Abstract:In order to study seepage characteristics and influencing factors in ultra-low permeability reservoirs, with samples taken from Ordos, experiments of single phase flow and oil-water phase flow were conducted. The results indicate there exists a threshold pressure gradient for single phase flows for part of samples. The flow is of non-darcy seepage when the pressure gradient is low and it changes into darcy flow at high pressure; but for other samples, no obvious non-darcy flow is found. The lower the core permeability is, the higher the pressure under which non-Darcy state will retain and less the flow volume will be. The flow curve for the core is not a straight line but a curve protruding to the shearing stress axis. The fluid is non-Newtonian and fake plastic fluid, which does not move besides some elastic deformation under a weak external force, and which moves under a strong external force, with an obvious yield stress. The relation between moving shearing stress and permeability indicates that the shearing stress decreases rapidly with the decrease of permeability. The apparent viscosity reduces slowly when the shearing rate increases The density of the fluid decreases after shearing. Irreducible water saturation and residual oil saturation become high and the two-phase region becomes narrow under the condition of two-phase seepage. The relative permeability value of oil-phase reduces quickly and the water-phase increases slowly with the increase of water saturation. The permeability, wettability and water-lock influence the seepage characteristics.