GB2346634A

GB2346634A - Floatation Device

Info

Publication number: GB2346634A
Application number: GB0001735A
Authority: GB
Inventors: Mark Carmichael
Original assignee: Specialised Petroleum Services Ltd
Current assignee: Schlumberger UK Holdings Ltd
Priority date: 1999-01-27
Filing date: 2000-01-27
Publication date: 2000-08-16
Also published as: GB0001735D0; GB9901738D0

Abstract

The invention provides a floatation portion in a casing or liner string, the floatation portion being located between a float shoe at one end of the string and a cementing plug or wiping plug at the other end of the string. After placement of the string it is possible to pressure up within the drill pipe 23 (Fig 2) with sufficient force to shear pins 9. This causes pipe 5 to part company with the housing 3, thereby allowing circulation of fluid through the outlet 11 at the lower end of the housing 3.

Description

APPARATUS AND METHOD RELATING TO A WELL CASING AND LINER FLOATATION DEVICE This invention is in the field of well drilling and well completions and incorporates apparatus and method in this field. Most specifically, the present invention relates to an apparatus and method of setting liner or casing strings in horizontal wells during oil, gas or other well completions.

In recent years it has become more common to drill at least part of a well bore at an inclined angle from the vertical. Indeed, in certain wells the angle of inclination can approach or even exceed 90 degrees, ie horizontal. However, while technology is readily available for drilling well bores at such deviated angles, other difficulties can still be experienced in completion methods. One such difficulty, for example, relates to the setting of casing or liner strings in a deviated well bore, particularly where the angle of inclination is near to the horizontal.

It is understood by those skilled in the art as a well approaches horizontal, the weight of the casing or liner causes the casing/liner string to tend to sit on the lower side of the hole. Inevitably, drag forces are therefore induced when attempting to slide the casing or liner string further into the hole. In an attempt to mitigate this disadvantage, it is common to rotate the casing or liner string while pushing it further into the hole, but these same drag forces can lead to the requirement of the torsional forces acting on the casing or liner to the near or greater than the torsional strength limitation of the string itself. Alternatively, the torsion required to rotate the casing/liner string in view of the drag forces as the string rests on the bottom of the hole can be near to or greater than the available rotary torsion. Thus, it may be seen that such mitigation techniques are often associated with difficulty or risk and accordingly it is more common to attempt to merely slide the casing or liner string into the hole without rotation.

It will be appreciated therefore that it is advantageous to attempt to provide a means for mitigation drag forces acting on casing or liner strings while they are being run in a deviated hole. Clearly an object of an operator in the field is to ensure that a string does not become stuck in the hole. Moreover, even if this itself can be avoided, it would be advantageous if the forces needed to overcome the resisting drag or friction could be reduced.

It is known in the art to attempt to overcome increased drag in a deviated well by reducing the coefficient of friction using various lubrications available. However, while such lubricating methods along longer pipe strings to be run into a deviated hole, this technique has not been completely successful. Unacceptable drag forces may still be generated, notwithstanding lubrication and? forces can still be met where the string becomes stuck for reason other than the mere friction acting between the string and the side of the well bore.

In the past an alternative method has been employed in order to overcome the aforementioned problem. This method involves the use of floating the casing, that is to say rendering the pipe string"lighter"than the surrounding fluid or mud in the well. Generally this is achieved by plugging the end of the pipe string portion, and thereafter filling that portion with a low density fluid in order to provide buoyancy. It would be appreciated that circulation is not possible during the running of a plugged string into the well bore, at least in the region of the plugged portion. Typically, after the plugged string has reached its intended destination, the plugs are drilled out and the low density fluid is expelled into the well bore or pipe annulus. Cementing or other operations may then follow.

An object of the present invention is to provide an improved method and apparatus for placing and cementing a liner in an extended reach well using floatation techniques.

According to a first aspect of the invention there is provided apparatus for running a casing or liner into an extended reach well, the apparatus comprising...

According to a second aspect of the invention there is provided a method of placing casing or liner in an extended reach well bore comprising the steps of:...

In order to provide a better understanding of the present invention, a more detailed description will follow with various example embodiments and methodology making reference to the accompanying drawings, in which: 'Figure 1 shows a sectional elevation of a floatation device being run on a running tool in a well casing; * Figure 2 is a symmetric diagram on a small scale than that of Figure 1 showing apparatus in accordance with the invention being run in a well bore.

Referring firstly to Figure 1 there is depicted a floatation device, generally at 1, which is suitable for attachment to the lower end of a running tool 2. The floatation device 1 comprises of a housing 3, inner sleeve 4, and a blank plug 5.

In use, the inner sleeve 4 is fixed to the housing 3 with the aid of a first set of shear pins 6.

In the example embodiment shown the inner sleeve 4 and housing 3 are retained on the end of the running tool 2 with the aid of dogs 7.

The blank plug 5 is sealably connected to the housing 3 via the seals 8 and second set of shear pins 9.

Attached to the outer surface of the housing 3 are a plurality of wiper fins which also sealably gauge the casing 10 in which the floatation device 1 is run.

Figure 2 shows a simplified illustration of the apparatus described with reference to Figure 1 being run during a well completion in an extended reach well. The well 20 has a horizontal or near horizontal portion 21 and accordingly it is advantageous to provide a means for increasing the buoyancy of the liner 22 which is being run in the well. The liner 22 is run on the end of drill pipe 23 until such time as the top of the liner 22 is in close proximity to the bottom of the casing 24.

Typically the well bore 20 and drill pipe or running string 23 are filled with drilling mud 25.

Attached to the lower end of the drill pipe 23 is a floatation device 26 in accordance with the present invention. The floatation device 26 effectively closes off the lower end of the drill pipe 23 while also sealing its outer circumference against the inner surface of the liner 22.

At the lower or bottom end of the liner 22 is provided a float shoe 27 which prevents well fluid 25 from entering up into the liner 22. Thus, the combination of the float shoe 27 and floatation device 26 enables a buoyant cavity 28 to be maintained within a desired area of the liner 22. Typically, the buoyancy fluid in the cavity 28 is air.

It will be appreciated by persons skilled in the art that a float collar (not shown) could be used as an alternative means of sealing the lower end of the liner, thereby rendering the float shoe 7 unnecessary.

The relatively buoyant liner as shown in Figure 2 may be more easily run in the well 20 than would be the case if no buoyancy device was employed. In particular, the buoying up of the liner serves to reduces platent drag and consequent comprehensive loading on the liner string.

After placement of the liner the present invention provides a means for establishing circulation and enabling subsequent processes such as cementing. For example, it is possible to pressure up within the drill pipe 23 with sufficient force to shear the pins 9. The effect of this shearing action is to cause the pipe 5, as illustrated in Figure 1, to part company with the housing 3, thereby allowing circulation of fluid through the outlet 11 at the lower end of housing 3.

Further modifications and improvements may be incorporated with the planning and the scope of the invention herein intended.

Claims

Claims: 1. A downhole assembly comprising of floatation portion in a casing or liner string, wherein floatation portion is provided between a float shoe or collar at one end thereof and an insert at the other end thereof, wherein the insert is provided with a releasable member that blocks a circulation passage through the insert, characterised in that the insert is a cementing plug or wiping plug.