Ultra-low permeability sandstone reservoirs are significantly influenced by development of natural fractures. Based on laboratory experiments, fractured ultra- low permeability sandstone reservoirs were detailedly characterized in terms of porositypermeability relationship, micro-pore structure, stress sensitivity, and oil-water two-phase flow. The results show that permeability of fractured reservoir was higher than that of non-fractured one under equal reservoir porosity. When the reservoir porosity ranged from 10% to 20%, the permeability of fractured reservoir was approximately 2-4 times higher than that of non-fractured one. Compared with experiments on non-fractured reservoir, fractured reservoir is featured by larger throat radius span, higher proportion of largeradius throats, larger radius of dominant throats, and major contribution of large-radius throats to permeability under equal permeability. Fractured reservoir is more stress-sensitive, and the corresponding permeability loss of effective stress increase was 1-2 times higher than that of non-fractured one. Oil-water two-phase flow in fractured reservoir is featured by higher bound water and residual oil saturations, shorter common-flow interval, rapid oil relative permeability decline and water relative permeability increase with the increase of water saturation, short water-free production period, rapid water-cut increase after water break-through and low ultimate recovery factor.

ultra-low permeability  /  sandstone reservoirs  /  fractures  /  porosity-permeability relationship  /  micro-pore structure  /  stress sensitivity  /  two-phase flow