Abstract
The dolomite reservoir of the fourth member of Dengying Formation in Moxi area of Sichuan Basin is thin, is fast in lateral variation, and has P-impedance difference from the surrounding rock; it is difficult to identify and predict the dolomite reservoir and fluid properties by conventional poststack seismic inversion. Through the correlation analysis of core test data and logging P-S-wave velocity, this work proposed a formula to calculate the shear wave velocity in different porosity ranges and solved the issue that some wells in the study area have no S-wave logging data. AVO forward analysis reveals that whether the gas reservoir of dolomite reservoir is located at the top of the fourth member of Dengying Formation is the main factor affecting the variation of AVO type. Through cross-plotting analysis of elastic parameters, it is found that P-S-wave velocity ratio and fluid factor are sensitive parameters to gas-bearing property of dolomite reservoir in the study area. By comparing the inversion results of prestack parameters such as density, P-wave impedance, S-wave impedance, P-S-wave velocity ratio, and fluid factor, it is found that the gas-bearing prediction of dolomite reservoir by using P-S-wave velocity ratio and fluid factor obtained from simultaneous prestack inversion had the highest coincidence rate with actual drilling data. At last, according to the distribution characteristics of fluid factor and P-S-wave velocity ratio, the favorable gas-bearing areas of dolomite reservoir in the fourth member of Dengying Formation in the study area are finely predicted, and the next favorable exploration areas were pointed out.
Highlights
Seismic inversion technology is based on seismic data to infer the spatial change and physical structure of the earth’s internal media, understand the distribution of various rock geophysical parameters, estimate the reservoir parameters, and predict the reservoir, so as to provide favorable basis for oilfield exploration and development
The P-S-wave velocity ratio of 1.4-1.65 is defined as gas reservoir, and the gas-bearing indicator factor of dolomite reservoir is highly consistent with the plane distribution of P-S-wave velocity ratio, which indicates that the prestack simultaneous inversion is of great significance for thin dolomite reservoir and gas water identification in the study area
The results show that the thickness of gas-bearing reservoir is highly consistent with the distribution characteristics of gas-bearing property and P-S-wave km thickness (m)
Summary
Seismic inversion technology is based on seismic data to infer the spatial change and physical structure of the earth’s internal media, understand the distribution of various rock geophysical parameters, estimate the reservoir parameters, and predict the reservoir, so as to provide favorable basis for oilfield exploration and development. Hampson et al [7] proposed the prestack simultaneous inversion technology based on the Fatti approximation [8], which is an important innovation of prestack inversion technology It restricts the seismic data from various angles and improves the inversion stability and obtains the rock elastic parameters with physical significance [8,9,10]. Accurately establish the seismic geological response models corresponding to the different physical properties and gas-bearing properties of the dolomite reservoirs in the fourth member of the Sinian Dengying Formation, identify the dolomite reservoirs and predict the distribution of gas layers, and improve the success rate of gas reservoir drilling. The technical problems faced by the research area are the focus of this article
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