Study On The Separation Technology And Mechanisms Of Produced Liquid By Na₂CO₃ Alkali-surfactant-polymer Flooding

In comparison with the NaOH ASP (alkali-surfactant-polymer) flooding, Na₂CO₃ ASP flooding has numerous advantages such as lower formation damage, simpler produced liquid composition and less scale deposition in oil well and surface production facilities. Research work on the chemical formulation of Na₂CO₃ ASP flooding and its pilot tests have increased dramatically during the last several years. However, no researched work has been done on the produced liquid of Na₂CO₃ ASP flooding, as all the research work which has been conducted on the the emulsification, stabilization and destabilization of ASP flooding produced liquid only targeted NaOH ASP flooding. Thus, it makes sense to conduct research work on the emulsification, stabilization and destabilization of the produced liquid of Na₂CO₃ ASP flooding.Physico-chemical properties, mechanisms concerning the emulsification and demulsification of Na₂CO₃ ASP flooding produced liquid, as well as demulsifiers and water clarifiers targeting Na₂CO₃ ASP flooding produced crude oil and water were researched in this study.Na₂CO₃; surfactant and polymer in Na₂CO₃ ASP flooding produced liquid intensify its emulsification via two major mechanisms, i.e. lowering of oil/water interfacial tension by alkali and surfactant, and increase of water phase viscosity by polymer, resulting in smalleroil droplets. The increase of water phase viscosity by polymer also tends to lower creamingand water membrane drainage rates of inverse crude oil emulsion. Low content of alkaline and surfactant hinder the flocculation and coalescence of oil droplets by increasing the negative charge density, viscosity and rigidity of oil/water interface. Surfactant at a content of 0.06% lowers the dynamic oil/water interfacial tension to 10.2～11.1mN/m. Polymer and surfactant at contents of 0.04% decreases the original median diameter of oil droplets in inverse produced liquid with an alkali content of 0.1% to as low as 2.64μm . The residual top oil water-cut of a 80% inverse produced liquid with contents of alkali, surfactant and polymer respectively at 0.12%, 0.02% and 0.04% was still as high as 6.93% after 150min static settling while the water phase oil content of a 80% inverse produced liquid with contents of alkali, surfactant and polymer respectively at 0.12%, 0.03% and 0 was as high as 1344mg/L after 30min static settling.The barium, sodium and sulfur contents of Na₂CO₃ ASP flooding produced crude oil were higher than those of water flooding produced crude oil while the iron, nickel and magnesium contents of the former are lower than those of the later. Suspended solid particles in the water phase of Na₂CO₃ ASP flooding produced liquid during phase separation are mainly aluminosilicate and silica particles ranging from 1μm to 7μm. Low interfacial tension is 26.1mN/m, strong negatively charged oil/water interface is -27.7mV for Zeta, strong repulsive force between oil droplets which hinders their flocculation and coalescence. Emulsification of Na₂CO₃ ASP flooding produced liquid is strong and diameter of oil droplets is l¹0μm. The produced liquid included the characteristics of slow separation, anionic surfactant and polymer bearing, high suspended solid particle content (156mg). The oil content of separated produced water from Na₂CO₃ ASP flooding produced liquid with low injected chemical contents but no demulsifier injection can not meet the 100mg/L limit for filter feed until the produced liquid has undergone 16h static settling.Quantum chemistry methods were used in the molecular design of demulsifier molecules. The predicted H-bond energy among various functional groups, water molecules and some typical functional groups on asphaltene molecules show that the H-bond energy between 2-methylbutylsulphonate anion and water molecules (-221.8535KJ/mol) is relatively high, followed by the H-bond energy between 2-methylbutylamide and water molecules(-109.4827KJ/mol) , while the H-bond energy between 5-aminonaphthol and water molecules (-92.6796KJ/mol) is relatively low. Sulfonic and amido- groups were picked up as functional groups in demulsifier molecules, leading to the development of a demulsifier named as GFD410-8 which was used to accomplish the oil/water separation of Na₂CO₃ ASP flooding produced liquid. With the dosage of GFD410-8 at 30mg/L, the field Na₂CO₃ ASP flooding produced liquid was well separated by continuous treatment with the water-cut of emulsified crude oil in the range of 4.4%～14.6% and the OIW of separated produced water in the range of 490mg/L～840mg/L, which are respectively far below the technical limits of 20% and 3000 mg/L for free-water knockout set in a relevant national standard GB50350-2005.The compound water clarifier CF1002 developed in this study features good clarification performance .on the low chemical content field Na₂CO₃ ASP flooding produced water. Treated with CF1002 at a dosage of 757mg/L, the field Na₂CO₃ ASP flooding produced water was well treated with suspended solid content at 8.4mg/L, which are respectively far below the technical limits of 20mg/L for polymer-containing produced water to be re-injected into high permeability reservoirs set in a relevant corporate standard of Daqing Oilfield Company Limited Q/SYDQ0605-2006.