Experimental Study on Sand Production Characteristics of Gas Reservoir-Type Gas Storage under Cyclic Loading

The current design of sand control completion for gas storage construction is mostly based on sand production theories for conventional oil and gas reservoirs. However, the patterns and mechanisms of sand production in reservoir sandstones under the cyclic injection and production characteristics of gas storage have not been systematically studied, resulting in insufficient targeted support for gas storage construction design. To address this issue, sand production simulation tests, uniaxial compression tests, and cyclic loading and unloading mechanical tests were carried out using red sandstone outcrop samples from the Hutubi gas storage in Xinjiang, under both conventional conditions and cyclic loading conditions representative of gas storage operations. The sand production patterns, sand production characteristics, and perforation damage morphologies under different conditions were investigated, and the sand production mechanism under cyclic loading in gas storage was revealed. The results showed that under conventional conditions, sand production occurs mainly in the early stage of stable production, with the sand production rate following a pattern of “increase, stabilization, and decay to zero” over approximately 30 minutes, after which the internal structure of the core stabilizes. Under cyclic loading conditions, the cumulative sand production was significantly increased, approximately 2–3 times that under conventional conditions, and continuous sand production is observed. Even when the production pressure is lower than the critical sand production pressure, sand is still generated due to rock fatigue damage as the number of cycles increases, indicating persistent risk. The median grain size (D₅₀) of the produced sand under conventional conditions is 162–193 μm, while under cyclic conditions, it is 120–125 μm, significantly lower than the former. Under conventional conditions, sand grains form larger aggregates with relatively intact cementation; under cyclic conditions, sand grains are more thoroughly fragmented; cement detachment is more pronounced, and increased intergranular displacement leads to a higher proportion of fine particles. Severe perforation damage is caused under cyclic loading, characterized by the formation of symmetrical V-shaped “dog-ear” shear failure zones, with a failure area of 431.17–496.59 mm², which is 2.2–3.0 times that under conventional conditions (162.39–194.58 mm²). The cavity volume, diameter, and extension height of the perforations are all significantly enlarged. After the rock enters the failure stage under cyclic loading, macroscopic fractures are developed, accompanied by discrete sand shedding, indicating that the late failure stage is the primary period of sand production in gas storage. Fatigue damage loosens the rock framework and fractures the cement, while multiple cycles of frictional displacement further exacerbate particle fragmentation and fining. The strength degradation and failure characteristics of rock under cyclic loading should be incorporated into sand control strategies for gas storage to enhance long-term operational safety. Important theoretical support for gas storage construction design and the optimization of sand control measures can be provided by these findings.