Two-phase medium amplitude versus offset (AVO) forward modeling method based on triple constraints

Abstract

The invention provides a two-phase medium amplitude versus offset (AVO) forward modeling method based on triple constraints. The two-phase medium AVO forward modeling method based on triple constraints comprises the following steps of: (1) calculating bulk modulus of a fluid saturation rock; (2) setting a pore flattening value; (3) calculating bulk modulus of a rock matrix, and constraining the bulk modulus by employing the first constraint; (4) calculating elastic parameters of a two-phase medium; (5) calculating two roots of an equation of Biot (1956), and constraining the roots by employing the second constraint; (6) calculating the speed of slow longitudinal waves, and constraining the speed by employing the third constraint; (7) calculating the bulk modulus of the rock matrix, and calculating the parameters of the two-phase medium; and (8) calculating reflection and transmission coefficients of a two-phase medium model. Therefore, the pore flattening of the rock serves as an object; constraint inversion is performed by employing the triple constraints; and the inversion precision and reliability are effectively improved.

Description

technical field [0001] The invention relates to the AVO (Amplitude Versus Offset, amplitude varies with offset) forward modeling problem in the field of exploration geophysics, and is a dual-phase medium AVO forward modeling method based on triple condition constraints, which is used to solve conventional dual-phase medium In the AVO forward modeling method, it is difficult to accurately set the petrophysical parameters of the rock, which effectively improves the accuracy and reliability of the dual-phase medium AVO forward modeling method. Background technique [0002] Dual-phase medium is a medium composed of solid rock and fluid in pores, which can accurately describe the actual formation structure and properties. Based on the conventional two-phase medium theory (Biot, 1956; Geertsma, 1961), Wang Shangxu (1990) derived the reflection and transmission coefficient equations of the two-phase medium similar to the Zoeppritz equation, which laid the foundation for the AVO for...

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Problems solved by technology

But the difficulty lies in solving the "reflection and transmission coefficient equations". For example, the equations of Wang Shangxu (1990) need to set six parameters of the two-phase medium (σ 11 , σ 22 , σ 12 , γ 11 , γ 22 , γ 12 ), the equations of Mou Yongguang (1996) need to set 10 parameters of the two-phase medium (A, N, Q, R, ρ 11 , ρ 22 , ρ 12 、m 1 、m 2 , V 2 ), which restricts the practical application of the equations

It is worth noting that Yong Xueshan (2006) based on the inversion of rock physical parameters (matrix minerals and elastic parameters of rock skeleton), established two-phase medium parameters (A, N, Q, R, ρ 11 , ρ 22 , ρ 12 、m 1 、m 2 , V 2 ) and P-wave velocity, S-wave velocity, density, porosity, fluid velocity and density. Its advantage is that the input parameters have clear physical meaning and are easy to set. Its defect is that the self-consistent theory (Berryman, 1995) for inversion calculation, it is necessary to invert the elastic parameters of matrix minerals and rock skeleton at the same time, and the calculation accuracy and reliability are low

Subsequently, Xiao Sihe (2009) added the input of the elastic parameters of the rock skeleton based on the research of Yong Xueshan (2006). Its defect is that the self-consistent theory is still used (only four types of special pore types can be calculated: spherical, needle-like, disk-like, and coin-like) for inversion calculation, and the calculation accuracy is low

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