Study On The Mechanisms Of The Formation Of Droplet Flow In Alkaline Flooding For Enhancing Heavy-oil Recovery

Alkaline flooding has great potential for enhancing the recovery of heavy oil, especiallyfor reservoirs in which the oil recovery by water flooding is low and thermal methods are notsuitable. This presents the results of a laboratory study for investigating the mechanisms ofalkaline flooding for improved heavy oil recovery, which can provide guidelines for theoptimization of designing the formula of chemical flooding for heavy oil.At first, the displacement mechanism of “droplet flow” during alkaline flooding forenhanced heavy oil recovery was put forward by the core flooding tests and microscopicvisualization tests. At the beginning of alkaline flooding, the alkaline solution can penetrateinto the crude oil and subsequently formation of “water columns” or “water droplets” coatedwith oil film; eventually “droplet flow” phenomenon appears. Depending on the Jamin effectby “droplet flow”, the fingering of the displacement agent is significantly inhibited; at thelater stage of alkaline flooding,“droplet flow” can be converted to high viscosity water-in-oil(W/O) emulsions, which can block the high-permeability water channels, thereby improvingthe sweep efficiency. And with the alkaline concentration increases,“droplet flow”phenomenon is more obvious and more W/O emulsions can be generated, the greaterimprovement in sweep efficiency, but the displacement efficiency decreases. A series ofsandpack flooding tests and3D physical model flooding test were conducted to assess theeffectiveness of “droplet flow” during alkaline flooding for enhanced heavy oil recovery, andthe effects of the main parameters on the displacement efficiency are also optimized.Secondly, the microscopic visualization tests were conducted for investigating themechanisms and controlling factors of the formation of “droplet flow” during alkalineflooding. When the alkaline solution with a certain pH value comes in contact with the heavyoil with a certain amount of the acidic components in porous media, a large number ofsurfactants can be produced by the rapid interfacial reactions between the alkaline solutionand the acidic components. Some surfactants are adsorbed on the solid surface and thewettability of the solid surface inverted to oil-wet quickly, which inhibit the flow of thealkaline solution along the pore walls. The other surfactants can be adsorbed on the oil-water interface, and leads to the drastic reduction of transient oil/water interfacial tension, whichresults in the penetration of alkaline solution in the heavy oil and creates some “watercolumns” coated with oil film. At the same time, the non-uniform distribution of in-situsurfactant makes the “water columns” divide into small discontinuous “water droplets” at thepoints where surfactant concentration is low. In addition, it can be concluded that the resin ofthe heavy oil is the key factor in forming “droplet flow”, and the asphaltene is the criticalfactor in keeping stability of “droplet flow”.Finally, this study investigated the surfactant, polymer and low molecular weightalcohols on the effect of the “droplet flow” during alkaline flooding for enhanced heavy oilrecovery. The results show that the surfactant can lower the interfacial tension to improve thedisplacement efficiency and the polymer can increase the viscosity of the water to improvesweep efficiency. However, the addition of surfactant and polymer has adverse effects on theformation of “droplet flow” during alkaline flooding, leading to lower sweep efficiency. Theaddition of low molecular weight alcohol can enhance the generation of “droplet flow” duringalkaline flooding and promote “droplet flow” to form low viscosity W/O emulsions.Therefore, these emulsions can be mobilized again to form continuous oil bank, which leadsto improvements in the sweep efficiency and displacement efficiency.