A wave velocity ratio and density inversion method

Abstract

The present invention provides a velocity ratio and density inversion method, which belongs to the field of oil and gas exploration technology. The velocity ratio and density inversion method of the present invention first inverts the compressional wave velocity and shear wave velocity reflection coefficient through the Smith two-parameter approximation formula, and then combines the approximate formula containing compressional wave velocity, compressional and shear wave velocity ratio and density reflection coefficient derived based on the Aki-Richards three-parameter method and the compressional wave velocity reflection coefficient inverted in the first step to re-establish the two-parameter formula for direct inversion of compressional and shear wave velocity ratio and density inversion, thereby realizing the pre-stack two-step inversion process of velocity ratio and density. The method fully considers the advantages of direct inversion in avoiding the cumulative error of multiple calculations and the high stability of pre-stack two-parameter inversion, solves the problems of inaccurate three-parameter density inversion and low velocity ratio signal-to-noise ratio, and provides more accurate pre-stack elastic parameter factors for reservoir prediction and fluid identification.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration, and in particular to a wave velocity ratio and density inversion method. Background Art

[0002] Prestack seismic inversion is one of the important geophysical techniques in oil exploration and development. The P-wave velocity ratio containing shear wave information often has stronger lithologic differentiation and fluid identification capabilities than impedance, and is a commonly used parameter for lithologic characterization and fluid identification. The density parameter is an effective parameter for describing reservoir physical properties. In conventional well logging for identifying oil and gas layers, density and resistivity are important criteria for distinguishing oil and water layers, and are key parameters for predicting the lateral distribution patterns of reservoirs and fluids. They are of great reference significance in predicting reservoir physical properties and characterizing the boundaries of lithologic traps.

[0003] Currently, prestack three-parameter simultaneous inversion is the most commonly used prestack seismic inversion technique. This technique effectively utilizes the AVO information contained in prestack seismic data. By simultaneously inverting multiple partially stacked data volumes, three parameters are obtained, providing more effective elastic parameters or parameter combinations for lithology and fluid identification. However, prestack three-parameter simultaneous inversion suffers from poor stability. Not only can it not directly invert the P-wave velocity ratio, but the resulting S-wave velocity has a poor signal-to-noise ratio, significantly reducing the accuracy of the velocity ratio. Furthermore, the density parameter makes the three-parameter inversion equation ill-conditioned, resulting in poor density accuracy and signal-to-noise ratio, making it generally unsuitable for direct reservoir prediction. Furthermore, noise significantly impacts the inversion results of this technique, severely affecting lateral tracing and interpretation of reservoirs.

[0004] The existing technology has at least the following deficiencies:

[0005] The signal-to-noise ratio of the P-wave and S-wave velocities obtained by the simultaneous inversion of the three pre-stack parameters is low; the density parameter obtained by the simultaneous inversion of the three pre-stack parameters cannot be directly used for reservoir prediction.

[0006] To solve the problems existing in the prior art, the present invention provides a velocity ratio and density inversion method, which fully considers the advantages of direct inversion in avoiding the cumulative errors of multiple calculations and the high stability of pre-stack two-parameter inversion. By re-deriving the two-parameter formula containing velocity ratio and density inversion, a pre-stack two-step inversion process of velocity ratio and density is established, which solves the problems of inaccurate three-parameter density inversion and low velocity ratio signal-to-noise ratio, and provides more accurate pre-stack elastic parameter factors for reservoir prediction and fluid identification.

[0007] The present invention provides a wave velocity ratio and density inversion method, comprising the following steps:

[0008] Obtain partial stacked angle gather data;

[0009] Obtain comprehensive wavelets for each partial superimposed data volume;

[0010] Obtain logging curves of P-wave and S-wave velocity and density;

[0011] Using density and compressional wave velocity logging data to obtain the Gardner formula The Gardner formula gives the numerical relationship between density and longitudinal wave velocity, which is as follows:

[0012]

[0013] in,

[0014] and represent the density and P-wave velocity of underground rocks respectively;

[0015] and is a constant;

[0016] The P-wave velocity reflectivity and S-wave velocity reflectivity are inverted using Smith's two-parameter approximation formula.

[0017] The Aki-Richards three-term AVO approximation and the P-wave velocity reflectivity inverted using the Smith two-parameter approximation formula are used to obtain a two-parameter AVO approximation containing velocity ratio and density, which is then used to invert velocity ratio reflectivity and density reflectivity.

[0018] Using the well logging velocity ratio and density curves of the target layer in the target work area, a low-frequency model of the velocity ratio and density of the target layer is established to obtain the compensated velocity ratio and density inversion results;

[0019] The compensated velocity ratio and density are used to predict and describe the reservoir characteristics of the work area.

[0020] Preferably, obtaining partially stacked angle gather data includes:

[0021] Extract pre-stack seismic angle gather data using seismic imaging methods based on field-collected seismic data;

[0022] The maximum angle and minimum angle intervals are equally divided into three intervals, and the three intervals are superimposed to form three partial superimposed data volumes.

[0023] Preferably, the obtaining of the integrated wavelet of each partially stacked data volume includes well seismic calibration and wavelet extraction to obtain the integrated wavelet of each partially stacked data volume.

[0024] Preferably, the obtaining of the logging curves of the P-wave and S-wave velocities and the density comprises: obtaining the logging curves of the P-wave and S-wave velocities and the density by using the acoustic logging curve, the dipole acoustic logging curve and the density logging curve.

[0025] Preferably, the Gardner formula is obtained by using density and P-wave velocity logging data. Values, including:

[0026] Taking the logarithm of both sides of the Gardner formula, we can get:

[0027]

[0028] According to the above formula, the natural logarithm of the well logging density and P-wave velocity in the work area is taken;

[0029] The least squares linear regression fitting can be used to obtain value;

[0030] in,

[0031] and represent the density and P-wave velocity of underground rocks respectively;

[0032] and is a constant.

[0033] Preferably, the inversion of the longitudinal wave velocity reflectivity and the shear wave velocity reflectivity using the Smith two-parameter approximation formula includes:

[0034] Smith's two-parameter approximation formula is as follows:

[0035]

[0036] in,

[0037] The angle of incidence is P-wave reflection coefficient of the seismic angle gather;

[0038] and denote the average longitudinal wave velocity and shear wave velocity, respectively;

[0039] is the angle of incidence;

[0040] and Indicates the change in the longitudinal and transverse wave velocities at the boundary between two layers of media;

[0041] is the ratio of the shear wave velocity to the longitudinal wave velocity of the saturated rock;

[0042] According to the above formula, A linear equation:

[0043]

[0044] in,

[0045] ;

[0046] is the longitudinal wave velocity reflectivity;

[0047] is the shear wave velocity reflectivity;

[0048] is the reflection coefficient of the stacked P-wave angle gather of the n-th angle seismic part;

[0049] The singular value decomposition algorithm is used to The linear equations are solved to obtain the longitudinal wave velocity reflectivity and the shear wave velocity reflectivity.

[0050] Preferably, the P-wave velocity reflectivity obtained by inverting the Aki-Richards three-term AVO approximation and the Smith two-parameter approximation formula is used to obtain a two-parameter AVO approximation containing the velocity ratio and density, and the velocity ratio reflectivity and the density reflectivity are inverted using the approximation, including:

[0051] The Aki-Richards three-term AVO approximation is as follows:

[0052]

[0053] in,

[0054] The angle of incidence is P-wave reflection coefficient of the seismic angle gather;

[0055] 、 and denote the average P-wave velocity, S-wave velocity and density, respectively;

[0056] is the angle of incidence;

[0057] 、 and Indicates the change in the longitudinal and transverse wave velocities at the boundary between two layers of media;

[0058] is the ratio of the shear wave velocity to the longitudinal wave velocity of the saturated rock;

[0059] According to the above formula, differentiating the wave velocity ratio yields:

[0060]

[0061] By transforming the above formula, we can get The expression is:

[0062]

[0063] Combining the above methods, we can obtain:

[0064]

[0065] Arranging the above formula, we can get the two-parameter AVO approximation formula with the unknowns being the wave velocity ratio and density:

[0066]

[0067] in:

[0068] ;

[0069] According to the above formula, we can construct A two-parameter linear equation is solved using the singular value decomposition algorithm. Solve a two-parameter linear equation and obtain the wave velocity ratio reflectivity and density reflectivity by inversion;

[0070] in,

[0071] It is the difference between the reflection coefficient of the seismic angle gather and the product of its component P-wave velocity reflectivity and the corresponding coefficient;

[0072] is the longitudinal wave velocity reflectivity;

[0073] is the shear wave velocity reflectivity;

[0074] is the wave velocity ratio reflectivity;

[0075] is the density reflectivity.

[0076] Preferably, the constructed The two-parameter linear equation is:

[0077]

[0078] in,

[0079] ;

[0080] It is the difference between the reflection coefficient of the n-th angle seismic angle gather and the product of its component longitudinal wave velocity reflectivity and the corresponding coefficient.

[0081] Preferably, obtaining the compensated wave velocity ratio and density inversion results includes performing trace integration and low-frequency compensation on the wave velocity ratio reflectivity and the density reflectivity to obtain the compensated wave velocity ratio and density inversion results.

[0082] Preferably, the low-frequency compensation for the velocity ratio reflectivity and density reflectivity is performed to obtain compensated velocity ratio and density inversion results, including using the low-frequency components of the velocity ratio and density calculated using logging data as the low-frequency components of the band-limited inversion results to obtain compensated velocity ratio and density parameters.

[0083] Compared with the prior art, the present invention has the following beneficial effects:

[0084] (1) The present invention establishes a two-step pre-stack velocity ratio and density inversion method. This method fully utilizes the advantages of high stability of pre-stack two-parameter inversion and the advantage of direct inversion that can avoid the cumulative error of multiple calculations, so that the inverted velocity ratio and density signal-to-noise ratio and accuracy are higher than those of traditional methods; the reservoir characteristics on the inversion section are clearer, which is more conducive to lateral tracking and prediction of the reservoir, and ultimately effectively improves the drilling rate of exploration wells and the development effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Figure 1 A synthetic angle gather seismic record profile obtained for one embodiment of the present invention;

[0086] Figure 2 A synthetic angle gather seismic record profile with Gaussian random noise obtained in accordance with an embodiment of the present invention;

[0087] Figure 3 Comparison of density reflectivity inverted by a conventional method and a method according to an embodiment of the present invention;

[0088] Figure 4 Comparison of the wave velocity ratio reflectivity inverted by the conventional method and the method of one embodiment of the present invention;

[0089] Figure 5 is the density profile obtained by simultaneous prestack inversion;

[0090] Figure 6 The inverted density profile of one embodiment of the present invention;

[0091] Figure 7 is the P-wave and S-wave velocity ratio section obtained by simultaneous pre-stack inversion;

[0092] Figure 8 The inverted P-wave and S-wave velocity ratio profile of one embodiment of the present invention;

[0093] Figure 9 This is a flow chart of a wave velocity ratio and density inversion method according to an embodiment of the present invention.

[0094] in, Figure 5-8 The scale in the figure is a legend, which is used to indicate the numerical range of the data expressed in the figure, which is consistent with its actual physical meaning and is used to prove that the inverted data conforms to the laws of actual physical data. DETAILED DESCRIPTION

[0095] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0096] The present invention provides a wave velocity ratio and density inversion method, comprising the following steps:

[0097] Obtain partial stacked angle gather data;

[0098] Obtain comprehensive wavelets for each partial superimposed data volume;

[0099] Obtain logging curves of P-wave and S-wave velocity and density;

[0100] Using density and compressional wave velocity logging data to obtain the Gardner formula The Gardner formula gives the numerical relationship between density and longitudinal wave velocity, which is as follows:

[0101]

[0102] in,

[0103] and represent the density and P-wave velocity of underground rocks respectively;

[0104] and is a constant;

[0105] The P-wave velocity reflectivity and S-wave velocity reflectivity are inverted using Smith's two-parameter approximation formula.

[0106] The Aki-Richards three-term AVO approximation and the P-wave velocity reflectivity inverted using the Smith two-parameter approximation formula are used to obtain a two-parameter AVO approximation containing velocity ratio and density, which is then used to invert velocity ratio reflectivity and density reflectivity.

[0107] Using the well logging velocity ratio and density curves of the target layer in the target work area, a low-frequency model of the velocity ratio and density of the target layer is established to obtain the compensated velocity ratio and density inversion results;

[0108] The compensated velocity ratio and density are used to predict and describe the reservoir characteristics of the work area.

[0109] According to a specific embodiment of the present invention, obtaining partially stacked angle gather data includes:

[0110] Extract pre-stack seismic angle gather data using seismic imaging methods based on field-collected seismic data;

[0111] The maximum angle and minimum angle intervals are equally divided into three intervals, and the three intervals are superimposed to form three partial superimposed data volumes.

[0112] According to a specific embodiment of the present invention, obtaining the comprehensive wavelet of each partial stacked data volume includes well seismic calibration and wavelet extraction to obtain the comprehensive wavelet of each partial stacked data volume.

[0113] According to a specific embodiment of the present invention, obtaining the logging curves of P-wave velocity and S-wave velocity and density includes: obtaining the logging curves of P-wave velocity and S-wave velocity and density using acoustic logging curves, dipole acoustic logging curves and density logging curves.

[0114] According to a specific embodiment of the present invention, the Gardner formula is obtained by using density and compressional wave velocity logging data. Values, including:

[0115] Taking the logarithm of both sides of the Gardner formula, we can get:

[0116]

[0117] According to the above formula, the natural logarithm of the well logging density and P-wave velocity in the work area is taken;

[0118] The least squares linear regression fitting can be used to obtain value;

[0119] in,

[0120] and represent the density and P-wave velocity of underground rocks respectively;

[0121] and is a constant.

[0122] According to a specific embodiment of the present invention, the inversion of the longitudinal wave velocity reflectivity and the shear wave velocity reflectivity using the Smith two-parameter approximation formula includes:

[0123] Smith's two-parameter approximation formula is as follows:

[0124]

[0125] in,

[0126] The angle of incidence is P-wave reflection coefficient of the seismic angle gather;

[0127] and denote the average longitudinal wave velocity and shear wave velocity, respectively;

[0128] is the angle of incidence;

[0129] and Indicates the change in the longitudinal and transverse wave velocities at the boundary between two layers of media;

[0130] is the ratio of the shear wave velocity to the longitudinal wave velocity of the saturated rock;

[0131] According to the above formula, A linear equation:

[0132]

[0133] in,

[0134] ;

[0135] is the longitudinal wave velocity reflectivity;

[0136] is the shear wave velocity reflectivity;

[0137] is the reflection coefficient of the stacked P-wave angle gather of the n-th angle seismic part;

[0138] The singular value decomposition algorithm is used to The linear equations are solved to obtain the longitudinal wave velocity reflectivity and the shear wave velocity reflectivity.

[0139] According to a specific embodiment of the present invention, the P-wave velocity reflectivity obtained by inverting the Aki-Richards three-term AVO approximation and the Smith two-parameter approximation formula is used to obtain a two-parameter AVO approximation containing the velocity ratio and density, and the velocity ratio reflectivity and the density reflectivity are inverted using the approximation, including:

[0140] The Aki-Richards three-term AVO approximation is as follows:

[0141]

[0142] in,

[0143] The angle of incidence is P-wave reflection coefficient of the seismic angle gather;

[0144] 、 and denote the average P-wave velocity, S-wave velocity and density, respectively;

[0145] is the angle of incidence;

[0146] 、 and Indicates the change in the longitudinal and transverse wave velocities at the boundary between two layers of media;

[0147] is the ratio of the shear wave velocity to the longitudinal wave velocity of the saturated rock;

[0148] According to the above formula, differentiating the wave velocity ratio yields:

[0149]

[0150] By transforming the above formula, we can get The expression is:

[0151]

[0152] Combining the above methods, we can obtain:

[0153]

[0154] Arranging the above formula, we can get the two-parameter AVO approximation formula with the unknowns being the wave velocity ratio and density:

[0155]

[0156] in:

[0157] ;

[0158] According to the above formula, we can construct A two-parameter linear equation is solved using the singular value decomposition algorithm. Solve a two-parameter linear equation and obtain the wave velocity ratio reflectivity and density reflectivity by inversion;

[0159] in,

[0160] It is the difference between the reflection coefficient of the seismic angle gather and the product of its component P-wave velocity reflectivity and the corresponding coefficient;

[0161] is the longitudinal wave velocity reflectivity;

[0162] is the shear wave velocity reflectivity;

[0163] is the wave velocity ratio reflectivity;

[0164] is the density reflectivity.

[0165] According to a specific embodiment of the present invention, the constructed The two-parameter linear equation is:

[0166]

[0167] in,

[0168] ;

[0169] It is the difference between the reflection coefficient of the n-th angle seismic angle gather and the product of its component longitudinal wave velocity reflectivity and the corresponding coefficient.

[0170] According to a specific embodiment of the present invention, obtaining compensated velocity ratio and density inversion results includes performing trace integration and low-frequency compensation on the velocity ratio reflectivity and density reflectivity to obtain compensated velocity ratio and density inversion results.

[0171] According to a specific embodiment of the present invention, the low-frequency compensation of the velocity ratio reflectivity and the density reflectivity is performed to obtain the compensated velocity ratio and density inversion results, including using the low-frequency components of the velocity ratio and density calculated using the logging data as the low-frequency components of the band-limited inversion results to obtain the compensated velocity ratio and density parameters.

[0172] According to a specific embodiment of the present invention, different lithologies correspond to different velocity ratios and density characteristics according to well logging intersection analysis, and the reservoir in the work area can be predicted and characterized on the inverted velocity ratio and density profile, thereby obtaining a favorable drilling area.

[0173] Example 1

[0174] According to a specific embodiment of the present invention, Figure 9 , the wave velocity ratio and density inversion method of the present invention is described in detail.

[0175] The present invention provides a wave velocity ratio and density inversion method, comprising the following steps:

[0176] Obtaining partial stack angle gather data, including: extracting pre-stack seismic angle gather data using a seismic imaging method based on field-collected seismic data; dividing the maximum angle and minimum angle intervals into three intervals, and stacking the three intervals into three partial stack data volumes;

[0177] Obtaining a comprehensive wavelet of each partial stacked data volume, including: well seismic calibration and wavelet extraction, obtaining a comprehensive wavelet of each partial stacked data volume;

[0178] Obtaining logging curves of P-wave velocity and S-wave velocity and density, including: obtaining logging curves of P-wave velocity and S-wave velocity and density using acoustic logging curves, dipole acoustic logging curves and density logging curves;

[0179] Using density and compressional wave velocity logging data to obtain the Gardner formula The Gardner formula gives the numerical relationship between density and longitudinal wave velocity, which is as follows:

[0180]

[0181] in,

[0182] and represent the density and P-wave velocity of underground rocks respectively;

[0183] and is a constant;

[0184] The P-wave velocity reflectivity and S-wave velocity reflectivity are inverted using Smith's two-parameter approximation formula.

[0185] The Aki-Richards three-term AVO approximation and the P-wave velocity reflectivity inverted using the Smith two-parameter approximation formula are used to obtain a two-parameter AVO approximation containing velocity ratio and density, which is then used to invert velocity ratio reflectivity and density reflectivity.

[0186] Using the logging velocity ratio and density curves of the target layer in the target work area, a low-frequency model of the velocity ratio and density of the target layer is established to obtain the compensated P-wave and S-wave velocity ratio and density inversion results;

[0187] The compensated velocity ratio and density are used to predict and describe the reservoir characteristics of the work area.

[0188] Example 2

[0189] According to a specific embodiment of the present invention, the wave velocity ratio and density inversion method of the present invention is described in detail with reference to the accompanying drawings.

[0190] The present invention provides a wave velocity ratio and density inversion method, comprising the following steps:

[0191] Obtain partial stacked angle gather data;

[0192] Obtain comprehensive wavelets for each partial superimposed data volume;

[0193] Obtain logging curves of P-wave and S-wave velocity and density;

[0194] Using density and compressional wave velocity logging data to obtain the Gardner formula The Gardner formula gives the numerical relationship between density and longitudinal wave velocity, which is as follows:

[0195]

[0196] in,

[0197] and represent the density and P-wave velocity of underground rocks respectively;

[0198] and is a constant;

[0199] The Gardner formula is obtained by using density and compressional wave velocity logging data Values, including:

[0200] Taking the logarithm of both sides of the Gardner formula, we can get:

[0201]

[0202] According to the above formula, the natural logarithm of the well logging density and P-wave velocity in the work area is taken;

[0203] The least squares linear regression fitting can be used to obtain value;

[0204] in,

[0205] and represent the density and P-wave velocity of underground rocks respectively;

[0206] and is a constant;

[0207] The Smith two-parameter approximation formula is used to invert the longitudinal wave velocity reflectivity and the shear wave velocity reflectivity, including:

[0208] Smith's two-parameter approximation formula is as follows:

[0209]

[0210] in,

[0211] The angle of incidence is P-wave reflection coefficient of the seismic angle gather;

[0212] and denote the average longitudinal wave velocity and shear wave velocity, respectively;

[0213] is the angle of incidence;

[0214] and Indicates the change in the longitudinal and transverse wave velocities at the boundary between two layers of media;

[0215] is the ratio of the shear wave velocity to the longitudinal wave velocity of the saturated rock;

[0216] According to the above formula, A linear equation:

[0217]

[0218] in,

[0219] ;

[0220] is the longitudinal wave velocity reflectivity;

[0221] is the shear wave velocity reflectivity;

[0222] is the reflection coefficient of the stacked P-wave angle gather of the n-th angle seismic part;

[0223] The singular value decomposition algorithm is used to The linear equations are solved to obtain the longitudinal wave velocity reflectivity and the shear wave velocity reflectivity.

[0224] The Aki-Richards three-term AVO approximation and the P-wave velocity reflectivity inverted using the Smith two-parameter approximation formula are used to obtain a two-parameter AVO approximation containing velocity ratio and density. This approximation is used to invert the velocity ratio reflectivity and density reflectivity, including:

[0225] The Aki-Richards three-term AVO approximation is as follows:

[0226]

[0227] in,

[0228] The angle of incidence is P-wave reflection coefficient of the seismic angle gather;

[0229] 、 and denote the average P-wave velocity, S-wave velocity and density, respectively;

[0230] is the angle of incidence;

[0231] 、 and Indicates the change in the longitudinal and transverse wave velocities at the boundary between two layers of media;

[0232] is the ratio of the shear wave velocity to the longitudinal wave velocity of the saturated rock;

[0233] According to the above formula, differentiating the ratio of longitudinal and transverse wave velocities yields:

[0234]

[0235] By transforming the above formula, we can get The expression is:

[0236]

[0237] Combining the above methods, we can obtain:

[0238]

[0239] The two-parameter AVO approximation formula obtained by rearranging the above formula is the unknown variables, namely the ratio of longitudinal and transverse wave velocities and the density:

[0240]

[0241] in:

[0242] ;

[0243] According to the above formula, we can construct A two-parameter linear equation is solved using the singular value decomposition algorithm. Solve a two-parameter linear equation and obtain the wave velocity ratio reflectivity and density reflectivity by inversion;

[0244] in,

[0245] It is the difference between the reflection coefficient of the seismic angle gather and the product of its component P-wave velocity reflectivity and the corresponding coefficient;

[0246] is the longitudinal wave velocity reflectivity;

[0247] is the shear wave velocity reflectivity;

[0248] is the wave velocity ratio reflectivity;

[0249] is the density reflectivity;

[0250] Using the logging velocity ratio and density curves of the target layer in the target work area, a low-frequency model of the velocity ratio and density of the target layer is established to obtain the compensated P-wave and S-wave velocity ratio and density inversion results;

[0251] The compensated velocity ratio and density are used to predict and describe the reservoir characteristics of the work area.

[0252] Example 3

[0253] According to a specific embodiment of the present invention, the wave velocity ratio and density inversion method of the present invention is described in detail with reference to the accompanying drawings.

[0254] The present invention provides a wave velocity ratio and density inversion method, comprising the following steps:

[0255] Obtaining partial stack angle gather data, including: extracting pre-stack seismic angle gather data using a seismic imaging method based on field-collected seismic data; dividing the maximum angle and minimum angle intervals into three intervals, and stacking the three intervals into three partial stack data volumes;

[0256] Obtaining a comprehensive wavelet of each partial stacked data volume, including: well seismic calibration and wavelet extraction, obtaining a comprehensive wavelet of each partial stacked data volume;

[0257] Obtaining logging curves of P-wave velocity and S-wave velocity and density, including: obtaining logging curves of P-wave velocity and S-wave velocity and density using acoustic logging curves, dipole acoustic logging curves and density logging curves;

[0258] Using density and compressional wave velocity logging data to obtain the Gardner formula The Gardner formula gives the numerical relationship between density and longitudinal wave velocity, which is as follows:

[0259]

[0260] in,

[0261] and represent the density and P-wave velocity of underground rocks respectively;

[0262] and is a constant;

[0263] The Gardner formula is obtained by using density and compressional wave velocity logging data Values, including:

[0264] Taking the logarithm of both sides of the Gardner formula, we can get:

[0265]

[0266] According to the above formula, the natural logarithm of the well logging density and P-wave velocity in the work area is taken;

[0267] The least squares linear regression fitting can be used to obtain value;

[0268] in,

[0269] and represent the density and P-wave velocity of underground rocks respectively;

[0270] and is a constant;

[0271] The Smith two-parameter approximation formula is used to invert the longitudinal wave velocity reflectivity and the shear wave velocity reflectivity, including:

[0272] Smith's two-parameter approximation formula is as follows:

[0273]

[0274] in,

[0275] The angle of incidence is P-wave reflection coefficient of the seismic angle gather;

[0276] and denote the average longitudinal wave velocity and shear wave velocity, respectively;

[0277] is the angle of incidence;

[0278] and Indicates the change in the longitudinal and transverse wave velocities at the boundary between two layers of media;

[0279] is the ratio of the shear wave velocity to the longitudinal wave velocity of the saturated rock;

[0280] According to the above formula, A linear equation:

[0281]

[0282] in,

[0283] ;

[0284] is the longitudinal wave velocity reflectivity;

[0285] is the shear wave velocity reflectivity;

[0286] is the reflection coefficient of the stacked P-wave angle gather of the n-th angle seismic part;

[0287] The singular value decomposition algorithm is used to The linear equations are solved to obtain the longitudinal wave velocity reflectivity and the shear wave velocity reflectivity.

[0288] The Aki-Richards three-term AVO approximation and the P-wave velocity reflectivity inverted using the Smith two-parameter approximation formula are used to obtain a two-parameter AVO approximation containing velocity ratio and density. This approximation is used to invert the velocity ratio reflectivity and density reflectivity, including:

[0289] The Aki-Richards three-term AVO approximation is as follows:

[0290]

[0291] in,

[0292] The angle of incidence is P-wave reflection coefficient of the seismic angle gather;

[0293] 、 and denote the average P-wave velocity, S-wave velocity and density, respectively;

[0294] is the angle of incidence;

[0295] 、 and Indicates the change in the longitudinal and transverse wave velocities at the boundary between two layers of media;

[0296] is the ratio of the shear wave velocity to the longitudinal wave velocity of the saturated rock;

[0297] According to the above formula, differentiating the ratio of longitudinal and transverse wave velocities yields:

[0298]

[0299] By transforming the above formula, we can get The expression is:

[0300]

[0301] Combining the above methods, we can obtain:

[0302]

[0303] The two-parameter AVO approximation formula obtained by rearranging the above formula is the unknown variables, namely the ratio of longitudinal and transverse wave velocities and the density:

[0304]

[0305] in:

[0306] ;

[0307] According to the above formula, we can construct A two-parameter linear equation is solved using the singular value decomposition algorithm. Solve a two-parameter linear equation and obtain the wave velocity ratio reflectivity and density reflectivity by inversion;

[0308] in,

[0309] It is the difference between the reflection coefficient of the seismic angle gather and the product of its component P-wave velocity reflectivity and the corresponding coefficient;

[0310] is the longitudinal wave velocity reflectivity;

[0311] is the shear wave velocity reflectivity;

[0312] is the wave velocity ratio reflectivity;

[0313] is the density reflectivity;

[0314] By using the well logging velocity ratio and density curves of the target layer in the target work area, a low-frequency model of the velocity ratio and density of the target layer is established to obtain compensated velocity ratio and density inversion results; wherein, obtaining the compensated velocity ratio and density inversion results includes performing trace integration and low-frequency compensation on the velocity ratio reflectivity and density reflectivity to obtain the compensated velocity ratio and density inversion results; specifically, performing the low-frequency compensation on the velocity ratio reflectivity and density reflectivity to obtain the compensated velocity ratio and density inversion results includes using the low-frequency components of the velocity ratio and density calculated using the well logging data as the low-frequency components of the band-limited inversion results to obtain the compensated velocity ratio and density parameters.

[0315] The compensated velocity ratio and density are used to predict and characterize the reservoirs in the work area, including: different lithologies correspond to different velocity ratios and density characteristics based on well logging intersection analysis, and the reservoirs in the work area are predicted and characterized on the inverted velocity ratio and density profiles, thereby obtaining the velocity ratio and density inversion of the favorable drilling area.

[0316] Figure 1 and Figure 2The synthetic angle gather seismic record profile obtained by the present invention and the synthetic angle gather seismic record profile with Gaussian random noise added are respectively shown;

[0317] Figure 3 and Figure 4 The comparison of density reflectivity and wave velocity ratio reflectivity inverted by the traditional method and the method of the present invention is shown respectively. Figure 3 and Figure 4 It can be seen that the traditional method is affected by noise, and the inversion result deviates greatly from the true value, while the result obtained by the method of the present invention has a smaller error with the true value;

[0318] Figure 5 and Figure 6 The density profiles of the pre-stack simultaneous inversion and the density profiles of the inversion method of the present invention are shown respectively. Figure 5 and Figure 6 It can be seen that the density inverted by the method of the present invention is in good agreement with the well logging curve, and the geological body characteristics are clearer on the density profile.

[0319] Figure 7 and Figure 8 The velocity ratio sections of the pre-stack simultaneous inversion and the inversion method of the present invention are shown respectively. Figure 7 and Figure 8 It can be seen that the velocity ratio inverted by the method of the present invention is in good agreement with the logging curve, and the geological body characteristics are clearer on the velocity ratio profile.

[0320] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A wave velocity ratio and density inversion method, characterized in that: The steps include: Obtain partial stacked angle gather data; Obtain comprehensive wavelets for each partial superimposed data volume; Obtain logging curves of P-wave and S-wave velocity and density; Using density and compressional wave velocity logging data to obtain the Gardner formula The Gardner formula gives the numerical relationship between density and longitudinal wave velocity, which is as follows: in, and represent the density and P-wave velocity of underground rocks respectively; and is a constant; The P-wave velocity reflectivity and S-wave velocity reflectivity are inverted using Smith's two-parameter approximation formula. The Aki-Richards three-term AVO approximation and the P-wave velocity reflectivity inverted using the Smith two-parameter approximation formula are used to obtain a two-parameter AVO approximation containing velocity ratio and density, which is then used to invert velocity ratio reflectivity and density reflectivity. Using the well logging velocity ratio and density curves of the target layer in the target work area, a low-frequency model of the velocity ratio and density of the target layer is established to obtain the compensated velocity ratio and density inversion results; The compensated velocity ratio and density are used to predict and describe the reservoir characteristics of the work area.

2. The wave velocity ratio and density inversion method according to claim 1, characterized in that: The obtaining of partial stacking angle gather data comprises: Extract pre-stack seismic angle gather data using seismic imaging methods based on field-collected seismic data; The maximum angle and minimum angle intervals are equally divided into three intervals, and the three intervals are superimposed to form three partial superimposed data volumes.

3. The wave velocity ratio and density inversion method according to claim 1, characterized in that: The method of obtaining the comprehensive wavelet of each partially stacked data volume includes well seismic calibration and wavelet extraction to obtain the comprehensive wavelet of each partially stacked data volume.

4. The wave velocity ratio and density inversion method according to claim 1, characterized in that: The method of obtaining the logging curves of P-wave velocity and S-wave velocity and density includes obtaining the logging curves of P-wave velocity and S-wave velocity and density by using the acoustic logging curve, the dipole acoustic logging curve and the density logging curve.

5. The wave velocity ratio and density inversion method according to claim 1, characterized in that: The Gardner formula is obtained by using density and compressional wave velocity logging data Values, including: Taking the logarithm of both sides of the Gardner formula, we can get: According to the above formula, the natural logarithm of the well logging density and P-wave velocity in the work area is taken; The least squares linear regression fitting can be used to obtain value; in, and represent the density and P-wave velocity of underground rocks respectively; and is a constant.

6. The wave velocity ratio and density inversion method according to claim 1, characterized in that: The method of inverting the longitudinal wave velocity reflectivity and the shear wave velocity reflectivity using the Smith two-parameter approximation formula includes: Smith's two-parameter approximation formula is as follows: in, The angle of incidence is P-wave reflection coefficient of the seismic angle gather; and denote the average longitudinal wave velocity and shear wave velocity, respectively; is the angle of incidence; and Indicates the change in the longitudinal and transverse wave velocities at the boundary between two layers of media; is the ratio of the shear wave velocity to the longitudinal wave velocity of the saturated rock; According to the above formula, A linear equation: in, ； is the longitudinal wave velocity reflectivity; is the shear wave velocity reflectivity; For the n Reflection coefficient of the angle seismic partial stacked P-wave angle gather; The singular value decomposition algorithm is used to The linear equations are solved to obtain the longitudinal wave velocity reflectivity and the shear wave velocity reflectivity.

7. The wave velocity ratio and density inversion method according to claim 1, characterized in that: The longitudinal wave velocity reflectivity obtained by inverting the Aki-Richards three-term AVO approximation and the Smith two-parameter approximation formula is used to obtain a two-parameter AVO approximation containing wave velocity ratio and density, and the wave velocity ratio reflectivity and density reflectivity are inverted using the approximation, including: The Aki-Richards three-term AVO approximation is as follows: in, The angle of incidence is P-wave reflection coefficient of the seismic angle gather; 、 and denote the average P-wave velocity, S-wave velocity and density, respectively; is the angle of incidence; 、 and Indicates the change in the longitudinal and transverse wave velocities at the boundary between two layers of media; is the ratio of the shear wave velocity to the longitudinal wave velocity of the saturated rock; According to the above formula, differentiating the wave velocity ratio yields: By transforming the above formula, we can get The expression is: Combining the above methods, we can obtain: Arranging the above formula, we can get the two-parameter AVO approximation formula with the unknowns being the wave velocity ratio and density: in: ； According to the above formula, we can construct A two-parameter linear equation is solved using the singular value decomposition algorithm. Solve a two-parameter linear equation and obtain the wave velocity ratio reflectivity and density reflectivity by inversion; in, It is the difference between the reflection coefficient of the seismic angle gather and the product of its component P-wave velocity reflectivity and the corresponding coefficient; is the longitudinal wave velocity reflectivity; is the shear wave velocity reflectivity; is the wave velocity ratio reflectivity; is the density reflectivity.

8. The wave velocity ratio and density inversion method according to claim 7, characterized in that: The constructed The two-parameter linear equation is: in, ； It is the difference between the reflection coefficient of the n-th angle seismic angle gather and the product of its component longitudinal wave velocity reflectivity and the corresponding coefficient.

9. The wave velocity ratio and density inversion method according to claim 1, characterized in that: Obtaining compensated wave velocity ratio and density inversion results, including performing trace integration and low-frequency compensation on the wave velocity ratio reflectivity and density reflectivity to obtain compensated wave velocity ratio and density inversion results.

10. The wave velocity ratio and density inversion method according to claim 9, characterized in that: Low-frequency compensation is performed on the velocity ratio reflectivity and the density reflectivity to obtain compensated velocity ratio and density inversion results, including the low-frequency components of the velocity ratio and density calculated based on the logging data, which are used as the low-frequency components of the band-limited inversion results to obtain the compensated velocity ratio and density parameters.

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