METHOD OF DRILLING A BOREHOLE IN AN EARTH FORMATION

Abstract

A borehole is drilled in an earth formation using consecutive steps of: (a) drilling a first open hole section of a borehole, employing a first drill string extending into the borehole from a surface on the earth, to a casing setting depth;(b) retrieving the first drill string from the borehole to the surface;(c) everting a tubular element in the open hole section, wherein axially advancing an inner tube section of the tubular element into the borehole through and in relative axial movement to an outer tube section of the same tubular element;(d) creating an annular seal between the outer tube section and an inward facing wall of the borehole;(e) inserting a second drill string through the inner tube section into the borehole; and(f) further deepening the borehole by drilling a second open hole section of the borehole.

Description

FIELD OF THE INVENTION

In a first aspect, the present invention relates to a method of drilling a borehole in an earth formation, wherein drilling a first open hole section of the borehole, employing a first drill string extending into the borehole from a surface on the earth, to a casing setting depth.

BACKGROUND OF THE INVENTION

Traditionally, particularly in the oil and gas industry, casing is set during drilling of a borehole in the earth. Such casing may aid the drilling and well completion process in one or more of several ways:

• preventing contamination of fresh water well zones;
• preventing unstable upper formations from caving in and sticking the drill string or forming large caverns;
• providing a strong upper foundation to use high-density drilling fluid to continue drilling deeper;
• isolating different zones, that may have different pressures or fluids, sometimes referred to as zonal isolation, in the drilled formations from one another;
• sealing off high pressure zones from the surface, avoiding potential for a blowout;
• preventing fluid loss into or contamination of production zones; and
• providing a smooth internal bore for installing production equipment.

In the planning stages of a well, a well engineer may pick strategic depths at casing will be set in order for drilling to reach the desired total depth. The casing setting depths may for example be based on subsurface data such as formation pressures, strengths, and makeup, and may preferably be balanced against the cost objectives and desired drilling strategy.

With the casing set depths determined, hole sizes and casing sizes follow. The borehole is drilled in intervals whereby a casing which is to be installed in a lower borehole interval is lowered through a previously installed casing of an upper borehole interval. As a consequence of this procedure the casing of the lower interval is of smaller diameter than the casing of the upper interval. Thus, the casings are in a nested arrangement with casing diameters decreasing in downward direction. As a consequence of this nested arrangement, a relatively large borehole diameter is required at the upper part of the borehole. Such a large borehole diameter involves increased costs due to heavy casing handling equipment, large drill bits and increased volumes of drilling fluid and drill cuttings. This is a major drawback of traditional drilling method using casing as described above.

In some instances, the well design may include liners instead of casing, the difference being that casing typically extends all the way up to surface, while liner is hung off at the bottom of a preceding casing or other liner. For the purpose of the present disclosure, liner and casing are relevant in the same way and the terms are interchangeable.

SUMMARY OF THE INVENTION

In a first aspect, there is provided a method of drilling a borehole in an earth formation, comprising consecutive steps of:

• (a) drilling a first open hole section of a borehole, employing a first drill string extending into the borehole from a surface on the earth, to a casing setting depth;
• (b) retrieving the first drill string from the borehole to the surface;
• (c) everting a tubular element in the open hole section, which tubular element comprises an inner tube section and an outer tube section connected to each other in a lower bending zone, wherein the inner tube section runs through the outer tube section and wherein a wall of the tubular element is, in said lower bending zone at a lower end of the inner tube section, induced to bend radially outward and in axially reversed direction so as to form the outer tube section which thereby is everted compared to the inner tube section, wherein said everting comprises axially advancing the inner tube section into the borehole through the outer tube section in relative axial movement compared to the outer tube section;
• (d) creating an annular seal between the outer tube section and an inward facing wall of the borehole;
• (e) inserting a second drill string through the inner tube section into the borehole;
• (f) further deepening the borehole by drilling a second open hole section of the borehole, employing the second drill string, to a second depth that is deeper than the casing setting depth.

BRIEF DESCRIPTION OF THE DRAWING

The appended drawing, which is non-limiting, comprises the following figures:

FIG. 1 schematically shows drilling of a first open hole section of a borehole;

FIG. 2 schematically shows a quantity of a hardening liquid in the first open hole section of FIG. 1;

FIG. 3 schematically shows the first borehole section of FIG. 1 having an everted tubular element of which a lower bending zone is submerged into the hardening liquid substance of FIG. 2;

FIG. 4 schematically shows further drilling of the borehole by drilling a second open hole section;

FIG. 5 schematically illustrates a close up of the annular seal and the lower bending zone from FIG. 4;

FIG. 6 schematically illustrates extending of the inner tube section of the everted tubular element of FIG. 3; and

FIG. 7 schematically shows coiled tubing used for creating the everted tubular element of FIG. 3.

The figures are schematic of nature, and not to scale. Like reference numbers are used for like features.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be further illustrated hereinafter by way of example only, and with reference to the non-limiting drawing. The person skilled in the art will readily understand that, while the invention is illustrated making reference to one or more specific combinations of features and measures, many of those features and measures are functionally independent from other features and measures such that they can be equally or similarly applied independently in other embodiments or combinations.

A method is presently proposed wherein a first open hole section is drilled to a casing setting depth. The drill string is retrieved, and instead of setting a casing in the traditional way a tubular element is everted in the open hole section, wherein an inner tube section of the tubular element is axially advanced into the borehole through and in relative axial movement to an outer tube section of the same tubular element. After creating an annular seal between the outer wall section and the inward facing wall of the borehole, the inverted tubular element functions as a traditional casing.

A second open hole section can be drilled with a drill string extending through the inner tube section of the tubular element. However, as the tubular element is expanded radially outward when being everted, the second borehole section does not have to be smaller than the first borehole section. Instead, the second borehole section may be cased by further everting the same tubular element as before.

Compared to drilling and setting traditional casing, the presently proposed method becomes more advantageous for each casing setting depth that is needed to reach the final destination depth.

It is remarked that drilling a mono-diameter well and everting a tubular element in such well is known and described in numerous publications including U.S. Pat. No. 7,946,349 and U.S. Pat. No. 9,482,070, and European patent application EP 3034189, the contents of each of which is incorporated herein by reference. However, the methods described in these publications use a complicated machine wherein the tubular element is continuously formed on-site from a band of flat metal strip wound on a reel. The flat metal sheet is unwound from the reel, fed to the drill string and bent around the drill string by means of a bending device after which the adjoining long edges of the bent metal sheet are continuously welded together to form a tubular element with a longitudinal welded seam. Accordingly, the tubular element is advanced into the borehole simultaneously with the drill string.

Such complicated machine is not needed in the present proposal, as the drill string is retrieved from the borehole prior to everting the tubular element. Thus, the present proposal can enjoy at least some of the benefits of the known pipe eversion drilling technology, without having to endure some of its drawbacks. Apart from not needing the complicated machine, the proposed approach has many other advantages, including that the tubular element can be seamless and in particular the tubular element can be brought on site as coiled tubing. Moreover, the drilling operation can be carried out with a standard (vertical) drilling rig and standard drill string.

It is further remarked that fabricating a mono-diameter well using expandable tubulars that are expanded by advancing an expansion tool, such as an expansion cone, through the tubulars to expand their diameter is known and described in numerous publications including for example U.S. Pat. No. 7,100,685 and U.S. Pat. No. 7,357,188. However, these methods typically take longer to complete and require more complex and heavy tools compared to the method presently proposed herein.

It is estimated that expandable tubular technologies may be better suited for wells having larger casing sizes and/or where the formation pressures are higher than average. Today, the theoretical limit of the pipe eversion technology is estimated to be somewhere between 7 to 9 inch outer diameter (OD) of the (unexpanded) inner tube section. As a typical rule of thumb, for typical tubing/CT the resulting OD of the outer tube section is about one inch larger than the OD of the inner tube section, this number being merely an indication as it may vary from case to case and tube to tube.

The presently proposed method may thus be competitive for open hole inner diameters of up to about 10 inch, and/or using an inner tube section having OD of up to 7 to 9 inch, specifically in the range of 4 to 9 inch or 4 to 7 inch. It is currently envisaged that the present proposal may be most competitive against competing technologies for somewhat smaller sizes of up to about 5.5 or 6 inch OD (for instance, in the range of 4 to 6 inch or in the range of 4 to 5.5 inch and/or medium to low pressure wells.

FIGS. 1 to 5 illustrate steps of one way of carrying out the proposed method. FIG. 1 schematically shows drilling a first open hole section 10 of a borehole 1 in an earth formation 2. A first drill string 5 is employed, which extends into the borehole 1 from a surface 6 of the earth. Any desired type of drill string may be used, including traditional jointed string or coiled tubing (CT). A bottom hole assembly includes a drill bit 22, which in this instance comprises a pilot bit 24 and an under-reamer 26. Alternatives may be employed, as desired. The first open hole section 10 extends to a casing setting depth D ₁.

Upon reaching the casing setting depth D₁, the first drill string 5 is retrieved to the surface 6. Furthermore, a hardening liquid substance 12 may be introduced into the borehole 1. FIG. 2 schematically shows the borehole 1 with the hardening liquid substance 12, after the drill string 5 has been retrieved. The hardening substance will be employed to create an annular seal as will be explained below.

Suitably, the hardening liquid substance is a cement, such as a concrete-based cement or a neat cement. Nonetheless alternatives exist in the market which may be used instead of or in addition to concrete or neat cements, such as resin-based substances (see, for example, “Resin emerging as alternative to cement” an article by Sally Charpiot and Paul Jones from OffShore Magazine May 2013 and/or GB2480546A). Resin-based substances for wellbore use are commercially available under the name WellLock® Resin from Halliburton. Suitable resins may be based on scorch-inhibited crosslinkable polymers using a tetrahydrocarbylpiperidin-1-oxyl or alkyloxy (TEMPO) compound or of a derivative, preferably an ether, ester or urethane derivative, of a TEMPO compound. There are also non-cementing substances that can be used to accomplish the seal in the context of the present disclosure, such as for instance a clay seal (e.g. bentonite).

Suitably, the borehole 1 also contains a non-hardening wellbore fluid 13, commonly used to contain the well. The wellbore fluid 13 may suitably be a drilling mud. The density of the hardening liquid substance may be higher than that of the wellbore fluid 13, so that the hardening liquid substance accumulates in the bottom of the first open hole section 10 around the casing setting depth D₁. The hardening liquid substance 12 is conveniently introduced into the borehole by spotting a quantity of the hardening liquid substance through the drill string 5, prior to, or while retrieving the drill string 5 to the surface 6, or during an interruption of retrieving the drill string 5 when is has partly been retrieved to the surface 6. Alternatively, the hardening liquid substance 12 may be cast into the borehole 1 after the first drill string 5 has been fully retrieved from the borehole 1. In some instances, it may be more convenient if the hardening liquid substance is introduced in the annular space between the outer tube section 9 and the inward facing wall of the borehole by spotting a quantity of the hardening liquid substance through such annular space from the surface 6. This may be accomplished using an appropriate side valve (not shown). The latter option may be an advantageous option in zones that have a very stable hole size that does not interfere in the hardening liquid getting to the bottom of the hole.

The next step is everting a tubular element 4 in the open hole section. This is illustrated in FIG. 3. The tubular element 4 comprises an inner tube section 8 and an outer tube section 9 connected to each other in a lower bending zone 14. The inner tube section 8 runs through the outer tube section 9. A wall of the tubular element is, in said lower bending zone 14 at a lower end of the inner tube section 8, induced to bend radially outward and in axially reversed direction, so as to form the outer tube section 9, which thereby is everted compared to the inner tube section 8. As seen in cross section, the lower end of the tubular element 4 has a shape that can be described by two U′s (UU) wherein the wall shows a curve 15. A so-called blind annulus 44 is formed between the inner tube section 8 and the outer tube section 9. The blind annulus 44 is an annular space that is closed in the lower bending zone 14 by the curved wall 15.

An upper end of the outer tube section 9 may be suitably landed on a wellhead device 50. This wellhead device 50 may form part of or be integrated into a blowout preventer (BOP). The outer tubular section 9 may be axially fixed to prevent axial movement. For instance, it may be connected to a ring or flange 59, for instance by welding and/or screwing, on in the wellhead device 50 or any other suitable structure at surface. Optionally, the outer tube section 10 may be fixed to the borehole wall, for instance by virtue of frictional forces between the outer tube section 9 and the borehole wall as a result of the eversion operation. Alternatively, or in addition, the outer tube section 9 may be anchored, for instance to the borehole wall.

Suitably, an upper end of the inner tube section 8 may pass through one, two or more annular seals 56, 58 provided in the wellhead device 50. The annular seals 56, 58 engage with the outside of the inner tube section 8 and allow sliding movement of the inner tube section 8 in its axial direction, and close off the blind annulus 44. The wellhead device 50 suitably comprises a conduit 52 which may be connected to a pump (not shown) for pumping a fluid into or out of the blind annulus 44.

Everting of the tubular element 4 comprises axially advancing the inner tube section 8 into the borehole 1 through the outer tube section 9 in relative axial movement compared to the borehole and the outer tube section 9. As the inner tube section 8 is advanced downward, the wall 15 in the lower bending zone 14 is radially bent over an angle of 180° thereby everting the tubular element 4. The everting operation is continued until the lower bending zone 14 is submerged in the hardening liquid substance 12. By allowing the liquid substance 12 to harden while the lower bending zone 14 is submerged into the hardening liquid substance 12, an annular seal 7 is created between the outer tube section 9 and an inward facing wall of the borehole 1. FIG. 3 schematically shows the first borehole section of FIG. 1 after having everted the tubular element 4 to the point that the lower bending zone 14 is submerged into the hardening liquid substance 12. An inside bore diameter ID of the inner tube section 8 is also indicated.

It is recognized that there are other technologies available to create the annular seal. For instance, the inside of the inner tube section 8 may locally be provided with a swellable material which swells as it becomes exposed to a fluid in the borehole. The eversion operation will eventually bring the swellable material to the borehole facing side of the tubular element 4 after the lower bending zone 14 has passed through the swellable material.

Preferably the hardening liquid substance 12 is retarded, to allow time to complete the eversion operation before hardening of the liquid substance is completed. Various technologies are available to retard a hardening liquid. Retardation over a time span of at least 4 hours, preferably at least 6 hours, more preferably at least 8 hours and most preferably at least 12 hours may be selected depending on the situation.

After the annular seal 7 has been created, a second drill string 5′, which may be the same drill string as previously used or another drill string, may be inserted in the borehole 1 through the inner tube section 8 of the tubular element 4. This is schematically shown in FIG. 4. Before inserting the second drill string 5′, the inner tube section 8 may have to be cut off circumferentially to remove at least a part of the tubular element that is exposed at the earth surface. The part of the inner tube section 8 below a cut rim is retained, and access into the borehole 1 is provided though the cut rim. Such cutting may be done while the annular seal 7 is forming (e.g. while the liquid substance 12 is hardening).

A second open hole section 20 may then be drilled to deepen the borehole 1 to a second depth that is deeper than the casing setting depth D₁. Any hardened cement that is left in the lower part of the inner tube section may be drilled out and reamed. A drilling annulus 32 is maintained between the inner tube section 8 and the second drill string 5′, which may be employed for circulation of a drilling fluid as is common in the art. As the drilling progresses, the drilling annulus 32 extends into the second open hole section 20.

Suitably, the second drill string 5′ comprises a retractable under-reamer 26 that has a gauge diameter larger than the inside bore diameter ID of the inner tube section. This way the second open hole section 20 can be drilled to a bore diameter that is larger than the inside bore diameter ID of the inner tube section 8. Various types of retractable under-reamers are available in the market.

During the drilling of the second open hole section 20, the second drill string 5′ is advanced into the borehole 1 as the borehole 1 is being drilled, whereas the tubular element 4 is kept stationary. Specifically, the lower bending zone 14 at a fixed depth, similar to a traditional casing which is supported on a casing shoe. If necessary, the inner tube section 8 may be temporarily secured with slips 35 to the drilling floor 40, at least for the duration needed to complete the drilling of the second open hole section 20.

The drilling of the second open hole section 20 may be continued until a further case setting depth D₂ is reached. The procedure may at that point be repeated, as many times as required to reach the final destination depth. Accordingly, the currently proposed method involves intermittently drilling, and further everting of the tubular element 4 during the drilling intermissions.

The annular seal 7 isolates any annular space that may exist between the outer tube section 9 and the borehole wall from the drilling annulus 32. By proper selection of the casing setting depth, the proposed method can be employed to drill in formations with different pressure-gradient regimes. FIG. 5 schematically shows a close up of the annular seal 7 and the lower bending zone from FIG. 4 after the hardened substance 12 has been drilled out. The borehole should be drilled clean enough such that any remaining substance 12 will not pose a significant barrier to further everting of the tubular element 4.

In order to further evert the tubular element 4, it may be needed to extend the inner tube section 8 with an extension tube 18 as illustrated in FIG. 6. Particularly when employing a seamless tubular element, extending may be necessary as during the drilling of the second open hole section 20 the borehole needed to be accessible for the second drill string 5′ through the inner tube section 8. Extension is suitably accomplished by sealingly abutting a bottom rim 16 of the extension tube 18 to a top rim 17 of the inner tube section 8 as indicated by arrows 19. There are various techniques available to sealingly connect well tubulars in abutment, including welding. A schematic welding head 21 is included in FIG. 6. The extension tube 18 is preferentially seamless, similar to the tubular element 4 that is already in the borehole 1.

As illustrated in FIG. 7, the tubular element 4 may be provided in the form of a coiled tubing 28. The inner tube section extends to a coiled-up portion 29 of the coiled tubing 28. During eversion, the inner tube section is supplied by uncoiling the coiled tubing 28 from the coiled-up portion 29, while axially advancing the inner tube section into the borehole 1. In order to provide access to the borehole 1 for subsequent further drilling, the coiled tubing 28 may have to be cut at or near the surface 6. This is preferably done at a suitable location that allows the coiled tubing (CT) to be re-abutted after drilling of the second borehole section. There is a prejudice in the art that CT drilling is unsuitable for drilling boreholes in formations with more than one pressure regime. The presently proposed method breaks with this prejudice. An important break-through is that the present proposal does not require to move different CT sizes to the drilling site. Neither does it require a customized tapering to accommodate estimations of different length and OD's for the specific borehole design. Today, CT is conveniently available in sizes ranging from 1 inch to about 5.5 inch OD maximum. Larger sizes exist but become logistically more difficult to transport to site as the coils tend to become larger.

To start the everting operation, it is recommended that a starting section of the tubular element 4 (whether it is coiled tubing or other tube material) has been pre-everted so that it can be landed on the wellhead device 50 in a pre-everted condition. The pre-eversion tool does not have to be on-site.

For purpose of interpretation of the present disclosure it is remarked that the term “consecutive” is used only to identify an order of steps relative to each other, but it is an open term in any other sense. Accordingly the term should not be construed as excluding the possibility of having any intermediate steps, or any subsequent steps or preceding steps. Neither should the term be interpreted as limiting the definition of any of the steps.

The terms “first” and “second” as such are not intended as qualifying terms, but these terms are merely intended to provide a unique nomenclature every feature in the claim for ease of reference. Accordingly, the “first drill string” and “second drill string” are not implied to be physically different drill strings; while they may be physically drill strings the terms may also represent the same physical drill string.

The term “surface” is may mean any surface above the borehole. The term thus includes: land surface, ocean floor surface, sea surface and other suitable surface above the borehole. Suitably, the term “surface” may be characterized by the location of the wellhead.

The term “casing setting depth” should be interpreted as including a reasonable margin as common in the art of well engineering. Casing setting depth is often determined at a depth where a change in formation pressure gradient occurs. However, the change is usually distributed over a certain depth range. Moreover, an actual casing may be set somewhat, up to for instance about 10 m (about 33 ft), above the actual bottom of the borehole section, rather than in absolute abutment with the bottom of the borehole. There may be various reasons for this, including the desire to have the ability to extend wellbore tools in the borehole to below the casing.

Ranges defined herein include the end values of the range.

The person skilled in the art will understand that the present invention can be carried out in many various ways without departing from the scope of the appended claims.

Claims

1. A method of drilling a borehole in an earth formation, comprising consecutive steps of: (a) drilling a first open hole section of a borehole, employing a first drill string extending into the borehole from a surface on the earth, to a casing setting depth;(b) retrieving the first drill string from the borehole to the surface;(c) everting a tubular element in the open hole section, which tubular element comprises an inner tube section and an outer tube section connected to each other in a lower bending zone, wherein the inner tube section runs through the outer tube section and wherein a wall of the tubular element is, in said lower bending zone at a lower end of the inner tube section, induced to bend radially outward and in axially reversed direction so as to form the outer tube section which thereby is everted compared to the inner tube section, wherein said everting comprises axially advancing the inner tube section into the borehole through the outer tube section in relative axial movement compared to the outer tube section;(d) creating an annular seal between the outer tube section and an inward facing wall of the borehole;(e) inserting a second drill string through the inner tube section into the borehole;(f) further deepening the borehole by drilling a second open hole section of the borehole, employing the second drill string, to a second depth that is deeper than the casing setting depth.

2. The method of claim 1, wherein during step (f) the second drill string is advanced into the borehole as the borehole is being drilled, whereas the tubular element is kept stationary whereby keeping the lower bending zone at a fixed depth.

3. The method of claim 2, wherein the inner tube is temporarily secured at or near the surface for at least the duration of step (f).

4. The method of claim 1, wherein step (f) is continued until reaching a further case setting depth; and subsequently carrying out step (b) again with respect to the second drill string, after which further everting the tubular element into the second open hole section, comprising axially further advancing the inner tube section into the borehole through the outer tube section in relative axial movement with the outer tube section.

5. The method of claim 1, wherein the tubular element is a seamless tubular element.

6. The method of claim 4, wherein said further everting comprises extending the inner tube section with an extension tube by sealingly abutting the extension tube to a top rim of the inner tube.

7. The method of claim 6, wherein said sealingly abutting comprises welding a bottom rim of said extension tube to the top rim of the inner tube.

8. The method of claim 6, wherein the tubular element and the extension tube are both seamless.

9. The method of claim 4, wherein creating a second annular seal between the outer tube section and an inward facing wall of the borehole in the second open hole section.

10. The method of claim 1, wherein the tubular element is provided in the form of coiled tubing, and wherein the inner tube section extends to a coiled-up portion of the coiled tubing, and wherein step (c) comprises supplying the inner tube by uncoiling the coiled tubing from the coiled-up portion while axially advancing the inner tube section into the borehole.

11. The method of claim 1, wherein after completing step (c) and prior to step (e) the inner tube section is circumferentially cut off whereby removing at least a part of the tubular element that is exposed at the earth surface and retaining a part of the inner tube section below a cut rim.

12. The method of claim 1, wherein after completing step (a) and prior to step (d) a hardening liquid substance is introduced into the borehole, and wherein step (d) comprises allowing hardening of the liquid substance while at least the lower bending zone is submerged into the hardening liquid substance.

13. The method of claim 12, wherein the hardening liquid substance is retarded to allow time to complete step (c) before hardening of the liquid substance is completed.

14. The method of claim 1, wherein the second drill string comprises an under-reamer having a gauge diameter larger than an inside bore diameter of the inner tube section to drill the second open hole section to a bore diameter that is larger than the inside bore diameter of the inner tube section.