JPS61277080A - Micro-induction type test apparatus for bed - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for measuring with high resolution a property or properties of borehole formations, in particular the slope of these formations. The present invention relates to a method and apparatus for measuring a property or properties of a borehole formation with high resolution to determine orientation.

Conventional Technology One of the most effective ancillary technologies in oil and gas exploration is the inclinometric record (DIPM), which provides reliable structural and stratigraphic information for exploration and development drilling programs.
Advances in inclinometer instrument design, magnetic tape recording, mechanical computerization, and analytical methods have made it possible to recognize features such as structural dips, faults, unconformities, barriers, channels, and reefs. becomes. Furthermore, the direction of sedimentation and the direction of narrowing can be inferred. When combined with data from other wells, the inclinometer information helps form an overall structural and stratigraphic image of the area being investigated.

Focused current type inclinometers have been widely adopted in the wireline logging industry, particularly for use in logging boreholes drilled with conductive drilling fluids. Focused current type inclinometers use at least three and usually four pads, each pad having one or more electrodes that radiate a focused current beam into an adjacent formation. The current flow at each current is proportional to the conductivity of the adjacent formation. A focused current type inclinometer is disclosed in U.S. Pat. No. 3,060,373 to Doll, issued October 23, 1962, February 1, 1981.
U.S. Pat. No. 4,251,773 of Cailliau et al., issued June 7, 1982; U.S. Pat.
No. 34,271. These inclinometers can achieve good vertical resolution at moderate recording speeds, and the fine resistivity sensors used in these instruments are as small as 5 mm (0.2 in.). Precision resolution can be obtained.

The large amount of data obtained by inclinometers, particularly high resolution focused current inclinometers, is advantageously exploited through the use of computers. For example, a comparison technique with a suitable computer is disclosed in U.S. Pat. No. 4,348,74 to C1avier et al., issued September 7, 1982.
No. 8, published October 19, 1982 by Chan
), U.S. Pat. No. 4,355,357. Also, U.S. Patent Application No. 3 filed on May 28, 1982
Improved slope measurements can also be obtained by other computer-implemented techniques, such as those described in 83.159.

Bond-in dated June 6, 1961
Other types of inclinometers have been proposed for use in boreholes drilled with conductive drilling fluids, including the electrical toroidal type inclinometer described in U.S. Pat. There is. None of these could popularize focused current type devices.

Unfortunately, electrical inclinometers, including focused current inclinometers, are completely unsatisfactory for use in boreholes drilled with electrically or non-conductive fluids such as oil-based muds. Met. Electrical inclinometers require a conductive medium to conduct current from the electrode system to the formation. This conductive medium is not present in boreholes drilled with air or oil based muds.

Various methods using pad-mounted electrodes have been employed to obtain slope information in wells drilled with non-conductive drilling fluids. One way is June 5, 1956
Doll's U.S. Patent No. 2,749, issued in Japan.
, No. 503, and more recently August 3, 1976.
Calvert, US Pat. No. 3,973,181, published in Japan, uses high frequency electromagnetic energy to measure the capacitive engagement of an electrode with a formation. Another method is described in The Oil and Gas Journal.
"New Dipmeter Tool Logs" published in the August 1, 1966 issue of Al), pages 124-26.
It is described in a paper by Fons titled "In Nonconductive Mud".

This method advocates the use of a single-electrode contact knife-shaped electrode to make direct contact with the formation.

Other methods for obtaining slope information in wells drilled with non-conducting drilling currents do not require any electrodes, e.g.
Grins, U.S. Pat. No. 3,376.950, dated April 9, 1968; Schwartz, U.S. Pat. No. 3, issued September 1, 1970
, 526,874, U.S. Pat. No. 3,564,91 to Des+ai et al., issued February 23, 1971.
No. 4 teaches an acoustic technique using an acoustic transducer attached to a pad. December 2, 1983
U.S. Pat. No. 4,422.043 to Nsador, published on June 0, discloses an electromagnetic logging type inclinometer.

Furthermore, techniques based on the principles of induction logging have been proposed for measuring slope by using coils mounted on a mandrel or coils mounted on a pad. In conventional induction logging, such as that disclosed in U.S. Pat. No. 2,582.314 to Doll, issued January 15, 1952, the The generated oscillating magnetic field induces electrical current in the formation around the borehole. These currents are 2
The magnetic field in turn contributes to inducing a voltage in one or more receiver coils. The voltage component of the received signal that is in phase with the transmitted current, known as the R-signal, is proportional to the conductivity of the formation.

Operating a mandrel tool in a borehole through a homogeneous medium creates a ground current loop that coincides with the primary electric field induced by the transmitter's primary magnetic field. The ground loop is therefore coaxial to the receive and transmit coils and the borehole. However, in situations where the surrounding formations are present, such as sloping beds or fractures, the average loop plane of the ground current loop changes from the consistent alignment described above. This phenomenon is exploited in mandrel-type induction inclinometers. In one early mandrel-type inclinometer, an array of coils was mechanically rotated so that the received signal changed with each period of rotation of the coil array.
I produce an amount. The modulation components include tilt, tilt orientation, and/or
or processed to obtain anisotropic indications. More recently, techniques have been proposed that utilize mechanically passive induction coil arrays to obtain measurements of slope, dip orientation, and/or anisotropy of formations. This type of system has 1 e.g.
No. 3,808,520 to Runge, issued April 30, 1974, November 24, 1981.
U.S. Patent No. 4, 30 by Mr. Moraguchi, published in Japan
No. 2,723, U.S. Pat. No. 4,36 to Sagesman, issued November 2-3, 1982.
No. 0,777.

Other induction techniques are based on properties such as conductivity, magnetic susceptibility, and inductivity.
and uses pad-mounted field generation and sensing techniques to measure the slope of geological formations. An early system was U.S. Patent No. 3,388 to Stripling, issued June 11, 1968.
, No. 323. The Stripling device has three circumferentially spaced sensors that are pressed against the wall of the borehole.

A composite magnetic field comprising a -order magnetic field and a secondary magnetic field is created and sensed by each sensor. Phase separation is applied to the sensed signal to obtain measurements of magnetic susceptibility and electrical conductivity. The sensor in Slipling's device has a coil wrapped around a core that is made of a high dielectric constant material to increase the flow of magnetic flux through the coil.

The coil is approximately 7.6 cm (3 inches) long and approximately 1.5 inches long.
With a diameter of 3 cm (half inch), the axes of these coils are tangential to a circle located in a plane perpendicular to the axis of the instrument. Separate transmit and receive coils are also contemplated. This device operates at a frequency of 60 KHz.

A pad configuration that attempts to reduce sensitivity to borehole diameter and borehole fluid conductivity is disclosed in Youmans, U.S. Pat. No. 3,539,911, issued November 10, 1970. . The pad has a pair of transmitter coils, said to be wound in series opposite each other, which are mounted within the pad at an acute angle from the longitudinal axis of the long sonde. The pad also has one receive coil, which is mounted between the transmit coils substantially parallel to the longitudinal axis. The mounting angle of the transmit coil is selected to provide what is termed the desired asymmetric probe field. The device operates at approximately 20 KHz and both in-phase and out-of-phase detection techniques are contemplated. The axial distance between the axes of the transmitting and receiving coils is said to affect the exploration mode, and mutual balance of the coil configurations is said to be achieved by adjusting that distance.

More recently, the Me
U.S. Pat. No. 4,019,126 to Ador discloses a device that attempts to avoid the temperature and pressure sensitivity of the Stripling device. The coil proposed by Mr. Om, who teaches that the sensing coil of an inductive inclinometer arm can be constructed without an extremely sensitive high permeability core, consists of two turns of 3.1 mm (one-eighth inch) diameter. of steel wire, each turn measuring approximately 1.9 cm (three-quarters of an inch) x 9 cm (three-eighths of an inch), and Mr. Maitre included two separate coils in each batt. It teaches that one coil can be used as a transmitter and the other as a receiver. The coil is arranged with its longitudinal axis parallel to the axis of the sonde.

the coil is engaged with a capacitor to form a tank circuit;
This is connected to the oscillator circuit. The operating frequency is said to be preferably in the range between 50 MHz and 200 MHz, with satisfactory operation occurring at lower frequencies.
Meter's device attempts to measure resistivity and permittivity.

The problem that the invention aims to solve An inductive inclinometer system mounted on the pad.

Generally unsatisfactory, some of these techniques are either sensitive to borehole diameter and fluid conductivity, or sensitive to borehole temperature and pressure. Furthermore, these systems themselves are
It does not have high sensitivity to the parameter itself that is being measured.

This is particularly troublesome when effects resulting from temperature, pressure, alignment inaccuracies, and operational instability affect the detected signal.

Means for Solving the Problems The object of the present invention is to evaluate one or more properties of a geological formation, such as electrical conductivity, permittivity, in the bed of the formation.

and/or to provide a novel sensor suitable for measuring tilt, orientation, etc. in a micro-inductive manner.

Another object of the invention is to provide a microinductive sensor suitable for use in boreholes drilled with non-conductive drilling fluids.

Another object of the present invention is to provide a microinductive sensor that works effectively at various borehole pressure and temperature conditions.

The above objects and others are achieved by a wall-engaging device according to the invention for micro-guided exploration of the properties of a formation through which a borehole passes. The device includes an antenna device mounted within a longitudinally elongated body. This long body is adapted to slide into engagement with the wall of the borehole. The antenna device includes a transmitting antenna for coupling electromagnetic energy into the earth's formations, a receiving antenna for sensing the characteristic signal, and a pseudo-electrostatic shielding element mounted coaxially with the magnetic dipole axis of the transmitting antenna. . The pseudo-static shielding element comprises a sheet of conductive non-magnetic material having a conductive center and a first annular band of narrow linear conductive segments. ,
and a second annular band of linear conductive segments, each of the conductive segments of the first annular band extending radially and integrally from the conductive center, The conductive segments of the second annular band are separated from the conductive segments of the first annular band by respective narrow radially extending spaces emanating from and across the first annular band. A second annular band is defined by a respective longitudinal space extending radially in pairs from each of the segments and emanating from within the first annular band.
are spaced from adjacent pairs of conductive strips of the annular band and are separated from each other by narrow radially extending spaces emanating from and across the second annular band.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now be understood from the description of the basic principles of one embodiment, which will now be described with reference to the simplified diagram of FIG.

The sensor 7 has one transmitting loop 10 and two receiving loops 12, 14, the receiving loops 12, 14 being normally positioned coaxially with and symmetrically around the transmitting loop 10. The transmission loop 10 includes an oscillating current source 1
6. Receive loop 12.14 is receiver 1
8 and are connected in series against each other. The sensor 7 is placed in the borehole 30 and positioned such that the planes of the transmitting loop 10 and the receiving loop 12.14 are parallel to the plane tangential to the wall of the borehole at the location where the formation 36 is to be probed. . The oscillating current flowing through the transmission loop 10 generates a primary magnetic field Bp. Typical lines of force for this magnetic field are shown in FIG. -The primary electric field (
(not shown) is induced. This negative order magnetic field causes oscillating currents called eddy currents to flow in nearby conductive materials. Eddy currents flow in a closed loop coaxial with the transmission loop 10 within the homogeneous material. A typical eddy current unit ground loop is 2
It is indicated by 0. These eddy currents are generated in the borehole 3o
The presence of an insulating mud or mud mass does not interrupt the individual current paths between the formations, since it does not cross the boundary between the formations and the surrounding formations. The magnitude of these eddy currents is proportional to the current in the transmission loop 10 and the conductivity of the formation, producing a relatively weak secondary magnetic field Bs. Typical magnetic field lines are shown in FIG. 1 and are detected by the receiving loop 12.14.

Normally, due to the presence of an extremely strong primary magnetic field Bp,
Detection of the secondary magnetic field Bs is extremely difficult.

To solve this problem, the receiving loops 12, 14 are placed coaxially with and symmetrically around the transmitting loop 10 and wired oppositely in series. In this configuration, the flux of the primary magnetic field Bp passing through the receiving loop 1-2.14 is the same and therefore the response to that negative magnetic field BP is cancelled.

As is clear from FIG. 1, the magnetic flux of the secondary field passing through the receiving loop 12 is stronger than the magnetic flux passing through the receiving loop 14 (ie, the magnetic field lines are closely spaced). A voltage VL therefore results from the current induced in the receiving loop 12.14 by the secondary magnetic field. This voltage VL is proportional to the conductivity of the formation.

The theoretical basis of this example will be better understood by explaining the sensor response in terms of geometric coefficient theory. This theory was first developed by Henri G. Doll to explain guided logging equipment.
This is a quasi-static approximation method used by Georges Doll. According to a low frequency approximation, the electric field generated by iwt in a current loop of radius ρ′ located at 2′, assuming that it depends on e, can be expressed as:

Here, (ρt z) is the observation point, F(k) and E(k
) is an elliptic integral. The normalized electric field Eφ is defined as follows.

Eφ=iμρ′Eφ (3) In the presence of a conducting medium, the current loop at (a, O) as maintained by the transmitting loop 1o is an eddy current ground loop as shown at 20. induce. This is expressed by the following formula.

Jφ (ρ', z') = ivμσ parallel φ (ρ1, z9
;a, of (4) This ground loop produces a secondary electric field given by the following equation.

ΔEφs(p,z)=iw pJφ(ρ'+z')Δ
ρ′Δzzj ρI Eφ(ρtz; ρ'tz')>v”
μ”aIaΔρ′Δzzj p I Eφ(ρtz; at
o) Ej(ρtz; ρ', z') (s) This is
A current is induced across the series counter-wired receive loops 12.14. This voltage is expressed as first order.

ΔV−2π(b, ΔEφg(lh+h1)−ΔEφ5(
bz, -h,))=2πXp"ahp'Δρ'Δz'E
φ(ρ'tZ'; as(b, EφCkheh1;
/”eZtsu-b,Eφ(ht-ha;ρ'tz')]
(6) In the above equation, (b,,h,) and (bz*-ha) are the receiving positions. These are chosen such that the direct mutual coupling between transmitter and receiver is zero. When there is no ground plane, nominal, bi=b2
So, h1=h.

Receive loop 12 by all ground loops in the formation
, 14 is of first order.

22, the geometric coefficient G(ρ'', 2') indicating where in the stratum the signal is coming from is expressed as follows.

GCp″pz′)=ρ′EφCp′ tz′, a,
O) t:b,Eφ(th phz; /)' m
Z')-b2Eφ(bat-ha;p't
z' )) (s) This geometric coefficient was found to peak at ρ2Le. Here, Le is a length determined by the dimensions of the antenna row and the distance from the sensor.

Since the geometric coefficients are symmetric around ρ=○.

The part of the formation that contributes most to the signal has a truncated cone shape.

The normalized geometric coefficient is a function of the distance of the antenna from the borehole wall, which is given by the following equation: % where the apparent conductivity is given by the following equation:

Here, G(ρl, zl) and G(ρ″, 2′) have the following relationship.

GCp'tz')cG Cp'tz')
Ql) Here.

This relates the voltage developed at the receiver to the conductivity of the formation.

It must be noted that the voltage developed across the receiving loop 12.14 by the formation signal given by equation (7) is proportional to w2μ2.

The primary voltage in the receiving loop 12.14, which is a direct mutual coupling, is proportional to the electric field given by equation (1), ie proportional to iwμ, unless canceled out. Although the direct mutual coupling is canceled by the symmetrical arrangement of the sensors, the stability of the cancellation does not depend on the ratio of the formation signal to the direct mutual coupling signal. The ratio of the formation signal to the -order signal is fiwμσLe. Here, Le is the effective length determined by the parameters of the antenna array. Therefore, the sensor should preferably operate at high frequency to increase stability. The resolution of the coil set is approximately Le, and the depth of exploration is approximately Le.

The theory of geometric coefficients is a quasi-static approximation method, and WμσLe2 is 1
It will not work extremely effectively unless it is much smaller. However, for many frequencies of interest, geometric coefficient theory is quite appropriate.

The problem of current loops including all wave effects and radiating onto a laterally anisotropic layered medium can be solved exactly. (ρ
The electric field generated by the current loop located at #, zl) is expressed by the following equation:

E where R is the Fresnel reflection coefficient for horizontally layered media, and layered media start at z=d.

When a ground plane exists, the electric field can be transformed as follows.

Here, P 1kzlz-z' l -1kz(z-dl)
+1kzldL−zle =e −
e φ Although the novel features of the present invention are useful for borehole measurements in general, the present invention is particularly useful for borehole measurements in boreholes drilled with non-conductive fluids and in boreholes drilled with structurally malleable fluids. It is particularly useful for use in exploring tectonic and stratigraphic slopes within boreholes. The "inclinometer" instrument according to the invention is generally shown in FIG.
It is located within 0. The borehole 30, possibly drilled using a non-conductive drilling fluid such as an oil-based mud, penetrates the shale layer 32,36 and the intervening sand layer 3.
Pass through typical geological formations caused by 4. This sand layer 34 includes a lined sand bed 42,46, such as a shale layer 44. Typical tectonic boundaries are represented by boundaries 38 between formations 32.34 and boundaries 40 between formations 34.36. Typical stratigraphic boundaries are boundary 48 and boundary 5.
It is hailed by 0. Additionally, the sand layer 42,46 may include various layers of sand with different properties, such as coarse and fine grains (not shown).

There may also be other stratigraphic features. The device 51 has an elongated central support member 52, which is connected to the borehole 3.
It is designed to move through 0. The long member 52 is 4
substantially identical pads 54(1), 54(2)
, 54 (3), 54 (4) (hidden), and these pads are attached to the respective arm mechanisms 5
6 (1), 56 (2), 56 (3), 56 (
4) is pressed against the wall of the borehole 30. These arm mechanisms are hidden together with the collar 60. The collar 10 is mounted on a long support member 52 and slides over the member 52 to form an arm mechanism 56 (1).
-56(4) to allow expansion and contraction.

Additionally, tool 51 includes a suitable centering guide assembly coupled to the upper end of elongated support member 52. The centering guide assembly includes flexible spring arms 62(1), 62(2)
), 62 (3), 62 (4) (hidden)
, which are connected to 3-64.66 as appropriate. One of the collars 64 , 66 is fixed to the support member 52 . The other collar is mounted on the support member 52 and slides over the support member 52 so that the spring arm 62 (1)
- Inflate and deflate 62(4). spring 62
(1)-62(4) includes pads 54(1)-54(4) and an associated arm mechanism 5.
6(1)-56(4) to center and maintain tool 51 within borehole 30.

At its upper end, the instrument 51 is connected to an armored multicore cable 68 for connection to ground equipment. The surface equipment is Sheave 11
, and a multicore cable 68 extends over this sheave to a suitable drum and winch mechanism 13 to raise and lower the implement 51 through the borehole 3o. Electrical connections between cable 68 and telemetry, control and power circuit 17 are made through a suitable multi-element slip ring and brush contact assembly (not shown) and cable 51. The depth of the instrument is determined by using a suitable measuring wheel mechanism 19, which is also connected to the telemetry, control and power circuit 17 by a cable 21. Other surface equipment includes a telemetry, control, processor 25 connected to the power circuit 17, and an operator terminal connected to the processor. Input/output device 27 is included.

The pad 54 may be as shown at 120 in FIG. 7 or as shown at 400 in FIG.
Alternatively, other types as described below may be used. These examples will be explained in the following description of a research device for an antenna arrangement in which the transmitting loop 10, the receiving loop 12, 14 and the individual shielding elements are fabricated from a photolithographic mask by printed circuit board technology. It will be understood from The printed circuit board is made of polyimide material clad with one ounce of copper. A thin coating of gold is placed over the copper to control oxidation. What is the material of the board?

The transmitter loop 10 was 1.5 mm thick and had considerable rigidity.The transmitter loop 10 is shown in FIG. The flat copper loop has a diameter of 2.0 cm and is cut at the point where the terminal lead 72.74 is provided. Receive loop 12 is shown in FIG. The flat copper loops are 1.0 cm in diameter and are cut at points to provide terminal leads 76,78. The receiving loop 14 is the same as the receiving loop 12. The transmitting loop 10 and the receiving loop 12.14 have a frequency of 10 MHz and 5
It had characteristics between 0MH2 and 0MH2. Transmission loop l
O was found to have an inductance of 88 nH and a series resistance of 0.6 Ω. The resonant frequency of these devices was several hundred MHz. Loop 10.12.
It will be appreciated that the size of 14 controls the magnitude of the output signal, the volume of debris explored (spatial resolution) and the depth of exploration. Generally, these factors increase with increasing loop size.

The research sensor has a transmission loop 10. Receive loop 12.1
4 was assembled by assembling individual printed circuit boards. The receiving loops 12, 14 were arranged "electromagnetically symmetrically" around the transmitting loop 10. Generally, electromagnetic symmetry is defined as Mac=Mbc. Here,
Antenna A.

The relative positions and orientations of B, C and antenna parameters are such that the mutual guidance between antennas C and A is used to cancel the mutual guidance between antennas C and B. Electromagnetic symmetry is achieved in this embodiment, for example, by physically positioning the receiving loop 12.14 coaxially with and symmetrically around the transmitting loop. The appropriate spacing between the sending loop and receiving loop is 0.69c.
It turned out that m. - However, closer spacing is possible if a certain loss of sensitivity is tolerated.

It was found that pseudo-capacitive coupling exists between various loop antennas and between the antenna and the geological formations. This pseudo-capacitive coupling is acceptable in many cases, but can be eliminated by the use of shielding elements if desired. A suitable shielding element is shown at 80 in FIG. The shield element 80 includes many conductive segments radiating from a conductive center, for example, 256 conductive segments 110 (1), 110 (2), . . . , 11
Consists of 0 (256). The shield element 80 is provided with slits in the radial direction to prevent azimuthal vortices from being generated therein due to the azimuth electric field induced by the magnetic field. It will be seen that the etched lines of shield element 80 extend to the edge of metal cladding 8o.

Additionally, the spacing of the 256 etched lines is extremely close to minimize disturbances to the magnetic field. A common electrical connection is provided only in this conductive center, which provides more complete shielding and free passage for radial currents. The shield 80 is square, and the length of each side is 10 cm. A shield terminal lead 82 is provided.

The reduced sensitivity of laboratory sensors to resonant coupling between the transmitting loop 10 and the receiving loops 12 and 14, as well as between the antenna array and the formation, reduces the sensitivity of the individual shielding elements to
Preferably, the transmit loop 10 and the receive loops 12 and 14
and between each of the receiving loops 12 and 14 and the external environment.
It was arranged symmetrically to and coaxially with the transmission loop 10 at a distance of mm. The individual shield elements 80 were also arranged symmetrically to and coaxially with the outer surfaces of the receiving loops 12 and 14 at a distance of 1.5 mm. The total thickness of the fully assembled laboratory sensor, including the shielding elements and the protective outer layer of circuit board material, was 2.0 cm. Furthermore, undesirable resonances that would increase the sensitivity of the sensor to changes in ambient conditions were eliminated when a shield such as 80 was included in a laboratory antenna arrangement.

A more practical configuration of the sensor is indicated generally by reference numeral 7o in FIG. This sensor 7° provides an absolute measurement of the conductivity of the formation and is equipped with an antenna arrangement 69, preferably metallized on the sides and back. The sensor 7o is set in a circular cavity centered on the metal body 122 of the exemplary pad 120 and secured by a suitable adhesive. The rear metallization 126 forms a highly conductive back surface, which serves to isolate the antenna arrangement 69 from the effects of the sonde and borehole described above. Additionally, the back surface 126 and conductive side metallization 127 cooperate to improve the focusing of the various magnetic fields, as described below. Although the metalization of the antenna device 69 may be omitted,
In this case, the functions of the back surface 126 and the side surfaces 127 are provided by the cavity itself. Although such improvements in focusing and separation are very effective, they are not necessary to provide a functional sensor.

The antenna device 69 of FIG. 7 is shown in detail in FIG.
The transmitting loop 10 and the receiving loops 12 and 14, if desired, are arranged essentially as described above for the laboratory configuration of the sensor, modified as required by the use of the rear surface 126, as appropriate. It is equipped with a pseudo-electrostatic shield element.

Other notable differences include the use of sidewalls for the antenna arrangement 69 to improve the focusing of the combined magnetic field, the manner in which the various elements of the sensor 70 are assembled, and the incorporation of one of the shielding elements. This includes: In addition, when forming the transmission loop 10, it is desirable to use a thick copper film in order to avoid excessive Joule heat generation. It will be understood that the dimensions shown here are for illustrative purposes only and that other dimensions are quite sufficient.

The back surface 126 is an antenna device due to the influence of the conductive material inside the borehole 30! 69 and provides a predictable and therefore correctable effect on the antenna device 69. Even in boreholes drilled with non-conductive drilling fluids, conductive materials cannot be practically reliably avoided, especially when arm mechanism 56 and tool support member 52 are metal. The back surface 126 acts much like a mirror for high frequency magnetic fields. The spatial resolution of the embodiment with a back surface remains unchanged, and the depth of the test is only very slightly reduced from the embodiment without a back surface. Theoretically, due to the current loop in the presence of a ground plane,
An electric field expressed by the following equation is generated.

Eφto-jw μI p'(Eφ(ρ*z;ρ'+
z')-Eφ(+o+z;ρ'+-z'+2d1))
(16) However, Eφ is determined by equation (3). The image theory was mentioned above. The analysis was also mentioned above.

A suitable position for the back surface 126 is approximately 1.0 of the receiving loop 14.
cm behind, but this distance is not critical and a shorter distance may be used if a thinner sensor is desired.

To compensate for the difference in magnetic flux coupled into the receive loops 12 and 14 by the image flow due to the back surface 126, one of the receive loops 12 and 14 is shifted from the strict physical axis of symmetry to maintain electromagnetic symmetry. must be maintained. In the antenna device 69 of the pad 120, the receiving loop 14
is moved approximately 0.08 mm closer to the transmitting loop 10.

The conductive cylindrical side wall 127 around the antenna device 69 has 2
It has two main effects, one of which is very effective and the other very troublesome. On the other hand, the cylindrical sidewall 127 significantly increases the resolution of the sensor 70, thus improving its response to thin floors. On the other hand, side wall 1
The metal surface of 27 and the conductive surface of pad 120 make the X signal considerably larger than the R signal and the
is made larger than the signal. However, the degree of electromagnetic symmetry and stability achieved by the present invention allows very large X signals to be canceled and high resolution to be achieved.

An important parameter in increasing resolution is the pad 120
It was found that the length of the hole in the direction parallel to the movement of . An improvement in resolution can be obtained if the longitudinal hole length is shortened.

The theory explaining focusing is also readily apparent at an intuitive level. High frequency magnetic fields are excluded from inside the metal by the skin effect. For example, the metal back surface 126 and metal sidewalls 127 remove high frequency magnetic fields from the metal body 122 while tightly confining the magnetic fields within the cavity. Furthermore, due to the boundary conditions imposed on the magnetic field, the high-frequency magnetic field
There is also a tendency to concentrate outside the cavity, parallel to the side walls of the cylindrical cavity.

The elements of the antenna device 69 are formed from a suitable material,
Assembled into a unitary package suitable for use in a borehole environment. The overall symmetry of sensor 70 makes it largely self-compensating for thermal expansion, pressure-induced compression, and thus scale invariants, while ensuring essentially stable dimensions. Excellent performance of sensor 7o is achieved. Therefore, components that significantly affect dimensional stability are formed from materials with low coefficients of thermal expansion and low compressibility. Non-conductive materials are
It is also preferable that the dielectric loss is low.

For example, when making the transmit loop 10, the receive loops 12 and 14, and the individual shielding elements.

Ceramic substrate materials are preferably used. Furthermore, the various ceramic substrates of the antenna device 69 can effectively act as spacer elements by appropriately selecting their thickness.

has a wall engaging surface 112 and an opposing surface 114;
An assembled antenna arrangement 69 consisting of base bodies 86, 88, 90, 92, 94 and 96 is shown in FIG. Each substrate is approximately 4.4 cm in diameter. The transmitting loop 10 is connected to a thin substrate 9 in the central plane of the antenna device 69.
It is located between 0 and 92 and connected to lead 100. With laminated substrates 90 and 98 approximately 1.5 mm and 0.675 cm, respectively, a spacing of 0.69 cm is obtained between transmit loop 10 and receive loop 12. Fifth
The shielding element, as shown at 80 in the figure, has a diameter of about 4
, -4 cm, so the number of segments is 12
Although there are only 8 shield elements, this shield element
The base body 90 and the base body 88 are disposed coaxially with each other. Laminated substrates 92 and 94 are approximately 1.5 mm and 0.665 cm, respectively.
m, a spacing of about 0.68 cm is obtained between the transmitting loop 10 and the receiving loop 14. Although a shielding element such as that shown at 80 in FIG. 5 has a diameter of only about 4°4 cm and therefore only 128 segments,
This shield element is arranged coaxially with the transmission loop 10 on the base 9.
2 and 94. Although the two additional shielding elements, shown at 80 in FIG. Each is provided between it and the environment. These shield elements are coaxial with the receiving loops 12 and 14 and spaced from the receiving loops 12 and 14 by the thickness of the substrates 86 and 96, each of which has a thickness of about 1.5 mm. It will be clear that these dimensions are for illustrative purposes only.

A screw (not shown) movable along the axis of the antenna device 69 into the antenna device 69 is provided to fine-tune the cancellation of the direct mutual coupling. If a tuning screw is used, the conductive central portion of the shield element, such as 80, through which the screw passes must be enlarged to receive the orifice of the tuning screw. The resulting ring-shaped conductive core must be open along a line to prevent the induction of eddy currents.

The shielding element provided on the surface 114 between the receiving loop 14 and its external environment, ie, the back surface 126 shown in FIG. 7, is formed on the substrate 96 as described above. Receive loop 1
2 and its external environment, i.e. the stratum to be tested.
The shielding element provided at 12 serves the additional function of protecting the antenna arrangement 69 from wear by the walls of the borehole 3o. The shielding element is therefore preferably fabricated from a block of suitable electrically conductive material, such as brass or stainless steel.

The transmitting loop, receiving loop or shielding elements of the antenna arrangement 69 are formed on either adjacent side of the base body between which they are inserted.

For example, the transmit loop 10 is connected to the substrate 9 closest to the surface 112.
2 or on the surface of the substrate 90 closest to the surface 114. The various substrates are bonded together along their respective adjacent surfaces with a suitable adhesive. Antenna installation M69
When assembling, transmit loop 10 and receive loop 12
Care must be taken to avoid structural deficiencies such as residual direct interconnection between and 14.

The receive loops 12 and 14 and the shielding elements must be coaxial with respect to the transmit loop 10.

All components, including the ceramic substrate, unshielded leads, and any fixtures used, should be arranged as symmetrically as possible, except as noted above.

At pad 120, each conductor 128 and 129 connects transmit loop 10 and receive loop 12 and 14 to a respective network 130 and 132, the purpose of which is described below. The circuitry 132 is connected by a cable 136 to the receiving circuit of the sonde body.

Cables 134 and 136 are of the flexible coaxial type. ferrite beads selected to have a large extinction coefficient in the frequency range are used in the unshielded low frequency leads and in the outer conductor of the coaxial cable;
High frequency currents in these structures are reduced.

Other pad configurations are also possible. For example, if the focusing and separating functions provided by the metallization of the antenna device 69 or by the cavity of the pad body 122 are not desired, the pad body may be constructed of a zodielectric material and the sensor 7 Sensors such as the following can be attached. Modifications of the antenna device 69 are also possible. For example, while decreasing the transmit loop-receive loop spacing generally reduces the output signal level, it is possible to reduce the transmit loop-receive loop spacing by more than half without significantly reducing performance4. . Furthermore, reduced area shielding can be made more effective.

An electrical circuit suitable for operating sensor 70 is shown in FIG. The pad 54 (1) comprises a transmitting loop 1o and receiving loops 12 and 14, which act like a dual secondary mutual inductance coil set. The transmitting loop 1° and the receiving loops 12 and 14 are
Connected via circuits 1!1130 and 132 to the transmitting section 141 and the receiving section 143, respectively, said circuitry is preferably tuned to their respective loop antennas. Networks 130 and 132 preferably include transmission loop 1
0 and receiving loops 12 and 14, pad 5
4 (1) Attached to the top. This is because tuning is adversely affected by changes in the electrical characteristics of the windings between the loop antenna and its respective network. Circuitry 130 is configured to drive transmit loop 10 in a balanced mode to reduce the monopole component of the electric field. Network 130 minimizes reflections from transmit loop 10, and such reflections typically have a real impedance of less than 1 ohm. Receive loops 12 and 14 are connected in series opposition via network 132 .
is a balanced unbalanced transformer.

It is a subtractive type network such as a 4-port hybrid junction or a differential amplifier, and the direct mutual inductance can be reduced to zero.

A calibration switch 138 is connected across the lead from receive loop 14 .

A sensor circuit 140 (1) composed of a transmitting section 141 and a receiving section 143 is arranged in the main body of the device 51.

The transmitting section 141 includes a continuous wave source oscillator 142 operating at the desired high frequency. This oscillator 142
The output of
The signal is then sent to the transmission loop 10 via. The source energy is
split at directional coupler 144 to receive section 14
3 is provided as a reference signal to a reference channel of a phase-sensitive detector 148 included in FIG. The signal channel of phase sensitive detector 148 is fed with the signals from receive loops 12 and 14 after passing through amplifier 149 . Phase sensitive detector 148 produces at its output a signal representative of the power ratio and phase shift of the signals received in receive loops 12 and 14. If there is no conductive stratum, the insertion loss of the sensor 7o will be 1120 dB or more, so it is necessary to improve the separation between the transmitting section 141 and the receiving section 143.

Essentially the same sensor circuits 140 (2), 140 (3
), and 140 (4) are bad 54 (2), 54
(3) and 54 (4), respectively. The power ratio and phase shift signals from sensor circuits 140 (1), 140 (2), 140 (3) and 140 (4) are sent to the input of multiplexer 150 where they are sampled and output to A/D converter 152. sent to. A/D
The output of converter 152 is connected to telemetry system 15.
Sent to input 4.

It is sent to equipment on the ground including processor 25.

For example, a formation signal detected by a laboratory sensor consists of two components, one influenced primarily by the formation's conductivity and the other primarily influenced by the formation's permittivity. be. The component that is affected by the dielectric constant (
The component affected by conductivity (R signal) is more preferable than the component (X signal). This is because the dielectric constant contrast of the formation is generally smaller than the conductivity contrast.@R times the signal,
Connected to the receiver in phase with the drive signal.

All other signals, including the The signals are phase shifted and connected to the receiving circuit.

Phase sensitive detection can be effectively used to remove any unwanted coherent signals or incoherent noise. However, the phase sensitive detector 14-8 must be periodically calibrated because cables, transformers, amplifiers, and other components can cause phase shifts in the sensor circuit. Since the direct mutual inductance is 90° out of phase with the drive signal, receive loop 1
By simply shorting one of 2 and 14, a relatively large quadrature signal can be generated. A calibration switch 138 (FIG. 8) is provided for this purpose. The angle thus measured is subtracted from 90° and the resulting calibration angle is stored in processor 25 to adjust the phase measurements of the formation for these various phase shifts. To determine the parameter proportional to conductivity, the measured amplitude is multiplied in processor 25 by the cosine of the adjusted phase measurement described above. All useless signal effects are removed in the sine component.

The operation of the device of the present invention will be understood by considering experimental results obtained with the experimental sensor described above. A laboratory formation was created consisting of alternating layers of brine and layers of granular, porous synthetic material saturated with brine. The above synthetic materials were manufactured by Ferro Corpora, Rochester, New York, USA.
Kerndite (Kell tion) manufactured by
undite (trademark)) FAO-100. The material looks very similar to clean sandstone when viewed under a scanning electron microscope. Its porosity is about 40%, its composition coefficient is 5.5, and its dielectric constant is a few darcis (Da
rcies). This sample has a resistivity of 1Ωm (
(resistivity of the shale) saturated with water. The circuitry used in the laboratory experiments was similar to sensor circuit 140 (1) and circuitry 130 and 132.

The oscillator and phase sensitive detector were elements of a Hewlatt-Packard type 8505A network analyzer. A broadband amplifier with a gain of 33 dB fed the signal channel of the network analyzer, while a source signal with 40 dB attenuation was fed into the reference channel. The network analyzer was under the control of a Hewlett Paracard Model 9845B computer, which also controlled the operation of the experimental setup.

The response of a laboratory sensor is readily apparent on an intuitive level by a simple model of N, known as the 'average loop response'.

This "average loop" is considered to be the single ground loop that best approximates the average value of the geometric coefficients obtained for all ground loop radii.

It has been found that the response of a laboratory sensor to a thin bed, such as the shale layer 44 of FIG. 2, depends on whether the thin bed is more resistive or more conductive than the debris. It has been found that a thin resistive bed reduces the eddy currents generated in the surrounding conductive formations and introduces a simple negative-going peak in the response centered at the location of the resistive layer. This response, the "normal" response, is shown in FIG. Thickness 0.64c
A thin resistive bed 158 of m insulating sheets is disposed between relatively conductive beds 156 (1) and 156 (2). Resistive bed 158 is easily detected as shown by the sharp negative-going peak of curve 157. A typical response pattern is shown for the layer sequence consisting of FIG. This layer sequence consists of a resistive bed t
60 (1), 160 (2), 160 (3), 1
60 (4) and 160 (5) and a conductive floor 170
(1), 170 (2), 170 (3), 170
(4) and 170 (5) are arranged alternately. Each resistive bed 160 was 1.26 cm thick and had a resistivity of 5.5 Ωm. Each conductive floor 170 has a thickness of 3.81 cm and a resistivity of 1.0Ω.
m, and the thickness of the conductive bed 170 was comparable to or greater than the average loop diameter. Conductive floor 1, as shown as curve 180
．． The response of the laboratory sensor to 70 is a series of single positive-going peaks, while the response of the thin resistive bed 160
The response of the laboratory sensor to was a series of single negative-going peaks.

The response of laboratory sensors to conductive layers is somewhat complex. From the averaging loop concept, the response of a laboratory sensor is zo-proportional to the arc length of the averaging loop as it passes through the thin conductive bed. The arc length is at its maximum when the edge of the average loop intersects the thin bed and locally minimum when the sensor is in the center of the thin bed.

Essentially, the thin bed is taken up by "bones" of geometrical coefficients. This "inversion" response is shown in FIG. 11, which shows a 0.64 cm thick, 1 Ωm layer embedded in a uniform 5.5 Ωm formation 190.

The signal level represented by curve 185 increases as the laboratory sensor approaches the thin conductive floor 180 and sharpens when the laboratory sensor is moved directly above the thin conductive floor 180. decreased, increased when the laboratory sensor was separated from the thin conductive floor 180, and decreased when the laboratory sensor was completely separated from the thin conductive floor 180. The asymmetry and noise in curve 185 is due to limitations of laboratory models and equipment.

The central slope obtained when scanning a single thin conductive bed, such as that shown at 180 in FIG. 11, will appear as an inversion of the signal for formations containing many such beds. This is shown in Figure 12, which shows a thickness of 10 cm.
m resistive bed 200 followed by a conductive bed 2
02 and relatively thick resistive beds 204 are shown alternating. The thin conductive floor 202 is 0.63 cm thick and has a resistivity of 1 Ωm. The relatively thick resistive bed 204 is 1.27 cm thick and has a resistivity of 5°5 Ωm. Away from the thick resistive bed 200, the trend of the response curve 200 becomes positive, as expected. In the honey laminated region consisting of alternating beds 20.2 and 204, the signal associated with the resistive region 204 will be large. This is an "inverted" response. The response of the laboratory sensor, shown by curve 210 in FIG.
In contrast to the "normal" response 180 shown in the figure. Approximately 2
．． Conductive beds smaller than 5 cm produce a 5 reversal tendency, while for larger beds no reversal tendency occurs.

The thickness of the conductive bed being tested does not interfere with the calculation of the slope, φt, which affects whether the response is normal or inverse. An essential property of the inclinometer is that it generates a signal that can be correlated across a large number of pads. This condition is satisfied in normal and inverted response patterns. Slope can be measured using appropriate correlation techniques (some of which are discussed above).

Sensor 70 operates over a wide frequency range.

The lower frequency limit at which sufficient signal strength can be obtained is approximately 1
MHz, but other dimensions and parameters can be chosen to lower this lower limit. However, since the formation signal voltage is proportional to the square of the frequency, it is preferable to operate at a high frequency. However, due to many factors, 1
The upper limit of frequency is limited. A fundamental limit is set by the skin effect, which confines the electromagnetic signal within a certain skin depth of the surface of the conductive body. This skin depth δ is expressed by the following formula.

When δ is measured in meters, μ is the magnetic permeability H/μ
, f is the frequency in Hz, and σ is the conductivity mho/m. As long as the skin depth is greater than the spatial length of the electric field generated by the transmit loop 10 and sensed by the receive loops 12 and 14, the resolution and depth of the sensor test will be independent of the conductivity of the formation. Such independence is desirable. Another limitation is antenna and cable self-resonance. The antenna loop used in laboratory sensors has a self-resonant frequency of several hundred M
Hz range, by installing relatively short cables these frequencies are reduced to about 90 MHz. At these frequencies or higher, the sensor is insensitive to the characteristics of the formation. With due care taken in cabling, it is reasonable to use frequencies of 100 MHz or higher.

Such laboratory experiments were conducted at 12 MHz, 25 MHz and 55 MHz to test the performance of the sensor at these various frequencies. As expected, the signal-to-noise ratio increased rapidly at higher frequencies. 55MHz
In ↓1, the skin depth in the 1Ωm stratum is 6.8c.
m, which is greater than the distance at which the formation signal is sensed.

When using ceramic technology suitable for borehole applications, sensor 70 must be capable of operating at power levels of 20W or higher. It was found that 20W of power can be supplied to a laboratory sensor.

The sensitivity of the laboratory sensor at low power levels was tested. During the reception band, it was set to 10KHz. The strata were composed of alternating layers with a resistivity of 5.5 Ωm and a thickness of 1°27 cm and layers with a resistivity of 1.0 Ωm and a thickness of 0°63 cm. At 100 mW it was found that there was essentially no noise, at 10 mW it became clear that there was some noise, and at 1 mW it became clear that there was considerable noise; It is not so much that the layer structure becomes unclear at all.

It was found that there is a correlation between the receiving bandwidth and the recording speed of the borehole. Receive bandwidth directly affects signal-to-noise ratio. This is because the thermal noise power is directly proportional to this. The laboratory device was capable of selecting the filter bandwidth of the IF stage between 10 KHz and IKHz. A video (power averaging) filter with a bandwidth of 30 Hz could also be used. It is useful to limit the bandwidth in increasing the signal-to-noise ratio. However, in order to obtain an appropriate recording speed, measurements must be made over a sufficiently wide band. Consider the case where it is desired to record at 1800 feet/hour and collect data every 0.2 inches. In this case, the receiver receives 3
Sampled 0 times. Therefore, the reception bandwidth is approximately 3
0 Hz or higher. In order to design and operate the sensor of the present invention, trade-offs between dynamic range, power consumption, recording speed, and signal-to-noise ratio need to be considered.

One embodiment of an electromagnetic object sensor for obtaining absolute measurements of a formation without relying on physical symmetry is shown in FIG. This sensor includes an antenna device 669 consisting of a frame 602 attached to a cylindrical cavity provided in a non-conductive pad body 622 and antennas 610, 612 and 614. Antenna device 669 in FIG.
is perpendicular to the plane of the pad body 622, but the antenna device 669 may be mounted with its axis parallel to the plane of the pad body 622 to obtain absolute measurements. It is also possible to attach it to a metal pad, which provides increased focusing and improved reliability due to the effect of the conductive side and back walls substantially as described above.

The ceramic frame 602 includes a transmitting loop antenna 610,
Receiving loop antenna 612 and receiving loop solenoid 6
14, which are formed on frame 602 using known photolithography techniques. antenna 61
The central planes 0, 612 and 614 are preferably common, but these planes can be staggered at the expense of increasing the thickness of the antenna device. The cavity in which the antenna assembly W669 is mounted is suitably sealed from the external environment at the surface of the pad body 622 (not shown).

Suitable descriptive values for the parameters of the antenna installation [669 are a=1cm, b=2cm, c=3am, Na
/Nb=4.732.

The operating principle is essentially as follows. Consider antenna A (inner solenoid 614) to have "Na" turns of radius a, and antenna B (center antenna 612) to have "Nb" turns of radius (where Nb=1). , and considering that antenna C (outer antenna 610) has "Nc" turns of radius C (where Nc = 1), receiver A
The voltages Va' and vbo generated at V and B, respectively, are as follows.

Va' = j (11 Mac I c
(18) Vb' = j (1) Mbc I c
(19) Radius and turns ratio Na/Nb
is chosen such that Mac = Mbe, so Vo= Va' - Vb' = +j t,y (Mac - Mbc) I c=
In the case of O(20) direct mutual cancellation, the formation signal can be easily obtained. Consider a basic stratigraphic ring of radius r at a distance of 2 from the pad, and let its cross-sectional area be ΔrΔ2. The voltage induced in this ring is
It is as follows.

ΔVf= j GJ Mfc I c
(21) However, Mfc is the mutual inductance between the ring and antenna C. The eddy current generated in the ring is as follows.

2πr This induces a voltage in antenna A expressed by the following equation.

ΔVa= j (11MafΔI f
(23) However, Maf is the mutual inductance between antenna A and the ring. Similarly, the signal of antenna B is expressed as:

The total signal available to the receiver pair is given by the differential voltage integrated over the formation.

The term in parentheses is the "geometric factor" and is multiplied by the conductivity of the formation.

Antenna arrangement 669, for example a zero phase sensitive detector operated in the circuit of FIG. 8, is used to improve the signal-to-noise ratio. It is preferable to perform high-resolution measurements at shallow depths, and furthermore, the geological signal is proportional to ω2,
Since the direct mutual signal is proportional to ω, high frequency operation can be used to further improve the signal-to-noise ratio.

The other antenna of antenna arrangement 669 is selected to operate as a transmitter. For example, the antenna 614 is
It is selected when it is desired to test deep locations, but the vertical resolution is correspondingly increased. Suitable illustrative values for the parameters of such a sensor are a=1 cm, b=2 cm, c=3 cm and Nc/
Nb=1°596.

Sensors such as 7 and 70, when oriented as shown in FIGS. 1 and 7, provide absolute measurements of the conductivity of the formation. Transmit loop 10 and receive loops 12 and 14
from the orientation maintained at sensor 7 by 90@
I found that setting it to gives a difference measurement. A sensor 270 of this type is shown in FIG. 14 in which the transmit loop 10 and the receive loops 12 and 14 are rotated 90@ in the radial plane of the borehole and thus rotated "edgewise" relative to the wall of the borehole 30. This sensor 270 operates on the same basic principle as sensor 7, but its interaction with the formation being tested is different. FIG. 14 shows a formation 280, such as a shale bed, that exists between formations 275 and 290, such as sand beds, which are located at boundaries 283 and 285, respectively. are in contact with each other along the The transmitting loop 10 generates a primary magnetic field illustrated in FIG. 14 by exemplary magnetic field lines Bp. This negative order magnetic field Bp generates an electric field that intersects the wall of the borehole 30 and deposits charge thereon. This results in an average unit ground loop 2
87, a secondary magnetic field Bs is induced, and the lines of magnetic force are:
It intersects the receive loops 12 and 14.

In order to qualitatively understand the response of the sensor 270 when the sensor 270 is pulled up the borehole 3o, the fifteenth
Explain the diagram. The response of sensor 270 to homogeneous and isotropic formation 290 is that sensor 270
80 (see curved section 308). When sensor 270 is raised near formation 280, this formation is relatively impermeable to non-conductive muddy fluids, and thus
Because formations 275 and 290 are more conductive, the eddy currents in the formation preferentially shift towards the more conductive layer 280. In other words, the average unit ground loop 14 is
The receiving loop 14 is shifted closer to the receiving loop 14 function plane than the receiving loop 12 plane. Therefore, the receiving loop 14 intersects the secondary magnetic field Bsp flux lines more than the receiving loop 12, forming a positive response peak (see curve section 310). The difference measurement decreases as the transmission loop 10 moves toward the conductive formation 280, and eventually the difference measurement becomes flat once again (see curve section 312). The transmission loop 10 is connected to the boundary 2 between the formation 280 and the formation 275.
When moving towards 83, this sequence of events is reversed. As the transmit loop 10 moves across the boundary 283, the difference measurement falls to a negative peak (curve section 31
(see 4). As the transmit loop 10 moves far enough away from the boundary 283, the difference measurement rises and becomes flat (curve section 31
(see 6).

FIG. 15 was obtained through laboratory experiments. Conductive layer 208 was simulated with a salt water bath, and relatively non-conductive formations 275 and 290 were simulated with water.

A sensor 270 or antenna device 669 with an axis oriented parallel to the formation through which the borehole passes is suitable for use in a borehole instrument such as 51 having pads such as 54, but the thickness of each pad 54 is Transmission loop 10
, the receiving loops 12 and 14, and the diameter of the desired shielding element. A preferred configuration is shown in FIG. 16, which allows the pad 54 to be reduced in thickness and provide good isolation for the antenna arrangement, and is shown in FIG.
As shown, a sensor 370 is located adjacent to the formation 300 within the borehole 30. The sensor 370 includes a back surface 302 and a transmitting half-loop 310. This sending half loop 3
Two receiving half-loops 312 and 314 are arranged symmetrically to and coaxially with respect to 10 . Transmit half-loop 310 includes leads 320 and 3 that pass through backside 302.
21 to the oscillating current source 16. Receive half-loops 312 and 314 are connected in series-opposed relationship by leads 323 and to receiver 18 by leads 322 and 324. The image flow created on the back surface 302 causes sensor 370 to perform essentially the same function as sensor 270 of FIG.

An exemplary pad 400 including a sensor 370 is shown in FIG. For example, a transmitter half loop 310 and a receiver half loop 3 formed using the ceramic technology described above.
An antenna device 369 including pads 12 and 314
00 is shown disposed within a rectangular cavity formed in a metal body 422 and secured with a suitable wear-resistant dielectric material 421. The antenna arrangement 369 is preferably centered within the cavity. The distance between antenna arrangement 369 and the wall of the cavity is selected based on the desired degree of focusing.

Antenna mounting [369 is the rear section 30 of the metal body 422
Backed by 2.

Wires 428 and 429 connect transmit half-loop 310 and receive half-loop 312 and 314 to respective networks 430 and 4.
Connect to 32. The circuit network 430 is connected to the transmitting circuit of the sonde body by a cable 434, and the circuit network 432 is connected to the transmission circuit of the sonde body by a cable 434.
A cable 436 connects to the receiving circuit of the sonde body. Cables 434 and 436 are of the flexible coaxial type.

Ferrite beads selected to have a large extinction coefficient in the frequency range of interest must be used in the unshielded low frequency leads and in the outer conductor of the coaxial cable to reduce high frequency currents in the structure.

Electrical circuitry suitable for sensor 370 has been described above. The operation of sensor 370 was also discussed above in connection with FIG. Since the output of sensor 370 can be correlated with the output of other similar sensors, any of a number of common tilt measurement techniques can be applied to measure tilt.

Although the invention has been described in terms of a number of specific embodiments, it will be understood that these embodiments are for illustrative purposes only and are not intended to limit the invention to these embodiments. Various modifications and combinations within the spirit and scope of the invention will be apparent to those skilled in the art. One modification suitable for making differential measurements is shown in FIGS. 18 and 19.

Transmitting loops 501 and 503 spaced apart in the same plane as shown in FIG. 18, or other suitable magnetic field generating means, e.g. The single transmission loops located in the plane of are maintained with their axes perpendicular to the plane of the test formation 510. Transmission loops 501 and 503
are connected to a source 505, ie, an oscillating current source, so as to each generate opposing primary magnetic fields indicated by exemplary magnetic field lines Bp. This resultant-order magnetic field induces eddy currents in the formation 510, and these eddy currents
Line a is defined in FIG. 18 at a position equidistant from the axis of
It is maximum in the plane indicated by -a'. Coplanar receiving loops 507 and 509 are mounted in mirror image relation to the plane represented by line a-a' and are preferably provided coaxially with transmitting loops 501 and 503 as shown. , these receiving loops even cut the flux lines of the secondary magnetic field resulting from the above-mentioned induced eddy currents. Receiving loop 50 connected in series to receiver 511
7 and 509 have electromagnetic symmetry.

- receiving loops 507 and 509 for order and secondary magnetic fields;
The response to the -order magnetic field is canceled out in a homogeneous isotropic stratum.For example, in the vicinity of a scrap area, only the response to the -order magnetic field is canceled out. A variation of the sensor of FIG. 18 is shown in FIG. 19, in which transmit antenna loop 510 and receive antenna loops 512 and 514 are provided in a common plane. Of course, the photolithography and assembly techniques described above are also effective in the case of the sensors of FIGS. 18 and 19. Modifications in these and other features are therefore to be expected and are included within the scope of the invention. Furthermore, it will be clear that an equivalent sensor as described above can be obtained even if the functions of the transmitting and receiving antennas are exchanged, so that electromagnetic symmetry of the transmitting and receiving antennas is expected. Although the preferred orientation of the axis of the electromagnetic symmetric antenna in each of the numerous embodiments has been described as perpendicular or parallel to the other antennas, in some cases intermediate orientations may be used in these embodiments, consistent with the spirit of the invention. Electromagnetic symmetry can be obtained.

[Brief explanation of drawings]

In the figures, similar parts are designated by the same reference numerals. FIG. 1 is a diagram for explaining the theory of operation, and FIG. 2 is a plan view of the borehole logging instrument. 3 is a plan view of the transmitting loop, FIG. 4 is a plan view of the receiving loop, FIG. 5 is a plan view of the pseudo-electrostatic shield, and FIG. 6 is a perspective view of the assembled antenna device. Figure 7 is a cross-sectional view of the logging pad, and Figure 8 is a circuit diagram of the electronic circuit. 9, 10, 11, and 12 are diagrams for explaining the response of the device, FIG. 13 is a sectional view of another antenna device, and FIG. 14 is a diagram for explaining the response of the device.
Diagram for explaining the theory of operation. FIG. 15 is a diagram for explaining the response of the device, FIG. 16 is a simplified perspective view of the sensor and rear element, FIG. 17 is a cross-sectional view of another logging pad, and FIGS. FIG. 19 is a diagram for explaining the theory of operation. 7... Sensor 10... Transmission loop 12.14.
...Reception loop 16...Current source 17...Telemetry, control, power circuit 18...Receiver 19...Wheel mechanism 25...
- Processor 27... Input/output device 30... Borehole 32.36.44... Shale layer 34... Sandstone 36... Geological layer 42.46...
・Sand bed 48.50... Boundary 51... Instrument 52... Support member 54... Pad 56... Arm mechanism
60... Collar 62... Spring arm 68... Multicore cable 80... Shield element 110... Conductive segment FIG, 3 F7G, 4 FIG
,! FIG. 13

Claims (23)

[Claims] (1) A wall-engaging device for microinductive testing of the properties of a geological formation traversed by a borehole, comprising a longitudinally extending body configured to slide into engagement with the wall of the borehole, and an antenna attached to the body. An apparatus comprising: a first antenna element for coupling electromagnetic energy; a second antenna element having a selected first position relative to the first antenna element for coupling electromagnetic energy; an antenna device comprising a third antenna element having a second position selected with respect to the element and coupling electromagnetic energy; and differentially coupling the second antenna element and the third antenna element. said first and second positions of said antenna device are selected such that said second and third antenna elements are arranged in electromagnetic symmetry with respect to said first antenna element. Featured device. (2) The first antenna element is 1MHz and 300MHz.
z, and receiving means connected to said differentially coupled second and third antenna elements. Device. (3) A patent further comprising means for energizing said differentially coupled second and third antenna elements within the frequency range of 1 MHz and 300 MHz, and receiving means connected to said first antenna element. An apparatus according to claim (1). (4) The first antenna element is made of a conductive member fitted to a stable frame member, and the second antenna element is made of a conductive member fitted to a stable frame member. , wherein said third antenna element comprises a conductive member fitably mounted to a stable frame member, and wherein said first, second and third antenna elements are essentially scale invariant with respect to each other. A device according to scope paragraph (1). (5) the first, second and third antenna elements are essentially coplanar, and the axes of the conductive members of the first, second and third antenna elements are coaxial; and perpendicular to the wall-engaging surface of the main body.
Equipment described in Section. (6) the frame comprises a ceramic disc section coaxially integrated with a ceramic cylindrical section, and the conductive member of the first antenna element includes a first loop having a preselected diameter; This is mounted coaxially with said disk section and fitted into said disk section, said second antenna element having a second conductive member having a preselected diameter different from the diameter of said first loop. a loop mounted coaxially with the disk section and adapted to fit the disk section, and the conductive member of the third antenna element positions the second and third antenna elements in electromagnetic symmetry. 6. A device according to claim 5, comprising a coil having a diameter and a number of turns selected such that it is fitted in said cylindrical section. (7) the first, second and third antenna elements are essentially coplanar, and the axes of the conductive members of the first, second and third antenna elements are coaxial; 4. A device according to claim 4, which is parallel to the wall-engaging surface of the body. (8) the frame comprises a ceramic disc section coaxially integrated with a ceramic cylindrical section, and the conductive member of the first antenna element includes a first loop having a preselected diameter; This is mounted coaxially with said disk section and fitted into said disk section, said second antenna element having a second conductive member having a preselected diameter different from the diameter of said first loop. a loop mounted coaxially with the disk section and adapted to fit the disk section, and the conductive member of the third antenna element positions the second and third antenna elements in electromagnetic symmetry. 8. A device according to claim 7, comprising a coil having a diameter and a number of turns selected such that it is fitted in said cylindrical section. (9) The first antenna element is made of a conductive member that is fitted to the stable frame member, and the second antenna element is made of a conductive member that is fitted to the stable frame member, and the second antenna element is made of a conductive member that is fitted to the stable frame member. the third antenna element is essentially the same as the second antenna element; the first, second and third antenna elements are scale invariant to each other and are integrally assembled; Claim 1, wherein the position and orientation of each of the second and third antenna elements are selected such that the second and third antenna elements are arranged electromagnetically symmetrically with respect to the first antenna element. The device described. (10) The plane of symmetry of the second and third antenna elements is oriented at right angles to the wall-engaging surface of the body so as to obtain a measurement of the difference in properties. ). (11) The main body includes a conductive back member oriented parallel to a wall-engaging surface thereof, and the first, second, and third antenna elements are connected to the back member and the wall-engaging surface of the main body. The apparatus according to claim 10, which is arranged between. (12) The plane of symmetry of the second and third antenna elements is oriented parallel to the wall-engaging surface of the body to obtain absolute measurements of the property. The device described. (13) The main body includes a conductive back member oriented parallel to a wall-engaging surface thereof, and the first, second, and third antenna elements are connected to the back member and the wall-engaging surface of the main body. The device according to claim (12), which is arranged between. (14) The first antenna element includes a conductive loop of a selected diameter formed by photolithography on a ceramic substrate, and the second antenna element includes a conductive loop formed by photolithography on a ceramic substrate. a conductive loop having a selected diameter, the third antenna element having a conductive loop having the same diameter as the conductive loop of the second antenna element and formed by photolithography on a ceramic substrate; An apparatus according to claim (9). (15) The first, second, and third antenna elements are coaxial loop antennas, and the loop antennas of the second and third antenna elements are essentially similar to the antenna loop of the first antenna element. A device according to claim 9, arranged symmetrically in the . (16) The first, second, and third antenna elements are coplanar loop antennas, and the loop antennas of the second and third antenna elements are essentially opposite to the antenna loop of the first antenna element. A device according to claim 9, arranged symmetrically in the . (17) further comprising a pseudo-electrostatic shielding element coaxially attached to the magnetic dipole axis of one of the antenna elements, the element being made of a sheet of a conductive non-magnetic material; a first annular band of thin linear conductive segments, each conductive segment extending integrally in a radial direction from the conductive center; Adjacent conductive segments are separated from each other by narrow radially extending spaces, said spaces being adjacent to said first
starting from and traversing the annular band, and further having a second annular band consisting of linear conductive segments, each conductive segment of the first annular band radially extending integrally from the segments in pairs, the conductive segments of said second annular band joining adjacent conductive strips of the second annular band by respective longitudinal spaces starting from said first annular band. Claims (1), (9), and (14) are separated from each other by narrow radially extending spaces commencing from and transverse to said second annular band. ), (15), and (16). (18) further comprising a third annular band made of linear conductive segments, the conductive segments integrally extending in pairs in the radial direction from each conductive segment of the second annular band; The conductive segments of the third annular band are separated from adjacent pairs of conductive strips of the third annular band by respective longitudinal spaces starting from the second annular band and starting from the third annular band. 18. A device according to claim 17, which extends in a narrow radial direction transversely. (19) further comprising a conductive back member attached to the body, wherein the first antenna element has a position selected to couple image current on the back surface, and the second antenna element has a position selected to couple image current on the back surface; Claim 1, wherein the third antenna element has a position selected to couple the image current at the rear surface, and the third antenna element has a position selected to couple the image current at the rear surface. The device described. (20) The back member is parallel to the wall-engaging surface of the main body, and each of the first, second, and third antenna elements is a coaxial half-loop antenna with each end disposed on the back member. and the half-loop antennas of the second and third antenna elements are arranged essentially symmetrically with respect to the half-loop of the first antenna element. equipment. (21) A wall-engaging device for micro-inductively testing properties of a geological formation traversed by a borehole, comprising: a longitudinally extending conductive body adapted to slide into engagement with the wall of the borehole; a transmitting antenna; , comprising means for energizing said transmitting antenna and means for detecting a magnetic field resulting from said engaged formation by coupling electromagnetic energy, and partially bounded by an integral conductive back surface and conductive side surfaces. the transmitting antenna is mounted to the body in a volume open to a wall-engaging surface of the body, coupling focused electromagnetic energy to the formation engaged by the wall-engaging surface of the body; A device configured to: (22) The detection means includes a receiving antenna, and the receiving antenna is integrated with the transmitting antenna and attached together with the transmitting antenna in the volume part,
22. A device according to claim 21, wherein the volume is adapted to accommodate the integrated transmitting and receiving antenna. (23) The back surface is oriented parallel to the wall-engaging surface of the body, and the transmitting and receiving antennas are disposed between the back surface and the wall-engaging surface of the body. (
22) The device described in item 22).