Again, this will further enhance the viscous fingering problem.Ĭraig and other researchers recommend that the unsteady state method not be used with strongly water wet cores. Also, in this method viscous oils are usually used to prolong the period of two-phase production (at flow breakthrough, no more information on relative permeability can be obtained). However, the use of high flow rate can aggregate viscous fingering problems. The fluid dispersion in the porous media increases with the flow rate, thus minimizing the boundary effect at the input end6. To minimize the boundary effect, the fluids can be flowed through the core at high rates to make the capillary forces insignificant compared to the viscous forces due to the flow of fluids. However, there are many difficulties associated with this method, such as capillary end effects, viscous fingering and channeling in heterogeneous medium, which cannot be properly accounted for.Ĭapillary end effect is a phenomenon in which the saturation is high at the inlet or outlet of the core. Equilibrium is not achieved, so the entire set of relative permeability curves can be obtained in a few hours.
In this method, the in-situ fluids are displaced at a constant rate with the effluent volumes being monitored continuously. Unsteady state is the quickest method of obtaining relative permeability. Fundamentals of Fluid Flow in Porous MediaĬhapter 2 Relative Permeability Three Phase Relative Permeability: Methods of Relative Permeability Measurements
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