Feasibility Of Viscosity Reducer Flooding For Enhancing Heavy Oil Recovery

The ordinary heavy oil reservoirs in Henan oilfield are restricted by the formation conditions,which means the oil recovery of most blocks is quite low.After multi-cycle steam stimulation,the oil-steam ratio is reduced,and the recovery factor cannot be further improved by throughput.In order to solve the problem,a method of injecting a new type of active polymer heavy oil viscosity reducer to improve the development effect was proposed.The active polymer heavy oil viscosity reducer studied in this experiment has both hydrophilic and hydrophobic groups in the molecular chain,thus it combines the good properties of polymers and surfactants.In addition,the active polymer viscosity reducer can change "water-in-oil" emulsified state to the "oil-in-water" state under the formation condition.The static evaluation of the viscosity reducer and indoor flooding experiments were conducted in this paper.The performance of the active polymer viscosity reducer were analysed in detail,including physical and chemical properties,adsorption characteristics,and its injectability and oil displacement effect under different concentrations of the viscosity reducer.Therefore,the paper tried to understand whether the active polymer viscosity reducer is suitable for heavy oil exploration experiment,and provide a theoretical basis for further enhanced oil recovery.The static experiments results showed that the viscosity of the viscosity reducer solution prepared from formation water with a salinity of 1870 mg/L ranged from 3.2 m Pa·s to 25.8 m Pa·s.Compared with the viscosity reducer solution in distilled water,the viscosity decreased by 79.75% to 97.05%,indicating that the salinity of formation water has a greater influence on viscosity.The initial oil-water interfacial tension reduced from 35 m N/m to 6.22 m N/m after adding 1500 mg/L of the active polymer viscosity reducer solution,indicating that it has good interfacial activity.The emulsion also has good stability through analyzing the stability index TSI value of the emulsion formed by the crude oil and the active polymer viscosity reducer.The adsorption characteristics experiments showed that the adsorption equilibrium time of different concentrations of viscosity reducer solution is about 7 h? 9 h,and the adsorption amount of 1200 mg/L viscosity reducer solution is 3.08mg/g.The ion exchange effect of the viscosity reducer solution and the oil sand surface was stronger.The amount of adsorption was large.The injection experiment showed that with the change of active polymer viscosity reducer concentration and core permeability,the resistance factor was 48.96 ? 69.37 and the residual resistance factor was 5.85 ? 25.11.The core flooding experiment showed that when 0.4 PV viscosity reducer with 1500 mg/L concentration was adopted.the oil recovery was increased by 9.36% with permeability of 500×10-3?m2.For a core experiment with a permeability of 900×10-3 ?m2,the degree of recovery can be increased by 8.89%.The active polymer viscosity reducer can also increase the recovery of heterogeneous reservoirs.It is suitable for core models with a permeability difference of less than 20,and the overall recovery can be increased by 9.96% to 12.2%.It is concluded that the active polymer viscosity reducer has good physical-chemical properties,injectivity and potential of enhanced recovery efficiency,which provide a theoretical reference to the development of heavy oil reservoirs in HN oilfield.