| According to the classification of lithology,the reserves of low-permeability conglomerate reservoir is 15.7%of the national low-permeability reservoir reserves,so it is very important to put them into industrial production.Baqu low-permeability conglomerate reservoir belongs to the middle porosity-low permeability reservoir with strong heterogeneity which leads to high water content and low water drive recovery.Polymer/surfactant flooding technology can reduce the effect of heterogeneity and control the water content effectively.In this paper,the properties of polymer and surfactant are evaluated separately by experiment.Then polymer and surfactant which are adaptive to reservoir are seleted to investigate solution behavior and oil displacement efficiency of binary system.In low-permeability reservoir,it is necessary to consider the injection problem of polymer in binary system,firstly,the particle size of 5 hydrophobic associating polymer with different molecular weight of 2 million to 7 million ranges from 130.1nm to226.0nm,which is 1/5?1/4 that of the reservoir pore throat size,that means polymer will not cause pore blockage theoretically.Through the optimization of surfactants,the results show that the interfacial tension of alkanolamide(CDEA)solution and crude oil is as low as 0.003409mN/m,when the mass concentration of CDEA is 0.2%.The stability factor of CDEA increases a little when the concentration is 0.1%?0.2%,then grow fast,but keep stable at last.When the concentration is 0.2%,the type of emulsion is O/W,the stability factor is 5.5.The selected polymer and surfactant are mixed to be binary system.CDEA with mass concentration of 0.2%is adaptive to five kinds of hydrophobic associating polymer.In polymer and surfactant system,the hydrophilic groups and hydrophobic side chains of polymer chains are easily to be replaced by surfactant,resulting in forming more dense network structure and higher viscosity of P/S system.The interfacial tension of binary system is also rising.And under the condition of low concentration,the type of emulsion of crude oil and P/S system of surfactant and polymer is O/W.In oil displacement experiment,the injectivity of binary system of CDEA of 0.2%and polymer with five different molecular weight is firstly evaluated,it shows that the higher relative molecular weight and higher concentration of polymer in P/S system,the worse the injecting ability of the two element system.When the resistance coefficient is over 81.0 and the residual resistance coefficient is over 40.6,the two element system can not be injected.What's more,the influence of core permeability on the injectivity of P/S system can not be ignored.Secondly,the injection rate and injection volume are optimized.The results shows that when the injection rate is 0.2mL/min,the increase of recovery is the largest,which is 15.5%when it can not only activate the crude oil but also stop forming dominant channel of water.With the increase of injected slug volume,the increment of recovery efficiency decreases,when the injection slug volume reaches 0.4PV,the displacement efficiency increases to 17.9%.Considering the cost,the best injection volume is 0.4PV.Finally,the effect of permeability contrast and variation coefficient on oil displacement efficiency of polymer/surfactant flooding is studied by inhomogeneous physical simulation experiments of double parallel and triple parallel cores.The results shows that as the permeability contrast varies from 2.04 to 15.07,The recovery rate of high-permeability layer is increasing,but the effect of low-permeability layer is getting worse.Combined with the curve of liquid production of high-permeability and low-permeability core,it can be seen that P/S system plays an obvious role in profile control and it can enhance oil recovery in high-permeability layer,activate low-permeability layer,improve the sweep efficiency and displacement efficiency at the same time. |
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