GB2190162A - Thermally insulated telescopic pipe coupling - Google Patents

Abstract

A thermally isolated expansion slip joint for a tubing string or pipe that carries high-temperature fluids or gases into a well bore or otherwise. The joint may be provided with casing slips and seals. The body is provided with a slidable mandrel having concentric inner and outer tubes forming an annular evacuated insulation space therebetween. The outer tube slides within and is sealed against a portion of the tubing string. The slip joint may be located in a down-hole packer having expandible slips to secure the packer to the well bore and an external seal to seal between the packer and the well bore. <IMAGE>

Description

SPECIFICATION Thermally insulated tubular sliding joint This invention pertains to thermally insulated tubular assemblies for the transport of fluids on the surface and down-hole in a well bore and to isolate the temperature of the fluid from components of the tubing string including accessory equipment within the well bore.

Thermally insulated tubular assemblies for transferring fluids at elevated temperatures in relative isolation from the surrounding environment are known. A typical tubular assembly is disclosed, for example, in U.S. Patent 4,538,834. Typically, these assemblies are utilized for the enhanced recovery of oil from an oil well by the injection of steam. The steam frequently has a temperature in the range of 650 F. It is desirable to isolate this high temperature from components of the steam-injecting tubular assembly or tubing string to prevent deterioration of the components and to reduce the temperature loss from the steam through the tubular assembly to the surrounding walls of the well bore or other components within the well bore.

The tubing string is frequently connected to the well bore casing far down in the well bore. Typically, a mechanism called a "packer" is employed to connect the downhole end of the tubing string to the well bore.

The packer is provided with seals that prevent the high-temperature, high-pressure steam from passing upwardly into the annulus between the tubing string and the well bore casing. The packer thus blocks the upward flow of high-pressure high-temperature fluid, forcing the fluid to flow out into the oil-producing formations, thus driving the oil to adjacent well bores for recovery.

The packer rigidly attaches the tubing string end to the well casing; therefore, provisions must be made for the accommodation of tubing longitudinal expansion (string elongation) which occurs due to changes in tubing string temperature. Expansion joints or slip joints are commonly used to accommodate this elongation, which may exceed 20 feet in some applications. Such slip joints may be built into the packer as an integral subassembly or may be provided as a completely separate unit at the bottom or top of the tubing string.

Insulated slip joints are also useful to above ground and below water gas or fluid distribution systems which carry gases or fluids at elevated temperatures. For surface distribution lines, a slip joint may be located anywhere in the line.

Heretofore, slip joints whether integral to the packer or a separate mechanism have created problems for steam injected oil recovery systems. The slip joint is provided with seals which at high temperatures deteriorate prematurely, requiring a costly repair since they may be located 5,000 feet or more below the surface of the top of the well bore.

The high temperature of the steam has created a second problem with the down-hole packer and slip joint in that much heat from the steam is conducted outwardly through the body of the unit to the well bore casing. This loss of heat is wasteful and also causes a phenomena known as "refluxing" to occur.

Refluxing occurs when the packer or slip joint unit surfaces become heated to the approximate temperature of the steam. Moisture that is trapped in the annulus between the tubing string and the casing becomes vaporized by the high temperature of the packer or slip joint surfaces, rising upwardly in the well bore. As the hot vapor contacts the colder surfaces of the casing higher up in the well bore, it then transfers much of its heat to the cooler surface and condenses. Gravity then allows the condensed liquid to flow back down in the well bore until it contacts the hot packer or slip joint unit again and repeats its vaporization cycle. Refluxing transfers an enormous amount of heat energy to the casing by increasing the overall heat transfer coefficient between the tubing string and the well bore.

All of these heat losses reduce the efficiency of the steam-injecting process.

Some attempts have been made to improve the seal deterioration problem by the selection of different sealing materials which are more compatible with the high temperatures. However, these attempts have not been totally successful. No solution for the refluxing problem has been successfully produced.

Regardless of its location, the slip joint should also be insulated to prevent the heat loss described above.

It is an object of this invention to provide an improved thermally insulted slip joint within a packer for use in insulated tubing or pipe systems.

It is another object of this invention to provide a sliding joint having concentric inner and outer tubes sealed to form an annular insulating chamber therebetween in a string or distribution system for carrying fluids at elevated temperatures.

One object of the invention is best obtained by providing a slidable mandrel for a packer in which the slidable mandrel includes an outer tube, preferably having an outer surface polished to slide past an internal seal of the packer, an inner tube concentric with the outer tube and spaced therefrom to define an annular space therebetween, the annular space being sealed and preferably evacuated to thermally isolate the heat from the high-temperature steam within the inner tube from the surfaces of the outer tube. The mandrel extends through the entire length of the packer so as to thermally isolate also the casing slips and other components of the packer as well as the internal and external seals of the packer.

The sliding mandrel can also be used alone and spaced from the packer as a separate slip joint or used above ground or submerged in water in other heated fluid distribution systems.

Using such a thermal isolation mandrel, heat flow to the external surfaces of the tubing is reduced, thus reducing the reflux action in the annulus between the tubing string and the well bore. In addition, the heat transfer to the components of the packer or separate slip joint is reduced, extending the life of the material of those components.

Figure 1 shows a schematic of a typical well bore packer employing a thermal isolation slip joint embodying the principles of the invention.

Fig. 1 shows a packer having a body 12.

The body includes a set of casing slips 14 that are radially expandable by conventional means to engage and lock the body against the casing of the well bore.

The body also includes an external seal 16 for sealing against the upward movement of hot fluids between the body and the casing.

The body includes an internal seal 18 which seals between a slidable mandrel 20 and the body.

The mandrel 20 is provided with a coupling 22 that connects the mandrel to up-hole steam injection tubing string 24 and a lower coupling 26 that connects the mandrel to a down-hole section of the tubing string 28. A typical packer thus far described is well known and is available through such companies as Hughes Oil Tool Company, having a location at Huntsville, Texas.

It is the unique feature of this invention that the slidable mandrel 20 includes an inner tube 32 concentrically located and spaced from an outer tube 34 to provide an annular insulating space 36 therebetween. The ends of the tubes are sealed by frustoconical structures 40 and 42, respectively. Preferably, the annular space 36 is evacuated and may be filled with an insulation material such as described in U.S. Patent 4,538,834. Preferably, the annular space will also include a getter material which will absorb gases migrating into the annular space.

The annular space 36 serves as a thermal barrier to impede transfer of heat from the inner tube 32, which is carrying the high-temperature steam or other fluids or gases, to the outer tube 34, which is in contact with the components of the body of the packer or slip joint. The thermal isolation also reduces the temperature exposure of the internal and external seals 16 and 18 and thus extends their useful life. The thermal isolation also reduces the temperature on the surfaces of the body, thus reducing the heat available for causing reflux in the annular space between the tubing string and the well bore casing.

The outer tube 34 of the slidable mandrel is preferably polished to form a better sealing surface with the seal 18 and also to allow the outer tube to slide relative to the seal due to the elongation of the tubing string when it becomes heated. For the integrated packer embodiment, the casing slips lock the packer relative to the well bore, the tubing string, when it expands upon being heated by the steam, can elongate as much as 20 feet in a typical well bore. This elongation of the tubing string is accommodated by the mandrel, as it will slide downwardly in the packer into the position shown in Fig. 1. As the tubing string cools when the injection of steam is discontinued, the mandrel will slide upwardly from the position shown in Fig. 1 to allow contraction of the length of the string.

For a surface line embodiment, ground anchors and external line attachments normally lock the tubing relative to the earth at locations remote to the slip joint; therefore, when the tubing expands upon being heated by the hot fluids, it can elongate several feet. This elongation of the tubing string is accommodated also by the mandrel.

While the preferred embodiment of the invention has been illustrated and described, it should be understood that variations will be apparent to one skilled in the art without departing from the principles herein. Accordingly, the invention is not to be limited to the specific form illustrated in the drawing.

Claims (4)

1. A thermally isolated well bore packer having an integral slip joint, comprising: an outer body having radially expandable casing slips for engaging and locking the body to the inside of a bore at a location in the bore below the top of the bore; external sealing means for sealing between the body and the well bore; an elongated sliding mandrel concentrically located within the body and having upper and lower ends; internal sealing means for sealing between the mandrel and the body; lower coupling means for joining the lower end of the mandrel to the insulated tubing string capable of carrying high-temperature fluids through the well bore below the packer; and upper coupling means for joining the upper end of the mandrel to the insulated tubing string above the packer; said mandrel including an inner tube and an outer tube concentric with and radially spaced from said inner tube to form an annular space therebetween, and means within the space to enhance the thermal isolation of the outer tube from the inner tube, whereby the heat from the tubing string is thermally isolated from the seals of the body and the casing slips.

2. A thermally isolated down-hole wellbore slip joint for a tubing string carrying high temperature fluid, comprising: a slidable mandrel having concentrically spaced inner and outer tubes defining an annular space therebetween, said annular space being thermally insulated to thermally isolate the outer tube from the inner tube; means for connecting one end of the mandrel to a first portion of the tubing string; means for slidably connecting the other end of the mandrel to a second opposite portion of the tubing string that is separated from the first portion; means for sealing between the second portion of the tubing string and the outer tube of the mandrel; said mandrel being slidable along said sealing means to maintain a seal while tubing string thermally elongates.

3. The slip joint of claim 2, said second portion of said tubing string including a packing, said packing including a set of releasible slips for securing the packing against axial movement in said well bore, and external sealing means for sealing between the well bore and the packing.

4. A thermally insulated slip joint for an elongated pipe for carrying fluids or gases at elevated temperature, comprising: a slidable mandrel having concentrically spaced inner and outer tubes defining an annular space therebetween, said annular spacing being thermally insulated to thermally isolate the outer tube from the inner tube; means for connecting one end of the mandrel to a first portion of the pipe; means for slidably connecting the other end of the mandrel to a second opposite portion of the pipe that is separated from the first portion; and means for sealing between the second portion of the pipe and the outer tube of the mandrel; said mandrel being slidable along said sealing means to maintain a seal while said pipe thermally elongates.