Water-sensitive damage mechanism and the injection water source optimization of low permeability sandy conglomerate reservoirs

Abstract

The global mobility theory was used to evaluate the experimental results of oil displacement with water of different salinities. The results of scanning electron microscopy, X diffraction of clay minerals, nonlinear seepage and nuclear magnetic resonance experiments and particle migration inhibition experiments before and after water flooding were compared to determine the mechanisms of water sensitive damage and enhanced water flooding mechanism of low permeability sandy conglomerate reservoirs in Wushi region of Beibuwan Basin, China. A production equation of the oil-water two phase flow well considering low-speed non-Darcy seepage and reservoir stress sensitivity was established to evaluate the effect of changes in reservoir properties and oil-water two-phase seepage capacity on reservoir productivity quantitatively, and injection water source suitable for the low permeability sandy conglomerate reservoirs in Wushi region was selected according to dynamic compatibility experimental results of different types of injected water. The seepage capacity of reservoir is the strongest when the injected water is formation water of 2 times salinity. The water-sensitive damage mechanisms of the reservoirs in Wushi region include hydration of clay minerals and particle migration. By increasing the content of cations (especially K+ and Mg2+) in the injected water, the water-sensitive damage of the reservoir can be effectively inhibited. The formation water of Weizhou Formation can be used as the injection water source of low permeability sandy conglomerate reservoirs in the Wushi region. Key words: Beibuwan Basin, low permeability reservoir, sandy conglomerate reservoir, water-sensitive damage, enhanced water flooding, effective driving coefficient, global mobility, water flooding