Preparation of a Micro Emulsion for Fracture-Flooding and Its Mechanisms of Improving Oil Displacement Effects

Fracture-flooding injects a large amount of water in a short period of time into those low-permeability sandstone reservoirs with insufficient injection and dramatic formation pressure drop, resulting in a significant increase in liquid production. However, there may not be a corresponding increase in oil production if no chemicals are used. In this study, a micro emulsion was prepared and used to improve the fracture-flooding effects. Its abilities to reduce interfacial tension, to change wettability, and to reduce oil viscosity were measured. Core displacement experiments were designed to simulate fracture-flooding using the micro emulsion and using water without chemicals. The oil displacement effects were compared, and the mechanisms of improving oil production for the micro emulsion were described. A pilot test was then conducted in a well group to verify its practicality. The results showed that the micro emulsion had nano-size droplets, reduced the interfacial tension between oil and water, changed the wettability of rock face, reduce the viscosity of the crude oil, and strengthened the imbibition process. In core displacements, the oil recovered by fracture-flooding with the micro emulsion was 24.9% higher than that by fracture-flooding with only water. The mechanisms were summarized as larger sweeping volume, higher displacement efficiency, and more oil-water replacements. The average oil production rate of the test well group was 55.6% higher than that of another well group with similar reservoir properties developed by fracture-flooding with only water. Therefore, the micro emulsion can improve the effects of fracture-flooding, which is of great significance for the promotion of the fracture-flooding technology and the efficient development of some low permeability reservoirs.