Crude oil degradation in oilfield produced water by immobilized microbes and oil recovery improvement after its reinjection

Oilfield produced water (OPW) with crude oil is a huge threat to the natural environment. For the treatment of OPW, degradation of crude oil in OPW by microorganisms and OPW activation by microbial metabolites for oil recovery improvement after reinjection may be an effective and sustainable approach. In this study, the degradation of crude oil in OPW by immobilized isolated bacteria was designed and the enhancement of oil recovery by reinjecting treated OPW was examined. Aldehyde fiber was found to show the optimum immobilization effect for three isolated oil-degrading-bacteria (Pseudomonas sp. ZJI-1, Acinetobacter sp. YMJ-1, and Gordonia sp. G1). The crude oil degradation rate of the immobilized bacteria reached 82.6% within 7 days. The contents of some bioactive molecules helpful for oil recovery, including rhamnolipid and acetic acid, increased continuously in the designed system. Core flooding tests demonstrated that oil recovery increased by 8.61% after the treated-OPW reinjection. In summary, the immobilized bacteria could effectively remove crude oil from OPW, increase the contents of rhamnolipid and acetic acid, and in particular, improve the oil production efficiency after reinjection.