Patent Application
20140312906
Earth formations may be used for various purposes such as hydrocarbon production, geothermal production, and carbon dioxide sequestration. In order to efficiently use an earth formation, the formation is characterized by performing measurements of many different properties using one or more tools conveyed through a borehole penetrating the formation. One category of tools includes tools that measure electrical characteristics of the earth formation such as resistivity or dielectric constant. Conventional resistivity and dielectric tools typically use a coil as an antenna to transmit electromagnetic signals into or receive electromagnetic signals from the formation in order to measure the resistivity or dielectric constant. Due to the physical size constraints imposed by the borehole, the desired transmitting efficiency for probing deep into the formation may be compromised. Hence, it would be well received in the drilling and geophysical exploration industries if designs of resistivity and dielectric tools could be improved to probe deeper into earth formations.
Disclosed is an apparatus for estimating a property of a subsurface material. The apparatus includes: a carrier configured to be conveyed through a borehole penetrating the subsurface material; a transmitter configured to transmit a first electrical signal; a first energy interface device disposed at the carrier, coupled to the transmitter, and configured to transmit at least one of electromagnetic energy and electrical energy into the subsurface material; a second energy interface device disposed at the carrier and configured to receive at least one of return electromagnetic energy and return electrical energy due to at least one of transmitted electromagnetic energy and transmitted electrical energy interacting with the subsurface material; a receiver coupled to the second antenna and configured to receive a second electrical signal from the second energy interface device; and a processor coupled to the receiver and configured to estimate the property using the second electrical signal; wherein at least one of the first energy interface device and the second energy interface device is a fractal-shaped antenna having a base motif figure and at least one scaled down replication of the base motif figure, the at least one replication being a change from the base motif by at least one of a linear displacement translation and a rotation, and a position of the replication upon the base motif figure is by at least one of rotation, translation, and stretching.
Also disclosed is a method for estimating a property of a subsurface material, the method includes: conveying a carrier through a borehole penetrating the subsurface material; transmitting at least one of electromagnetic energy and electrical energy into the subsurface material using a first energy interface device disposed at the carrier and coupled to a transmitter configured to transmit a first electrical signal to the first energy interface device; receiving at least one of return electromagnetic energy and return electrical energy from the subsurface material due to the at least one transmitted electromagnetic energy and transmitted electrical energy interacting with the formation using a second energy interface device disposed at the carrier and coupled to a receiver configured to receive a second electrical signal from the second energy interface device; and estimating the property using a processor coupled the receiver and configured to estimate the property using the second electrical signal; wherein at least one of the first energy interface device and the second energy interface device is a fractal-shaped antenna having a base motif figure and at least one scaled down replication of the base motif figure, the at least one replication being a change from the base motif by at least one of a linear displacement translation and a rotation, and a position of the replication upon the base motif figure is by at least one of rotation, translation, and stretching.
The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
A detailed description of one or more embodiments of the disclosed apparatus and method presented herein by way of exemplification and not limitation with reference to the figures.
Disclosed are apparatus and method for estimating resistivity or its inverse conductivity, dielectric constant, or some other property of an earth formation. A downhole tool, in one or more embodiments, is configured to transmit electromagnetic signals into the earth formation using a fractal-shaped antenna and receive return electromagnetic signals from the earth formation using the same or another fractal-shaped antenna. The fractal-shaped antenna increases the efficiency of the antenna for a given amount of area or volume that is constrained by the physical dimensions of the borehole. The increased efficiency enables the downhole tool to probe deeper into the earth formation than would be possible using a conventional antenna. Further, the fractal-shaped antenna may be designed to have a plurality of non-harmonic resonant frequencies, as demonstrated by modeling using numerical tools, to enable probing various regions of the formation under different conditions requiring different probing frequencies.
The downhole tool 10 may be configured to measure the resistivity, or its inverse conductivity, or a dielectric constant of the formation 4. Resistivity measurements involve a first energy interface device 12 transmitting electromagnetic or electrical energy of a certain frequency (generally from about 100 kHz to about 10 MHz) into the formation 4. The electromagnetic energy relates to electromagnetic waves or signals while the electrical energy relates to electrical current, which may be galvanic or displacement. Galvanic current relates to galvanic coupling where electrons flow directly from the first energy interface device 12 into the formation 4 (or subsurface material of interest) while displacement current relates to current flowing due to capacitive coupling. In embodiments where the transmitted energy is electromagnetic energy, the first energy interface device is an antenna, which may be referred to as the first antenna 12. In embodiments where the transmitted energy is electrical energy, the first energy interface device 12 is one or more electrodes. The transmitted electromagnetic or electrical energy induces circulating electric currents in the formation 4. The transmitted electrical energy causes electrical current to flow in the formation 4. The circulating currents or other currents in turn emit return energy or signals that are received by a second energy interface device 13. In embodiments where the return energy or signals are electromagnetic, the second energy interface device 13 is an antenna, which may be referred to as the second antenna 13. In one or more embodiments, one antenna is used for both transmitting and receiving electromagnetic signals (i.e., the first antenna 12 and the second antenna 13 are the same antenna). In embodiments where the return energy signals are electrical, the second energy interface device 13 is one or more electrodes. Return electrical signals may be measured as a voltage difference between one electrode and a reference voltage, such as a tool body potential, or between two or more electrodes.
It can be appreciated that lower formation resistivity will induce higher circulating currents or other currents in the formation 4. Hence, the magnitude of the return electromagnetic or electrical signals is related to the magnitude of the resistivity or conductivity of the formation 4. In one or more embodiments, changes in the measured resistivity or conductivity with depth are displayed or plotted as an image. The image may be in an azimuthal or radial direction from the borehole or it may be a 360 degree circumferential image around the borehole.
As illustrated in
The downhole tool 10 may be configured to measure the dielectric constant (also referred to as dielectric permittivity) of the formation 4. These types of measurements, in one or more embodiments, involve transmitting electromagnetic energy that propagates through the formation 4 using the first antenna 12 and is received using the second antenna 13. In these embodiments, the received electromagnetic energy may also be referred to as return electromagnetic energy. The frequency of the transmitted electromagnetic energy is generally higher than the frequency used for resistivity logging and is generally from about 20 MHz and into the GHz range. Measurements of the propagation electromagnetic signals in order to determine the dielectric permittivity include signal attenuation and signal phase-shift. Using these measurements in addition to the conductivity and magnetic permeability of the formation, the dielectric constant may be determined using Maxwell's equations as known in the art. In addition, porosity of the formation may be determined using measurements of the signal propagation time using equations known in the art knowing that the propagation time in a formation that is a water filled matrix is substantially higher than that in a hydrocarbon filled matrix. These types of measurements may also be performed using one fractal-shaped antenna in conjunction with one or more electrodes.
It can be appreciated that signal attenuation and phase-shift measurements may be performed by comparing the received electromagnetic signals to a reference signal, which may be generated by a processor. In one or more embodiments, the reference signal may be the transmitted electromagnetic signal or electrical signal transmitted to the first antenna 12 by the transmitter.
Reference may now be had to
In one or more embodiments, the first antenna 12 and/or second antenna 13 may be disposed in a recess 30 in the tool body 16 as illustrated in the cross-sectional view of a section of the tool body 16 in
In one or more embodiments, the first antenna 12 and/or the second antenna 13 is disposed circumferentially for 360 degrees about a longitudinal axis of the downhole tool 10 either on the outer surface of the tool body 16 as illustrated in
In one or more embodiments for resistivity or dielectric logging, the first antenna 12 and/or the second antenna 13 may disposed on a pad 50 as illustrated in
In one or more embodiments, the antenna 12 and/or the antenna 13 may have a plurality of connections 20 as illustrated in
It can be appreciated that the downhole tool 10 may be calibrated for the various formation properties of interest that may be determined by the tool 10 by analysis, field calibration, and/or laboratory calibration. Calibration by analysis involves using known software packages for modeling antennas and propagation of electromagnetic signals through materials having the various electrical properties of interest. Field calibration involves calibrating the downhole tool 10 in one or more formations having known electrical properties. Laboratory calibration involves calibrating the downhole tool 10 in a laboratory using reference materials having known electrical properties of interest to simulate various formation electrical properties. Any of these methods may be used to calibrate the tool 10 such that the tool 10 will output an accurate value of a measured property of interest when the tool probes the formation having that value. Calibration values may be stored in a look-up table that a processor may reference a received signal to in order to estimate the property of interest.
It can be appreciated that in one or more embodiments the first antenna 12 may be a conventional antenna (e.g., a coil) operated in conjunction with a fractal-shaped second antenna 13 or the first antenna 12 may be fractal-shaped and operated in conjunction with a conventional second antenna 13. Alternatively, both the first antenna 12 and the second antenna 13 may be fractal-shaped antennas as described above. In one or more embodiments, the transmitting energy interface device (i.e., the first energy interface device 12) is one or more electrodes while the receiving energy interface device (i.e., the second energy interface device 13) is a fractal-shaped antenna. Alternatively, in one or more embodiments, the transmitting energy interface device is a fractal-shaped antenna while the receiving energy interface device is one or more electrodes. In general, an electrode may be in electrical contact with the borehole wall or subsurface material of interest for galvanic coupling when electrons can flow from the electrode to the subsurface material of interest or for capacitive coupling with a nonconductive material of interest for displacement current flow. In one or more embodiments, the one or more electrodes 70 used for the first energy interface device 12 or the second energy interface device 13 are disposed on the extendable pad 50 as illustrated in
It can be appreciated that the fractal-shaped antenna may be used in other applications in a borehole. In one or more embodiments, the fractal-shaped antenna is used to enable wireless communications between two or more downhole tools disposed in a bottomhole assembly (BHA), between downhole tools disposed in different drill pipes in a drill string, or between permanent downhole valves, sensors, or processing systems. An example of a BHA is the downhole tool and drill bit assembly shown
In downhole communication embodiments, each fractal-shaped antenna may be coupled to a transmitter, a receiver, or a transceiver, which combines the functions of the transmitter and receiver in one unit, depending on the desired communication function. For example, a downhole tool configured to sense a property may only be required to transmit measurement data to the downhole electronics. In this case, the sensor will only need to be coupled to a transmitter and the downhole electronics will only need to be coupled to a receiver although each may be coupled to a transceiver for standardization purposes. Further, the transmitter, receiver, or transceiver may include an interface for converting signals into or from a format required for communication. The interface may include a digital-to-analog converter (DAC) or an analog-to-digital converter (ADC) for communicating signals to or from a digital communication format. Alternatively, signals may be communicated in an analog format (e.g., AM or FM) and may require an interface to convert from one analog format to another analog format.
The fractal-shaped antennas for communication may be configured as the fractal-shaped antennas are for transmitting electromagnetic energy into and receiving electromagnetic energy from subsurface materials as discussed above (e.g., transmission direction and sensitivity direction directed outward from tool or having an outward vector component) for signal transmission through the drilling fluid in the annulus and/or the formation. Alternatively, the fractal-shaped antenna for communication may have a transmission direction and sensitivity direction directed inward into the tool (or have an inward vector component) for signal transmission through the drilling fluid internal to the drill string. The above embodiments may be particularly useful when communicating between drill pipes. When downhole tools are in the same housing or BHA, then the fractal-shaped antennas may be directed towards each other.
In support of the teachings herein, various analysis components may be used, including a digital and/or an analog system. For example, the downhole electronics 9, the computer processing system 11, the transmitter 14, the receiver 15, or the switching network 61 may include digital and/or analog systems. The system may have components such as a processor, storage media, memory, input, output, communications link (wired, wireless, pulsed mud, optical or other), user interfaces, software programs, signal processors (digital or analog) and other such components (such as resistors, capacitors, inductors and others) to provide for operation and analyses of the apparatus and methods disclosed herein in any of several manners well-appreciated in the art. It is considered that these teachings may be, but need not be, implemented in conjunction with a set of computer executable instructions stored on a non-transitory computer readable medium, including memory (ROMs, RAMs), optical (CD-ROMs), or magnetic (disks, hard drives), or any other type that when executed causes a computer to implement the method of the present invention. These instructions may provide for equipment operation, control, data collection and analysis and other functions deemed relevant by a system designer, owner, user or other such personnel, in addition to the functions described in this disclosure.
Further, various other components may be included and called upon for providing for aspects of the teachings herein. For example, a power supply (e.g., at least one of a generator, a remote supply and a battery), cooling component, heating component, magnet, electromagnet, sensor, electrode, transmitter, receiver, transceiver, antenna, controller, optical unit, electrical unit or electromechanical unit may be included in support of the various aspects discussed herein or in support of other functions beyond this disclosure.
The term “carrier” as used herein means any device, device component, combination of devices, media and/or member that may be used to convey, house, support or otherwise facilitate the use of another device, device component, combination of devices, media and/or member. Other exemplary non-limiting carriers include drill strings of the coiled tube type, of the jointed pipe type and any combination or portion thereof. Other carrier examples include casing pipes, wirelines, wireline sondes, slickline sondes, drop shots, bottom-hole-assemblies, drill string inserts, modules, internal housings and substrate portions thereof.
Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” are intended to be inclusive such that there may be additional elements other than the elements listed. The conjunction “or” when used with a list of at least two terms is intended to mean any term or combination of terms. The terms “first” and “second” do not denote a particular order, but are used to distinguish different elements.
While one or more embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.
It will be recognized that the various components or technologies may provide certain necessary or beneficial functionality or features. Accordingly, these functions and features as may be needed in support of the appended claims and variations thereof, are recognized as being inherently included as a part of the teachings herein and a part of the invention disclosed.
While the invention has been described with reference to exemplary embodiments, it will be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications will be appreciated to adapt a particular instrument, situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
