Patent Description:
Sufficient pressure isolation between casing strings has been an oil industry problem since its inception. Cement is used to seal the annulus between concentric casing strings, but cement fundamentally shrinks as it cures, resulting in micro channels and micro-annuli in the cement. The micro channels and micro-annuli can permit gas to flow between the casing strings. Sometimes the gas can flow for thousands of feet between the tubulars and can be measured at the surface wellhead. Further, downhole media can flow from one zone of the well to another via the micro channels (casing-to-casing leak path). Such problems occur more frequently in gas wells because of higher pressures and lower media viscosity. Moreover, casing-to-casing annular (CCA) pressure at the surface can be an indicator of much more serious conditions, such as a downhole circulation or a blowout in the most serious instances.

In recent years, new cements have been created with the aim of having less shrinkage during curing. These newer cement chemistries are generally composites with other materials such that the net behavior of the cement actually expands slightly during curing. These improvements in cement chemistries have resulted in better performance for sealing between casing strings (CCA sealing), but they have not solved the problem entirely. In particular, micro channels can still develop in the casing after the curing of the cement, which results in CCA leaks that are not detected until long after the casing is cemented. Currently, retrofit methods for repair of these CCA leaks in gas wells have been difficult to implement and are largely ineffective.

<CIT> discloses a downhole tool for conveyance within a tubular secured in a wellbore extending into a subterranean formation. The downhole tool includes a sealing material and a laser apparatus operable to cut a slot in the tubular. The downhole tool is operable to provide melted sealing material within the slot.

<CIT> discloses a method for forming a downhole plug within an abandoned well casing for preventing the flow of gas through the plug and reaching the surface, particularly for CO<NUM> sequestration projects. A milling tool mills out a longitudinal section of the perimeter of the well casing and surrounding cement and detritus to expose the well bore. A heater containing solid metallic alloy is lowered into the casing and the alloy is melted so that it fills the milled out area and flows into the face of the well bore.

<CIT> discloses a method of sealing a region of a sand screen of an Open Hole Gravel Pack without the need to perforate the sand screen and a tool for use in such. The tool being a eutectic/ bismuth based alloy well plugging/sealing tool having a tubular heater body with an internal cavity capable of receiving a chemical heat source.

<CIT> discloses a sealing tool for conveyance within a tubular member within a wellbore extending into a subterranean formation. The sealing tool includes a mandrel and a eutectic sealing material disposed about the mandrel.

<CIT> discloses an expandable downhole tool having a tubular body with eutectic alloy located on an outer surface thereof.

<CIT> discloses a thermally deformable annular packer having a ring section set within the annulus between tubing and casing, wherein the ring section includes a chamber acting to release and relieve pressure which may increase as the thermal packer is set.

By way of overview and introduction, the present application discloses methods and systems for repairing a leak in a casing of a well. In one or more embodiments, the system can include an underreamer, a cleaning tool (e.g., hydrojet), a tubular (e.g., scab liner), an annular packer tool, and a heater. In accordance with one or more embodiments of the method, a leak such as a casing-to-casing annular (CCA) leak is located in a casing of the well. The casing can include an inner casing string ("inner casing") and an outer casing string ("outer casing") with cement separating the inner and outer casings.

After the location of the leak is determined, an underreamer is used to remove a portion of the inner casing and sometimes the cement at the location of the leak, thereby creating an annular-shaped opening in the inner casing. This annular-shaped opening is then cleaned to remove any debris. It will be appreciated that the formed opening can be a concentric annular, partially eccentric annular, or fully eccentric annular in shape, for example.

A scab liner is inserted into the well and an annular packer tool is attached to the scab liner. The annular packer tool includes one or more segments of heat-deforming material (e.g., eutectic metal) on its outer surface. The scab liner and the annular packer tool are inserted into the well at a location adjacent to the created annular-shaped opening. A heater (e.g., thermite heater) is inserted into the well at a location adjacent to the annular packer tool, and then initiated. Initiation of the heater heats the location adjacent to the annular packer tool such that the segments of heat-deforming material of the annular packer tool melt. The melted heat-deforming material then flows into the annular-shaped opening and solidifies after cooling. Solidification of the heat-deforming material in the annular-shaped opening plugs the annular-shaped opening, thereby repairing (sealing) the previously identified leak in the casing.

These and other aspects of the present systems and methods are described in further detail below with reference to the accompanied drawing figures, in which one or more illustrated embodiments and/or arrangements of the systems and methods are shown. The systems and methods of the present application are not limited in any way to the illustrated embodiment and/or arrangement. It should be understood that the systems and methods as shown in the accompanying figures are merely exemplary of the systems and methods of the present application, which can be embodied in various forms as appreciated by one skilled in the art. Therefore, it is to be understood that any structural and functional details disclosed herein are not to be interpreted as limiting the present systems and methods, but rather are provided as a representative embodiment and/or arrangement for teaching one skilled in the art one or more ways to implement the present systems and methods.

<FIG> is a cross-section of a portion of a well <NUM> that has a leak in a casing <NUM> after the casing is cemented in accordance with one or more embodiments. The casing <NUM> comprises an inner casing <NUM> and an outer casing <NUM>, which surrounds the inner casing <NUM>. The inner casing <NUM> and outer casing <NUM> are separated by a cement sheath <NUM>. In one or more embodiments, the outer casing <NUM> can be a <NUM> and <NUM>/8ths inch (<NUM>-<NUM>/<NUM>") (<NUM>) outer diameter (OD) casing and the inner casing can be a <NUM> and <NUM>/8ths inch (<NUM>-<NUM>/<NUM>") (<NUM>) OD casing. However, it should be understood that the sizes of the inner casing <NUM> and the outer casing can vary, and thus are not limited to the above embodiment.

Leaks can develop between the inner casing <NUM> and the outer casing <NUM> over time. The root cause of these leaks is often a lack of sufficient sealing of the cement between the inner casing <NUM> and outer casing <NUM>. This lack of sufficient sealing between the casing strings can occur for one or more of the following reasons: <NUM>) cement shrinkage during curing; <NUM>) poor casing centralization that yields non-uniform cement sealing stress; <NUM>) cement leakage, particularly in horizontal wells as an annulus develops in the upper part of the casing seal; <NUM>) development of micro-cracks due to excessive mechanical or thermal stresses that can cause the cement to fail (crack) and develop a leak; <NUM>) mud channeling, particularly in deviated wells with poor centralization, which to leave a mud channel on a thin side of the casing which is not displaced with cement, resulting in future leakage; <NUM>) gas channeling; and (<NUM>) micro-annuli. Gas channeling can occur as a result of cement slurry hardening as it goes through the gelation state, and the resulting shrinkage of the cement causes reduction in hydrostatic pressure. This shrinkage and reduction in hydrostatic pressure allows an influx of gas from permeable formations to form channels for gas to migrate between formation zones or between a zone and the surface of the well. Micro-annuli are concentric gaps created between tubular and cement due to high pressures such as fracturing causing the casing to elastically deform, excessive compression of the cement, then opening of an annulus as the pressure is reduced.

Gas wells are especially susceptible to leaks in the casing <NUM> (e.g., casing-to-casing annular [CCA] leaks) and are equally difficult to repair once they occur. The present systems and methods allow for the effective repair of casing leaks, particularly in a well that has already been cemented using conventional techniques.

<FIG> a cross-section of a portion of a well during and after repair of the leak via the systems and methods of the present application in accordance with one or more embodiments. As shown in <FIG>, a CCA leak <NUM> can develop in the cement sheath <NUM> of the casing <NUM>. In other words, a CCA leak <NUM> develops in the cement sheath <NUM> because the cement is not sealing between the inner casing <NUM> and the outer casing <NUM>. In one or more embodiments, the method for repairing the leak begins by determining the location of the leak. There are several ways to determine the location of the CCA leak <NUM> in the casing <NUM>. For example, in one or more embodiments, the CCA leak <NUM> can be detected by identifying the inflow and outflow positions of the leak using one or more acoustic logging tools. The acoustic logging tools can be used in the well while the well is shut-in, for example. In one or more embodiments, the acoustic logging tools are used to listen for fluid and glass flows behind the casing. It will be appreciated that any number of suitable detection techniques can be used.

Once the location of the CCA leak <NUM> is determined, one or more portions of the inner casing <NUM> near the location of the leak <NUM> is removed so as to expose the leak. In one or more embodiments, at least one portion of the inner casing <NUM> that is removed is above the location of the leak <NUM> (i.e., above the inflow point).

In one or more embodiments, the one or more portions the inner casing <NUM> is removed using an underreamer to remove the selected portion of the inner casing <NUM>. In one or more embodiments, in addition to removing the portion of the inner casing <NUM>, an adjacent portion of the cement sheath <NUM> is also removed. For instance, the cement sheath <NUM> adjacent to the removed inner casing portion can also be removed, thereby revealing the outer casing <NUM> (see <FIG>). The removal of each portion of the inner casing <NUM> and, in some embodiments, an adjacent portion of the cement sheath <NUM>, results in an annular-shaped opening <NUM> or "donut" being formed. In one or more embodiments of the present method, the step of removing the at least one portion of the inner casing <NUM> includes determining a length of the inner casing <NUM> to remove based on the locations of inflow and outflow positions of the leak in the casing. For example, in an embodiment in which there is a <NUM>-<NUM>/<NUM>" (<NUM>) outer casing and a <NUM>-<NUM>/<NUM>" (<NUM>) inner casing, the annular-shaped opening <NUM> can be approximately <NUM> feet (<NUM>) in length. However, the size of the one or more formed annular-shaped openings <NUM> can vary depending on the distance between the inflow and outflow positions of the leak, as well as the size of inner and outer casings.

After the at least one annular-shaped opening <NUM> in the inner casing <NUM> is created (e.g., via underreaming), the at least one annular-shaped opening <NUM> is cleaned. In one or more embodiments, the annular-shaped opening <NUM> can be cleaned via a cleaning tool, such as a hydro-jetting tool ("hydrojet"). In one or more embodiments, the cleaning tool can be a laser tool, a sonic/acoustic tool, or a vibration tool, for example. Cleaning of the annular-shaped opening <NUM> cleans the debris and any remnants of the cement sheaths (excess cement) from the annular-shaped opening <NUM>.

After the annular-shaped opening <NUM> is cleaned, a tubular <NUM> (e.g., scab liner) is inserted to a location adjacent to the annular-shaped opening <NUM>. As shown and described in exemplary embodiments discussed below, the tubular <NUM> is a scab liner. In one or more embodiments, the scab liner is a <NUM>" (<NUM>) scab liner. However, in other embodiments, the diameter of the scab liner can vary depending on the size of the well and the size casing. The scab liner <NUM> is inserted along with an annular packer tool <NUM> that is attached to the scab liner along the outer surface of the scab liner <NUM>. In other words, the annular packer tool <NUM> is disposed such that it surrounds the scab liner <NUM> and the annular packer tool <NUM> is disposed between the scab liner <NUM> and the inner casing <NUM>. Since the scab liner <NUM> has a smaller inner diameter than the inner casing <NUM>, the location of the scab liner <NUM> represents a local constricted area.

In one or more embodiments, the annular packer tool <NUM> can be a modified version of the TDAP tool as produced by BiSN Tec Ltd, except that that the annular packer tool <NUM> of the present application does not include springs, annular seals, or axial hole for cementing as provided in TDAP tool of BiSN Tec Ltd. A diagram of an exemplary annular packer tool <NUM> attached to the scab liner <NUM> is shown at <FIG>. The annular packer tool <NUM> is cylindrical in shape and is sized to run on the outside of the scab liner <NUM>, which is also cylindrical. The annular packer tool <NUM> thus surrounds the scab liner <NUM> and can be positioned at the desired select position of the scab liner <NUM> for placement in the desired repair location relative to the leak which is located radially outward from the annular packer tool <NUM>.

The annular packer tool <NUM> has previously been utilized in methods as a proactive measure for preventing leaking during the construction phase of the well. For example, in previous methods, the annular packer tool is run with a casing string during the well construction phase. The annular packer tool <NUM> is used in a completely different manner and matter in the systems and methods of the present application as compared to its prior uses, and particularly for repairing existing leak in the casing of a well.

Specifically, in one of more embodiments of the present application as shown in <FIG>, the annular packer tool <NUM> comprises one or more segments <NUM> (cylinders) of heat-deforming material on its outer surface. In one or more embodiments, the heat-deforming material <NUM> comprises a low-melting point metal, such as a eutectic metal. For example, the eutectic metal can comprise bismuth (Bi) and tin (Sn) (e.g., a bismuth-tin alloy). While the exemplary embodiments discussed herein often refer to the heat-deforming material <NUM> as eutectic metal segments, in other embodiments, the heat-deforming material <NUM> can comprise one or more other low-melting point materials or metals that are not considered eutectic metals.

In at least one embodiment, the annular packer tool <NUM> can also include other portions of one or more metals that have a higher melting point than the activation temperature of the heat-deforming material (e.g., eutectic metal) segments <NUM>. For example, in one or more embodiments, the annular packer tool <NUM> can comprise centralizers <NUM> (e.g., carbon steel guides) that have the same or larger diameter as the eutectic metal segments <NUM> are configured to fix the ends of the annular packer tool <NUM> to the scab liner <NUM> such that the annular packer tool <NUM> remains on the scab liner <NUM>. The annular packer <NUM> is inserted on the scab liner <NUM> to a location that is adjacent to the annular-shaped opening <NUM>.

As the scab liner <NUM> and the annular packer tool <NUM> are inserted in the well at a location adjacent to the annular-shaped opening <NUM>, the scab liner <NUM> is secured to a portion of the inner casing <NUM>. In at least one embodiment, the well can include a production liner <NUM> (e.g., <NUM>" (<NUM>) production liner) and the scab liner <NUM> can be tied back to the production liner <NUM> (e.g., via a tie or other fixture). In one or more embodiments, to attach the scab liner <NUM> and the production liner <NUM>, an upper part of the production liner <NUM> can have a polished bore receptacle (PBR) and the bottom of the scab liner <NUM> can have a seal assembly. As the scab liner <NUM> is lowered, the seal assembly enters and seals in the PBR. In at least one embodiment, the scab liner can alternatively be tied back to a wellhead of the well. In one or more embodiments, the scab liner can be held at a location adjacent to the annular-shaped opening <NUM> with a running tool.

Once the scab liner <NUM> with the attached annular packer tool <NUM> is located adjacent to the annular-shaped opening <NUM>, a heater <NUM> is inserted into the well <NUM> inside the scab liner <NUM> and thus can be positioned inside the annular packer tool <NUM>. The heater <NUM> is lowered in the well <NUM> to a predetermined location adjacent to the annular packer tool <NUM>. The heater <NUM> can be, for example, an electric heater, an inductive heater, or a chemical heater (e.g., thermite heater).

In one or more embodiments, the heater <NUM> is lowered into the well <NUM> via an electric line <NUM>. In such an embodiment, the heater <NUM> is attached to the electric line <NUM> and both are then selectively lowered into the well to a predetermined location adjacent to the annular packer tool <NUM> with the scab liner <NUM> being between the heater <NUM> and the annular packer tool <NUM>. Once the heater <NUM> has been lowered to the location adjacent to the annular packer tool <NUM>, the heater <NUM> is initiated, thereby heating the location adjacent to the annular packer tool <NUM>. The heat from the heater <NUM> thus passes through the scab liner <NUM> to the annular packer tool <NUM> that surrounds the scab liner <NUM>.

The initiated heater <NUM> is configured to heat the location adjacent to the annular packer tool <NUM> to a temperature above an activation temperature of the one or more segments of heat-deforming material <NUM> (without adversely impacting the scab liner <NUM>). As such, the increased temperature causes the heat-deforming material segments <NUM> to melt. In embodiments in which the annular packer tool <NUM> also includes portions of metal with a higher melting point than the activation temperature of the heat-deforming material (e.g., eutectic metal) segments <NUM>, the heater <NUM> is configured to heat the location adjacent to the annular packer tool <NUM> to a temperature above the activation temperature of the heat-deforming material segments <NUM> but below the melting point of the other metal portions. As the heat-deforming material melts, the melted heat-deforming material flows into the at least one adjacent annular-shaped opening <NUM>. In at least one embodiment, the preferred activation temperature of the heat-deforming material (e.g., eutectic metal) when the heat-deforming material is a Bi-Sn alloy is approximately <NUM> greater than the highest expected temperature experienced during service in the well. In one or more embodiments, the activation temperature can be in the range of <NUM> to <NUM>. However, it should be understood that higher or lower temperatures for the activation temperature of the heat-deforming material can be selected in other embodiments.

In one or more embodiments in which the scab liner is held in place by the running tool, the heater <NUM> can be run through the running tool and into the scab liner <NUM> adjacent to the heat-deforming material segments <NUM> (e.g., eutectic metal). In such an embodiment, the heater can then be initiated to melt the heat-deforming material.

As mentioned earlier, the annular packer tool <NUM> is constructed such that when the heat-deforming material segments <NUM> melt, the melted metal flows into the opening <NUM>. The centralizers <NUM> that border the ends of the metal segments <NUM> limit where the melted heat-deforming material can flow until the melted heat-deforming material can solidify within the opening <NUM>.

After the heat-deforming material segments <NUM> of the annular packer tool <NUM> has melted, the heater <NUM> is turned off or deactivated such that the reaction that causes the increase in temperature in the heater <NUM> is neutralized and the temperature around the heater <NUM> is lowered below the activation temperature of the heat-deforming material. As such, due to the decrease in temperature, the melted heat-deforming material solidifies within the at least one annular-shaped opening <NUM>. Once the heater <NUM> has cooled, the heater <NUM> is removed from the location adjacent to the annular packer tool <NUM>. In one or more embodiments, the heater <NUM> is removed from the location adjacent to the annular packer tool <NUM> via the electric line <NUM>.

As shown in <FIG>, as the heat-deforming material (e.g., eutectic metal) solidifies in the annular-shaped opening <NUM>, the heat-deforming material expands volumetrically in the annular-shaped opening <NUM>. This volumetric expansion exerts radial stress on the portion of the inner casing <NUM> and outer casing <NUM> that surrounds the annular-shaped opening <NUM>. Once the heat-deforming material solidifies in the annular-shaped opening <NUM>, it forms a seal <NUM>. This seal <NUM> forms a metal-to-metal seal with the metal of the inner casing <NUM> and the metal of the outer casing <NUM> that surrounds the annular-shaped opening <NUM>, thereby providing a gas-tight seal at the location of the CCA leak.

In one or more embodiments, the scab liner <NUM> remains in the well after the leak has been repaired/sealed, and thus permanently or semi-permanently constricts the area of the well in which the leak was repaired. For example, in one or more embodiments in which the scab liner <NUM> is held in place by the running tool, once the heater is deactivated and the heat-deforming material solidifies within the opening <NUM>, the heater is removed, and the running tool is retrieved, but the scab liner can remain in the well.

Moreover, since the packer tool <NUM> is located between the scab liner <NUM> and the outer casing <NUM> within the opening <NUM>, the heat-deforming material (e.g., eutectic metal) that flows and then cools and hardens is bonded to both the scab liner <NUM> and the outer casing <NUM>. The cooled, hardened heat-deforming material that is formed thus in effect plugs the opening <NUM> and also causes the scab liner <NUM> to be bonded to the outer casing <NUM>. The packer tool <NUM> is thus left in place and can be at least partially embedded within the hardened heat-deforming material. The annular packer tool <NUM> is thus sacrificed and left in place along with the scab liner <NUM>.

As such, the present system and methods for repairing an existing leak in a casing effectively sections off one or more portions of the casing around the leak. This is accomplished by removing the inner casing <NUM> and cement sheath at these portions of the casing (e.g., via underreaming) and filling the created void in the casing (annular-shaped opening <NUM>) with heat-deforming material from the annular packer tool <NUM> to form a gas-tight, metal-to-metal seal. Via the gas-tight, metal-to-metal seal, the present systems and methods provide an effective and durable repair of the casing compared to prior solutions.

As also mentioned, one or more production liners <NUM> can be provided and can be secured within the inner casing <NUM>. The production liner <NUM> and the scab liner <NUM> preferably having the same inner diameter.

The present method and system thus provides a solution to remedying leaks that occur in the already formed cement sheath <NUM> of the well that is located between the two sheaths <NUM>, <NUM>. The tool (i.e., the packer tool <NUM>) that repairs (e.g., plugs) the leak is delivered to a location radially inward of the inner casing <NUM> but is carried radially outward of the scab liner <NUM>. After positioning the tool at the desired location that corresponds to an opening that is formed through the inner casing <NUM> and the cement sheath <NUM> so as to expose the inner surface of the outer casing <NUM>. The melted heat-deforming material flows radially outward into such opening resulting in repair of the cement sheath, thereby forming a seal between the scab liner <NUM> and the outer casing <NUM>.

Although much of the foregoing description has been directed to systems and methods for repairing a leak in a casing of a well, the system and methods disclosed herein can be similarly deployed and/or implemented in scenarios, situations, and settings far beyond the referenced scenarios. It should be further understood that any such implementation and/or deployment is within the scope of the system and methods described herein.

It is to be further understood that like numerals in the drawings represent like elements through the several figures, and that not all components and/or steps described and illustrated with reference to the figures are required for all embodiments or arrangements. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. It will be further understood that the terms ""including," "comprising," or "having," "containing," "involving," and variations thereof herein, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

It should be noted that use of ordinal terms such as "first," "second," "third," etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Notably, the figures and examples above are not meant to limit the scope of the present disclosure to a single implementation, as other implementations are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present disclosure can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present disclosure are described, and detailed descriptions of other portions of such known components are omitted so as not to obscure the disclosure. In the present specification, an implementation showing a singular component should not necessarily be limited to other implementations including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present disclosure encompasses present and future known equivalents to the known components referred to herein by way of illustration.

The foregoing description of the specific implementations will so fully reveal the general nature of the disclosure that others can, by applying knowledge within the skill of the relevant art(s) (including the contents of the documents cited and incorporated by reference herein), readily modify and/or adapt for various applications such specific implementations, without undue experimentation, without departing from the general concept of the present disclosure. Such adaptations and modifications are therefore intended to be within the meaning and range of equivalents of the disclosed implementations, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance presented herein, in combination with the knowledge of one skilled in the relevant art(s). It is to be understood that dimensions discussed or shown are drawings are shown accordingly to one example and other dimensions can be used without departing from the disclosure.

The subject matter described above is provided by way of illustration only and should not be construed as limiting. Various modifications and changes can be made to the subject matter described herein without following the example embodiments and applications illustrated and described, and without departing from the scope of the invention encompassed by the present disclosure, which is defined by the set of recitations in the following claims and by structures and functions or steps which are equivalent to these recitations.

Claim 1:
A method for repairing a leak in a casing (<NUM>) of a well (<NUM>), wherein the casing comprises an inner casing (<NUM>) and an outer casing (<NUM>) with a first space formed therebetween, the method comprising:
removing a portion of the inner casing to create an opening in the inner casing so that the first space is accessible;
inserting a scab liner (<NUM>) and an annular packer tool (<NUM>) attached to the scab liner to a location adjacent to the opening, wherein the annular packer tool surrounds the scab liner and comprises one or more segments (<NUM>) of heat-deforming material on an outer surface of the annular packer tool;
tying the scab liner to a production liner (<NUM>) or a wellhead of the well to secure the scab liner;
inserting a heater (<NUM>) into the well and positioning the heater at a location that is internally within the scab liner and is adjacent to the annular packer tool;
activating the heater to a temperature above an activation temperature of the one or more segments of heat-deforming material, thereby causing the heat-deforming material to melt, and wherein the melted heat-deforming material flows into the opening; and
reducing the temperature of the location adjacent to the annular packer tool to below the activation temperature of the heat-deforming material to cause the melted heat-deforming material to solidify within the opening and within the first space.