LAUSR

Abstract Microbial potential of crude oil degradation coupled to methane production has attracted much attention as a basis for microbial enhanced energy recovery (MEER) technology. Here we performed laboratory incubation experiments mimicking in situ temperature and pressure conditions of subsurface oil reservoirs to evaluate the effectiveness of biological augmentation and stimulation for MEER. Using our high temperature and pressure incubation system, we successfully obtained a microbial community capable of methanogenic crude oil degradation from the Yamagata oil reservoir in Japan. To evaluate the potential of biological augmentation, we inoculated the microbial culture from Yamagata into production water from the Akita oil reservoir in which the indigenous microbial community cannot degrade crude oil. We observed methane production associated with toluene degradation, indicating that biological augmentation could be successful. We also evaluated the potential of biological stimulation, i.e. the effects of supplementing with different nutrients on crude oil degradation using the Yamagata oil reservoir sample. Intriguingly, addition of specific yeast extracts (YEs) resulted in notably enhanced methane production associated with the degradation of longer-chain n-alkanes as well as toluene. We further assessed the effectiveness of combining the biological augmentation and stimulation by inoculating the microbial culture from Yamagata together with the effective YE into the Akita production water, and found a large amount of methane production coupled to toluene and n-alkane degradation during the incubation. Taken together, our results suggest that the bio-augmentation and stimulation strategies demonstrated here could be a powerful tool for energy recovery from petroleum reservoirs both with and without innate crude oil degradation.