Patent Grant
7195075
1. Field of the Invention
This invention relates generally to a method and apparatus useful in the exploration of subterranean regions and, more particularly, to a method and apparatus useful in the exploration for, and production of, hydrocarbons from subterranean regions. In various aspects, the present invention relates to a method and apparatus for a new type of wire that combines high conductivity and low thermal expansion that can be used to reduce temperature sensitivity effects in induction logging tools and other instruments that require wires with low thermal expansion and low electrical resistance.
2. Description of the Related Art
As shown in
Induction tool measurements used in logging applications, made by the downhole induction logging tool 100, for example, are very sensitive to changes in the position and/or the diameter of either or both the receiver and/or the transmitter coils. The dimensions of all the parts of an induction tool should be as invariant as possible even as the temperature of the induction tool varies over a wide range from typical surface temperatures of about 68° F. (20° C.), or lower (sub-zero surface temperatures could be experienced, for example, during testing and calibration in Alaska, for example), to downhole temperatures of about 500° F. (260° C.), or higher (generally, the deeper the well, the higher the downhole temperature), in the deeper wells. Low thermal expansion materials have typically been used, such as low thermal expansion ceramics, for example, silicon nitride (Si2N3).
The wire in the coils of the induction tools are typically made of thin copper (Cu) filaments. Copper (Cu) is selected for its low electrical resistance (high electrical conductivity). However, copper (Cu) is less than optimal for these induction tool applications due to its relatively high thermal expansion. The effect of the thermal expansion of copper (Cu) can produce significant changes in the signals measured, particularly in the shallower induction measurements that are associated with shorter receiver-transmitter spacings.
As shown in
The purpose of the strands 210 is to provide the maximum surface area for a given cross-section of the litz wire 200. At the typical frequencies used in downhole induction tools, in a range from about 8 kHz to about 200 kHz, the electrical current flows in a thin layer at or near the surface of each of the strands 210 of the litz wire 200. By using several strands 210, the overall resistance of the litz wire 200 is reduced at these typical frequencies. However, if no method to reduce the thermal expansion of the litz wire 200 is used, the thermal expansion of the litz wire 200 with increased temperature produces changes in the signal level of the downhole induction tool 100 that are tolerable for receiver-transmitter induction coil spacings greater than about 20 inches (50 cm), but that are not tolerable for receiver-transmitter induction coil spacings less than about 20 inches (50 cm). For receiver-transmitter induction coil spacings less than about 20 inches (50 cm), the effect of the thermal expansion of the litz wire 200 with increased temperature is very significant, producing intolerable changes in the signal level of the downhole induction tool 100, making the achievement of more stable measurements much more difficult.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one aspect of the present invention, a device is provided, the device comprising a downhole tool comprising a wire comprising at least one strand comprising a low thermal expansion material. The low thermal expansion material may have a low electrical resistance material disposed thereon.
In another aspect of the present invention, a device is provided, the device comprising a downhole tool comprising a wire comprising a plurality of strands, each of the plurality of the strands comprising a low thermal expansion material. The low thermal expansion material has a low electrical resistance material disposed thereon.
In yet another aspect of the present invention, a device is provided, the device comprising a downhole tool comprising a wire comprising first strands in a central portion of the wire, the first strands comprising a low thermal expansion material. The device also comprises the wire comprising second strands in a peripheral portion of the wire, the second strands comprising a low electrical resistance material.
In still yet another aspect of the present invention, a method is provided, the method comprising providing a wire comprising at least one strand for use in a downhole tool, the at least one strand comprising a low thermal expansion material. The low thermal expansion material may have a low electrical resistance material disposed thereon.
In another aspect of the present invention, a method is provided, the method comprising providing a wire comprising a plurality of strands for use in a downhole tool, each of the plurality of the strands comprising a low thermal expansion material. The low thermal expansion material has a low electrical resistance material disposed thereon.
In still another aspect of the present invention, a method is provided, the method comprising providing a wire for use in a downhole tool, the wire comprising first strands in a central portion of the wire, the first strands comprising a low thermal expansion material. The method also comprises providing the wire comprising second strands in a peripheral portion of the wire, the second strands comprising a low electrical resistance material.
In yet another aspect of the present invention, a device is provided, the device comprising a wire comprising at least one strand for use in a downhole tool, the at least one strand comprising means for decreasing thermal expansion of the wire. The at least one strand also comprises means for decreasing electrical resistance of the wire disposed on the means for decreasing thermal expansion of the wire.
In still yet another aspect of the present invention, a device is provided, the device comprising a wire comprising a plurality of strands for use in a downhole tool, each of the plurality of the strands comprising means for decreasing thermal expansion of the wire. Each of the plurality of the strands also comprises means for decreasing electrical resistance of the wire disposed on the means for decreasing thermal expansion of the wire.
In another aspect of the present invention, a device is provided, the device comprising a wire for use in a downhole tool, the wire comprising first strands in a central portion of the wire, the first strands comprising means for decreasing thermal expansion of the wire. The device also comprises the wire comprising second strands in a peripheral portion of the wire, the second strands comprising means for decreasing electrical resistance of the wire.
It is an object of the present invention to provide a method and apparatus to reduce the thermal expansion of wire, such as the wire used in one or more coils in a downhole induction tool, while preserving the low resistance of the wire. It is another object of the present invention to provide a method and apparatus to combine high conductivity and low thermal expansion of wire used for downhole induction tool applications. It is yet another object of the present invention to reduce temperature effects in downhole induction logging tools and in other instruments that require a wire with low thermal expansion and low electrical resistance.
These and other objects of the present invention will become apparent to those of skill in the art upon review of the present specification, including the drawings and the claims.
The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which the leftmost significant digit(s) in the reference numerals denote(s) the first figure in which the respective reference numerals appear, and in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
Illustrative embodiments of a method and a device according to the present invention are shown in
In various illustrative embodiments, the downhole tool may include a downhole drilling tool, a downhole sensor tool, such as the downhole induction logging tool described herein, a downhole transformer, a downhole electrical motor, a downhole antenna, a downhole receiver, a downhole transmitter, a downhole acoustic device, and the like.
In various alternative illustrative embodiments, the strand 410 may comprise only the low thermal expansion material 420 (with a diameter d), without having any low electrical resistance material 430 disposed on the low thermal expansion material 420. For example, in these various alternative illustrative embodiments, the low thermal expansion material 420 may comprise only molybdenum (Mo). In various other alternative illustrative embodiments, the strand 410 may comprise substantially only the low thermal expansion material 420 (with the diameter d), having a very thin layer of a low electrical resistance material 430 (with the outer diameter D only slightly larger than the diameter d) disposed on the low thermal expansion material 420. For example, in these various other alternative illustrative embodiments, the very thin layer of the low electrical resistance material 430 may be such that the difference D−d between the outer diameter D (of the low electrical resistance material 430) and the diameter d may be in a range from about 1 micron to about 200 microns, so that the low electrical resistance material 430 may have a thickness in a range from about 0.5 micron to about 100 microns. For example, in these various other alternative illustrative embodiments, the low thermal expansion material 420 may comprise substantially only molybdenum (Mo), having a very thin “flash protection” layer of about 15 microns of gold (Au) disposed on the molybdenum (Mo), also helping the molybdenum (Mo) to be more corrosion-resistant at elevated downhole temperatures.
In various illustrative embodiments, the ratio of the diameter d (of the low thermal expansion material 420) to the difference D−d between the outer diameter D (of the low electrical resistance material 430) and the diameter d may be in a range from about 1000 to 1 to about 2 to 1, or, more precisely, an optimal amount of low electrical resistance material and low thermal expansion material, for a specific application that considers temperature range and conductivity requirements, could be derived from equations that describe thermal expansion and mechanical equilibrium of the materials, and considerations about the bonding strength between the materials and the properties of the insulating coating. In particular, the ratio of the diameter d to the difference D−d may be about 3 to 1. The ratio of the diameter d to the difference D−d may determine the overall resistance of the strand 410. As shown in
In various illustrative embodiments, the low thermal expansion material 420 may have a thermal expansion coefficient lower than the thermal expansion coefficient of copper (Cu). For example, the low thermal expansion material 420 may comprise graphite (C), chromium (Cr), iridium (Ir), molybdenum (Mo), niobium (Nb), osmium (Os), rhodium (Rh), tantalum (Ta), titanium (Ti), tungsten (W), and vanadium (V), and/or any alloys thereof, and/or alloys such as Invar (a Fe—Ni alloy), Kovar (a Fe—Ni—Co alloy), and the like. In particular, the low thermal expansion material 420 may comprise molybdenum (Mo). For example, molybdenum (Mo) has a thermal expansion coefficient lower than the thermal expansion coefficient of copper (Cu) by a factor of about 3.2, and a conductivity (reciprocal of resistivity) about one-third the conductivity of copper (Cu).
In various illustrative embodiments, the low electrical resistance material 430 may have an electrical resistance lower than the electrical resistance of the low thermal expansion material 420. For example, the low electrical resistance material 430 may comprise aluminum (Al), copper (Cu), gold (Au), and silver (Ag), and/or any alloys thereof. In particular, the low electrical resistance material 430 may comprise copper (Cu). Having the low electrical resistance material 430 comprise copper (Cu) may increase the solderability of the strand 410. Having the low electrical resistance material 430 comprise copper (Cu) may also lower and/or reduce the series resistance of a wire comprising the strands 410.
In various illustrative embodiments, the insulating material 440 may comprise glass fiber, polyester, teflon®, polyimide, and the like. In particular, the insulating material 440 may comprise polyimide-ML, which is particularly useful for high temperatures in excess of about 392° F. (200° C.). The insulating material 440 provides electrical isolation between the strands 410.
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Any of the above-disclosed embodiments of a method and a device according to the present invention enables the dimensions (diameter and/or length and/or thickness) of the wire for logging and/or other downhole applications to be more stable when subject to temperature changes. Additionally, many of the above-disclosed embodiments of a method and a device according to the present invention enable the low resistance of the wire for logging and/or other downhole applications to be preserved with appropriate selection of the relative proportions of the low thermal expansion material and the low electrical resistance material. In addition, any of the above-disclosed embodiments of a method and a device according to the present invention enables temperature corrections to be reduced due to the lower radial expansion of coils made from the wire for logging and/or other downhole applications.
The particular embodiments disclosed above, and described with particularity, are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a–b”) disclosed herein is to be understood as referring to the power set (the set of all subsets) of the respective range of values, in the sense of Georg Cantor. Accordingly, the protection sought herein is as set forth in the claims below.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3909555 | Harris | Sep 1975 | A |
| 5892176 | Findlay et al. | Apr 1999 | A |
| Number | Date | Country | |
|---|---|---|---|
| 20050133271 A1 | Jun 2005 | US |
