Summary
Fines migration is a phenomenon of practical importance in the petroleum-production and drilling industry. The movement of clay particles, induced by incompatible aqueous-phase chemistry or high flow rate, obstructs pore throats downstream of the fluid flow, leading to permeability reductions that can be as large as two orders of magnitude. Magnetic-resonance-imaging (MRI) methods derived from the Carr-Purcell-Meiboom-Gill (CPMG) method (Meiboom and Gill 1958) can map T2 distributions in porous rocks, hence showing the spatial variation of the pseudo-pore-size distribution.
In this work, the traditional water-shock experiment was used to mobilize clay particles in the aqueous phase flowing in Berea core plugs. Spin-echo single-point imaging (SE-SPI), a phase-encoding MRI method derived from the CPMG method, was used to determine spatially resolved T2 spectra of the samples, and therefore the pseudo-pore-size distributions.
The shift in the T2 spectra of the core inlet and outlet showed opposite trends. The pore-size distribution of the inlet and outlet, inferred from T2 distributions, were shifted to larger and smaller values, respectively. Therefore, the average pore size was increased at the inlet of the core and reduced at the outlet of the core. This MRI method provides a new analytical approach to screen reservoirs for potential fines-migration problems.
Magnetic resonance imaging of dense and light non-aqueous phase liquid in a rock fracture
