Pre-stack fracture quantitative prediction method and system based on rock physics

Abstract

The invention provides a prestack crack quantitative forecast method and system based on rock physics. The prestack crack quantitative forecast method includes the steps of: dividing a prestack CMP gather into multiple azimuth gathers: the azimuth gather 1, the azimuth gather 2,...the azimuth gather n according to the size of an azimuth and an incident angle in the prestack CMP gather of a reservoir to be measured; performing superposition and offset processing on each azimuth gather, and calculating a longitudinal wave reflection coefficient of each azimuth gather; calculating a tangential anisotropic coefficient Delta T of the crack in the reservoir to be measured according to a Ruger exact equation and each azimuth gather and the longitudinal wave reflection coefficient thereof; and calculating the crack density e of the reservoir to be measured according to the tangential anisotropic coefficient Delta T. The prestack crack quantitative forecast method and system based on rock physics can accurately realize the quantitative estimation of the crack density, further accurately performs oil and gas reservoir forecast and guides the deploy of the exploitation well position, and reduces the oil and gas reservoir forecast risk.

Description

technical field [0001] The invention relates to the field of petroleum and natural gas seismic exploration inversion and quantitative interpretation, in particular to a method and system for quantitative prediction of pre-stack fractures based on rock physics. Background technique [0002] AVOAz (Amplitude versus offset and azimuth) inversion is to invert the density of underground fractures and the development direction of fractures by using the variation law of reflected P-wave amplitude with incident angle and azimuth angle. A large number of geophysicists have studied the approximate relationship between reflection and transmission in anisotropic media. The most famous and widely used one is Ruger's concept of weak anisotropy, combined with Thomsen's anisotropy parameters, proposed The formula for the change of the longitudinal wave reflection coefficient with the azimuth angle and incident angle in the HTI medium is the exact formula of the Ruger equation, and the speci...

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Problems solved by technology

On the other hand, none of these existing methods can study the fluid properties filled in fractures, which is very important for the guidance of subsequent well development work

[0011] In actual fracture prediction, due to the influence of various factors, it is difficult to accurately estimate the density and development direction of fractures, especially the quantitative prediction of fracture density

Due to the constraints of various factors, the traditional ellipse fitting method cannot accurately obtain the fracture density and direction. Although the later developed inversion method based on the trinomial equation makes up for many shortcomings of the ellipse fitting method, it still cannot realize the fracture density and direction. Quantitative prediction of density

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