Experimental Study on Poisson's Ratio of Silty-Fine Sand with Saturation

The influence of saturation on the Poisson's ratio v of reservoir sediments has an engineering significance in the field of oil and nature gas exploration. Based on a self-developed combined (BE-EE-RC) test system, under the dehydration path, the Poisson's ratio variation of reservoir silty-fine sand in Hangzhou Bay, China, was investigated. Results show that the P- and S-wave velocities vary non-monotonically with decreasing saturation at different net stresses, and reach a maximum at the optimum saturation S-r((opt)); Biot's theory with respect to variation in V-p with S-r matches well with the measured e data. With a small amount of gas intrusion, Poisson's ratio of saturated sand shows a sudden drop and gradually stabilizes; then, it attenuates slowly and reaches the minimum value at S-r((opt)). Once the saturation degree decreases to the level lower than S-r((opt),) it rapidly increases. Based on the soil-water characteristic curve (SWCC) and mesoscopic evolution of internal pore water morphology, the variation in Poisson's ratio v can be divided into four segments of saturation: the boundary effect stage, the primary transition stage, the secondary transition stage, and the unsaturated residual stage. Ultimately, a prediction model for Poisson ratio's v of the silty-fine sand was proposed to consider the saturation variation.

Automated summary

The influence of saturation on the Poisson's ratio v of reservoir sediments has significance in oil and gas exploration. Using a self-developed test system, the Poisson's ratio variation of reservoir silty-fine sand in Hangzhou Bay, China was studied. The results showed non-monotonic variations of P- and S-wave velocities with decreasing saturation, reaching a maximum at the optimum saturation S-r((opt)). With gas intrusion, the Poisson's ratio of saturated sand dropped suddenly, stabilized, attenuated, and reached a minimum at S-r((opt)).