| Many blocks have been carried on Polymer flooding in main reservoir of Sazhong oilfield since 1996, some completed blocks have good performance that improved the recovery efficiency by 10-14% and the cumulative recovery degree reached more than 50%. At present, wells with the water cut more than 98% accounting 43.6% of the total wells and they have been shut-in in the block where polymer flooding has been transferred to subsequent water flooding. The production of these wells resulted in high produced fluid, high water cut and inefficient circulation between injection and production, which will increase the cost of production. But there are about 50% of the reserves not produced in polymer flooding reservoir. Moreover there is still no effective technology to improve oil recovery further after polymer flooding. Surfactant/polymer binary compound flooding system remove the alkali in the formula comparing with the ASP flooding, which can maximize viscoelasticity of polymer, weaken corrosion and scaling caused by alkali, maintain ultra-low interfacial tension, reduce the cost of production and improve the environmental performance of chemical displacement agent obviously, at the same time the oil displacement effect is close to the ASP flooding. Therefore, it is necessary to carry out the experiments on characteristics and displacement with non-alkali binary compound system in order to explore the effective method to improve oil recovery further after polymer flooding.This paper focused on the class I reservoir in the west of Sazhong in the Daqing oilfield. First the characteristics of the binary compound system were studied, including rheological property, interfacial tension and injection ability. The influence of the injection system, core permeability, polymer concentration, surfactant concentration and polymer relative molecular mass to interfacial tension and injection ability was analyzed. Isothermal adsorption curve of polymer and surfactant was studied by static method in binary system, and the dynamic adsorption retention was studied by using the natural cores. By the simulation of emulsion, emulsion stability, viscosity and the effect that polymer and surfactant have on rheological effect on the oil-water interface of binary system were studied. Based Darcy's law and material balance method, the determination experiment of relative permeability curve was carried out, the influence of the injection system, core permeability, polymer concentration, surfactant concentration, polymer relative molecular mass and rock wettability to the relative permeability curve was analyzed. Oil displacement experiment was carried out by outcrop columnar core and outcrop homogeneous core and gets the influence of the polymer average molecular mass, mass concentration, surfactant concentration and capillary number change of the binary compound system on oil displacement efficiency. Finally the development effect and economic benefit of non-alkali binary flooding block were summarized.Researches show that with the increase of polymer relative molecular mass, concentration and salinity, the viscosity of the polymer system, the first normal stress difference, energy storage modulus and energy consumption modulus increase, at the same time interfacial tension increase. With the increase of surfactant concentration, the viscosity of binary systems firstly reduces significantly then reduces slowly, and the interfacial tension decrease. Shearing has an effect on rheological property and interfacial tension of polymer system, which all parameter values declined. Experiment of injection ability in the binary compound system showed that polymer with low molecular weight have higher formation compatibility, and inject ability of the binary system greatly enhanced after simulating shearing action. Adding polymer in the binary compound system, the adsorption of surfactant on oil sand is reduced. With the increase of the times of adsorption in the binary compound system, interfacial tension increase in order. Strong lipophilicity, residual oil and low permeability will lead to the adsorption of surfactant in cores in the binary compound oil displacement system increases. On one hand, the stability of the emulsion of binary system is due to polymer and surfactant adsorption on the surface of the oil/water boundary forming solid adsorption film with viscoelastic characteristics, which can effectively prevent coalescence instability caused by collision between droplets. On the other hand, the polymer can increase the solution viscosity in the continuous phase, and form the network structure between polymer molecular because of chain winding, which will prevent the free movement of the droplets and boost the emulsion stability. Cores with high permeability and strong hydrophilic have high recovery; oil displacement effect of the binary compound system is better than that of water flooding and polymer flooding, and the higher the concentration of polymer, the bigger the polymer molecular weight, the better oil displacement effect of the binary compound system. With the increase of polymer average relative molecular weight, mass concentration and the capillary number in the binary compound system, the oil displacement efficiency of the binary compound system increase, total recovery increase. As for the outcrop homogeneous long core, when the concentration of surfactant in main slug of non alkali binary system up to 0.2%, the viscosity of the system reach above 30mPa.s, the recovery of non alkali binary system after polymer flooding increase by more than 10% OOIP, achieving the ideal effect. According to the influence surfactant concentration and the viscosity of the system have on the the oil displacement effect and system performance in comprehensive evaluation results, the concrete scheme in the pilot test is give. The recovery in the whole test field and the center well is greatly improved, and the effect of increasing oil is obvious. Numerical simulation showed that without drill down, the expected eventually recovery degree was 59.25%in the whole experimental zone,5.9% higher than that of water flooding; the expected eventually recovery degree of central district was 60.1%,6.3%higher than that of water flooding. Estimate according to the final recovery of 5.9, the cumulative oil production of 25.48 X 104t, the total cost is ?23879×104, the average oil exploitation cost of ?937.1 per ton in the whole process of testing. The field test results show that this technique is successful and obtains good economical benefit. |
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