MICROBIAL CONVERSION OF RESIDUAL OIL TO METHANE EXTENDED PERIOD OF PETROLEUM PRODUCTION

After secondary or even tertiary recovery,a significant portion of petroleum remains in the reservoir.A novel approach to this problem is the bioconversion of hydrocarbons entrained in marginally producing fields and/or depleted reservoirs to methane.Data from numerous laboratory experiments and filed observations show that residual oil could be transformed to biogenic methane by an anaerobic consortium.This suggests the possibility of new methane generation from existing residual oil deposits in-situ and in real time to form a renewable source of natural gas.Other than viable methanogenic microbes present in the system,various evidences of methanogenesis can be derived from light isotopic methane,heavy isotopic carbon dioxide and heavy isotopic inorganic dissolved carbon,biodegraded wet gas and compositional gradients within oil column.Methods of stimulating secondary biogenic methane generation involve the introduction of hydrogen and nutrients,including nitrogen,phosphorous and potassium compounds,into reservoirs,modification of the formation environment based on geological and geochemical analysis and removal of intermediate metabolite products.The varied geology,aqueous che-mistry and microbiology of different production sites will most likely demand site-specific strategies.