Deepwater ultra-shallow natural gas reservoir rock physical shear wave velocity prediction method

Abstract

The invention relates to the technical field of geological exploration, in particular to a deep water ultra-shallow natural gas reservoir rock physical shear wave velocity prediction method, which comprises the following steps: calculating the equivalent bulk modulus, shear modulus and density of a mixed matrix of various minerals according to the shale content; calculating the bulk modulus and the shear modulus of the skeleton; calculating the bulk modulus and the shear modulus of the saturated rock through the model, and calculating the density of the saturated rock through the density of the rock matrix; distributing longitudinal and transverse velocities in a suspension state and a bearing state, and calculating equivalent longitudinal and transverse wave velocities; taking the longitudinal wave velocity as a known condition, and constructing an inversion objective function by using the equivalent longitudinal wave velocity; comparing the actual longitudinal wave speed with the calculated longitudinal wave speed; and realizing nonlinear inversion of the shear wave velocity according to an algorithm, and obtaining the shear wave velocity of the work area to be inverted. According to the method, rock physical models in a particle suspension state and a bearing state are considered at the same time, and shear wave velocity prediction and direct inversion of the shear wave velocity of the deepwater ultra-shallow natural gas reservoir are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of geological exploration, and more specifically, to a method for predicting the rock physical shear wave velocity of deep - water ultra - shallow natural gas reservoirs. Background Art

[0002] Deep - water ultra - shallow natural gas reservoirs generally have the characteristics of loose particles, high porosity and high permeability, and have important oil and gas exploration and development value. Rock physical shear wave velocity inversion is an important technical means for seismic data interpretation and oil and gas resource evaluation. Through rock physical modeling, physical property parameters (porosity, saturation and shale content) can be related to seismic P - and S - wave velocities, so as to realize the prediction of shear wave velocity using well - logging data. Generally speaking, seismic inversion is a non - linear optimization problem, that is, the relationship between seismic elastic parameters and physical property parameters is mostly a complex non - linear relationship. Inversion itself includes two key aspects: one is to construct an inversion solution equation using rock physical modeling methods; the other is to optimize and construct an optimization algorithm suitable for solving complex inversion problems.

[0003] In the prior art, there are methods to calculate the P - wave velocity of submarine sediments based on the equal - sphere particle contact model and Gassmann equation, and to predict the elastic parameters of marine sediments based on the particle contact model and equivalent medium theory. There are also methods to propose the bulk compliance factor and shear compliance factor based on the Biot theory of porous media to achieve the prediction of sediment velocity. However, the above - mentioned studies usually consider a single particle contact relationship, with limited application scope, and it is difficult to ensure the accuracy and rationality of predicting the rock physical shear wave velocity of deep - water ultra - shallow natural gas reservoirs. Summary of the Invention

[0004] In order to overcome the problem in the above - mentioned prior art that usually only a single particle contact relationship is considered to predict the sediment velocity, resulting in limited application scope and difficulty in ensuring the accuracy and rationality of predicting the rock physical shear wave velocity of deep - water ultra - shallow natural gas reservoirs, the present invention provides a method for predicting the rock physical shear wave velocity of deep - water ultra - shallow natural gas reservoirs.

[0005] To solve the above - mentioned technical problems, the technical solution adopted by the present invention is: a method for predicting the rock physical shear wave velocity of deep - water ultra - shallow natural gas reservoirs, the method comprising:

[0006] Calculating the equivalent bulk modulus, shear modulus and density of the matrix of a mixture of multiple minerals;

[0007] In the load - bearing state, according to the equivalent bulk modulus and shear modulus of the matrix, calculating the equivalent bulk modulus and shear modulus of the skeleton composed of closely arranged equal - sphere particles when the porosity is the critical porosity;

[0008] Calculate the shear modulus and bulk modulus of the rock skeleton based on the bulk modulus of the matrix, the bulk modulus of the skeleton, and the shear modulus of the skeleton;

[0009] Calculate the bulk modulus of the pore fluid according to the patchy partially saturated fluid-filled model;

[0010] Calculate the bulk modulus and shear modulus of the saturated rock based on the bulk modulus of the matrix, the bulk modulus of the rock skeleton, the shear modulus of the rock skeleton, and the bulk modulus of the pore fluid, and calculate the density of the saturated rock according to the fluid density and the density of the matrix;

[0011] Calculate the bulk modulus of the suspended sediment in the suspended state;

[0012] Calculate the P-wave and S-wave velocities in the suspended state according to the bulk modulus of the suspended sediment and the density of the saturated rock, and calculate the P-wave and S-wave velocities in the load-bearing state according to the bulk modulus of the saturated rock, the shear modulus of the saturated rock, and the density of the saturated rock;

[0013] According to the P-wave and S-wave velocities in the suspended state and the P-wave and S-wave velocities in the load-bearing state, introduce a loosening parameter to distribute the P-wave and S-wave velocities in the suspended state and the P-wave and S-wave velocities in the load-bearing state, and calculate the equivalent P-wave and S-wave velocities;

[0014] Construct an inversion objective function based on the equivalent P-wave and S-wave velocities and the actual measured P-wave velocity;

[0015] According to the inversion objective function, inversely calculate the S-wave velocity value of the predicted reservoir.

[0016] Preferably, calculate the bulk modulus K m , shear modulus μ m and density ρ m of the matrix of the multi-mineral mixture by the Voigt-Reuss-Hill average modulus estimation method;

[0017] K m = [(V sh K c + (1 - V sh )K q ) + (V sh / K c + (1 - V sh ) / K q ) -1 / 2

[0018] μ m = [(V sh μ c + (1 - Vsh ) μ q ) + (V sh / μ c + (1 - V sh ) / μ q ) -1 ) / 2

[0019] ρ m = V sh ρ c + (1 - V sh ) ρ q

[0020] Where V sh is the shale content, K c and K q are the bulk modulus values of the shale component and the sand component in the matrix component respectively, μ c and μ q are the shear modulus values of the shale component and the sand component in the matrix component respectively, ρ c and ρ q are the density values of the shale component and the sand component in the matrix component respectively.

[0021] Preferably, according to the equivalent bulk modulus K m of the matrix and the shear modulus μ m of the matrix, the equivalent bulk modulus K s of the skeleton composed of closely packed equal spherical particles and the shear modulus μ s of the skeleton when the porosity is the critical porosity are calculated through the Hertz-Mindlin model;

[0022]

[0023] Where n is the coordination number; φ c is the critical porosity value, which depends on the lithology and sedimentary environment and is given by the data of the work area; v m is the particle Poisson's ratio and v m = (3K m - 2μ m ) / (6K m + 2μ m ); P is the effective pressure, which depends on the depth.

[0024] Preferably, according to the equivalent bulk modulus K m of the matrix, the equivalent bulk modulus K s of the skeleton at the critical porosity, and the shear modulus μ s of the skeleton, the shear modulus μ dry of the rock skeleton and the bulk modulus K dry;

[0025]

[0026] and

[0027] Preferably, the equivalent bulk modulus of the pore fluid is calculated by the patch partial saturation fluid filling model;

[0028] K f =(K w -K hc )(1 - S hc ) e +K hc

[0029] where K f is the equivalent bulk modulus of the pore fluid, K w , K hc are the bulk moduli of brine and hydrocarbons (oil, gas) respectively, S hc = 1 - S w is the hydrocarbon fluid saturation, and e is an empirical constant term.

[0030] Preferably, according to the matrix bulk modulus, the bulk modulus of the rock skeleton, the shear modulus of the rock skeleton, and the equivalent bulk modulus of the pore fluid, the bulk modulus K Sat of the saturated rock is calculated by the Gassmann equation, and since the influence of the fluid on the shear modulus of the saturated rock is weak, the shear modulus μ Sat is approximately equal to the shear modulus of the dry rock;

[0031]

[0032] μ Sat = μ dry

[0033] The density ρ sat of the saturated rock is calculated based on the fluid density and the matrix density, and the fluid density is a constant;

[0034] ρ Sat = φρ f + (1 - φ)ρ m .

[0035] Preferably, in the suspended state, the equivalent bulk modulus K R of the suspended sediment is calculated by the Wood model,

[0036]

[0037] where φ is the porosity and K f is the fluid equivalent modulus.

[0038] Preferably, according to the density ρ of the saturated rock sat and the equivalent bulk modulus K of the floating sediment R calculate the P-wave and S-wave velocities in the suspended state. Since the fluid does not resist shear, the S-wave velocity is zero:

[0039]

[0040] V s1 = 0

[0041] According to the bulk modulus K of the saturated rock Sat , the shear modulus μ of the saturated rock Sat and the density ρ of the saturated rock sat calculate the P-wave and S-wave velocities in the load-bearing state:

[0042]

[0043] Preferably, calculate the equivalent P-wave and S-wave velocities according to the P-wave and S-wave velocities in the suspended state and the P-wave and S-wave velocities in the load-bearing state;

[0044]

[0045] where is the looseness parameter, which characterizes the looseness of the sediment.

[0046] Preferably, the inversion objective function is:

[0047]

[0048] where is the actual measured P-wave velocity at the i-th sampling point, is the calculated P-wave velocity, where φ i is the porosity at the i-th sampling point, is the looseness parameter at the i-th sampling point.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention simultaneously considers the rock physical models in the particle suspended state and the load-bearing state and realizes the prediction of the S-wave velocity. For the weakly consolidated characteristics of deep-water ultra-shallow sediments, it is equivalent to an equivalent containing the suspended state and the load-bearing state. By introducing the looseness parameter, the P-wave and S-wave velocities in the suspended state and the P-wave and S-wave velocities in the load-bearing state are allocated, which has reasonable rock physical significance. The present invention realizes the direct inversion of the S-wave velocity of deep-water ultra-shallow gas reservoirs. The inversion objective function established by this method only contains two parameters to be inverted, φ i and which improves the calculation efficiency and enhances the inversion stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is the flow chart of the method for predicting the shear wave velocity of the rock physics of the deep water ultra-shallow natural gas reservoir of the present invention;

[0051] Figure 2 It is the inversion result diagram of the shear wave velocity calculated according to the method of the present invention in a certain exploration work area. Specific embodiments

[0052] The technical solution of the present invention will be further specifically described below through specific embodiments in conjunction with the drawings:

[0053] Embodiment 1

[0054] As Figure 1 shown, a method for predicting the shear wave velocity of the rock physics of a deep water ultra-shallow natural gas reservoir, the method comprising:

[0055] S1: Calculate the equivalent bulk modulus of the multi-mineral mixed matrix, the shear modulus of the matrix, and the density of the matrix; in the load-bearing state, according to the equivalent bulk modulus of the matrix and the shear modulus of the matrix, calculate the equivalent bulk modulus of the skeleton composed of closely arranged equal spherical particles and the shear modulus of the skeleton when the porosity is the critical porosity; according to the equivalent bulk modulus of the matrix, the equivalent bulk modulus of the skeleton, and the shear modulus of the skeleton, calculate the shear modulus of the rock skeleton and the bulk modulus of the rock skeleton;

[0056] S2: Calculate the equivalent bulk modulus of the pore fluid according to the patchy partially saturated fluid filling model;

[0057] S3: Calculate the bulk modulus of the saturated rock and the shear modulus of the saturated rock according to the bulk modulus of the matrix, the bulk modulus of the rock skeleton, the shear modulus of the rock skeleton, and the equivalent bulk modulus of the pore fluid, and calculate the density of the saturated rock according to the fluid density and the density of the matrix;

[0058] S4: In the suspended state, calculate the equivalent bulk modulus of the suspended sediment;

[0059] S5: Calculate the P-wave and S-wave velocities in the suspended state according to the equivalent bulk modulus of the suspended sediment and the density of the saturated rock, and calculate the P-wave and S-wave velocities in the load-bearing state according to the bulk modulus of the saturated rock, the shear modulus of the saturated rock, and the density of the saturated rock; according to the P-wave and S-wave velocities in the suspended state and the P-wave and S-wave velocities in the load-bearing state, and introducing a loosening parameter to distribute the P-wave and S-wave velocities in the suspended state and the P-wave and S-wave velocities in the load-bearing state, calculate the equivalent P-wave and S-wave velocities;

[0060] S6: Construct an inversion objective function according to the equivalent P-wave and S-wave velocities and the actual measured well P-wave velocity;

[0061] S7: Calculate the shear wave velocity value of the predicted reservoir through inversion calculation according to the inversion objective function.

[0062] It should be noted that the method of the present invention can be carried out in the order of steps S1 to S7, but it is not limited to being carried out in the above steps. Since there is no sequence between step S2 and step S1, step S2 can also be executed first and then step S1; since there is no sequence between step S4 and steps S1 to S3, the order of step S4 is not limited either.

[0063] It should be noted that first, a petrophysical model of a deep-water ultra-shallow natural gas reservoir is established. The multi-mineral mixed matrix is regarded as a mixture of a shale part and a sand part, and the equivalent bulk modulus and shear modulus of the multi-mineral mixed matrix are calculated according to the shale content. In the load-bearing state, the mineral particles are in contact and extruded with each other, and at this time the sediment has a relatively large stiffness. The suspension state refers to the state where the particles are distributed in the fluid, and the solid and the fluid form an extremely loose mixture.

[0064] Example 2

[0065] A method for predicting the shear wave velocity of a deep-water ultra-shallow natural gas reservoir petrophysics, the method comprising:

[0066] Calculate the equivalent bulk modulus K of the multi-mineral mixed matrix through the Voigt-Reuss-Hill average modulus estimation method m , the shear modulus μ of the matrix m and the density ρ of the matrix m ;

[0067] K m = [(V sh K c +(1 - V sh )K q )+(V sh / K c +(1 - V sh ) / K q ) -1 / 2

[0068] μ m = [(V sh μ c +(1 - V sh )μ q )+(V sh / μ c +(1 - V sh ) / μ q ) -1 / 2

[0069] ρ m = Vsh ρ c +(1 - V sh )ρ q

[0070] where V sh is the shale content, K c and K q are the bulk modulus values of the shale component and the sand component in the matrix component respectively, μ c and μ q are the shear modulus values of the shale component and the sand component in the matrix component respectively, ρ c and ρ q are the density values of the shale component and the sand component in the matrix component respectively.

[0071] It should be noted that the HS model can also be used to calculate the equivalent bulk modulus K m of the matrix, the shear modulus μ m of the matrix and the density of the matrix.

[0072] In the load-bearing state, according to the equivalent bulk modulus K m of the matrix and the shear modulus μ m of the matrix, the equivalent bulk modulus K s of the skeleton composed of closely arranged equal spheres with a porosity of the critical porosity and the shear modulus μ s of the skeleton are calculated through the Hertz-Mindlin model;

[0073]

[0074] where n is the coordination number; φ c is the critical porosity value, which depends on the lithology and sedimentary environment and is given by the data of the work area; v m is the particle Poisson's ratio and v m =(3K m - 2μ m ) / (6K m + 2μ m ); P is the effective pressure, which depends on the depth.

[0075] According to the equivalent bulk modulus K m of the matrix, the equivalent bulk modulus K s of the skeleton at the critical porosity, and the shear modulus μ s of the skeleton, the shear modulus μ dry of the rock skeleton and the bulk modulus K dry of the rock skeleton are calculated through the Hashin-Shtrikman model;

[0076]

[0077] And

[0078] Calculate the equivalent bulk modulus of the pore fluid through the patch partial saturation fluid filling model;

[0079] K f =(K w -K hc )(1 - S hc ) e +K hc where K f is the equivalent bulk modulus of the pore fluid, K w , K hc are the bulk moduli of brine and hydrocarbons (oil, gas) respectively, S hc =1 - S w is the hydrocarbon fluid saturation, and e is an empirical constant term.

[0080] Calculate the bulk modulus K of the saturated rock through the Gassmann equation according to the matrix bulk modulus, the bulk modulus of the rock skeleton, the shear modulus of the rock skeleton, and the equivalent bulk modulus of the pore fluid, and since the influence of the fluid on the shear modulus of the saturated rock is weak, the shear modulus μ Sat is approximately equal to the shear modulus of the dry rock; Sat μ

[0081]

[0082] μ Sat =μ dry

[0083] Calculate the density ρ of the saturated rock according to the fluid density and the matrix density, and the fluid density is a constant; sat ρ

[0084] ρ Sat =φρ f +(1 - φ)ρ m .

[0085] In the suspended state, calculate the equivalent bulk modulus of the suspended sediment;

[0086] According to the equivalent bulk modulus of the suspended sediment and the density of the saturated rock, and introducing a looseness parameter, allocate the P-wave and S-wave velocities of the suspended state and the P-wave and S-wave velocities of the bearing state, calculate the P-wave and S-wave velocities of the suspended state, and calculate the P-wave and S-wave velocities of the bearing state according to the bulk modulus of the saturated rock, the shear modulus of the saturated rock, and the density of the saturated rock;

[0087] Calculate the equivalent P-wave and S-wave velocities according to the P-wave and S-wave velocities of the suspended state and the P-wave and S-wave velocities of the bearing state;

[0088] Construct an inversion objective function based on the equivalent P-wave and S-wave velocities and the actual measured P-wave velocity in well logging; and inversely calculate the S-wave velocity value of the predicted reservoir according to the inversion objective function.

[0089] Example 3

[0090] A method for predicting the S-wave velocity of a deep-water ultra-shallow gas reservoir rock physics, the method comprising:

[0091] Calculate the equivalent bulk modulus K of a multi-mineral mixed matrix by the Voigt-Reuss-Hill average modulus estimation method m , the shear modulus μ of the matrix m and the density of the matrix: ρ m ;

[0092] K m = [(V sh K c + (1 - V sh )K q ) + (V sh / K c + (1 - V sh ) / K q ) -1 / 2

[0093] μ m = [(V sh μ c + (1 - V sh )μ q ) + (V sh / μ c + (1 - V sh ) / μ q ) -1 / 2

[0094] ρ m = V sh ρ c + (1 - V sh )ρ q

[0095] where V sh is the shale content, K c and K q are the bulk modulus values of the shale component and the sand component in the matrix components respectively, μ c and μ q are the shear modulus values of the shale component and the sand component in the matrix components respectively, ρ c and ρ q are the density values of the shale component and the sand component in the matrix components respectively.

[0096] In the load-bearing state, according to the equivalent bulk modulus K of the matrix m and the shear modulus μ of the matrix m , the equivalent bulk modulus K of the skeleton composed of closely arranged equal spheres with a porosity of the critical porosity is calculated by the Hertz-Mindlin model s and the shear modulus μ of the skeleton s ;

[0097]

[0098] where n is the coordination number, generally 8 or 9 can be taken; φ c is the critical porosity value, which depends on the lithology and sedimentary environment and is given by the data of the work area; v m is the particle Poisson's ratio and v m =(3K m -2μ m ) / (6K m +2μ m ); P is the effective pressure, which depends on the depth.

[0099] According to the equivalent bulk modulus K of the matrix m , the equivalent bulk modulus K of the skeleton at the critical porosity s , and the shear modulus μ of the skeleton s , the shear modulus μ of the rock skeleton dry and the bulk modulus K of the rock skeleton are calculated by the Hashin-Shtrikman model dry ;

[0100]

[0101] And

[0102] The equivalent bulk modulus of the pore fluid is calculated by the patchy partially saturated fluid filling model;

[0103] K f =(K w -K hc )(1 - S hc ) e +K hc

[0104] where K f is the equivalent bulk modulus of the pore fluid, K w , K hc are the bulk moduli of brine and hydrocarbons (oil, gas) respectively, S hc =1 - S w is the hydrocarbon fluid saturation, and e is the empirical constant term.

[0105] Calculate the bulk modulus K of the saturated rock through the Gassmann equation based on the matrix bulk modulus, the bulk modulus of the rock skeleton, the shear modulus of the rock skeleton, and the equivalent bulk modulus of the pore fluid. Sat , and since the influence of the fluid on the shear modulus of the saturated rock is weak, the shear modulus μ Sat is approximately equal to the shear modulus of the dry rock;

[0106]

[0107] μ Sat = μ dry

[0108] Calculate the density ρ of the saturated rock based on the fluid density and the matrix density sat , and the fluid density is a constant;

[0109] ρ Sat = φρ f + (1 - φ)ρ m .

[0110] In the suspended state, calculate the equivalent bulk modulus K of the suspended sediment through the Wood model R ,

[0111]

[0112] f where φ is the porosity and K

[0113] is the fluid equivalent modulus.

[0114] Calculate the P-wave and S-wave velocities of the suspended state based on the density ρ sat of the saturated rock and the equivalent bulk modulus K of the floating sediment. Since the fluid does not resist shear, the S-wave velocity is zero:

[0115]

[0116] V s1 = 0

[0117] Calculate the P-wave and S-wave velocities of the bearing state based on the bulk modulus K Sat of the saturated rock, the shear modulus μ Sat of the saturated rock, and the density ρ sat of the saturated rock:

[0118]

[0119] Based on the P-wave and S-wave velocities of the suspended state and the P-wave and S-wave velocities of the bearing state, and introducing a loose parameter, distribute the P-wave and S-wave velocities of the suspended state and the P-wave and S-wave velocities of the bearing state to calculate the equivalent P-wave and S-wave velocities;

[0119]

[0120] wherein is the loosening parameter, characterizing the looseness of the sediment.

[0121] According to the inversion objective function, the shear wave velocity value of the predicted reservoir is obtained through inversion calculation. The inversion objective function is as follows:

[0122]

[0123] wherein is the actual measured longitudinal wave velocity at the i-th sampling point, is the calculated longitudinal wave velocity, where φ i is the porosity at the i-th sampling point, is the loosening parameter at the i-th sampling point.

[0124] Using the simulated annealing algorithm, according to the above objective function, the shear wave velocity value of the predicted reservoir is obtained through inversion. By constructing the objective function, comparing the calculated longitudinal wave velocity with the actual longitudinal wave velocity, and realizing the shear wave velocity inversion calculation through Monte Carlo sampling statistics under the framework of simulated annealing.

[0125] As Figure 2 shown, through the above method, the shear wave velocity inversion result calculated according to the method of the present invention in a certain exploration work area can be obtained. It can be seen that the present method can ensure the accuracy and rationality of the prediction of the shear wave velocity of the rock physics of deep-water ultra-shallow gas reservoirs.

[0126] Obviously, the above embodiments of the present invention are merely examples for clearly explaining the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A method for predicting the shear wave velocity of a deep-water ultra-shallow natural gas reservoir rock physics, characterized in that, The method includes: Calculating the equivalent bulk modulus of a multi-mineral mixed matrix, the shear modulus of the matrix, and the density of the matrix; In the load-bearing state, according to the equivalent bulk modulus of the matrix and the shear modulus of the matrix, calculating the equivalent bulk modulus of the skeleton composed of closely arranged equal-sphere particles with a porosity of the critical porosity and the shear modulus of the skeleton; According to the equivalent bulk modulus of the matrix, the equivalent bulk modulus of the skeleton, and the shear modulus of the skeleton, calculating the shear modulus of the rock skeleton and the bulk modulus of the rock skeleton; Calculating the equivalent bulk modulus of the pore fluid according to the patchy partially saturated fluid filling model; According to the bulk modulus of the matrix, the bulk modulus of the rock skeleton, the shear modulus of the rock skeleton, and the equivalent bulk modulus of the pore fluid, calculating the bulk modulus of the saturated rock and the shear modulus of the saturated rock, and calculating the density of the saturated rock according to the fluid density and the density of the matrix; In the suspended state, calculating the equivalent bulk modulus of the suspended sediment; According to the equivalent bulk modulus of the suspended sediment and the density of the saturated rock, calculating the P-wave and S-wave velocities in the suspended state, and calculating the P-wave and S-wave velocities in the load-bearing state according to the bulk modulus of the saturated rock, the shear modulus of the saturated rock, and the density of the saturated rock; According to the P-wave and S-wave velocities in the suspended state and the P-wave and S-wave velocities in the load-bearing state, and introducing a loosening parameter to allocate the P-wave and S-wave velocities in the suspended state and the P-wave and S-wave velocities in the load-bearing state, calculating the equivalent P-wave and S-wave velocities; Constructing an inversion objective function according to the equivalent P-wave and S-wave velocities and the actual measured P-wave velocity of the well logging; According to the inversion objective function, inversely calculating the S-wave velocity value of the predicted reservoir; 2. The method for predicting the shear wave velocity of a deep-water ultra-shallow natural gas reservoir rock physics according to claim 1, wherein Calculate the equivalent bulk modulus K of a multi-mineral mixed matrix by the Voigt-Reuss-Hill average modulus estimation method m , the shear modulus μ of the matrix m and the density ρ of the matrix m ; K m = [(V sh K c + (1 - V sh )K q ) + (V sh / K c + (1 - V sh ) / K q ) -1 / 2 μ m = [(V sh μ c + (1 - V sh ) μ q ) + (V sh / μ c + (1 - V sh ) / μ q ) -1 / 2 ρ m = V sh ρ c +(1 - V sh )ρ q Where V sh is the shale content, K c and K q are the bulk modulus values of the shale component and the sand component in the matrix component respectively, μ c and μ q are the shear modulus values of the shale component and the sand component in the matrix component respectively, ρ c and ρ q are the density values of the shale component and the sand component in the matrix component respectively.

3. The method for predicting the shear wave velocity of a deepwater ultra-shallow natural gas reservoir rock physics according to claim 2, wherein According to the equivalent bulk modulus K of the matrix m and the shear modulus μ of the matrix m , the equivalent bulk modulus K of the skeleton composed of closely arranged equal spheres when the porosity is the critical porosity is calculated by the Hertz-Mindlin model s and the shear modulus μ of the skeleton s ; where n is the coordination number; φ c is the critical porosity value, which depends on lithology and sedimentary environment and is given by the data of the work area; v m is the particle Poisson's ratio and v m =(3K m -2μ m ) / (6K m +2μ m ); P is the effective pressure, which depends on depth.

4. The method for predicting the shear wave velocity of a deep-water ultra-shallow natural gas reservoir rock physics according to claim 3, characterized in that According to the equivalent bulk modulus K of the matrix m and the equivalent bulk modulus K of the skeleton at the critical porosity s and the shear modulus μ of the skeleton s , the shear modulus μ of the rock skeleton is calculated by the Hashin-Shtrikman model dry and the bulk modulus K of the rock skeleton dry ; And 5. The method for predicting the shear wave velocity of a deepwater ultra-shallow natural gas reservoir rock physics according to claim 3, characterized in that Calculating the equivalent bulk modulus of the pore fluid through the patchy partially saturated fluid filling model; K f = (K w - K hc )(1 - S hc ) e + K hc where K f is the equivalent bulk modulus of the pore fluid, K w , K hc are the bulk moduli of brine and hydrocarbons (oil, gas) respectively, S hc = 1 - S w is the hydrocarbon fluid saturation, and e is an empirical constant term.

6. The method for predicting the shear wave velocity of a deep-water ultra-shallow natural gas reservoir rock physics according to claim 5, characterized in that Calculate the bulk modulus K of the saturated rock through the Gassmann equation based on the matrix bulk modulus, the bulk modulus of the rock skeleton, the shear modulus of the rock skeleton, and the equivalent bulk modulus of the pore fluid Sat , and since the influence of the fluid on the shear modulus of the saturated rock is weak, the shear modulus μ Sat is approximately equal to the shear modulus of the dry rock; μ Sat = μ dry Calculate the density ρ of the saturated rock based on the fluid density and the matrix density sat , where the fluid density is a constant; ρ Sat = φρ f + (1 - φ)ρ m .

7. The method for predicting the shear wave velocity of a deep-water ultra-shallow natural gas reservoir rock physics according to claim 6, wherein In the suspended state, calculating the equivalent bulk modulus KR of the suspended sediment through the Wood model: where φ is the porosity and K f is the fluid equivalent modulus.

8. The method for predicting the shear wave velocity of a deepwater ultra-shallow natural gas reservoir rock physics according to claim 7, wherein According to the density ρ of the saturated rock sat and the equivalent bulk modulus K of the floating sediment R calculate the P-wave and S-wave velocities in the suspended state. Since the fluid does not resist shear, the S-wave velocity is zero: V s1 ＝0 Based on the bulk modulus K of the saturated rock Sat 、the shear modulus μ of the saturated rock Sat and the density ρ of the saturated rock sat calculate the P-wave and S-wave velocities in the bearing state:

9. The method for predicting the shear wave velocity of a deepwater ultra-shallow natural gas reservoir rock physics according to claim 8, wherein According to the P-wave and S-wave velocities in the suspended state and the P-wave and S-wave velocities in the load-bearing state, calculating the equivalent P-wave and S-wave velocities; Among them is the loosening parameter, which characterizes the looseness of the sediment.

10. The method for predicting the shear wave velocity of a deep-water ultra-shallow natural gas reservoir rock physics according to claim 9, characterized in that, The inversion objective function is: where is the actual logging compressional wave velocity at the i-th sampling point, is the calculated compressional wave velocity, where φ i is the porosity at the i-th sampling point, is the unconsolidated parameter at the i-th sampling point.

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