Abstract:

Efficiently dispersed viscosity reducer is the key to cold production of heavy oil. Viscosity reducer not only has a static oil washing ability, but also can diffuse into the spaces between colloid and asphaltenes in heavy oil, and break the structure of heavy oil. Based on the research of microscopic viscosity reduction mechanism, experiments on static oil washing, microscopic oil displacement, single sand-layer displacement, double-layer commingling production and separate oil displacement were carried out with L-A viscosity reducer which is suitable for cold huff and puff production of heavy oil. L-A viscosity reducer has a good effect on cold production of heavy oil. The main mechanism is that the viscosity reducer can form strong hydrogen bonds among its molecules. After intercalating into the molecules of heavy oil, the viscosity reducer filtrates and diffuses into the space between the lamellate colloid molecules and the lamellate asphaltenes molecules, reducing the hydrogen bonding force among the heavy oil molecules. The static oil washing efficiency of the L-A viscosity reducer at a mass fraction of 3% can reach 11.3%, and on microscopic displacement level, the L-A viscosity reducer can peel the heavy oil from particle surface. Single-layer displacement experiments show that the optimum viscosity-reducing mass fraction is 2%-3%, and the oil displacement efficiency reaches 48% at a lower flooding rate (1 mL/min). Double-layer experiments show that if the permeability ratio is not greater than 2, the maximum oil displacement efficiency at a low flooding rate can reach 40%, and the overall oil displacement efficiency decreases with the increase of the flooding rate and the increase of the permeability ratio between layers.

Key words: heavy oil reservoir, viscosity reducer, dispersion mechanism, hydrogen bond, oil washing efficiency, sand-filled pipe displacement, oil displacement efficiency