Microbial effects on hydraulic conductivity estimation by single-well injection tests in a petroleum-contaminated aquifer

Single-well injection tests in a petroleum-contaminated region stimulate microbial growth and cause bioclogging because of the intrusion of elevated dissolved oxygen (DO), which may affect the hydraulic conductivity (K) estimation. In this study, we developed a mathematical model considering multispecies and multiphase reactive transport and bioclogging for a single-well injection test in a confined aquifer to investigate the microbial effects on parameter estimation. The finite-difference method was used to solve the model. The temporal heads in the injection well in both cases of clean and petroleum-contaminated aquifers were compared. The results indicated that the bioclogging led to an abnormal bulge of the drawdown-time curve at an intermediately late time of injection. Based on sensitivity analysis and Cooper-Jacob straight-line fitting associated with the least square method, the underestimation degree of K was 17.7% with default parameters, 11.9% with double injection rate Q, 31.1% with double maximum biomass growth rate mu(maxJ) and 39.5% with double initial contaminant concentration C-2(ini). Moreover, introducing an approximate Damkohler number indicated that increasing Q reduced the underestimation by flushing and diluting the essential materials for microbial growth to the downstream and that larger C-2(ini) and mu(maxJ) resulted in an increase in underestimation due to the increase in favorable conditions and strong growth ability of microbes. Finally, we suggest that when petroleum contamination is inevitable in a single-well injection test, moderate increases in Q and the test duration can reduce the underestimation degree of K to a considerable extent.