Experimental study on the types and infuential factors of residual oil in oil reservoirs after early polymer flooding

In order to explore the distribution characteristics of remaining oil after early polymer flooding to provide the basis for the subsequent potential tapping, a heterogeneous micro-pore etch model was developed based on reservoir thin section, mercury pen- etration and other experimental data to carry out laboratory microscopic displacement experiments on the types and distribution laws of residual oil after early polymer flooding. Then, focusing on two major influential factors (e.g. injection rate and injection system), 8 experimental schemes of heterogeneous microscopic model were designed respectively for 4 injection systems (e.g. water flooding, early low-concentration polymer flooding, early high-concentration polymer flooding and early polymer-surfactant binary flooding) under two displacement conditions (e.g. low-speed and high-speed displacement). Finally, the effects of injection rate and injection system on the distribution forms of film-ike residual oil, Y- shape residual oil, column like residual oil and cluster like residual oil were analyzed. It is indicated that in the same injection system, the effect of injection rate on cluster-ike residual oil is the greatest. In addition, the sweep efficiency of water flooding and early low-concentration polymer flooding can be increased effectively by increasing the injection rate, and correspondingly the distribution of residual oil is reduced, while for early high-concentration polymer flooding and binary flooding, the effect of injection rate on the form and distribution of residual oil is not obvious. After being displaced by different injection systems, the main forms of residual oil are different. The reducing effect of injection systems on cluster-like residual oil at low injection rate is ranked as polymer surfactant binary flooding>high-concentration polymer flooding>low- concentration polymer flooding>water flood- ing. In conclusion, the studies on the enrichment laws of remaining oil and their main control factors in the case of early polymer flooding by means of micro-pore model can provide the support for the researches on early polymer flooding.