Effect of modified montmorillonite particles on generation of in-situ W/O emulsion and oil displacement mechanism in enhanced heavy oil recovery

Abstract

Water-in-oil (W/O) emulsions can enhance the sweep efficiency and control the mobility ratio of oil and water simultaneously in heavy oil development. However, the W/O emulsions formed by heavy oils and injected fluids are prone to be with low phase inversion point and low maximum internal phase volume, which leads to serious tonguing and fingering especially in heterogeneous reservoirs. The authors thus proposed a new method of stabilizing W/O emulsions with modified montmorillonite particles (MMPs) to increase the phase inversion point as well as the internal phase volume to enable economically viable recovery of heavy oils. This paper evaluated the emulsions injected with different types of MMPs in terms of stability, maximum internal phase volume, and rheology. The optimal contact angle and particle concentration for modification were 105° and 3000 ppm, and under such conditions, the maximum internal phase volume fraction of the emulsions was increased to 85% and the viscosity by 40 times. In addition, the selected MMPs were then injected into multiple homogeneous cores of different permeabilities to verify the injectability and the viability to form W/O emulsions via pressure curves and NMR two-dimensional spectrum. The results showed that the modified particles can be injected into cores with permeability above 200 mD, but only in cores with permeability above 500 mD can a significant W/O emulsion be observed. Finally, three sets of heterogeneous core flooding tests were conducted in an online NMR system to determine the reasonable timing for injection of the MMPs and to verify its ability to enhance sweep efficiency by monitoring variations in NMR imaging, oil recovery, water cut, and pressure. Our work provides useful insights into the enhancement of sweep efficiency in heterogeneous heavy oil reservoirs by particle-stabilized W/O emulsions.