Abstract
This paper addresses the problem of instability and sand production in poorly consolidated sandstones subjected to a water influx. New phenomenological evidences were collected in a series of unprecedented experiments, improving the understanding on the sand production mechanisms. Two different groups of experiments studied behavior, morphology, and stability of sand arches in two-phase saturated sand samples. The effects of changes in fluid flow velocity and water saturation were deeply analyzed, and the distributions of porosity and water saturation in the arched region were mapped during the sand production process.
The results showed that single-phase saturated sands did not develop enough cohesive strength to support a stable arch and sand was produced massively, generating a high-porosity and unstable zone. However, a small increase in wetting-phase saturation developed enough cohesive strength to stabilize an arch, reducing sand production. Within a defined range, a progressive increase in wetting phase saturation did not impact arch stability and sand production was sporadic and minimum. As the wetting-phase saturation exceeded critical value instability occurred; the arch was enlarged and massive amounts of liquefied sand were produced. A decrease in the non-wetting phase flow rate did not affect the stability of the arched zone and reduced sand production. Finally, it was observed that dilated, unconfined and agglomerated blocks of sands, with uniform porosity and wetting-phase saturation, filled the space inside the arched region.
