Abstract
In order to explore the development methods suitable for heterogeneous low permeability reservoirs and study the distribution characteristics of residual oil, photoetched glass and artificial core models with three permeability ratios of 1, 6, and 9 were prepared in this research. Three displacement schemes including polymeric surfactant flooding, polymeric surfactant with binary flooding, and binary flooding were designed at the same expenses to obtain the displacement mechanism of various residual oil saturations. The results show that the best displacement efficiency can be achieved by polymeric surfactant flooding, followed by polymeric surfactant with binary flooding, and binary flooding for the models with the same permeability ratio. Binary flooding mainly activates cluster and oil drop residual oils, polymeric surfactant with binary flooding mainly activates cluster, oil film, and column residual oils, whereas polymeric surfactant flooding mainly activates cluster, oil drop, and column residual oils. In addition, with the increase of the model permeability ratio, the recovery ratio of water flooding decreases, whereas the enhanced oil recovery and the variations in residual oil saturation gradually increase after carrying out different displacement measures. The viscoelastic and shearing effects of the polymeric surfactant flooding system can better displace the residual oil, assisting in the further development of heterogeneous low permeability reservoirs.
Highlights
Due to the complex pore structure and severe heterogeneity of low permeability reservoirs, causing large volumes of residual oil in the pores, it is imperative to take reasonable measures to reduce the effect of reservoir heterogeneity on ultimate recovery
Polymer retention in the pores increases the cost of oilfield development, as most of the residual oil remains in the reservoir [12,13,14,15,16]
Oil displacement experiment of the photoetching glass model consists of the following processes: (1) saturate with oil after vacuuming the photoetching glass model, (2) water flooding at a constant rate of 0.03 mL/h until the end of oil production from the model, (3) inject the three displacement systems at a constant speed of 0.03 mL/h and observe the distribution of residual oil in the model, (4) calculate the oil displacement efficiency and all kinds of residual oil saturation after the experiment, and (5) replace the model and repeat the above steps
Summary
Due to the complex pore structure and severe heterogeneity of low permeability reservoirs, causing large volumes of residual oil in the pores, it is imperative to take reasonable measures to reduce the effect of reservoir heterogeneity on ultimate recovery. The main mechanism of enhanced oil recovery by polymeric surfactant flooding is to improve oil displacement efficiency by emulsification while realizing mobility control. Very few studies on visual displacement experiments are carried out for low permeability reservoirs and quantitative analysis of different types of residual oil saturation; the mechanism that leads to low recovery ratio at the micro level is not clear. Oil displacement experiment using a photoetching glass model can visually see the deformation, migration, and accumulation of fluid in the pore structure; the distribution of different types of residual oil is different when different displacement fluids are injected. It is crucial to study the root causes that affect the fluid distribution and the formation of residual oil so as to find effective methods to improve the recovery rate of low permeability reservoirs. The above research can provide theoretical support for the development of low permeability reservoirs
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