Seismic responses of tight gas sand of different water saturations: A physical model research

摘要

Due to the low-porosity/low-permeability character of tight sand, the gas-water mixed fluids in reservoir may not be evenly distributed, therefore the fluid substitution researches based on the rock physics theory that require fluid uniform distribution are not accurate. In this paper we focus on the velocity-water saturation relationship by ultrasonic transmission measurement. On this basis we build tight gas sand physical model of different water saturations, conduct data acquisition and processing and give the variation of seismic responses. The results show that in near offset the AVO response make little variation in low water saturation period, when saturation reaches certain value the rock physical properties of tight sand appear great changes, as a result the AVO response shows bigger change, the amplitude curve of different saturations can be distinguished. But in far offset the AVO curves of different saturation intersect together. In the post-stack section, the change of water saturation give rise to the different attenuation, the amplitude ratio between top and bottom of the reservoir shows a good correspondence with saturation, therefore this parameter is a good indicator to determine the gas content of tight sand.