Abstract
In this study, we investigate the elastic moduli of the empty grain framework (the 'frame' moduli) in unconsolidated sands and consolidated sandstones. The work was done to improve the interpretation of seismic amplitude anomalies and amplitude variations with offset (AVO) associated with hydrocarbon reservoirs. We developed a laboratory apparatus to measure the frame Poisson's ratio and Young's modulus of unconsolidated sands at seismic frequencies (0.2 to 155 Hz) in samples approximately 11 cm long. We used ultrasonic pulse velocity measurements to measure the frame moduli of consolidated sandstones. We found that the correlation coefficient between the frame Poisson's ratio sigma A and the mineral Poisson's ratio sigma M is 0.84 in consolidated sandstones and only 0.28 in unconsolidated sands. The range of sigma A values in unconsolidated sands is 0.115 to 0.237 (mean = 0.187, standard deviation = 0.030), and sigma A cannot be estimated without core or log analyses. Frame moduli analyses of core samples can be used to calibrate the interpretation of seismic amplitude anomalies and AVO effects. For use in areas without core or log analyses, we developed an empirical relation that can be used to estimate sigma A in unconsolidated sands and sandstones from sigma M and the frame P-wave modulus.
