Method for Preparing a Wellbore

The present application is a continuation-in-part of U.S. patent application Ser. No. 17/927,690, filed on Nov. 23, 2022, which is a 371 National Stage entry of Patent Cooperation Treaty Application No. PCT/NO2021/050134, filed on May 26, 2021, which claims priority from Norwegian patent application No. 20200624, filed on May 27, 2020, the disclosures of which are hereby incorporated by specific reference thereto.

The present invention relates to a method for preparing a wellbore by providing a section of piping with at least a part of its external surface shaped to include a pattern of indents and/or protrusions. The present invention also relates to a section of piping having a shaped external surface and to a method for producing a section of piping having a shaped external surface.

The preparation of a wellbore begins with the setup of a rig above a drilling site. A bore is then created in the formation below the rig using a drill bit at the end of a drill string which is lowered downhole to the desired depth. Once drilling is complete, the resulting bore is lined using connected sections of piping referred to as casing in order to both protect the surrounding formation and stabilize the wellbore. Several concentric layers of piping may be present (casing within casing). The drilling and the placement of the casing may be carried out in stages, progressing to greater and greater depths at each stage. Another piped structure, referred to as tubing, is lowered into the lined wellbore and it is through this tubing that hydrocarbons and/or other substances to be extracted are carried from the formation to the rig and the surface.

It is common to fill any gaps between the casing and the formation, between nested and adjacent sections of casing, and in some cases between the casing and the tubing, with a filler such as concrete or a similar material. Particularly in sections of the wellbore that are horizontal or inclined, eccentricity of the casing or tubing can be an issue. This occurs when parts of the piping structure sag, bend, or drop so that they are no longer centered within the wellbore. An example of eccentricity of concentric casing strings and a tubing string is shown in. In FIG.A the casing stringsand the innermost tubing string are centered within a wellbore which has been drilled through formation(the piping sections are coaxial in that the longitudinal axes of the casing string, tubing string, and wellbore are aligned). In, the tubing and casing sectionshave dropped so as to sit against a lower wall of the wellbore in contact with the formationand with adjacent casing sections. Where casing and tubing strings are in contact as shown in, it is difficult to produce a sufficient seal when filling regions between adjacent parts of the casing strings, tubing, and formation. Filleris not able to access these regions.

The integrity of the final wellbore structure, including the borehole, casing, tubing, and filler, is crucial to maximizing the efficiency of the extraction process. Methods to improve this are therefore desirable.

According to a first aspect of the present invention, there is provided a method for preparing a wellbore comprising: positioning one or more sections of piping within the wellbore as part of a piping string by attaching the one or more sections to additional similar sections of piping, wherein at least a region of an external surface of the one or more sections of piping is shaped to include a pattern of indents and/or protrusions, and wherein the shaped region of the external surface is located so as to be exposed to a surrounding external environment when the section of piping is coupled to the additional similar sections of piping as part of the piping string.

The patterning on the external surface of the piping section ensures that filler material is able to enter a space created by the indents and/or protrusions between the piping external surface and an adjacent structure to provide an effective seal. This is possible even if the piping is not centered within the wellbore and is in contact with or sits close to the adjacent structure. The adjacent structure may, for example, be a section of casing external to the piping section or a region of the surrounding formation. Using a section of piping having a modified external surface in this way improves the integrity of the final wellbore structure. The additional similar sections of piping may or may not also have a shaped external surface.

The modification can be applied downhole, but a simple way to achieve the associated advantages is to provide sections of piping for which the modification is already present and install these prepared sections in a wellbore, for example as part of a casing or tubing string. The modification may therefore be achieved using a shaped mould, by way of a specialized tool, or in another manner during production, or by adapting the piping in a factory, at a storage or service facility, or on a rig before placing it downhole. Reference to a section of piping can be to any type of piping, including at least a section of piping, such as casing and/or tubing, which can be used to form a piping string within a wellbore by coupling a plurality of similar sections together end to end. One, some, or all of the sections of piping within the string can have an external surface that is shaped to include a pattern of indents and/or protrusions.

The external surface refers to a surface facing outwards towards the surrounding formation or structure within a wellbore. For a section of piping, such as tubing or casing, the external surface will be the convex surface facing outwards away from the longitudinal axis of the piping, with the internal surface referring to the piping surface within the pipe bore and facing towards the longitudinal axis. In embodiments, at least a part of the external surface which will be positioned so as to contact a filler material during use is modified to include one or more indents or protrusions. In embodiments, at least a part of the external surface which does not form part of a coupling element for connection to similar piping sections is modified.

The shaped part of the external surface is exposed to a surrounding external environment when the section or sections of piping are coupled to other sections as part of a longer piped structure (a longer section of tubing or casing, for example). Use of the term exposed to a surrounding external environment in this context refers to the fact that it can directly face other structures, such as the surrounding formation, additional larger diameter casing sections, or concrete filler, and is not covered by parts of adjacent piping sections within the same piping string, for example within a coupling structure. The exposed parts of the external surface are those that would be visible if the compound piping string were to be assembled at the surface from the component piping sections by joining them together end to end either directly or using an additional attachment member. When filler, such as concrete, is used to seal against the external surface of the pipe section, after the piping string has been assembled and placed downhole, the filler is able to reach the shaped sections of the external surface. Where these are in contact with adjacent structures due to eccentricity of the piping string, filler can still reach the shaped regions by filling the indents in the surface. This is a great advantage in terms of improving wellbore integrity.

In embodiments, the method comprises drilling a borehole through a formation prior to locating the piping section within the borehole.

In embodiments, the at least one section of piping comprises coupling structures at either end for attachment to the additional similar sections of piping, and the external surface extends between these two coupling structures. The external surface does not, therefore, include the outer surface of any coupling structure (although this can also be modified in some examples). The coupling structures may be screw threads in some examples. If screw threads are present, threads can be provided internal to the piping at one end and external to the piping at the other end for coupling to a similar section of piping at either end. These screw threads will not be exposed to a surrounding external environment when the piping section is coupled at either end to another piping section within a string, but rather will directly face another part of the same string. Other types of coupling structure can be used, such as mating pins and holes, clips, and so on. An additional attachment member can be used to mate to the coupling structure at either end of adjacent pipes within the wellbore to hold the two together in some cases. These coupling structures will then also form a part of the piping string. The end regions of the piping will usually then be contained within the attachment member once the larger piping structure is assembled from a number of smaller sections, and will not be exposed to a surrounding external environment in use.

In embodiments, an external surface of one or both of the coupling structures that will be exposed to a surrounding external environment in use is also shaped to include a pattern of indents and/or protrusions. This helps to provide optimal sealing also where coupling points are present. If the coupling structures simply comprise an internal threaded connection at one end and an external threaded connection at another end, only the structure with the internal threaded connection will include a part that will be exposed to the surrounding external environment in use.

In embodiments, at least a region of the external surface midway between the two ends of the one or more sections of piping is shaped to include a pattern of indents and/or protrusions. The central regions of the piping may be most likely to sag, so that surface shaping in these regions can more effectively reduce leak rate in these areas.

In embodiments, the method comprises filling a region directly adjacent the shaped region of the external surface with a filler material so that the filler material fills one or more spaces formed by the indents and/or protrusions. The spaces may be formed in between the shaped external surface and an adjacent structure, for example another casing string contacted by the piping string. The filler material will, on filling the spaces, contact at least some of the shaped region. In embodiments, the filler material is concrete. Traditional wellbores use concrete to fill between casing and formation, between sections of casing that are nested or contained within one another, and/or in some cases also between tubing and casing. Other types of filler material can also be used. As compared to a flat pipe surface, leak rate is greatly reduced due to improved sealing in areas that this filler would otherwise be unable to reach. The surface modification reduces contact area between the piping external surface and any adjacent structure in areas where the two are directly adjacent, allowing the filler to access spaces created between the contacting structures.

In embodiments, the method comprises modifying the region of the external surface of the one or more sections of piping.

In embodiments, the modifying comprises positioning one or more conductive elements of a tool around the one or more sections of piping, connecting the piping to the tool, and connecting the conductive elements to a power source to remove parts of the external surface by a process of electrolysis. Other methods, such as milling, etching, engraving, adding material, smelting, molding, and so on, can also be used to achieve the modified or shaped external surface as desired. Use of electrolysis, however, allows for a high level of control in terms of achieving the desired shape. It is also easy to implement on a rig or downhole using a reasonably compact tool.

In embodiments, the method comprises modifying the region of the external surface of the one or more sections of piping prior to inserting the one or more sections in the wellbore. Modification may be carried out in a factory, storage facility, service facility, or on a rig before installation downhole. Standard sections of casing or tubing can be modified easily and as needed.

In embodiments, the method comprises modifying the region of the external surface downhole after positioning the one or more sections of piping within the wellbore.

In embodiments, the section of piping is a section of wellbore casing or tubing.

In embodiments, at least a region of the internal surface of the one or more sections of piping that is exposed to a surrounding external environment when the section of piping is coupled to additional similar sections of piping within a wellbore is also provided with a pattern of indents and/or protrusions. In embodiments, the section of piping comprises coupling structures at either end for attachment to the additional similar sections of piping, and the internal surface extends between these two coupling structures. In embodiments, at least a region of the internal surface midway between the two ends of the one or more sections of piping is shaped to include a pattern of indents and/or protrusions. The whole of the internal surface of the piping section may be shaped to include a pattern of indents and/or protrusions.

Where the internal surface sits against a section of piping for which the external surface has also been modified, sealing is particularly effective. The shapes of the facing internal and external surfaces can be selected to provide optimal sealing by creating spaces of a desired size between the two surfaces, as well as maximizing support by ensuring that any contact points are well distributed across the facing surfaces. Piping can be produced as standard with a modified internal and external surface, meaning that it can be used to improve sealing as part of a larger piping string within a compound system of nested casing and tubing strings.

In embodiments, the method comprises positioning the at least one piping section in the wellbore within another piping section of larger diameter, wherein the piping section of larger diameter is modified to include a pattern of indents and/or protrusions on at least a part of its internal surface that will be exposed to a surrounding external environment in use. In embodiments, the method comprises filling a space between the at least one piping section and the piping section of larger diameter using a filler.

In embodiments, the pattern of indents and/or protrusions on the external and internal surfaces are different. This ensures that voids are present between contacting surfaces when the piping sits either within or outside of another similar section of piping having a different diameter. The two patterns can be selected to optimize void space while providing well-distributed contact points, as discussed above.

In embodiments, the pattern of indents and/or protrusions on the external and internal surfaces comprise a plurality of radial grooves, slanting ringed grooves, and/or one or more helical grooves, and the distance between adjacent grooves in a direction along the length of the one or more sections of piping is different for the internal and the external surfaces. The distance between adjacent grooves refers to the tightness of the spiral or helix for a spiral or helical groove, and the number of rings along a particular length of the pipe for radial and slanting ringed grooves. Longitudinal grooves can also be used, or a combination of longitudinal and radial grooves, in some embodiments. Where longitudinal grooves are used on the internal and external surfaces, the distance between longitudinal grooves can be different for the internal and external surfaces. It is also possible to use one type of groove for the internal surface and another type for the external surface (helical grooves for one and longitudinal grooves for the other, for example).

In embodiments, the method comprises modifying the region of the internal surface of the piping section. The modification of the internal and external surfaces can be carried out simultaneously. In a similar manner as for the external surface, the modifying to the internal surface can comprise positioning one or more conductive elements of a tool within the one or more sections of piping, connecting the piping to the tool, and connecting the conductive elements to a power source to remove parts of the internal surface by a process of electrolysis. Other methods, such as milling, etching, engraving, adding material, smelting, molding, and so on, can also be used to achieve the modified or shaped internal surface as desired. Use of electrolysis, however, allows for a high level of control in terms of achieving the desired shape. It is also easy to implement on a rig or downhole using a reasonably compact tool. In embodiments, modifying the external and internal surfaces of the at least one section of piping comprises inserting the piping section into a tool comprising a first cathode internal to the inserted piping section and a second cathode external to the inserted piping section, coupling the cathodes and the piping section to a power source as part of the same circuit, and providing the patterns of indents and/or protrusions via a process of electrolysis.

In embodiments, the tool comprises two separate fluid circulation systems for passing electrolytes around the first cathode and the second cathode respectively. The fluid systems can share the same fluid tank, from which fluid travels into the area inside the respective cathode and back. A separate tank and separate fluid can also be provided for each of the circulation systems, so that the fluid in the two systems doesn't mix in use. Including separate fluid circulation systems helps to prevent hotspots and uneven corrosion of the piping section and ensures that differing pressures around the first and second cathode does not lead to a lack of fluid around one cathode. In embodiments, fins are positioned within the fluid system to ensure turbulent flow and ample mixing of the fluid. The fins can be positioned on or near to the cathodes. These fins also improve mixing and reduce localized heating. Each of the fluid systems passes fluid through a region between a respective cathode and the piping surface when the tool is in use. The fluid may be an electrolyte.

In embodiments, substantially the whole of the external surface of the one or more sections of piping is provided with a pattern of indents and/or protrusions. This configuration provides the best protection in that the improved sealing can be achieved wherever an eccentric casing or tubing section may be present.

In embodiments, the pattern comprises a series of radial grooves, slanted ringed grooves, or one or more helical grooves. Radial grooves refer to circular grooves extending around the piping outer surface in a plane substantially perpendicular to the longitudinal axis of the piping. Slanted ringed grooves refer to circular grooves extending around the piping outer surface in a plane that is angled relative to a plane perpendicular to the longitudinal axis of the piping. Helical grooves refer to one or more grooves that wrap around the piping several times to form a spiral-shaped indent on the outer surface. These specific patterns are easy to produce, and provide for a good balance between maintaining piping strength and integrity and allowing for an optimal seal between the piping and any surrounding structure.

In embodiments, the density of the indents and/or protrusions changes in a direction along the external surface parallel to the longitudinal axis of the piping. The density of the indents refers to the distance between grooves in a direction along the external surface parallel to the longitudinal axis of the piping. A smaller distance between adjacent indents or grooves on the surface will mean a higher density of indents. The patterning can, in this way, maximise sealing effectively while also minimizing the cost of providing the adaptation. Denser regions of patterning can be applied in regions where sagging or eccentricity of the piping is most likely, such as in sections of a wellbore which are not vertically orientated, in wells that are highly deviated or have a high level of tortuosity, or further from connections between piping sections. A plurality of piping sections can be assembled end to end to form a longer piped structure (a piping string). In such a case, the density of patterning on the external surface can vary from pipe section to pipe section (the density may or may not be constant for any particular section). The sections can be arranged to account for the conditions within a particular wellbore in this way, which makes the system particularly adaptable. Some pipe sections can include radial, ringed, or helical grooves which are closer together, and some with grooves that are further apart, for example. The depth of the grooves can also be adapted to suit the conditions within a specific wellbore. Similar considerations will apply to longitudinal grooves, dents, or other types of patterning that can result in the creation of indents and/or protrusions in a surface of the piping section.

Simulation may be used to determine the optimal patterning in a particular case, such as by optimizing the density and/or depth of the indents and/or protrusions.

According to a second aspect of the present invention, there is provided a section of piping for use as part of a wellbore structure, wherein at least part of an external surface of the section of piping that is exposed to a surrounding external environment when the piping is coupled to additional sections of piping within a pipe string and positioned downhole is provided with a pattern of indents and/or protrusions. The additional sections of piping may be similar to or the same as the at least one section of piping.

In embodiments, the section of piping is a section of wellbore casing or tubing.

In embodiments, the section of piping comprising coupling structures at either end for attachment to another similar section of piping, and the external surface extends between these two coupling structures.

In embodiments, at least a region of the external surface midway between the two ends of the one or more sections of piping is shaped to include a pattern of indents and/or protrusions.

In embodiments, a region of the internal surface of the one or more sections of piping that is exposed to a surrounding external environment when the piping is coupled to additional sections of piping within a pipe string and positioned downhole is also provided with a pattern of indents and/or protrusions.

In embodiments, substantially the whole extent of the external surface of the one or more sections of piping is provided with a pattern of indents and/or protrusions.

In embodiments, the pattern comprises a series of radial grooves, slanted rings grooves, or one or more helical grooves.

In embodiments, the density of the indents and/or protrusions changes in a direction along the external surface parallel to a longitudinal axis of the piping.

According to a third aspect of the present invention, there is provided a method for producing a section of piping for use as part of a wellbore structure, the method comprising: providing a pattern of indents and/or protrusions on at least a part of the external surface of the section of piping, wherein the at least a part of the external surface is located on the piping so as to be exposed to a surrounding external environment when the piping is coupled to similar piping sections as part of a piping string and positioned downhole.

According to a fourth aspect of the present invention, there is provided a tool for modifying an internal and/or external surface of a piping section, the tool comprising: an internal conductive element shaped to fit inside the piping section; an external conductive element shaped to surround the piping section; a coupling apparatus for coupling one or both of the internal and external conductive elements to a power source; and a connection device for electrical coupling of the piping section to the power source. In embodiments, the tool comprises the power source.

In embodiments, the tool comprises at least one fluid circulation system for moving fluid through a space between each of the external and internal conductive elements and a facing surface of the piping section.

In embodiments, the tool comprises a first circulation system for moving fluid through a space between the external conductive element and an external surface of the piping section and a second circulation system for moving fluid through a space between the internal conductive element and the internal surface of the piping section. Two separate circulation systems can be helpful because a higher pressure in the internal cathode can result in a reduction in the amount of fluid flowing around this cathode. Separate systems mean that the amount of fluid applied to each cathode can be properly controlled. The two circulation systems can draw fluid from (and in most cases also send fluid back to) a fluid storage unit, which can be the same or different for the two systems.

In embodiments, the tool comprises a masking device for covering a part of an outer surface of the internal conductive element.

In embodiments, the position of the external conductive element and the internal conductive element are fixed relative to one another, so that the piping section can be inserted into the tool in between the two conductive elements.

In embodiments, the masking device represents a separate part which is removable from the tool for replacement of this part. The masking device may be a frame which sits around the internal cathode, for example, or inside the external cathode. The device can be easily removed from the tool for replacement to produce different surface patterns. Two masking devices may be present or a compound masking device for masking parts of the internal and the external cathode.

In embodiments, the tool comprises fins for creating a turbulent flow in the fluid passing between the external and internal conductive elements.

shows some examples of a section of pipingwhere the external surfaceof the casing has been modified to include a pattern of protrusionsand indents. In most cases, the pipingwill be modified across the whole or substantially the whole of its external surfaceto provide the most effective sealing. The internal surface may or may not be modified. Any modification which reduces an area of contact with a surrounding structure will enable filler to enter a region or regions between the piping and the surrounding structure and will improve sealing capability at that surface. In general, the aim of the surface modification is to minimize contact with an adjacent external structure and to provide a space or spaces between the two surfaces, whilst maintaining a desired piping integrity and strength, as well as wellbore integrity.

The optimal modification will depend on a specific situation, butillustrate some preferred patterns. Spiral/helical or radial grooves, such as those shown, provide indents or grooves which are well distributed across the modified area to allow filler material to access a region between the piping and a contacting structure to provide a good seal. Contact between the surface and an adjacent structure is also well distributed across the surface when this type of patterning is used. Filler material will fill the spiral or ring-shaped regions within the grooves when applied.

illustrate the function of the surface modification when filleris used during the installation of a section of pipinghaving a modified external surfaceand an unmodified internal surfacesitting next to and contacting a region of the surrounding formation. The section shown zoomed-in inillustrates indentsand protrusionsproviding spacescontaining filler.