Effect of decrease in pore water salinity induced by hydrate decomposition in clayey silt sediment on the destabilization-migration-clogging characteristics of illite

The clayey silt sediments are characterized by low permeability and high clay content, which makes fines migration not negligible. This work investigated the fines migration characteristics of illite under the condition of pore water salinity decreased, analyzed the effect on reservoir seepage characteristics, and evaluated the fines migration capability. The results show that the rapid decrease in pore water salinity caused by the decomposition of hydrate with high saturation produces higher particle concentration and results in more serious damage. At lower production pressures(0.1 MPa), the stability of illite was directly destroyed and flocculated to form aggregates that directly clogged the pores. The illite still tends to adsorb to the wall at higher production pressure(2.0 MPa), and then destabilizes and segregates under the effect of fluid dynamic. At higher production pressures, suspended particles are less likely to flocculate, which is more likely to block pores through bridging. The evaluation results of fines migration capability further clarified that salinity has a significant effect on fines migration characteristics and reservoir seepage capacity damage under different production pressures. This work demonstrates it is necessary to pay attention to the effect of fines migration on reservoir seepage characteristics when developing hydrate mining strategy.