The Uncertainty Analysis of the Key Factors That Affect the AVO Attributes in Sandstone Reservoir

Abstract

AbstractTraditional seismic AVO forward study usually uses constant parameters to construct rock physics models, and such parameters in real formations have uncertainties in an exploration area. This work employed laboratory measurements of cores from the target formation to simplify the rock physics model with relationships of reservoir sandstone porosities and P‐ and S‐wave impedances under a dry condition. To study influences of model parameter uncertainties, the probability density functions of key model parameters were introduced based on core measurements and well logging analysis. Using the Monte‐Carlo method and Gassmann fluid replacement technique, the AVO responses of models were obtained for saturation fluids as brine, oil and gas. The comparative analysis indicates that the velocity uncertainty of covering mud is the primary factor affecting the fluid cluster's distribution and deviation from water background trend on AVO intercept‐gradient crossplots, while the porosity uncertainty of sand is also significantly affecting but less than covering mud. Thus, the correct interpretation of AVO anomalies for real seismic data requires forward simulation on a probabilistic rock physics model to acquire the information on reservoir physical properties and fluids as much as possible.