Preparation and EOR Mechanism of Microemulsion

Low-permeability tight reservoirs are difficult to develop effectively. Conventional surfactants have high adsorption losses and poor matching with the tight reservoir pore roar radius. To further improve crude oil recovery, Microemulsion named ME-1 was developed with methyl T9 decanoate MS-9 as the oil phase, and the phase behavior was studied by quasi-ternary phase diagram to screen the main surfactant, co-surfactant, and salinity, with the composition of 20% AEO-9 + 13.3% propylene glycol methyl ether + 25% MS-9 + 41.7% distilled water + 1% KCl. The performance evaluation results showed that: The particle size of ME-1 system was 86.1 nm, and the oil-water interfacial tension was 0.08–0.13 mN/m, which could reverse the surface wettability of oil-wet mica flakes (116.38°) to water-wet (53.06°). NMR characterized its static and dynamic percolation recovery as 32.56% and 41.17%, respectively, and the 2.5-dimensional microscopic model showed that ME-1 could effectively increase the swept volume and oil washing efficiency. The experimental results show that the microemulsion can rely on the small size feature to effectively enter into the micro and nanopore pore throat, trigger the wetting inversion, promote the oil phase flow, and break up the crude oil into the small-scale state for recovery. In summary, this system can be used in tight reservoirs to enhance recovery, providing key technical support and theoretical support for effective mobilization and efficient development of low permeability tight fractured oil.