CN113138425B - Logging-while-drilling electromagnetic wave data acquisition method and device - Google Patents
Logging-while-drilling electromagnetic wave data acquisition method and device Download PDFInfo
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Abstract
The invention discloses a logging while drilling electromagnetic wave data acquisition method, which comprises the following steps: performing frequency reduction processing on the electromagnetic wave feedback signal to obtain a signal to be processed containing the phase and the amplitude of the feedback signal; continuously sampling the signal to be processed by using a first sampling time interval; according to k sampling point data in a signal to be processed calculation period, calculating phase difference and amplitude ratio information corresponding to a feedback signal in each calculation period in real time, wherein actual time corresponding to a first number of sampling points which are continuously sampled is recorded, the actual time is compared with first time, whether the value of a first timer for generating sampling time intervals needs to be adjusted is diagnosed according to a comparison result, and the first time is the product of the first number and the first sampling time intervals. The phase position of the sampling point is always kept at the same phase position relative to the feedback signal before mixing, so that stratum data acquired by the logging while drilling instrument in the long-time working process are continuously, reliably and effectively obtained.
Description
Technical Field
The invention relates to the technical field of logging while drilling, in particular to a logging while drilling electromagnetic wave data acquisition method and device.
Background
Logging while drilling is a technique that identifies formation information and boundary distance information during real-time drilling and provides services for evaluating hydrocarbon reservoirs and optimizing drilling trajectories. In recent years, logging while drilling technology has rapidly developed, and not only have some original measurement methods improved, but also a plurality of new logging while drilling methods have appeared. Wherein a bit resistivity instrument (RAB) provides azimuthal gamma and real-time resistivity images; the quantitative imaging logging of multiple detection depths is performed, such as resistivity images generated by RAB and density imaging images measured by a VISION system.
Currently, the international three major petroleum technical service company is focused on the development direction of logging-while-drilling in the field of logging, and a logging-while-drilling instrument is developed. The instrument can provide parameters such as neutron porosity, lithology density, resistivity of a plurality of detection depths, gamma, drilling azimuth, well inclination, tool face and the like, and can basically meet the requirements of stratum evaluation, geosteering and drilling engineering application. Depending on the needs of the user, these instruments come in a variety of different combinations and specifications, respectively, one common combination being MWD + gamma + resistivity, which combination typically provides geosteering services, and can also be used for formation evaluation in combination with porosity data of adjacent formations.
One core technology in the logging while drilling technology based on the combination of MWD+gamma+resistivity is to obtain the resistivity of the stratum by calculating the phase difference and amplitude ratio information of electromagnetic wave signals, and because the frequency of the electromagnetic wave signals is higher, generally 400KHz and 2MHz, high hardware resources are occupied when the high-frequency signals are directly sampled, so that the AD sampling rate and Flash storage are very challenging.
In the prior art, a mixer is generally used for performing down-conversion processing on a high-frequency electromagnetic wave signal fed back from a stratum, and then an electronic processor device is used for performing multi-point sampling on each calculation period so as to calculate phase difference and amplitude ratio information of the electromagnetic wave signal by using a plurality of sampling point data in the same calculation period, thereby obtaining resistivity information of the stratum. However, when multi-point sampling is performed, due to the error of an internal device (such as a crystal oscillator) of the processor, the sampling frequency after frequency division has a certain gap from a theoretical value, and the actual phase of an electromagnetic wave signal fed back by a stratum and the phase of the sampled signal are further deviated, so that the accuracy of the calculation of the phase difference and the amplitude ratio of the subsequent electromagnetic wave is affected.
Therefore, a method for performing a phase deviation compensation process on the electromagnetic wave acquisition data before calculating the phase difference and the amplitude ratio of the electromagnetic wave signal is needed in the prior art to eliminate the phase deviation between the sampling data and the actual feedback signal caused by the error of the internal device of the processor.
Disclosure of Invention
In order to solve the technical problems, the invention provides a logging-while-drilling electromagnetic wave data acquisition method, which comprises the following steps: receiving an electromagnetic wave feedback signal in real time and performing frequency reduction processing on the signal to obtain a signal to be processed containing the phase and amplitude information of the feedback signal; setting a first timer for generating a first sampling time interval, and continuously sampling the signal to be processed by using the first sampling time interval, wherein the period of the signal to be processed is k times of the first sampling time interval; and calculating the phase difference and amplitude ratio information of the feedback signal in real time according to k sampling point data in a calculation period corresponding to the signal to be processed, wherein the actual time corresponding to a preset first number of sampling points is recorded, the actual time is compared with the first time, and whether the clock count value of the first timer needs to be adjusted or not is diagnosed based on the actual time, so that the phase offset generated after the feedback signal is sampled due to the error of the processor is compensated, and the first time is the product of the first number and the first sampling time interval.
Preferably, the method further comprises: and setting a second timer for generating a transmitting antenna switching time interval, and switching electromagnetic wave signals of different types according to the transmitting antenna switching time interval to transmit to a stratum where a drill bit reaches a real-time position in a drilling process, wherein the transmitting antenna switching time interval is at least 200 times larger than the first sampling time interval.
Preferably, when the electromagnetic wave signal is switched, after a preset delay time is maintained, data of a preset second number of continuous sampling points are acquired and stored in a data memory.
Preferably, in comparing the actual time with the first time, diagnosing whether the clock count value of the first timer needs to be adjusted based on the actual time and the first time, the method includes: judging whether the absolute value of the difference value between the actual time and the first time exceeds a preset error threshold value, if so, continuously judging whether the difference value is a positive number, and if so, subtracting 1 from the clock count value of the first timer; and if the number is negative, adding 1 to the clock count value of the first timer.
Preferably, the delay time is less than and approximately half of the transmit antenna switching time interval.
Preferably, in the recording of the actual time step corresponding to the first number of sampling points of the continuous sampling, the method includes: and setting a first timer for monitoring the actual time, controlling the first timer to start to count, controlling the first timer to be closed when the number of the sampling data which are continuously acquired currently reaches the first number, diagnosing whether deviation compensation is needed, and restarting the first timer after compensation adjustment is completed.
On the other hand, the invention also provides a logging while drilling electromagnetic wave data acquisition device, which processes the acquired electromagnetic wave signals by using the method so as to use the processed electromagnetic wave signals for phase difference and amplitude ratio calculation, and comprises: an electromagnetic wave signal receiving circuit for receiving an electromagnetic wave feedback signal in real time; the frequency mixing circuit is used for carrying out frequency reduction processing on the feedback signal to obtain a signal to be processed containing the phase and amplitude information of the feedback signal; the sampling circuit is used for continuously sampling the signal to be processed by using a first sampling time interval, and the period of the signal to be processed is k times of the first sampling time interval; the central processing unit is used for setting a first timer used for generating the first sampling time interval, calculating phase difference and amplitude ratio information of the feedback signal in real time according to k sampling point data in a calculation period corresponding to the signal to be processed, recording actual time corresponding to a preset first number of sampling points in continuous sampling, comparing the actual time with first time, and diagnosing whether the clock count value of the first timer needs to be adjusted based on the actual time, so as to compensate phase offset generated after the feedback signal is sampled due to the error of the processor, wherein the first time is the product of the first number and the first sampling time interval.
Preferably, the apparatus further comprises: and an electromagnetic wave signal transmitting circuit for switching different types of electromagnetic wave signals to be transmitted to a stratum where a drill bit arrives at a real-time position in a drilling process according to a transmitting antenna switching time interval generated by a second timer in the central processing unit, wherein the transmitting antenna switching time interval is at least 200 times larger than the first sampling time interval.
Preferably, when the electromagnetic wave signal is switched by the electromagnetic wave signal transmitting circuit, the central processing unit is further configured to acquire data of a preset second number of consecutive sampling points after a preset delay time is maintained, and store the data in a data memory connected to the central processing unit.
Preferably, the central processing unit is further configured to determine whether an absolute value of a difference between the actual time and the first time exceeds a preset error threshold, if so, continue to determine whether the difference is a positive number, and if so, decrease a clock count value of the first timer by 1; and if the number is negative, adding 1 to the clock count value of the first timer.
One or more embodiments of the above-described solution may have the following advantages or benefits compared to the prior art:
the invention discloses a logging while drilling electromagnetic wave data acquisition method and device. The method and the device solve the problem of inaccurate calculation of the phase difference and the amplitude ratio of the electromagnetic wave in the later period caused by errors of AD sampling time intervals due to the system clock errors generated by the central processing unit. The invention sets the first timer and the second timer which can be adjusted at any time, and monitors the accumulated error of the AD sampling time interval in real time by using the first timer so as to timely compensate clock (phase) deviation by the first timer after the accumulated error reaches the threshold value. Therefore, the phase position of the sampling point is always kept at the same phase position relative to the electromagnetic wave feedback signal before mixing, so that the amplitude and phase information of the electromagnetic wave signal are accurately recorded, and stratum data acquired by the logging while drilling instrument in a long-time working process are still reliable and effective. That is, the invention enables the logging while drilling instrument to maintain equivalent calculation precision of electromagnetic wave phase difference and amplitude ratio in the long-time working process, thereby providing real-time reliable resistivity data in the drilling process, and having great significance for implementing high-precision drilling.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate the invention and together with the embodiments of the invention, serve to explain the invention, without limitation to the invention. In the drawings:
fig. 1 is a step diagram of a logging while drilling electromagnetic wave data acquisition method according to an embodiment of the present application.
Fig. 2 is a schematic diagram of an electromagnetic wave data acquisition method for logging while drilling according to an embodiment of the present application.
Fig. 3 is a flowchart of an implementation of a logging-while-drilling electromagnetic wave data acquisition method according to an embodiment of the present application.
Fig. 4 is a schematic structural diagram of an electromagnetic wave data acquisition device for logging while drilling according to an embodiment of the present application.
Fig. 5 is a circuit diagram of an implementation of an electromagnetic wave data acquisition device for logging while drilling according to an embodiment of the present application.
Detailed Description
The following will describe embodiments of the present invention in detail with reference to the drawings and examples, thereby solving the technical problems by applying technical means to the present invention, and realizing the technical effects can be fully understood and implemented accordingly. It should be noted that, as long as no conflict is formed, each embodiment of the present invention and each feature of each embodiment may be combined with each other, and the formed technical solutions are all within the protection scope of the present invention.
Logging while drilling is a technique that identifies formation information and boundary distance information during real-time drilling and provides services for evaluating hydrocarbon reservoirs and optimizing drilling trajectories. In recent years, logging while drilling technology has rapidly developed, and not only have some original measurement methods improved, but also a plurality of new logging while drilling methods have appeared. Wherein a bit resistivity instrument (RAB) provides azimuthal gamma and real-time resistivity images; the quantitative imaging logging of multiple detection depths is performed, such as resistivity images generated by RAB and density imaging images measured by a VISION system.
At present, one core technology in the logging while drilling technology based on the combination of MWD+gamma+resistivity is to obtain the resistivity of a stratum by calculating the phase difference and amplitude ratio information of electromagnetic wave signals, and because the frequency of the electromagnetic wave signals is higher, generally 400KHz and 2MHz, high-frequency signals are directly sampled, and high hardware resources are occupied, so that the AD sampling rate and Flash storage are very challenging.
In the prior art, a mixer is generally used for performing down-conversion processing on a high-frequency electromagnetic wave signal fed back from a stratum, and then an electronic processor device is used for performing multi-point sampling on each calculation period so as to calculate phase difference and amplitude ratio information of the electromagnetic wave signal by using a plurality of sampling point data in the same calculation period, thereby obtaining resistivity information of the stratum. However, when multi-point sampling is performed, due to the error of an internal device (such as a crystal oscillator) of the processor, the sampling frequency after frequency division has a certain gap from a theoretical value, and the actual phase of an electromagnetic wave signal fed back by a stratum and the phase of the sampled signal are further deviated, so that the accuracy of the calculation of the phase difference and the amplitude ratio of the subsequent electromagnetic wave is affected.
Therefore, a method for performing a phase deviation compensation process on the electromagnetic wave acquisition data before calculating the phase difference and the amplitude ratio of the electromagnetic wave signal is needed in the prior art to eliminate the phase deviation between the sampling data and the actual feedback signal caused by the error of the internal device of the processor.
In order to solve the technical problem, the invention sets the first timer for generating the first sampling time clock in the central processing unit, monitors the time of the continuous sampling process of the electromagnetic wave feedback signal subjected to the frequency reduction processing by utilizing the first controller in real time, and adjusts the clock count value in the first timer when the monitored real-time error exceeds a preset error threshold value so as to continuously sample the electromagnetic wave feedback signal subjected to the subsequent frequency reduction processing by utilizing the first sampling time interval after the adjustment, thereby compensating the phase offset generated after the electromagnetic wave feedback signal is sampled due to the self error of the processor.
In addition, in order to obtain more stable and accurate sampling point data, when the current electromagnetic wave signal transmitter starts to transmit electromagnetic waves to the stratum where the drill bit reaches the real-time position in the while-drilling process, the acquired sampling point data do not need to be stored, and after the preset delay time is reached, a certain amount of sampling point data are acquired to ensure that the more stable sampling data are obtained, so that more accurate calculation results of the phase difference and amplitude ratio information of the electromagnetic wave signal are facilitated.
Fig. 4 is a schematic structural diagram of an electromagnetic wave data acquisition device for logging while drilling according to an embodiment of the present application. As shown in fig. 4, the apparatus of the present invention includes: an electromagnetic wave signal receiving circuit 100, a mixing circuit 200, a sampling circuit 300, a central processing unit 400, an electromagnetic wave signal transmitting circuit 500, and a waveform generator 600. The electromagnetic wave signal receiving circuit 100 is configured to receive an electromagnetic wave feedback signal in real time. The mixing circuit 200 is configured to mix the first signal with the natural original frequency with the electromagnetic feedback signal, and then perform a down-conversion process to obtain a signal to be processed containing the phase and amplitude information of the feedback signal. The sampling circuit 300 is configured to continuously sample the signal to be processed using the first sampling time interval. Wherein the time period of the signal to be processed is k times the first sampling time interval (k is a positive integer, preferably k=4). The central processor 400 is provided with a first timer T2 and a second timer T1. The first timer T2 is configured to generate a clock signal representing a first sampling time interval using the first frequency division number. The second timer T1 is configured to generate a clock signal representing a transmit antenna switching time interval using the second frequency division number. The central processing unit 400 is configured to obtain phase and amplitude data of the electromagnetic wave reflection signal corresponding to each sampling point according to k sampling points in a calculation period (time period of the signal to be processed) corresponding to the signal to be processed, and calculate, based on the phase and amplitude ratio information corresponding to the electromagnetic wave feedback signal in each calculation period in real time. The electromagnetic wave signal transmitting circuit 500 is configured to switch electromagnetic wave (transmitting) signals with different transmitting frequencies according to the transmitting antenna switching time interval generated by the second timer T1, so as to transmit electromagnetic wave (transmitting) signals with corresponding frequencies to the stratum where the drill bit reaches the real-time position during the while-drilling process. Wherein the transmit antenna switching time interval is at least 200 times greater than the first sampling time interval. The waveform generator 600 is configured to generate the first signal with the natural frequency under the control of the cpu 400 and send the first signal to the mixer circuit 200.
Fig. 5 is a circuit diagram of an implementation of an electromagnetic wave data acquisition device for logging while drilling according to an embodiment of the present application. The device according to the invention will be described in detail with reference to fig. 4 and 5. Firstly, the acquisition device of the present invention includes multiple signal receiving paths, each signal receiving path is connected to a central processing unit (U1) 400, and is configured to perform a series of processing such as frequency reduction and sampling on a high-frequency electromagnetic wave feedback signal received in real time, so as to obtain corresponding sampling point data, and transmit the data to the central processing unit 400, so as to perform subsequent phase difference and amplitude ratio information calculation processing. In the embodiment of the invention, the structures of each signal receiving path are the same, and the signal receiving path comprises a receiving antenna, a first preprocessing circuit, a mixer, a second preprocessing circuit and an AD converter which are connected in sequence. It should be noted that the number of signal receiving paths configured in the present invention is not particularly limited, and those skilled in the art may set the number according to actual needs. Preferably, the number of signal receiving paths configured with reference to fig. 5 is two. The following describes a specific structure of one of the signal receiving paths.
Further, the electromagnetic wave signal receiving circuit 100 includes receiving antennas R1, R2 and a signal preprocessing circuit. The receiving antennas R1 and R2 are used for receiving high-frequency electromagnetic wave feedback signals representing formation resistivity in the logging while drilling process in real time. The first preprocessing circuit is configured to perform preprocessing including RC filtering and signal amplification on the received high-frequency electromagnetic wave feedback signal, so as to obtain a high-frequency electromagnetic wave feedback signal that can be input to the mixer circuit 200.
The mixer circuit 200 includes a mixer U6. The mixer U6 is connected with the first preprocessing circuit and is used for performing down-conversion processing on the high-frequency electromagnetic wave feedback signal and the first signal received from the first preprocessing circuit and outputting a signal to be processed of 2 kHz.
The sampling circuit 300 includes a second preprocessing circuit and AD converters U12, U13. The second preprocessing circuit is correspondingly connected with the output end of the mixer U6, and is used for filtering, amplifying and conditioning the 2kHz signal to be processed through the RC filter, the signal amplifiers U8 and U9 and the signal conditioners U11 and U10 respectively, and adjusting the 2kHz signal to be processed into the signal to be processed in the range suitable for sampling by the AD converter. The AD converters U12, U13 are configured to continuously sample the (conditioned) signal to be processed inputted from the signal conditioners U11, U10 under the control of a first sampling interval (first sampling interval) controlled by the first timer T2.
The electromagnetic wave signal transmitting circuit 500 includes 6 transmitting antennas (TR 1, TR2, TR3, TR4, TR5, TR 6), and a multiplexer U14 correspondingly connected to the 6 antennas, respectively. Wherein each transmitting antenna corresponds to a corresponding transmitting target. Specifically, the 6 transmitting antennas are respectively: a near antenna (TR 1) having a first transmission frequency, a near antenna (TR 2) having a second transmission frequency, a middle antenna (TR 2) having the first transmission frequency, a middle antenna (TR 4) having the second transmission frequency, a far antenna (TR 5) having the first transmission frequency, and a far antenna (TR 6) having the second transmission frequency. The multiplexer U14 also has 6 selection channels, which are respectively connected to the 6 transmit antennas. The multiplexer U14 is configured to select a corresponding channel under the control of the transmit antenna switching time interval, so as to transmit, by using the transmit antenna of the corresponding channel, an electromagnetic wave transmit signal meeting a current transmit target to a stratum where the drill bit reaches a real-time position during the while-drilling process. At this time, the second timer T1 is configured to control the multiplexer U14 to switch channels of different transmitting antennas according to the self-generated transmitting antenna switching time interval, so that each adjacent transmitting antenna switching time period can transmit electromagnetic wave transmission signals with different frequencies and different source distances. Preferably, the first frequency of the electromagnetic wave emission signal is 2MHz; the second frequency of the electromagnetic wave transmission signal is 500KMHz. It should be noted that, referring to fig. 5, in the practical application process, the electromagnetic wave transmitting signal is received by the receiving antenna after passing through the drilling fluid and the stratum, so as to obtain the electromagnetic wave feedback signal, but the frequency of the electromagnetic wave feedback signal is consistent with the frequency of the electromagnetic wave transmitting signal.
For example: switching the channel where the TR1 is located to the channel where the TR2 is located, the channel where the TR2 is located to the channel where the TR3 is located, the channel where the TR3 is located to the channel where the TR4 is located, the channel where the TR4 is located to the channel where the TR5 is located, the channel where the TR5 is located to the channel where the TR6 is located, and the channel where the TR6 is located to the channel where the TR1 is located at every fixed transmitting antenna switching time interval 2T sequentially, and repeating the cycle sequentially; or reverse circulation.
Further, the waveform generator 600 is configured to generate a first signal that can be a natural frequency of the mixer U6 under the control of the central processor 400, and output the signal to the mixer U6 in the above-mentioned mixer circuit 200. Wherein the frequency of the first signal corresponds to the frequency of the electromagnetic wave transmitting signal. Preferably, when the frequency of the electromagnetic wave transmission signal is 2MHz, the frequency of the first signal is 2.002MHz; when the frequency of the electromagnetic wave transmitting signal is 500KHz, the frequency of the first signal is 502KHz.
As shown in fig. 5, the central processor U1 selects the antenna TR1 (or TR2/TR3/TR4/TR5/TR 6) to transmit a high-frequency electromagnetic wave signal, and selects a corresponding transmission frequency of 2MHz (or 500 kHz) through the multiplexer U14; electromagnetic wave transmitting signals are received by the receiving antennas R1 and R2 after passing through drilling fluid and stratum; the 2MHz signal received by R1 is sent to a first path input end of a mixing circuit U6 after passing through filtering and amplifying circuits U2 and U3; the 2MHz signal received by R2 is sent to the second input of the mixer circuit U6 after passing through the filter and amplifier circuits U4 and U5. The waveform generator U7 generates a first signal of 2.002MHz and feeds the signal to the two inputs of the mixer circuit U6, respectively. The mixer U6 outputs two paths of 2kHz signals, and the first path of signal receiving path sends the signals to be processed of 2kHz to the AD converter U12 for sampling after passing through the amplifying circuit U9 and the signal conditioning circuit U10; the second signal receiving path sends the signal to be processed of 2kHz to the AD converter U13 for sampling after passing through the amplifying circuit U8 and the signal conditioning circuit U11. The central processing unit U1 controls the waveform generator U7 to output a waveform representing a first signal having a frequency of 2.002MHz (or 502 kHz) through pins RG1, RG2, RG3, and RD4, controls the sampling interval time of the AD converter U13 through pins RD2, RD3, and RD4, and performs data reading, and controls the sampling interval time of the AD converter U12 through pins RD5, RD6, and RD7, and performs data reading.
The electromagnetic wave data acquisition device for logging while drilling according to the embodiment of the invention provides a corresponding application environment for the electromagnetic wave data acquisition method for logging while drilling, and after the acquisition device is described, the electromagnetic wave data acquisition method for logging while drilling (hereinafter referred to as an acquisition method) according to the embodiment of the invention is described based on the device. Fig. 1 is a step diagram of a logging while drilling electromagnetic wave data acquisition method according to an embodiment of the present application. Fig. 2 is a schematic diagram of an electromagnetic wave data acquisition method for logging while drilling according to an embodiment of the present application. The acquisition method according to the invention will be described with reference to fig. 1 and 2.
Firstly, in step S110, the electromagnetic wave signal receiving circuit 100 receives the high frequency electromagnetic wave feedback signal in real time, and performs the frequency-reducing process on the currently received high frequency electromagnetic wave feedback signal by using the mixing circuit to obtain a signal to be processed containing the phase and amplitude information of the feedback signal, and then proceeds to step S120. Typically, the frequency of the high-frequency electromagnetic wave feedback signal is 2MHz or 500KMHz, and the frequency of the signal to be processed output by the frequency mixing circuit after the frequency reduction processing is 2kHz.
The central processor 400 sets a first timer T2 for generating a first sampling time interval with which the AD converters U12, U13 in the sampling circuit 200 are controlled to continuously sample the signal to be processed (of 2 kHz) by the AD converter (at the first sampling time interval) to proceed to step S130. Wherein the time period of the signal to be processed is k times the first sampling time interval (k is a positive integer, preferably k=4). In the practical application process, the time period corresponding to the frequency of the signal to be processed after the down-conversion process (may be referred to as a down-conversion time interval) is generally a calculation period of the cpu 400 during the phase difference and amplitude ratio calculation process of the electromagnetic wave signal. The first sampling time interval is a time period corresponding to a sampling point acquired in one calculation period.
In order to improve the accuracy of the calculation result of the phase difference and amplitude ratio information of the electromagnetic wave signal, the final calculation result (phase difference and amplitude ratio information) is often generated by performing multi-point (k) sampling in one calculation cycle. For this reason, in the embodiment of the present invention, when sampling data points, the sampling time interval is determined to be 1/k times of the above-mentioned down-conversion time interval, so that k pieces of sampling point data (phase and amplitude data) are acquired in one calculation period. In the embodiment of the present invention, the central processor 400 preferably calculates the phase difference and amplitude ratio information of the electromagnetic wave signal using a four-point sampling algorithm (k=4), thereby obtaining the resistivity information of the formation. For example: the first timer T2 controls the sampling interval time dt of the AD converter by using the first sampling interval generated by the first timer T2, so that the AD converter samples a point every other dt, and sends a sampling point data (phase and amplitude data of the electromagnetic wave reflection signal corresponding to the sampling point) to the central processing unit. If the frequency corresponding to the down-conversion time interval is 2kHz and k=4, then the current first sampling time interval is 125 μs and the frequency corresponding to the first sampling time interval is 8kHz.
In step S130, the central processing unit 400 calculates, in real time, the phase difference and the amplitude ratio information of the electromagnetic wave feedback signal representing the formation resistivity information in each calculation period by using a multi-point sampling algorithm according to k sampling point data in the calculation period corresponding to the signal to be processed.
In order to solve the above-mentioned problem that the sampling clock actually provided to the sampling circuit has a phase deviation from the sampling clock that should be obtained theoretically due to the error of the internal device (e.g., crystal oscillator for providing the system clock) of the cpu 400 in the prior art, that is, the first sampling time interval dt actually provided to the AD converter by the first timer T2 is approximately 125 μs, instead of exactly 125 μs. In this way, the electromagnetic wave feedback signal received by the receiving antenna and the sampled sampling point data are caused to generate phase deviation. In this case, for measurement while drilling technology with very high real-time requirements, if the deviation is not corrected in time, a larger accumulated phase deviation is generated after accumulation of a plurality of calculation periods, and at this time, the accuracy of the calculation result of the final phase difference and amplitude ratio information is seriously affected, so that reliable formation resistivity data cannot be obtained. For this reason, the embodiment of the present invention utilizes the following step S140 to monitor the deviation in real time and correct the deviation in time.
In step S140, the central processing unit 400 records the actual (monitoring) time corresponding to the first number (n) of sampling points continuously, compares the current actual monitoring time with the first time CNT, and diagnoses whether the value of the first timer T2 needs to be adjusted according to the comparison result, so as to compensate the phase offset generated after the sampling of the electromagnetic wave feedback signal due to the error of the processor itself, thereby continuously sampling the subsequent signal to be processed according to the first sampling time interval after the deviation adjustment processing. The first time CNT is the product of the first number n and the first sampling time interval dt, which refers to the time theoretically required for receiving and reading n sampling points.
It should be noted that, if the first number is set too large, the accuracy of the calculation result of the final electromagnetic wave signal phase difference and the amplitude ratio information due to the accumulated deviation amount is very critical, and if the first number is set too small, the accumulated deviation is too small to be recognized, so that it is difficult to determine whether the clock compensation process is required for the first timer T2 (it is difficult to determine the accurate timing of the accurate clock compensation process). Therefore, in the embodiment of the present invention, it is preferable that the first time for continuously sampling the first number of sampling point data is at least a time corresponding to 5 to 10 transmit antenna switching time intervals, that is, 10T (transmit antenna switching time interval is 2T), and T is approximately equal to a time for continuously sampling 100 sampling point data. Further, n is an integer of 1000 or more and 2000 or less.
Before the step S140 is performed, the cpu 400 needs to set the first timer T3 for recording the first time CNT and control the first timer T3 to start. It should be noted that, when the accuracy of the first sampling time interval dt is high, the value of n may be set to be slightly larger.
Further, a first register PR2 is provided in the first timer T2, and the first register PR2 counts with a change of a system clock of the cpu 400, and when the current count value reaches a (first) frequency division number corresponding to the first timer T2, the first register PR2 controls the first timer T2 to generate a sampling pulse to sample a point. Thus, the first timer T2 generates a clock signal having a frequency of the first sampling time under the control of the first register PR2, and generates one sampling pulse at every first sampling time interval. The value of the first timer T2 refers to the real-time count value of the system clock pulses of its internal first register PR 2.
Further, referring to fig. 2, in the step S140 of recording the actual time corresponding to the first number of sampling points, the central processor 400 further sets a first timer T3 for monitoring the actual time, and controls the start of the first timer T3 to start timing, the central processor 400 counts the number of sampling point data acquired in real time in the continuous sampling process, and when the number of sampling point data acquired continuously at present reaches the first number, the first timer T3 is controlled to be turned off (stop timing), the central processor 400 diagnoses whether offset compensation is required, and after compensation adjustment is completed or it is determined that compensation adjustment is not required, the first timer T3 is restarted. In this way, the first timer T3 is used to monitor the actual time during each acquisition of n sampling points, and to timely compensate and adjust the accumulated phase deviation.
More specifically, in the step S140, the actual monitoring time is compared with the first time, and whether the value of the first timer T2 needs to be adjusted is diagnosed according to the comparison result, and whether the absolute value of the difference between the current actual time and the first time exceeds the preset error threshold is further determined. If the current difference value exceeds the preset value, continuously judging whether the current difference value is positive, and if the current difference value is positive, subtracting 1 from the value of the first timer T2. If the current difference is negative, the value of the first timer T2 is added by 1. The error threshold is preferably a time corresponding to one system clock cycle of the cpu 400, that is, a time corresponding to one system clock cycle obtained by dividing the system clock by the first frequency division number (for example, 100 ns). In addition, if the absolute value of the current difference value does not exceed the error threshold, the process returns to step S120, where the AD converter is continuously controlled to continuously sample the analog signal to be processed at 2kHz and monitor the corresponding actual time in real time, so as to calculate the phase difference and amplitude ratio information of the electromagnetic wave signal by using a multi-point sampling algorithm according to the read sampling point data in step S130.
For example, for a 2kHz signal to be processed (analog), if the first sampling time interval dt should be 125 μs, and the setting of dt is controlled by the first register PR2 in the first timer T2, if CNT is greater than 125n, the current clock count value recorded by PR2 is decremented by 1, and if CNT is less than 125n, the current clock count value recorded by PR2 is incremented by 1.
In this way, the embodiment of the invention sets the first timer T2 and the first timer T3 which can be flexibly adjusted, monitors the possible phase deviation generated in the long-time logging-while-drilling process by utilizing the first timer T3, and performs the phase deviation compensation processing by adjusting the real-time counting numerical value of the first register in the first timer T2 after the deviation reaches the error threshold value affecting the calculation result of the phase difference and the amplitude ratio information of the subsequent electromagnetic wave signals, thereby solving the problems in the prior art and ensuring the high precision and the continuous reliability of the phase and the amplitude value of the electromagnetic wave signals recorded by the long-time logging-while-drilling technology.
Further, according to the requirements of logging while drilling technology, in order to obtain more accurate and fine resistivity information of the underground stratum, different types of electromagnetic wave emission signals are required to be continuously emitted to the underground stratum in the process of drilling. The types of electromagnetic wave emission signals include: the method comprises the steps of transmitting a first type of electromagnetic wave transmission signal with a first transmission frequency by a near antenna, transmitting a second type of electromagnetic wave transmission signal with a second transmission frequency by the near antenna, transmitting a third type of electromagnetic wave transmission signal with the first transmission frequency by a middle antenna, transmitting a fourth type of electromagnetic wave transmission signal with the second transmission frequency by the middle antenna, transmitting a fifth type of electromagnetic wave transmission signal with the first transmission frequency by a far antenna, and transmitting a sixth type of electromagnetic wave transmission signal with the second transmission frequency by the far antenna. For this reason, the present invention also uses step S150 to switch the electromagnetic wave signal type at each transmitting antenna switching time interval in real time according to a preset sequence (for example, sequentially cycling from the first class to the sixth class and back to the first class, or sequentially cycling from the sixth class to the first class and back to the sixth class).
In step S150, the cpu 400 sets a second timer T1 for generating a transmission antenna switching time interval, and switches different types of electromagnetic wave signals according to a preset sequence according to the transmission antenna switching time interval, so as to transmit the electromagnetic wave signals to the stratum where the drill bit reaches the real-time position during the while-drilling process. Wherein the transmit antenna switching time interval 2T is at least 200 times greater than the first sampling time interval dt. Specifically, the central processor 400 is provided with a clock signal capable of generating a signal representing a switching time interval of the transmitting antenna.
The first timer T2 is internally provided with a corresponding second register, the second register also counts along with the change of the system clock pulse of the central processing unit 400, when the current count value reaches the (second) frequency division number corresponding to the second timer T1, the second register controls the second timer T1 to generate a switching pulse, so that the channel switching control is performed on the multiplexer in the electromagnetic wave signal transmitting circuit 500 connected with the central processing unit 400, and the electromagnetic wave signal transmitting circuit 500 switches from transmitting one type of electromagnetic wave transmitting signals to transmitting the other type of electromagnetic wave transmitting signals according to a preset sequence. Thus, the second timer T1 generates a clock signal having the frequency of the transmit antenna switching time under the control of the second register, and generates one switching pulse at every transmit antenna switching time interval. The value of the second timer T1 refers to the real-time count value of the system clock pulses of its internal first register PR 2.
Further, since the type of electromagnetic wave signal transmitted by the electromagnetic wave signal transmitting circuit 500 is continuously switched during the downhole measurement while drilling, not all received electromagnetic wave feedback signals are stable and reliable, in other words, not all received and read sampling point data can be advantageous for calculating accurate electromagnetic wave signal phase difference and amplitude ratio information. Thus, embodiments of the present invention utilize step S160 to collect stable and reliable sample point data characterizing current formation resistivity state information during transmission of a current type of electromagnetic wave transmission signal.
In step S160, when the electromagnetic wave transmitting signal is switched (from each antenna switching time), the cpu 400 acquires the data of the preset second number of consecutive sampling points after maintaining the preset delay time, and stores the data in the data memory (e.g., FLASH memory) connected to the cpu 400. Because no synchronous signal exists between the continuous sampling process and the signal transmitting process of the AD converter, if the sampled data is stored too early, the data before the current type of transmitting signal can be acquired, and the phenomenon of untimely data updating is caused; if the sampled data is stored too late, it is possible that the current type of transmitted signal has switched to the next type, resulting in data loss, and therefore the timing of the data storage is critical. Preferably, the delay time is about half of the transmit antenna switching time interval, and more preferably less than and close to half of the transmit antenna switching time interval. In addition, the second number is the total number of sample point data for the current type of transmission signal, and the size of the number is not particularly limited, and is preferably less than the number (e.g. 40) of sample point data acquired in a quarter of the transmission antenna switching time interval.
For example, when saving the sample point data, the cpu 400 keeps the preset delay time T from each antenna transmission switching time, and then saves 40 data points continuously sampled by the AD to the Flash memory, that is, saves the sample point data of 10 calculation cycles at a time.
As shown in fig. 2, the central processor U1 (S201) controls the waveform generator U7 to output a first signal of 2.002MHz (or 502 kHz) while starting the second timer T1 (203) operation S202 by starting the second register (a register for starting the second timer constructed when the second timer is set) and starting the first timer T2 (207) operation S206 by starting the first register (a register for starting the first timer constructed when the first timer is set). S203 the second timer T1 switches the transmit antenna once every transmit antenna switching time 2T, wherein the transmit antenna switching time interval 2T is much longer than the AD sampling interval time dt, typically with t=100×dt. The first timer T2 sets the frequency division coefficient of the system clock signal of 4MHz to 500 through the first register PR2 in S207, that is, sets the first sampling time interval dt to 125±Δμs, which indicates that the dt is not exactly equal to 125 μs in hardware, but is an approximate value, and the AD converter continuously samples the signal to be processed of 2kHz at the first sampling time interval dt. S208 the first timer T3 counts the actual monitoring time corresponding to the AD continuously sampled 1000 points to be CNT, S209 if CNT >125ms (125 μs×n, n=1000), the central processor U1 subtracts 1 from the value of the first register PR2, and repeats this step until cnt=125 ms; s209 if CNT <125ms, the central processor U1 (201) adds 1 to the value of the first register PR2, and repeats this step until cnt=125 ms. When storing the sampling point data, the central processing unit U1 delays the time T at each antenna transmitting time, and stores 40 data points continuously sampled by the AD into the Flash memory, that is, stores the sampling point data of 10 calculation periods at a time.
Fig. 3 is a flowchart of an implementation of a logging-while-drilling electromagnetic wave data acquisition method according to an embodiment of the present application. As shown in fig. 3, after the program is started, the main function is entered. Step S301 initializes the second timer T1, step S305 initializes the first timer T2 and step S316 initializes the first timer T3, i.e., sets the count registers tmr1=0, tmr2=0, tmr3=0, respectively, while setting the frequency division number of the first register PR2 within the first timer T2 to 500, i.e., the frequency of the divided clock signal representing the first sampling time interval to 8kHz for the clock signal to 4MHz, i.e., the first sampling time interval period to 125 μs. Step S302 the cpu 400 controls to start the second timer T1 and step S306 controls to start the first timer T2, i.e. to set t1con=1, t2con=1. For the 16-bit second timer T1, the time for entering the interrupt is 16.384ms, and the timing is repeated 61 times to set the transmission antenna switching time interval to 1S (step S303), and the antenna is switched once every 1S time in step S304 to change the type of the electromagnetic wave transmission signal. The first sampling time interval set by the first timer T2 in step S307 is about 125 μs, and the central processor 400 controls to start the first timer T3, i.e., set t3con=1 in step S308, and samples 1 point by the AD converter in step 309, and causes the central processor 400 to obtain the sampling point data of the point.
In addition, step S310 calculates the number of data points sampled by the AD from the time when the first timer T3 is started, and if the number of data points sampled is less than 1000 (the first number of data points), returns to step S309AD to continue sampling data; if the 1000 th data point is sampled, the process proceeds to step S311, where the timer value CNT is recorded by the first timer T3, and the timer is stopped. If the allowable error threshold of CNT is 100ns, that is, within the range of [125ms-100ns,125ms+100ns ], the data of AD sampling are considered to be valid, and the phase difference and amplitude ratio information calculated by the four-point sampling algorithm has high accuracy. If CNT-125ms >100ns in step S312, the value of the first register PR2 of the first timer T2 is reduced by 1 in step S313, and then the process proceeds to step S308. Step S314, if CNT-125ms < -100ns, proceed to step S308 after adding 1 to the value of the first register PR2 of the first timer T2. If neither step S312 nor step S314 is true, indicating that CNT is in the range of [125ms-100ns,125ms+100ns ], then the value of the first register PR2 need not be changed, at which point the phase and amplitude information calculated by the four-point sampling algorithm is highly accurate.
On the other hand, referring to fig. 4 and fig. 5 again, based on the above-mentioned acquisition method, the present invention further provides an electromagnetic wave data acquisition device for logging while drilling (hereinafter referred to as "acquisition device"), which processes the electromagnetic wave signal obtained by the above-mentioned acquisition method, so as to use the processed electromagnetic wave signal for phase difference and amplitude ratio calculation. Wherein, above-mentioned collection system includes: an electromagnetic wave signal receiving circuit 100, a mixing circuit 200, a sampling circuit 300, and a central processing unit 400. The electromagnetic wave signal receiving circuit 100 is configured to receive an electromagnetic wave feedback signal in real time. The mixer circuit 200 is configured to perform a down-conversion process on the electromagnetic feedback signal to obtain a signal to be processed containing the phase and amplitude information of the feedback signal. The sampling circuit 300 is configured to continuously sample the signal to be processed using the first sampling time interval. Wherein the time period of the signal to be processed is k times of the first sampling time interval.
The central processor 400 is configured to set a first timer for generating a first sampling time interval, and calculate, in real time, phase difference and amplitude ratio information corresponding to the electromagnetic wave feedback signal in each calculation period according to k sampling point data in the calculation period corresponding to the down-conversion time interval. The central processor 400 is further configured to record an actual time corresponding to a preset first number of sampling points in continuous sampling, compare the actual time with the first time, and diagnose whether to adjust a clock count value of the first timer according to a comparison result, so as to compensate for a phase offset generated after sampling the electromagnetic wave feedback signal due to an error of the processor itself. Further, the first time is a product of the first number and the first sampling time interval.
In addition, the above-mentioned collection system still includes: an electromagnetic wave signal transmitting circuit 500. The electromagnetic wave signal transmitting circuit 500 is configured to switch different types of electromagnetic wave (transmitting) signals for transmission to the formation where the drill bit arrives at the real-time position during the while-drilling process at the transmission antenna switching time interval generated by the second timer within the central processor 400. Wherein the transmit antenna switching time interval is at least greater than 200 times the first sampling time interval.
Further, when the type of the electromagnetic wave signal is switched by the electromagnetic wave signal transmitting circuit 500, the cpu 400 is further configured to obtain data of a predetermined second number of consecutive sampling points after maintaining the predetermined delay time, and store the data in a data memory connected to the cpu 400.
In addition, the cpu 400 is further configured to determine whether the absolute value of the difference between the current actual time and the first time exceeds a preset error threshold, if so, continuously determine whether the current difference is a positive number, and if so, subtracting 1 from the clock count value of the first timer; if the number is negative, the clock count value of the first timer is increased by 1.
The invention discloses a logging while drilling electromagnetic wave data acquisition method and device. The method and the device solve the problem of inaccurate calculation of the phase difference and the amplitude ratio of the electromagnetic wave in the later period caused by errors of AD sampling time intervals due to the system clock errors generated by the central processing unit. The invention sets the first timer and the second timer which can be adjusted at any time, and monitors the accumulated error of the AD sampling time interval in real time by utilizing the first timer so as to timely compensate clock (phase) deviation by the first timer after the accumulated error reaches a threshold value. Therefore, the phase position of the sampling point is always kept at the same phase position relative to the electromagnetic wave feedback signal before mixing, so that the amplitude and phase information of the electromagnetic wave signal are accurately recorded, and stratum data acquired by the logging while drilling instrument in a long-time working process are still reliable and effective. That is, the invention enables the logging while drilling instrument to maintain equivalent calculation precision of electromagnetic wave phase difference and amplitude ratio in the long-time working process, thereby providing real-time reliable resistivity data in the drilling process, and having great significance for implementing high-precision drilling.
The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the scope of the present invention are intended to be included in the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.
Claims (10)
1. The electromagnetic wave data acquisition method for logging while drilling is characterized by comprising the following steps of:
receiving an electromagnetic wave feedback signal in real time and performing frequency reduction processing on the signal to obtain a signal to be processed containing the phase and amplitude information of the feedback signal;
setting a first timer for generating a first sampling time interval, and continuously sampling the signal to be processed by using the first sampling time interval, wherein the period of the signal to be processed is k times of the first sampling time interval;
calculating the phase difference and amplitude ratio information of the feedback signal in real time according to k sampling point data in a calculation period corresponding to the signal to be processed, wherein,
recording the actual time corresponding to a preset first number of sampling points in continuous sampling, comparing the actual time with first time, and diagnosing whether the clock count value of the first timer needs to be adjusted based on the actual time to compensate the phase offset generated after the feedback signal is sampled due to the error of the processor, wherein the first time is the product of the first number and the first sampling time interval.
2. The method according to claim 1, wherein the method further comprises:
and setting a second timer for generating a transmitting antenna switching time interval, and switching electromagnetic wave signals of different types according to the transmitting antenna switching time interval to transmit to a stratum where a drill bit reaches a real-time position in a drilling process, wherein the transmitting antenna switching time interval is at least 200 times larger than the first sampling time interval.
3. The method according to claim 2, wherein when switching the electromagnetic wave signal, after a preset delay time, data of a preset second number of consecutive sampling points are acquired and stored in a data memory.
4. A method according to any one of claims 1 to 3, wherein in the step of comparing the actual time with a first time, based on which it is diagnosed whether an adjustment of the clock count value of the first timer is required, comprising:
judging whether the absolute value of the difference value between the actual time and the first time exceeds a preset error threshold value, if so, continuously judging whether the difference value is a positive number, and if so, subtracting 1 from the clock count value of the first timer; and if the number is negative, adding 1 to the clock count value of the first timer.
5. A method according to claim 3, wherein the delay time is less than and approximately half the transmit antenna switching time interval.
6. A method according to any one of claims 1 to 3, characterized in that in the step of recording the actual time corresponding to the first number of sampling points of successive samples, it comprises:
and setting a first timer for monitoring the actual time, controlling the first timer to start to count, controlling the first timer to be closed when the number of the sampling data which are continuously acquired currently reaches the first number, diagnosing whether deviation compensation is needed, and restarting the first timer after compensation adjustment is completed.
7. A logging-while-drilling electromagnetic wave data acquisition apparatus for performing a phase deviation compensation process on an acquired electromagnetic wave signal using the method as claimed in any one of claims 1 to 6 to use the processed electromagnetic wave signal for phase difference and amplitude ratio calculation, the apparatus comprising:
an electromagnetic wave signal receiving circuit for receiving an electromagnetic wave feedback signal in real time;
the frequency mixing circuit is used for carrying out frequency reduction processing on the feedback signal to obtain a signal to be processed containing the phase and amplitude information of the feedback signal;
The sampling circuit is used for continuously sampling the signal to be processed by using a first sampling time interval, and the period of the signal to be processed is k times of the first sampling time interval;
a central processing unit for setting a first timer for generating the first sampling time interval and calculating the phase difference and amplitude ratio information of the feedback signal in real time according to k sampling point data in a calculation period corresponding to the signal to be processed,
recording the actual time corresponding to a preset first number of sampling points in continuous sampling, comparing the actual time with first time, and diagnosing whether the clock count value of the first timer needs to be adjusted based on the actual time to compensate the phase offset generated after the feedback signal is sampled due to the error of the processor, wherein the first time is the product of the first number and the first sampling time interval.
8. The apparatus of claim 7, wherein the apparatus further comprises:
and an electromagnetic wave signal transmitting circuit for switching different types of electromagnetic wave signals to be transmitted to a stratum where a drill bit arrives at a real-time position in a drilling process according to a transmitting antenna switching time interval generated by a second timer in the central processing unit, wherein the transmitting antenna switching time interval is at least 200 times larger than the first sampling time interval.
9. The apparatus of claim 8, wherein when the electromagnetic wave signal is switched by the electromagnetic wave signal transmitting circuit, wherein,
the central processing unit is also used for acquiring data of a preset second number of continuous sampling points after keeping a preset delay time, and storing the data into a data memory connected with the central processing unit.
10. The device according to any one of claims 7 to 9, wherein,
the central processing unit is further configured to determine whether an absolute value of a difference between the actual time and the first time exceeds a preset error threshold, if so, continuously determine whether the difference is a positive number, and if so, subtracting 1 from a clock count value of the first timer; and if the number is negative, adding 1 to the clock count value of the first timer.
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