A method for correcting seismic amplitude attenuation in optical fiber wells

Abstract

The present invention discloses a method for correcting optical fiber downhole seismic amplitude attenuation, which is applied to the field of geophysical exploration seismic data processing and addresses the problem that optical fiber signal transmission attenuation is difficult to directly measure during downhole seismic acquisition. The present invention designs a U-shaped downhole seismic acquisition optical fiber, which includes two optical fibers, and the endpoints are connected by mutually interconnected U-shaped optical fibers. Optical fiber seismic data of an upward transmission portion of amplitude data and a downward transmission portion of amplitude data are collected, and the amplitude value data of the two portions are picked up. A data correction amount is obtained according to the ratio of the amplitude value data of the two portions and the amplitude value data of the downward transmission portion of the amplitude data, thereby correcting the optical fiber seismic data of the upward transmission portion of the amplitude data.

Description

Technical Field

[0001] The invention belongs to the field of geophysical exploration seismic data processing, and in particular relates to a technology for correcting abnormal attenuation of seismic amplitude in optical fiber wells. Background Art

[0002] In recent years, distributed optical fiber sensing (DAS) technology has gradually matured. Fiber-optic vertical seismic profiling (DAS-VSP) has become an important means of acquiring downhole seismic data due to its advantages, including full-well coverage, high density, high efficiency, high-temperature and high-pressure resistance, and low cost. DAS-VSP technology can provide high-precision reservoir parameters, enhance the ability to accurately describe the reservoir surrounding the well, and enable dynamic monitoring of oil and gas reservoirs. A large amount of downhole seismic data has been collected simultaneously using both fiber-optic and geophone sensors in multiple exploration areas both domestically and internationally. Comparative analysis and empirical evidence indicate that the amplitude attenuation of fiber-optic data is significantly higher than that of existing electronic geophones, resulting in inaccurate calculations of the true amplitude compensation parameter (TAR) and the seismic absorption factor (Q). This is attributed to fiber-optic signal transmission attenuation, which is affected by a combination of factors, including fiber length, temperature, and pressure, making it difficult to directly measure during downhole seismic acquisition. Summary of the Invention

[0003] To solve the above technical problems, the present invention proposes a correction method for optical fiber well seismic amplitude attenuation, which uses an enhanced optical fiber observation method to obtain well seismic data, and then calculates the abnormal attenuation of optical fiber well seismic amplitude through processing means and performs effective correction.

[0004] The technical solution adopted by the present invention is: a method for correcting seismic amplitude attenuation in an optical fiber well, comprising:

[0005] B1. Enhanced fiber optic data acquisition: Specifically, a U-shaped downhole seismic acquisition fiber is designed and lowered into the observation well to acquire fiber optic downhole seismic data.

[0006] B2. Processing the fiber-optic well seismic data obtained in step B1, specifically comprising: performing cable noise suppression, DC drift removal, and random noise suppression on the fiber-optic well seismic data collected in step B1 to obtain processed fiber-optic seismic data; wherein the upwardly transmitted portion of the amplitude data is used as the first processed fiber-optic seismic data, denoted as S1; and the downwardly transmitted portion of the amplitude data is used as the second processed fiber-optic seismic data, denoted as S2;

[0007] B3. Obtaining amplitude data: Specifically, for each trace of S1 at different depths obtained in step B2, pick up the peak amplitude value at the first arrival position, and record the peak amplitude value corresponding to the trace of a certain depth of S1 as A1;

[0008] On each trace of different depths of S2 obtained in step B2, pick up the peak amplitude value of the first arrival position, and record the peak amplitude value corresponding to the trace of a certain depth of S2 as A2;

[0009] B4. Data normalization. Specifically: normalize A2 of all depths obtained in step B3.

[0010] B5. Calculate the data correction amount. Specifically, calculate the data correction amount θ based on A1 in step B3 and A2 after processing in step B4.

[0011] B6. Data correction processing. Specifically: using the data correction amount θ obtained in step B5, perform correction processing on S1 obtained in step B2.

[0012] The beneficial effects of the present invention are as follows: the present invention uses an enhanced optical fiber observation method to obtain in-well seismic data. The specific optical fiber is specially processed, and two optical fibers are included in the optical cable, and a U-shaped optical fiber design is adopted at the end points to connect with each other; the upward transmission part of the collected amplitude data is used as the first processed optical fiber seismic data, recorded as S1; the downward transmission part of the collected amplitude data is used as the second processed optical fiber seismic data, recorded as S2; the abnormal attenuation of the optical fiber in-well seismic amplitude is calculated based on S2, and then S1 is effectively corrected by the abnormal attenuation of the optical fiber in-well seismic amplitude. The method of the present invention can effectively improve the reliability of in-well seismic data. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the observation system of this embodiment;

[0014] Figure 2 This is a schematic diagram of collecting optical fiber seismic data in this embodiment;

[0015] Figure 3 Schematic diagram of the amplitude values ​​obtained in this embodiment;

[0016] Figure 4 Schematic diagram of normalized amplitude values ​​in this embodiment;

[0017] Figure 5 Schematic diagram of correction amount calculation in this embodiment. DETAILED DESCRIPTION

[0018] This invention addresses the technical problem of abnormal amplitude attenuation in optical fiber data. It proposes a method for acquiring downhole seismic data using an enhanced optical fiber observation method, and then using innovative processing techniques to calculate and effectively correct the abnormal attenuation of optical fiber downhole seismic amplitude. The method specifically includes several steps, including enhanced optical fiber data acquisition, optical fiber seismic data processing, amplitude data acquisition, data normalization, data correction calculation, and data correction processing. These steps are described in detail below with reference to the accompanying figures.

[0019] 1) Enhanced fiber optic data collection:

[0020] Design a U-shaped well seismic acquisition fiber, and lower it into the observation well to collect fiber-optic well seismic data. Figure 1 shown.

[0021] The U-shaped downhole seismic acquisition optical fiber is different from ordinary straight optical fibers. It refers to an optical fiber that has been specially processed by folding it in the middle. The modified optical fiber contains two optical fibers in the optical cable, one for transmitting upward and the other for downward transmission, and the end points adopt a U-shaped optical fiber anti-breakage design that is interconnected.

[0022] The observation well mentioned refers to an operation well for collecting in-well seismic data, which must meet the engineering and safety requirements of in-well seismic data collection.

[0023] The fiber optic well seismic data mentioned above refers to standardized seismic data that meets the requirements of the industry standard SYT 5454-2017.

[0024] 2) Fiber optic seismic data processing:

[0025] The optical fiber well seismic data obtained in step 1) is processed, specifically including processing means such as cable noise suppression, DC drift removal, and random noise suppression, to obtain processed optical fiber seismic data. Since the present invention adopts a U-shaped optical fiber observation method, the first section of the optical fiber, i.e., the upward transmission part of the amplitude data, is the first processed optical fiber seismic data, denoted as S1; the second section, i.e., the downward transmission part, is the second processed optical fiber seismic data, denoted as S2. Figure 2 shown. Figure 2 The horizontal axis is depth, in meters, and the vertical axis is time, in milliseconds.

[0026] The aforementioned optical cable noise suppression refers to the use of fitting subtraction and other processing methods to reduce the optical fiber resonance noise caused by poor coupling between the optical cable and the wellbore. DC drift removal refers to the use of low-pass filtering and other processing methods to eliminate the zero-point drift noise caused by long-term recording. Random noise suppression refers to the method of eliminating randomly generated abnormal fluctuation signals. These noise suppression methods can all be completed using existing commercial seismic processing software.

[0027] In particular, during the processing, special attention should be paid to protecting the relative relationship between the amplitudes of the data, and strictly avoiding processing steps that change the amplitude, such as channel equalization and automatic gain compensation.

[0028] 3) Amplitude data acquisition:

[0029] On each trace of the processed fiber optic seismic data obtained in step 2), the peak amplitude value at the initial arrival position is picked up to obtain amplitude value data. A first amplitude value data is picked up on the first processed fiber optic seismic data, and the amplitude value data corresponding to a certain depth on the first processed fiber optic seismic data is recorded as A1; a second amplitude value data is picked up on the second processed fiber optic seismic data, and the amplitude value data corresponding to a certain depth on the second processed fiber optic seismic data is recorded as A2. Figure 3 shown. Figure 3 The horizontal axis is the depth, in meters, and the vertical axis is the amplitude, which is dimensionless.

[0030] 4) Data normalization:

[0031] Normalize the second amplitude data obtained in step 3) to obtain the ratio of the amplitude values ​​at the same depth. The first value Δ1 is calculated from the starting depth, that is, Δ1 represents the ratio of the starting depth amplitude value, and the second amplitude value data is multiplied to obtain the normalized second amplitude value data. like Figure 4 shown. Figure 4 The horizontal axis is the depth, in meters, and the vertical axis is the amplitude, which is dimensionless.

[0032] 5) Calculation of data correction amount:

[0033] The first amplitude data obtained in step 3) is subtracted from the normalized second amplitude data obtained in step 4) and divided by 2 to obtain the data correction amount. The correction amount is the abnormal attenuation in the optical fiber data, such as Figure 5 shown. Figure 5 The horizontal axis is the depth, in meters, and the vertical axis is the amplitude, which is dimensionless.

[0034] 6) Data correction processing:

[0035] The first optical fiber seismic data S1 obtained in step 2) is corrected using the data correction amount θ obtained in step 5), specifically: Get the data S1 after data correction processing ′ .

[0036] In particular, in this step, only the first fiber optic seismic data S1 is corrected and the second fiber optic seismic data S2 is discarded. This is because the first fiber optic seismic data has a higher signal-to-noise ratio and more complete seismic information, while the second fiber optic data is after the first fiber optic data, has a longer transmission distance, and has a larger signal-to-noise attenuation.

[0037] Those skilled in the art will appreciate that the embodiments described herein are intended to aid the reader in understanding the principles of the present invention, and it should be understood that the scope of the present invention is not limited to such specific descriptions and embodiments. Various modifications and variations are readily apparent to those skilled in the art. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of the claims.

Claims

1. A method for correcting seismic amplitude attenuation in optical fiber wells, characterized in that: include: B1. Enhanced fiber optic data acquisition: Specifically, a U-shaped downhole seismic acquisition fiber is designed and lowered into the observation well to acquire fiber optic downhole seismic data. B2. Processing the fiber-optic well seismic data obtained in step B1, specifically comprising: performing cable noise suppression, DC drift removal, and random noise suppression on the fiber-optic well seismic data collected in step B1 to obtain processed fiber-optic seismic data; wherein the upwardly transmitted portion of the amplitude data is used as the first processed fiber-optic seismic data, denoted as S1; and the downwardly transmitted portion of the amplitude data is used as the second processed fiber-optic seismic data, denoted as S2; B3. Obtaining amplitude data: Specifically, for each trace of S1 at different depths obtained in step B2, pick up the peak amplitude value at the first arrival position, and record the peak amplitude value corresponding to the trace of a certain depth of S1 as A1; On each trace of different depths of S2 obtained in step B2, pick up the peak amplitude value of the first arrival position, and record the peak amplitude value corresponding to the trace of a certain depth of S2 as A2; B4. Data normalization. Specifically, normalize A2 at all depths obtained in step B3. Step B4 specifically comprises: obtaining the ratio of the amplitude values ​​of S1 and S2 at the same depth, and normalizing A2 at all depths based on the first ratio. B5. Calculation of data correction amount. Specifically: Calculate the data correction amount θ based on A1 in step B3 and A2 after processing in step B4. The calculation formula for the data correction amount θ in step B5 is: Among them, A ′ 2 represents the peak amplitude value corresponding to a certain depth of S2 after normalization in step B4; B6. Data correction processing. Specifically: using the data correction amount θ obtained in step B5, perform correction processing on S1 obtained in step B2.

2. A method for correcting seismic amplitude attenuation in optical fiber wells according to claim 1, characterized in that: The calculation formula for the correction process in step B6 is: Among them, S1 ′ represents the first processed fiber optic seismic data after correction.

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