Method for determining fluid by utilizing seismic fluid impedance

Abstract

The invention discloses a method for determining a fluid by utilizing seismic fluid impedance. The method comprises the following steps: exciting and recording a seismic wave to obtain an angle gather; eliminating signal frequency distortion caused by a normal moveout correction stretching effect; extracting longitudinal wave reflectivity attributes and weighted transverse wave reflectivity attributes from the compensated angle gather; computing improved fluid factors; obtaining logging data to obtain a fluid impedance curve; performing iterative inversion to obtain a section of the fluid impedance; qualitatively analyzing fluid anomalies in pores by the fluid factors, and describing spatial distribution of the fluid by the fluid impedance. The method helps accurately extract the fluid factors and directly identify components of the fluid in the pores without an assumption of a velocity ratio of the longitudinal wave to the transverse wave as well as the relation between density and the longitudinal wave velocity, which reduces ambiguity of gas layer identification, realizes direct conversion from the fluid factors to the fluid impedance and improves the precision of gas reservoir identification.

Description

technical field [0001] The invention belongs to the hydrocarbon detection technology of petroleum geophysical prospecting, and relates to a fluid determination method using seismic fluid impedance. Background technique [0002] Seismic data is playing an increasingly important role in petroleum exploration and development. It has changed from a single function used to find structural oil and gas reservoirs to a multifunctional function of lithology identification and fluid detection. The most common technique for fluid detection using seismic data utilizes the amplitude information carried by seismic signals penetrating the subsurface medium. For pre-stack seismic data, the amplitude information usually refers to the amplitude variation with offset (AVO) feature to detect gas layers; while for post-stack seismic data, gas layers appear as bright spots, dark spots, flat spots and phases on the profile reverse etc. The "bright spot" technology began in the 1970s and is known...

AI Technical Summary

Problems solved by technology

Extracting elastic parameters from P-wave and S-wave impedance avoids the qualitative problem of identifying fluids with amplitude waveform attributes, but since the seismic data is band-limited, the P-wave and S-wave impedance can be inverted from the P-wave and S-wave reflectivity traces Sometimes it is necessary to provide P-wave and S-wave logging data at the same time to establish the initial model, and the inversion results depend on the provided initial model, and the inversion error will definitely affect the calculation of subsequent parameters

Moreover, λρ and Poisson's ratio are still ambiguous when detecting fluids, especially when Type II AVO water-bearing sandstones and Type I gas-bearing sandstones appear together, it is difficult to distinguish

In addition, when extracting the S-wave reflectivity by the Fatti formula, it is necessary to pre-assume the ratio of the longitudinal and shear wave velocities, which is also difficult to satisfy in actual operation

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