Migration mechanisms of solid particles in rough fractures and the effects on permeability

The low-permeability sandstone reservoir in the Lufeng block of the South China Sea exhibits poor physical properties, significant heterogeneity, and weak cementation, resulting in an unsatisfactory fracturing effect. The flowback fluids contain a diverse array of solid particles to elucidate the damage mechanisms associated with solid particle migration on hydraulic fractures, a quantitative evaluation of micro-fracture damage within the reservoir was conducted through physical flow experiment combined with fracture roughness assessment technology. This study aimed to identify the key factors affecting particle migration damage and establish a multivariate regression relationship between permeability and fracture roughness, thereby proposing a novel damage evaluation method for offshore low-permeability reservoirs. The results indicate (1) the predominant types of solid particulate damage include formation particles, residues from fracturing fluids, and crushed proppant particles; notably, the degree of damage follows this order: formation particles > fluid residues > proppant particles. (2) Sand production experiments reveal that the sand production rate ranks as follows: formation particles < fracturing fluid residues < proppant particles; similarly, particle size adheres to this sequence: formation particles < fracturing fluid residues < proppant particles. These observations suggest that migration of formation particles is primarily responsible for reservoir damage. (3) The fracture roughness assessment method demonstrates a consistent trend with permeability damage results; furthermore, regression fitting indicates a strong correlation between these two variables, underscoring the high reliability of this methodology. It provides a theoretical foundation for optimizing field operations and mitigating reservoir damage while facilitating efficient development strategies for offshore low-permeability reservoirs.