Apparent Permeability Evolution Due to Colloid Migration Under Cyclic Confining Pressure: On the Example of Porous Limestone

The paper presents the methodology and results of core tests to assess the impact of colloid migration on apparent permeability under cyclic confining pressure. In the work, porous limestone cores were used. The research methodology differs from similar works in that the core was blown with nitrogen at a high pressure gradient between loading and unloading cycles to clean the pores. Blowings cause permeability dynamics that contradict classical theory, according to the results of multi-cycle core tests. Forward and reverse blowings disturb the porous medium’s internal equilibrium, resulting in a change in apparent permeability between core test cycles. This phenomenon can only be explained by colloid migration, which provides pore throat blocking and unblocking during nitrogen injection. A visual comparison of micrographs before and after the tests revealed that the surface structure of the pores remained unchanged, but mobile particles ranging in size from several microns to 50 microns were observed in each observed pore. The proposed mechanism for changing apparent permeability during gas injection and cyclic confining pressure correlates well with the results of core tests.