The poor volumetric sweep efficiency of water and invalid cycles caused by rock layer heterogeneity are major problems in crude oil production. In this study, four pairs of columns under different conditions containing different particle sizes of sand were tested to simulate heterogeneous rock layers. The results indicated that microbially induced calcium carbonate precipitation (MICP) was more durable than bioclogging (e.g., Sporosarcina pasteurii and extracellular polymeric substances (EPS)) even in the absence of a nutrient supply. The permeability reduction due to the MICP brought oil recovery improvement from about 44% to 83% in laboratory displacement experiments. Both pH and ammonium concentration slightly increased, reaching values of approximately 9.0 and 8.5 g L⁻¹, respectively. Permeability, an effective hydraulic indicator of pore volume, decreased from 16.0 D to 0.6 D due to plugging. The nuclear magnetic resonance (NMR) transverse relaxation time (T2) curve decreased due to the filling of voids by calcium carbonate precipitation after treatment. Moreover, the ureolysis reaction was still possible at high salinity and elevated temperature (<50 °C) despite the prolonged flow diversion period. This work further emphasizes the potential application of MICP to enhanced oil recovery (EOR).

Physic-chemical behavior and rheological property of PAM conditioned sludge are explored. Rheological analysis could act as a useful indicator to reveal the mechanism of sludge dewatering.