Patent Description:
In hydrocarbon exploration and production processes, wellbores or boreholes are created for supporting production of hydrocarbons, including for oil and gas generation. Such wellbores or boreholes may be drilled with a drill string that may include tubing and jointed tubulars or continuous coiled tubing. The tubing may generally include a drilling assembly or a bottom hole assembly (BHA). The tubing may be attached to an end advancing a drill string into the wellbores or boreholes. The BHA may include one or more sensors and other tools, including directional tools to assist a drilling process. Further, the drill string may include a drill bit that is operated by a motor in the BHA, for instance. A propagation resistivity Z-antenna may be one such sensor or directional tool that is provided in the drill string. The propagation resistivity Z-antenna may be an antenna representing a magnetic dipole oriented along the tool or a z-axis associated with the tool. The Z-antennae may include a number of ferromagnetic bars oriented along a tool axis with a common winding that may encompass all the ferromagnetic bars, as well as significant parts of a tool steel body incorporating the ferromagnetic bars. Such a structure is subject to complicated repair and maintenance efforts as the structure has to be durable for downhole conditions. For example, the antenna must be removed, uncoiled, recoiled, and calibrated as part of any repair and maintenance effort. <CIT>, <CIT> and <CIT> disclose arrangements of the prior art.

A downhole antenna tool is provided according to claim <NUM>. The substrate may include respective recesses in which the individual ones of the antenna bars are positioned and may include a cushion layer between the antenna bars and the substrate for mechanical decoupling of the antenna bars from the substrate.

A method of assembly or manufacture of a downhole antenna tool is provided according to claim <NUM>. The method may further include providing a mechanical decoupling using, for example, a cushion layer between the individual antenna bars and the substrate.

Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:.

While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. Instead, the preferred embodiments are intended to cover all alternatives, modifications, and equivalents, as may be included within the scope of the invention as defined by the appended claims.

So that the manner in which the features and advantages of the embodiments of downhole antennas with distributed windings, as well as methods to manufacture, operate, and others, which will become apparent, may be understood in more detail, a more particular description of the embodiments of the present disclosure briefly summarized previously may be had by reference to the embodiments thereof, which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the disclosure and are therefore not to be considered limiting of the present disclosure's scope, as it may include other effective embodiments as well.

A downhole antenna tool with one or more antenna bars having distributed windings and methods to manufacture and operate the downhole antenna tool is described hereinafter with reference to the accompanying drawings in which aspects are shown. The downhole antenna tool and associated manufacture or operation may be available in many different forms and should not be construed as limited to the illustrated aspect set forth herein; rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. In an embodiment, usage of the term "about" or "substantially" includes +/-<NUM>% of the cited magnitude.

It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.

The present disclosure is to a downhole antenna tool that resolves the above-stated concern using distributed windings on one or more antenna bars with a predetermined core shape, such as one of a trapezoidal shape or a rectangular shape, and by releasably coupling the one or more antenna bars to a substrate of the downhole antenna tool. The one or more antenna bars are also mechanically decoupled from the substrate for example by a cushion layer between the antenna bars and the substrate. Mechanical decoupling refers to reduced transmission of mechanical forces, such as movement and impact, from the substrate to the antenna bars. Releasable coupling refers to any attachment between the antenna bars and the substrate being releasable so that the antenna bars may be removed from the substrate and replaced or maintained as required. In this manner, an efficient system for a downhole antenna tool is disclosed that may be easily removed from the substrate as it is already mechanical decoupled in the manufacturing stage. Additionally easy removal and replacement is encouraged by the structure of the present tool as the antenna bars are easily accessible on the substrate.

<FIG> illustrates an example system <NUM> of a drill string <NUM> with a downhole antenna tool <NUM> comprising one or more downhole bars with distributed windings according to an aspect of the present disclosure. The drill string <NUM> may be comprised in a tubular piping <NUM> within a borehole. The drill string <NUM> may be motorized to rotate a drill head <NUM> through soil layers <NUM>. An external support structure <NUM> is provided external to the drilling operations, with a pit <NUM> that may include a drill fluid, e.g., mud, that may be pressurized through the drill string <NUM> via line <NUM> using motor <NUM>, and that may be egressed out of line <NUM>. The drill head <NUM> includes a drill bit and opening to discharge the drill fluid, which helps with the drilling process. The drill fluid returns via the borehole back to the pit <NUM>.

<FIG> illustrates details of a version of a downhole antenna tool <NUM> with tiles <NUM> used as part of a Z-antenna that is improved by aspects of the present disclosure. The tiles <NUM> may be ferrite tiles glued to the substrate <NUM> of the downhole antenna tool <NUM>. <FIG> illustrates details of a process to manufacture the tiles <NUM> of the downhole antenna tool from <FIG>. For example, tiles <NUM> may be formed from ferrite tape strips <NUM> that are laminated together, and are then encapsulated in an elastomer <NUM>. The tape may include nanocrystaline material. The nanocrystaline material may be packaged in an elastomer. In a further example, the ferrite core may be composed of manganese-zinc ferrite (MnZn) with a ceramic core. The resulting structure is brittle and may not function well for longer bar lengths. Such a core, however, requires core segmentation and is inert to mud in downhole conditions. Reference numeral <NUM> illustrates different magnifications of the tiles.

<FIG> also illustrates various cut-section and full-section views of a tile <NUM> packaged in an elastomer <NUM>. An alternate to the ferrite tile may be constructed from nanocrystalline FeCuNbSiB-Iron alloy. The FeCuNbSiB material is apparent to a person of ordinary skill in the art as to composition and associated processing for such implementations. A tile constructed from FeCuNbSiB and including iron forms a nanocrystalline tape core. As illustrated in reference number <NUM>, laminated tape strips are used to form the nanocrystalline tile, and may be available in lengths greater than <NUM>. While such a construction may be more robust than a ferrite bar, it requires protection from mud in the downhole environment.

The above-referenced core <NUM> may be alternatively manufactured by laminating ribbons or tape that is <NUM> micrometers (µm) in length. The laminated ribbons or tape compose about <NUM>%-<NUM>% of the cross-section. An interlayer insulation of oxide and epoxy bonding may be used in the lamination procedure. Further, the interlayer insulation may be <NUM>-<NUM> thickness. A packaging process in the manufacturing of the tiles may include a compression molding of the insulated laminated tiles. The molding may use compounds with low compound velocities and low pressure differentials within the mold.

<FIG> illustrate a side view <NUM> and a perspective cross-sectional view <NUM> of a downhole antenna tool, in accordance with aspects of the present disclosure. The views illustrate one or more antenna bars <NUM> in recessed areas <NUM> of the downhole antenna tool. Further, the one or more antenna bars <NUM> may be mechanically decoupled in the recessed areas. For example, a cushioning layer may be provided for mechanically decoupling the one or more antenna bars <NUM> from a substrate <NUM> providing the recessed areas <NUM>. In an aspect, the cushioning layer may be a silicone tape, other relevant material, such as a hydrogenated nitrile rubber (HNBR)-inlay compound or other radial sealing compound offering radial pretension. The downhole antenna tool may be associated with the drill string <NUM> via fixtures <NUM>, <NUM>, which may be the ends of the antenna substrate <NUM>. A first fixture <NUM> may be an end insert and a second fixture <NUM> may be a wire collector pocket. Further, a material that is used to form the downhole antenna tool may form part of the substrate <NUM> (and optionally, the fixtures <NUM>, <NUM>) to which the antenna bars <NUM> are fixed. In <FIG>, a perspective cross-sectional view <NUM> of a downhole antenna tool is illustrated with the antenna bars <NUM> within recessed areas <NUM> of the downhole antenna tool. Face <NUM> of the downhole antenna tool illustrates a supporting passage for drill fluid and may include the above-referenced fixtures <NUM>, <NUM>, for instance.

<FIG> illustrates winding details in different views <NUM>-<NUM> of a downhole antenna bar <NUM> with distributed windings for a downhole antenna tool, in accordance with an aspect of the present disclosure. The general view <NUM> is supported by upper cross sectional view <NUM> across axis marked BB in general view <NUM>; by side view <NUM> across axis marked CC in general view <NUM>; and by lower cross sectional view <NUM> across axis marked AA in general view <NUM>. The different views <NUM>-<NUM> illustrate coil carriers <NUM>, <NUM> in a first fixture and in a second fixture (such as fixtures <NUM>, <NUM> in <FIG>), above and below the coil area to geode the coil in a parallel arrangement (i.e., not twisting the coil). The wire is guided within the coil carrier <NUM> to the core <NUM> and wound around the core <NUM> in the manner illustrated. Further, as illustrated in view <NUM>, wire guiding on the bottom side of the core <NUM> offers additional shielding effects from the downhole environment and operative interference of signals. The core <NUM> may be dimensioned at <NUM>±<NUM> in its width, making it wider relative to its thickness, as illustrated in the profile or views AA <NUM> and CC <NUM>.

In the present disclosure, one or more antenna bars with winding, such as antenna bar <NUM>, are prepackaged and are provided with pressure-proof connectors that connect each bar of the one or more antenna bars to an antenna wiring harness. Thereafter, replacement of each bar does not require a complete antenna rebuild, but may be achieved by, for example, replacement of a defective antenna bar at issue during a repair and maintenance operation. The antenna bars may be ferromagnetic bars with windings thereon. While the turns of wire forming the windings on the antenna bar are illustrated as contacting each other, the turns need not touch each other in aspects of the disclosure, but can be spaced apart. Further, in other aspects, the windings can be spread over the entire bar. Still further, the number of turns, the width, end-to-end distance, and height of the antenna bar may be adjusted to suit to the application requirements. In an aspect, individual ones of the antenna bars may be situated at a predetermined height from a center of the downhole antenna tool, within respective recesses. The predetermined height allows the individual ones of the antenna bars to be adjacent to an outer surface of the substrate and within the respective recesses depending on the application requirements.

The windings and the antenna bars are encapsulated in a suitable coating that may be a downhole-conditions-proof insulating material such as polyether ether ketone (PEEK) or rubber. Each coated antenna bars may be recessed in suitable grooves or recessed areas as illustrated in <FIG>, around the downhole antenna tool circumference. A substrate may be a separate component of the downhole antenna tool, but may be part of a singular material used to make a substantial (e.g., <NUM>%) portion of the downhole antenna tool. For example, the substrate may be manufactured integral to the tool. These aspects make the antenna bars extremely durable. The present disclosure also enables a downhole antenna tool that has superior technical advantages other than the durability, as a result of the above-referenced structures. For example, an advantage achieved in the present aspects include reduced common-mode coupling, lower repair and maintenance (R&M) costs, faster R&M turnaround time, and faster antenna build times. In an aspect, the antenna bars may be suspended in the protective coating within the respective recesses.

<FIG> illustrates mechanical decoupling of the downhole antenna bar <NUM> from a substrate <NUM> of the downhole antenna tool <NUM>, according to aspects of the present disclosure. In <FIG> antenna bar <NUM> is illustrated with an applied protective coating, but is referred to herein generally as the antenna bar to illustrate its relative location to components providing the mechanical decoupling to the substrate <NUM>. The mechanical decoupling is at least enabled via one or more of a flex spring <NUM>, washer 712B, and a connector cover 712A, as well as with silicone (e.g., silicone tape) and/or HNBR-inlay <NUM> forming a cushioning layer with for radial protection. A copper shield <NUM> may be used between antenna winding on antenna bar <NUM> and the substrate body <NUM> to further reduce eddy current losses, particularly at higher frequencies. The downhole antenna bar <NUM> may be situated between a manifold <NUM> and an end-block portion <NUM> of the substrate (integrally part of or that is separately attached to the substrate) of the downhole antenna tool <NUM>. The connector cover 712A protects an upper and a lower bed piece 726A, 726B associated with the substrate <NUM>. A fixation ring <NUM> and z-inserts <NUM> are provided to stabilize the coils of the antenna bars, e.g., bar <NUM>. A pocket 714A is provided in the flex spring <NUM> for locking a rod bracket <NUM> from the end-block portion <NUM> through the components 712A, 712B, <NUM>, and into manifold <NUM>. The ends <NUM> of the rod bracket <NUM> are illustrated as having narrow tips to engage manifold <NUM>.

A packaging process for the antenna bar of <FIG> may use HNBR elastomer that is molded with the antenna bar <NUM> in its respective recessed area of the substrate <NUM>. Alternatively, a compound that has chemical robustness, low vulcanization temperatures, and ability to dampen mechanical vibration may be used for the packaging process. The packaging process or a manufacturing process for the present downhole antenna tool includes application of the molding over the antenna bar. The molding creates a specific geometry that may be predetermined for aerodynamic properties of the drill string and the tool. The present packaging may adapt a printed circuit board assembly (PCBA) to account for pretension and to compensate for swelling and thermal expansion. In an alternate implementation, a chemical vapor deposited polymer may be used as part of a coating or the molding process. The coating or molding process supports media separation, which eliminates core corrosion and chemical degradation.

<FIG> provides a flowchart <NUM> for manufacturing a downhole antenna tool having one or more antenna bars with distributed windings, in accordance with an aspect of the present disclosure. The method of manufacture includes using bars that are made of a nominal alloy composition of ferrous, copper, niobium, silicon, and boron. The bars are provided for the downhole antenna tool according to dimensions and positioning determined for the tool in sub-process <NUM>. In an aspect, the dimensions and positioning may be determined based in part on an intended application of the downhole antenna tool. In sub-process <NUM>, coils are wound on the bars, individually, through respective coil carriers that may be coupled to the individual bars. The bars, with the coils, are then subject to a coating for protection against downhole conditions in sub-process <NUM>. The coating may be applied prior to placing the bars in respective recesses of a substrate or may be performed after placing the bars in the respective recesses. In sub-process <NUM>, verification may be performed to determine that the coating for the one or more coils is sufficiently over the coils so that the coils are protected against downhole environment conditions apparent in downhole operations. When such verification generates a negative result, the coating may be repeated either over a prior coating or by stripping and recoating the bars with the wound coils. In sub-process <NUM>, when the verification sub-process <NUM> generates a positive result, the one or more bars are positioned in the respective recesses of the substrate so that the one or more bars are mechanically decoupled from the substrate. The ability of the bars to be mechanically decoupled from the substrate can be achieved in any appropriate way. For example, the bars can be attached to the substrate using a cushion layer of silicone or other appropriate material that will then allow selective decoupling when necessary or desired. In addition, washers, connectors, and other components may be used to releasably couple the bars to the substrate while still providing the ability to mechanically decouple the bar from the substrate.

The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, other the recesses can be put into arrangements other than those described, such as all being in a vertical or other arrangement. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.

Claim 1:
A downhole antenna tool (<NUM>) comprising:
a substrate (<NUM>) comprising a plurality of antenna bars (<NUM>) that are releasably coupled to the substrate (<NUM>);
coils wound on individual ones of the plurality of antenna bars (<NUM>) through associated coil carriers of the individual ones of the plurality of antenna bars (<NUM>); and characterised by
a protective coating over the coils;
wherein the plurality of antenna bars (<NUM>) are mechanically decoupled from the substrate (<NUM>).