A downhole data compression system for three-dimensional acoustic logging

Abstract

The invention relates to the technical field of acoustic well logging, and discloses a downhole data compression system for three-dimensional acoustic well logging, comprising: a main control subsection and a receiving subsection composed of a plurality of receiving stations; the main control subsection is used for controlling a plurality of receiving stations in the receiving subsection to collect downhole data according to a data collection instruction on the well; the plurality of receiving stations are used for respectively collecting downhole data at different source distances; each receiving station is used for respectively collecting downhole data at different orientations at corresponding source distances by using a plurality of receiving transducers thereof, and processing the downhole data collected by the plurality of receiving transducers to obtain primary compressed data corresponding to the receiving station; the main control subsection is also used for processing the primary compressed data of each receiving station based on a differential pulse code modulation algorithm to obtain secondary compressed data; and the secondary compressed data is transmitted to the well surface to realize rapid transmission of downhole data.

Description

Technical Field

[0001] The invention relates to the technical field of acoustic well logging, and in particular to a downhole data compression system for three-dimensional acoustic well logging. Background Art

[0002] Well logging technology is the "eye" of oil and gas exploration and development, which can detect the formation information of the wellbore and its surroundings. Acoustic logging is an important well logging method, which determines the geological characteristics of the formation and the wellbore engineering conditions by measuring the acoustic properties of the wellbore or the medium beside the well. It has important applications in reservoir evaluation, determination of petroleum engineering parameters and seismic calibration.

[0003] In recent years, the detection characteristics of acoustic logging technology and instruments in the three dimensions of axial, radial and circumferential have achieved rapid development, especially in the new three-dimensional acoustic imaging logging technologies such as multipole array acoustic logging, azimuth remote detection acoustic logging, and through-casing acoustic logging. In order to further meet the needs of the oil and gas industry for detailed reservoir description and improved recovery, the next generation of intelligent acoustic logging instruments needs to detect larger three-dimensional spaces with higher accuracy and faster speed.

[0004] The above-mentioned status quo and development trend have resulted in an ever-increasing amount of data from three-dimensional acoustic logging instruments. However, the real-time transmission rate of existing cable methods is limited, resulting in a slow operation speed for this type of logging, and poor on-site and real-time processing and interpretation, which has severely restricted the extensive application of this type of instrument. It is urgent to solve the problem that a large amount of underground data cannot be quickly and real-timely transmitted to the ground.

[0005] In order to deal with the problem of difficulty in real-time transmission of 3D acoustic logging data, one is to adopt the working mode of "uploading all data". This passive response method uploads all logging data in each working cycle; the second is to adopt the working mode of "storing all data underground and only uploading part of the data in real time". This method only uploads part of the data in real time, which can greatly improve the logging speed; the third is to improve the data transmission capacity of instruments and cables. This method improves the transmission speed of the transmission line by improving the internal bus interface and cable transmission encoding method in the process of transmitting logging data from the underground acquisition end to the ground, which has a certain effect; the fourth is to reduce the amount of data to be transmitted. This method reduces the total amount of data that needs to be transmitted from the underground to the ground by compressing the underground data, thereby alleviating the problem of large amount of 3D acoustic logging data and difficulty in real-time transmission. This method can take into account both real-time and fast transmission and on-site processing, and has broad application prospects.

[0006] However, the first technology has a very slow logging speed, which seriously affects the on-site efficiency; the second technology cannot perform simultaneous logging and processing, and the subsequent reading of stored data is also time-consuming; the third technology is limited by the cable transmission bandwidth, and the improvement effect is not obvious; compared with the first three technologies, the fourth technology can effectively improve the data transmission efficiency by compressing the data at the downhole data transmission end, but this method currently only compresses the data at the downhole data transmission end, the data compression rate is not enough, and the time required for the compression operation accounts for a large proportion of the working cycle, resulting in a heavier workload for the main processor. Summary of the invention

[0007] The purpose of the present invention is to provide a downhole data compression system for three-dimensional acoustic logging, which can improve the compression effect of downhole data and reduce the workload of the main processor.

[0008] In order to solve the above technical problems, an embodiment of the present invention provides a downhole data compression system for three-dimensional acoustic logging, comprising: a main control subsection and a receiving subsection, the receiving subsection comprising a plurality of receiving stations evenly distributed along the axial direction of the logging instrument, each receiving station comprising a plurality of receiving transducers evenly distributed along the circumferential direction of the logging instrument; wherein the main control subsection is connected to each receiving station in the receiving subsection;

[0009] The main control sub is used to control multiple receiving stations in the receiving sub to collect downhole data according to the data collection instructions on the well;

[0010] Multiple receiving stations are used to collect downhole data at different source distances;

[0011] Each receiving station is used to use its own multiple receiving transducers to respectively collect downhole data at different azimuths at the corresponding source distance, and compress the downhole data collected by each receiving transducer to form compressed data at each azimuth at the corresponding source distance; obtain the relative value between the compressed data at each azimuth except the 0° azimuth and the compressed data at the 0° azimuth, and transmit the compressed data at the 0° azimuth and the relative value between the compressed data at each other azimuth and the compressed data at the 0° azimuth as primary compressed data to the main control sub;

[0012] The main control short section is also used to obtain the difference between each data except the first data and the previous data in the primary compressed data based on the differential pulse code modulation DPCM algorithm for the primary compressed data of each receiving station according to the similarity between adjacent data in the primary compressed data, and quantize and encode the first data in the primary compressed data and the difference between each data except the first data and the previous data, so as to transmit the quantized and encoded values ​​as secondary compressed data to the well.

[0013] Optionally, each receiving station is specifically used to perform time delay processing on the compressed data at each azimuth except the 0° azimuth according to the distribution positions of its own multiple receiving transducers on the receiving station, and obtain the difference between the compressed data at each azimuth except the 0° azimuth after the time delay processing and the compressed data at the 0° azimuth based on the similarity between the compressed data at each azimuth except the 0° azimuth after the time delay processing and the compressed data at the 0° azimuth, and use the difference as the relative value between the compressed data at each azimuth except the 0° azimuth and the compressed data at the 0° azimuth.

[0014] Optionally, each receiving station is specifically used to compress the downhole data collected by each receiving transducer of itself based on the wavelet transform method; wherein the wavelet basis function adopted by the wavelet transform method is the db4 wavelet, and the number of decomposition layers adopted is less than or equal to 3 layers.

[0015] Optionally, the data acquisition instruction is periodically sent to the main control subsection;

[0016] The main control sub is also used to perform the following two operations in parallel according to the data acquisition instructions of the current cycle: controlling multiple receiving stations in the receiving sub to collect downhole data of the current cycle and transmitting the secondary compression data corresponding to multiple receiving stations of the previous cycle to the surface.

[0017] Optionally, the data storage module of the master control sub comprises a first compressed data area and a first data area to be transmitted, the first compressed data area is used to store secondary compressed data corresponding to multiple receiving stations in the current cycle, and the first data area to be transmitted is used to store secondary compressed data corresponding to multiple receiving stations in the previous cycle;

[0018] The main control short section is also used to perform the following two operations in parallel by performing ping-pong operations on the first compressed data area and the first data area to be transmitted: controlling multiple receiving stations in the receiving short section to collect downhole data of the current cycle and transmitting the secondary compressed data corresponding to multiple receiving stations of the previous cycle to the surface.

[0019] Optionally, each receiving station is also used to perform the following two operations in parallel: collecting data at the corresponding source distance of the current cycle and transmitting the primary compressed data of the corresponding receiving station of the previous cycle to the main control short section.

[0020] Optionally, the data storage module of each receiving station includes a second compressed data area and a second data area to be transmitted, the second compressed data area is used to store primary compressed data corresponding to the receiving station in the current cycle, and the second data area to be transmitted is used to store primary compressed data corresponding to the receiving station in the previous cycle;

[0021] Each receiving station is also used to perform the following two operations in parallel by performing ping-pong operations on the second compressed data area and the second data area to be transmitted: collecting downhole data at the corresponding source distance of the current cycle and transmitting the primary compressed data of the corresponding receiving station in the previous cycle to the main control short section.

[0022] Optionally, each receiving transducer is further used to receive a full wave train waveform of an acoustic wave including a sliding longitudinal wave at a corresponding azimuth at a corresponding source distance as downhole data at a corresponding azimuth at a corresponding source distance;

[0023] Each receiving station is also used to remove useless data in the full wave train waveform of the sound wave collected by each receiving transducer according to the arrival time of the sliding longitudinal wave in the full wave train waveform of the sound wave collected by each receiving transducer.

[0024] Optionally, each receiving station has eight receiving transducers.

[0025] Optionally, a plurality of receiving transducers are evenly distributed in a circumferential direction of the logging instrument at the receiving station at intervals of 45°.

[0026] The downhole data compression system for three-dimensional acoustic logging provided by the present invention has at least the following beneficial effects:

[0027] Since in the three-dimensional acoustic logging instrument, the main control subsection is used to receive data acquisition instructions, control the receiving subsection to collect downhole data, and transmit the finally obtained downhole data to the well, therefore, the receiving subsection in the instrument is the acquisition end, and the main control subsection is the transmission end. In the present invention, the collected data is first processed by each receiving station of the receiving subsection, and the data finally obtained by each receiving station is the compressed data of the 0° azimuth and the relative value between the compressed data of each other azimuth and the compressed data of the 0° azimuth, which is equivalent to the primary compression of the downhole data in the acquisition end of the downhole data; then, the primary compressed data of each receiving station is processed again in the main control subsection based on the DPCM algorithm, and the data finally obtained by the main control subsection is the first data in the data after primary compression and the quantized coding value of the difference between each data except the first data and the previous data, which is equivalent to the secondary compression of the downhole data in the transmission end of the downhole data.

[0028] Therefore, the present invention does not compress downhole data only at the transmission end, but first performs primary compression at the acquisition end, and then performs secondary compression at the transmission end, which is equivalent to reconstructing the functions of each module of the three-dimensional acoustic logging instrument, so that the three-dimensional acoustic logging instrument has a multi-level data compression function, improves the compression effect of downhole data, reduces the amount of data transmitted inside the instrument and uploaded in real time, and achieves the purpose of reducing data transmission time and reducing the acquisition cycle of the three-dimensional acoustic logging instrument, thereby improving the efficiency of three-dimensional acoustic logging. At the same time, each module performs coordination based on data compression to avoid the compression operation being concentrated on the transmission end, thereby reducing the workload of the transmission end (i.e., the main processor). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] One or more embodiments are exemplarily described by the pictures in the corresponding drawings, and these exemplary descriptions do not constitute limitations on the embodiments.

[0030] Figure 1 A schematic diagram of a downhole data compression system for three-dimensional acoustic logging according to an embodiment of the present invention Figure 1 ;

[0031] Figure 2 is a schematic diagram of axial distribution of multiple receiving stations in a receiving short section provided according to an embodiment of the present invention;

[0032] Figure 3 is a schematic diagram of circumferential distribution of multiple receiving transducers in a receiving station provided according to an embodiment of the present invention;

[0033] Figure 4 A schematic diagram of a downhole data compression system for three-dimensional acoustic logging according to an embodiment of the present invention Figure 2 ;

[0034] Figure 5 is a process flow chart of primary compression in a receiving station according to an embodiment of the present invention;

[0035] Figure 6 is a processing flow chart of secondary compression in a main control short section provided according to an embodiment of the present invention;

[0036] Figure 7 The present invention provides a flowchart of a downhole data compression system for three-dimensional acoustic logging according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. However, it will be appreciated by those skilled in the art that in the embodiments of the present invention, many technical details are proposed in order to enable the reader to better understand the present invention. However, even without these technical details and various changes and modifications based on the following embodiments, the technical scheme claimed in the present invention can be implemented. The division of the following embodiments is for the convenience of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined and referenced with each other without contradiction.

[0038] One embodiment of the present invention relates to a downhole data compression system for three-dimensional acoustic logging. The specific structure of the downhole data compression system for three-dimensional acoustic logging of this embodiment is as follows: Figure 1 As shown, it includes: a main control sub and a receiving sub, the receiving sub includes a plurality of receiving stations evenly distributed along the axial direction of the logging instrument, each receiving station includes a plurality of receiving transducers evenly distributed along the circumferential direction of the logging instrument; wherein, the main control sub is connected to each receiving station in the receiving sub. It can be understood that the axial direction of the logging instrument is the vertical direction of the logging.

[0039] Specifically, the main control subsection is used to control multiple receiving stations in the receiving subsection to collect downhole data according to the data collection instructions on the well. Multiple receiving stations are used to collect downhole data at different source distances. Each receiving station is used to use its own multiple receiving transducers to collect downhole data at different azimuths at the corresponding source distances, and compress the downhole data collected by each receiving transducer to form compressed data at each azimuth at the corresponding source distance. Then, the relative value between the compressed data at each azimuth except the 0° azimuth and the compressed data at the 0° azimuth is obtained, and the relative value between the compressed data at the 0° azimuth and the compressed data at each other azimuth and the compressed data at the 0° azimuth is transmitted to the main control subsection as primary compressed data. The main control short section is also used to obtain the difference between each data except the first data and the previous data in the primary compressed data based on the differential pulse code modulation (DPCM) algorithm for the primary compressed data of each receiving station according to the similarity between adjacent data in the primary compressed data, and quantize and encode the difference between the first data in the primary compressed data and each data except the first data and the previous data, so as to transmit the quantized and encoded values ​​as secondary compressed data to the well.

[0040] In this embodiment, since in the three-dimensional acoustic logging instrument, the main control subsection is used to receive data acquisition instructions, control the receiving subsection to collect downhole data, and transmit the finally obtained downhole data to the well surface, the receiving subsection in the instrument is the acquisition end, and the main control subsection is the transmission end. In this embodiment, the collected data is first processed by each receiving station of the receiving subsection, and the data finally obtained by each receiving station is the compressed data of the 0° azimuth and the relative value between the compressed data of each other azimuth and the compressed data of the 0° azimuth, which is equivalent to the primary compression of the downhole data in the acquisition end of the downhole data; then, the primary compressed data of each receiving station is processed again in the main control subsection based on the DPCM algorithm, and the data finally obtained by the main control subsection is the first data in the data after primary compression and the quantized coding value of the difference between each data except the first data and the previous data, which is equivalent to the secondary compression of the downhole data in the transmission end of the downhole data. Therefore, in this embodiment, the downhole data is not compressed only at the transmission end, but primary compression is first performed at the acquisition end, and then secondary compression is performed at the transmission end, which is equivalent to reconstructing the functions of each module of the three-dimensional acoustic logging instrument, so that the three-dimensional acoustic logging instrument has a multi-level data compression function, improves the compression effect of downhole data, reduces the amount of data transmitted within the instrument and uploaded in real time, and achieves the purpose of reducing data transmission time and reducing the acquisition cycle of the three-dimensional acoustic logging instrument, thereby improving the efficiency of three-dimensional acoustic logging. At the same time, each module coordinates and cooperates based on data compression to avoid compression operations being concentrated on the transmission end, thereby reducing the workload of the transmission end (i.e., the main processor).

[0041] The implementation details of the downhole data compression system for three-dimensional acoustic logging of this embodiment are described in detail below. The following content is only provided for the convenience of understanding the implementation details and is not necessary for implementing this solution.

[0042] First, the composition and working principle of the 3D acoustic logging tool are explained:

[0043] In order to better carry out multi-dimensional high-precision detection, the transmitting subsection of the three-dimensional acoustic logging instrument is integrated, while the receiving subsection is arrayed. Among them, the transmitting subsection integrates sound sources such as monopoles, dipoles, quadrupoles and even phased arrays, so that the instrument can perform directional radiation and use the propagation characteristics of various sound waves for logging, enhancing the environmental adaptability of the method and instrument and reducing uncertainty. The receiving subsection adopts an array azimuth receiving acoustic system, which is composed of many receiving transducers distributed in the axial and circumferential directions of the instrument. It has the characteristics of array and azimuth, and can realize the reception of acoustic signals under different azimuths, different source distances and different spacing conditions, and increase the resolution and reliability of instrument imaging. Figure 2The figure shows a schematic diagram of the axial distribution of multiple receiving stations in the receiving subsection in the well logging tool. The receiving subsection is composed of multiple receiving stations 22 installed on the tool axis 21 (in the axial direction of the well logging tool), and the spacing between adjacent receiving stations is the same. Figure 3 The figure shows a schematic diagram of the circumferential distribution of multiple receiving transducers in each receiving station 22. Each receiving station 22 is composed of multiple receiving transducers 221. The multiple receiving transducers 221 are fixed on the mechanical skeleton 222 at intervals in the circumferential direction of the instrument (circumferential direction of the logging instrument). This embodiment does not limit the number of receiving transducers in the receiving station, and the intervals between the multiple receiving transducers depend on the number of receiving transducers. Figure 3 It is only for illustration, and 8 receiving transducers are shown, and the 8 receiving transducers are distributed on the receiving station at an interval of 45°.

[0044] In each working cycle of the 3D acoustic logging instrument, the instrument works in different transmission modes successively. In each transmission mode, all receiving transducers receive independent logging signals. The instrument structure and working mode of "multiple transmission modes + multiple receiving channels" lead to a sharp increase in the amount of data at each depth sampling point of the 3D acoustic logging instrument. At the same time, with the continuous improvement of detection depth and accuracy, the amount of data of this type of instrument is showing an increasing trend. The real-time transmission of all data to the ground by cable faces increasing difficulties and a series of problems, such as slow logging speed and poor real-time processing and interpretation, which is particularly evident in long-range detection reflection acoustic logging.

[0045] The current situation of difficulty in real-time data transmission can be greatly improved by using a method of downhole data compression. Therefore, this embodiment provides a downhole data compression system for three-dimensional acoustic logging.

[0046] In a specific implementation, the downhole data compression system of the three-dimensional acoustic logging of this embodiment can be as follows: Figure 4 As shown. The system mainly consists of a primary compression system and a secondary compression system. The primary compression system consists of multiple receiving stations 41 in the receiving short section, and the secondary compression system consists of a main control short section 42. The receiving station 41 and the main control short section 42 are connected through an instrument internal bus 43 to perform bidirectional data transmission and reception. The bus includes a differential clock line (CLK) 431 and a differential data line (DAT) 432.

[0047] The receiving station 41 is composed of a plurality of receiving transducers 411, a data acquisition module 412, a primary compression module 413, a random access memory (RAM) module 414, and an internal bus driver module 415. The plurality of receiving transducers 411 are evenly distributed around the instrument to sense acoustic logging signals from different directions and convert them into electrical signals. The data acquisition module 412 performs pre-amplification, program-controlled gain amplification, and band-pass filtering on the analog signal output by the receiving transducer 411, and then completes analog-to-digital conversion under the control of the primary compression module 413, so that the logging information enters the primary compression module 413 in the form of digital signals. The core of the primary compression module 413 is the Field Programmable Gate Array (FPGA) processor, which is the control center of the entire receiving station 41 and implements the following three functions in parallel: 1) Control the data acquisition process of the acoustic logging signal; 2) Complete the primary compression of the data acquisition end; 3) As the controller of the instrument internal bus 43, perform format conversion and analysis of the sent and received data, so as to communicate with the main control short section 42. The RAM module 414 is used to expand the storage space of the FPGA processor and cache the collected data and temporary data in the primary compression process. Under the control of the primary compression module 413, the internal bus driver module 415 converts the data transmission mode through hardware to realize data exchange between the instrument internal bus 43 and the primary compression module 413.

[0048] The main control sub 42 includes four parts: an internal bus driver module 421, a secondary compression module 422, a RAM module 423, and a telemetry bus driver module 424. The internal bus driver modules (421, 415) are used in pairs to realize bidirectional data transmission between the main control sub 42 and the receiving station 41. The secondary compression module 422 uses an FPGA processor as the core to realize the following three functions: 1) as the main controller of the instrument internal bus 43, to control the transmission and reception of data; 2) to complete the secondary compression of the data at the transmission end; 3) to control the telemetry bus driver module 424, to receive the command issued by the telemetry sub and upload the logging data after secondary compression. The RAM modules (423, 414) in the main control sub and the receiving station have the same function and are both used for data caching. The telemetry bus driver module 424 is a bridge between the main control sub 42 and the telemetry bus, realizing the hardware conversion of the data format between the two.

[0049] Since the primary compression of the acquisition end of the 3D acoustic logging data is performed in the receiving station, the secondary compression at the transmission end is performed in the main control sub. The primary compression reduces the amount of data that needs to be transmitted to the main control sub in the receiving station, and reduces the data transmission time in the internal bus of the instrument. The secondary compression at the transmission end further compresses the primary compressed data that reaches the main control sub, further reducing the amount of data that the main control sub needs to upload to the telemetry sub.

[0050] In view of the one-to-many relationship between the instrument master control short section and the receiving station, and the time for the receiving station to perform the acquisition function accounts for a small proportion of the acquisition cycle, the data compression task in this embodiment is mainly completed at the receiving station, and the primary compression and the secondary compression use different data compression methods. The data compression methods used for the primary compression and the secondary compression (i.e., the compression of the receiving station and the compression of the master control short section) are specifically described below.

[0051] Figure 5 The following is the process flow of primary compression at each receiving station, including:

[0052] In step 51, the primary compression module waits for the completion of the logging data acquisition work in this cycle.

[0053] In step 52, the useless data at the front of each full wave train waveform in the receiving station is removed. The cut-off position of the useless data in the full wave train waveform is estimated based on the arrival time of the sliding longitudinal wave in different receiving stations and is a fixed value. Specifically, each receiving transducer is also used to receive the full wave train waveform of the acoustic wave containing the sliding longitudinal wave at the corresponding azimuth under the corresponding source distance as the downhole data at the corresponding azimuth under the corresponding source distance. Each receiving station is also used to remove the useless data in the full wave train waveform of the acoustic wave of each receiving transducer according to the arrival time of the sliding longitudinal wave in the full wave train waveform of the acoustic wave collected by each receiving transducer.

[0054] In step 53, the remaining part of each waveform is subjected to data compression based on wavelet transform to form a primary compression sequence, that is, each receiving station is specifically used to compress the data collected by each receiving transducer of itself based on the wavelet transform method. In order to ensure the low distortion of the primary compression, this embodiment uses a layer of wavelet transform method to reduce the amount of logging data by half, ensuring that key information is not lost and the amount of data and time transmitted by the internal bus are stable. The wavelet transform data compression method includes multiple steps such as selecting wavelet basis functions, data preprocessing, determining filter coefficients, determining the number of decomposition layers, discrete wavelet transform (DWT) transformation and approximate component extraction. In order to achieve the best effect of acoustic logging data compression, the wavelet basis function selects the db4 wavelet with high time and frequency resolution; the data preprocessing performs symmetrical extension on the full wave train waveform to reduce the edge block effect; the determination of the filter coefficient is mainly to optimize the coefficient of the db4 wavelet to make it applicable in the hardware processor and reduce the calculation time. In order to ensure the reliability and practicality of data restoration, the wavelet transform decomposition generally does not exceed 3 layers in actual use. In this embodiment, a layer of discrete wavelet transform is used to ensure low distortion of primary compression and facilitate subsequent secondary compression. This transform is equivalent to passing the input data through high-pass and low-pass filters respectively, so as to obtain the approximate component and detail component of the next layer, where the approximate component is the compressed result that needs to be saved.

[0055] In step 54, the relative value series of the primary compression sequence at other azimuths and the 0° azimuth in the receiving station are obtained, that is, each receiving station compresses the downhole data collected by each receiving transducer to form compressed data at each azimuth under the corresponding source distance, and obtains the relative value between the compressed data at each azimuth except the 0° azimuth and the compressed data at the 0° azimuth. In this process, according to the distribution positions of multiple receiving transducers on the receiving station, the compressed data at each azimuth except the 0° azimuth is subjected to time delay processing, and according to the similarity between the compressed data at each azimuth except the 0° azimuth after the time delay processing and the compressed data at the 0° azimuth, the difference between the compressed data at each azimuth except the 0° azimuth after the time delay processing and the compressed data at the 0° azimuth is obtained, and the difference is used as the relative value between the compressed data at each azimuth except the 0° azimuth and the compressed data at the 0° azimuth, so as to ensure that the amplitude of the relative value waveform obtained is as small as possible.

[0056] In step 55, the primary compression sequence of the 0° azimuth and the relative value sequences of other azimuths are processed into data blocks and saved in the RAM module, waiting for the data upload request of the next cycle.

[0057] Secondary compression is performed in the secondary compression module of the main control subsection, which further compresses the primary compressed data transmitted to the main control subsection and stored in the RAM module. Secondary compression is based on the DPCM algorithm, and the primary compression sequence of the 0° azimuth and the relative value sequence of other azimuths in each receiving station are processed in the same process. Figure 6 The following is the processing flow of secondary compression in the main control sub, which includes:

[0058] In step 61, a certain primary compression sequence or relative value sequence data to be processed in the RAM module is read and put into the FIFO buffer inside the FPGA.

[0059] In step 62, the sequence is subjected to an integrated operation of difference calculation, quantization and prediction based on the DPCM algorithm. The differential pulse code modulation (DPCM) algorithm is an algorithm that uses the correlation between adjacent samples to compress data. The basic principle is to use the correlation between signal sampling points to achieve the purpose of compression by storing the quantized coded value of the difference between each sampling point and the previous sampling point. Since the difference between adjacent sampling points is usually small, fewer bits can be used to store the quantized coded values ​​of these differences, thereby achieving data compression.

[0060] Among them, the difference operation is to find the difference between the current input raw data and the predicted value of the previous raw data; the quantization operation performs non-uniform quantization on the difference sequence according to the requirements of the encoding module; the prediction operation obtains the predicted value sequence based on the difference between the first raw data and the quantized value. These three operations are integrated steps that are mutually input and inseparable when implementing the DPCM algorithm.

[0061] In step 63, the quantized difference sequence is adaptively encoded. This operation reduces the number of bits required to represent the data by re-encoding, thereby achieving the purpose of data compression, and the encoded data is the final compressed data. In this embodiment, the adaptive encoding adopts an 8-bit encoding method, and the bit widths of the symbol domain, paragraph code domain and interval code domain are determined according to the range of the quantized difference.

[0062] In step 64, the secondary compression result is stored in the RAM module, waiting for the data upload request of the teletransmission short section in the next working cycle.

[0063] After the compressed data is uploaded to the surface computer on the well, it is necessary to perform a decompression operation to restore the logging data before further processing and interpretation can be performed. When decompressing, it is performed in the reverse order of the two-level compression downhole, that is, the following three steps are performed: First, the uploaded data is decompressed based on the DPCM algorithm to obtain the primary compression sequence of the 0° azimuth in each receiving station and the relative value sequence of other azimuths. Second, based on the results of the first step, the primary compression sequence of all azimuths in all receiving stations is restored. Third, the primary compression sequence is decompressed based on the wavelet transform to obtain the original full-wave waveform of all azimuths in all receiving stations.

[0064] The above content is the specific structure and specific compression method of the downhole data compression system of the three-dimensional acoustic well logging of this embodiment. The following is a specific description of the workflow of the downhole data compression system of the three-dimensional acoustic well logging of this embodiment:

[0065] In cable 3D acoustic logging, the instrument works repeatedly according to the set working cycle, completing the logging data collection, compression and real-time upload of the corresponding depth point in each working cycle. In order to work more efficiently and coordinately and minimize the working cycle, the system's receiving station, main control sub and universal telemetry sub need to work closely together according to specific working methods. Figure 7 The following is the working method of the system in one cycle, taking the main control sub as a reference, including:

[0066] In step 71, the master control sub receives the depth interrupt command (i.e., the data acquisition instruction on the well) from the telemetry sub and performs data acquisition and upload initialization. The data acquisition instruction will be periodically sent to the master control sub, which is the data acquisition instruction of the current cycle.

[0067] At this time, the main control sub performs step 72 and step 73 in parallel.

[0068] In step 72, the master control subsection starts a new cycle of acquisition process, which includes the following sub-steps:

[0069] Step 721, the main control subsection sends a collection control command to the transmitting subsection and the receiving station. Driven by the command, the transmitting subsection excites the sound field, and the receiving station successively performs data collection and primary compression operations and stores the data in the compressed data area.

[0070] Step 722: The master control subsection reads the primary compressed data of the previous cycle in the receiving station. At this time, the receiving station receives the data request of the master control subsection and transmits the primary compressed data of the data area to be transmitted to the master control subsection through the internal bus of the instrument.

[0071] Step 723, the master control subsection performs secondary compression on the received primary compressed data and stores the data into the compressed data area.

[0072] In step 73, the secondary compressed data of the previous cycle is uploaded. This step includes the following sub-steps:

[0073] Step 731, the master control sub waits for and receives a data upload request from the telemetry sub.

[0074] Step 732, determine whether the data of the previous cycle has been transmitted and perform corresponding operations. If the transmission is completed, do not respond to the request; if the transmission is not completed, perform the operation of step 733.

[0075] Step 733, extract and upload one frame of secondary compressed data in the data area to be transmitted in sequence.

[0076] Two points need to be explained in relation to the above workflow: first, when the main control sub performs two parallel operations, the priority of uploading data is higher, which can be achieved through the interrupt function of the processor; second, the RAM of the main control sub and the receiving sub are divided into two areas: the compressed data area and the data area to be transmitted. Through ping-pong operation, the two can achieve the effect of parallel operation of collecting and saving new logging data in one cycle and uploading the data of the previous cycle, which can further reduce the working cycle of the instrument.

[0077] That is, the main control subsection is also used to perform the following two operations in parallel according to the data acquisition instruction of the current cycle: control multiple receiving stations in the receiving subsection to collect downhole data of the current cycle and transmit the secondary compressed data corresponding to multiple receiving stations in the previous cycle to the surface. The data storage module of the main control subsection includes a first compressed data area and a first data area to be transmitted. The first compressed data area is used to store the secondary compressed data corresponding to multiple receiving stations in the current cycle, and the first data area to be transmitted is used to store the secondary compressed data corresponding to multiple receiving stations in the previous cycle. The main control subsection is also used to perform the above two operations in parallel by performing a ping-pong operation on the first compressed data area and the first data area to be transmitted.

[0078] Each receiving station is also used to perform the following two operations in parallel: collecting data at the corresponding source distance of the current cycle and transmitting the primary compressed data of the corresponding receiving station in the previous cycle to the main control short section. The data storage module of each receiving station includes a second compressed data area and a second data area to be transmitted, the second compressed data area is used to store the primary compressed data of the corresponding receiving station in the current cycle, and the second data area to be transmitted is used to store the primary compressed data of the corresponding receiving station in the previous cycle. Each receiving station is also used to perform the above two operations in parallel by performing a ping-pong operation on the second compressed data area and the second data area to be transmitted.

[0079] The downhole data compression system for three-dimensional acoustic logging of this embodiment has the following beneficial effects:

[0080] (1) Through primary compression at the acquisition end and secondary compression at the transmission end, the compression rate of 3D acoustic logging data is greatly improved, which greatly reduces the amount of data and time required for real-time transmission of cables to the ground.

[0081] (2) Primary compression is performed at the receiving station, and secondary compression is performed at the main control subsection. This not only reduces the amount of data and time required to be transmitted from the receiving station to the main control subsection, but also reduces the workload of the main control subsection in reading the receiving station data, compressing the data, and transmitting the data to the telemeter, thus helping to reduce the instrument's operating cycle.

[0082] (3) The primary compression adopts a layer of wavelet transform data compression algorithm, which not only ensures the stability of data volume and low distortion of data, but also maintains the re-compressibility of data; the secondary compression adopts DPCM algorithm, which ensures the low complexity and low running time of the algorithm.

[0083] (4) The RAM of the main control sub and the receiving sub are divided into two areas: the compressed data area and the data area to be transmitted. Through ping-pong operation, the two functions of collecting and saving new logging data in one cycle and uploading the data of the previous cycle can be operated in parallel, which can reduce the working cycle of the instrument.

[0084] (5) The logging data can be quickly transmitted to the ground computer, supporting the working mode of measuring and processing at the same time, and the real-time performance of on-site processing and interpretation is good.

[0085] Those skilled in the art can understand that the above embodiments are specific embodiments of the present invention, and in practical applications, various changes can be made to them in form and detail without departing from the spirit and scope of the embodiments of the present invention. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the embodiments of the present invention, so the protection scope of the embodiments of the present invention shall be based on the scope defined in the claims.

Claims

1. A downhole data compression system for three-dimensional acoustic logging, characterized in that: include: A main control sub and a receiving sub, wherein the receiving sub comprises a plurality of receiving stations evenly distributed along the axial direction of the logging instrument, and each receiving station comprises a plurality of receiving transducers evenly distributed along the circumferential direction of the logging instrument; wherein the main control sub is connected to each receiving station in the receiving sub; The main control sub is used to control multiple receiving stations in the receiving sub to collect downhole data according to the data collection instructions on the well; Multiple receiving stations are used to collect downhole data at different source distances; Each receiving station is used to use its own multiple receiving transducers to respectively collect downhole data at different azimuths under the corresponding source distance, and compress the downhole data collected by each receiving transducer to form compressed data at each azimuth under the corresponding source distance; obtain the relative value between the compressed data at each azimuth except the 0° azimuth and the compressed data at the 0° azimuth, and transmit the compressed data at the 0° azimuth and the relative value between the compressed data at each other azimuth and the compressed data at the 0° azimuth as primary compressed data to the main control sub; The main control short section is also used for obtaining the difference between each data except the first data and the previous data in the primary compressed data based on the differential pulse code modulation DPCM algorithm for the primary compressed data of each receiving station according to the similarity between adjacent data in the primary compressed data, and quantizing and encoding the difference between the first data and each data except the first data in the primary compressed data and the previous data, so as to transmit the quantized and encoded values ​​to the well as the secondary compressed data; Among them, each receiving station is specifically used to perform time delay processing on the compressed data of each azimuth except the 0° azimuth according to the distribution positions of its own multiple receiving transducers on the receiving station, and obtain the difference between the compressed data of each azimuth except the 0° azimuth after the time delay processing and the compressed data of the 0° azimuth according to the similarity between the compressed data of each azimuth except the 0° azimuth after the time delay processing and the compressed data of the 0° azimuth, and use the difference as the relative value between the compressed data of each azimuth except the 0° azimuth and the compressed data of the 0° azimuth.

2. The downhole data compression system for three-dimensional acoustic logging according to claim 1, characterized in that: Each receiving station is specifically used to compress downhole data collected by each receiving transducer of itself based on the wavelet transform method; wherein the wavelet basis function adopted by the wavelet transform method is the db4 wavelet, and the number of decomposition layers adopted is less than or equal to 3 layers.

3. The downhole data compression system for three-dimensional acoustic logging according to claim 1, characterized in that: The data acquisition instructions are periodically sent to the main control subsection; The main control sub is also used to perform the following two operations in parallel according to the data acquisition instructions of the current cycle: controlling multiple receiving stations in the receiving sub to collect downhole data of the current cycle and transmitting the secondary compression data corresponding to multiple receiving stations of the previous cycle to the surface.

4. The downhole data compression system for three-dimensional acoustic logging according to claim 3, characterized in that: The data storage module of the master control sub comprises a first compressed data area and a first data area to be transmitted, wherein the first compressed data area is used to store the secondary compressed data corresponding to multiple receiving stations in the current cycle, and the first data area to be transmitted is used to store the secondary compressed data corresponding to multiple receiving stations in the previous cycle; The main control short section is also used to perform the following two operations in parallel by performing ping-pong operations on the first compressed data area and the first data area to be transmitted: controlling multiple receiving stations in the receiving short section to collect downhole data of the current cycle and transmitting the secondary compressed data corresponding to multiple receiving stations of the previous cycle to the surface.

5. The downhole data compression system for three-dimensional acoustic logging according to claim 1, characterized in that: Each receiving station is also used to perform the following two operations in parallel: collecting data at the corresponding source distance of the current cycle and transmitting the primary compressed data corresponding to multiple receiving stations in the previous cycle to the main control short section.

6. The downhole data compression system for three-dimensional acoustic logging according to claim 5, characterized in that: The data storage module of each receiving station includes a second compressed data area and a second data area to be transmitted, the second compressed data area is used to store the primary compressed data corresponding to the receiving station in the current cycle, and the second data area to be transmitted is used to store the primary compressed data corresponding to the receiving station in the previous cycle; Each receiving station is also used to perform the following two operations in parallel by performing ping-pong operations on the second compressed data area and the second data area to be transmitted: collecting downhole data at the corresponding source distance of the current cycle and transmitting the primary compressed data corresponding to the receiving station in the previous cycle to the main control short section.

7. The downhole data compression system for three-dimensional acoustic logging according to claim 1, characterized in that: Each receiving transducer is also used to receive a full wave train waveform of an acoustic wave including a sliding longitudinal wave at a corresponding azimuth at a corresponding source distance as downhole data at a corresponding azimuth at a corresponding source distance; Each receiving station is also used to remove useless data in the full wave train waveform of the sound wave collected by each receiving transducer according to the arrival time of the sliding longitudinal wave in the full wave train waveform of the sound wave collected by each receiving transducer.

8. The downhole data compression system for three-dimensional acoustic logging according to claim 1, characterized in that: Each receiving station has 8 receiving transducers.

9. The downhole data compression system for three-dimensional acoustic logging according to claim 8, characterized in that: A plurality of receiving transducers are evenly distributed in the circumferential direction of the logging tool at the receiving station at an interval of 45°.

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