A stable method for brittle earthquake prediction in HTI medium

Abstract

The application provides a stable brittle seismic prediction method for HTI medium, which comprises the following steps: inputting azimuth time domain seismic data of multiple angles, seismic parameters and an initial model of three anisotropy parameters; constructing an azimuth amplitude difference forward operator, establishing an azimuth amplitude difference inversion objective function, and realizing stable inversion of the three anisotropy parameters; selecting seismic data of three incident angles of a certain azimuth, adopting an isotropic YPD equation to realize inversion of the seismic parameters, and calculating a brittle indicator factor under the isotropic assumption; constructing a display expression between the brittle indicator factor under the isotropic assumption and the brittle indicator factor under the HTI assumption and the anisotropy parameters, and calculating the brittle indicator factor of the HTI medium. The brittle indicator factor of the HTI medium is more stably predicted.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas exploration and development, and particularly relates to a stable method for predicting brittleness of HTI medium. BACKGROUND

[0002] The high-angle fractures of unconventional oil and gas reservoirs make them exhibit weak azimuthal anisotropy on seismic, which can be approximated as HTI medium. The low natural productivity of the reservoirs requires fracturing modification, and brittleness is one of the important indicators for evaluating the fracturability of the reservoirs. Generally, the ratio of Young's modulus to Poisson's ratio is used as a brittleness indicator on seismic. However, the current seismic prediction of brittleness of HTI medium mainly stays in the extension of conventional methods, and the stability of brittleness prediction is poor. Therefore, it is of great significance to design a more stable brittleness prediction method suitable for HTI medium for evaluating the fracturability of unconventional oil and gas reservoirs. The present application proposes a stable method for predicting brittleness of HTI medium to more reasonably estimate the brittleness indicator of HTI medium.

[0003] The existing seismic prediction method of brittleness of HTI medium is mainly based on the AVO inversion theory of HTI medium, which simultaneously inverts six elastic and anisotropic parameters such as Young's modulus and Poisson's ratio by using anisotropic YPD equation. Finally, the brittleness indicator is calculated by using the inversion results of Young's modulus and Poisson's ratio. The disadvantage is that the six-parameter inversion has strong multi-solution and poor stability, and the errors of Young's modulus and Poisson's ratio obtained when the signal-to-noise ratio of seismic data is low are large, thereby affecting the prediction of brittleness. Unlike the existing method, the present application constructs a display expression of the brittleness indicator of HTI medium based on the assumption of isotropy by comparing the similarity of the reflection coefficient equation of HTI medium and the reflection coefficient equation of isotropic medium. In this way, the Young's modulus and Poisson's ratio under the assumption of isotropy can be obtained by performing three-parameter seismic inversion in a specific direction based on the isotropic YPD equation, and three anisotropic parameters can be obtained by using the azimuthal amplitude difference inversion, thereby realizing the prediction of brittleness.

[0004] The disadvantage of the prior art is that when performing seismic inversion of HTI medium, six parameters need to be inverted at the same time, which increases the condition number of the eye operator, enhances the multi-solution of the inversion result, reduces the stability, and further reduces the prediction accuracy of Young's modulus and Poisson's ratio, thereby affecting the reliability of the prediction of brittleness. SUMMARY

[0005] In view of the above problems, the present application is proposed to provide a stable method for predicting brittleness of HTI medium to overcome the above problems or at least partially solve the above problems.

[0006] According to one aspect of the present application, a stable method for predicting brittleness of HTI medium is provided, and the stable method comprises:

[0007] input multiple azimuth time domain seismic data of angles, seismic parameters and initial model of three anisotropy parameters;

[0008] construct azimuth amplitude difference forward operator, establish azimuth amplitude difference inversion objective function, realize stable inversion of three anisotropy parameters;

[0009] select seismic data of three incident angles of a certain azimuth, realize inversion of the seismic parameters by using isotropic YPD equation, and calculate brittle indicator factor under isotropic assumption;

[0010] construct explicit expression between brittle indicator factor under isotropic assumption and brittle indicator factor under HTI assumption and anisotropy parameters, and calculate brittle indicator factor of HTI medium.

[0011] Optionally, the seismic parameters specifically include: Young's modulus, Poisson's ratio, density.

[0012] Optionally, the multiple azimuth time domain seismic data of angles specifically include: azimuth angle 30° incident angle 4.5°, azimuth angle 30° incident angle 13.5°, azimuth angle 30° incident angle 22.5°, azimuth angle 150° incident angle 4.5°, azimuth angle 150° incident angle 13.5° and azimuth angle 150° incident angle 22.5°.

[0013] Optionally, the amplitude difference inversion objective function of the HTI medium is:

[0014] The amplitude difference inversion objective function of the HTI medium is min J = || Gm - d || 2 + λ || m - m0 || 2 (1)

[0015] solving formula (1) obtains anisotropy parameter estimation result

[0016]

[0017] λ is model constraint weight, which is given according to signal-to-noise ratio of seismic data, is initial model of anisotropy parameters, m = (δ (V) , ε (V) , γ (V) ) T is prediction result of anisotropy parameters, G is azimuth amplitude difference forward operator, and d is azimuth amplitude difference seismic data;

[0018]

[0019] θ i is incident angle, is azimuth angle, is incident angle θ i , and azimuth angle is seismic data.

[0020] Optionally, the building azimuthal amplitude difference forward operator specifically comprises:

[0021] The azimuthal amplitude difference forward operator is

[0022]

[0023] W is a wavelet matrix, I is a unit matrix, and D is a difference matrix

[0024]

[0025]

[0026]

[0027]

[0028] wherein k is the square of the ratio of transverse wave velocity to longitudinal wave velocity.

[0029] Optionally, the seismic data of three incidence angles of a certain azimuth are selected, the inversion of the seismic parameter is realized by using the isotropic YPD equation, and specifically comprises:

[0030] The isotropic YPD equation is as follows:

[0031]

[0032] The estimation result is

[0033]

[0034] In formula (6), d ISO is seismic data of three incidence angles of a certain azimuth, λ ISO is a model constraint weight of Young's modulus, Poisson's ratio and density, is an initial model of Young's modulus, Poisson's ratio and density, G ISO is a forward operator, is an estimation result of Young's modulus under the isotropic assumption, is an estimation result of Poisson's ratio under the isotropic assumption, and ρ is an estimation result of density under the isotropic assumption, and Δ is a difference, indicating that the elastic parameters of the lower medium are reduced from the elastic parameters of the upper medium.

[0035]

[0036]

[0037]

[0038]

[0039]

[0040] where k is the square of the ratio of transverse wave velocity to longitudinal wave velocity.

[0041] Optionally, the calculating the isotropic assumed brittleness indicator specifically includes:

[0042] The isotropic assumed brittleness indicator is

[0043] Optionally, the constructing the display expression between the isotropic assumed brittleness indicator and the HTI assumed brittleness indicator and the anisotropy parameter specifically includes:

[0044] Ignoring the influence of the anisotropy parameter at large angles, let the sin of the anisotropy parameter be 2 θtan 2 θ=0

[0045] The YPD equation of the HTI medium

[0046]

[0047] Further arranging formula (10) obtains

[0048]

[0049] where

[0050]

[0051]

[0052] where k is the square of the ratio of transverse wave velocity to longitudinal wave velocity, E is the Young's modulus of the HTI assumption, and σ is the Poisson's ratio of the HTI assumption.

[0053] Optionally, the calculating the brittleness indicator of the HTI medium specifically includes:

[0054]

[0055] Optionally, the initial model of the seismic parameters and the three anisotropy parameters further includes wavelet data.

[0056] The application provides a stable method for predicting brittleness of HTI medium, which comprises the following steps: inputting azimuth time-domain seismic data of multiple angles, initial models of seismic parameters and three anisotropy parameters; constructing a forward operator of azimuth amplitude difference, establishing an inversion objective function of azimuth amplitude difference, and realizing stable inversion of the three anisotropy parameters; selecting seismic data of three incident angles of a certain azimuth, realizing inversion of the seismic parameters by using an isotropic YPD equation, and calculating a brittleness indicator under the assumption of isotropy; constructing a display expression between the brittleness indicator under the assumption of isotropy and the brittleness indicator under the assumption of HTI and the anisotropy parameters, and calculating the brittleness indicator of HTI medium.

[0057] The above description is only a summary of the technical scheme of the application, in order to more clearly understand the technical means of the application, the content of the specification can be implemented, and in order to make the above and other purposes, characteristics and advantages of the application more obvious and easy to understand, the following specific embodiments of the application are described. BRIEF DESCRIPTION OF DRAWINGS

[0058] In order to more clearly illustrate the technical scheme of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0059] Figure 1 A flow chart of a stable method for predicting brittleness of HTI medium is provided for the embodiments of the application.

[0060] Figure 2 A predicted result graph of Young's modulus of seismic data with an azimuth angle of 150° is provided for the embodiments of the application.

[0061] Figure 3 A predicted result graph of Poisson's ratio of seismic data with an azimuth angle of 150° is provided for the embodiments of the application.

[0062] Figure 4 A predicted result of density of seismic data with an azimuth angle of 150° is provided for the embodiments of the application.

[0063] Figure 5 A predicted result graph of a brittleness indicator of seismic data with an azimuth angle of 150° is provided for the embodiments of the application.

[0064] Figure 6 A predicted result graph of a brittleness indicator of HTI medium is provided for the embodiments of the application. DETAILED DESCRIPTION

[0065] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0066] The terms "comprising" and "having," and any variations thereof, in the specification, embodiments, claims, and drawings of this invention are intended to cover non-exclusive inclusion, such as including a series of steps or units.

[0067] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0068] like Figure 1 As shown, the first step is to input azimuth time-domain seismic data from six angles, along with Young's modulus, Poisson's ratio, density, and three anisotropy parameters to obtain the initial model and wavelet data. The six angles selected for this study are azimuth 30° with an incident angle of 4.5°, azimuth 30° with an incident angle of 13.5°, azimuth 30° with an incident angle of 22.5°, azimuth 150° with an incident angle of 4.5°, azimuth 150° with an incident angle of 13.5°, and azimuth 150° with an incident angle of 22.5°.

[0069] Step 2: Construct the forward modeling operator for azimuth amplitude difference, establish the objective function for azimuth amplitude difference inversion, and achieve stable inversion of the three anisotropic parameters.

[0070] The objective function for HTI medium amplitude difference inversion is:

[0071] minJ=||Gm-d||2+λ||m-m0||2 (1)

[0072] Solving (1) yields the anisotropic parameter estimation results.

[0073]

[0074] λ represents the model constraint weights, which are given based on the signal-to-noise ratio of the seismic data. For the initial model of anisotropic parameters, m = (δ (V) ,ε (V) ,γ (V) ) T Here are the anisotropy parameter prediction results, where G is the azimuth amplitude difference forward modeling operator and d is the azimuth amplitude difference seismic data.

[0075]

[0076] θ i For the angle of incidence, for azimuth angle, for incident angle θ i , azimuth angle is seismic data.

[0077] azimuth amplitude difference forward operator is

[0078]

[0079] W is wavelet matrix, I is unit matrix, D is difference matrix

[0080]

[0081]

[0082]

[0083]

[0084] wherein k is the square of the ratio of transverse wave velocity to longitudinal wave velocity.

[0085] Third step: select the seismic data of three incident angles of a certain azimuth, realize the three-parameter inversion of Young's modulus, Poisson's ratio and density by using isotropic YPD equation, and calculate the brittle indicator factor of isotropic assumption.

[0086] At this time, the isotropic YPD equation is as follows:

[0087]

[0088] The estimation result is

[0089]

[0090] In formula (6), d ISO is the seismic data of three incident angles of a certain azimuth, λ ISO is the model constraint weight of Young's modulus, Poisson's ratio and density, is the initial model of Young's modulus, Poisson's ratio and density, G ISO is the forward operator, is the estimation result of Young's modulus under isotropic assumption, is the estimation result of Poisson's ratio under isotropic assumption, is the estimation result of density under isotropic assumption, Δ is difference, which represents the elastic parameters of lower medium minus the elastic parameters of upper medium.

[0091]

[0092]

[0093]

[0094]

[0095] So, the brittle indicator factor under isotropic assumption is

[0096] Step 4: Establish the explicit expression between the brittle indicator factor under isotropic assumption and the anisotropic parameters, and calculate the brittle indicator factor of HTI medium.

[0097] The YPD equation of HTI medium can be written as

[0098]

[0099] Here, the influence of anisotropic parameters at large angles is ignored, and sin 2 θtan 2 θ=0

[0100] So it becomes

[0101]

[0102] Further rearranging equation (10) gives

[0103]

[0104] Where

[0105]

[0106]

[0107] So

[0108]

[0109] Thus, the brittle indicator factor of HTI medium can be calculated. Here, k is the square of the ratio of transverse wave velocity to longitudinal wave velocity.

[0110] Figures 2-4 are the inversion results of anisotropic parameters δ (V) , ε (V) and γ (V) , respectively, Figure 5 is the brittle indicator factor under isotropic assumption predicted based on three angle seismic data with azimuth of 150° Figure 6 is the brittle indicator factor of HTI medium predicted by the method of the present case.

[0111] Beneficial effects: the purpose of the present application is to establish the explicit expression of the brittle indicator under isotropic assumption and the brittle indicator and anisotropic parameters under HTI assumption by using the similarity of YPD equation under HTI assumption and YPD equation under isotropic assumption, so as to convert the conventional six-parameter inversion into twice three-parameter inversion to avoid the instability brought by six-parameter inversion. In order to improve the stability of the brittle indicator of HTI medium, the present application adopts the strategy of azimuthal amplitude difference inversion to predict three anisotropic parameters; then based on YPD equation, the prestack three-parameter inversion is realized by using the seismic data of three angles in a certain azimuth to calculate the Young's modulus and Poisson's ratio and thus the brittle indicator under isotropic assumption; finally, the explicit expression of the brittle indicator under isotropic assumption and the brittle indicator and anisotropic parameters under anisotropic assumption is established to obtain the brittle indicator of HTI medium. The method of the present application can more stably predict the brittle indicator of HTI medium.

[0112] The above detailed description of the embodiments of the present application, the purpose, technical solutions and beneficial effects of the present application are further described in detail, and it should be understood that the above is only the specific embodiment of the present application and is not used to limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A brittle seismic prediction stabilization method for HTI medium, characterized in that, The method comprises: inputting azimuthal time-domain seismic data of multiple angles, seismic parameters and an initial model of three anisotropy parameters; The azimuthal amplitude difference forward operator is constructed, the azimuthal amplitude difference inversion objective function is established, and stable inversion of three anisotropy parameters δ (V) , ε (V) , and γ (V) is realized. selecting seismic data of three incident angles of a certain azimuth, inverting the seismic parameters by using an isotropic YPD equation, and calculating a brittle indicator factor under the isotropic assumption; constructing an explicit expression between the brittle indicator factor under the isotropic assumption and the brittle indicator factor and the anisotropy parameters under the HTI assumption, and calculating the brittle indicator factor of the HTI medium; Ignoring the influence of anisotropy parameter at large angles, let the anisotropy parameter sin 2 θtan 2 θ = 0; the YPD equation of the HTI medium further arranging formula (10) to obtain wherein, Eiso is the isotropic Young's modulus estimate, Piso is the isotropic Poisson's ratio estimate; wherein k is the square of the ratio of transverse wave velocity to longitudinal wave velocity, E is the Young's modulus under the HTI assumption, and σ is the Poisson's ratio under the HTI assumption; the calculation of the brittle indicator factor of the HTI medium specifically comprises: where BI is a brittleness indicator for HTI media, Isotropic assumed brittleness indicator.

2. The brittle seismic prediction stabilization method for HTI medium according to claim 1, characterized in that, the seismic parameters specifically comprise the Young's modulus, the Poisson's ratio and the density.

3. The brittle seismic prediction stabilization method for HTI medium according to claim 1, characterized in that, the azimuthal time-domain seismic data of multiple angles specifically comprise azimuth 30° incident angle 4.5°, azimuth 30° incident angle 13.5°, azimuth 30° incident angle 22.5°, azimuth 150° incident angle 4.5°, azimuth 150° incident angle 13.5° and azimuth 150° incident angle 22.5°.

4. The brittle seismic prediction stabilization method for HTI medium according to claim 1, characterized in that, the azimuthal amplitude difference inversion objective function of the HTI medium is: min J=||Gm-d||2+λ||m-m0||2 (1) solving formula (1) to obtain anisotropy parameter estimation results λ is the model constraint weight, which is given according to the signal-to-noise ratio of seismic data, is the initial model of anisotropy parameters, m = (δ (V) , ε (V) , γ (V) ) T is the prediction result of anisotropy parameters, G is the azimuthal amplitude difference forward operator, d is the azimuthal amplitude difference seismic data, and I is the unit matrix. θ i is the angle of incidence, is the azimuth angle, is the angle of incidence is θ i , the azimuth angle is seismic data.

5. The brittle seismic prediction stabilization method for HTI medium according to claim 4, characterized in that, the construction of the azimuthal amplitude difference forward operator specifically comprises: the azimuthal amplitude difference forward operator is W is a wavelet matrix, I is a unit matrix, and D is a difference matrix wherein k is the square of the ratio of transverse wave velocity to longitudinal wave velocity.

6. The brittle seismic prediction stabilization method for HTI medium according to claim 5, characterized in that, the selection of the seismic data of three incident angles of a certain azimuth, and the inversion of the seismic parameters by using the isotropic YPD equation specifically comprises: the isotropic YPD equation is as follows: the estimation results are d in formula (6) ISO is the seismic data of three incidence angles in a certain direction, λ ISO is the model constraint weight of Young's modulus, Poisson's ratio and density, is the initial model of Young's modulus, Poisson's ratio and density, G ISO is the forward operator, is the Young's modulus estimation result under the assumption of isotropy, is the Poisson's ratio estimation result under the assumption of isotropy, is the density estimation result under the assumption of isotropy, Δ is the difference, indicating the elastic parameters of the lower medium minus the elastic parameters of the upper layer. where θ i is the angle of incidence and k is the square of the ratio of transverse to longitudinal wave velocities.

7. The HTI medium brittleness earthquake prediction stability method according to claim 6, characterized in that, the calculation of the brittle indicator factor under the isotropic assumption specifically comprises: The isotropic assumed brittleness indicator factor is 8. The HTI medium brittleness earthquake prediction stability method according to claim 1, characterized in that, the initial model of the seismic parameters and the three anisotropy parameters further comprises wavelet data.

Images