A new expression for fluid factor using AVO intercept and gradient: theory and application on deep marine reservoir

Mohammed Farfour, John Castagna

Numerous AVO fluid indicators have been introduced and proven to be sensitive to hydrocarbon presence. Mathematically, fluid indicators measure the deviation of seismic responses of hydrocarbon-saturated reservoirs from their background in a specific domain. We introduce a new expression for the fluid factor commonly used in AVO analysis and interpretation. The expression is a function of common AVO intercept and gradient and a weighting coefficient that helps suppressing the contribution of lithology and other factors not related to fluid content. The coefficient also assists in calibrating the fluid factor to the local geology. The performance of the proposed fluid factor is compared with other existing fluid factors. All the fluid factors are tested on a worldwide collection of P and S velocity and density measurements. The test is followed by an application on real data from the Northwest Shelf of Australia. Three wells are used in the application; two are used for calibration while the third is used as blind well. The fluid factor detects the gas zones at the three well locations and identifies prospects that have not been drilled.