RU2733110C1 - Downhole multifrequency introscope for investigation of near-borehole space - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to means of geophysical exploration of borehole environment and can be used in oil, gas and engineering geology, hydrogeology and geocryology for studying physical properties of rocks, separation of reservoirs and determination of their saturation (water, oil, gas), as well as assessment of permafrost conditions of soils and detection of local inhomogeneities located in borehole environment. Disclosed is downhole multifrequency introscope for investigation of near-wellbore, which includes ground part consisting of computer module 107 and associated repeater 106, and downhole part consisting of located along one axis of optical-electric converter 101 of logging cable 108, well radiator 102 and upper 103 and lower 104 well receivers. Well emitter 102 is provided with an electrical antenna which is configured to emit harmonic radio signals into the borehole well in series at a plurality of frequencies selected from the frequency range of 1 to 50 MHz in accordance with the radiation program received by downhole radiator 102 from the ground portion, and recording values of current amplitude and complex resistance at the input of its antenna at each radiation of the radio signal and transmission of measured values in digital form to the ground part. Top and bottom 104 well receivers are remote from downhole radiator 102 by two fixed distances and are equipped with electric antennae configured to receive radio signals transmitted through the rocks occurring in the near borehole space, wherein well receivers 103 and 104 are configured to record amplitude values of the axial component of the electric field of the received radio signal and phase difference of measured field between antennae of receivers 103 and 104 and transmission of said values in digital form to ground part. Computing module 107 is configured to generate a radiation program for transmission thereof to downhole emitter 102, receiving from it and from downhole receivers 103 and 104 values of registered values in digital form through retransmitter 106, calculations based on these values of electric resistance and dielectric permeability of rocks lying in near-borehole space. Retransmitter 106 is configured to match computing module with logging cable.

EFFECT: technical result is high accuracy of determining information parameters, characterizing rocks, lying in borehole environment.

8 cl, 5 dwg

Description

Technology area

The present invention relates to tools for geophysical surveying of the near-wellbore space, in particular, to an electromagnetic logging device for determining the electrical resistance and dielectric constant of rocks located near the wellbore. The invention can be used in oil, gas and engineering geology, hydrogeology and geocryology to study the physical properties of rocks, identify reservoir beds and determine the nature of their saturation (water, oil, gas), as well as assess the frozen-thawed state of soils and detect local heterogeneities located in the near-wellbore space.

State of the art

Well logging (GIS) is a complex of physical methods used to study rocks in the near-wellbore space, as well as to monitor the technical condition of wells. Logging, also known as production geophysics, is designed to study the properties of rocks immediately adjacent to the wellbore (survey radius up to 1.5 m). Based on the logging results, the necessary geological constructions are performed.

It is also known that the electrical properties of rocks depend on the degree of their porosity and the properties of the fluid filling the pores: fresh or mineralized water, oil, gas, ice. Therefore, electrometric well survey methods and especially non-contact electromagnetic logging methods are widely used in all branches of geology.

Devices and measuring systems are known from the prior art for electromagnetic and, in particular, dielectric well logging. Among them, the closest to the proposed invention are the following.

Known device for dielectric inductive logging, disclosed in the description to the USSR AS No. 212387 (publ. 05/28/1969). The known device consists of a generator part and a receiving part. The generator is a two-stage transmitter consisting of a quartzised master oscillator and a power amplifier. The generator output is loaded on the generator coil. The receiving part of the device is two-channel, it has two spaced receiving frames, resonant amplifiers and high-frequency amplifiers, mixing stages and frequency conversions, a common local oscillator, amplifiers and an intermediate frequency, a phase-measuring unit and a recording device.

Known equipment for electromagnetic logging, disclosed in the description of the USSR AS No. 374565 (publ. 03/20/1973). The known equipment contains a generator, a synchronized switching device containing a generator switching and receiving switching units, two emitters, a receiver, a conversion device, a logging cable, three recorders, a device for information processing.

Known device for electromagnetic logging, disclosed in the description to the USSR AS No. 1469490 (publ. 03/30/1989). The known device contains a generator unit, a probe, a receiving-converting part, a measuring-telemetric part and a ground part. The generator unit includes a master oscillator of two frequencies and two power amplifiers. The two 3-piece probes are composed of transmitter coils and two receiver coils. The receiving-converting part contains an oscillator-local oscillator, mixers-multiplexers, limiters. The measuring and telemetry part includes a control unit, a phase difference and a period shaper, a phase difference meter, an intermediate frequency period meter, a multiplexer, a transmitter and a communication line. The ground part contains a receiver, a register-pointer of the measured values, a phase shift register, a register of a measurement period, a divider, a phase shift converter, and digital-to-analog converters.

The technical solutions presented above use probes consisting of generator antennas that excite a high-frequency harmonic electromagnetic field in the surrounding rocks and measuring antennas that allow recording the amplitude and phase of the signal that has passed through the rocks. A limitation of the existing devices is the use of frame-type antennas - coils whose axis coincides with the axis of the borehole - as emitting and receiving devices (HzHz measuring devices). The main advantages of such systems are their compactness, relative simplicity of design and weak dependence on the antenna effect of the logging cable and wires connecting the receiving and transmitting antennas.

The main disadvantages of such devices include the low efficiency of magnetic antennas, since at emitter-receiver distances of more than 2 m in a normal section, it is not possible to obtain a reliable signal at high frequencies (more than 20 MHz), at which, in fact, the influence of the dielectric constant begins to appear. ... This causes insufficient depth of research (the distance from the axis of the well, at which the surrounding rocks still affect the recorded parameters), which does not allow judging the properties of rocks in the unchanged part of the formation outside the drilling mud invasion zone.

Another disadvantage of these devices is the use of one, rarely two operating frequencies, which does not allow determining the frequency dispersion of the electrical properties of the formation, which carries important information about the textural and structural features of the host rock fluids.

Disclosure of the essence of the invention

The technical problem underlying the present invention is to provide the possibility of obtaining informative parameters characterizing rocks that occur in the near-wellbore space.

The technical result achieved with the implementation of the present invention is to improve the accuracy of determining the informative parameters characterizing rocks occurring in the near-wellbore space.

In accordance with the present invention, the technical result is achieved by a multi-frequency borehole introscope for studying the near-wellbore space, includes a surface part consisting of a computing module and an associated repeater, and a borehole part, which is connected to the repeater by means of a logging cable, consisting of optical-electric a logging cable transducer, a borehole transmitter and upper and lower borehole receivers, while:

the borehole transmitter is equipped with an electric antenna, which is configured to emit harmonic radio signals into the near-borehole space sequentially at several frequencies selected from the frequency range from 1 to 50 MHz in accordance with the radiation program received by the borehole transmitter from the surface part, and recording the values of the current amplitude and complex resistance at the input of its antenna for each radio signal emission and transmission of measured values in digital form to the ground part;

the upper and lower borehole receivers are removed from the borehole transmitter by two fixed distances and are equipped with electric antennas capable of receiving radio signals that have passed through rocks lying in the near-borehole space, while said borehole receivers are made with the ability to record the amplitude values of the axial component of the electric field received the radio signal and the phase difference of the measured field between the antennas of the receivers and transmitting these values in digital form to the ground part;

the computing module is configured to generate a radiation program for transmitting it to the borehole transmitter, receiving from them the values of the registered values in digital form through a repeater, calculating on the basis of these values the electrical resistance and dielectric constant of rocks lying in the borehole space;

the repeater is configured to match the computing module with the logging cable.

The measurements are carried out in a wide frequency range of 1 - 50 MHz, in which the dispersion of the electrical properties of rocks associated with the boundary polarization caused by the tortuosity of pore channels in the rock is most pronounced. The study of an additional parameter of dispersion of electrical properties makes it possible to characterize the structure of rocks and improve the accuracy of determining the nature of saturation of layers.

The introscope in accordance with the present invention employs special designs of borehole emitters and receivers that allow measurements of high-frequency electric fields using electrical antennas that are free from the antenna effect. Each of the above-mentioned devices of the downhole part is located in a dielectric housing, in which the same type of two-arm radiating or receiving electric antennas are placed, and each of the antennas contains an electronic circuit operating from an autonomous power source and located in the antenna body, and the exchange of data and commands between the downhole radiator , receivers and ground part are provided with optical channels with optical-electrical converters.

The difference from known devices for dielectric logging and the main advantages of the claimed introscope are the following properties:

- the use of axial symmetrical isolated electric antennas in the field emitter and receivers provides a significant increase in the "depth" of research, that is, the determination of the electrical properties of rocks at large distances relative to the borehole axis and unaltered by its influence (zone of drilling mud penetration, etc.);

- carrying out measurements sequentially at several frequencies from the range of 1 - 50 MHz allows to quantify the coefficients of frequency dispersion of electrical properties of rocks, both resistance and dielectric constant, and use these parameters for more accurate calculation of the water saturation coefficient;

- during each measurement, simultaneously with the received signal, the voltage and complex impedance at the input of the radiating antenna are recorded, which make it possible to evaluate the electrical characteristics of the medium near the radiating antenna and, thereby, increase the accuracy of determining the electrical characteristics of unaltered rocks by making appropriate corrections.

Brief Description of Drawings

The present invention is illustrated by the drawings, in accordance with which:

- figure 1 shows a block diagram of a multi-frequency borehole introscope for studying the near-wellbore space;

- figure 2 shows a functional diagram of a downhole transmitter;

- figure 3 shows a functional diagram of a downhole receiver;

- figure 4 shows a functional diagram of the repeater;

Fig. 5 shows a fragment of the graphical user interface of the software of the computing module.

Implementation of the invention

The introscope in accordance with the present invention can be used in exploration and production uncased wells. Such wells can be drilled for oil, gas, solid minerals, as well as for various engineering and geological works. Wells can be cased with fiberglass or polyethylene. The structural design of the introscope allows its use in wells filled with water or oil-based drilling mud, as well as in dry wells.

The introscope is designed to measure in a borehole the amplitude and phase of the axial component of the electric field excited in the harmonic frequency range of 1-50 MHz. The main parameters obtained at the output of the computational module of the introscope are the effective electrical resistance (ρ _eff ) and the effective dielectric constant (ɛ _eff ) of rocks, calculated at a specific frequency of the electromagnetic field emitted by the borehole emitter.

In accordance with figure 1, the declared introscope structurally consists of two parts - downhole and ground. In more detail, the downhole part consists of a coaxial optical-electrical transducer 101, a logging cable 108, a downhole transmitter 102, an upper downhole receiver 103 and a lower downhole receiver 104, which are sequentially connected via an optical channel by optical fiber communication lines 109, 110 and 111. Fiber-optic line communication 109 connects the optical-electrical converter 101, the fiber optic communication line 110 connects the downhole transmitter 102 and the upper downhole receiver 103, the fiber optic communication line 111 connects the upper downhole receiver 103 and the lower downhole receiver 104.

The downhole part is configured to move along the wellbore, which is provided by the logging hoist 105. In one particular case, the downhole part can be moved along the wellbore with a predetermined step in order to obtain measurements of the parameters of the electric field radiated into the near-wellbore space in multiple measurement points downhole. In another particular case, the borehole part can be configured to move along the wellbore continuously at a predetermined speed sufficient to obtain measurements of the parameters of the electric field emitted into the near-wellbore space in a continuous mode in the amount required for subsequent interpretation.

The surface portion is connected to the downhole portion via a logging cable 108 and consists of an associated repeater 106 and a computing module 107.

The borehole transmitter 102, in accordance with figure 2, consists of a series-connected antenna 201, a unit for measuring radiation parameters 202, a power amplifier 203, a frequency synthesizer 204 and a processor 205. In this case, the processor 205 is additionally connected with the power amplifier 203, with a unit for measuring parameters radiation 202, through an analog-to-digital converter (ADC) 206, as well as with a power control unit and optical-electrical converters 207, to which fiber-optic communication lines 109 and 110 are connected.

The power control unit and optical-electrical converters 207, upon a command received from the computing module 107 via the fiber-optic communication line 109, can put the downhole transmitter 102 into a "sleep" mode with micro-consumption and back into an "operating" mode. In the operating mode, the power control unit and optical-electrical converters 207 transmits the commands received for this device from the fiber-optic communication line 109 to the processor 205, the rest of the commands are relayed to the fiber-optic communication line 110. At the command received by the processor 205 from the computing module 107, the frequency synthesizer 204 begins to sequentially generate harmonic oscillations at frequencies from the range of 1 - 50 MHz in accordance with the specified program. This signal is amplified by the power amplifier 203, through the unit for measuring the radiation parameters 202 is fed to the antenna 201 and radiated into the near-wellbore space. The unit for measuring radiation parameters 202 records the voltage across the antenna 201 and its complex impedance. This data is fed through the ADC 206, to the processor 205, and through the power control unit and optical-electrical converters 207 and the optical fiber 1 to the computing module 107.

The upper borehole receiver 103, in accordance with figure 3, consists of a series-connected antenna 301, a radio frequency amplifier 302, a mixer 303, an intermediate frequency amplifier 304, an analog-to-digital converter (ADC) 305, a processor 306. In this case, the processor 306 is additionally connected with frequency synthesizer 307, which is connected to mixer 303. Processor 306 is also connected to power control unit and optical-electrical converters 308, to which fiber-optic communication lines 110 and 111 are connected.

The power control unit and optical-electrical converters 308 operates similarly to the power control unit and optical-electrical converters 207 of the borehole transmitter 102. The electromagnetic field transmitted from the borehole transmitter 101 through the rocks is converted into an electrical signal in the antenna 301. This signal, through the RF amplifier 302, is fed to the mixer 303. The signal from the frequency synthesizer 307 is also received here. The signal frequency is determined by the data processor 306. Mixing, the signals are converted into an intermediate frequency signal, the amplitude of which is proportional to the signal from the antenna 301. This signal is fed to the intermediate frequency amplifier 304 and then to the ADC 305. The digitized signal is transmitted to the processor 306. The processor 306 generates a data set for transmission to the computing module 107 through the power control unit and optical-electrical converters 308.

The lower borehole receiver 104 is similar to the upper borehole receiver 103, except that instead of the fiber optic link 110, it is connected to the fiber optic link 111.

The repeater 106, in accordance with figure 4, consists of a series-connected matching unit 402, a processor 403 and a digital interface 404, while the processor 403 is additionally connected to the current generator 405. The matching unit 402 and the current generator 405 are connected to the collector 401 of the logging hoist 105 The digital interface 404 can be USB or Wi-Fi and is designed to provide data exchange between the repeater 106 and the computing module 107.

The processor 403, through the matching unit 402, receives or transmits data transmitted via the digital interface 404 from the computing module 107 to the reservoir 401 of the logging elevator 105 and then through the logging cable 108 to the optical-electrical transducer 101. The processor also provides the operation of the current generator 405 required to power the optical-electrical transducer 101 in accordance with the electrical characteristics of the logging cable 108. The repeater 106 is powered from the 220V network through the power supply 406.

The computing module 107 is configured to transmit commands to the downhole transmitter 102, receivers 103 and 104, receive from them parameters characterizing the propagation of a high-frequency electric field in the near-wellbore space, and calculate, based on such parameters, the effective values of the electrical resistivity and dielectric constant of rocks in the near-wellbore space for a specific frequency of the electromagnetic field emitted by the borehole transmitter 102.

The study of the near-wellbore space using the claimed introscope is carried out as follows. The downhole part is moved along the wellbore survey interval. In this case, each depth corresponds to a set of measurements of the phase and amplitude of the signal proportional to the strength of the electromagnetic field excited by the borehole transmitter and passed through the rocks in the near-wellbore space, as well as the current at the input of the transmitter antenna and the complex resistance of the antenna at this frequency. Measurements are carried out at several frequencies in the most informative range from 1.25 to 50 MHz. Specific frequencies from 2 to 50 are set when preparing the device for measurements. The entire rig is moved in the borehole at a predetermined pitch using the logging cable 108.

The interpretation is carried out iteratively by the fitting method by comparing the measured field with the calculated one. The selection is carried out at all measured frequencies simultaneously by minimizing the functionality.

The collection of measurements at the output of each of the borehole receivers 103 and 104 can be visualized as "frequency spectra" plots (501), as shown in FIG. 5. The vertical axis is the depth, the horizontal axis is the operating frequencies, and the color is the intensity of the measured field parameter.

Evaluation of the influence of the invasion zone is carried out by comparing the values of ρ _eff and ɛ _eff , calculated from measurements at small and large separations of the installation.

Figure 5 shows the graphical user interface of the software of the computing module 107. The left part shows the frequency spectrum of the field In (Ez) 501. The window 502 presents a visualization of the derived experimental frequency dependence of the field at a specific depth. Fields 503 and 504 correspond to the derivation of the interpretation parameters: the calculated values of the effective dielectric constant ɛ _eff , the effective electrical resistivity of the rocks ρ _eff and the frequency dispersion coefficients 505 and 506, corresponding to the fitted theoretical curve.

The dispersion coefficients at each depth opposite the reservoir are used to determine the exponent in the Archie-Dakhnov equation (MN coefficient), which, in turn, is used to calculate the water saturation coefficient Kw (or oil saturation (Kn = 1-Kw).

Claims (12)

1. Downhole multifrequency dielectric introscope for exploring the near-wellbore space, including the surface part, consisting of a computing module and an associated repeater, and connected to the repeater by means of a logging cable, a downhole part consisting of an optical-electric transducer of a logging cable, a downhole transmitter and upper and lower borehole receivers, while: the borehole transmitter is equipped with an electric antenna, which is configured to emit harmonic radio signals into the near-borehole space sequentially at several frequencies selected from the frequency range from 1 to 50 MHz in accordance with the radiation program received by the borehole transmitter from the surface part, and recording the values of the current amplitude and complex resistance at the input of its antenna for each radio signal emission and transmission of measured values in digital form to the ground part; the upper and lower borehole receivers are removed from the borehole transmitter by two fixed distances and are equipped with electric antennas capable of receiving radio signals that have passed through rocks lying in the near-borehole space, while said borehole receivers are made with the ability to record the amplitude values of the axial component of the electric field received the radio signal and the phase difference of the measured field between the antennas of the receivers and transmitting these values in digital form to the ground part; the computing module is configured to generate a radiation program for its transmission to the downhole transmitter, receive from it and from the downhole receivers the values of the recorded values in digital form through the repeater, based on these values of electrical resistance and dielectric constant of rocks lying in the near-wellbore space; the repeater is configured to match the computing module with the logging cable. 2. An introscope according to claim 1, wherein the downhole portion is movable along the wellbore with a predetermined step. 3. An introscope according to claim 1, wherein the downhole portion is movable along the wellbore continuously at a predetermined speed. 4. The introscope of claim 1, wherein the wireline is a single core wireline. 5. The introscope of claim 1, wherein the electrical antennas of the borehole transmitter and receivers are identical axially symmetrical insulated electrical antennas. 6. The introscope of claim 1, wherein the downhole transmitter and receivers are housed in dielectric housings. 7. The introscope of claim 1, wherein the downhole transmitters and receivers are self-powered. 8. Introscope according to claim 1, in which the exchange of data and commands between the downhole transmitter, receivers and the surface part is provided with optical channels with optical-electrical converters.

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