Study On The Environmental Behavior And Pollution Characteristics Of Chemicals For Alkali-surfactant-polymer Flooding

Alkali-surfactant-polymer(ASP) compound flooding is a new method for tertiary oil recovery mentioned at the 80s of the 20th century. It is compounded by the alkaline, surfactant and polymer, containing the common advantage of surfactant and polymer flooding. It can improve oil displacement efficiency, increase the involved volume, meanwhile, it can reduce the usage of surfactant sharply. So it has been widely used in major oil fields, being a major measure to increase the oil productivity. However, as the ASP chemicals are applicated largely, the environment will be damaged inevitably. It is necessary to study and evaluate the pollutants environmental behaviors and impacts of ASP chemicals to provide a theoretical basis for environmental management of oil field and the reliable technology guarantee for the next ASP large-scale application.In this paper, according to the existing domestic and overseas environmental standards and evaluation methods, the main environmental particular pollutants in ASP are identified as alkali (sodium hydroxide), surfactant (linear alkylbenzene sulfonates, unsulphonic oil) and polyacrylamide (acrylamide) by modern analytical method. And the impact of main environmental particular pollutants in ASP on environment are analyzed in detail.The alkali and unsulphonic oil in ASP can cause enormous harms to ecological environment, showing the characteristics of durable and tractable. The toxicity of surfactant is related to the concentration and structure of surfactant. The polyacrylamide (PAM) is less environmental contamination and non-toxic to plants and animals, but its degradation product acrylamide (AM) can cause great harm to human beings and environment.The environmental behavior of ASP flooding chemicals in soil are studied with great focuses by experiments. The transfeering behavior under natural or simulated rainfall conditions of cell contaminant(sNaOH, LAS, PAM)and ternary pollutants are studied through the soil column experiments in different soils(black soil,loess soil,saline alkali soil), different times and different amount of pollutants. Effect of soil types (black soil,loess soil,saline alkali soil), time and amount of pollutants on the law of transferring in soil are investigated and the vertical migration law in soil are found. Moreover, the adsorption and degradation of PAM and LAS on the environment (river, soil) are also studied. LAS degradate fast in the environment. PAM has a high adsorptive affinity on soil and it is very difficult desorbed.This paper explained the conditions and building process of the migration and transformation model, established the mathematical equations and took series of possible extension in comprehensive consideration of soil solute transport mechanism, law of conservation of mass and the convection-dispersion of soluble contaminants in the homogeneous soil/water environment system under the ideal situation. Then, the equations, together with the initial conditions and the associated boundary conditions, make a specific meaningful soil solute transport model. In this paper, a one-dimensional soil column simulation of LAS migration in 3 months has been used as a validity comparison to the model application in the saturated soil environment. The results show that, for the description of contaminants migration process in saturated soil environment, model has a strong applicability. Contraposing the typical condition that ASP chemical agents have leaked of Daqing oilfield, simulation calculations have been carried out in the precondition of idealizing the complex soil environment. The distribution of contaminants concentration and the prediction of the range of theoretical migration have been figured out by means of calculations and analysis. After ASP chemical agents accidentally leaking within one year, the value of LAS concentration accumulate in a short period of time, then stay in the soil surface regularly. The highest concentration value is 14.5 mg/L. PAM, another sort of contaminants, due to its special physical and chemical properties, the concentration of PAM is about 4.5 mg/L after 10 years though it was regularly distributed. The edge of migration deep into 1.9 m, it follows that the migration process has been slow. As for NaOH, which can penetrate into the aquifer from the soil surface in only three months because of its great water solubility and high reactivity. But the concentration can be negligible, for the impact of water pH is also within the scope of national safety standards. After the independent thorough analysis of the accidental leaked contaminants, a general common migration law of the soluble contaminants in the soil environment can be drawn as a conclusion.Based on the comprehensive analysis of environmental behaviors of ASP pollutants in soil, we can conclude that most particular pollutants in ASP stay in the soil surface.Even much more pollutants on soil surface under rainfall conditions, it will not affect groundwater of daqing; LAS is not a durable pollutant, for it has a fast degradation speed. The polyacrylamide (PAM) is non-toxic, the degradation product acrylamide (AM) of PAM can cause great harm to human beings and environment, but it can degradate quickly in the environment, so they should not be contained in the main pollutants of ASP flooding. The alkali equivalent to the general alkaline pollutant, and the unsulphonic oil can be seemed as benzene pollutant. They are very common in the development of oil field, showing the characteristics of durable and intractable, so they should worth more attention of human beings.