Method and device for determining concentration of surfactant solution for oil displacement by imbibition

A method for selecting an optimal concentration of a surfactant solution from among a set of surfactants having a range of concentrations, wherein the surfactant is for oil displacement by imbibition, comprising steps of:

• Step 1:
• providing a tank for holding the surfactant solution and a capillary tube with one end located inside the tank;
• Step 2:
• adding the surfactant solution with a first preset concentration into the tank until a liquid level of the surfactant solution is above minimum scale of the capillary tube;
• Step 3:
• injecting crude oil into the capillary tube, a liquid level difference ΔH is generated between a liquid level of the capillary tube and the liquid level of the tank, the liquid level difference ΔH is a dynamic value which varies over time;
• recording data of the liquid level difference ΔH varying over time, and calculating an imbibition dynamic and resistance ratio of the surfactant solution with the first preset concentration based on the data;
• cleaning the tank and capillary tube;
• Step 4:
• repeating the steps 2) and 3) for each surfactant solution with concentration ranging from a second preset concentration to an Nth (N=3, 4, 5 . . . ) preset concentration to calculate a plurality of corresponding imbibition dynamic and resistance ratios;
• Step 5:
• determining the optimal concentration under the best oil displacement effect of the surfactant solution based on the imbibition dynamic and resistance ratios of the surfactant solutions with concentration ranging from the first to Nth preset concentration wherein the optimal concentration corresponds to the largest imbibition dynamic and resistance ratio;
• wherein the imbibition dynamic and resistance ratio of the surfactant solution is calculated using the formula:
• η=ΔHi/ΔHe×100%;
• where η is the imbibition dynamic and resistance ratio, ΔHi is a height of the initial liquid level difference ΔH, and ΔHe is a height of the liquid level difference ΔH after equilibrium.