Compact sandstone thin layer characterization method based on Newton transient extraction transformation

Abstract

The invention discloses a compact sandstone thin layer characterization method based on Newton transient extraction transformation, and the method comprises the steps: constructing a new Newton group delay estimation formula according to the combination of the property of short-time Fourier transform and a Newton algorithm for the first time; more concentrated time-frequency characterization can be realized through Newton instant extraction transformation. Compared with previous transient extraction transformation, the method has the advantages that time positioning can be obtained more accurately, geologic structure features can be effectively depicted in compact sandstone thin layer characterization, and stratum boundaries can be identified.

Description

Technical Field

[0001] The invention relates to an oil and gas geophysical signal processing method, and in particular to a compact sandstone thin layer characterization method based on Newton transient extraction transformation. Background Art

[0002] As the key and difficult point in the exploration and development of tight sandstone gas, tight sandstone reservoirs have many complex characteristics, such as thin and narrow vertical structure, dispersed development, poor physical properties, strong heterogeneity, and uneven distribution of gas and water. These complex characteristics make the thin-layer seismic reflection signal affected by factors such as single-layer thickness, physical property differences, and fluids, which limits the effectiveness of traditional seismic exploration processing and interpretation methods.

[0003] Time-frequency analysis is an important tool for studying non-stationary seismic signals. It can effectively describe the change law of seismic signal frequency over time, thereby realizing the fine analysis of seismic signals. The instantaneous frequency of the pulse-like signal is almost perpendicular to the time axis in the time-frequency plane, resulting in a very large chirp rate of the signal. The transient extraction transform (TET) can produce a time-frequency characterization result (TFR) with concentrated energy for the pulse-like signal by only extracting the time-frequency coefficients on the group delay (GD) trajectory, which can achieve more accurate time positioning. However, due to the error in the GD estimation formula of TET, there is a situation in which one frequency point corresponds to multiple time points in the actual application of TET, resulting in inaccurate time positioning. To solve this problem, it is necessary to newly define and restrict the group delay estimation formula to obtain more accurate reservoir time response characteristics. Summary of the invention

[0004] In order to solve the interference problem caused by errors in the group delay estimation formula of the transient extraction transformation, the present invention proposes a dense sandstone thin layer characterization method based on Newton transient extraction transformation.

[0005] The present invention provides a method for characterizing a dense sandstone thin layer based on Newton transient extraction transformation, the method comprising:

[0006] Input the seismic signal to be analyzed and perform short-time Fourier transform to obtain the time-frequency result of the signal;

[0007] According to the obtained short-time Fourier result of the signal, the group delay estimation formula of the signal is calculated;

[0008] Based on the short-time Fourier transform properties and Newton algorithm, the signal Newton group delay estimation formula is obtained;

[0009] The extraction operator is defined according to the extraction principle, and the Newton transient extraction transform of the seismic data is calculated. The single-frequency profile is obtained according to the feature extraction of the single frequency.

[0010] Optionally, the input seismic signal to be analyzed is subjected to short-time Fourier transform to obtain a time-frequency result of the signal, including:

[0011] Input the formation signal x(t) to be analyzed, and the formula corresponding to the short-time Fourier transform V(t,ω) is:

[0012]

[0013] in is the imaginary unit of the complex number, ω is the frequency (ω≠0), t is the time, τ is the movement of the window center during the movement process, controls the movement of the window center in the t direction, and g(t) is the Gaussian window function, which is in the form of:

[0014]

[0015] Where δ represents the standard deviation of the Gaussian window in the t direction.

[0016] Optionally, the group delay estimation formula of the signal is calculated based on the short-time Fourier result of the obtained signal: The formula is:

[0017]

[0018] Among them, Re(·) and They represent the real part of a complex number and the first-order partial derivative of (·) with respect to ω.

[0019] Optionally, the signal Newton group delay estimation formula is obtained based on the short-time Fourier transform property and the Newton algorithm: The formula is:

[0020]

[0021] in It means to find the first-order partial derivative of (·) with respect to t.

[0022] Optionally, an extraction operator is defined according to the extraction principle, and the Newton transient extraction transform of the seismic data is calculated and extracted according to the characteristics of the single frequency to obtain a single frequency profile, including the following steps:

[0023] a. According to the extraction principle, the extraction operator NTEO is defined as:

[0024]

[0025] where δ(·) represents the Dirac function.

[0026] b. According to the extraction principle, the Newton transient extraction transform NTET(t,ω) of seismic data is constructed as follows:

[0027]

[0028] By extracting the features of a certain frequency from the calculation results, a single-frequency profile can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the prior art solutions and advantages, the following briefly introduces the drawings required to be used in the embodiments or the prior art descriptions:

[0030] Figure 1 It is a flow chart of a method for characterizing a thin layer of dense sandstone based on Newton transient extraction transformation of the present invention;

[0031] Figure 2 This is a seismic thin-layer profile of a tight sandstone gas field in western Sichuan, China;

[0032] Figure 3 The results of processing tight sandstone gas fields by transient synchronous extraction transformation: (a) single-frequency profile with extraction frequency of 30 Hz, (b) single-frequency profile with extraction frequency of 48 Hz;

[0033] Figure 4 The results of processing a tight sandstone gas field using the method of the present invention are as follows: (a) a single-frequency profile with an extraction frequency of 30 Hz, and (b) a single-frequency profile with an extraction frequency of 48 Hz. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with the accompanying drawings.

[0035] Example 1: See Figure 1 , showing the process of some embodiments of a method for characterizing a thin layer of dense sandstone based on Newton transient extraction transformation, including the following steps:

[0036] Step S1: input the seismic signal to be analyzed and perform short-time Fourier transform to obtain the time-frequency result of the signal;

[0037] As an example, this step may include the following steps:

[0038] The first step is to input the formation signal x(t) to be analyzed, where t is time;

[0039] In the second step, the Gaussian window function g(t) is used to directly process the seismic profile to obtain the short-time Fourier transform V(t,ω) of the signal:

[0040]

[0041] in is the imaginary unit of the complex number, ω is the frequency (ω≠0), τ is the movement of the window center during the movement process, controls the movement of the window center in the t direction, and g(t) is the Gaussian window function, which is in the form of:

[0042]

[0043] Where δ represents the standard deviation of the Gaussian window in the t direction.

[0044] Step S2 calculates the group delay estimation formula of the signal according to the short-time Fourier result of the obtained signal, and the formula corresponding to the group delay estimation formula of the signal is:

[0045]

[0046] Among them, Re(·) and They represent the real part of a complex number and the first-order partial derivative of (·) with respect to ω.

[0047] Step S3 calculates the signal Newton group delay estimation formula based on the short-time Fourier transform property and the Newton algorithm as follows:

[0048]

[0049] in It means to find the first-order partial derivative of (·) with respect to t.

[0050] Step S4 defines an extraction operator according to the extraction principle and calculates the Newton transient extraction transform of the seismic data, and obtains a single frequency profile according to the feature extraction of the single frequency.

[0051] As an example, this step may include the following steps:

[0052] The first step is to define the extraction operator NTEO according to the extraction principle:

[0053]

[0054] where δ(·) represents the Dirac function.

[0055] In the second step, the Newton transient extraction transform NTET(t,ω) of seismic data is constructed according to the extraction principle:

[0056]

[0057] By extracting the features of a certain frequency from the calculation results, a single-frequency profile can be obtained.

[0058] Embodiment 2:

[0059] A seismic thin-layer section of a tight sandstone gas field in western Sichuan (see Figure 2), set the number of sampling points to 1126. When using transient extraction transformation to process the single-frequency profiles of 30Hz and 48Hz, although it shows a certain level of hierarchy, the boundary characterization is not clear enough (see Figure 3 (a)(b)). In contrast, the seismic profile processed by the method of the present invention at the same frequency better maintains the continuity of the data, provides more accurate time positioning, clear stratigraphic structure, and retains more stratigraphic details, and the result appears to be more reasonable (see Figure 4 (a)(b)).

[0060] The above examples are only used to illustrate the present invention, and the various implementation steps of the method may be adjusted. Any equivalent transformation and improvement based on the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A characterization method for thin layers of dense sandstone based on Newton transient extraction transformation, characterized in that: The following steps are involved: Input the seismic signal to be analyzed and perform short-time Fourier transform to obtain the time-frequency result of the signal; The group delay estimation formula of the signal is calculated based on the short-time Fourier result of the obtained signal; Based on the short-time Fourier transform properties and Newton algorithm, the signal Newton group delay estimation formula is obtained; According to the extraction principle, the extraction operator is defined and the Newton transient extraction transform of the seismic data is calculated. According to the feature extraction of single frequency, the single frequency profile is obtained.

2. The method according to claim 1, characterized in that: Input the seismic signal to be analyzed and perform short-time Fourier transform to obtain the time-frequency results of the signal, including: Input the formation signal x(t) to be analyzed, and the short-time Fourier transform V(t,ω) obtained is: in is the imaginary unit of the complex number, ω is the frequency (ω≠0), t is the time, τ is the movement of the window center during the movement process, controls the movement of the window center in the t direction, and g(t) is the Gaussian window function, which is in the form of: Where δ represents the standard deviation of the Gaussian window in the t direction.

3. The method according to claim 1, characterized in that The group delay estimation formula of the signal is calculated based on the short-time Fourier result of the signal The formula is: Among them, Re(·) and They represent the real part of a complex number and the first-order partial derivative of (·) with respect to ω.

4. The method according to claim 1, characterized in that: Based on the short-time Fourier transform properties and Newton algorithm, the signal Newton group delay estimation formula is obtained The formula is: in It means to find the first-order partial derivative of (·) with respect to t.

5. The method according to claim 1, characterized in that According to the extraction principle, the extraction operator is defined and the Newton transient extraction transform of the seismic data is calculated. According to the feature extraction of the single frequency, the single frequency profile is obtained, which includes the following steps: a. According to the extraction principle, the extraction operator NTEO is defined as: where δ(·) represents the Dirac function; b. According to the extraction principle, the Newton transient extraction transform NTET(t,ω) of seismic data is constructed as follows: By extracting the features of a certain frequency from the calculation results, a single-frequency profile can be obtained.

Images