Study on distribution characteristics of microscopic residual oil in low permeability reservoirs

Abstract

In order to develop methods to further enhance oil recovery after water flooding in low permeability reservoirs by improving oil displacement efficiency, the displacement mechanism of residual oil was studied by the application of different pertinent measures. For in-depth investigation of oil displacement and variations in residual oil saturation, a large number of visual glass model displacement experiments were performed with different methods, such as changing the displacement direction, cyclic water flooding, displacement pressure difference variation and polymer flooding. In this paper, the models were divided into three (low, medium and high) permeability levels, and the residual oil after water flooding was categorized in five different types: cluster, oil film, oil drop, columnar and blind end residual oil. The experimental results showed that cluster residual oil accounted for the largest proportion after water flooding. In addition, with the increase in model permeability, cluster residual oil saturation increased and other types of residual oil saturations decreased. Compared to other methods, polymer flooding showed maximum displacement efficiency for the same displacement pressure and permeability model. The procedure was then followed by changing the displacement direction, cyclic water flooding and changing the displacement pressure difference. The different residual oil types can be activated by different methods, for example, cluster and columnar residual oil by changing the displacement direction, cluster and columnar residual oil by cyclic water flooding, cluster and oil drop residual oil by increasing displacement pressure difference. Moreover, all of the above mentioned five (05) types of residual oil can be activated by polymer flooding.