CN112081586A - Multi-spectrum stratum boundary far detection method and device - Google Patents
Multi-spectrum stratum boundary far detection method and device Download PDFInfo
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- 238000001514 detection method Methods 0.000 title claims abstract description 24
- 238000001228 spectrum Methods 0.000 title abstract description 11
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims abstract description 38
- 239000011889 copper foil Substances 0.000 claims abstract description 36
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 10
- 238000004804 winding Methods 0.000 claims abstract description 10
- 230000008859 change Effects 0.000 claims description 16
- 238000000034 method Methods 0.000 claims description 12
- 230000035699 permeability Effects 0.000 claims description 4
- 238000005755 formation reaction Methods 0.000 claims 3
- 238000005553 drilling Methods 0.000 abstract description 11
- 230000005684 electric field Effects 0.000 description 17
- 238000005259 measurement Methods 0.000 description 10
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 5
- 229910052782 aluminium Inorganic materials 0.000 description 5
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- 230000005674 electromagnetic induction Effects 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/12—Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
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Abstract
The invention discloses a multi-spectrum stratum boundary far detection method and a device, wherein a coil with a circular structure is wound in a multi-turn winding mode, a copper foil is wrapped on one half of the coil, and the coil wrapped with the copper foil is placed in a stratum; rotating the coil for one circle, and judging the orientation of the layer interface according to the induced electromotive force amplitude of the coil; and electromagnetic waves with different frequencies are transmitted, and the distance of the layer interface is judged by measuring the amplitude and the phase angle of induced electromotive force according to different attenuations of the electromagnetic waves with different frequencies in a medium after the coil receives signals. The invention solves the problems that the traditional round receiving signal is weak and the traditional half coil can only adopt a single turn to measure, and has important significance for detecting the formation boundary by logging while drilling.
Description
Technical Field
The invention belongs to the technical field of electric field measurement, and particularly relates to a multi-spectrum stratum boundary far detection method and device.
Background
In the well logging industry, with the development of well logging technology, the traditional vertical well cannot meet the requirement of geological exploration, and the application of well logging while drilling is more and more extensive. The logging-while-drilling can detect the resistivity of the stratum in advance and can realize the evaluation of the advanced stratum, so that a logging-while-drilling instrument can advance towards a reservoir in the stratum.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a multi-spectrum method and apparatus for detecting far boundaries of strata to solve the above-mentioned deficiencies in the prior art, so as to quickly solve the orientation and distance of the boundaries of strata.
The invention adopts the following technical scheme:
a method of multi-spectral far boundary detection of a formation, comprising the steps of:
s1, winding a coil with a circular structure by adopting a multi-turn winding mode, wrapping a copper foil on one half of the coil, and placing the coil wrapped with the copper foil in a stratum;
s2, rotating the coil for a circle, and judging the orientation of the layer interface according to the induced electromotive force amplitude of the coil;
and S3, emitting electromagnetic waves with different frequencies, and judging the layer interface distance by measuring the amplitude and the phase angle of the induced electromotive force according to different attenuations of the electromagnetic waves with different frequencies in a medium after the coil receives signals.
Specifically, in step S2, the coil rotates once to form a plurality of peaks, where the maximum part of the peak corresponds to the position of the angular bisector of the uncoated copper foil coil, and at this time, the field strength at the corresponding position is the maximum, and the corresponding position is the layer interface position.
Specifically, step S3 specifically includes:
s301, calculating the induced electromotive force of the receiving coil when the layer interface does not exist as V1, wherein the amplitude and the phase angle are abs (V1) and angle (V1), respectively;
s302, when a layer interface parallel to the normal line of the coil exists in the position of the angular bisector of the non-copper-clad coil, the induced electromotive force of the receiving coil is marked as V2, and the amplitude and the phase angle are abs (V2) and angle (V2) respectively;
s303, recording the distance d between the transmitting coil and the layer interface, wherein the layer where the transmitting coil is located is a first layer medium, and the electric conductivity is sigma1(ii) a The other side of the layer interface is a second layer medium with the conductivity of sigma2The reflection coefficient of the layer interface is
Wherein
Mu is vacuum magnetic conductivity;1and2the complex dielectric constant of the first layer medium and the second layer medium is expressed as
′1、′2Is the real part of the dielectric constant of the first layer medium and the second layer medium, omega is the angular frequency of the electromagnetic wave, j is the imaginary unit, j2＝-1；
S304, obtaining phase angle change alpha of a field where electromagnetic waves generated by the transmitting coil are reflected to the receiving coil through the layer interface, obtaining the phase angle change relation of the field as angle (V2) -angle (V1) ═ alpha when the layer interface exists according to the field superposition principle, and solving an equation to obtain the phase angle realization layer interface distance d.
Further, the phase angle change α is:
wherein arctan () represents a tangent value of a reflection coefficient, λ is a wavelength of an electromagnetic wave in a vacuum, μrIs the relative permeability of the first layer of medium,ris the relative dielectric constant of the first layer of dielectric;
the phase angle realizes that the layer interface distance d is:
specifically, in step S3, for an infinite homogeneous formation, L is the distance between the transmitter coil and the receiver coil, σ is the electrical conductivity, μ is the magnetic conductivity, and ω is the dielectric constant, and for electromagnetic waves of two frequencies, ω is the angular frequency, respectively1、ω2The induced electromotive forces generated by the receiving coil are respectively V1 and V2, the corresponding amplitude and phase angle are respectively abs (V1), angle (V1), abs (V2) and angle (V2), and the amplitude relationship is as follows:
the phase angle relationship is:
wherein e is a natural index, j is an imaginary unit, j is2＝-1。
The invention also provides a multi-spectrum stratum boundary far detection device which comprises a coil, wherein the coil is of a circular structure and is wound in a multi-turn mode, and a copper foil is wrapped on one half of the coil.
Specifically, the coil and the copper foil are hermetically connected.
Specifically, the number of turns of the transmitting coil is 10-500, and the number of turns of the receiving coil is 10-500.
Compared with the prior art, the invention has at least the following beneficial effects:
the invention relates to a multi-spectrum stratum boundary far detection method, which belongs to the field of logging while drilling, wherein an electric field becomes uneven when a layer interface exists, the electric field at the position of the layer interface is enhanced due to the existence of reflected waves, the electric field at the position of a back layer interface is weakened, the size of the field intensity can be judged by rotating a constructed half coil according to induced electromotive force, and the position of the layer interface is further judged. And adopting different working frequency modes, and realizing the judgment of the stratum boundary distance according to the amplitude phase angle by measuring different induced electromotive forces. Through the constructed half coil, the problems that the traditional round receiving signal is weak and the traditional half coil can only adopt a single turn to measure are solved, and the half coil has important significance for logging while drilling and detecting the formation boundary.
Furthermore, when the layer interface exists, the electromagnetic field at the coil is not non-uniform any more, and a plurality of peak values of induced electromotive force appear by rotating the receiving coil for a circle, namely the induced electromotive force of the coil without the copper foil is the largest when the coil is over against the layer interface, the induced electromotive force of the coil with the copper foil is the smallest when the coil is back against the layer interface, and the layer interface azimuth information is judged according to the peak values and the rotation angle. By identifying the layer interface layering, the logging-while-drilling instrument can quickly identify the azimuth information of the reservoir interface, so that the drill collar moves towards the reservoir direction, and the drilling rate is improved.
Furthermore, by detecting the distance information of the layer interface, the drill collar instrument can identify the information such as the thickness of the reservoir layer in the reservoir layer through the layer interface distance.
Furthermore, because the receiving coil is single, the distance information of the layer interface cannot be solved by the electromagnetic field with single frequency, the receiving coil generates different induced electromotive forces by transmitting electromagnetic waves with different frequencies, and the distance information of the layer interface is calculated according to the amplitude of the induced electromotive forces and the phase angle change rule.
According to the multi-spectrum stratum boundary far detection device, according to the constructed coil model, the electric field can be measured through the model, and further the stratum boundary can be measured according to the detection characteristics of the half coil.
Furthermore, the copper foil is coated outside the coil, and the electromagnetic induction of the electromagnetic field in the stratum to the coated coil is eliminated by utilizing the shielding principle of the conductor to the electromagnetic field, namely the coated coil cannot generate induced electromotive force. The copper foil is coated and sealed, so that an electromagnetic field can not generate electromagnetic induction on the coated coil through a gap, namely, only the coil which is not coated with the copper foil generates induced electromotive force by the receiving coil.
Furthermore, due to the existence of the layer interface, the reflected signal is very weak, and the induced electromotive force amplitude of the receiving coil can be improved by arranging the multi-turn coil, so that the actual measurement is facilitated.
In summary, when a layer interface exists, the field at the receiving coil becomes non-uniform, the induced electromotive forces generated by the traditional circular receiving coil in the non-uniform electric field can be mutually offset, so that the induced electromotive forces generated by the coil are mutually offset, and therefore, when the layer interface exists, the invention adopts the half coil to carry out measurement. Since the half coil in the form of a half turn cannot be wound by a plurality of turns when actually measuring the induced electromotive force. If the winding is carried out for a plurality of turns, a closed loop is formed, and the integration result of the induced electromotive force is zero. The invention adopts a copper foil winding mode to solve the problem, coats copper foil on half of the lead of the coil on the basis of the traditional circular coil, forms a multi-turn half coil by utilizing the shielding effect of the copper foil, and effectively improves the amplitude of the induced electromotive force.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a diagram of a coil model for multi-spectral remote detection of formation boundaries in accordance with an embodiment of the present invention;
FIG. 2 is a graph of an electric field distribution at a coil location in the presence of a layer interface according to an embodiment of the present invention;
FIG. 3 is a diagram of an induced electromotive force model measured by an aluminum plate boundary in an experiment according to an embodiment of the present invention;
FIG. 4 is an induced electromotive force amplitude image of a half-coil rotating one cycle according to the present invention;
FIG. 5 is a phase angle image of induced electromotive force of a half-coil rotating one cycle according to the present invention;
FIG. 6 is an induced electromotive force amplitude image of the novel half coil according to the variation of the layer interface distance in the embodiment of the present invention;
fig. 7 is an induced electromotive force phase angle image of the novel half coil according to the variation of the layer interface distance in the embodiment of the present invention.
Wherein: 1. a coil; 2. copper foil; 3. an aluminum plate; 4. a transmitting coil; 5. a receiving coil; 6. vector network analyzer.
Detailed Description
In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "one side", "one end", "one side", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be construed as limiting the present invention. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Various structural schematics according to the disclosed embodiments of the invention are shown in the drawings. The figures are not drawn to scale, wherein certain details are exaggerated and possibly omitted for clarity of presentation. The shapes of various regions, layers and their relative sizes and positional relationships shown in the drawings are merely exemplary, and deviations may occur in practice due to manufacturing tolerances or technical limitations, and a person skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions, according to actual needs.
Referring to fig. 1, the present invention provides a multi-spectral far-from-boundary detection device for a formation, including a coil 1 and a copper foil 2, wherein the coil 1 is a circular structure, half of the coil 1 is wrapped with the copper foil 2, and the coil 1 is wound by multiple turns to increase the size of a measurement signal.
The coil 1 and the copper foil 2 are completely sealed, and by utilizing the high conductivity of the copper foil 2, the copper foil 2 can form an equipotential body when placed in an electric field, and the electric field in the copper foil 2 is zero; the conductivity of the copper foil 2 can shield the effect of an electric field on the coil 1, so that the coated coil 1 does not generate induced electromotive force, and the measurement of the electric field is realized by using the other half of the coil 1 which is not coated; and judging the distance and the direction of the layer interface by adopting a working mode of multiple frequencies according to the size of the received signal.
When the layer interface exists, the induced electromotive force generated by the single-turn receiving coil is V1Induced electromotive force V-V for a receiving coil wound with N turns1N, in order to increase the signal size of the receiving coil obviously, the transmitting coil of the invention has 10-500 turns and receivesThe coil has 10 to 500 turns.
The copper content > of the coil-coated copper foil was 98.8%, the thickness was 70 μm, and the conductivity >1E 7S/m.
The method specifically comprises the following steps: the coil 1 is rotated to judge the position and distance of the layer interface according to the magnitude and the rotation angle of the induced electromotive force, and has important significance for real-time inversion and geological guidance of logging while drilling.
Because of the existence of the layer interface, the reflected wave and the incident wave are mutually offset at the measuring coil, the signal measured by the coil is very small, the coil can realize multi-turn measurement, the measuring signal is effectively improved, and compared with the traditional circular coil, the measuring signal is greatly enhanced.
The invention discloses a multi-spectrum stratum boundary far detection method, which comprises the following steps:
s1, winding a coil 1 with a circular structure by adopting a multi-turn winding mode, hermetically wrapping a copper foil 2 on a half structure of the coil 1 with the circular structure, and placing the half coil 1 wrapped with the copper foil 2 in a stratum, wherein the radius of the coil 1 is smaller than the wavelength of electromagnetic waves, the frequency of the electromagnetic waves emitted by a transmitting coil is 10 kHz-100 kHz when a layer interface is detected, the wavelength of the electromagnetic waves is far greater than 3 km-30 km, and the radius of a receiving coil is 0.1m, so that the radius is far smaller than the wavelength of the electromagnetic waves, and the field at the position of the coil 1 is approximately regarded as vector fields with the same direction and different field intensities;
the transmitting coil is a circular coil, the normal line of the plane where the coil is located is superposed with the axis of the drill collar, the receiving coil can be any regular polygon (including a circle), and the center of the receiving coil is coaxial with the center of the transmitting coil, so that the shape of the receiving coil is ensured to be symmetrical about the center in the rotating process; when a layer interface exists, the field at the receiving coil is as shown in the following diagram (layer interface x is 0.5m) due to the existence of the layer interface.
Referring to fig. 1, taking a circular receiving coil as an example, when a layer interface exists, the integration result along the right half side of the coil is positive, and the integration result along the left half side of the coil is negative, so that the induced electromotive force of the whole coil becomes very small due to mutual cancellation of the left and right half side coils.
S2, rotating the coil 1 for a circle, judging the position of the layer interface according to the amplitude of the induced electromotive force of the coil 1, and forming a plurality of peak values in the coil 1 rotating for a circle due to the winding asymmetry of the coil 1, wherein the maximum part of the peak values corresponds to the position of an angular bisector of half of the coil 1 which is not coated with the copper foil 2, namely the field intensity of the corresponding position is maximum at the moment, and the corresponding position is the position of the layer interface;
the receiving coil and the transmitting coil are coaxial and are wound on the drill collar, when the drill collar rotates and advances during logging, the transmitting coil and the receiving coil rotate along with the drill collar, when the receiving coil meets a layer interface (the layer interface is parallel to the drill collar), the distribution of fields is as shown in the figure 1, because the receiving coil is wound with copper foil, only half of the coil generates induced electromotive force during rotation, when the coil rotates to a region with a larger electric field (x is larger than 0 in the figure 1), the induced electromotive force reaches the maximum, and at the moment, the corresponding azimuth angle is the azimuth of the layer interface.
S3, emitting electromagnetic waves with different frequencies by adopting working modes with different frequencies, and judging the layer interface distance by measuring the amplitude and the phase angle of induced electromotive force according to the different attenuation of the electromagnetic waves with different frequencies in a medium through signals received by the receiving coil 1.
S301, calculating the induced electromotive force of the receiving coil when the layer interface does not exist as V1, wherein the amplitude and the phase angle are abs (V1) and angle (V1), respectively;
s302, when a layer interface parallel to the normal line of the coil exists in the position of the angular bisector of the non-copper-clad coil, the induced electromotive force of the receiving coil is marked as V2, and the amplitude and the phase angle are abs (V2) and angle (V2) respectively;
s303, recording the distance d between the transmitting coil and the layer interface, wherein the layer where the transmitting coil is located is a first layer medium, and the electric conductivity is sigma1(ii) a The other side of the layer interface is a second layer medium with the conductivity of sigma2The reflection coefficient of the layer interface is
Wherein
Mu is vacuum magnetic conductivity;1and2the complex dielectric constant of the first layer medium and the second layer medium is expressed as
′1、′2Is the real part of the dielectric constant of the first layer medium and the second layer medium, omega is the angular frequency of the electromagnetic wave, j is the imaginary unit, j2＝-1；
S304, obtaining phase angle change alpha of a field where electromagnetic waves generated by the transmitting coil are reflected to the receiving coil through the layer interface, obtaining the phase angle change relation of the field as angle (V2) -angle (V1) ═ alpha when the layer interface exists according to the field superposition principle, and solving an equation to obtain the phase angle realization layer interface distance d.
The phase angle change α is:
wherein arctan () represents a tangent value of a reflection coefficient, λ is a wavelength of an electromagnetic wave in a vacuum, μrIs the relative permeability of the first layer of medium,ris the relative dielectric constant of the first layer of dielectric;
the phase angle realizes that the layer interface distance d is:
assuming that the relative dielectric constants of the first layer of medium and the second layer of medium are both 5, and the relative magnetic conductivities of the first layer of medium and the second layer of medium are both 1; the conductivity of the first layer of medium is 0.01S/m, and the conductivity of the second layer of medium is 0.5S/m; the circle center coordinates of the transmitting coil (0,0,0) and the receiving coil (0,0,0.5), the radiuses of the transmitting coil and the receiving coil are both 0.03m, the number of turns of the transmitting coil is 100, and the number of turns of the receiving coil is 50; layer interface position x ═ 1; the transmitting coil current 1A is a sinusoidal alternating current with a frequency of 100 kHz. The angular bisector of the receiving coil without the copper foil coil is the-x axis, the receiving coil is rotated, the induced electromotive force amplitude curve of the receiving coil is shown in figure 4, and the phase angle curve is shown in figure 5, so that when the receiving coil is rotated by 180 degrees, namely the angular bisector without the copper foil coil is located on the x axis, the angular bisector is opposite to the layer interface, the amplitude reaches the trough, the phase angle reaches the crest, and the position information of the layer interface can be identified.
When the angular bisector of the receiving coil without the copper foil coil is the x axis, the layer interface is moved, the amplitude and the phase angle curve of the induced electromotive force are shown in fig. 6 and 7, the amplitude is gradually reduced along with the distance of the layer interface, when the curve is stable, the reflection information of the layer interface cannot be detected, the phase angle tends to 90 degrees, the stratum can be considered to be a uniform stratum at the moment, the induced electromotive force of the receiving coil is only the direct coupling electromotive force, the phase angle is 90 degrees, and the change rule of the phase angle curve is met.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 2, when a layer interface exists, the reflection field of the layer interface is superimposed with the incident field at the receiving coil, the field intensity at one side of the layer interface is increased, the field intensity at the position of the back layer interface is decreased, the induced electromotive force generated by the traditional circular coil in the superimposed field intensity is greatly decreased, and the stability of the measurement signal is poor. Meanwhile, in order to improve the signal strength of the receiving coil, researchers have proposed that half of the full coil is used to measure the electric field, and since a closed loop cannot be formed, the half coil of this type can only be a single turn, and the signal improvement effect is not great. The half-coil detection device provided by the invention realizes multi-turn measurement under the condition of a guaranteed closed loop, and greatly improves the signal size of a receiving coil.
In order to describe the measurement mode of the half-coil detection device in detail, a conventional circular transmitting coil and a half-receiving coil detection device are arranged above an aluminum plate 3, a test model of the half-coil detection device is shown in fig. 3, one end of a vector network analyzer 6 is connected with a transmitting coil 4, the other end of the vector network analyzer is connected with a receiving coil 5, and the vector network analyzer 6 measures the size of a received signal through the receiving coil 5. In order to measure the orientation information of the layer interface, the receiving coil 5 is rotated, and the induced electromotive force received under different rotation angles is measured by the vector network analyzer 6, so that the orientation information of the layer interface is analyzed. In order to measure the distance information of the layer interface, the aluminum plate is gradually far away from the receiving coil (the aluminum plate is always parallel to the axis of the coil), the induced electromotive force of the receiving coil 5 is measured through the vector network analyzer 6, and then the distance of the layer interface is calculated according to the expression. The measuring device can be placed in other media for measurement, and the measuring method is not limited to the measuring method provided by the invention.
In order to verify the capability of the half-coil detection device in detecting the layer interface orientation, a simulation calculation model is constructed, the half-coil detection device is simulated to be placed in an electric field shown in figure 2, a receiving coil 5 is rotated, and the magnitude of the induced electromotive force amplitude measured by the device is calculated, as shown in figure 4, the induced electromotive force has a peak value, and the corresponding rotation angle is 180 degrees, so the orientation of the stratum boundary can be judged by rotating a coil 1. The maximum change in phase angle when rotated 180 ° is demonstrated by the change in phase angle of fig. 5, which also demonstrates the orientation of the layer interface.
Referring to fig. 6 and 7, in order to verify the capability of the half-coil detection device of the present invention in detecting the layer interface distance, a simulation calculation model is constructed to simulate the separation of the layer interface from the receiving coil 5, the amplitude and the phase of the induced electromotive force measured by the device of the present invention are calculated, and the determination of the layer interface distance is realized according to the change of the amplitude and the phase of the induced electromotive force. The amplitude of the induced electromotive force gradually decreases with the distance of the layer interface, mainly due to the attenuation of electromagnetic waves, and when the distance is more than 10m, the induced electromotive force does not change any more, mainly due to the fact that the specific gravity of the background signal is large, and therefore the detection depth is 10 m. The phase angle change can be seen to be no longer changed at about 10m, and the detection depth is also concluded to be 10m as long as the proportion of the phase angle of the background signal is larger.
The invention relates to a multi-spectrum stratum boundary far detection method and a multi-spectrum stratum boundary far detection device. In the field of logging while drilling, when a layer interface exists, an electric field becomes uneven, wherein the field intensity of the electric field at the position of the layer interface is enhanced due to the existence of reflected waves, the field intensity of the electric field at the position of the layer interface is weakened, the constructed half coil can judge the magnitude of the field intensity through rotating according to induced electromotive force, and further the position of the layer interface is judged. And adopting different working frequency modes, and realizing the judgment of the stratum boundary distance according to the amplitude phase angle by measuring different induced electromotive forces. Through the constructed half coil, the problems that the traditional round receiving signal is weak and the traditional half coil can only adopt a single turn to measure are solved, and the half coil has important significance for logging while drilling and detecting the formation boundary.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (8)
1. A method for multi-spectral far boundary detection of a formation, comprising the steps of:
s1, winding a coil with a circular structure by adopting a multi-turn winding mode, wrapping a copper foil on one half of the coil, and placing the coil wrapped with the copper foil in a stratum;
s2, rotating the coil for a circle, and judging the orientation of the layer interface according to the induced electromotive force amplitude of the coil;
and S3, emitting electromagnetic waves with different frequencies, and judging the layer interface distance by measuring the amplitude and the phase angle of the induced electromotive force according to different attenuations of the electromagnetic waves with different frequencies in a medium after the coil receives signals.
2. The method of claim 1, wherein in step S2, the coil rotates one circle to form a plurality of peaks, and the maximum part of the peak corresponds to the position of the angular bisector of the uncoated copper foil coil, and the corresponding position has the highest field strength and is the layer interface position.
3. The method of claim 1, wherein step S3 is specifically:
s301, calculating the induced electromotive force of the receiving coil when the layer interface does not exist as V1, wherein the amplitude and the phase angle are abs (V1) and angle (V1), respectively;
s302, when a layer interface parallel to the normal line of the coil exists in the position of the angular bisector of the non-copper-clad coil, the induced electromotive force of the receiving coil is marked as V2, and the amplitude and the phase angle are abs (V2) and angle (V2) respectively;
s303, recording the distance d between the transmitting coil and the layer interface, wherein the layer where the transmitting coil is located is a first layer medium, and the electric conductivity is sigma1(ii) a The other side of the layer interface is a second layer medium with the conductivity of sigma2The reflection coefficient of the layer interface is
Wherein
Mu is vacuum magnetic conductivity;1and2the complex dielectric constant of the first layer medium and the second layer medium is expressed as
′1、′2Is a first layer medium and a second layer mediumReal part of dielectric constant of layer medium, omega is angular frequency of electromagnetic wave, j is imaginary unit, j2＝-1；
S304, obtaining phase angle change alpha of a field where electromagnetic waves generated by the transmitting coil are reflected to the receiving coil through the layer interface, obtaining the phase angle change relation of the field as angle (V2) -angle (V1) ═ alpha when the layer interface exists according to the field superposition principle, and solving an equation to obtain the phase angle realization layer interface distance d.
4. The method of claim 3, wherein the phase angle change α is:
wherein arctan () represents a tangent value of a reflection coefficient, λ is a wavelength of an electromagnetic wave in a vacuum, μrIs the relative permeability of the first layer of medium,ris the relative dielectric constant of the first layer of dielectric;
the phase angle realizes that the layer interface distance d is:
5. the method of claim 1, wherein in step S3, for an infinite homogeneous formation, the distance between the transmitter coil and the receiver coil is L, the conductivity is σ, the permeability is μ, and the dielectric constant is ω, the angular frequency of the electromagnetic wave is ω, and the angular frequency of the electromagnetic wave is ω, respectively1、ω2The induced electromotive forces generated by the receiving coil are respectively V1 and V2, the corresponding amplitude and phase angle are respectively abs (V1), angle (V1), abs (V2) and angle (V2), and the amplitude relationship is as follows:
the phase angle relationship is:
wherein e is a natural index, j is an imaginary unit, j is2＝-1。
6. A multi-spectral far-boundary detector for earth formations using the method of claim 1, comprising coils (1), wherein the coils (1) are in a circular structure and are wound by a plurality of turns, and half of the coils (1) are wrapped with copper foils (2).
7. A device according to claim 6, characterized in that the connection between the coil (1) and the copper foil (2) is sealed.
8. The device of claim 6, wherein the number of turns of the transmitting coil is 10-500 turns, and the number of turns of the receiving coil is 10-500 turns.
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