JP2724178B2 - Nuclear magnetic logging - Google Patents

Description

The present invention relates to an apparatus used in a well, particularly to a nuclear magnetic logging apparatus used in an underground well.

The most accurate and easy-to-use well logging device for measuring saturation and permeability of residual oil in the formation is the Nuclear Magnetic Logger (NM
L). In this logging device, a magnetic field generated from a solenoid coil is used to polarize protons in a fluid contained in a formation adjacent to the logging device. Next, the solenoid coil is turned off. At this time, the movable protons affected by the magnetic field of the solenoid coil precess around the geomagnetic field at each Larmor frequency. This precession is measured as a damped sinusoidal voltage induced in another sensing coil of the logging instrument. The induced voltage decays rapidly, typically on the order of 20-50 milliseconds. The reason is that these fluids spin - spin or transverse direction (Transverse) relaxation time T ₂ * is for extremely short.

The initial amplitude of the nuclear magnetic signal is proportional to the "free fluid", or productive fluid, in the formation adjacent to the well. Drilling mud
When Mn-EDTA is added and introduced into the formation, only the residual nuclear magnetic signal is obtained from any oil phase in the formation adjacent to the well. Therefore, NML log-inject-log (log-in
The ject-log) procedure provides a very accurate measurement of residual oil saturation in the formation.

Spin-lattice time of the fluid in the formation
Itudinal) relaxation time T ₁ is associated with (one or more) pore size of the fluid has invaded (and pore distribution). The size and distribution of these pores is related to a capillary pressure curve, which in a known manner is related to the permeability of the formation.

NML is a method for measuring T ₁ by repeating the polarization cycle sequentially extended polarization time. T ₁ is so much longer than the sine decay time T ₂ *, just can not be determined directly T ₁ from the sinusoidal decay curve by one measurement.

NML logging is extremely useful but has some drawbacks. One of the major disadvantages of NML is that the signal-to-noise ratio is poor and the accuracy during continuous logging operations is limited to the order of magnitude of porosity. This accuracy is sufficient for measuring the free fluid index. However, because residual oil saturation is typically less than one-third of the total porosity, NML is required to measure residual oil saturation with the accuracy required to achieve high oil recovery.
Must be used in a stationary state. Typically, data is collected at one well location for approximately 15 minutes to reduce residual oil saturation to 1
The data is averaged to obtain at least% accuracy.
However, if the logging device is kept stationary for such a long time, it takes time to collect the data of the whole formation, and the logging device may stick to the well.

Another disadvantage of NML is that the depth of exploration in the formation is shallow. Also, due to the poor signal-to-noise ratio, only signals from a few centimeters above the wellbore wall can be detected.

A further disadvantage is that it requires the repetition of polarization cycles in order to obtain a plurality of discontinuous measurements of T ₁ decay curve. Therefore, the time required for measurement is further extended. Also an extremely inaccurate shape of T ₁ decay curve since only a small number of measurements can not be obtained, the T ₁ decay curve will contain incorrect information about the size and distribution of the pores in the formation (hence The capillary pressure or permeability determined on this basis is also inaccurate). This is a serious drawback of NML logging.

Improvements have been proposed for using superconducting quantum interference devices (SQUIDs) as detectors in prior art nuclear magnetic logging instruments. In this proposal, the logging device was modified to use two opposing superconducting magnets in place of conventional polarization solenoids to increase the depth of search in the wellbore. However, the use of SQUIDs as underground log detectors has not yet been put to practical use. The reason is cryogenic and safety issues when using liquid helium in a well environment. More specifically, there is one problem that liquid helium cannot be safely vented downhole because it expands more than 600 times by evaporation. Further, there is a problem that it is difficult to provide an appropriate underground operation time in a high temperature environment in the underground. These problems have hampered the use of SQUIDs as detectors in nuclear magnetic logging instruments.

However, the present invention overcomes the above-mentioned limitations and disadvantages of the prior art and provides a nuclear magnetic logging device with a detector capable of detecting a sinusoidal magnetic field and a slowly varying magnetic field of an underground well.

SUMMARY OF THE INVENTION The present invention measures the nuclear magnetic response of a formation using one or more detectors that can detect simultaneously a sinusoidal magnetic field and a slowly varying magnetic field resulting from the precession of a movable nucleus around the geomagnetic field. A logging device is provided.

Means for generating a magnetic field that can be excited or degaussed in response to a preselected control signal; detecting sinusoidal and slowly fluctuating changes in the magnetic field when said magnetic field generating means is demagnetized Detector means for outputting a signal indicating the change; and an electronic element package for generating the preselected control signal and receiving a signal from the detector means.

Preferably, the detector of the apparatus of the present invention is a high temperature superconducting quantum interference device (SQUID). Alternatively, one or more laser-pumped helium magnetometers may be used as detectors. In a preferred embodiment of the device according to the invention, a micro Joule-Thomson cooler or a thermoelectrically cooled Peltier module is used. These are integrated on the same wafer as the SQUID to keep any high-temperature SQUID below its superconducting transition temperature. Further, the SQUID (s) may be flux-coupled to an axial gradiometer configuration to minimize motion-induced magnetic field noise.

According to a preferred embodiment of the device of the present invention, there is provided a means of using a SQUID sensor in a nuclear magnetic log recorder without any need for cryogenic liquid cooling. Non-limiting examples of such as rare earth - barium - copper oxide material, for example yttrium - barium - such as copper oxide _{(YBa 2 Cu 3 O 7)} , one of the high-temperature superconducting materials that exhibit superconducting at temperatures above 90K or more SQ
Manufacture UID. SQUID is deposited by epitaxial growth on a substrate with high thermal conductivity, such as SrTiO ₃ or MgO. The wafer substrate is then cooled to about 80K and bonded to the cooling stage of a micro Joule-Thomson cooler (or Peltier module for higher temperature superconducting materials). SQUI
D and the wafer are surrounded and insulated by a vacuum casing of non-metallic structure such as G-10 fiber glass to reduce heat load and keep the cooling stage of the cooler below the superconducting transition temperature of the SQUID material.

SQUID detector and laser pump type helium magnetometer are D
Responding to all frequencies up to C, the response of the resonant coil detector used in current NMLs according to the prior art is limited to a narrow frequency range, with zero response at DC. Thus, SQUID detector and laser-pumped helium magnetometer may be measured substantially simultaneously and directly the attenuation of both the T ₂ * and T ₁ of a single NML logging instrument in a single measurement.

In addition to the SQUID element, the SQUID electronic element may be heat-exchangeably fixed to the cooling stage of the cooler. This reduces noise and further improves performance.

One or more SQUID detectors may be flux coupled to the superconducting sensing coil of the axially hierarchical measurement structure. The coil may also be manufactured from a high temperature superconducting material and may be heat exchange fixed to the cooling stage of the cooler. The function of the detection loop is to increase the magnetic flux sensitivity of the detector. The axial hierarchical measurement structure is a preferred structure for reducing magnetic flux noise caused by the movement of a well-located well in a geomagnetic field. In this configuration, one loop of the hierarchical measuring coil is centered inside the polarizing coil, and a second, counter-wound loop extends outside the polarizing coil. Thus, the inner loop detects all signals from polarized protons in the formation and the outer loop does not substantially detect proton signals. A uniform magnetic field, such as a geomagnetic field, produces an equal and opposite magnetic flux in each loop, thus effectively canceling the geomagnetic field. Similarly, a laser-pumped helium magnetometer can be used as a differential pair, one fixed inside the polarization coil and the other outside the polarization coil.

Thus, according to a preferred embodiment of the present invention, there is provided a SQUID detection module that can be used in a wellbore logging vessel that does not require cryogenic liquid, which improves the signal-to-noise ratio of nuclear magnetic logging,
It is possible to direct measurement of T ₁ decay curve of the formation.

That is, an object of the present invention is to provide a nuclear magnetic logging apparatus in which the signal-to-noise ratio is improved by several orders of magnitude compared to the current NML according to the prior art.

Another object of the present invention is to provide a NML device capable of measuring the total T ₁ decay curve of the formation directly without requiring a continuous plurality of polarization cycles.

The above and other advantages and objects of the present invention will be apparent from the following detailed description with reference to the accompanying drawings.

FIG. 1 shows a well 10 drilled in a formation 20 and a nuclear magnetic log 11 placed in the well by a cable 9. The logarithm 11 contains a solenoid coil 12, which generates a polarizing magnetic field vector 13 in the formation adjacent to the logarithm. The geomagnetic field (He) 14 is the magnetization vector (M
o) Form an angle θ with 15. When the polarization field is switched off, the proton spin 15 precesses around the geomagnetic field 14 as shown. If the detector is a resonant coil 17 tuned to the Larmor frequency, it will detect the precessing proton spin Mo. The measurement package 19 supplies power of about 1 Kw to the polarization coil 12 and detects a voltage induced in the resonance coil 17 by the precessing spin 15.

FIG. 2 shows a typical signal 16 expected to be detected in a resonant coil 17 by a precessing proton spin 15.
Signal is sinusoidally decaying at the Larmor frequency at a much shorter time constant T ₂ * than T _1. T ₂ * indicates the time constant of the sine signal envelope attenuation. The Larmor frequency of precession is
γ × He [where γ for protons is 4.26 kHz / g]. T
Since ₁ attenuation is large gap between the tuning Larmor frequency 2000Hz for is resonant coil of the order of 1 second should be noted that the attenuation of T ₁ is not observed. Figure 2 also shows the measurement delay, which will be described later, shows an extension of the signal envelope back to the point t ₀ indicating a porosity φF of the logging instrument occupied free fluid in the adjacent formation (in phantom).

In the laboratory, the SQUID detector was found to be more advantageous for detecting NMR signals than the conventional resonant coil. SQUID
Detects the magnetic field (more precisely, the total magnetic flux) that connects the detection loop, whereas conventional NMR coils detect the voltage (flux change rate) induced in the loop. Therefore, SQUID is D
Responding to all frequencies up to C (ie, having a very wide frequency response), the response of the resonant coil is limited to a narrow frequency range (defined by the Q of the coil), with zero response at DC. The superiority of the SQUID compared to the resonant coil when used as a detector is when the NMR frequency is low, when the spin photon relaxation time T ₁ is long, and when the transverse relaxation time T ₂ *
Is maximized when is short. In addition, other non-SQs that can measure DC or near DC and have a wide frequency response
UID type detector, for example, laser-pumped helium magnetometer also can be used as a detector for the detection of both T ₁ attenuation that varies T ₂ * sine attenuation and slow.

When performing downhole nuclear magnetic logging of the formation, the state of time T ₁ is longer T ₂ * time short occurs in reality. Primarily,
The Larmor frequency of the proton in the geomagnetic field is about 2000 Hz, which is 10-500 MHZ used in laboratory NMR spectrometers.
Extremely low compared to z. Second, the T ₁ relaxation time of the local layer is fairly long and typically about 1.0 second, T ₂ * relaxation times are short typically about 20 to 50 milliseconds. Since such a high T ₁ / T ₂ * ratio when the downhole nuclear magnetic logging is observed, advantageously detector having a wide frequency response of the SQUID, or similar high sensitivity as compared with the conventional resonance coil detector The conclusion is that there is.

The method of comparing the signal-to-noise (S / N) ratio of the SQUID detector and the resonant coil detector and measuring the degree of improvement is described in R.
A. Webb's paper `` New Technique For Improved Low-Temp
erature SQUID NMR Measure-ments ”, (Rev. Sci. Inst
rum., Vol. 48, No. 12, pp. 1585-1594, December 1977).

Typical experimental values are used for the SQUID noise figure, coil Q, and the like.

Using typical values in the formation T ₁ = 100 ms, T ₂ * = 20 ms, ω ₀ = 2 * π * (2 × 10 ³ ) = 1.26 × 10 ⁴ , the S / N of the SQUID is It is more than 139 times the S / N of the coil.

In the case of NML logging, S compared to the resonant coil detector
The S / N improvement of the QUID detector is even greater. The reason is,
This is because the conventional NML has a dead time of about 25 ms after the polarization magnetic field is switched off. This measurement delay or dead time is due to the coupling and calling between the polarizing coil and its circuit and between the detection coil and its circuit. This delay is shown in FIG. Since the delay or dead time is a significant portion of the T ₂ * decay majority of the signal is attenuated before the start of recording NML. For example, when T ₂ * is 25 ms and the NML immobility time is 25 ms, 1 / e of the signal attenuates before detection starts.

SQUID and similar detectors do not have this problem. Unlike at the Larmor frequency as fast lateral phase shift resonant coil is not only sensitive to the sensitive and DC to the nuclear spin (T ₂ *), SQUID, or similar detector measures the z component of the magnetization at a frequency to DC. Thus, instrument dead times on the order of 25 milliseconds do not significantly reduce the signal level of a SQUID or similar detector. Examples of similar detectors above are non-SQUID detectors that can measure DC or near DC,
For example, a laser pump type helium magnetometer is used. Such a magnetometer can also be used both the T ₁ attenuation that varies T ₂ * sine attenuation and slow as detector for detecting substantially simultaneously.

In general, optical pump magnetometers use a lamp or laser containing alkali metal or helium, the light of which passes through a cell containing vapor of the same element and impinges on a photodetector on the other side of the vapor cell. Optical pump magnetometers utilize this electron population in alkali vapor gas or metastable helium to continuously measure the strength of the magnetic field. The output of the photodetector is amplified and provided to a coil surrounding the vapor cell. This electro-optical system is an oscillator having a frequency that is directly proportional to the strength of the magnetic field. Magnetometers use optical pumping to produce atomic or electron spin precession, much like NML produced proton precession. Resonant absorption and re-radiation of the energy of various or specific resonance lines is a function of the strength of the magnetic field.

Another important advantage of the SQUID or similar detector used in nuclear magnetic logging downhole is to be able to directly measure T ₁ decay curve. T ₁ required for measuring pore size and permeability
There is no need to repeat the polarization cycle to obtain a decay curve. Since T ₁ is typically on the order of one second, direct measurement of the T ₁ decay curve requires that the detector respond with a VLF (Very Long Wave) of 1 Hz or less. Thus, SQUID, or similar detector must be sensitive to both the lateral phase shift and thermal relaxation T ₁ of the spin. Since T ₁ is typically 50 times T _{2 in} the formation, a SQUID or similar detector may detect a signal even with a longer spin lattice relaxation time T ₁ .

FIG. 3 shows the resonance coil 17 of FIG.
Shows a typical form of a signal that is expected to be detected when substituting with. This signal has a time constant T ₂ * proportional to Mo Sin ² θ
A sine component of the Larmor frequency to attenuate in, Mo Cos ²
consisting of a non-sinusoidal signal component attenuated by constant T ₁ time proportional to theta. The sine component T ² * decay is due to the component of the polarized nuclear spin perpendicular to the geomagnetic field He, and the T ₁ component is due to the nuclear spin component aligned parallel to the geomagnetic field He. The Larmor frequency sine T ₂ *, using a low-pass filter made of electronic elements, using an eddy current container made of copper as a shield around the sensing coil, or using a digital filter that acts on the recorded data in real time or by post-processing software. Damping
It may be separated from the T ₁ attenuation near DC. Although longer T ₁ decay can not be measured in coil 17, SQUID18 sine T ₂ * decay and T ₁
Both the decay and the decay are measured substantially simultaneously. Also, the sine T ₂
* Decay and both the T ₁ attenuation that varies slowly as a detector to detect substantially simultaneously, unmeasured is another possible such DC or near-DC laser-pumped helium magnetometer SQUI
D-type detectors may be used.

FIG. 4A shows the SQUID detector 20 and the cooling module 21 on the substrate 30. The cooling module is preferably a micro Joule-Thomson cooler. In Fig. 4A, one SQUI
Although only the D detector 20 is shown, more than one such SQUID detector can be provided on the substrate 30.
The substrate 30 itself is used as a cooling stage of a Joule-Thomson cooler. Therefore, good heat exchange contact is made between the SQUID and the cooling stage. SQU with SQUID at the lowest possible temperature
Such heat exchange contacts are needed to optimize the noise figure of the ID. The SQUID is manufactured on the substrate as close as possible to the Joule-Thomson heat source to ensure the maximum possible cooling. The SQUID may be either an RF bias type or a DC bias type, but only the DC bias type will be described here. SQUID is manufactured from a high temperature superconducting material, such as a rare earth-barium-copper oxide material. But this is SQUI
It is only a non-limiting example of a D material. As used herein, the term "high temperature superconducting material" refers to the boiling point of liquid nitrogen (i.e., ~ 77).
K) means a material with a higher superconducting transition temperature.

According to FIG. 4B, the DC SQUID is made of YBa ₂ Cu ₃ O
₇ consists of two granular weak bonds formed by epitaxially growing a rare earth-barium-copper oxide material. The granular weak bond is about 15μ long and 1μ thick and is defined by insulating gaps 47,48. Weak bonds are actually described between weakly Josephson-bonded semiconductor particles and are therefore described by the term "granular". If the weak coupling is too narrow (<< 15μ), the current around the central insulation 46 will be too high and will quench the superconducting material, thus reducing the SQUI.
D does not work. The portion 46 of FIG. 4B is square, but other geometries may be used. Also, when the weak coupling is too wide, excessive current will flow, resulting in a "hierarchical" operating characteristic of the SQUID. Therefore SQUID does not work properly.

In the text, YBa ₂ Cu ₃ O ₇
Was described. However, any high temperature superconducting material having an oxygen deficient perovskite structure can be used. YB
When a ₂ Cu ₃ O ₇ is used, the substrate must have the same molecular structure as YBa ₂ Cu ₃ O _{7 in} order to perform epitaxial growth. The substrate must have a molecular structure similar to that of the material), and the substrate must be a good conductor of heat at a temperature near liquid nitrogen in order to achieve good heat exchange with the cooling module 21. A non-limiting example of such a substrate is SrTiO ₃ or MgO. For example, the “a” lattice constant of SrTiO ₃ is 3.9 ° and the corresponding lattice constant of YBa ₂ Cu ₃ O ₇ is 3.83 °. Y
Epitaxial growth of oriented crystals is important to obtain the maximum critical magnetic field and current possible in Ba ₂ Cu ₃ O ₇ superconductors. Preferably, the SQUID remains superconducting during the polarization cycle (when subjected to magnetic fields above 1 kilogauss). Preferably, the SQUID has a critical magnetic field strength greater than any expected polarization field.

Epitaxial growth of SQUID material on SrTiO ₃ substrate
It is performed by various techniques known to those skilled in the art, such as molecular beam epitaxy, electron beam evaporation, sputtering from single and multiple targets, ablation of a single target with a pulsed excimer laser, sol-gel, plasma oxidation. For example, when using molecular beam epitaxy, a thin layer (〜20 μ) of Y—Ba—Cu is first deposited on a SrTiO ₃ substrate with accurate stoichiometry and then oxidized to YBa ₂ Cu ₃ O ₇ . Next, a thin layer of gold is deposited on the YBa ₂ Cu ₃ O ₇ layer.
Finally, a photoresist layer is placed on the gold layer, and the pattern is drawn according to the design drawing by photolithography. Next, ion milling is performed on the photoresist and gold inside the SQUID design drawing. That is, the resist and the gold covering the central portion 46 and the gaps 47 and 48 in FIG. 4B are removed. Thus, gold and resist remain in those portions of the layer that are designed to maintain superconductivity.
Next, the portion designed to maintain superconductivity is protected by gold, and the exposed YBa ₂ Cu ₃ O of the central portion 46 and the gaps 47, 48 using a 0.3 to 3 MeV oxygen ion beam. Oxygen is implanted into ₇ to make them insulator regions. Finally, the remaining gold is removed by ion milling to form a complete planar structure.

A plurality of SQUID sensors may be formed on a substrate in the manner described above. The advantage of multiple sensors is that adding the SQUID output further improves the signal to noise ratio because the SQUID noise of each sensor is random and uncorrelated.

Microcoolers work by Joule-Thomson expansion of a working gas, such as nitrogen. Since there is no cryogenic fluid or moving parts, there is very little vibration and therefore little noise. Micro Joule-Thomson coolers are commercially available, e.g., MMR Technologies, Inc., Mountain Vie.
w, there is a California System I cooler. However, these MMR Technologies coolers are made from glass or silicon and cannot be used as epitaxial substrates for YBa ₂ Cu ₃ O ₇ SQUID. As shown in FIG. 4A, the micro Joule-Thomson cooler 40 is comprised of three main parts: an exchanger 41, an expanding capillary 42, and a liquid reservoir 43. Cooler is SrTi by optical processing technology
It may be manufactured from an O ₃ wafer 30. When the optical processing technique is used, for example, a mask for a cooler portion as shown in FIG. 4A is first manufactured. Next, a viscous aqueous solution of gelatin activated with ammonium bichromate is applied to the wafer 30.
The solution applied to the wafer 30 is dried, covered with a mask, irradiated with ultraviolet light through openings in the mask, and developed in warm water. After drying, this resist forms a tough elastic film that is resistant to abrasive etching with powdered Al ₂ O ₃ . Unirradiated gelatin is washed away with warm water, leaving an unprotected SrTiO ₃ pattern.

Abrasive etching is performed on a wafer partially coated with resist, with Al ₂ O ₃ having sufficient hardness in a particle size range of 10 to 30 μm.
Alternatively, it is performed by injecting another powder. This spray sweeps the entire surface of the wafer. As a result, trenches having substantially vertical sidewalls with a precisely adjusted depth in the range of 2-100 microns are etched into the wafer 30. The remaining resist is removed by a chemical solution of gelatin.

To complete the cooler portion, the cover plate is bonded to the etched wafer using various adhesives available such as low temperature epoxy. Some care must be taken to prevent the adhesive from flowing into the micron-sized grooves.

The cooler working gas is contained in a pressurized tank, typically at 140 bar pressure, and expands in a Joule-Thomson cooler into a larger, lower pressure collection tank (not shown) inside the well. . The collection tank is several times larger (typically at least 10 times) as large as the pressurized tank, so that the expanded gas does not reach high pressure so that the cooling function is not reduced. The operating time of the cooler is 140 bar nitrogen gas 1
Typically about 12 hours. Alternatively, a closed gas cycle compressor can be used, but such moving members cause vibration and reduce the signal-to-noise ratio (S / N). When the SQUID is manufactured from a material having a superconducting transition temperature higher than 180 K, a Peltier module can be used as the cooling module 21. The reason is that current Peltier modules have a cooling temperature of about 180K.

The cooler cooling stage and the SQUID are surrounded by a vacuum vessel (not shown). The vacuum vessel provides the necessary vacuum space to reduce heat leakage into the cooling stage and the SQUID sensor. The vacuum vessel may be composed of any non-metallic and non-magnetic material that has a low thermal conductivity at the temperature of liquid nitrogen. SQUID
A super-insulating flake (for example, aluminized mylar) may be added inside the vacuum space to improve the heat insulation of the device. However, the super-insulating flakes need to be cut vertically to reduce eddy currents inside the super-insulation.

FIG. 5 shows an axial hierarchical measuring coil used in the practice of the present invention. The function of these coils is to improve the magnetic flux sensitivity and reduce magnetic noise due to the movement of the logging instrument in the geomagnetic field. The sensing coils 51, 52 are coaxial and counter-wound so that the uniform magnetic field in the coils is accurately canceled.
One sensing coil 51 is centered inside the polarizing coil 12 and the other coil 52 is located substantially outside the polarizing coil. A sensing coil 51 centered inside the polarizing coil 12 detects a maximum signal from the formation 20, and a sensing coil 52 outside the polarizing coil detects substantially no signal from the formation. These coils may be flux coupled to one or more SQUIDs, or each SQUID may have its own coil group.

However, the SQUID itself may function as a magnetic flux sensor in the logging device, and the logging device may be fixed to the wellbore wall to suppress vibration. When using a flux-coupled coil, the SQUID sensor is shielded from the magnetic field by a superconducting shield of YBa ₂ Cu ₃ O ₇ surrounding the SQUID. The superconducting lead reaching the coil is inserted through a small opening in the superconducting shield.

The hierarchical measurement coil may be an epitaxial thin film deposited on a SrTiO ₃ substrate in a manner similar to SQUID fabrication. Or
The coil may be manufactured from a plurality of short superconducting YBa ₂ Cu ₃ O ₇ wires. This wire can be manufactured from a gold or silver tube packed with a compacted powder of YBa ₂ Cu ₃ O ₇ . The tube is sealed, swaged to a small diameter, reheated to 900 ° C or higher, and slowly cooled (~ 20 hours). The wire produced in this way has no maximum achievable critical current, but 1000 A / cm at zero magnetic field
^It can have values above 200 A / cm ² above ² and 1000 Gauss.

Similarly, a detector consisting of a laser-pumped helium magnetometer is used in pairs, one magnetometer being located inside the polarization coil and the other magnetometer being located outside the polarization coil. These two magnetometers are also differentially combined to reject signals arising from motion in the earth's magnetic field.

Although a DC granular weakly coupled thin film SQUID has been described above, other types of SQUIDs can be manufactured in accordance with the teachings of the present invention. Examples include tunnel junction SQUIDs (superconductor-insulator-superconductor, superconductor-standard metal-superconductor and superconductor-semiconductor-superconductor), thin film weak couplings such as Dayem and Grime's There are various hybrid combinations of bonding, point contact SQUID and thin film and point contact SQUID. Similarly, S
QUID may be single-junction RF biased or double-junction DC SQU
It may be an ID.

FIG. 6 is a block diagram of the electronic components required to make the DC SQUID 620 known in the art differentiate. The electronic device comprises a bias current source 610, amplification means 600, 601, 602, modulation means 603, 604, 605, feedback means 607, 608, filter means 606, monitor means 609, and zero offset 612. Now, DC SQUIDs operate in feedback mode and SQUID as selected by bias current.
SQUID at the apex of the sharp current-voltage operating characteristic curve
Is preferably maintained. Modulation and feedback occur at any frequency such that the electronic element can track any change in the magnetic field of the log. FIG. 6 shows a 100 kHz modulation oscillator 604.

More specifically, the detected signal is magnetically coupled to the SQUID 620 via the input coil 621. When the SQUID 620 is itself a detector, the input coil 621 is not present and the detected magnetic flux is the magnetic flux passing through the insulated central portion of the SQUID (eg, portion 46 in FIG. 4B). The SQUID is modulated by the modulation and feedback coil 622 by the modulation oscillator 622 at a frequency sufficient to allow the electronic element to track any changes in the magnetic field. This frequency is preferably 100 kHz. A phase shifter 603 is connected to the oscillator. SQUID moves the selected operating point (selected by the bias current) vertically up and down along a stepped operating characteristic curve when sensing a change in the magnetic field. The amplification means 600,601,602 amplify this change,
This is filtered by the filter means 606 and unmodulated feedback is provided to the SQUID 620 via the feedback means 607, 608 and the modulation and feedback coil 622. In particular, the amplification means includes an amplifier 600 having an amplification factor of × 100 and an amplification factor of × 10
A tuned amplifier 601 having a quality of Q〜3 at 0 and an amplification factor of × 0
And 300 broadband amplifiers 602. Broadband amplifier 602 is connected to amplifier 611. More specifically, filter means 6
Note that 06 includes 100 and 200 kHz traps. Feedback maintains the SQUID at the selected operating point. The amount and type of feedback is detected by monitor means buffer amplifier 609 and provided as an output indicating the magnetic field change sensed by the SQUID.

It will be appreciated by those skilled in the art that many modifications and variations are possible within the scope of the present invention with respect to the devices and descriptions described herein. Accordingly, it will be apparent that the devices and methods illustrated in the accompanying drawings and described herein are non-limiting descriptions and the scope of the invention is not limited to these descriptions.

[Brief description of the drawings]

FIG. 1 is a schematic illustration of a nuclear magnetic logging device showing a nuclear magnetic logging device with an associated magnetic field vector and the relationship between the magnetic field vector and the geomagnetic field, and FIG. 2 uses a resonant coil tuned to the Larmor frequency. Fig. 3 shows a typical NML signal detected, Fig. 3 shows a typical NML signal detected using a SQUID as a detector instead of a resonance coil, and Fig. 4A shows an integrated NML signal on the same wafer substrate. Explanatory drawing of SQUID detector and microminiature Joule-Thomson cooler provided in Fig. 4B is SQUID
Fig. 5 shows the details of the SQUI that can be used in the present invention.
FIG. 6 is an explanatory diagram showing an axial hierarchical measurement structure of a superconducting coil flux-coupled to D. FIG. 6 is an explanatory diagram of a typical measurement electronic element for a SQUID detector. 9 ... cable, 10 ... well, 11 ... logarithm, 12 ... solenoid coil, 13 ... polarization magnetic field vector, 14 ... geomagnetic field, 15 ... proton spin, 17 ... resonance coil, 19 …… Measurement package, 20 …… Stratum.

Claims (11)

(57) [Claims] A means for generating a magnetic field which can be excited or demagnetized according to a preselected control signal; and detecting a sine change and a slowly changing change of the magnetic field when the magnetic field generating means is demagnetized. A detector means being a superconducting quantum interference device (SQUID) for outputting a signal indicating a change; an electronic element package for generating the preselected control signal and receiving a signal from the detector means; A pair of superconducting detection coils for performing flux-coupled axial hierarchical measurements, one of said coils being incorporated in the magnetic field generating means and the other being disposed outside the magnetic field generating means. vessel. 2. The SQUID detector means for maintaining the SQUID detector means at a temperature lower than the superconducting transition temperature of the superconducting material.
2. The nuclear magnetic logging device according to claim 1, further comprising cooling means for the D detector means. 3. The nuclear magnetic logging device according to claim 1, wherein said magnetic field generating means is a solenoid coil. 4. The nuclear magnetic logging device according to claim 1, wherein said SQUID uses a high-temperature superconducting material. 5. The nuclear magnetic logging device according to claim 2, wherein said cooling means uses a Joule-Thomson cooling cycle. 6. The nuclear magnetic logging device according to claim 4, wherein the high-temperature superconducting material is substantially an oxygen-deficient perovskite. 7. The high temperature superconducting material is substantially YBa ₂ Cu ₃ O ₇
The nuclear magnetic logging device according to claim 6, wherein 8. The nuclear magnetic logging device according to claim 1, further comprising a superconducting shield disposed around said SQUID. 9. The nuclear magnetic logging device according to claim 2, wherein said SQUID and said cooling means are provided adjacent to each other on a thermally conductive substrate. 10. The nuclear magnetic logging system according to claim 9, wherein said substrate is SrTiO ₃ . 11. The nuclear magnetic logging device according to claim 9, wherein said substrate is made of MgO.