A continuous frequency keying modulation method applied to mud pulse system

Abstract

The application provides a continuous gradual frequency shift keying modulation method applied to a mud pulse system, and comprises the following steps: S1, determining coding data according to information collected by a downhole sensor; S2, calculating the maximum rotating speed of a motor of a mud pulse generator in a corresponding code element period according to the coding data; S3, calculating the rotating acceleration and deceleration of the motor in the code element period according to the determined maximum rotating speed of the motor; S4, controlling the rotating speed of the motor fan blade of the mud pulse generator according to the determined rotating acceleration and deceleration of the motor, so that the rotating speed is continuously and gradually changed, and the pressure wave of the mud is modulated; and finally, the modulated pressure waveform is received by an uphole sensor. By using the continuous gradual frequency shift keying modulation method, the inter-code interference caused by the rotating inertia of the motor can be reduced, the transmission reliability of the downhole information is improved, and the signal interference caused by the instantaneous change of the motor speed is avoided.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of pulse regulation, and particularly relates to a continuous gradual frequency shift keying modulation method applied to a mud pulse system. BACKGROUND

[0002] With the digitalization and intelligentization of exploration and development, the traditional downhole data transmission technology is facing more and more challenges. Information transmission modes are divided into two types: wired transmission and wireless transmission. The wired transmission modes such as cable transmission, optical fiber transmission and intelligent rod transmission have good transmission speed and reliability, but the development cost is huge and the cost is high. In the wireless transmission mode, electromagnetic wave transmission and acoustic wave transmission can cause general reliability and difficulty in demodulation and data acquisition due to the complex conditions and noise interference in the well.

[0003] As a wireless transmission mode, the mud pulse transmission has the advantages of good reliability, low development cost, no need for special rods and wiring, and has become the most widely used data transmission mode at present. In the mud pulse transmission, the traditional continuous wave signal modulation modes include amplitude shift keying (ASK), phase shift keying (PSK) and frequency shift keying (FSK). Among them, the amplitude shift keying is difficult to distinguish different code elements in the later demodulation process due to signal attenuation and noise interference; the phase shift keying can cause information distortion due to the phase drift caused by the interference factors in the well, and the phase drift is difficult to follow a rule and is difficult to compensate through a software algorithm. In this way, the phase mutation between code elements can require the transient of the motor speed, and the control requirement of the motor is very high.

[0004] FSK transmits information through the change of frequency. Compared with the change of amplitude or phase, the change of frequency is not sensitive to signal attenuation and noise interference, which makes FSK maintain high signal integrity and reliability in a noisy environment. In addition, compared with the phase shift keying (PSK) which needs to control the phase accurately and the amplitude shift keying (ASK) which is sensitive to amplitude, FSK has relatively low requirements on hardware. However, the frequency shift keying changes the rotor speed to change the mud pulse frequency, and the frequency stability of the pulse signal is required to be high. Since the frequency of the pulse often changes, it is difficult to realize stable frequency of the generated pulse in the case of high-speed data transmission. Therefore, an urgent need exists for a method to solve the problems existing in the FSK. SUMMARY

[0005] The purpose of the present application is to solve the above problems existing in the prior art, and a continuous gradual frequency shift keying modulation method applied to a mud pulse system is provided.

[0006] The object of the present application can be achieved by the following technical solution: a continuous gradual frequency shift keying modulation method applied to a mud pulse system, the continuous gradual frequency shift keying modulation method comprising the following steps:

[0007] S1 determining the coded data according to the information collected by the downhole sensor; the collected information is binary data;

[0008] S2 calculating the maximum motor speed of the mud pulse generator in the corresponding symbol period according to the coded data;

[0009] S3 calculating the motor rotation acceleration and deceleration in the symbol period according to the determined maximum motor speed;

[0010] S4 controlling the rotation speed of the mud pulse generator motor fan blade to be continuously gradual to modulate the pressure wave of the mud according to the determined motor rotation acceleration and deceleration; and finally receiving the modulated pressure waveform by the uphole sensor.

[0011] Preferably, in step S1, the collected information is binary data; the information capacity of the coded symbol is determined based on the motor acceleration capability, frequency range of the mud pulse generator and the required code rate.

[0012] The continuous gradual frequency shift keying modulation method is universal, and the transmitted coded data is not only common binary data, but also applicable to transmitting binary data of other bits, such as transmitting three-bit binary data. Taking the transmission of two-bit binary data as an example, the data contains four different symbol information, which are 00, 01, 10 and 11, and the information amount carried by one symbol is 2 bits; for three-bit binary data, the information amount carried by each symbol is 3 bits.

[0013] Preferably, in step S2, the motor rotation of the mud pulse generator presents a process of uniform acceleration and then uniform deceleration in a symbol period, and when the motor running time t = T / 2, the motor speed reaches the maximum motor speed corresponding to the coding, and T is the symbol period.

[0014] Taking the collected data as two-bit binary data as an example, the collected data contains four symbol information, which are 00, 01, 10 and 11, and the motor speed of the mud pulse generator in the corresponding symbol period can be determined according to the symbol information, and the corresponding relationship is as follows:

[0015]

[0016] V 00 represents the motor speed of the coding 00, V 01 represents the motor speed of the coding 01, V 10 represents the motor speed of the coding 10, and V 11This indicates the motor speed, V, coded as 11. 00 V 01 V 10 and V 11 The units for all values ​​are rpm; 'a' is the maximum rotational acceleration that the motor can maintain a stable speed, in r / min. 2 ; t is the motor running time, T is the symbol period, both in seconds;

[0017] When the motor runs for t = T / 2, the motor speed reaches the maximum speed corresponding to the code. The correspondence between the code element information and the maximum speed of the motor within that code element period is as follows:

[0018]

[0019]

[0020] Where V 00 max represents the maximum motor speed within the code period where the code is 00, V 01 max represents the maximum motor speed within the code period encoded as 0 or 1, V 10 max represents the maximum motor speed within the code period of code 10, V 11 max represents the maximum motor speed within the code period coded as 11, V 00 max、V 01 max、V 10 max and V 11 The unit for max is rpm; a is the maximum rotational acceleration that the motor can maintain stably, in r / min. 2 T represents the symbol period, measured in seconds.

[0021] It should also be noted that the continuous gradient frequency keying modulation method is universal, and the transmitted encoded data is not limited to two-bit binary data. It is also applicable to transmitting binary data of other bit lengths. When the number of bits of transmitted data changes, the formulas for the change of motor speed in each symbol period and the maximum motor speed should also be modified accordingly.

[0022] Preferably, in step S3, the relationship between the motor rotational acceleration and the maximum motor speed within the code information is as follows:

[0023]

[0024] Where a1 represents the motor's rotational acceleration during the symbol period, in r / min. 2 V represents the maximum motor speed within the symbol period, in rpm; T represents the symbol period, in seconds.

[0025] The relationship between the motor's rotational deceleration and the maximum motor speed within this code element information is as follows:

[0026]

[0027] wherein a2 represents the motor rotation deceleration in the symbol period, in r / min 2 ; V represents the maximum motor rotation speed in the symbol period, in rpm; T represents the symbol period, in s.

[0028] Preferably, in step S4, the specific process of modulating the pressure wave of the mud is as follows:

[0029] The structure of the mud pulse generator: the mud pulse generator contains stator vanes and rotor vanes, the cross-sectional shape of the stator vanes and the rotor vanes is the same, the stator vanes are fixed, and the rotor vanes are controlled to rotate by the motor;

[0030] The working mode of the vanes: when the stator vanes coincide with the rotor vanes, the mud passage area is the largest, and the pressure acting on the pressure sensor is the smallest; as the rotor vanes rotate, the mud passage area gradually decreases, and the pressure acting on the pressure sensor gradually increases; when the rotor vanes are completely misaligned with the stator vanes, the mud passage area is 0, and the pressure acting on the pressure sensor reaches the maximum; when the motor speed remains unchanged, the frequency of the mud pressure wave remains unchanged; as the motor speed increases and decreases, the frequency of the mud pressure wave also increases and decreases accordingly;

[0031] Modulation of the pressure wave: according to the determined motor rotation acceleration and deceleration, the rotation speed of the rotor vanes is controlled to change the mud passage area, generating pressure waves of different frequencies, so that the coded data information is converted from the change of the motor rotation speed to the change of the frequency of the mud pressure wave, to distinguish the different information contained in the symbol; after modulation, the frequency of the mud pulse is shown as a process of increasing from 0 to a constant value f and then decreasing to 0.

[0032] Since the mud pulse generator contains stator vanes and rotor vanes, the rotation of the rotor vanes causes the passage area formed by the stator vanes and the rotor vanes to change, and due to the throttling effect, the pressure received by the uphole pressure sensor from the mud also presents a waveform change. When the motor vane speed remains unchanged, the generated pressure waveform is a sine wave with a constant frequency, and the continuous gradual change of the motor vane speed causes the frequency of the pressure waveform to gradually change, so according to the size of the maximum motor speed in the symbol period corresponding to each symbol information and the motor acceleration and deceleration, the mud pulse is continuously and gradually frequency-key modulated, and the data is transmitted through the mud pulse.

[0033] wherein when the mud pulse is modulated by the continuous and gradual frequency-key modulation method to transmit n-bit binary data, the maximum information transmission rate is as follows:

[0034]

[0035] wherein V bps is the maximum information transmission rate of the motor, in bps; V max is the maximum rotating speed of the motor, in rpm; p is the number of blades of the motor fan; and n is the number of bits of the binary data transmitted.

[0036] When transmitting two-bit binary data, the maximum information transmission rate based on mud pulse using continuous frequency-shift keying modulation is:

[0037]

[0038] wherein V bps is the maximum information transmission rate of the motor, in bps; V max is the maximum rotating speed of the motor, in rpm; and p is the number of blades of the motor fan.

[0039] Taking the transmission of two-bit binary data as an example, after modulation, the maximum frequency of mud pulses corresponding to each symbol information is:

[0040]

[0041] wherein f 00 max is the maximum frequency of mud pulses corresponding to the symbol information coded as 00 within a symbol period, f 01 max is the maximum frequency of mud pulses corresponding to the symbol information coded as 01 within a symbol period, f 10 max is the maximum frequency of mud pulses corresponding to the symbol information coded as 10 within a symbol period, and f 11 max is the maximum frequency of mud pulses corresponding to the symbol information coded as 11 within a symbol period, f 00 max, f 01 max, f 10 max, and f 11 max, all in HZ; and T is the symbol period, in s.

[0042] It should be noted that when the number of binary data bits changes, the formula for the maximum frequency of mud pulses should be changed accordingly.

[0043] The modulated pressure waveform received by the sensor on the well: The mud flows from top to bottom through the fan gap of the mud pulse generator. The rotor fan in the mud pulse generator changes the conduction area between the stator fan during rotation. This change causes the flow of mud in the well to be throttled, thereby causing changes in mud pressure. The pressure sensor on the well detects these pressure changes, thereby receiving the modulated pressure waveform.

[0044] Compared with the prior art, the present application has the following advantages:

[0045] 1. Improve the reliability of data transmission: By using the continuous frequency shift keying modulation method, the application can significantly reduce the inter-symbol interference caused by the inertia of the motor, thereby improving the reliability of the transmission of downhole information, because the motor speed and the frequency of the mud pulse are zero at the beginning and end of each symbol period, which avoids the signal interference that may be caused by the instantaneous change of the motor speed.

[0046] 2. Improve the accuracy of signal analysis: By accurately controlling the acceleration and deceleration of the motor, the application can generate more accurate and stable mud pressure waveforms, reducing the difficulty of downhole motor control and data extraction from the waveforms. Such waveforms make it more accurate to extract data information from mud pressure waves, reducing the possibility of misdecoding, thereby improving data transmission accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 Flow chart of continuous frequency shift keying modulation for mud pulse system.

[0048] Figure 2 Diagram of motor speed change corresponding to symbol information.

[0049] Figure 3 Diagram of mud pulse generation by motor fan blade rotation.

[0050] Figure 4 Diagram of mud pulse corresponding to motor speed change.

[0051] Figure 5 Diagram of mud pulse generation by continuous frequency shift keying modulation of a segment of binary data. DETAILED DESCRIPTION

[0052] The specific embodiments of the application will be further described below in conjunction with the drawings and specific examples:

[0053] A continuous frequency shift keying modulation method applied to a mud pulse system, the method flow chart is shown in Figure 1 , mainly including determining the encoded data according to the information of the downhole sensor, determining the maximum motor speed of the mud pulse generator in the corresponding symbol period according to the encoded data, determining the acceleration and deceleration of the motor rotation in the period according to the maximum motor speed in the symbol period, controlling the continuous gradual change of the mud pulse generator motor fan blade speed to modulate the mud pressure wave, and receiving the modulated pressure waveform by the uphole sensor.

[0054] Determine the encoded data according to the information of the downhole sensor. When the encoded information is n-bit binary data, there are 2 n different symbol information for one symbol, and the speed change of the mud pulse generator motor also requires the formation of 2n One gear, the corresponding generated mud pulse will have 2 n One frequency. As the number of coded binary data bits increases, the requirements and difficulty of downhole motor speed control also increase, in addition, when the minimum and maximum recognition frequency of mud pulse is too different, the difficulty of receiving mud pulse and extracting information on the surface will increase, and the error rate will increase. Therefore, this embodiment selects a two-bit binary coding method, which reduces the control difficulty of the downhole motor while ensuring a certain data transmission rate, and improves the recognizability of mud pulse information.

[0055] According to the coded data, the maximum motor speed of the mud pulse generator in the corresponding symbol period is determined. After selecting the two-bit binary data coding method, the motor speed change process of the mud pulse generator in each symbol period can be calculated according to different symbol information, and the maximum motor speed in each symbol period is calculated, which can more intuitively and conveniently understand and control the motor speed change. The schematic diagram of two-bit binary symbol information corresponding to the motor speed change is shown in Figure 2 In one symbol period, the motor speed change corresponding to all symbol information is from 0 to a constant value R and then decreases to 0, and the constant value corresponding to different symbol information is different.

[0056] According to the maximum motor speed in the symbol period, the acceleration and deceleration of the motor rotation in the period are determined. In this embodiment, the data to be transmitted is two-bit binary data. Based on the rotation of the mud pulse generator motor fan blade, the normal flow and the maximum speed of the mud pulse generator motor fan blade are reasonably distributed to maintain the acceleration stability of each symbol motor speed change. The maximum motor speed is selected to be 300 rpm, that is, when the symbol information is 11, the maximum motor speed reaches 300 rpm, and the maximum acceleration reaches 25 r / s 2 According to the preset rule distribution, when the symbol information is 00, the maximum motor speed is 75 rpm, and the maximum acceleration is 6.25 r / s 2 ; When the symbol information is 01, the maximum motor speed is 150 rpm, and the maximum acceleration is 12.5 r / s 2 ; When the symbol information is 10, the maximum motor speed is 225 rpm, and the maximum acceleration is 18.75 r / s 2 The information transmission rate in this embodiment is 5 bit / s.

[0057] The continuous gradual change of the mud pulse generator motor fan blade speed modulates the mud pressure wave. The mud pulse generator includes rotor fan blades and stator fan blades, the stator fan blades are fixed, and the rotor fan blades are controlled to rotate by the motor. The pipeline is filled with mud, which flows downward through the through port formed by the stator fan blades and the rotor fan blades from the top, and the pressure sensor at the top of the pipeline receives the pressure change of the mud in the pipeline. The schematic diagram of the mud pulse generated by the motor fan blade rotation is shown inFigure 3 As shown, the dark fan blades represent the stator fan blades, and the light fan blades represent the rotor fan blades. When the rotor fan blades coincide with the stator fan blades, the conductive area between the fan blades is the largest, the mud flows downward, and the pressure sensor at the top of the pipeline receives the smallest pressure from the mud. As the rotor fan blades rotate, the conductive area between the fan blades decreases, and the pressure sensor receives an increasing pressure. When the rotor fan blades rotate to be completely misaligned with the stator fan blades, the conductive area between the fan blades is 0, and the pressure sensor receives the largest pressure. As the rotor fan blades rotate, the conductive area between the fan blades increases, and the pressure sensor receives a decreasing pressure. When the rotor fan blades rotate to coincide with the stator fan blades, the conductive area between the fan blades is the largest, and the pressure sensor receives the smallest pressure from the mud. During the rotation of the motor control rotor fan blades, the pressure received by the pressure sensor presents a sinusoidal waveform, and the motor rotation generates mud pulses, and the frequency of the mud pulses changes with the change of the motor rotation speed. The motor speed change corresponds to the mud pulse diagram as shown in FIG. 4. Figure 4 As shown, the symbol period time is set to 0.4s in this embodiment. In one symbol period, the motor speed increases from 0 to a constant value R and then decreases to 0, and the mud pulse frequency increases from 0 to a constant value f and then decreases to 0. The motor speed constant value R changes, and the mud pulse frequency constant value f changes accordingly. When the code information is 00, the maximum motor speed is 75 rpm, and the maximum mud pulse frequency is 5HZ. When the code information is 01, the maximum motor speed is 150 rpm, and the maximum mud pulse frequency is 10HZ. When the code information is 10, the maximum motor speed is 225 rpm, and the maximum mud pulse frequency is 15HZ. When the code information is 11, the maximum motor speed is 300 rpm, and the maximum mud pulse frequency is 20HZ.

[0058] The continuous gradual change of the motor fan blade speed of the mud pulse generator modulates the mud pressure wave. When the motor speed remains unchanged, the mud pulse frequency remains unchanged. According to a certain rule, the motor speed changes, and the mud pulse frequency also changes, thereby modulating the mud pulse. The data parameters used in this embodiment are shown in Table 1.

[0059]

[0060] Table 1

[0061] Table 1 includes symbol information and corresponding motor maximum speed, motor maximum rotation acceleration, mud pulse maximum frequency, and symbol period time.

[0062] The well-mounted sensor receives the modulated pressure waveform. In this embodiment, a two-bit binary code is modulated by the mud pulse based on the continuous gradual frequency key modulation of the mud pulse system, and the diagram is as shown in FIG. 5. Figure 5The downhole information is coded as binary information, and then the motor of the mud pulse generator is controlled to drive the rotor fan blade to rotate according to a preset rule, so that the pressure sensor on the well surface receives the change of the mud pressure and receives the mud pulse modulated according to the preset rule.

[0063] In the embodiment, the number of the motor fan blades of the mud pulse generator is 4, the transmission symbol information is two-bit binary data, the selected symbol period is 0.4s, and the information transmission rate is 5 biit / s. By increasing the number of the motor fan blades of the mud pulse generator within a reasonable range, appropriately increasing the number of bits of the transmission symbol information according to the motor speed at which the motor can normally keep the mud flowing and rotating stably, and reasonably reducing the symbol period time, the information transmission rate can be improved to a certain extent.

[0064] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or replacements made by the skilled in the art within the essential scope of the present application shall also fall within the protection scope of the present application.

Claims

1. A method of continuous frequency shift keying modulation applied to a mud pulse system, comprising: The continuous frequency keying modulation method comprises the following steps: S1, determining the encoding data according to the information collected by the downhole sensor; S2, calculating the maximum motor speed of the mud pulse generator in the corresponding code period according to the encoding data; S3, calculating the motor rotation acceleration and deceleration in the code period according to the determined maximum motor speed; S4, controlling the rotation speed of the mud pulse generator motor fan blade to be continuously changed according to the determined motor rotation acceleration and deceleration, so as to modulate the pressure wave of the mud; finally, the modulated pressure waveform is received by the uphole sensor; In step S1, the collected information is binary data; based on the motor acceleration capability, frequency range and required code rate of the mud pulse generator, the information capacity of the encoding code element is determined; In step S2, in a code period, the motor rotation of the mud pulse generator presents a process of uniform acceleration and then uniform deceleration, when the motor running time t = T / 2, the motor speed reaches the maximum motor speed corresponding to the encoding, and T is the code period; In step S3, the relationship between the motor rotation acceleration and the maximum motor speed in the code period is as follows: wherein a1 represents the motor rotation acceleration in a symbol period, in r / min 2 ; V represents the maximum motor rotation speed in a symbol period, in rpm; and T represents the symbol period, in s. The relationship between the motor rotation deceleration and the maximum motor speed in the code period is as follows: wherein a2 represents a motor rotation deceleration in a symbol period, in r / min 2 ; V represents a maximum motor rotation speed in a symbol period, in rpm; and T represents a symbol period, in s. In step S4, the specific process of modulating the mud pressure wave is as follows: The structure of the mud pulse generator: the mud pulse generator contains stator blades and rotor blades, the cross-sectional shape of the stator blades and the rotor blades is the same, the stator blades are fixed, and the rotor blades are controlled to rotate by the motor; The working mode of the fan blade: when the stator blades coincide with the rotor blades, the mud flow area is maximum, and the pressure acting on the pressure sensor is minimum; with the rotation of the rotor blades, the mud flow area gradually decreases, and the pressure acting on the pressure sensor gradually increases; when the rotor blades are completely staggered with the stator blades, the mud flow area is 0, and the pressure acting on the pressure sensor reaches the maximum; when the motor speed remains unchanged, the frequency of the mud pressure wave remains unchanged; with the increase or decrease of the motor speed, the frequency of the mud pressure wave also increases or decreases accordingly; The modulation of the pressure wave: according to the determined motor rotation acceleration and deceleration, the rotation speed of the rotor blades is controlled, so that the mud flow area changes, different frequency pressure waves are generated, and the encoding data information is converted into the frequency change of the mud pressure wave by the change of the motor speed, so as to distinguish the different information contained in the code element; after modulation, the frequency of the mud pulse presents a process of increasing from 0 to a constant value f and then decreasing to 0.

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