Research on plugging characteristics of microorganism induced calcite precipitation in sandstone environment

Microorganism-induced calcite precipitation (MICP) has been proposed to increase crude oil recovery for more than two decades. It is only recently that mine trials have emerged. The present study was conducted to advance the application of MICP for enhanced crude oil recovery. The changes of core permeability and bacterial biomass on permeability reduction rate during MICP treatment were investigated by core blocking experiments and reverse unblocking experiments. The permeability conditions for biomass and calcite production blocking were explored. Based on this, the changes in mechanical properties of the cores by MICP were explored by unconfined pressure experiments. Finally, the mineral composition and mineral phases were analyzed by XRD and SEM. Our study shows that MICP is much less effective at permeabilities less than 66mD. The decrease in permeability presented in the experiment comes from the blocking effect of the injection end of the core on the bacteria. The compressive strength of the MICP-treated cores was increased by 10.05% and was more resistant to brittle damage. Also calcite is attached to the sandstone matrix. The characteristic peaks of calcite were observed in the cores treated with MICP by SEM and XRD. In addition, under the same culture conditions, the mineral morphology in the sandstone environment is quite different from that in the shake flask. In the sandstone environment, calcite is tightly adsorbed on the sandstone matrix, showing a typical rhombic hexahedral structure, and in the shake flask environment, it is more Spherical or spherical aggregates. Based on the above study, the blocking mode of MICP is proposed. The free agglomerated calcite particles form a physical seal in the pore throat and the biofilm mineralizes directly in the sandstone matrix together to seal the sandstone cores. The results of this study report a new mineral morphology difference in MICP. It is also a theoretical support for further improving the MICP for enhanced oil recovery.