Study On Physical Changes Of Rock And Enhanced Oil Recovery Of WAG In Low Permeability Reservoirs

In our country,the proportion of low permeability oil and gas production increased year by year.The low permeability resource is becoming more and more important to replace traditional resources.The method of WAG can not only storage greenhouse gases,but also improve oil recovery by combining the characteristics of water flooding and gas flooding.Based on the microscopic visualization experiment and long-core experimental to study various oil displacement mode of remaining oil distribution,oil and gas water movement and the recovery efficiency.It is very important to understand the principle of improve recovery efficiency.Firstly,the microscopic visualization model was used to study the mechanism of CO2 flooding.The state and distribution of residual oil were analyzed qualitatively,and the quantitative method for analyzing residual oil was obtained by microscopic seepage experiment,which used for the analysis of the saturation of residual oil and recovery of kinds of flooding method.Results show that the residual oil is mainly the shape of H column,cluster.Gas flooding process prone to "leaping movement" and bubble breakage phenomenon.The rate of recovery is highest 72.42% when gas and water ratio is 1:1,the displacement speed is 0.10mL/min.Secondly,the effect of different displacement methods was studied by using long core experiments device.The slug size,conversion injection time,gas-water ratio and injection rate is considered.Then the optimal injection parameters of WAG are obtained.The results showed that the recovery rate was 63.20% when directly using WAG,the gas-water ratio is 1:1,the slug size is 0.2PV,and the injection rate is 0.10cc/min.Which is 31.07% higher than that of continuous water flooding,which is 17.06% higher than continuous CO2 flooding.Finally,the study on the change of physical properties after WAG was carried out.The pore permeability parameters were measured by gas permeability device,nuclear magnetic resonance(NMR)and CT scanning.The results show that the change of two core porosity is 2.92% and 3.33%.The change in permeability was 28% and 37.04%.The pore structure of the core is more complicated and the heterogeneity of the pore and throat is enhanced after WAG.The proportion of small pore throat increases,and the WAG causes the radius of pore throat to become smaller,and the permeability is greatly reduced,which is not conducive to oil production.The research results have deepened the understanding of the recovery of oil and gas in the low permeability reservoirs,which is of great significance to guide the production practice of low permeability reservoirs.