MEOR CASE STUDIES FROM INDIA'S OIL AND NATURAL GAS CORPORATION, LTD

One technology for improving oil recovery is a process known as Microbial Enhanced Oil Recovery (MEOR). Microbial metabolism in the formation can produce solvents, surfactants, gases, acids, polymers, and of course more bacteria, which can alter the physical and chemical characteristics of the oil in the reservoir, promoting additional oil recovery. Recent field trials by India's Oil and Natural Gas Corporation evaluated a consortium of naturally occurring microbes developed by investigators at The Energy Research Institute and the Institute for Reservoir Studies, New Delhi, India. These deep-subsurface microbes, known as extremophiles, thrive without oxygen in high temperature (90° C), high salinity (2%), high pressure (4500 psi) environments. Extremophiles commonly found in formation fluid include Clostridium, Bacillus, Thermotoga, Thermoanaerobacter and Thermococcus species. Extremophile cultures and nutrients were delivered into the formation by a prescribed process sequence of pre-flush, microbe injection and post-flush followed by well closure and incubation for 21 days; a process called Huff and Puff. This sequence was designed to alter the physical and chemical characteristics of the formation and associated fluids in a manner that could maximize additional oil recovery. Application of this method to twelve wells in four well fields produced significant, positive results in nine wells. In the best performing fields, the microbial consortium was isolated from the same candidate-well formation and a three fold increase in oil production and a significant reduction in water cut was achieved. MEOR performance was dependent in part on the characteristics of the formation and on the ability to deliver nutrients and microbes into the formation. Results from reservoirs with high asphaltene and resin content, and poor petrophysical properties were disappointing. This paper contrasts the petrophysical properties of those fields where positive results were obtained with those fields for which there was limited success or no success at all. Guidelines for the future application of the MEOR process in these types of fields will be outlined and a procedure for preselecting fields for future evaluation will be discussed.