A fiber-optic downhole seismic exploration method for "double-complex" areas

Abstract

The present invention discloses a fiber-optic downhole seismic exploration method for "double-complex" areas, which is applied to the field of downhole geophysics. It addresses the problem that existing technologies cannot effectively collect data in "double-complex" areas, and thus cannot obtain the accurate velocity and thickness of shallow thick conglomerates. The present invention preprocesses fiber-optic downhole seismic data to obtain reliable deep micro-logging data and fiber-optic seismic exploration data, extracts velocity and thickness information of the surface layer, geophysical parameters of the medium-deep complex area, and reservoir information, and can obtain the velocity and thickness of special lithology in the surface complex area, and provide well control parameters of the medium-deep layer for well drive seismic processing.

Description

Technical Field

[0001] The present invention belongs to the field of well geophysics, and in particular relates to a seismic data acquisition, data analysis and processing technology. Background Art

[0002] With the continuous advancement of distributed fiber optic technology, it has been rapidly promoted and applied in the field of reservoir geophysics, especially in borehole seismic. Borehole seismic methods have significant advantages in velocity determination, layer calibration, and reservoir prediction. Exploration in areas with uneven distribution of shallow, thick conglomerates and complex deep structures has always been a difficult issue in the seismic field. How to obtain accurate velocity and thickness of shallow, thick conglomerates, as well as deep and ultra-deep structural characterization and reservoir prediction, is an urgent problem that needs to be solved in oil and gas exploration and development. For shallow, thick conglomerates, the more common method in the industry is to use micro-logging and acoustic logging to obtain relevant information. Micro-logging can obtain surface velocity and low-velocity zone thickness, but this method has limited detection depth and cannot obtain formation information hundreds of meters underground. Acoustic logging can only provide formation velocity information, not formation wavefield information. At the same time, acoustic logging has low-frequency drift, and the obtained velocity information has errors, which significantly affects the accuracy of velocity modeling in seismic processing.

[0003] For exploration and development in deep and ultra-deep complex zones, the most commonly used methods in the industry are VSP and acoustic logging methods based on conventional geophones. VSP methods can provide accurate velocity and corridor calibration, offering an effective technique and means for oil and gas reservoir prediction. However, the downhole instruments in these methods are subject to significant temperature and pressure limitations, which can affect instrument performance in high-temperature and high-pressure zones, making it impossible to directly obtain accurate target zone information. Furthermore, their reliability is significantly impacted by the accuracy of seismic data processing. With the recent maturation of distributed fiber-optic sensing (optical fiber) technology, fiber-optic VSP seismic data with higher spatial sampling rates and improved consistency can be obtained, largely unrestricted by well temperature and pressure. This data can obtain accurate geophysical information in both shallow and deep complex zones, providing parameters for well-drive surface seismic processing, improving the quantification of seismic processing parameters, and enabling high-precision prediction of near-well reservoir development, providing valuable guidance for refined oil and gas exploration and development. Summary of the Invention

[0004] To solve the above technical problems, the present invention proposes a fiber-optic downhole seismic exploration method for "double-complex" areas, which collects, processes and interprets surface seismic data and medium-deep seismic data respectively, providing an effective technical means for the exploration and development of oil and gas reservoirs in complex structural areas.

[0005] The technical solution adopted by the present invention is: a fiber-optic well seismic exploration method for "double-complex" areas, comprising:

[0006] S1. Determine a joint acquisition plan for shallow and medium-deep seismic data; the joint plan specifically includes: for shallow seismic data, a lightweight seismic source is used at the wellhead for excitation, and optical fiber is used in the well to receive the data; for medium-deep seismic data, an optical fiber is laid into a large wellbore, a controllable vibrator is used on the surface for excitation, and optical fiber is used in the well to receive the data;

[0007] S2, performing acquisition using the combined acquisition scheme of step S1 to obtain surface fiber optic seismic data and mid-deep fiber optic well seismic data;

[0008] S3. Preprocessing the surface fiber optic seismic data and the mid-deep fiber optic well seismic data to obtain VSP data; the preprocessing includes: data decoding, noise suppression, first arrival picking, and consistency joint processing;

[0009] S4. Based on the first arrivals picked up by the surface fiber optic seismic data, the time-depth relationship, layer velocity, and average velocity of the stratum are calculated, thereby establishing a velocity model of the lateral surface structure in the complex area;

[0010] S5. Based on the combined data processed in step S3 and the surface structure velocity model established in step S4, fiber-optic well seismic data processing is performed, including amplitude compensation, wavefield separation, deconvolution, NMO, and corridor stacking processing, to obtain NMO and corridor stacking profile data for calibration and reservoir analysis;

[0011] S6. Calibration and reservoir prediction are performed using the time-depth relationship of the strata obtained in step S4 and the NMO and corridor stacked profile data obtained in step S5.

[0012] Beneficial effects of the present invention: The present invention proposes an exploration method for "double-complex" areas of surface and deep layers based on fiber-optic seismic data in wells, which collects, processes and interprets surface seismic data and medium-deep seismic data respectively, providing an effective technical means for the exploration and development of oil and gas reservoirs in complex structural areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The surface optical fiber deep micro-logging data and the medium-deep optical fiber well seismic data obtained by field acquisition of the present invention;

[0014] Among them, (a) is the surface optical fiber deep micro-logging data, and (b) is the medium-deep optical fiber well seismic data.

[0015] Figure 2 This is the process of processing seismic data in optical fiber wells according to the present invention.

[0016] Figure 3 The thickness and velocity changes of special lithology in complex surface areas obtained by the present invention.

[0017] Figure 4 The velocity plane map of special lithology in complex surface areas obtained by the present invention based on fiber optic deep micro-logging data;

[0018] Among them, (a) is the thickness contour map of low-velocity conglomerate, and (b) is the velocity contour map of low-velocity conglomerate.

[0019] Figure 5 The present invention is based on a bridge calibration diagram of seismic data in optical fiber wells. DETAILED DESCRIPTION

[0020] The present invention utilizes high-density fiber-optic seismic data preprocessing to obtain reliable deep micro-logging data and fiber-optic VSP data. This data extracts velocity and thickness information from shallow, complex zones, as well as geophysical parameters and reservoir information from mid- to deep-layer complex zones. This allows for analysis of the velocity and thickness of shallow conglomerates in different regions, and provides well-control parameters for mid- to deep-layer well-drive seismic processing. The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0021] 1) In response to the geological research needs of the "double complex" areas, different acquisition schemes were designed. A combination of optical fiber and lightweight seismic sources was used for the surface layer, and a combination of optical fiber and controllable seismic sources was used for the medium and deep layers, resulting in a joint acquisition scheme for optical fiber seismic data for the surface and medium and deep layers.

[0022] The surface seismic data acquisition plan is to drill to the surface below the special lithology, use a light source for excitation within 10m from the wellhead, and receive the data through optical fiber in the well. During the on-site acquisition, the source output parameter test is carried out to determine the surface data acquisition parameters.

[0023] The medium-deep seismic data acquisition scheme is to lay optical fiber into a large borehole, use a controllable vibrator on the ground for excitation, and receive the data through the optical fiber in the well. During the field acquisition, acquisition parameter tests are conducted to determine the parameters for medium-deep data acquisition.

[0024] The joint acquisition scheme is as follows: since the light source of the surface acquisition scheme can be placed at the wellhead, more accurate surface velocity can be obtained; the light source excitation obtains surface seismic data, and the controllable source excitation obtains medium-deep seismic data; the two schemes are combined to obtain the seismic data finally used.

[0025] 2) Acquisition is performed according to the joint acquisition plan designed in step 1) to obtain high-quality surface fiber optic seismic data and mid-deep fiber optic well seismic data.

[0026] The surface optical fiber deep micro-logging data is vertical seismic profile data obtained by a surface seismic data acquisition scheme.

[0027] The medium-deep fiber optic well seismic data is vertical seismic profile data obtained by a medium-deep seismic data acquisition program.

[0028] Figure 1 (a) is the surface optical fiber deep micro-logging data, Figure 1 Middle (b) shows seismic data from a medium-deep fiber optic well. It can be seen that the first arrival is clear and accurate first arrivals can be picked up; the reflected wave energy in (b) is strong and the wave group characteristics are obvious.

[0029] like Figure 2 As shown, the processing process of surface fiber optic seismic data and mid-deep fiber optic well seismic data is given, which specifically includes steps 3)-6).

[0030] 3) Preprocessing the data from step 2) includes data decoding, noise suppression, first arrival picking, etc., and finally performing consistency joint processing to obtain preprocessed VSP data.

[0031] Optionally, noise suppression includes random noise suppression, optical cable coupling noise suppression, optical fiber data time synchronization noise suppression, optical fiber data DC drift noise suppression, etc.

[0032] The data decoding is to load the seismic data obtained from the field seismic instrument into the processing system and rearrange the data for subsequent processing.

[0033] The first arrival picking process uses a human-computer interaction amplification method to amplify the first arrival position to an appropriate size, ensuring that the error of the first arrival picking is within 1ms. The accuracy of the first arrival picking in this step is crucial for subsequent analysis.

[0034] In particular, when collecting mid- to deep-seated seismic data using vibroseis excitation, the well-source distance is typically around 100 meters. This can introduce errors when calculating surface velocities, necessitating joint processing with surface seismic data. Due to differences in excitation methods, the acquired data exhibit differences in amplitude, phase, and time difference. During this joint processing, time difference correction is performed based on surface fiber-optic deep micro-logging data, while amplitude consistency processing and phase conversion are performed based on mid- to deep-seated fiber-optic wellbore seismic data.

[0035] 4) Using the first arrivals of the surface seismic data collected in step 3), the time-depth relationship, interval velocity, and average velocity of the strata are calculated. The vertical thickness and velocity variations of specific lithologies in the complex area are analyzed. Surface seismic data from multiple wells is then used to establish a velocity and thickness model for the surface structure in the complex area. The thickness model obtained in this step is supported by surface seismic processing, which is not the focus of this invention and will not be elaborated on in detail.

[0036] Figure 3It can be seen that at the well point, the well enters low-velocity conglomerate at 78.4m with a velocity of 2699m / s, and enters high-velocity conglomerate at 223.5m with a velocity of 3033m / s.

[0037] Figure 4 Middle (a) is the contour map of low-velocity conglomerate thickness. The overall trend of low-velocity conglomerate thickness in the work area gradually becomes thinner from south to north. Figure 4 Middle (b) is the velocity contour map of low-speed conglomerate. The overall trend of the low-speed conglomerate velocity in the work area gradually decreases from south to north.

[0038] 5) Using the pre-processed joint seismic data in step 3), combined with the velocity model in step 4), joint seismic data processing is performed, including spherical diffusion compensation, wave field separation, deconvolution, NMO flattening, and corridor stacking processing, to obtain NMO and corridor stacking profile data for calibration and reservoir analysis; specifically:

[0039] Perform spherical diffusion compensation on the pre-processed joint seismic data to obtain compensated joint seismic data, so that the energy of the data from shallow to deep is reasonably compensated;

[0040] Perform wavefield separation on the compensated data to separate the downgoing waves from the upgoing waves to obtain the upgoing wavefield and the downgoing wavefield;

[0041] Extract the deconvolution operator on the downgoing wave field and perform deconvolution on the upgoing wave field to suppress multiple waves and improve the resolution;

[0042] Perform NMO flattening on the deconvolved upgoing waves to obtain a NMO flattened profile, and correct the one-way time to the two-way time for easy comparison with the ground seismic profile.

[0043] The dynamic correction flattened section is processed by corridor stacking to obtain the corridor stacking section, which is used for bridge calibration and reservoir analysis.

[0044] The combined seismic data is the combination of pre-processed surface optical fiber deep micro-logging data and mid-deep optical fiber well seismic data.

[0045] Optionally, deconvolution processing methods include predicted wavelet deconvolution and expected output wavelet deconvolution, etc., which can be selected based on the deconvolution effect.

[0046] Optionally, wavefield separation processing methods include median filtering, linear filtering, frequency-wavenumber (FK) filtering, etc. One method or a combination of methods is selected based on the data situation.

[0047] 6) Oil and gas reservoir prediction:

[0048] Using the VSP time-depth relationship data obtained in step 4) and the dynamic correction flattened profile and corridor stack profile data obtained in step 5), combined with acoustic logging data, calibration and reservoir prediction are performed. Based on the fine horizon calibration, reservoir velocity changes and seismic reflection characteristics are analyzed to provide data support for oil and gas field trap evaluation.

[0049] Figure 5 This is a bridge calibration diagram of fiber-optic VSP data. The upper part shows the depth-domain logging data and depth-domain corridor, the lower left side shows the NMO profile of the VSP data, the middle part shows the time-domain corridor, and the right side shows the surface seismic profile through the well. Through joint calibration, the reflection characteristics of each geological layer are finely calibrated, indicating the development location of the reservoir.

[0050] Those skilled in the art will appreciate that the embodiments described herein are intended to aid understanding of 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, and the like made within the spirit and principles of the present invention are intended to be included within the scope of the claims.

Claims

1. A fiber-optic downhole seismic exploration method for "double-complex" areas, characterized by: include: S1. Determine a joint acquisition plan for shallow and medium-deep seismic data; the joint acquisition plan specifically includes: for shallow seismic data, a lightweight seismic source is used at the wellhead for excitation, and optical fiber is used in the well to receive the data; for medium-deep seismic data, an optical fiber is laid into a large wellbore, a controllable vibrator is used on the surface for excitation, and optical fiber is used in the well to receive the data; S2, performing acquisition using the combined acquisition scheme of step S1 to obtain surface fiber optic seismic data and mid-deep fiber optic well seismic data; S3. Preprocessing the surface fiber optic seismic data and the mid-deep fiber optic well seismic data to obtain VSP data; the preprocessing includes: data decoding, noise suppression, first arrival picking, and consistency joint processing; S4. Based on the first arrivals picked up from the surface fiber optic seismic data, the time-depth relationship, layer velocity, and average velocity of the formation are calculated to establish the lateral surface structure velocity in the complex area; the consistency joint processing described in step S3 specifically includes: performing time difference correction processing based on the surface fiber optic deep micro-logging data, and performing amplitude consistency processing and phase conversion processing based on the medium-deep fiber optic well seismic data; S5. Based on the combined data processed in step S3 and the surface structure velocity model established in step S4, fiber-optic well seismic data processing is performed, including amplitude compensation, wavefield separation, deconvolution, NMO, and corridor stacking processing, to obtain NMO and corridor stacking profile data for calibration and reservoir analysis; S6. Calibration and reservoir prediction are performed using the time-depth relationship of the strata obtained in step S4 and the NMO and corridor stacked profile data obtained in step S5.

2. The optical fiber downhole seismic exploration method for "double complex" areas according to claim 1, characterized in that: For shallow seismic data, the well is drilled to the surface below the special lithology, and a light source is used for excitation within 10m from the wellhead, and the optical fiber in the well is used for reception.

3. The optical fiber downhole seismic exploration method for "double complex" areas according to claim 1, characterized in that: The surface fiber optic seismic data described in step S2 is: vertical seismic profile data obtained by the surface seismic data acquisition scheme; The medium-deep fiber optic well seismic data is vertical seismic profile data obtained by the medium-deep seismic data acquisition program.

4. The optical fiber downhole seismic exploration method for "double complex" areas according to claim 3, characterized in that: Step S4 is specifically as follows: using the first arrival of the surface seismic data picked up in step S3, calculate the time-depth relationship, layer velocity, and average velocity of the formation, analyze the vertical velocity changes of special lithologies in complex areas, and use multi-well surface seismic data to establish the horizontal surface structure velocity in complex areas.

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