MRI of Fines Migration in Berea Sandstone

Fines migration is a phenomenon of practical importance in the petroleum production and drilling industry. Clay particle peptization, induced by incompatible aqueous phase chemistry, obstructs pore throats downstream of the fluid flow leading to permeability reductions that can be as large as two orders of magnitude [A1] . Magnetic resonance imaging (MRI) methods based on Carr-Purcell-Meiboom-Gill (CPMG) are able to map T₂ distributions in porous rocks, hence showing the spatial variation of the pseudo pore size distribution [A2] .
The traditional water-shock experiment is used to mobilize kaolinite in the aqueous phase flowing in a Berea core plug. Spin Echo - Single Point Imaging (SE-SPI), a phase encoding MRI method based on the CPMG method, is utilized to determine spatially resolved T₂ spectra of the sample, and therefore the pseudo pore size distribution.
The shift in the T₂ spectra of the core inlet and outlet show opposite trends. The pore size distribution of the inlet and outlet, inferred from T₂ distributions, are shifted to larger and smaller values respectively.

This suggests that while permeability is reduced in the outlet end of the core, it is significantly increased at the inlet end. The ratio of surface areas before and after deionized water injection is another indication of fines movement. Surface area ratio profile increases from less than one at the inlet end to values greater than one at positions close to the outlet end, suggesting once again migration and subsequent filtration of clay particles within the core.