GB2250043A

GB2250043A - Tubing conveyed perforating gun assembly and tubing perforation method

Info

Publication number: GB2250043A
Application number: GB9025166A
Authority: GB
Inventors: Christopher Bird; William Sinclair Laught Petrie
Original assignee: Halliburton Co
Current assignee: Halliburton Co
Priority date: 1990-11-20
Filing date: 1990-11-20
Publication date: 1992-05-27
Anticipated expiration: 2010-11-20
Also published as: GB9025166D0; GB2250043B

Abstract

In the completion of an oil or gas well including a lower casing part (2) to be perforated, a perforating gun assembly is mounted by an upper part (15) at the lower end of a completion string (6). A releasable coupling initially connects the upper part (15) to a lower part including perforating guns (9) and a firing head (10). After firing, the coupling is released to permit the lower part of the assembly to fall to the bottom of the well, and the upper connecting part (15) together with additional components are then recovered through the completion string (6). With this arrangement, the internal diameter of the completion string may match that of the lower casing part (2). <IMAGE>

Description

TUBING CONVEYED PERFORATING GUN ASSEMBLY AND TUBING PERFORATION METHOD This invention relates to a tubing conveyed perforating gun assembly and to a tubing perforation method employing a tubing conveyed perforating gun assembly.

It is well known during the completion of an oil or gas well to use a perforating gun (also referred to as a "perforator") to perforate the well casing to permit oil or gas located in formations surrounding the casing to flow through the perforations into the casing for recovery.

In one prior art perforating technique, known as underbalance perforating, a completion string having an outside diameter smaller than the inside diameter of the casing to be perforated is run into the well to locate a perforating gun, which is secured to the completion string, at the correct position for perforating the casing. A packer is then set inside the casing above the perforating gun between the completion string and the perforating gun and, if desired, the completion string is purged of completion fluid and filled with a clean relatively light fluid, for example diesel oil. The fluid pressure of the fluid below the packer is then set to a pressure less than that present in the surrounding formation, and the perforating gun is fired.Because of the underpressure in the casing, as compared with the formation pressure, the perforation of the casing is immediately followed by an inrush of material through the perforations itb the casing.

This in-rush of material reduces clogging of the perforations and has been found to be beneficial in terms of long term production from the well.

After firing, the perforating gun is dropped from the completion string by selective or automatic operation of a tubing release device by which the gun is connected to the completion string, leaving the body of the tubing release device connected to the completion string. Oil and/or gas from the formation may then flow through the perforations into the casing and thence through the body of the tubing release device into the completion string.

Whilst the above technique has been found to be desirable in wells in which the outside diameter of the completion string (including the perforating gun) is less than the inside diameter of the well casing to be perforated, it cannot be utilised in so-called "monobore completions" in which the inside diameter of the completion string is substantially the same as or larger than the inside diameter of the casing to be perforated. In a monobore completion a completion string having an inside diameter substantially equal to or larger than the inside diameter of the casing to be perforated is run into a larger diameter portion of the well located above the casing to be perforated until the lower end of the completion string is located just above the upper end of the casing to be perforated.A packer is then set between the completion string and the casing close to the bottom of the completion string. Perforation of the well casing is then carried out using a wireline carried perforating gun which is run through the completion string into the casing to be perforated. The use of a wireline carried perforating gun has a number of well recognised disadvantages, and in particular is disadvantageous because it is not readily compatible with establishing high underbalance conditions at the time of firing. Also, the length of casing which can be perforated in a single shot is limited because of the limited load carrying ability of the wireline. Both of these difficulties could be overcome if a tubing conveyed perforating gun was used instead of a wireline conveyed perforating gun.However, it has been thought heretofore that the use of a tubing conveyed perforating gun would necessitate a restriction at the lower end of the completion string, which was itself considered undesirable. For this reason, wireline carried perforating guns were tolerated, notwithstanding the recognised advantages of such tubing conveyed guns.

It was thought a restriction at the lower end of the completion string was necessary if a tubing conveyed perforating gun was used because the portion of the tubing release device fixed to the perforating gun assembly and jettisoned with the perforating gun after firing must have an outside diameter which is less than the inside diameter of the casing to be perforated in order to ensure that the perforating gun will fall to the bottom of the well when released. From this follows the fact that the body of the tubing release device which must be carried at the lower end of the completion string must be capable of mating with a releasable element having an inside diameter smaller than the inside diameter of the casing to be perforated.Such a tubing release device body would of necessity have a bore of a smaller diameter than the casing to be perforated and would thus form a restriction at the lower end of the completion string.

It is an object of the present invention to provide a perforating gun assembly which can be run into a well on a monobore completion string and yet which, in the completed well, does not result in any restriction in the flow area of the completion string.

It is a further object of the present invention to provide a method of completing an oil or gas well in which a tubing conveyed perforating gun is utilised and yet in which there is no restriction between the inside diameter of the casing which is perforated and the inside diameter of the completion string.

According to one aspect of the present invention there is provided a perforating gun assembly comprising a lower explosive carrying part; an upper connecting part which in use of the gun is connected to a well completion string to allow the perforating gun assembly to be run into a well on the completion string; and a coupling which is releasable to release the lower part from the upper part after the gun has been fired, wherein the upper connecting part is recoverable through the completion string after the gun has been fired.

Preferably, the upper connecting part is connected in use to one of the nipples which is provided at the lower end of the completion string. Such nipples are routinely provided on completion strings for safety purposes and for subsequent working of the well. By utilising one of these nipples for securing the perforating gun assembly to the completion string the upper part of the perforating gun assembly can readily be removed from the well after the lower part has been jettisoned by release of the coupling.

If desired, the perforating gun assembly may include one or more tubing joints to space the perforating guns below the lower end of the completion string. Also, the perforating gun assembly may include other components desirable for effecting operation of the assembly, eg. one or more debris/flow subs and one or more impact subs to reduce impact forces transmitted from the perforating gun to the completion string. Any such additional components included within the perforating gun assembly are preferably located above the coupling so that they may be recovered from the well with the upper connecting part of the assembly for re-use.

The coupling may be of any suitable type, for example mechanically operated, pressure operated, or automatic According to another aspect of the present invention there is provided a method of completing an oil or gas well having a first length of casing to be perforated, and a second length of casing located above the first length of casing and having an inside diameter larger than that of the first length of casing, the method comprising: running into the well a completion string having a perforating gun assembly connected thereto until the lower end of the completion string is located adjacent the upper end of the first length of casing; firing the perforating gun assembly to perforate the first length of casing; releasing a coupling provided within the perforating gun assembly to allow the part of the perforating gun assembly located below the coupling to fall to the bottom of the well; and removing the remainder of the perforating gun assembly from the well through the completion string.

The above and further features and advantages of the invention will become clear from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawings in which: Figure 1 illustrates schematically a well prior to completion; Figure 2 shows the well of Figure 1 after a completion string and perforating gun assembly have been run into the well; Figure 3 illustrates the well of Figures 1 and 2 after the perforating gun assembly has been fired and the explosive carrying portion released; and Figure 4 illustrates the well of Figures 1-3 after the upper portion of the perforating gun assembly has been removed Referring firstly to Figure 1 there is illustrated a well 1 having, at the lower end thereof, a first length of casing 2 having an inside diameter A and, thereabove, a second length of casing 3 having an inside diameter B which is larger than A. The casing 2,3 is typically steel tubing which has been cemented into position in conventional manner. As illustrated, the sections 2,3 are interconnected by a transition portion 4 which includes a zone 5 having a diameter intermediate A and B.The transition portition 4 is located a short distance above the zone from which oil or gas is to be produced, and in order to complete the well it is necessary to perforate the tubing 2 in the zone of oil and/or gas bearing formations to permit oil and/or gas from the formations to enter the well for recovery.

Referring now to Figure 2 a completion string 6 and perforating gun assembly 7 has been run into the well 1.

The inside diameter C of the completion string 6 is substantially the same as or greater than the inside diameter A of the casing 2 and the lower end 6A of the completion string 6 is located a short distance above the upper end 2A of the casing 2. After removal of the perforating gun assembly, as described in more detail hereinafter, the completion string 6 will form a monobore completion of the well.

The perforating gun assembly 7 is connected to the completion string 6 utilising a nogo nipple 16 located close to the lower end of the completion string 6. It is conventional in the oil and gas industry to incorporate several nipples within the completion string for a variety of purposes, and one of these nipples is conveniently used in the illustrated body of the invention for the purpose of connecting the perforating gun assembly to the completion.

The perforating gun assembly 7 comprises a lower part 8 incorporating the perforating guns 9 and a suitable firing head 10. The perforating guns 9 and firing head 10 may be of any convenient design and may, for example, be formed by a VANNGUN assembly and a pressure firing system as supplied by Vann Systems Division of Halliburton Company, of P.O. Box 4449, Houston, Texas U.S.A. It will be appreciated by those skilled in the art that the exact design of perforating gun and firing head is not critical to the present invention Located above the firing head 10 are optionally one or more tubing joints 11 which may be used to space the perforating guns 9 by the desired distance below the lower end of the completion string 6.

Located above the optional tubing joints 11 is a tubing release device 12 which may be operated either automatically or selectively to release the perforating guns 9, firing head 10 and optional tubing joints 11 from the remainder of the components of the perforating gun assembly.

The tubing release device 12 may be of any convenient type and may, for example, be a pressure actuated tubing release as supplied by Vann Systems. Located above the tubing release 12 are optionally an impact sub 13 for reducing shock transfer from the lower part of the perforating gun assembly to the upper part thereof and a debris/flow sub 14 for preventing debris interfering with operation of the firing head 10 and/or tubing release 12. Located above the optional components 13,14 is an upper connecting part 15 of the perforating gun assembly which is operative to releasably connect the entire perforating gun assembly to the nogo nipple 16 located at the lower end of the completion string 6.

Conveniently, the connecting part 15 may be constituted by a lock mandrel as supplied by Otis Engineering Corporation, a Halliburton Company. The lock mandrel incorporates a structure which may be releasably locked to the nogo nipple 16 and is capable of supporting the weight of the perforating gun assembly. In this respect, it will be appreciated that the perforating guns 9 may extend over several thousand feet and that the total weight of the perforating gun assembly may be several tens of thousands of pounds. Otis lock mandrels, as referred to above, may be supplied in a form capable of supporting weights up to 92000 pounds, and are accordingly well able to withstand the axial loading imposed by the weight of the perforating gun assembly.

In use, the perforating gun assembly and completion string are run into the well to the position illustrated. A suitable packer 17 is then set between the lower end of the completion string and the surrounding casing to isolate the zone of the well located below the packer from the annulus formed above the packer between the completion string and the casing 3. The completion fluid located within the casing 2 and in the interior of the completion string 6 may then be displaced, if desired, and replaced by a suitable medium, for example diesel oil or nitrogen which can be reduced in pressure to produce underbalance conditions within the casing 2 - i.e. to reduce the pressure within the casing 2 to a level below that in the surrounding formations.The perforating guns 7 are then fired to perforate the casing and any surrounding cement and penetrate the oil/gas bearing formations surrounding the well. As will be appreciated by those skilled in the art, under pressure conditions existing within the well will cause an immediate rush of formation fluid into the well thereby flushing debris from the perforations and improving the long term yield of the well.

After a suitable period of flow the completion string 6 is shut. If the tubing release 12 is of the automatic type the perforating gun 7, firing head 10, and tubing joints 11 will have fallen to the bottom of the well as soon as the guns have been fired. If the tubing release 12 is of the wireline operated type a wireline is run into the well to operate the tubing release and allow the components below it to fall to the bottom of the well. This configuration is illustrated in Figure 3. Next, a suitable wireline is run into the well to remove the connecting part 15, optional components 13 and 14, and the body of the tubing release 12. It will be appreciated that after the perforating guns 9 and optional tubing joints 11 have been released from the remainder of the perforating gun assembly the weight of the remaining components is relatively small, and these components can readily be hauled from the well on a wireline. These components may be re-used as appropriate. After the upper connecting part 15, optional components 13,14 and the body of the tubing release 12 have been pulled from the well the well is left in the configuration shown in Figure 4, i.e. there is unimpaired flow from the interior of the casing 2 to the interior of the completion string 6.

Whilst the invention has been described with reference to a particular embodiment of the invention, it will be appreciated that many changes may be made to the invention without departing from the scope thereof. In particular, the use of a lock mandrel of the type referred to in the description of the particular embodiment of the invention is not essential, and the invention may be operated utilising any releasable connection capable of securing the perforating gun assembly to the completion string or to the casing below the completion string and capable of withdrawal through the completion string after the perforating gun assembly has been fired. Further, although a particular perforating gun and firing head have been referred to in the description of the preferred embodiment, any convenient perforating gun and firing head may be used. In particular, the firing head may be of the type which is run into the perforating gun assembly after the perforating gun assembly has been located in the well, thereby adding an additional safety feature to the invention.

Claims

CLAIMS:

1. A perforating gun assembly for perforating an oil or gas well casing, the said assembly comprising: a lower, explosive carrying part; an upper, connecting part which in use of the gun is connected to a well completion string to allow the assembly to be run into the well on the completion string; and a coupling which is releasable to release the lower part from the upper part after the gun has been fired, whereupon the upper connecting part is recoverable through the completion string.

2. An assembly according to claim 1, wherein the upper connecting part is adapted for connection in use of the assembly to a nipple provided at the lower end of the completion string.

3. An assembly according to claim 1 or 2, comprising one or more tubing joints to space the perforating guns below the lower end of the completion string.

4. An assembly according to claim 1,2 or 3, further comprising one or more debris/flow subs, one or more impact subs and/or other components located above the coupling for eventual recovery from the well casing together with the upper connecting part.

5. An assembly according to any one of claims 1 to 4, wherein the said coupling is releasable automatically in response to firing of the guns.

6. An assembly according to any one of claims 1 to 4, wherein the coupling is operated by a wireline.

7. An assembly according to any preceding claim, wherein a wireline is provided for recovery of the upper connecting part after release of the lower part of the assembly.

8. A method of completing an oil or gas well having a first, lower length of casing to be perforated and a second, upper length of casing located above the first length of casing and having an inside diameter longer than that of the first length, the method comprising the steps of: running into the well a completion string having a perforating gun assembly connected thereto to locate the lower end of the completion string adjacent the upper end of the first length of casing; firing the perforating gun assembly to perforate the first length of casing; releasing a coupling provided in the said assembly to release that part of the assembly located below the coupling to fall to the bottom of the well; and removing the remainder of the assembly from the well through the completion string.

9. A perforating gun assembly substantially as herein described with reference to the accompanying drawings.

10. A method of completing an oil or gas well substantially as herein described.