used in the oil and gas industry to recover valuable energy resources from subterranean areas. Each pipe can have a length of 6 10 meters and the pipes are connected together to form a casing string. Bore casings are used to line the sides of the bore hole and are different from the 15 rotating pipes which have a lower cutter to cut the hole. A known type of connection for bore casings is made by cutting a thread in each end of the pipe. The thread is internal at one end of the pipe and is called a box thread, and the thread is external at the other end and is called a 20 pin thread. The advantage of this type of joint is that the joint is flush and there are no extruding parts. The present invention is particularly directed to an improved thread design for the flush joined pipes for the oil and gas industry, but there may be 25 circumstances where the invention will have suitability for other types of threaded pipes. It is known to cut a thread into a thick walled pipe. The thread is usually the standard industry API thread [API = American Petroleum Industry]. This type 30 of thread is not suitable for a thinner walled pipe as it leads to too much wall loss during cutting of the thread and will weaken the connection.

2 The present invention is particularly directed to an improved thread design for a thinner walled bore casing pipe for the oil and gas industry, but there may be circumstances where the invention will have suitability for other types of pipes. 5 Another difficulty with threaded pipe joins is in the initial threading engagement of adjacent pipes. Often difficulties are experienced in the initial "mating" of the external "pin" thread on the end of one pipe with the internal "box" thread on the end of the adjacent pipe. There would be an advantage if 10 it were possible to facilitate the starting of these two mating parts. Any references to methods, apparatus or documents of the prior art are not to be taken as constituting any evidence or admission that they formed, or form part of the common general knowledge. 15 It is an object of the present invention to provide a threaded pipe which may overcome at least some of the abovementioned disadvantages or provide a useful or commercial choice in the marketplace. 20 SUMMARY OF THE INVENTION According to a first aspect of the present invention there is provided a bore casing for use in the oil and gas industry, the casing having a box end with an internal thread and a pin end with an external end, the casing adapted to be 25 threadingly connected to other said casings to form part of a casing string, the thread having a pitch of larger than 0.20 inches. The casing typically comprises a pipe and preferably a thin wall pipe. 30 The bore casing will also be referred to as a pipe, but it should be understood that the pipe will be used as a casing and not as a rotating "drill" pipe. The bore casing may also comprise production casing and tubing.

3 Suitably, the pitch is between 0.240-0.300 inches. Preferably, the pitch is about 0.250 inches. The increased pitch and lead may facilitate the starting of the threading 5 engagement of two pipes to each other. The pipe may be made of any suitable material and a suitable material may comprise steel. 10 The pipe may have any suitable length. A suitable length of pipe may range from between 3-10m with a preferred length being between 6-10m The pipe may have any suitable diameter. A suitable diameter may range from between 80mm-30mm, with a preferred diameter of 88.9-273mm. 15 The pipe may have a wall thickness which is less than the standard wall thickness. Suitably, the wall thickness of the pipe is between 4mm-9mm Suitably, the depth of the thread is between 0.03 inches to 0.06 inches. The 20 depth of the thread is most suitably about 0.04 inches. The thread suitably tapers from a larger diameter adjacent the outer end of the thread to a smaller diameter adjacent the inner end of the thread. The taper is suitably shallow. Suitably, the thread taper is between 0.03-0.05 25 inches per linear inch of pipe. Preferably, the thread taper is about 0.04 inches per linear inch of pipe. The combination of the shallow taper and the depth of the thread can allow sufficient length of thread to be cut into the pipe wall of a pipe with limited wall 30 thickness. Suitably the beginning of the thread is formed with a blunt start to facilitate the starting of the threading inter-engagement of the pipes. The blunt start may be formed by removing the imperfect thread at the start of the thread.

4 It should be appreciated that no unnecessary limitation should be placed on the invention merely be exemplification of certain pipe lengths, diameters and manufacturing materials. 5 BRIEF DESCRIPTION OF THE DRAWINGS Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient 10 information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows: 15 Figure 1. Illustrates the internal "box" threaded end of a pipe. Figure 2. Illustrates in greater detail part of the box thread. Figure 3. Illustrates in greater detail the blunt start of the box thread. 20 Figure 4. Illustrates the external "pin" threaded other end of the pipe of figure 1. Figure 5. Illustrates the pin thread in greater detail . 25 Figure6. Illustrates an existing pipe thread design. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 30 Referring initially to Figure 1 there is illustrated, in section, one end of a pipe 10. The end has an internal thread 11 of special design cut into it. This end of the pipe with the internal thread is commonly known as the "box" or "female" end.

5 The other end of the same pipe 10 is illustrated in figure 3 and this end is provided with an external thread 12. This end of the pipe with the external thread is commonly known as the "pin" or "male" end. 5 In use, two or more pipes can be threadingly connected together by mating the male end of one pipe with the female end of the other pipe. The pipe is typically made of high strength steel and can have a length of 6 1Om and a diameter of between 8-30cm. 10 The thread is cut into each end of the pipe using a manual or CNC lathe machine preferably with a hollow spindle to allow the pipe to pass through the head stock of the lathe and to be clamped in the chuck adjacent to where the thread is to be machined. This ensures maximum rigidity when performing the 15 thread cutting operation. A thread is machined using a single point "full form" threading insert which is the same profile as the thread form for either the pin or the box connection. Correct pitch is set on the machine and the thread is machined to the correct 20 pitch diameter which is then gauged using the pitch diameter gauge. Other thread elements such as lead, taper, thread height and thread profile are checked for conformity. The internal "box" thread 11 is better illustrated in figure 2. The thread profile 25 13 has a pitch and lead of 0.250 inches, and a thread depth 14 of 0.040 inches. Similarly the external "pin" thread 12 has an identical pitch and depth. 30 Thus the pitch of the thread is relatively wide and the depth of the thread is relatively shallow, the advantage of which will be described in greater detail below.

6 The box thread 11 has a taper which is larger at the outer end of the pipe and smaller at the inner end of the pipe. The taper is slight and is about 0.04 inches per linear inch of the thread. 5 Similarly, the pin thread 12 has an opposite taper which is smaller at the end of the pipe and larger at the inner end of the thread. The taper is the same as that of the box thread. The combination of the shallow taper and the relatively small pitch depth 10 allows maximum thread length along the pipe of the type which has a limited wall thickness. A standard API thread would not achieve this. The box thread 11 is also shaped to facilitate starting the threading interengagement between two pipes. Referring to figure 3 the initial part of the 15 box thread is modified to provide a blunt start 14. The first turn 14 of the box thread is bevelled to break the sharp edge of the thread. This facilitates the starting of the two mating parts of adjacent pipes. Figure 6 illustrates a prior art thread design which has disadvantages. 20 In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. The term "comprises" and its variations, such as "comprising" and "comprised of" is used throughout in an inclusive sense and not to the exclusion of any 25 additional features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art. Throughout the specification and claims (if present), unless the context requires otherwise, the term "substantially" or "about" will be understood to not be limited to the value for the range qualified by the terms.

7 Any embodiment of the invention is meant to be illustrative only and is not meant to be limiting to the invention. Therefore, it should be appreciated that various other changes and modifications can be made to any embodiment described without departing from the spirit and scope of the invention.

Claims (10)

1. A bore casing for use in the oil and gas industry, the casing having a box end with an internal thread and a pin end with an external end, the casing adapted to be threadingly connected to other said casings to form part of a casing string, the thread having a pitch of larger than 0.20 inches.

2. A bore casing according to claim 1 comprising a thin wall pipe.

3. A bore casing according to claim 1, comprising production casing and tubing.

4. A bore casing according to any one of claims 1 to 3, wherein the pitch is between 0.240-0.300 inches.

5. A bore casing according to claim 4, wherein the pitch is about 0.250 inches.

6. A bore casing according to claim 5, wherein the beginning of the thread is formed with a blunt start to facilitate the starting of the threading inter engagement of the pipes.

7. A bore casing according to any one of claims 1 to 6 wherein the pipe is comprised of steel.

8. A bore casing according to any one of claims 1 to 7 wherein the pipe ranges from between 3-10m in length with a preferred length being between 6-1Om

9. A bore casing according to any one of claims 1 to 8 having a diameter ranging from between 80mm-30mm, with a preferred diameter of 88.9

27.3mm. 9 10. A bore casing according to any one of claims 1 to 9 wherein wall thickness of the pipe is between 4mm-9mm. 11. A bore casing according to any one of claims 1 to 10 wherein the depth of the thread is between 0.03 inches to 0.06 inches and preferably about 0.04 inches. 12. A bore casing according to any one of claims 1 to 11 wherein the thread suitably tapers from a larger diameter adjacent the outer end of the thread to a smaller diameter adjacent the inner end of the thread. 13. A bore casing according to claim 12 wherein the thread taper is between 0.03-0.05 inches per linear inch of pipe. 14. A bore casing according to claim 13, wherein the thread taper is about 0.04 inches per linear inch of pipe. 15. A bore casing substantially as hereinbefore described with reference to figures 1-5.