Method and system for realizing separable acquisition of DAS acoustic response through acoustic excitation and space selection under shaft flow condition

Abstract

The invention provides a method and a system for realizing separable acquisition of DAS acoustic response through acoustic excitation and space selection under a shaft flow condition. Comprising the following steps: constructing a controllable acoustic excitation condition in a shaft, and obtaining DAS acoustic time domain signals at different spatial positions along the shaft; determining a dominant frequency interval, and calculating by adopting frequency domain conversion and a characteristic frequency band energy ratio to obtain a measurable position of distributed acoustic sensing; constructing a space window to divide DAS acoustic response, and identifying acoustic response sections related to wellbore fluid flow based on axial energy change characteristics; background acoustic constraint based on reference sound pressure is introduced, and an acoustic response signal after background suppression is obtained; in combination with an acoustic response action range excited by artificial acoustics, separable acquisition of DAS acoustic response is realized; the invention further discloses a system and a storage medium which are suitable for different shaft experiments or monitoring scenes.

Description

Technical Field

[0001] This invention belongs to the field of fluid acoustics experimental technology, specifically relating to a method and system for separable acquisition of DAS acoustic response through acoustic excitation and spatial selection under well flow conditions, and an acoustic response acquisition method and system architecture applicable to different well experimental or monitoring scenarios. Technical Background

[0002] Distributed Acoustic Sensing (DAS) is widely used in wellbore flow state identification, flow disturbance monitoring, and related acoustic experimental research due to its advantages such as continuous distribution along the wellbore, high spatial resolution, and real-time acquisition of acoustic information. By analyzing the acoustic response excited by fluid flow in the wellbore, it can provide important basis for flow mechanism research, experimental result interpretation, and engineering parameter inversion. However, under wellbore flow conditions, the acoustic signals acquired by DAS typically contain acoustic components generated by multiple factors, including fluid flow, anthropogenic acoustic excitation, and background disturbance. These different acoustic components superimpose in both the time and frequency domains, making direct differentiation difficult. Existing technologies for processing wellbore DAS acoustic signals often rely on overall energy, spectrum, or empirical characteristics for signal interpretation, typically failing to adequately consider the distribution characteristics of the acoustic response within the wellbore space. In cases of complex wellbore flow conditions and non-uniform spatial distribution of the acoustic response, directly processing based on friction-line DAS data can easily lead to the acoustic response related to fluid flow being masked by background acoustic components, making it difficult to achieve stable and repeatable acoustic response acquisition. Furthermore, when anthropogenic acoustic excitation is introduced into the wellbore, its acoustic response typically only shows significant enhancement within a limited range within the wellbore space, and not all locations within the wellbore can effectively perceive this acoustic excitation. If the DAS acquisition location is not selected in conjunction with the spatial range of the acoustic excitation, it is difficult to accurately obtain the effective acoustic response related to fluid flow from the friction-line acoustic data. Therefore, there is an urgent need for a method and system that can combine the spatial range of action formed by artificial acoustic excitation under well flow conditions, and achieve the separation and acquisition of DAS acoustic response and background acoustic through spatial selection, so as to be applicable to different well experiment or monitoring scenarios. Summary of the Invention

[0003] The purpose of this invention is to provide a method and system for the separable acquisition of distributed acoustic sensing (DAS) acoustic responses under wellbore flow conditions. Addressing the problems of existing wellbore acoustic monitoring where acoustic responses are superimposed on the acoustic components of the flowing background, and where the spatial distribution of the acoustic response is non-uniform and difficult to stably acquire, this invention constructs position-controllable acoustic excitation conditions and, combined with the spatial distribution characteristics of the acoustic response within the wellbore, selects the acquisition location of the distributed acoustic sensor. A reference sound pressure is introduced as a background constraint, thereby enabling the effective separation and acquisition of DAS acoustic responses that were originally indistinguishable from the flowing background under wellbore conditions.

[0004] This invention includes the following steps: S100 constructs controllable acoustic excitation conditions inside the wellbore to obtain DAS acoustic time-domain signals at different spatial locations along the wellbore. S200, determine the dominant frequency range, and use frequency domain transformation and characteristic frequency band energy ratio calculation to obtain the measurable location of the distributed acoustic sensor; S300 constructs a spatial window to divide the DAS acoustic response and identifies acoustic response segments related to wellbore fluid flow based on axial energy change characteristics. S400 introduces background acoustic constraints based on reference sound pressure to obtain the acoustic response signal after background suppression; The S500, combined with the acoustic response range of artificial acoustic excitation, enables the separable acquisition of the DAS acoustic response.

[0005] The present invention also provides a system for achieving separable acquisition of DAS acoustic response under wellbore flow conditions through acoustic excitation and spatial selection, for performing the above method steps. The system 30 includes an acoustic excitation construction unit 301, a spatial selection sensing unit 302, an acoustic response segment identification unit 303, an acoustic background constraint unit 304, and an acoustic excitation characteristic verification unit 305. It can process DAS measurement signals and achieve separable acquisition of DAS acoustic response and flow background under wellbore flow conditions.

[0006] In addition, the present invention also provides a storage medium storing a computer program that, when run on a processor, causes the processor to perform the various steps of the DAS acoustic response separation acquisition described above.

[0007] The method and system provided by this invention do not depend on a specific disturbance structure or specific device form, and can be applied to different wellbore flow experiments or monitoring scenarios. They have the advantages of flexible implementation, wide applicability, and easy integration with existing DAS systems, and provide a general method and system architecture for the stable acquisition and comparative analysis of acoustic response under wellbore flow conditions. Attached Figure Description

[0008] Figure 1 This is a general flowchart of a method for achieving separable acquisition of DAS acoustic response through acoustic excitation and spatial selection under wellbore flow conditions; Figure 2 A schematic diagram of the axial DAS acoustic response energy distribution in the wellbore after background suppression; Figure 3 This is a schematic diagram of a system for separable acquisition of DAS acoustic response through acoustic excitation and spatial selection under wellbore flow conditions. Detailed Implementation

[0009] To further illustrate the technical solution of the present invention, a specific embodiment is provided below to illustrate the implementation process of the method for achieving separable acquisition of DAS acoustic response through acoustic excitation and spatial selection under wellbore flow conditions. This embodiment describes the method steps S100 to S500 accordingly, showing the specific implementation of the present invention under wellbore flow conditions, and explains the relevant processing flow and system structure in conjunction with schematic diagrams.

[0010] Example 1: As Figure 1 As shown, this invention proposes a method for achieving separable acquisition of DAS acoustic response through acoustic excitation and spatial selection under wellbore flow conditions, comprising the following steps: S100 constructs controllable acoustic excitation conditions inside the wellbore to obtain DAS acoustic time-domain signals at different spatial locations along the wellbore. S200, determine the dominant frequency range, and use frequency domain transformation and characteristic frequency band energy ratio calculation to obtain the measurable location of the distributed acoustic sensor; S300 constructs a spatial window to divide the DAS acoustic response and identifies acoustic response segments related to wellbore fluid flow based on axial energy change characteristics. S400 introduces background acoustic constraints based on reference sound pressure to obtain the acoustic response signal after background suppression; The S500, combined with the acoustic response range of artificial acoustic excitation, enables the separable acquisition of the DAS acoustic response.

[0011] According to the method described in the embodiments of the present invention, the DAS acoustic response can be separably acquired under wellbore flow conditions, so that the acoustic response related to fluid flow can be distinguished from the background acoustic components, providing support for the acquisition and analysis of wellbore flow acoustic response.

[0012] Furthermore, in step S100, controllable acoustic excitation conditions are constructed within the wellbore to obtain DAS acoustic time-domain signals at different spatial locations along the wellbore. This can be achieved using the following scheme: In this embodiment, a wellbore flow disturbance experimental device is used as the implementation platform. A cylindrical disturbance body with a length of 32 mm and a diameter of 15 mm is placed in a wellbore with a total length of 5 m and an inner diameter of 32 mm as an acoustic excitation condition. Liquid is pumped into the wellbore at a flow rate of 3 m / s to construct a locally controllable flow disturbance and acoustic excitation region. Single-mode sensing optical fibers are axially arranged along the inner wall of the wellbore and set at different circumferential positions. The sensing optical fibers are connected to a DAS signal acquisition device, which has a sampling frequency of 5 kHz and a spatial resolution of 0.5 m to acquire DAS acoustic time-domain signals at different spatial positions along the wellbore.

[0013] Further, in step S200, the dominant frequency range is determined, and the measurable location of the distributed acoustic sensor is obtained by frequency domain transformation and characteristic frequency band energy ratio calculation. The following scheme can be adopted: In this embodiment, to determine the dominant frequency range of artificial acoustic excitation under wellbore flow conditions, the Strouhal number is introduced to characterize the relationship between acoustic excitation characteristics and flow conditions; wherein the Strouhal number is defined as: ; In the formula, It is a dimensionless Strauhaus number with a value of 0.2; The dominant frequency (Hz) corresponding to the artificial acoustic excitation under wellbore flow conditions; D The characteristic scale for artificial acoustic excitation is 0.015m. U The characteristic flow velocity inside the wellbore is taken as 3 m / s; Furthermore, considering the fluctuations in flow conditions and the discreteness of acoustic excitation response, a characteristic frequency band is constructed centered on the dominant frequency. , used to characterize the effective frequency range corresponding to artificial acoustic excitation; Subsequently, the DAS acoustic time-domain signals at different circumferential positions within the characteristic frequency band were analyzed. Discretize the data: ; In the formula, Circumferential position Axial position of wellbore z DAS acoustic time-domain continuous signal at the location; Circumferential position Axial position of wellbore z DAS acoustic discrete-time domain signal at the location; t For continuous time variables; n Discrete sampling point index; T s The sampling period is 0.2ms in this embodiment; f sThe sampling frequency is set to 5000Hz in this embodiment; frequency domain transformation is performed on the DAS acoustic discrete time domain signal: ; In the formula, Circumferential position Axial position of wellbore z The DAS acoustic frequency domain response at that location; Circumferential position Axial position of wellbore z DAS acoustic discrete-time domain signal at the location; Apply a window function to the time domain; N The number of sampling points within a single time window; f For frequency variables; f s The sampling frequency is 5000Hz in this embodiment; j The imaginary unit; The energy distribution of the acoustic response at the circumferential position in the frequency domain is characterized in the form of a power spectrum: ; In the formula, Circumferential position Axial position of wellbore z The DAS acoustic signal at the frequency f The energy spectrum at that location; Circumferential position Axial position of wellbore z The DAS acoustic frequency domain response at that location; T The duration of a single time window is 1 second in this embodiment; and... The internal frequency band energy is calculated, and the prominence of the artificial acoustic excitation response at different circumferential positions within the dominant frequency range is quantitatively compared. ; In the formula, Circumferential position Axial position of wellbore z In the dominant frequency band Internal frequency band energy; Circumferential position Axial position of wellbore z The DAS acoustic signal at the frequency f The energy spectrum at that location; At the same time, a reference power spectrum is defined within the same frequency band. A pre-defined acoustic reference standard is used to characterize the effective response benchmark level of artificial acoustic excitation in the dominant frequency range and to calculate the bandgap energy: ; In the formula, A reference energy spectrum characterizing the acoustic response benchmark level of artificial acoustic excitation in the dominant frequency range; f 1. f 2 represents the upper and lower limits of the dominant frequency range corresponding to artificial acoustic excitation under wellbore flow conditions; The reference frequency band energy serves as a normalization benchmark for acoustic response energy at different circumferential positions; Furthermore, the energy ratio of the characteristic frequency band is calculated. The Used to characterize circumferential position At this point, the relative intensity of the acoustic response energy of the artificial acoustic excitation within the dominant frequency range relative to a reference standard; when A larger value indicates the circumferential position. The perceptibility of artificial acoustic excitation response is higher. By comparing the characteristic frequency band energy ratios at different circumferential positions, the measurable location of the distributed acoustic sensor can be determined. The calculation formula is as follows: ; In the formula, Circumferential position The characteristic frequency band energy ratio at that location; Circumferential position Axial position of wellbore z In the dominant frequency band Internal frequency band energy; The reference frequency band energy serves as a normalization benchmark for acoustic response energy at different circumferential positions; Circumferential position Axial position of wellbore z The DAS acoustic signal at the frequency f The energy spectrum at that location; The reference energy spectrum characterizes the acoustic response benchmark level of artificial acoustic excitation in the dominant frequency range.

[0014] Furthermore, in step S300, multiple spatial windows are constructed to spatially divide the DAS acoustic response distributed along the wellbore axis at measurable locations. Based on the energy change of the acoustic response along the wellbore axis, acoustic response segments related to the wellbore fluid flow are identified. The following scheme can be adopted: In this embodiment, after determining the measurable position in step S200, the wellbore axial data is extracted only at the sensing channel corresponding to the measurable position. The DAS monitoring data is divided into a series of axial spatial windows along the wellbore axis. Window length is The adjacent window step is And satisfy: ; In the formula, This represents the step length between adjacent axial spatial windows; The length of a single axial spatial window; With the above settings, the response segment gradually appears in multiple adjacent windows, reducing the impact of window boundaries on the determination of the response segment; in each of the above spatial windows Inside, to Calculate the root mean square energy: ; In the formula, For the first i Axial space window W i The root mean square energy of the DAS acoustic response within the device; To be at the selected measurable location Above, axial position of the wellbore z The DAS acoustic time-domain signal at the location; T The duration within a single time window is 1 second in this embodiment; the window energy sequence arranged along the axial direction is obtained through calculation: ; In the formula, E The window energy sequence is arranged along the wellbore axis; For the first n Axial space window W n The root mean square energy of the DAS acoustic response within the device; Furthermore, to avoid the absolute energy of a single window being affected by background fluctuations, the energy difference between adjacent windows and the relative rate of change are introduced as criteria, defined as follows: ; In the formula, For the first i Energy difference between each axial spatial window and the previous window; For the first i The relative rate of change of energy between each axial spatial window and the previous window; When an acoustic response induced by fluid flow occurs, the window energy sequence exhibits a continuous increase or a localized sudden increase along the axial direction; therefore, a set of windows that meets the following conditions can be identified as candidate response windows: ; In the formula, The preset energy difference judgment threshold; This is a preset relative rate of change threshold; Furthermore, candidate windows that appear consecutively in the axial direction are merged to obtain the acoustic response segment related to fluid flow, denoted as: ; In the formula, Location of the acoustic response section related to fluid flow within the wellbore; For the first i The axial center position corresponding to each axial space window; The window index range that continuously satisfies the candidate criteria.

[0015] Furthermore, in step S400, within the acoustic response range, a background acoustic constraint characterized by a reference sound pressure is introduced into the DAS acoustic time-domain signal to obtain a background-suppressed acoustic response signal. This can be achieved using the following scheme: In this embodiment, the area within the axial direction of the wellbore, excluding the acoustic response section, is included. The set of windows corresponding to the other axial positions is denoted as the background window set: ; In the formula, This is the set of axial positions corresponding to the background window; z i For the first i The axial position corresponding to each axial space window; The location of the acoustic response segment identified in step S300; At measurable location At this point, the DAS acoustic time-domain signals corresponding to each window within the background window set are... Its root mean square energy is calculated and defined as: ; In the formula, Background window z i The root-mean-square acoustic energy at the location; To be at a measurable location Location, axial position of the wellbore z i The DAS acoustic time-domain signal at the location; This is the set of axial positions corresponding to the background window; Furthermore, the energy of the background window is statistically characterized to obtain the reference sound pressure level. Its definition is: ; In the formula, The reference sound pressure level is represented by the overall average acoustic level obtained from the statistical analysis of the background acoustic energy at each axial position within the background window set. This is the set of axial positions corresponding to the background window; Background window z i The root-mean-square acoustic energy at the location; In the acoustic response range Internally, the window energy at each axial position Background constraint processing is performed, and the acoustic response energy after background suppression is defined as: ; In the formula, Within the acoustic response range, the axial position z i The acoustic energy corresponding to the window; For reference sound pressure level; Axial position after background suppression z i Acoustic response energy; when When this happens, it can be truncated to zero or excluded from subsequent calculations and decisions to avoid interference from the background-dominant window in subsequent decisions; after the above processing, in the axial response section Acoustic response distribution after background suppression: ; In the formula, Axial position after background suppression z i Acoustic response energy; The location of the acoustic response section related to fluid flow within the wellbore.

[0016] Furthermore, in step S500, within the acoustic response segment, the acoustic response signal after background suppression is verified based on the effective range of the acoustic response formed by artificial acoustic excitation, thereby achieving the separable acquisition of the DAS acoustic response. The following scheme can be adopted: In this embodiment, the artificial acoustic excitation is formed by a cylindrical disturbance body under wellbore flow conditions; since the structure, size and arrangement of the disturbance body in the wellbore are fixed, the acoustic response energy that it can excite is within a limited range under a given flow condition. Based on the acoustic response segment determined in step S300 and the acoustic response energy after background suppression obtained in step S400 The background window energy corresponding to the non-response segment is statistically analyzed, and the standard deviation of the background energy is calculated as the lower limit of the identifiable energy for artificial acoustic excitation, ensuring that the selected response is significantly higher than the natural fluctuation level of the flowing background. ; In the formula, The standard deviation of the window energy within the background window set; The minimum energy threshold for reliable identification of artificial acoustic excitation under current operating conditions; Simultaneously, the energy distribution after background suppression within the acoustic response range... Statistical analysis was conducted, and the 95th percentile was selected as the upper limit of energy corresponding to artificial acoustic excitation under current conditions, namely: ; In the formula, The quantile operator is 95%. In the current embodiment, this represents the upper limit of the effective energy corresponding to artificial acoustic excitation. By following the steps above, the range of excitation energy corresponding to artificial acoustic excitation under the current operating conditions can be determined. Subsequently, axial positions that satisfy the energy range constraints are selected within the acoustic response range, and those that satisfy: ; In the formula, The upper and lower limits of the stable and effective energy of artificial acoustic excitation under current operating conditions; Axial direction of the wellbore z i The acoustic response energy after background suppression; The location with the largest acoustic response energy after background suppression within the above range is selected, and the corresponding DAS acoustic response signal is used as the DAS acoustic response signal output to characterize the wellbore fluid flow, thereby realizing the separable acquisition of the DAS acoustic response.

[0017] like Figure 3 As shown, the present invention also provides a system 30 for achieving separable acquisition of DAS acoustic response through acoustic excitation and spatial selection under wellbore flow conditions; the system 30 includes a processor, a memory, and a computer program stored in the memory and executable on the processor; when the computer program is executed by the processor, it is used to implement the operations described in steps S100 to S500 in the method embodiment of the present invention.

[0018] The system 30 includes the following functional modules: Acoustic excitation construction unit 301 is used to construct controllable acoustic excitation conditions within the wellbore, so that a propagable acoustic response is formed during the flow process in the wellbore. The spatial selection sensing unit 302 is used to determine the measurable location in the distributed acoustic sensing that can stably sense the acoustic excitation response based on the spatial distribution law of the acoustic response corresponding to the acoustic excitation under well flow conditions. The acoustic response segment identification unit 303 is used to compare the DAS acoustic response at different positions along the well shaft axis within the spatial range corresponding to the measurable position, and identify the acoustic response segment related to the well shaft fluid flow. The acoustic background constraint unit 304 is used to introduce a flowing background constraint within the acoustic response section to suppress acoustic components related to the background and obtain an acoustic response distribution that is distinct from the flowing background. The acoustic excitation characteristic verification unit 305 is used to select the DAS acoustic response signal to characterize the wellbore fluid flow from the acoustic response after background suppression, based on the excitation energy range corresponding to artificial acoustic excitation under the current conditions, thereby realizing the separable acquisition of the DAS acoustic response. Furthermore, the system 30 can be deployed in a computer, well site data acquisition terminal, remote processing server or cloud platform to process DAS measurement signals and output the separated acoustic response results; Furthermore, the system can transmit the processing results to the well site monitoring system or data analysis platform via a communication interface to support wellbore flow state analysis and related experiments or monitoring.

[0019] The present invention also provides a computer-readable storage medium storing a computer program that, when the computer program is run on a processor, causes the processor to execute the method described in steps S100 to S500 of the method embodiment of the present invention for achieving separable acquisition of DAS acoustic response through acoustic excitation and spatial selection under well flow conditions. The computer program includes instructions for performing the following operations: (1) Instructions for constructing controllable acoustic excitation conditions in the wellbore and obtaining DAS acoustic time-domain signals at different spatial locations along the wellbore; (2) Instructions for determining the measurable location of distributed acoustic sensors based on the spatial distribution of acoustic response under wellbore flow conditions; (3) Instructions for identifying acoustic response segments related to wellbore fluid flow within the spatial range corresponding to the measurable location; (4) Instructions for introducing flow background constraints and performing background suppression processing on the acoustic response; (5) Instructions for selecting DAS acoustic response signals to characterize wellbore fluid flow based on the excitable energy range corresponding to artificial acoustic excitation; The computer-readable storage medium may be a read-only memory (ROM), random access memory (RAM), flash memory, solid-state drive (SSD), disk, memory card, or other medium capable of storing program code.

[0020] The above parameters are only an example setting in this embodiment. Those skilled in the art can reasonably adjust the parameters according to the wellbore size, flow velocity range and noise level, without affecting the implementation effect of the method of the present invention. Through the above processing, even under different wellbore structures or different acoustic excitation intensities, the acoustic response segment related to fluid flow can be stably identified. It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the present invention; the scope of protection of the present invention shall be determined by the appended claims, and the embodiments in this specification do not constitute a limitation on the claims.

Claims

1. A method for achieving separable acquisition of DAS acoustic response through acoustic excitation and spatial selection under wellbore flow conditions, characterized in that, Includes the following steps: S100 constructs controllable acoustic excitation conditions inside the wellbore to obtain DAS acoustic time-domain signals at different spatial locations along the wellbore. S200, determine the dominant frequency range, and use frequency domain transformation and characteristic frequency band energy ratio calculation to obtain the measurable location of the distributed acoustic sensor; S300 constructs a spatial window to divide the DAS acoustic response and identifies acoustic response segments related to wellbore fluid flow based on axial energy change characteristics. S400 introduces background acoustic constraints based on reference sound pressure to obtain the acoustic response signal after background suppression; The S500, combined with the acoustic response range of artificial acoustic excitation, enables the separable acquisition of the DAS acoustic response.

2. The method according to claim 1, wherein, The S100 includes: acquiring DAS acoustic time-domain signals along the shaft axis at a preset spatial sampling interval to form a time-domain signal set distributed along the shaft space.

3. The method according to claim 1, wherein, The S200 includes: determining the dominant frequency range of artificial acoustic excitation under wellbore flow conditions using the Strouhal number; performing frequency domain transformation on the DAS acoustic time-domain signal within the dominant frequency range to obtain the spectral characterization of the acoustic response; and determining the measurable location of the distributed acoustic sensor by calculating the characteristic frequency band energy ratio.

4. The method according to claim 1, wherein, The S300 includes: constructing multiple spatial windows to spatially divide the DAS acoustic response distributed along the well shaft at measurable locations, and identifying acoustic response segments related to well shaft fluid flow based on the root mean square acoustic energy of the acoustic response along the well shaft axis.

5. The method according to claim 1, wherein, S400 includes: within the acoustic response segment, introducing a background acoustic constraint characterized by a reference sound pressure on the DAS acoustic time-domain signal to obtain a background-suppressed acoustic response signal, wherein the reference sound pressure is the overall average acoustic level obtained by statistically analyzing the background acoustic energy at each axial position within the background window set.

6. The method according to claim 1, wherein, The S500 includes: within the acoustic response segment, verifying the acoustic response signal after background suppression based on the acoustic response range formed by artificial acoustic excitation, thereby realizing the separable acquisition of the DAS acoustic response.

7. A system 30 for separable acquisition of DAS acoustic response through acoustic excitation and spatial selection under wellbore flow conditions, characterized in that, It includes an acoustic excitation construction unit 301, a spatial selection sensing unit 302, an acoustic response segment identification unit 303, an acoustic background constraint unit 304, and an acoustic excitation characteristic verification unit 305.

8. A storage medium that enables the separable acquisition of DAS acoustic response through acoustic excitation and spatial selection under wellbore flow conditions, characterized in that, It stores a computer program thereon, which, when run on a processor, causes the processor to perform the method of any one of claims 1 to 6.

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