A Novel Method for Direct Fluid Factor Extraction

Prestack seismic inversion is by far the most effective method for fluid discrimination. A novel method was developed that uses variable points-constraint strategy to direct extract Gassmann fluid item (GFI) from prestack data. The initial objective function was build combining likelihood function, priori information and GFI approximate equation. The final objective function was acquired by adding a variable number of constraint points to the initial objective function. Three different points-constraint patterns were discussed, and different constraint effects were illustrated using synthetic data. Instead of initial model, this method used constraint model to improve the accuracy and stability of the extraction results. It did not need to obtain P-wave velocity, S-wave velocity and density first, and therefore can avoid accumulation of error that often happens with indirect approach. Model validation and actual application results showed that the proposed method could produce good results even if the SNR of prestack data is pretty low.