Provided for non-commercial research and educational use only. Not for reproduction, distribution or commercial use. This chapter was originally published in the book Advances in Applied Microbiology, Vol 66, published by Elsevier, and the attached copy is provided by Elsevier for the author's benefit and for the benefit of the author's institution, for non-commercial research and educational use including without limitation use in instruction at your institution, sending it to specific colleagues who know you, and providing a copy to your institution’s administrator. All other uses, reproduction and distribution, including without limitation commercial reprints, selling or licensing copies or access, or posting on open internet sites, your personal or institution’s website or repository, are prohibited. For exceptions, permission may be sought for such use through Elsevier's permissions site at: http://www.elsevier.com/locate/permissionusematerial From: Noha Youssef, Mostafa S. Elshahed, and Michael J. McInerney, Microbial Processes in Oil Fields: Culprits, Problems, and Opportunities. In Allen I. Laskin, Sima Sariaslani, and Geoffrey M. Gadd, editors: Advances in Applied Microbiology, Vol 66, Burlington: Academic Press, 2009, pp. 141-251. ISBN: 978-0-12-374788-4 © Copyright 2009 Elsevier Inc. Academic Press. Author's personal copy CHAPTER 6 Microbial Processes in Oil Fields: Culprits, Problems, and Opportunities Noha Youssef, Mostafa S. Elshahed, and Michael J. McInerney1 Contents I. Introduction 142 II. Factors Governing Oil Recovery 144 III. Microbial Ecology of Oil Reservoirs 147 A. Origins of microorganisms recovered from oil reservoirs 147 B. Microorganisms isolated from oil reservoirs 148 C. Culture-independent analysis of microbial communities in oil reservoirs 155 IV. Deleterious Microbial Activities: Hydrogen Sulfide Production (or Souring) 163 A. Current souring control approaches 163 B. Microbial control of souring 164 V. Microbial Activities and Products Useful For Oil Recovery 167 A. Paraffin control 171 B. Biogenic acid, solvent, and gas production 188 C. Biosurfactant production 194 D. Emulsifiers 205 E. Exopolymer production and selective plugging 206 F. In situ hydrocarbon metabolism 212 Department of Microbiology and Molecular Genetics, Oklahoma State University, 1110 S Innovation Way, Stillwater, Oklahoma 74074 1 Corresponding author: Department of Botany and Microbiology, University of Oklahoma, 770 Van Vleet Oval, Norman, Oklahoma 73019 Advances in Applied Microbiology, Volume 66 # 2009 Elsevier Inc. ISSN 0065-2164, DOI: 10.1016/S0065-2164(08)00806-X All rights reserved. 141 Author's personal copy 142 Youssef et al. VI. Implementation of Meor 214 A. Treatment strategies 215 B. Nutrients selection 217 C. Monitoring the success of MEOR field trials 218 VII. Current and Future Directions 220 A. Biosurfactant formulations 220 B. Understanding the microbial ecology of oil reservoirs 222 VIII. Conclusions 224 Acknowledgments 225 References 225 Abstract Our understanding of the phylogenetic diversity, metabolic cap- abilities, ecological roles, and community dynamics of oil reservoir microbial communities is far from complete. The lack of apprecia- tion of the microbiology of oil reservoirs can lead to detrimental consequences such as souring or plugging. In contrast, knowledge of the microbiology of oil reservoirs can be used to enhance productivity and recovery efficiency. It is clear that (1) nitrate and/or nitrite addition controls H2S production, (2) oxygen injec- tion stimulates hydrocarbon metabolism and helps mobilize crude oil, (3) injection of fermentative bacteria and carbohydrates gen- erates large amounts of acids, gases, and solvents that increases oil recovery particularly in carbonate formations, and (4) nutrient injection stimulates microbial growth preferentially in high perme- ability zones and improves volumetric sweep efficiency and oil recovery. Biosurfactants significantly lower the interfacial tension between oil and water and large amounts of biosurfactant can be made in situ. However, it is still uncertain whether in situ biosur- factant production can be induced on the scale needed for eco- nomic oil recovery. Commercial microbial paraffin control technologies slow the rate of decline in oil production and extend the operational life of marginal oil fields. Microbial technologies are often applied in marginal fields where the risk of implementa- tion is low. However, more quantitative assessments of the efficacy of microbial oil recovery will be needed before microbial oil recovery gains widespread acceptance. Key Words: Petroleum microbiology, Biosurfactants, Sulfate reducers, Souring, Plugging, Oil recovery. ß 2009 Elsevier Inc. I. INTRODUCTION World population is projected to increase by nearly 45% over the next 4 decades and by the middle of the century there will be more than 9 billion people (U.S. Census Bureau, International Data Base, August 2006; Author's personal copy Microbial Oil Recovery 143 http://www.census.gov/ipc/www/idb/worldpopinfo.html). The per capita energy consumption is a good predictor of the standard of living, which means that the demand for energy will continue to increase with the world’s population and its desire to improve living standards (Hall et al., 2003). The economic prosperity and security of nations will depend on how societies manage their energy resources and needs. An important question is how will we meet the future demand for more energy. Historically, the combustion of fossil fuels–oil, coal, and natural gas–has supplied more than 85% of world energy needs (Energy Information Agency, 2006). The reliance on fossil fuel energy has increased CO2 emissions and fostered global climate change. For these reasons, it is advantageous to diversify our energy sources with the inclusion of more carbon-free or carbon-neutral fuels. However, even the most optimistic projections suggest that renewable energy sources will comprise less than 10% of the world’s requirements through 2030 (Energy Information Agency, 2006). The most critical energy need is in the transportation sector. The use of nonpetroleum sources such as ethanol and of unconventional oil sources (shale oil, gas-to-liquids, and coal-to-liquids) will increase substantially, but each will only account for <10% of the demand by 2030 (Energy Information Agency, 2007). Thus, crude oil will likely continue as the dominant source of transportation fuels in the near future. Current technologies recover only about one-third to one-half of the oil contained in the reservoirs. Globally, about 1 trillion barrels (0.16 Tm3)of oil have been recovered, but about 2–4 trillion barrels (0.3–0.6 Tm3) remain in oil reservoirs and are the target of enhanced oil recovery (EOR) technologies (Hall et al., 2003). In the United States, more than 300 billion barrels (47.6 Gm3) of oil remain unrecoverable from U.S. reser- voirs, after conventional technologies reach their economic limit (Lundquist et al., 2001). A critical feature of U.S. oil production is the importance of marginal wells whose production is <1.6 m3 of oil or <1600 m3 of natural gas per day. Currently, 27% of the oil (about the same amount imported from Saudi Arabia) and 8% of the natural gas produced in the U.S. onshore (excluding Alaska) is produced from mar- ginal wells. These wells are at risk of being prematurely abandoned and it is estimated that about 17.5 million m3 of oil was lost because of the plugging and abandonment of marginal wells between 1994 and 2003. New technologies to recover entrapped oil and to slow the decline in oil production in marginal wells are needed to increase oil reserves. The amount of oil recovered by EOR technologies is not large, about 0.3 million m3 per day (Anonymous, 2006), even though a number of economic incentives have been used to stimulate the development and application of EOR processes. Chemical-flooding technologies such as micellar or alkaline-surfactant-polymer flooding displace tertiary oil efficiently, but they have been marginally economic because of high Author's personal copy 144 Youssef et al. chemical costs. Chemical losses because of adsorption, phase partitioning, trapping, and bypassing when mobility control is not maintained can be severe (Green and Willhite, 1998; Strand et al., 2003; Weihong et al., 2003). The only way to compensate for these losses is by increasing the volume of the surfactant solutions (Green and Willhite, 1998). Further, the imple- mentation of these processes is complicated by reservoir heterogeneity and the need for large capital investment. All of these factors make chemical flooding a high-risk venture. Microbially EOR (MEOR) processes have several unique characteris- tics that may provide an economic advantage. Microbial processes do not consume large amounts of energy as do thermal processes, nor do they depend on the price of crude oil as many chemical processes do. Because microbial growth occurs at exponential rates, it should be possible to produce large amounts of useful products rapidly from inexpensive and renewable resources. The main question is whether microbial processes do, in fact, generate useful products or activities in amounts and at rates needed for significant oil recovery (Bryant and Lockhart, 2002). In this chapter, we will review what is known about the microbiology of oil fields from cultivation-dependent and cultivation-independent approaches. The technical feasibility of MEOR processes will be assessed by analyzing laboratory and