Patent Description:
In a process for placing cement in the annulus of a well, normally the annulus between casing and wellbore (e.g. in a perf, wash cement well abandonment operation), there are three distinct steps:.

Following the wash, the setting of plugging material (cement) behind the casing is the next step in the process. There are at least <NUM> alternative techniques for displacing the annulus content (wash fluid or "spacer fluid") to cement but the one with which this application is concerned involves a cementing head with nozzles which create "jets" of cement, or pulses of energy in cement, which force cement through apertures in the casing and displace the existing fluid in the annulus behind/outside the casing, thereby creating a cement bond in the outer annulus.

This process will be referred to a "cementing" and the plugging material as "cement" but it is to be understood that it is not necessarily limited to the use of cement and any suitable plugging material could be employed; the terms "cement" and "cementing" should be understood accordingly.

The jet technique for cementing is, in the experience of the applicant, the most effective technique. Nonetheless, jet cementing procedures have not always been successful and the applicant has done a considerable amount of development to investigate through physical experiments, field work and CFD analysis what factors and parameters, including pressures, flow rates, etc., affect the success of a downhole cementing operation. Some of this work is described in co-pending patent application number <CIT>. The contents of <CIT>
<CIT> discloses an apparatus comprising: a setting section surrounded by a first sleeve, said first sleeve being expandable and impermeable to a material; an inflating means for inflating said first sleeve, said inflating means ensuring that the first sleeve can be in contact with a first zone of a tube which is permeable to said material, so that said first zone of said tube becomes impermeable to said material; and further comprising a second sleeve portion partially permeable to said material on a second zone and attached to said first sleeve so that: a path is provided between said first sleeve and said second sleeve portion and so that, when the first sleeve is inflated the second zone can be in contact with said tube allowing the material to flow in the path and through the second zone. Also disclosed is the associated method for treatment of a near zone and/or a far zone of a well with the disclosed apparatus. <CIT> discloses a method and to a tool to consolidate a wellbore by displacing conventional cement slurry or any other settable fluid, without any permanent casing. A bladder is inflated inside the bore to act as a mold and to form an annulus that can be filled by cement slurry or any other settable fluid. When the cement or the resin is set, the form is retrieved by straight pull; leaving a cement or resin sheath to support the formation without requiring any re-drilling. The sheath can be perforated if necessary (in the producing zone). Applications include without limitations temporary cementation of mono-diameter wells, through-tubing repair of an open hole, or cementation of a slotted liner in water, oil or gas wells
<CIT> discloses a method of conducting a perf wash cement ("P/W/C") abandonment job in an offshore oil or gas well annulus, in particular the washing or cementing operation using a rotating head with nozzles dispensing wash fluid or cement at pressure. Certain values of parameters of a washing or cementing job have been found surprisingly to affect the quality of the job, or the degree to which they affect the quality of the job has been unexpected. These include including rotation rate of the tool, the direction of translational movement of the tool, and the volume flow rate and pressure per nozzle of cement or wash fluid (and hence nozzle size).

The physical design of the cementing tool has been the focus of more recent efforts by the applicant, culminating in the filing of two patent applications on cementing tool geometry, of which this is one. The contemporaneously filed patent application entitled Behind Casing Wash and Cement in the name of the same applicant and with the same inventors.

The inventors believe, based on actual perf, wash, cement jobs in the North Sea and also on extensive computational fluid dynamics (CFD) work, that one important factor in the success of the cementing operation is the diameter of the cementing tool in relation to the internal diameter ("drift diameter") of the casing.

The inventors have found through both practical experience and through CFD modelling work that reducing the gap between the cementing tool and the annulus dramatically influences the energy of the flow behind the casing and the ability of the cement effectively to displace the existing fluid (wash fluid, normally drilling mud) in the outer annulus. Displacement of the fluid is important because, if the cement mixes substantially with wash fluid then an effective cement bond may not be achieved.

In general, when performing downhole operations, it is desirable to minimize the outer diameter of tools in order to reduce the chances of debris, such as steel burr or swarf from a perforation operation, becoming lodged in the gap between the tool and casing. This can result in the tool becoming jammed in the casing (so called "stuck pipe") and can be expensive to remedy.

There is therefore a conflict between making the outer diameter of cementing tool as large as possible, whilst keeping the risk of stuck pipe to an acceptable level.

A potential problem with using a relatively large diameter cementing tool arises when the casing is deformed at some point above the region to be cemented, thereby creating in effect a smaller pathway for the tool. Cause for such a restriction can be geological events like subsidence or effective horizontal stress larger than the collapse capacity of the casing. There may be other reasons why it is required to be able to pass the tool through a narrower section of tubing or casing than the section to be treated by the tool (typically referred to as a patch), for example if the tool is to be passed through a section of concentric smaller diameter tubing above a larger diameter region for cementing (typically established by window milling).

The cementing tool is, in essence, a hollow cylinder with apertures in it which function as nozzles for creating outwardly directed jets of cement when pressurized cement is passed into the tool. The tool is run on drill string and is rotated as well as being moved axially such that the jets of cement create pulses of pressure in the casing which are transmitted through perforations in the casing and energize the fluid in the outer annulus, thereby displacing it to cement.

The inventors have conceived an improved design of cementing tool which has a variable outer diameter, such that it can be passed down the casing in a narrow configuration and, when the time comes for cement to be injected, its diameter can be increased. In this way, the tool may be passed through restrictions in the casing etc, and if stuck pipe should occur during a cementing operation, the diameter of the tool may be reduced to free the tool.

The cement tool may have an inner core of steel which contains its activation and deactivation functions. After activation the design cementing pressure drop (normally <NUM> Psi/<NUM>. 24MPa) will energize an outer sleeve and expand the overall OD to a given preset maximum. The sleeve may be constructed by steel reinforced elastomers similar to a BOP annular element. As the cement operation is concluded the differential pressure over the cement tool will be zero and the outer diameter reduced again.

According to the invention a tool and method, along with optional features, are provided as defined in the appended claims.

In this application the term drift diameter refers to the maximum diameter of object which can pass freely down a certain specification of casing. Whilst the internal diameter of the casing may vary slightly, the drift diameter provides a precise value for a given standard casing size. For example the typical drift diameter for <NUM><NUM>/<NUM> inch (<NUM>) casing is <NUM> inches (<NUM>).

In this application, the word "perf" or "perforation" shall, unless the context requires otherwise, mean any aperture in a casing through which cement or wash fluid may pass and is not limited to apertures formed by an explosive charge, e.g. from a so- called "perf gun".

In connection with all aspects of the invention and their respective optional features, the casing diameter may be 10¾ inch (<NUM>), <NUM><NUM>/<NUM> inch (<NUM>) or 7¾ inch (<NUM>) diameter, optionally 10¾ inch (<NUM>) or <NUM><NUM>/<NUM> inch (<NUM>) diameter or in the range 5½" to <NUM>" (<NUM> to <NUM>).

Referring firstly to <FIG>, a cementing tool <NUM> is shown in highly schematic form. The aspect ratio of the real tool would be considerably longer, but it is illustrated in this way for clarity. The tool <NUM> comprises in essence a hollow cylindrical shape with two apertures <NUM> in the cylindrical wall <NUM>. These apertures <NUM> are lined with a wear resistant material to avoid them being worn away when cement is jetted through them - this is not shown in the drawing but is in itself conventional.

The tool <NUM> is attached to drill string <NUM> on which it would be run into a well. Beneath the tool <NUM> (distally with respect to the surface) is a valve <NUM> which may be operated by dropping a ball down the drill pipe. The casing <NUM> of the well is shown. The region of casing <NUM> shown in <FIG> has been prepared for abandonment by being perforated, and the perforations are shown at <NUM>. Behind or outside the casing is an annulus indicated generally at <NUM>; the outer boundary of the annulus would be the rock formation, though this is omitted in <FIG> for clarity. As is conventional and would be understood by the person of ordinary skill in this art, the purpose of the cementing tool is to jet cement into the annular region between the cement tool and the casing and then into the outer annulus <NUM> through the perforations <NUM> in the casing <NUM>.

<FIG> shows a relatively large distance between the casing <NUM> and the cylindrical wall <NUM> of the tool <NUM>. In this example the outer diameter of the tool is <NUM> inches (<NUM>) and the inner diameter or, more strictly, the drift diameter of the casing is <NUM> inches (<NUM>). At some point above the tool <NUM> (proximally with respect to the surface) there may be deformed regions of the casing <NUM>, or other obstructions in the casing <NUM>, which effectively reduce the drift and it is desirable to be able to run the cementing tool <NUM> past these obstructions. In some cases, there may be narrower concentric tubing or casing above (proximally of) the region to be cemented, through which the cementing tool must be passed.

Turning now to <FIG>, this shows the same casing and tool as <FIG>, but with the tool <NUM> in an expanded state. The diameter of the cylindrical wall <NUM> has been increased so as to reduce the size of the annular region between the tool and the casing. It has been found that this increases the energy of cement pulses in the annulus between the tool and casing and thereby increases the energy of cement pulses in the outer annulus <NUM>. This results in the cement more efficiently displacing existing fluid in the outer annulus <NUM>, resulting in better quality cement and cement bond to casing and formation.

Before delivering cement, the valve <NUM> distal of the tool is closed; cement being pumped down the drill string into the tool <NUM> increases the pressure within the tool, which has the effect of increasing the diameter of the tool as well as jetting the cement through the nozzles <NUM>. The expandable structure of the cylindrical wall of the tool is described below. Annular shoulders <NUM> of elastomeric material above and below the expandable wall <NUM> connect it to the drill string <NUM>, allowing for expansion of the cylindrical wall <NUM>.

Referring now to <FIG>, a transverse cross section of the cement tool <NUM> is shown, in its un-expanded state. The casing is not shown in this view. The cylindrical wall <NUM> of the tool <NUM> comprises steel elements <NUM> alternating with elastomeric elements <NUM>. The steel and elastomer elements <NUM>, <NUM> are securely fastened together by well-known vulcanization techniques. In <FIG>, the elastomeric elements <NUM> are in a relaxed state. Steel wires <NUM> connect the steel elements <NUM> across the elastomeric elements <NUM>. In <FIG>, the steel wires <NUM> are slack. The nozzles <NUM> can be seen to be formed in two of the steel elements <NUM>.

Turning now to <FIG>, which is similar in most respects to <FIG>, the tool <NUM> is shown in an expanded state. The elastomeric elements <NUM> are stretched such that the overall diameter of the tool is increased. The wires <NUM> extending across the elastomeric regions <NUM> limit the degree of expansion and thereby allow the tool to be designed to expand to a predetermined diameter when pressurized by cement. The circumferential tension to stretch the elastomeric elements <NUM> is provided by the pressurized cement being delivered through the tool and creating a pressure difference between the interior and exterior of the cylindrical wall <NUM>.

It is believed to be important to determine the maximum outer diameter with reasonable accuracy. As detailed in the contemporaneous filing to this one, entitled "behind casing wash and cement", the difference in size between casing drift diameter and cementing tool outer diameter can be significant. For the non-expandable tool described in that patent application, the range for this diameter difference is considered to be from <NUM> to <NUM> inches (<NUM> to <NUM>). However, with an expandable tool, the risk of stuck pipe may be mitigated by the ability to reduce the tool diameter by reducing pressure, so a range of <NUM> to <NUM> inches (<NUM> to <NUM>) of diameter difference may be preferred, with an optional range of perhaps <NUM> to <NUM> inches (<NUM> to <NUM>).

The tool may be used in any size of casing but normally <NUM><NUM>/<NUM> inch (<NUM>), 7¾ inch (<NUM>) or 10¾ inch (<NUM>) outer diameter casings are used.

It should be understood that these diagrams are highly simplified. Steel and elastomer expandable downhole tools are available for different purposes, e.g. forming selectively activatable packing elements, and could be adapted for a downhole cementing tool.

In a modification, the elastomeric material may extend around the whole circumference, with steel members embedded in in a similar manner to a car tyre. Nozzle apertures would then be formed through both steel and elastomer. Other systems for expanding the tool also may be possible, such as a hydraulically actuated mechanism allowing the external diameter to be adjusted selectively from the surface in a continuous manner, rather than having two specific diameters and no other possible diameters.

Some or all of the outer profile of the tool may be of variable diameter. Ideally the region of the tool in which the nozzles are located has variable diameter. The remainder of the length of the tool may also have variable diameter, in particular the region above or proximal of the nozzles. CFD and practical work using designs of fixed diameter cementing tools with substantially the same diameter over their full length have shown that maximizing overall tool diameter is very effective. It is speculated that the region of tool above or proximal of the nozzles may form a choke, boosting the pressure and energy of the flow in the annulus between tool and casing. An expandable region of the tool above (proximally of) the cement nozzles may be provided. This expandable region could have a diameter slightly smaller than the drift diameter of the casing when deployed, whilst the region of the tool in which nozzles are located could have a fixed smaller diameter.

In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as additional embodiments of the present invention.

Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.

Claim 1:
A cementing tool (<NUM>) for use in oil and gas well decommissioning operations, wherein the well has a casing (<NUM>) of specified drift diameter, the tool (<NUM>) comprising:
a generally cylindrical body (<NUM>) with an interior void; and
at least one nozzle aperture(<NUM>) formed in the body (<NUM>) for passing cement from the interior void to an exterior of the body (<NUM>);
wherein the body (<NUM>), or a portion of it, has a selectively adjustable outer diameter;
characterised in that the body (<NUM>) or portion is adjustable between a first outer diameter and a second, larger, outer diameter, wherein the second diameter is <NUM> to <NUM> inches (<NUM> to <NUM>) smaller than the drift diameter of the casing (<NUM>).