Study of Distribution and Potentiality Exploiting of Microscosmic Residual Oil in Strong Water-washing Layer after Polymer Flooding

The distribution of residual oil after polymer flooding becomes highly dispersed, the degree of water-washing is gradually aggravated in the reservoir and distribution proportion increases year by year. How to dig the potential of residual oil in the strong water-washing layer is very important to further enhance oil recovery after polymer flooding. According to the data of pressure-coring wells and water-flooded layers before and after polymer flooding, this paper deepens the understanding of the potentials of remained oil reserves in the strong water-washing layer after polymer flooding and the quantitative distribution of the microscopic residual oil. Based on the previous statistic data of residual oil saturation, together with the application of modern physical modeling and laser confocal scanning microscope techniques, the author established the model of strongly-watered natural core, performed the laboratory experiment of the oil increment effect by different oil displacement systems. The results show the bound state remaining oils in strong water-washing layers were similar to free residual oils after polymer flooding, mainly in 4 forms:particle surface adsorption, intergranular adsorption, cluster, pore surface film. The percentage of free residual oils in medium water-washing rock is 3.7% higher than that of in strong water-washing rock; In the strong water-washing core samples after polymer flooding, the bound state residual oil reduced by weak base ASP flooding is 7.1% higher than that of by high concentration polymer flooding, with the obvious effect in reducing film-like remaining oil on the pore surface, and the ultimate recovery factor enhanced by 4.7% than that of high concentration polymer flooding.