A measurement value transmission system for downhole sensing

Abstract

This invention relates to the field of downhole telemetry technology and discloses a measurement value transmission system for downhole sensing, comprising a downhole end, a surface end, a mud pulser, and a flowing drilling fluid column. The downhole end acquires downhole measurements and downhole pressure, generates a data frame containing the corresponding data of the downhole measurements and the frame transmission time, and transmits a measurement pressure pulse via the mud pulser. The surface end acquires surface pressure, mud flow velocity, transmission distance, and mud sound velocity, sends downlink probe pulses and receives uplink response pulses, records relevant times, and determines the downlink propagation time, uplink propagation time, bidirectional closure error, downhole clock error, and arrival deviation. The surface end only accepts candidate frames and recovers surface measurements when the bidirectional closure error and arrival deviation are both no greater than half a chip duration and the cyclic redundancy check passes. This invention is used for pressure pulse transmission of downhole measurements during drilling.

Description

Technical Field

[0001] This invention relates to the field of downhole telemetry technology, and more specifically, to a measurement value transmission system for downhole sensing. Background Technology

[0002] In measurement-while-drilling (MWD) and downhole sensing operations, sensors are inserted into the wellbore along with the drill string. Measurements such as temperature, pressure, attitude, gamma, or vibration need to be transmitted back to the surface during drilling. Mud pulse telemetry utilizes the drilling fluid circulation channel to transmit pressure pulses. The downhole end typically completes acquisition, quantization, framing, and mud pulser driving. The surface end uses a riser pressure sensor, acquisition unit, and decoder to identify synchronization words from the surface pressure, recover frame bits, and perform cyclic redundancy checks. This approach eliminates the need for wired drill pipe or removing downhole storage components, making it suitable for use under conventional drilling fluid circulation conditions.

[0003] During field operation, drilling fluid continuously flows from the surface to the downhole, while the measured pressure pulses typically return from downhole to the surface. Pump pressure disturbances, drill string movement, changes in wellbore conditions, local changes in flow channels, and end reflections are all superimposed on the surface pressure record. If the surface end relies primarily on synchronization word matching, pressure thresholds, and cyclic redundancy checks, it may still identify reflected pulses or combinations of noise pulses as candidate frames, especially when pulse intervals are close, noise energy is concentrated, or frame start points recur. The arrival time of candidate frames may not match the actual downhole transmission event, leading to measurement mismatch, resynchronization of old frames, or the erroneous discarding of valid frames.

[0004] Existing mud pulse processing typically revolves around pulse coding, channel response estimation, surface multi-point noise reduction, downhole proximity pressure sensor noise reduction, and downlink command recognition or checksum determination. These processes can improve pressure signal detection and bit error identification, but they lack sufficient constraints on the temporal consistency of candidate frames to determine whether they originate from the current downhole transmission event. For field systems already equipped with downhole pressure acquisition, standpipe pressure acquisition, mud velocity, well depth / transmission distance, and mud sound velocity measurements, a processing method is needed that integrates the downhole end, surface end, mud pulser, and flowing drilling fluid column into the same transmission link. This method should enable the surface end to filter candidate frames based on the uplink and downlink detection times and measurement frame arrival times without altering the drill string and drilling fluid circulation channels. Summary of the Invention

[0005] This invention provides a measurement value transmission system for downhole sensing, which solves the technical problems mentioned in the background art.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution.

[0007] A measurement value transmission system for downhole sensing includes a downhole end, a surface end, a mud pulser, and a flowing drilling fluid column. The flowing drilling fluid column is located between the surface riser pressure end and the mud pulser, serving as a propagation channel for downlink detection pulses, uplink response pulses, and measurement pressure pulses.

[0008] The downhole end acquires downhole measurement values ​​and downhole pressure, and generates a data frame containing the corresponding data of the downhole measurement values ​​and the frame transmission time;

[0009] The ground end obtains ground pressure, mud flow velocity, transmission distance and mud sound velocity, sends downlink detection pulses, and records the ground detection pulse sending time, ground detection pulse receiving time and frame arrival time according to the ground pressure to form candidate frames;

[0010] The downhole end records the downhole detection pulse timing based on the downhole pressure, sends an uplink response pulse through the mud pulser, and records the downhole detection pulse timing.

[0011] The ground end determines the downlink propagation time and uplink propagation time based on the mud flow velocity, transmission distance, and mud sound velocity. It also determines the bidirectional closure error based on the aforementioned four moments, downlink propagation time, and uplink propagation time. The bidirectional closure error characterizes the difference between the measured round-trip time of the downlink probe pulse and the uplink response pulse and the physically predicted round-trip time.

[0012] The ground end determines the downhole clock error when the bidirectional closure error is no more than half a chip duration. The arrival deviation is determined based on the frame transmission time, downhole clock error, uplink propagation time, and frame arrival time. Candidate frames are accepted and ground measurement values ​​are restored only when both the bidirectional closure error and arrival deviation are no more than half a chip duration and the cyclic redundancy check passes. The chip duration is the minimum time grid for encoding the position of the measured pressure pulse.

[0013] Compared with the prior art, the present invention has the following substantial features and significant progress:

[0014] This invention treats the downhole end, surface end, mud pulser, and flowing drilling fluid column as a single pressure pulse transmission link. It obtains mutually verifiable on-site times through downlink detection pulses, uplink response pulses, and measured pressure pulses. Combined with mud flow velocity, transmission distance, and mud sound velocity, it determines the downlink propagation time, uplink propagation time, bidirectional closure error, downhole clock error, and arrival deviation. This adds arrival time determination consistent with the current drilling fluid circulation channel to the on-site end, in addition to cyclic redundancy verification. Thus, even if reflected pulses or noise pulses form a synchronization word, they must simultaneously meet the bidirectional closure error and arrival deviation conditions to be accepted. This reduces the risk of candidate frame misreception and measurement mismatch, while retaining the original mud pulser, riser pressure acquisition, and drilling fluid circulation channels, facilitating on-site access during drilling measurements. Attached Figure Description

[0015] Figure 1 This is a system architecture and pressure pulse transmission mechanism diagram of a measurement value transmission system for downhole sensing according to the present invention. Detailed Implementation

[0016] The following description is provided in conjunction with the accompanying drawings. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the invention; those skilled in the art can make equivalent substitutions or combinations for the specific implementations.

[0017] This implementation is applicable to scenarios where downhole measurement values ​​are transmitted via pressure pulses in measurement while drilling, logging, or downhole sensing operations. It is particularly suitable for scenarios where there is continuously downward-flowing drilling fluid within the drill string, the downhole end needs to transmit downhole measurement values ​​to the surface end, and the surface end needs to identify candidate frames from surface pressure and reconstruct surface measurement values. This implementation adds a determination that the candidate frame's time is consistent with the current physical propagation time within the pressure pulse propagation channel formed by the downhole end, surface end, mud pulser, and flowing drilling fluid column.

[0018] See Figure 1 A measurement value transmission system for downhole sensing in this embodiment includes a downhole end 100, a surface end 300, a mud pulser 140, and a flowing drilling fluid column 200. The flowing drilling fluid column 200 is located between the surface riser pressure end and the mud pulser 140, serving as a propagation channel for downlink detection pulses, uplink response pulses, and measurement pressure pulses.

[0019] Specifically, the ground station 300 determines the downhole clock error when the bidirectional closure error is no greater than half a chip duration. It determines the arrival deviation based on the frame transmission time, downhole clock error, uplink propagation time, and frame arrival time. Candidate frames are accepted and ground measurements are restored only when both the bidirectional closure error and arrival deviation are no greater than half a chip duration and the cyclic redundancy check passes. Therefore, even if a combination of pressure pulses or random noise generated by reflections appears at a pulse position in the ground pressure that is similar to the synchronization word, it must simultaneously meet the bidirectional closure error, arrival deviation, and cyclic redundancy check to be accepted as a valid candidate frame.

[0020] See Figure 1 The downhole end 100 represents the downhole acquisition, framing, detection response, and measurement pressure pulse transmission area. The downhole end 100 includes a downhole sensor 110, a controller 130, and a downhole pressure sensor 120, and works in conjunction with a mud pulser 140. In an optional engineering implementation, the downhole end 100 may also include signal conditioning and analog-to-digital conversion circuitry and a drive circuitry. The signal conditioning and analog-to-digital conversion circuitry amplifies, filters, limits, and converts the downhole measurements to digital data. The drive circuitry drives the mud pulser 140 according to the drive control output from the controller 130.

[0021] The downhole sensor 110 is used to acquire downhole measurement values. These values ​​can be one or more of the following: temperature, pressure, attitude, gamma, vibration, or other measured physical quantities acquired by the downhole sensor 110 at the time of acquisition. However, all data in the data frame are entered into the subsequent transmission process as corresponding downhole measurement values. When multiple downhole sensors 110 exist, the controller 130 distinguishes between different sensors 110 by sensor number, preventing mismatches between downhole measurement values ​​from different sources when recovered at the surface end 300.

[0022] Downhole pressure sensor 120 is used to acquire downhole pressure. Downhole pressure sensor 120 enables downhole end 100 to identify downhole probe pulses within the downhole pressure, and controller 130 records the timing of the downhole probe pulse arrival. The downhole pressure acquired by downhole pressure sensor 120 also provides a direct physical signal for downhole end 100 to determine whether a downhole probe pulse has arrived.

[0023] The controller 130, located within the downhole end 100, is used to generate data frames and control the mud pulser 140 to send measurement pressure pulses. The controller 130 also records the downhole receive probe pulse times and downhole return probe pulse times. For downhole probe pulses, the controller 130 receives the downhole pressure provided by the downhole pressure sensor 120, identifies the arrival event corresponding to a fixed known waveform, and records the downhole clock reading corresponding to that arrival event as the downhole receive probe pulse time. For uphole response pulses, the controller 130 outputs drive control to the mud pulser 140 at the downhole return probe pulse time, causing the mud pulser 140 to send an uphole response pulse, and records the downhole return probe pulse time as the downhole transmission time of that uphole response pulse.

[0024] The mud pulser 140 is used to send uplink response pulses and measurement pressure pulses. The mud pulser 140 is directly connected to the flowing drilling fluid column 200; therefore, the pressure disturbance generated by the mud pulser 140 enters the flowing drilling fluid column 200 and propagates along the fluid column 200 towards the surface end 300. For the uplink response pulse, the mud pulser 140 responds to the drive control output by the controller 130 at the time of the downhole probe pulse; for the measurement pressure pulse, the mud pulser 140 responds to the pulse position encoding result of the frame bits in the data frame by the controller 130.

[0025] The flowing drilling fluid column 200 is formed by the drill string cavity and the continuously flowing drilling fluid within it. Located between the surface riser pressure end and the mud pulser 140, the flowing drilling fluid column 200 serves as the propagation channel for the downlink probe pulse, the uplink response pulse, and the pressure measurement pulse. The downlink probe pulse propagates downstream along the flowing drilling fluid column 200, while the uplink response pulse and the pressure measurement pulse propagate upstream along the same direction. Due to the continuous downward flow of the drilling fluid, the propagation speed of the pressure wave relative to the surface end 300 is modified differently in the downstream and upstream directions, resulting in differences in the downlink and uplink propagation times.

[0026] The ground end 300 represents the area for pressure acquisition, field measurement input, candidate frame formation, and measurement value recovery on the ground side. The ground end 300 includes a riser pressure sensor 310, a data acquisition unit, a decoder 320, a mud velocity meter, a drilling rig depth measurement system, and a mud sound velocity meter.

[0027] A riser pressure sensor 310 is used to acquire surface pressure. The riser pressure sensor 310 is connected to the flowing drilling fluid column 200, enabling the surface end 300 to record the time of surface probe pulse transmission, the time of surface probe pulse reception, and the frame arrival time from the surface pressure. A data acquisition unit samples the surface pressure at a sampling frequency sufficient to distinguish pulse width and chip duration, allowing the decoder 320 to generate candidate frames based on the surface pressure. The decoder 320 generates candidate frames and performs bidirectional closure error, arrival deviation, and cyclic redundancy check determinations, and recovers the surface measurement values ​​after receiving candidate frames.

[0028] A mud velocity meter is used to obtain mud flow velocity, a drilling rig depth measurement system is used to obtain transmission distance, and a mud sound velocity meter is used to obtain mud sound velocity. Mud flow velocity, transmission distance, and mud sound velocity are all physical quantities directly obtained on-site. Mud flow velocity characterizes the speed at which drilling fluid moves in the downlink direction, transmission distance characterizes the current channel length between the surface riser pressure end and the downhole pressure end, and mud sound velocity characterizes the propagation rate of pressure waves relative to the drilling fluid. The decoder 320 reads these on-site quantities before each bidirectional closure error calculation and can use the downlink propagation time, uplink propagation time, and downhole clock error corresponding to the most recent bidirectional closure error to determine one or more subsequent candidate frames.

[0029] Furthermore, the implementation methods for the downlink probe pulse, uplink response pulse, and the four time points are as follows:

[0030] The downlink probe pulse is transmitted from the surface terminal 300 to trigger the downhole terminal 100 to generate an uplink response pulse that can be received by the surface terminal 300. The downlink probe pulse can be generated by an existing pump or bypass valve of the surface terminal 300, and the downlink probe pulse has a fixed known waveform. The fixed known waveform can be a combination of pressure transitions, pulse width combinations, or short sequence pulse combinations that are easy to identify in existing mud pulse telemetry, as long as the fixed known waveform can be identified in both surface pressure and downhole pressure and can provide stable event characteristic points.

[0031] In one specific embodiment, the fixed known waveform of the downlink probe pulse consists of three pressure pulses of equal width, each pressure pulse lasting the pulse width, with a two-chip interval between the start of two adjacent pressure pulses, followed by a silence interval of at least two chip durations after the third pressure pulse. The uplink response pulse uses the same fixed known waveform as the downlink probe pulse, or a fixed known waveform composed of three pressure pulses of equal width that are not confused with the downlink probe pulse. In the same measurement value transmission system, the fixed known waveforms of the downlink probe pulse and the uplink response pulse are written into the controller 130 and decoder 320 before downhole operation and remain unchanged throughout a single downhole operation. Each pressure pulse in the fixed known waveform is formed according to its pulse width, and the detectable pressure change of each pressure pulse should be no less than a pressure threshold.

[0032] Both the controller 130 and the decoder 320 use the correlation peak time of a fixed known waveform as a unified event feature point. For the pressure sequence to be detected, a template sampling sequence corresponding to the fixed known waveform is first established within a detection window of six chip lengths. Then, the normalized correlation value is calculated for each sampling point. The normalized correlation value is determined according to the following formula:

[0033]

[0034] in, For sampling sequence number Normalized correlation value at time; These are pressure sampling points for surface or downhole pressure after the mean has been removed; To fix the sampling points of a known waveform template; To maintain a fixed known waveform template length, when the ground terminal 300 records the time of the ground-transmitted probe pulse, the decoder 320 uses the starting point of its own template of the fixed known waveform as the ground-transmitted probe pulse time. When the downhole terminal 100 records the time of the downhole received probe pulse or the ground terminal 300 records the time of the ground received probe pulse, the controller 130 or the decoder 320 selects a normalized correlation value that reaches its maximum value and is not less than [a certain value]. The earliest sampling point is taken as the correlation peak time. If there is no normalized correlation value not less than 1 within the detection window... If a sampling point is not identified, the corresponding downlink probe pulse or uplink response pulse is determined to be not stably identified.

[0035] When the surface terminal 300 sends a downlink probe pulse, the decoder 320 records the time of the surface probe pulse transmission based on the surface pressure. The time of the surface probe pulse transmission is the surface clock reading when the surface terminal 300 sends the downlink probe pulse. A fixed known waveform's start crossing a predetermined trigger level, a fixed known waveform's peak time, or a fixed known waveform's related peak time can be selected as a unified event characteristic point. To maintain comparability between the surface probe pulse transmission time and the downhole probe pulse reception time, the surface terminal 300 and the downhole terminal 100 should use the same fixed known waveform event characteristic point rule.

[0036] Downhole terminal 100 records the timing of downhole probe pulses based on downhole pressure. Specifically, downhole pressure sensor 120 continuously acquires downhole pressure, and controller 130 identifies downhole probe pulses within the downhole pressure. When a downhole probe pulse reaches downhole terminal 100, a pressure change corresponding to a fixed, known waveform appears in the downhole pressure. Controller 130 identifies this pressure change using conventional waveform correlation, matched filtering, threshold cross-validation, or peak detection methods, and records the downhole clock reading corresponding to the detected event feature point as the timing of the downhole probe pulse.

[0037] After recording the downhole probe pulse timing, the downhole end 100 sends an upward response pulse via the mud pulser 140 and records the downhole probe pulse return timing. The downhole probe pulse return timing can be either the downhole clock reading from the controller 130 to the mud pulser 140 indicating drive control, or the downhole clock reading at which the mud pulser 140 actually begins generating the upward response pulse; the selection rules should be consistent within the same system. If the mud pulser 140 has a fixed drive delay that can be determined by the controller 130, the controller 130 can incorporate this fixed drive delay into the recording rules for the downhole probe pulse return timing, so that the downhole probe pulse return timing corresponds to the event of the upward response pulse entering the flowing drilling fluid column 200.

[0038] The ground terminal 300 records the time of the ground receiving probe pulse based on the ground pressure. After the upward response pulse propagates back along the flowing drilling fluid column 200 to the ground terminal 300, the decoder 320 detects the upward response pulse according to the aforementioned event characteristic point rule of fixed known waveforms, and records the corresponding ground clock reading as the time of the ground receiving probe pulse.

[0039] Therefore, the times of transmitting the detection pulse from the surface, receiving the detection pulse from the downhole, returning the detection pulse from the downhole, and receiving the detection pulse from the surface constitute four moments of a bidirectional detection event. The times of transmitting and receiving the detection pulse from the surface are on the surface time axis, while the times of receiving and returning the detection pulse from the downhole are on the downhole time axis. Since there may be a fixed deviation between the downhole time axis and the surface time axis, this embodiment eliminates the fixed component of the downhole clock error through bidirectional closure error. In order to ensure that this fixed component can be stably canceled out within a detection cycle, the running rates of the downhole clock and the surface clock can be routinely calibrated before going downhole, so that the clocks at both ends have comparable running rates within one or more measurement cycles.

[0040] Before going downhole, when calibrating the running rate of the downhole clock and the surface clock, the readings of the surface clock and the downhole clock, taken at known calibration intervals, are read respectively, and the running rate error is calculated. The running rate error is determined by the following formula:

[0041]

[0042] in, This refers to the travel rate error; and The downhole clock readings are taken during the two calibration reads. and This refers to the ground clock readings during the two calibration reads. The calibration pass condition is that the product of the downhole clock error usage time after the most recent bidirectional closure error and the time rate error is not greater than one-quarter of a chip duration, determined by the following formula:

[0043]

[0044] in, The downhole clock error usage duration represents the time interval between the most recent bidirectional closure error and the current candidate frame determination. If Greater than The decoder 320 no longer uses the saved downhole clock difference to accept candidate frames and retransmits downlink probe pulses.

[0045] Furthermore, the implementation methods for downlink propagation time, uplink propagation time, and bidirectional closure difference are as follows:

[0046] At the surface end 300, the downlink and uplink propagation times are determined based on the mud flow velocity, transmission distance, and mud sound velocity. The downlink propagation time characterizes the time it takes for the downlink probe pulse to propagate downstream along the flowing drilling fluid column 200, while the uplink propagation time characterizes the time it takes for the uplink response pulse and the measuring pressure pulse to propagate upstream along the flowing drilling fluid column 200. The direction from the surface end 300 to the downhole end 100 is defined as the downlink direction, along which the drilling fluid flows continuously downward, and pressure disturbances propagate relative to the drilling fluid at the mud sound velocity.

[0047] When the surface end 300 sends a downlink probe pulse, the downlink probe pulse propagates downstream along the flowing drilling fluid column 200. The mud flow velocity and the mud sound velocity are superimposed in the same direction from the surface end 300 to the downhole end 100. Therefore, the decoder 320 corrects the mud sound velocity in the downstream direction based on the mud flow velocity and determines the downlink propagation time by combining it with the transmission distance. The downlink propagation time can be determined by the following formula:

[0048]

[0049] in, This refers to the downlink propagation time, expressed in time. The transmission distance is measured in length and is obtained from the drilling rig depth measurement system. The velocity of sound in mud is measured in velocity and is obtained from a mud velocity meter. The velocity is the mud flow rate, measured in units of speed, and is obtained from a mud velocity meter. This formula applies to working conditions where the sound velocity of mud is greater than the mud flow velocity.

[0050] When the downhole end 100 sends an upward response pulse or a measurement pressure pulse, the upward response pulse and the measurement pressure pulse propagate counter-currently along the flowing drilling fluid column 200. The mud flow velocity and the mud sound velocity are opposite in the direction from the downhole end 100 to the surface end 300. Therefore, the decoder 320 corrects the mud sound velocity in the counter-current direction using the mud flow velocity and determines the upward propagation time based on the transmission distance. The upward propagation time can be determined using the following formula:

[0051]

[0052] in, This refers to the uplink propagation time, expressed in time. Transmission distance, in units of length; The sound velocity of mud is expressed in velocity. The value represents the mud flow velocity, expressed in units of speed. To avoid the denominator being meaningless, the following conditions must be met during implementation: .when Not greater than If any of the following is missing: mud flow velocity, transmission distance, or mud sound velocity, the decoder 320 will not use this set of field quantities to accept candidate frames. Instead, it will pause accepting candidate frames and reacquire the mud flow velocity, transmission distance, and mud sound velocity, or resend the downlink probe pulse.

[0053] Decoder 320 determines the bidirectional closure error based on four time points, downlink propagation time, and uplink propagation time. The bidirectional closure error characterizes the difference between the measured round-trip time and the physically predicted round-trip time for the downlink probe pulse and uplink response pulse. Let the time of the ground probe pulse transmission be... The timing of the downhole detection pulse is The timing of the downhole detection pulse is The ground-received detection pulse time is The two-way closure error can be determined by the following formula:

[0054]

[0055] in, This is a two-way closure difference, expressed in time difference. The time of the ground-based probe pulse is taken from the ground time axis; The timing of the detection pulse received downhole is taken from the downhole time axis. The timing of the downhole detection pulse is taken from the downhole time axis. The timing of the ground-received probe pulses is taken from the ground time axis. This refers to the downlink propagation time; This refers to the time of upward propagation.

[0056] The aforementioned two-way closure error can offset the fixed component of the downhole clock error. If the downhole time axis has a fixed deviation relative to the surface time axis, then It contains fixed components of downlink propagation time and downhole clock error. The downhole clock error includes the uplink propagation time and contains a fixed component of the downhole propagation time with the opposite sign. After the two observation time differences are added together, the fixed components of the downhole clock error cancel each other out, and the remaining amount should be close to the sum of the downlink propagation time and the uplink propagation time. If the detection event originates from the downlink detection pulse and the uplink response pulse in the current flowing drilling fluid column 200, and the mud velocity, transmission distance, and mud sound velocity are consistent with the current pressure pulse propagation channel, then the bidirectional closure error should not exceed half a chip duration.

[0057]

[0058] in, The chip duration is the minimum time interval for encoding the position of the pressure pulse. Half a chip duration is obtained from the existing pulse position encoding time base and used as a common time criterion for bidirectional closure error and arrival deviation. If the bidirectional closure error is greater than half a chip duration, the ground end 300 does not update the downlink propagation time, uplink propagation time, and downhole clock difference, and retransmits the downlink probe pulse. This process avoids using probe events corresponding to reflections, noise, old channel states, or time recording anomalies for candidate frame determination.

[0059] Furthermore, the implementation methods for downhole clock bias, frame transmission time, and arrival deviation are as follows:

[0060] The ground terminal 300 determines the downhole clock error when the bidirectional closure error is no greater than half a chip duration. The downhole clock error is used to convert the frame transmission time to the surface time axis. Since the frame transmission time in the data frame generated by the downhole terminal 100 belongs to the downhole time axis, while the frame arrival time recorded by the ground terminal 300 belongs to the surface time axis, if the downhole clock error is not determined, the ground terminal 300 cannot perform a consistency comparison between the event of the downhole terminal 100 actually sending a measurement pressure pulse and the event of the ground terminal 300 detecting a candidate frame.

[0061] After the bidirectional closure error has passed, decoder 320 uses downlink detection events to determine the downhole clock error. The downhole clock error can be determined using the following formula:

[0062]

[0063] in, This refers to the downhole clock error, expressed in time. This refers to the timing of receiving detection pulses downhole; The timing of the ground-based detection pulse; This represents the downlink propagation time. The downhole clock error is an estimated fixed deviation obtained when the most recent bidirectional closure error passed, used to convert the frame transmission time in subsequent data frames to the surface time axis.

[0064] The data frame generated by the downhole terminal 100 includes the frame transmission time. The frame transmission time is the downhole clock reading at the start of data frame transmission. After the data frame includes the frame transmission time, the surface terminal 300 can examine the arrival time of each candidate frame frame by frame, instead of only checking whether there is a synchronization word and check value in the surface pressure. The frame transmission time, combined with the downhole clock difference, forms the transmission reference for the data frame on the surface time axis; combined with the uplink propagation time, the expected arrival time can be obtained.

[0065] The validity period of the downhole clock difference is also limited by the number of candidate frames. In one embodiment, after the most recent bidirectional closure difference is passed, the decoder 320 can use the downhole clock difference to determine a maximum of thirty-two candidate frames; when the number of determined candidate frames reaches thirty-two, or the downhole clock difference usage time no longer meets the requirement... At this time, decoder 320 retransmits downlink probe pulses before accepting new candidate frames. This process ensures that the clock drift error generated when converting the frame transmission time to the ground time axis is less than half of the half-chip duration criterion.

[0066] The estimated time of arrival can be determined using the following formula:

[0067]

[0068] in, The estimated arrival time is in time. The frame transmission time is taken from the data frame; For underground clock error; This represents the uplink propagation time. In the formula... This means converting the frame transmission times on the underground timeline to the surface timeline. This indicates the estimated time required for the measured pressure pulse to propagate counter-currently from the bottom end 100 along the flowing drilling fluid column 200 to the surface end 300.

[0069] After the ground terminal 300 obtains the ground pressure through the riser pressure sensor 310 and the data acquisition unit, the decoder 320 searches for synchronization words in the ground pressure and forms candidate frames. For each candidate frame, the decoder 320 records the frame arrival time. The frame arrival time is the ground clock reading when the ground terminal 300 detects the candidate frame preamble. The arrival deviation, used to characterize the difference between the actual arrival time and the expected arrival time of the candidate frame, can be determined by the following formula:

[0070]

[0071] in, The deviation is expressed in time difference. The frame arrival time is taken from the ground timeline; The arrival time is the expected time. The smaller the arrival deviation, the more likely the candidate frame is to come from the measured pressure pulse corresponding to the frame transmission time in the data frame; when the arrival deviation is greater than half a chip length, it means that the arrival time of the candidate frame cannot be consistent with the current uplink propagation time and downhole clock difference, and the decoder 320 discards the candidate frame.

[0072]

[0073] in, The chip duration is specified. The ground station 300 accepts candidate frames only if the bidirectional closure error is no greater than half a chip duration, the arrival deviation is no greater than half a chip duration, and the cyclic redundancy check passes. If any one of these conditions is not met, the ground station 300 discards the candidate frame. When the ground station 300 continuously discards candidate frames, the decoder 320 can return to the step of retransmitting downlink probe pulses to update the downlink propagation time, uplink propagation time, and downhole clock difference.

[0074] Furthermore, the implementation methods for data frames, quantization numbers, check values, and measured pressure pulses are as follows:

[0075] The downhole terminal 100 generates a data frame containing the corresponding data of the downhole measurement values ​​and the frame transmission time. The data frame sequentially includes a synchronization word, sensor number, acquisition time, quantization number, frame transmission time, and checksum. The data corresponding to the downhole measurement values ​​includes the quantization number. The synchronization word is located at the beginning of the data frame and is used to enable the surface terminal 300 to search for candidate frames in the surface pressure. The sensor number is used to distinguish different downhole sensors 110. The acquisition time indicates the actual downhole time at which the downhole measurement value was acquired. The quantization number indicates the data written into the data frame after quantization of the downhole measurement value. The frame transmission time is used for frame-by-frame arrival time review. The checksum is used for cyclic redundancy check.

[0076] Data frames can be represented by the following single-line concatenation relationship:

[0077]

[0078] in, For data frames; Synchronization word; Number the sensors; The time of data collection; For quantized numbers; The frame transmission time; This is a checksum; This indicates field connection. During field connection, the controller 130 writes each field according to the pre-defined field length, field order, and field boundaries of the downhole end 100 and the surface end 300, so that the surface end 300 can read the sensor number, acquisition time, quantization number, frame transmission time, and check value according to the same field boundaries after recovering the candidate frame bits.

[0079] In one specific embodiment, the synchronization word is fixed as a sixteen-bit sequence. The sensor number uses an 8-bit unsigned integer encoding; the acquisition time uses a 32-bit unsigned integer encoding; the quantization number uses a 16-bit two's complement binary encoding; the frame transmission time uses a 32-bit unsigned integer encoding; and the check value uses a 16-bit unsigned integer encoding. Both the acquisition time and frame transmission time are encoded in time quantization units, which are determined according to the following formula:

[0080]

[0081] in, A unit for quantifying time; This refers to the chip duration. The acquisition time field is written when writing the data frame. A 32-bit unsigned integer, the frame transmission time field is written to A 32-bit unsigned integer. The field byte order follows the high-order bit-first transmission order, and the frame bit sequence number increases sequentially starting from the most significant bit of the synchronization word. The ground terminal 300 parses candidate frames according to the same field length, the same field order, the same time quantization unit, and the same field byte order.

[0082] Downhole end 100 acquires downhole measurement values ​​at the acquisition time via downhole sensor 110, and converts the downhole measurement values ​​into quantized numbers according to the quantization step size. The quantization step size is the unit of the measured physical quantity represented by each integer division when converting the downhole measurement value into an integer. The quantized number can be determined by the following formula:

[0083]

[0084] in, For quantized numbers; The sensor is numbered The downhole sensor 110 at the time of data acquisition Obtained downhole measurement values; This is the quantization step size; This represents a standard quantization operation that takes the nearest integer. The quantization step size can be predetermined based on the measurement range of the downhole sensor 110 and the required resolution of the surface end 300, and must remain consistent in both the downhole end 100 and the surface end 300.

[0085] The checksum is generated from the sensor number, acquisition time, quantization count, and frame transmission time. The checksum can be generated using a conventional cyclic redundancy check (CRC) method, and the checksum coverage fields must include at least the sensor number, acquisition time, quantization count, and frame transmission time. Including the frame transmission time in the checksum coverage fields prevents bit errors during pressure pulse transmission, but it is still used in the estimated arrival time calculation. After the ground unit 300 recovers the candidate frame bits, the decoder 320 recalculates the checksum for the corresponding fields in the candidate frame using the same CRC generation method and compares it with the checksum in the candidate frame.

[0086] Cyclic redundancy check (CRC) uses a 16-bit CRC check, and the generator polynomial is determined by the following formula:

[0087]

[0088] in, This is the generator polynomial for cyclic redundancy check (CR). The initial value for CR is... The input bit order is the most significant bit first in the field byte order. No input reflection is performed, and no output reflection is performed. The final XOR value is... The verification coverage field is concatenated in the order of sensor number, acquisition time, quantization number, and frame transmission time. The decoder 320 recalculates the check value for the same coverage field in the candidate frame, and the cyclic redundancy check passes only if the recalculated check value is identical bit-by-bit to the check value in the candidate frame.

[0089] The downhole end 100 is used to sequentially read frame bits. Each frame bit occupies two chips; when the bit is zero, the mud pulser 140 is driven in the first chip, and when the bit is one, the mud pulser 140 is driven in the second chip. Each drive is sustained by a pulse width, which is less than the chip duration. The chip duration is the minimum time grid for encoding the position of the measured pressure pulse, and the pulse width limits the duration of the pressure pulse formed by each action of the mud pulser 140. By making the pulse width less than the chip duration, the two chip positions of one frame bit can be distinguished temporally by the surface end 300.

[0090] The measurement pressure pulse is generated by the mud pulser 140 under the drive control of the controller 130. The controller 130 sends a synchronization word starting from the frame transmission time and drives the mud pulser 140 according to the frame bit order in the data frame. After entering the flowing drilling fluid column 200, the measurement pressure pulse propagates in the counter-current direction to the surface end 300. Attenuation, pump noise, drill string movement noise, and reflections are allowed during propagation, but the surface end 300 will not accept a candidate frame simply because it has a synchronization word and passes cyclic redundancy check. Instead, it further performs bidirectional closure error and arrival deviation determination.

[0091] Furthermore, the implementation methods for ground sampling, candidate frame formation, and ground measurement value recovery are as follows:

[0092] The ground terminal 300 is used to identify pulses from the ground pressure through bandpass filtering and pressure thresholding, search for synchronization words in the pulse sequence, record the arrival time of candidate frames, and recover frame bits according to the chip duration. Specifically, the riser pressure sensor 310 continuously acquires the ground pressure, and the data acquisition unit samples the ground pressure at a sampling frequency. The sampling frequency should ensure that each pulse width corresponds to a sufficient number of sampling points, and that the chip duration corresponds to a reliably distinguishable sampling point interval.

[0093] To ensure that the ground terminal 300 can stably recover frame bits, the sampling frequency is set according to the following conditions:

[0094]

[0095] in, The sampling frequency; The pulse width; The sampling frequency is the chip duration. This condition ensures at least eight sampling points within each pulse width and at least sixteen sampling points within each chip duration. If the sampling frequency does not meet this condition, the decoder 320 will not accept candidate frames and will prompt the user to reset the sampling frequency or redetermine the chip duration and pulse width.

[0096] The decoder 320 performs conventional bandpass filtering on the sampled surface pressure to match the pulse time band, thereby reducing low-frequency pump pressure fluctuations and high-frequency random disturbances. The decoder 320 then uses a pressure threshold to identify the pulse from the surface pressure. The pressure threshold can be determined based on the conventional noise level of the surface pressure or an existing receiver threshold; the specific value strategy for the pressure threshold does not change the two-way closure error and arrival deviation determination in this embodiment. The pressure threshold is used to identify pressure events in the surface pressure that may correspond to the measured pressure pulse, while the two-way closure error and arrival deviation are used to further examine whether the candidate frame matches the physical propagation time of the current flowing drilling fluid column 200.

[0097] The bandpass filter employs a linear-phase finite-impulse response bandpass filter. The lower and upper frequency limits of the bandpass filter are determined using the following formulas:

[0098]

[0099]

[0100] in, This is the lower cutoff frequency of the bandpass filter; This is the upper limit frequency of the bandpass filter; For chip duration; The pulse width is given. The finite impulse response filter order is not less than [value missing]. The smallest even number, the filtering delay is subtracted when the recorded frame arrives. If Not less than Decoder 320 according to The sampling frequency condition is raised again to make the upper limit frequency of the bandpass filter lower than the Nyquist frequency.

[0101] The pressure threshold is determined by the ground pressure silence interval before the synchronization word search. The ground pressure silence interval is selected as the interval of no-measurement pressure pulses preceding the most recent downlink probe pulse and with a length of not less than ten chip durations. The decoder 320 first calculates the average value of the ground pressure silence interval, and uses this average value as the zero reference. After subtracting the average value of the ground pressure silence interval from each sampling point, the root mean square noise value of the ground pressure silence interval is calculated. The pressure threshold is determined by the following formula:

[0102]

[0103] in, Pressure threshold; The average value of the ground pressure during the silent interval is used to form a zero baseline; This represents the root mean square noise value of the ground pressure in the silent interval. The decoder 320 performs bandpass filtering on the sampled ground pressure, then takes the absolute value of the pressure change relative to the zero reference at each sample point after bandpass filtering and compares it with a pressure threshold. If the absolute value of the pressure change is greater than the pressure threshold, and the duration of the corresponding pressure change is not less than [a certain value], then [the signal is considered]. and not greater than At that time, the decoder 320 records the pressure change as a pulse.

[0104] After identifying the pulse, the decoder 320 searches for a synchronization word in the pulse sequence. When a pulse position combination corresponding to the synchronization word is found, the decoder 320 records the arrival time of the candidate frame and, starting from that candidate frame, recovers the subsequent frame bits according to the chip duration. During frame bit recovery, the decoder 320 determines whether a frame bit is zero or one based on which of the two chips corresponding to each frame bit contains a pulse. If neither of the two chips corresponding to a frame bit detects a pulse, or if both chips detect a pulse, the decoder 320 treats the candidate frame as an unstable recovery candidate frame and discards it.

[0105] For each candidate frame whose frame bits can be recovered, the decoder 320 reads the sensor number, acquisition time, quantization count, frame transmission time, and checksum in the order of the data frame fields. The decoder 320 first confirms whether the most recent bidirectional closure error is no greater than half a chip duration, and then determines the arrival deviation based on the frame transmission time, downhole clock difference, uplink propagation time, and frame arrival time. If the bidirectional closure error is greater than half a chip duration, it indicates that the most recent detection event is inconsistent with the physically estimated round-trip time of the current flowing drilling fluid column 200. The decoder 320 discards the candidate frame and retransmits the downlink detection pulse. If the bidirectional closure error is no greater than half a chip duration but the arrival deviation is greater than half a chip duration, it indicates that the actual arrival time of the candidate frame is inconsistent with the frame transmission time, downhole clock difference, and uplink propagation time of that frame. The decoder 320 discards the candidate frame.

[0106] When both the bidirectional closure error and arrival deviation are no greater than half a chip duration, the decoder 320 performs a cyclic redundancy check (CRC). If the CRC fails, the decoder 320 discards the candidate frame. If the CRC passes, the decoder 320 accepts the candidate frame and recovers the ground measurements. This acceptance order ensures that candidate frames simultaneously satisfy physical propagation time consistency and data field integrity, reducing the risk of reflected pulses or noise pulses being mistakenly identified as valid candidate frames.

[0107] The quantization values ​​from 300 pairs of received candidate frames at the ground end are used to reconstruct ground measurements using the quantization step size. The ground measurements can be determined using the following formula:

[0108]

[0109] in, These are ground-measured values; The number of quantizations in the accepted candidate frames; This is the quantization step size; Number the sensors; The decoder 320 records ground measurements using the sensor number and acquisition time as an index, and can also record the arrival deviation of the candidate frame to track transmission quality. The arrival deviation is recorded only for log recording or maintenance analysis.

[0110] When three consecutive candidate frames are discarded due to arrival deviations exceeding half a chip duration or cyclic redundancy check failure, the decoder 320 immediately retransmits the downlink probe pulse. If any bidirectional closure error exceeds half a chip duration, the decoder 320 immediately retransmits the downlink probe pulse without waiting for three consecutive candidate frames. Before the new bidirectional closure error passes, the decoder 320 suspends accepting candidate frames, retaining only ground pressure sampling and synchronization word search results as log entries.

[0111] As an optional implementation, the mud sound velocity is greater than the mud flow velocity, and a continuous drilling fluid pressure wave path exists from the surface to the well. The running rates of the downhole clock and the surface clock have been calibrated before being run into the well. The fixed known waveform can be identified by the surface pressure and the downhole pressure, and the sampling frequency is sufficient to distinguish the pulse width and chip duration. At this time, the mud flow velocity, transmission distance, and mud sound velocity read by the decoder 320 can reflect the physical state of the current flowing drilling fluid column 200. The bidirectional closure difference calculated from the four times formed by the downlink probe pulse and the uplink response pulse is no greater than half a chip duration. The decoder 320 saves the downlink propagation time, the uplink propagation time, and the downhole clock difference. Subsequently, when the measured pressure pulse arrives at the surface end 300, the arrival deviation between the candidate frame arrival time and the expected arrival time is no greater than half a chip duration, and the cyclic redundancy check passes. The surface end 300 accepts the candidate frame and restores the surface measurement value.

[0112] As an optional implementation, the measuring pressure pulse emitted by the mud pulser 140, when propagating in the flowing drilling fluid column 200, is affected by end reflections or local changes in the flow channel, resulting in a pulse combination in the surface pressure that approximates the position of the synchronization word. This pulse combination may be initially formed into a candidate frame by the decoder 320, or it may accidentally result in a pass result during cyclic redundancy check. However, the arrival time of this candidate frame does not correspond to the expected arrival time determined by the frame transmission time, downhole clock difference, and uplink propagation time in the data frame, thus the arrival deviation is greater than half a chip duration. Based on this, the decoder 320 discards the candidate frame, preventing the reflected pulse from being accepted as a valid candidate frame.

[0113] As an optional implementation, periodic pressure disturbances caused by pump noise exist in the surface pressure. If a certain pressure disturbance is close to the pulse position of the synchronization word within a local time range, the decoder 320 can generate a candidate frame. However, this candidate frame is not generated by the measured pressure pulse sent by the mud pulser 140 at the frame transmission time from the downhole end 100, and cannot simultaneously satisfy the bidirectional closure error and arrival deviation conditions. When the surface end 300 calculates the expected arrival time using the most recent bidirectional closure error through the stored downhole clock difference and uplink propagation time, the frame arrival time of this candidate frame is inconsistent with the expected arrival time, and the decoder 320 discards the candidate frame.

[0114] As an optional implementation, the mud sound velocity is not greater than the mud flow velocity, or any one of the mud flow velocity, transmission distance, and mud sound velocity is missing. In this case, the downlink propagation time or uplink propagation time cannot be reliably determined according to the physical relationships of this implementation. The decoder 320 does not use this set of field quantities to accept candidate frames, does not update the downlink propagation time, uplink propagation time, and downhole clock difference, and reacquires the mud flow velocity, transmission distance, and mud sound velocity, or retransmits the downlink probe pulse. This processing avoids erroneous acceptance of candidate frames when the field quantities are incomplete or do not meet the physical conditions.

[0115] As an optional implementation, the downlink probe pulse may not be stably identified under downhole pressure, or the uplink response pulse may not be stably detected under surface pressure. In this case, the downhole or surface probe pulse timing may be missing or have a large error, and the bidirectional closure error calculated by the decoder 320 may be greater than half a chip duration. The surface unit 300 does not update the downlink propagation time, uplink propagation time, or downhole clock difference, and retransmits the downlink probe pulse. Through this processing, erroneous probe events will not be included in subsequent frame transmission time conversion and arrival deviation calculations.

[0116] As an optional implementation, decoder 320 may search for multiple candidate synchronization words within a certain ground pressure range. Decoder 320 records the arrival time of each candidate frame and calculates the expected arrival time and arrival deviation based on the transmission time of each candidate frame. Only candidate frames that simultaneously satisfy the conditions of bidirectional closure error not exceeding half a chip duration, arrival deviation not exceeding half a chip duration, and passing cyclic redundancy check are accepted; the remaining candidate frames are discarded. Thus, ground terminal 300 can maintain the correspondence with the actual transmission events of downhole terminal 100 even when synchronization words recur or noise pulses are dense.

[0117] It should be noted that the downhole sensor 110 can be a pressure, temperature, attitude, gamma, or vibration sensor suitable for the downhole environment, and its output enters the controller 130 or signal conditioning and analog-to-digital conversion circuit. The downhole pressure sensor 120 should be arranged to obtain the downhole pressure related to the pressure disturbance of the flowing drilling fluid column 200, so that the controller 130 can identify the downhole probe pulse. The controller 130 can be a conventional embedded controller, microcontroller, or digital signal processor used in downhole tools, and has the clock readout capability to record the downhole probe pulse reception time, downhole probe pulse return time, acquisition time, and frame transmission time.

[0118] It should be noted that the mud pulser 140 can adopt the pulser structure used to generate pressure pulses in existing mud pulse telemetry equipment. Its specific mechanical form is not limited, as long as it can generate upward response pulses and measured pressure pulses according to the drive control of the controller 130. The mud pulser 140 is connected to the flowing drilling fluid column 200, so that pressure disturbances can enter the flowing drilling fluid column 200.

[0119] It should be noted that the riser pressure sensor 310 is used to obtain ground pressure, and the data acquisition unit samples the ground pressure at a sampling frequency. The decoder 320 can be implemented by a ground-based industrial computer, an embedded decoding device, or a programmable controller.

[0120] Although embodiments of this application have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of this application, and all such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A measurement value transmission system for downhole sensing, comprising a downhole end, a surface end, a mud pulser, and a flowing drilling fluid column, wherein the flowing drilling fluid column is located between the surface riser pressure end and the mud pulser, serving as a propagation channel for downlink detection pulses, uplink response pulses, and measurement pressure pulses, characterized in that: The downhole end acquires downhole measurement values ​​and downhole pressure, and generates a data frame containing the corresponding data of the downhole measurement values ​​and the frame transmission time; The ground end obtains ground pressure, mud flow velocity, transmission distance and mud sound velocity, sends downlink detection pulses, and records the ground detection pulse sending time, ground detection pulse receiving time and frame arrival time according to the ground pressure to form candidate frames; The downhole end records the downhole detection pulse timing based on the downhole pressure, sends an uplink response pulse through the mud pulser, and records the downhole detection pulse timing. The ground end determines the downlink propagation time and uplink propagation time based on the mud flow velocity, transmission distance, and mud sound velocity. It also determines the bidirectional closure error based on the aforementioned four moments, downlink propagation time, and uplink propagation time. The bidirectional closure error characterizes the difference between the measured round-trip time of the downlink probe pulse and the uplink response pulse and the physically predicted round-trip time. The ground end determines the downhole clock error when the bidirectional closure error is no more than half a chip duration. The arrival deviation is determined based on the frame transmission time, downhole clock error, uplink propagation time, and frame arrival time. Candidate frames are accepted and ground measurement values ​​are restored only when both the bidirectional closure error and arrival deviation are no more than half a chip duration and the cyclic redundancy check passes. The chip duration is the minimum time grid for encoding the position of the measured pressure pulse.

2. The measurement value transmission system for downhole sensing according to claim 1, characterized in that, The flowing drilling fluid column is formed by the drill string cavity and the drilling fluid flowing continuously downward therein; the downward probe pulse propagates downstream along the flowing drilling fluid column, and the upward response pulse and the measuring pressure pulse propagate upstream along the flowing drilling fluid column.

3. The measurement value transmission system for downhole sensing according to claim 1, characterized in that, The downhole end includes a downhole sensor, a controller, and a downhole pressure sensor; the surface end includes a riser pressure sensor, a data logger, a decoder, a mud velocity meter, a drilling rig depth measurement system, and a mud velocity meter. The downhole sensor is used to acquire the downhole measurement value; the downhole pressure sensor is used to acquire the downhole pressure; the controller is used to generate the data frame and control the mud pulser to send the measured pressure pulse; the riser pressure sensor is used to acquire the surface pressure; the data logger is used to sample the surface pressure at a sampling frequency; the decoder is used to form the candidate frame and perform the determination of the bidirectional closure error, the arrival deviation, and the cyclic redundancy check; the mud velocity meter is used to acquire the mud flow velocity; the drilling rig depth measurement system is used to acquire the transmission distance; and the mud velocity meter is used to acquire the mud sound velocity.

4. A measurement value transmission system for downhole sensing according to claim 1, characterized in that, Both the downlink detection pulse and the uplink response pulse have fixed, known waveforms; the downhole end is used to identify the downlink detection pulse in the downhole pressure, record the downhole detection pulse receiving time, and drive the mud pulser to emit the uplink response pulse at the downhole detection pulse receiving time. The ground terminal is used to detect the uplink response pulse in the ground pressure and then record the time of the ground receiving detection pulse.

5. A measurement value transmission system for downhole sensing according to claim 1, characterized in that, The downlink propagation time is used to characterize the time it takes for the downlink probe pulse to propagate downstream along the flowing drilling fluid column, and the uplink propagation time is used to characterize the time it takes for the uplink response pulse and the measuring pressure pulse to propagate upstream along the flowing drilling fluid column; the surface end is used to determine the downlink propagation time and the uplink propagation time by correcting the mud sound velocity in the opposite direction with the mud flow velocity and combining it with the transmission distance.

6. A measurement value transmission system for downhole sensing according to claim 1, characterized in that, The downhole clock difference is used to convert the frame transmission time to the ground time axis; the ground terminal is used to not update the downlink propagation time, the uplink propagation time and the downhole clock difference when the bidirectional closure difference is greater than half a chip duration, and to retransmit the downlink probe pulse.

7. A measurement value transmission system for downhole sensing according to claim 1, characterized in that, The data frame sequentially includes a synchronization word, sensor number, acquisition time, quantization number, frame transmission time, and check value. The downhole measurement value corresponds to the quantization number, and the check value is generated by the sensor number, the acquisition time, the quantization number, and the frame transmission time.

8. A measurement value transmission system for downhole sensing according to claim 7, characterized in that, The downhole end is used to acquire the downhole measurement value at the acquisition time through the downhole sensor, and convert the downhole measurement value into the quantized number according to the quantization step size; the sensor number is used to distinguish different downhole sensors.

9. A measurement value transmission system for downhole sensing according to claim 7, characterized in that, The downhole terminal is used to sequentially read frame bits. Each frame bit occupies two chips. When the bit is zero, the mud pulser is driven in the first chip. When the bit is one, the mud pulser is driven in the second chip. Each drive is a continuous pulse width, and the pulse width is less than the chip duration.

10. A measurement value transmission system for downhole sensing according to claim 7, characterized in that, The ground terminal is used to find pulses from the ground pressure through bandpass filtering and pressure threshold, search for the synchronization word in the pulse sequence, record the arrival time of the candidate frame, and recover the frame bits according to the chip duration; the ground terminal is also used to discard the candidate frame when any one of the following conditions is not met: the bidirectional closure error is not greater than half a chip duration, the arrival deviation is not greater than half a chip duration, and the cyclic redundancy check passes; the ground terminal is also used to recover the ground measurement value from the quantization number in the received candidate frame according to the quantization step size, and record the ground measurement value with the sensor number and the acquisition time as indexes.

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