The Research Of Seismic Wave Forward Modeling For Oil-gas Reservoir And AVO Analysis

Not only in theory research of seismic exploring technology but also in practice, the reflection and transmission laws of seismic wave on the interface play a very important role. The main research idea is: constructing oil-gas reservoir models by the theories of rock physics, using wave field numerical modeling to get synthetic seismogram of different oil-gas reservoir models, analyzing AVO phenomenon of these records, getting important recognitions and conclusions for AVO analysis and making people more impressive for different AVO phenomenon.Fist, construct reservoir models. The factors which affect seismic properties are too much. How to select a suitable rock physical model to construct reservoir models is very important for AVO analysis. In this paper, rock physical models which are cited include Voigt-Reuss bounds, Gassmann equation and the theory of constituent media.Second, simulate seismic wave field. The staggered-grid different scheme is arithmetic of high efficiency and precision in wave field numerical modeling. This method is widely applied to study seismic wave propagation in all kinds of media. In this paper, we adopt high precision staggered-grid technique to simulate seismic wave field, use FCT method to eliminate numerical dispersion and use PML to absorb boundary reflection.Third, analyze AVO phenomenon. Because the sandstone’s and shale’s porosity varied with depth take on different response, we can divide the AVO phenomenon of gas sands into 4 classes according to impedance and Possion’s ratio of gas sands and shale. Deep Hard gas sands represent AVO class I. Transparent gas sands near impedance cross point of sandstone and shale represent AVO class II. Shallow soft gas sands represent AVO class III. When soft gas sands are capped by relatively stiff cap-rock shale, there will be AVO class IV. Gas sands of class II, class III, and class IV are sensitive to fluid substitution, while class I gas sands are not. Based on the backup of the three techniques, we can use wave field numerical modeling to simulate AVO phenomenon of different oil-gas reservoir models. Fist of all, I simulate simple reservoir models saturated with gas. And then, we simulate wave field of Grane field in the North Sea and analyze the difference between synthetic records and actual data. Moreover, we compute fluid substitution for target layers and predict AVO phenomenon of target layers saturated with different fluid. The results indicate that: The simulative AVO phenomenon of reservoir saturated with oil is consistent with actual phenomenon; When target reservoir is saturated with gas the amplitude is strongest and the AVO phenomenon is most obvious, and then the oil, whereas the brine is weakest; If target layers are saturated with gas, we will see“bright spots”in horizontal stacking section.