Home – Home – Jornals – Russian Geology and Geophysics 2014 number 7

A “difference spectra” method is proposed for the qualitative assessment of changes of illite-smectite structures accompanying the flooding of oil reservoirs. The method permits one to get an open system and to reduce the application of procedures based on the Markov’s chains formalism. A computer simulation is made to obtain spectra by subtracting the spectrum of a glycol–saturated object from the spectrum of air-dried preparation throughout the range of concentrations of illite and smectite components with the structure short–range order factor R = 0 or R = 3. It has been established that in the case of filtration, the maximum and minimum of the spectra in the range of 12.5–9.4 Å are complicated by a number of local extremes, whose position is specified by the structure of the intermediate phases. The flooding process initially involves mixed–layered phases with R = 0, leading to a partial segregation of the structures into phases with one and two grids of interlayer H₂O. When the secondary particles of mica break, phases with R = 3 appear at the boundaries of nanoblocks, first, only with 1H₂O and then, only with 2H₂O in the labile interlayers. Their coexistence with the phases with R = 0 in the sample proves the existence of percolation effects due to the two-phase filtration in the porous medium. In the fully flooded reservoir, a mechanical mixture of illite-smectite phases of different nature with R = 0 and with different ratios of components is always predominant. Transformation of mica that can drastically reduce oil production begins long before the appearance of flooding zones, which are revealed by standard logging methods.