Downhole detection system based on differential coil sensor

Abstract

The invention discloses an in-well detection system based on a differential coil sensor, which comprises a DSP (Digital Signal Processor) module, and the DSP module is sequentially connected with an isolation module, a driving module, an MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) module and a coil system module; the coil system module is also connected with a pre-amplifier module; the pre-amplifier module is sequentially connected with a conditioning module, an anti-aliasing filtering module and a digital-to-analog conversion module; the digital-to-analog conversion module is connected with the DSP module; according to the system, the DSP is used as a core controller, sensor signals can be processed and analyzed, accurate control instructions are provided, and high-precision signal processing, flexible signal processing capacity, programmability, real-time processing capacity, a digital filtering function and convenient storage and transmission capacity are achieved. Meanwhile, the method can effectively counteract induced electromotive force, generated by a primary field, of a receiving coil in a traditional transient electromagnetic method, pure secondary field measurement is achieved, and the method has good application prospects in the field of through-casing well logging measurement.

Description

Technical Field

[0001] The invention belongs to the technical field of well detection, and in particular relates to a well detection system based on a differential coil sensor. Background Art

[0002] At present, most domestic oil fields have entered the high water content exploitation stage. The remaining oil underground is unevenly distributed and the oil-water relationship is complex, which has significantly increased the difficulty of exploitation. Therefore, it is crucial to use effective geophysical methods to conduct stratigraphic exploration and prediction for the exploration and exploitation of oil and gas reservoirs. Currently, the commonly used logging methods mainly include ground detection and downhole detection. Among them, ground detection uses magnetotelluric or ground seismic methods to detect large geological structures at a depth of thousands of meters, but the detection accuracy of small geological structures is insufficient. Ground logging uses the initial geological exploration data of the mine to obtain geological structure information. The exploration holes are hundreds of meters apart, and there are blind spots between the holes. Downhole geophysical exploration is mainly carried out through the method of through-casing logging, such as electrode through-casing resistivity logging, frequency domain electromagnetic logging, etc., and its detection accuracy has been improved, but this type of technology still has some disadvantages: for example, electrode through-casing resistivity logging requires the construction of a set of electrodes in contact with the casing, which is easily affected by casing deformation, corrosion, etc., and the test instrument probe is expensive and the subsequent maintenance cost is high; frequency domain electromagnetic logging receives formation response signals, but the metal casing has a strong shielding effect on its electromagnetic waves, which limits the further application of this method in the field of logging. Therefore, a new through-casing logging method has been developed and combined with the existing methods to improve the accuracy of exploration.

[0003] Transient electromagnetic method is a representative of through-casing resistivity logging technology. It has the advantages of being sensitive to resistivity, no direct coupling, and corresponding detection distance and time characteristics. However, the common receiving method for through-casing resistivity logging using transient electromagnetic method is to use an induction coil to measure the rate of change of the magnetic field. When the transmitting current is turned off, the receiving coil itself generates an induced electromotive force, which is superimposed on the induced electromotive force formed by the underground eddy current field, causing distortion of the early signal of transient electromagnetic measurement, forming a detection blind area. A new detection system is urgently needed to improve the accuracy of exploration. Summary of the invention

[0004] The object of the present invention is to provide a well detection system based on a differential coil sensor.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A well detection system based on a differential coil sensor includes a DSP module, which is sequentially connected to an isolation module, a drive module, a MOSFET module, and a coil system module; the coil system module is also connected to a preamplifier module, which is sequentially connected to a conditioning module, an anti-aliasing filter module, and a digital-to-analog conversion module; the digital-to-analog conversion module is connected to the DSP module;

[0007] The DSP module, isolation module, driver module, and MOSFET module constitute the transmitting circuit; the preamplifier module, conditioning module, anti-aliasing filter module, digital-to-analog conversion module, and DSP module constitute the receiving circuit;

[0008] The DSP module is used to send logic square wave signals, control the transmitting circuit, send the square wave signals to the isolation module, and process and analyze the coil signals to provide precise control instructions; the core functions include high-precision signal processing, flexible signal processing capabilities, programmability, real-time processing capabilities, digital filtering functions, and convenient storage and transmission capabilities;

[0009] The isolation module is used to convert the square wave signal generated by the DSP into a suitable output signal; it includes amplification, filtering, isolation and conditioning to ensure the reliability and purity of signal transmission. Through amplification and filtering, the small signal is amplified to a range suitable for the output end to ensure the purity of the signal. The input end signal is made suitable for the working requirements of the output end, the reliability and stability of the signal transmission are guaranteed, and the output signal is sent to the drive module;

[0010] The driving module is used to amplify the signal of the control circuit so that it can drive the MOSFET module, and drive the coil system module to transmit electromagnetic wave signals to the formation;

[0011] The MOSFET module uses the electric field effect of the control input loop to control the current of the output loop. It is a voltage-controlled semiconductor device with the advantages of high input resistance, low noise, low power consumption, large dynamic range, easy integration, no secondary breakdown phenomenon, and wide safe working area.

[0012] The coil system module includes two identical transmitting coils that are parallel and coaxial up and down and a receiving coil located at the zero magnetic flux plane between the two transmitting coils; the two transmitting coils are connected in series and form a loop with the MOSFET module; the receiving coil is connected to the preamplifier module.

[0013] The coil system module is used to transmit electromagnetic wave signals to the formation and receive secondary field response signals of the formation;

[0014] The preamplifier module is used to amplify, impedance match, signal condition, signal isolate and signal select the formation secondary field response signal received by the receiving coil; through the preamplifier, the amplitude of the signal is effectively increased, the reflection and loss of the signal are reduced, and the transmission efficiency of the signal is improved;

[0015] The conditioning module is used to amplify, buffer or calibrate the received signal, and send the signal to the anti-aliasing filter module; the signal-to-noise ratio of the signal can be improved by the conditioning circuit, thereby improving the performance of the entire system.

[0016] The anti-aliasing filter module is used to reduce the aliasing frequency component in the output level; the anti-aliasing filter is placed before the digital-to-analog conversion module to limit the bandwidth of the received signal in order to roughly or completely meet the sampling theorem. It is a low-pass filter used to reduce the aliasing frequency component in the output level to a negligible level.

[0017] The digital-to-analog conversion module is used to convert analog signals into digital signals, and then transmit them to the DSP module.

[0018] Preferably, the DSP module is connected to a host computer, and the host computer is used to display the data processed by the DSP in real time, realize data collection, processing, display and storage, and send control commands to the slave computer.

[0019] Preferably, the digital-to-analog conversion module is an AD converter.

[0020] The present invention sends a logic square wave signal through DSP, controls the transmitting circuit to drive the differential coil to send electromagnetic waves to the formation through the isolation and driving module, stimulates the secondary field response of the formation, and sends the secondary field response signal of the formation received by the receiving coil to the DSP for data analysis and processing after passing through the preamplifier circuit, anti-aliasing filtering and AD acquisition, and displays it in real time in the host computer.

[0021] The beneficial effects of the present invention are:

[0022] Compared with the traditional transient electromagnetic logging method, the present invention solves the problem of early signal distortion in the traditional logging method, thereby forming a shallow detection blind area. The system of the present invention can effectively offset the induced electromotive force generated by the primary field of the receiving coil, realize pure secondary field measurement, and can also measure the pure secondary field coupled to the center of the earth on the zero magnetic flux plane of the primary field synthesized by the double-coil source. In addition, compared with the single-coil source of the traditional transient electromagnetic method, the design of the double-coil source of the present invention makes the energy of the coupling field to the center of the earth more concentrated, which helps to reduce the side effects and improve the lateral resolution of the detection, and can effectively identify the layered interface of different media in the formation.

[0023] The system of the present invention uses DSP as the core controller, which can realize the processing and analysis of sensor signals and provide accurate control instructions, including high-precision signal processing, flexible signal processing capability, programmability, real-time processing capability, digital filtering function and convenient storage and transmission capability. At the same time, this method can effectively offset the induced electromotive force generated by the primary field of the traditional transient electromagnetic method receiving coil, realize pure secondary field measurement, and has good application prospects in the field of through-casing logging measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the system structure of the present invention;

[0025] Figure 2 This is the simulation experiment result diagram; Figure 2 (a) When the upper and lower stratified media are gas and water respectively, the response curves are measured at the stratification interface and 1m and 2m above and below the stratification interface respectively without casing. (b) When the upper and lower stratified media are gas and water respectively, the response curves are measured at the stratification interface and 1m and 2m above and below the stratification interface respectively without casing. (c) When the upper and lower stratified media are gas and water respectively, the response curves are measured at the stratification interface and 1m and 2m above and below the stratification interface respectively with nickel-based alloy casing double-transmitter and single-receiver coil system. (d) When the upper and lower stratified media are gas and water respectively, the response curves are measured at the stratification interface and 1m and 2m above and below the stratification interface respectively with nickel-based alloy casing single-transmitter and single-receiver coil system. DETAILED DESCRIPTION

[0026] In the following description, a large number of specific details are provided to provide a more thorough understanding of the present invention. However, it is apparent to those skilled in the art that the present invention can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present invention, some technical features well known in the art are not described.

[0027] Unless otherwise defined, the up, down, left, right, front, back, inside and outside directions involved in this document are based on the up, down, left, right, front, back, inside and outside directions in the figures shown in the present invention, and are explained here together.

[0028] A well detection system based on a differential coil sensor includes a DSP module 1, which is sequentially connected to an isolation module 2, a drive module 3, a MOSFET module 4, and a coil system module 5; the coil system module 5 is also connected to a preamplifier module 6, which is sequentially connected to a conditioning module 7, an anti-aliasing filter module 8, and a digital-to-analog conversion module 9; the digital-to-analog conversion module 9 is connected to the DSP module 1;

[0029] The DSP module 1, the isolation module 2, the drive module 3, and the MOSFET module 4 constitute a transmitting circuit; the preamplifier module 6, the conditioning module 7, the anti-aliasing filter module 8, the digital-to-analog conversion module 9, and the DSP module 1 constitute a receiving circuit;

[0030] The DSP module 1 is used to send a logic square wave signal, control the transmitting circuit, send the square wave signal to the isolation module 2, and process and analyze the coil signal to provide accurate control instructions;

[0031] The isolation module 2 is used to convert the square wave signal generated by the DSP into a suitable output signal; including amplification, filtering, isolation and conditioning, to ensure the reliability and purity of signal transmission. Through amplification and filtering, the small signal is amplified to a range suitable for the output end to ensure the purity of the signal. The input end signal is made suitable for the working requirements of the output end, the reliability and stability of the signal transmission are guaranteed, and the output signal is sent to the driving module 3;

[0032] The driving module 3 is used to amplify the signal of the control circuit so that it can drive the MOSFET module 4, and drive the coil system module 5 to transmit electromagnetic wave signals to the formation;

[0033] The MOSFET module 4 controls the current of the output circuit by controlling the electric field effect of the input circuit, and is a voltage-controlled semiconductor device with the advantages of high input resistance, low noise, low power consumption, large dynamic range, easy integration, no secondary breakdown, and wide safe working area.

[0034] The coil system module 5 includes two identical transmitting coils 51 that are parallel and coaxial in the upper and lower directions and a receiving coil 52 located at the zero magnetic flux plane between the two transmitting coils 51 ; the two transmitting coils 51 are connected in series and form a loop with the MOSFET module 4 ; the receiving coil 52 is connected to the preamplifier module 6 .

[0035] The coil system module 5 is used to transmit electromagnetic wave signals to the formation and receive secondary field response signals of the formation;

[0036] The preamplifier module 6 is used to amplify, impedance match, signal condition, signal isolate and signal select the formation secondary field response signal received by the receiving coil 52; through the preamplifier, the amplitude of the signal is effectively increased, the reflection and loss of the signal are reduced, and the transmission efficiency of the signal is improved;

[0037] The conditioning module 7 is used to amplify, buffer or calibrate the received signal, and send the signal to the anti-aliasing filter module 8; the signal-to-noise ratio of the signal can be improved by the conditioning circuit, thereby improving the performance of the entire system.

[0038] The anti-aliasing filter module 8 is used to reduce the aliasing frequency component in the output level; the anti-aliasing filter is placed before the digital-to-analog conversion module to limit the bandwidth of the received signal in order to approximately or completely satisfy the sampling theorem. It is a low-pass filter used to reduce the aliasing frequency component in the output level to a negligible level.

[0039] The digital-to-analog conversion module 9 is used to convert analog signals into digital signals, and then transmit them to the DSP module 1. The digital-to-analog conversion module 9 is an AD converter.

[0040] The DSP module 1 is connected to a host computer 10, and the host computer 10 is used to display the data processed by the DSP in real time, realize data collection, processing, display and storage, and send control commands to the lower computer.

[0041] The present invention sends a logic square wave signal through the DSP module 1, controls the transmitting circuit to drive the differential coil to send electromagnetic waves to the formation through the isolation module 2 and the driving module 3, stimulates the formation secondary field response and sends the formation secondary field response signal received by the receiving coil to the DSP module 1 after passing through the preamplifier circuit module 6, the conditioning module 7, the anti-aliasing filter module 8 and the digital-to-analog conversion module 9 for data analysis and processing and real-time display in the host computer 10.

[0042] In order to verify the effectiveness of the method, two groups of simulation experiments were carried out for comparison. The experimental group selected the system structure of the present invention, and the control group selected a single-transmitter and single-receiver transient electromagnetic detection system for comparison with the detection system of the present invention. The difference between the two systems lies in the different coil system modules. The present invention is a dual-transmitter and single-receiver coil system, and the control group is a single-transmitter and single-receiver coil system.

[0043] The recognition of the gas-water stratification interface by the experimental group and the control group when no casing is placed is simulated. Specifically, the upper layer of the formation is defined as gas, with a conductivity of 0.001S / m, a relative magnetic permeability of 1, and a relative dielectric constant of 1; the lower layer of the formation is defined as muddy water, with a conductivity of 4S / m, a relative magnetic permeability of 1, and a relative dielectric constant of 1; the gas-water stratification interface is set at the middle position Z=0; by changing the position of the coil system to observe the response signal waveform at different positions, the coil system's recognition ability for the gas-water stratification interface can be determined. The response signal waveform diagram is shown in Figure 2(a), 2(b). Five measuring points were selected for the simulation, located at the gas-water stratification interface and 1 meter and 2 meters above and below it, respectively, and are represented by a. According to the response signal diagram, it can be seen that the response signals at different positions measured by the control group tend to overlap, and the stratum stratification interface cannot be identified; while in the experimental group, when the receiving coil is located at the gas-water stratification interface, the amplitude of the response signal changes most significantly; when the receiving coil is located above and below the gas-water stratification interface, the amplitude of the response signal tends to 0. This shows that the system of the present invention used this time is effective in identifying the gas-water stratification interface.

[0044] The experimental group and the control group simulated the identification of the gas-water stratification interface when placing the nickel-based alloy casing. The upper part of the formation is defined as gas, and the lower part is muddy water; Z = 0 is the gas-water stratification interface. Five measurement points were selected for the simulation, which are the gas-water stratification interface and the positions 1 meter and 2 meters above and below it. The corresponding response signal waveform is shown in the figure below. Figure 2 (c), 2(d). It can be seen from the response signal diagram that the response signals at different positions measured by the control group tend to overlap, and the gas-water stratification interface cannot be identified; when the receiving coil of the experimental group is located at the gas-water stratification interface, the amplitude of the response signal changes most significantly; and when the receiving coil is located above and below the gas-water stratification interface, the amplitude of the response signal tends to 0. The gas-water stratification interface can still be effectively identified.

[0045] Through the above two groups of simulation experiments, it can be seen that the well detection system based on differential coil sensor studied in the present invention can effectively offset the induced electromotive force generated by the primary field of the receiving coil, realize pure secondary field measurement, and at the same time it has a good recognition effect on the layered interface.

[0046] It should be noted that, in this article, relational terms such as one and two are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions. The sentence "includes an element defined by ... does not exclude the existence of other identical elements in the process, method, article or device including the element".

[0047] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A well detection system based on a differential coil sensor, characterized in that: It includes a DSP module, which is sequentially connected to an isolation module, a driving module, a MOSFET module, and a coil system module; the coil system module is also connected to a preamplifier module, which is sequentially connected to a conditioning module, an anti-aliasing filter module, and a digital-to-analog conversion module; the digital-to-analog conversion module is connected to the DSP module; The DSP module is used to send square wave signals and process and analyze coil signals; The isolation module is used to convert the square wave signal generated by the DSP into an output signal; The driving module is used to amplify the output signal so that it can drive the MOSFET module, and drive the coil system module to transmit electromagnetic wave signals to the formation; The MOSFET module is used to control the current of the output loop; The coil system module is used to transmit electromagnetic wave signals to the formation and receive secondary field response signals of the formation; The preamplifier module is used to amplify the signal, perform impedance matching, signal conditioning, signal isolation and signal selection; The conditioning module is used to amplify, buffer or calibrate the received signal and send the signal to the anti-aliasing filtering module; The anti-aliasing filter module is used to reduce the aliasing frequency component in the output level; The digital-to-analog conversion module is used to convert analog signals into digital signals, and then transmit them to the DSP module.

2. A well detection system based on a differential coil sensor according to claim 1, characterized in that: The DSP module is connected to a host computer, and the host computer is used to display the data processed by the DSP in real time, realize data collection, processing, display and storage, and send control commands to the lower computer.

3. A well detection system based on a differential coil sensor according to claim 1, characterized in that: The digital-to-analog conversion module is an AD converter.

4. A well detection system based on a differential coil sensor according to claim 1, characterized in that: The coil system module comprises two identical transmitting coils which are parallel and coaxial up and down and a receiving coil which is located on a zero magnetic flux plane between the two transmitting coils.

5. A well detection system based on a differential coil sensor according to claim 4, characterized in that: The two transmitting coils are connected in series and form a loop with the MOSFET module; the receiving coil is connected to the preamplifier module.

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