Effect of dry-wet alternations on the mechanical strength of deep tight sandstone

Abstract

The working fluid used for gas drilling and the excessive differences in production pressure during the gas production process causes repeated fluctuations between increasing and decreasing water saturation of the rock. These repeated fluctuations result in dry-wet state alternations of the rock, which weakens the rock strength. Weakening rock strength will lead to sand shedding, which damages reservoirs because of particle migration, solid blockage, and sand production. This will also change the stress sensitivity of deep tight sandstone, thus affecting gas well production. Therefore, this study conducted both a dry-wet alternation experiment and a stress sensitivity experiment after dry-wet alternation using deep tight sandstone. During the experiment, the changes of the rock dynamic Young's modulus, Poisson's ratio, and stress sensitivity coefficient were monitored. The experimental results show that the dynamic Young's modulus and Poisson's ratio of rock samples decreased after dry-wet alternations. Furthermore, these alternations increase the stress sensitivity of the rock matrix and weaken the stress sensitivity of fractured rock samples. • The mechanism of weakening the strength of deep tight sandstone by dry-wet alternation is analyzed. • The influence of dry-wet alternation on stress sensitivity of deep tight sandstone is analyzed. • Dry-wet alternation may be one of the reasons for sand production in deep tight sandstone.