Screening and field application of microbial-flooding activator systems

This study aims to further enhance the oil recovery of reservoirs in the Zhong-2 Block of the Gudao Oilfield by identifying the most effective microbial-flooding activator systems and applying them in the field. We began by analyzing the structure of the reservoirs' endogenous microbial communities to understand the potential impact of microbial flooding. This was followed by determining commonly used activator systems based on their abilities to stimulate oil-displacement functional bacteria. Through laboratory experiments on oil displacement efficiency and sweep characteristics, we determined the optimal activator injection method (injection ratio) and the requisite bacterial concentration for maximal microbial-flooding efficacy. Finally, we selected the optimal activator systems and applied them to field tests. Our findings suggest the target block is highly receptive to microbial-flooding. In terms of performance, the activator systems ranked as No. 3 > No. 4 > No. 1 > No. 2. Interestingly, a deep activator system, when compared to the top-performing No. 3 system, exhibited a higher bacterial concentration peak and longer peaking duration. Optimal oil displacement effects were observed at a 1:4 vol ratio between the No. 3 activator and deep activator systems, with bacterial concentrations of up to 10⁶ cells/mL or above. Field tests with the selected activator systems, following a specific injection protocol, demonstrated a notable increase in oil production and a reduction in water cut.