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Russian Geology and Geophysics

2014 year, number 7

CHANGES IN THE STRUCTURES OF MIXED-LAYER ILLITESMECTITE DURING FLOODING OF TERRIGENEOUS OIL RESERVOIRS

G.A. Krinari1, M.G. Khramchenkov1, Yu.Sh. Rakhmatulina2
1Institute of Geology and Petroleum Technologies, Kazan Federal University, ul. Kremlevskaya 4/5, Kazan, 420008, Russia
2Institute of Ecology and Subsoil Assets, Tatarstan Academy of Sciences, ul. Daurskaya 28, Kazan, 420087, Russia
Keywords: Oil production, mixed-layer illitesmectite, micas, XRD, computer simulation

Abstract

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 shortrange 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 12.59.4 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 mixedlayered 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.

DOI: http://dx.doi.org/10.1016/j.rgg.2014.06.010