孔隙型热储层中溶解性有机质在硝酸盐还原过程中的迁移转化实验研究

Experimental study on transportation and transformation of dissolved organic matter during nitrate reduction in the porous thermal reservoir

以新近系明化镇组热储层细砂为岩土介质,分别在25、45℃开展硝酸盐运移的室内土柱模拟实验。采用CXTFIT 2.1软件、三维荧光光谱技术,探索溶解性有机质(DOM)在硝酸盐还原过程中的迁移转化动力学规律。结果表明:25、45℃时硝酸盐的迁移转化遵循一级衰减动力学假设的溶质对流-弥散方程,其纵向弥散系数和衰减系数均随温度的升高而明显增加,这也可由荧光峰B 1和T 1的变化进一步得到证实。由于淋出液中溶解性有机碳随孔隙体积数增加而降低、且随温度的升高而升高,而特征紫外吸光度却相反,这说明甲醇等小分子有机物更易于作为电子供体参与硝酸盐还原反应,且高分子芳香族有机化合物在较高温度下更易于参加硝酸盐的还原反应。两个温度下,淋出液荧光指数大于1.9且快速增加并趋于稳定,生物源指数为1.14~1.27,这说明模拟的孔隙型热储层中DOM以内源输入为主,模拟的水-岩系统微生物环境逐渐稳定。

The column experiments of nitrate transport were carried out at 25,45℃in the porous thermal reservoir which was composed of Minghuazhen Formation in Neogene period.Three dimensional fluorescence spectrum,combined with CXTFIT 2.1,was used to investigate dynamic changes in the transportation and transformation of dissolved organic matter(DOM)during nitrate reduction.The results showed that the transportation and transformation of nitrate at 25,45℃followed first-order reaction kinetics in convection-dispersion equation.The simulated values of the first-order decay coefficient and hydrodynamic dispersive coefficient were markedly increased with temperature,which could also be further confirmed by variations in fluorescence peaks B 1 and T 1.The effluent dissolved organic carbon decreased over pore volume and increased with the increase of temperature.However,the variation of specific ultraviolet absorbance value was inverse,indicating that small molecular weight organics,such as methanol,were more likely as electron donors during denitrification and the polymer aromatic organic compounds were more likely to participate in the nitrate reduction at higher temperatures.At two temperature levels,the fluorescence index values were all above 1.9,increasing rapidly and then tending to be s table.And the biological index values were between 1.14 and 1.27,indicating that DOM in simulated pore thermal reservoir was dominated by endogenous input,and the microbial environment of the simulated water-rock system was gradually stable.