外加直流电场下粘土矿物的膨胀特性研究

实验研究了外加直流电场作用下粘土膨胀率的变化。结果表明,在电场作用下,粘土膨胀率降低,电解膨率大小与粘土性质、电场强度、体相溶液矿化度及施加电场时机等有关。在相同电场强度条件下,膨胀性强的蒙脱石的电解膨率最大,而伊利石、高岭石的电解膨率较小。蒙脱石的电解膨率随着电场强度的增加而增加,当电场强度高于临界值(本实验中为2 V/m)时,电解膨率值基本不变。随着NaCl浓度的增加,蒙脱石的电解膨率以指数规律降低。施加电场时机对电场降低粘土膨胀率的效果有较大影响:在注入蒸馏水的同时施加电场可以有效防止粘土膨胀;在注入蒸馏水之后施加电场可以有效降低粘土膨胀率;先施加低强度电场(EFS=2 V/m)然后再注入蒸馏水,可以造成粘土的膨胀,即使提高电场强度,粘土膨胀率仍然很大。

EXPANSION CHARACTERISTICSOF CLAY MINERALSUNDER THE APPLIED DIRECT CURRENT ELECTRIC FIELD

The variation rule of expansion ratio of clay under the applied direct current electric field was studied experimentally.The results of experiments indicated that the expansion ratio of clay declined under the electric field and the electric shrinkage rate of clay varied with the characteristics of clay,the electric field strength(EFS),the salinity of bulk phase solution and the time of exerting electric field.The electric shrinkage rate of montmorillonite was the largest while that of kaolinite and illite was lesser under the same EFS.The electric shrinkage rate of montmorillonite increased with increasing EFS and didn't increase again when EFS was higher than the critical value(2 V/m in this paper).The electric shrinkage rate of montmorillonite exponential declined with increasing salinity under the same EFS.The exerting electric time had some effect on the decrease of expansion ratio under the electric field: exerting DC electric field while injecting low salinity water could prevent effectively the swelling of clay;exerting DC electric field after injecting low salinity water could reduce effectively the expansion ratio of clay;while exerting low strength DC electric field(EFS=2 V/m) before injecting low salinity water could cause the expansion of clay and the expansion ratios were larger than the original state although exerting the higher strength DC electric field(EFS=12 V/m).The findings in this paper indicated that the applied DC electric field had the capability of reducing the expansion ratio of clay,which offered the theoretical foundation for applying the applied DC electric field to protecting or restoring the damage of swelling clay and improving the permeability of reservoir.