Fluid identification method based on three-term frequency dependence AVO inversion

Abstract

More and more attentions are paid to the frequency dispersion phenomenon recently due to the fact that a great amount of information relating to fluid is carried. Even though the frequency dependence AVO inversion method is proved to be an effective method for judging fluid types, the reliability of the frequency dependence AVO inversion method relies on the accuracy degree of an AVO inversion approximation formula and the value of Vs/Vp in a frequency dispersion inversion formula to a great extent. Therefore, the invention provides a fluid identification method based on three-term frequency dependence AVO inversion. The method is based on an Aki&Richards three-term inversion approximation formula, and the Aki&Richards three-term inversion approximation formula is introduced to a frequency domain and is substituted into the Vs/Vp which is obtained through prestack AVO inversion and changes along with sampling points. According to the method, two-dimensional physical model data with holes filled with different fluids in sequence are selected and used firstly for verifying the feasibility and the advantages of the method, the result shows that more reliable longitudinal wave frequency dispersion gradient values can be obtained through the fluid identification method based on the three-term frequency dependence AVO inversion, and the fluid types can be identified more effectively and non-reservoir energy can be suppressed. The application results of actual data show that the final result obtained through the fluid identification method based on the three-term frequency dependence AVO inversion can be better matched with actual fluid types, yields and other well information.

Description

technical field [0001] The invention belongs to the field of petroleum exploration, and relates to a method for identifying fluids by using three-term frequency-dependent AVO inversion. Background technique [0002] AVO technology developed rapidly in the 1990s, and many geophysicists constantly revised and developed AVO technology according to different requirements, and obtained Zoeppritz equation approximation algorithms suitable for different geological and seismic situations, such as Aki & Richard approximation formula, Shuey approximation formula, Smith & Gidlow approximation formula and Fatti approximation formula, etc., so that qualitative AVO fluid detection technology develops into quantitative elastic parameter calculation, pre-stack elastic wave impedance inversion and crack detection and other technologies. However, AVO technology is based on the theory of elastic waves, and does not consider the dispersion characteristics of seismic waves. The dispersion of sei...

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Problems solved by technology

[0004] However, this method is based on the Smith & Gidlow two-term inversion approximation formula and the assumption that Vs / Vp is a constant value (usually 0.5), and the Smith & Gidlow two-term inversion approximation formula is based on the Gardner approximation formula The density change rate item is approximated to the P-wave velocity change rate item, so that the final P-wave velocity change rate is not accurate enough; Vs / Vp is the main parameter to distinguish the fluid type in the reservoir, and it is also an important parameter to distinguish the reservoir from the non-reservoir. Index, the traditional frequency-dependent AVO inversion method sets this value as a constant, which cannot accurately identify fluid types and classify reservoirs and non-reservoirs in the inversion

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