147
Microbial biotechnology for enhancing oil recovery: Current developments and future prospects H. Al-Sulaimani1, S. Joshi2, Y. Al-Wahaibi1, S. Al-Bahry2, A. Elshafie2, A. AlBemani1 1
Department of Petroleum and Chemical Engineering, College of Engineering, Sultan Qaboos University, PO Box 33, Al-Khod, 123, Sultanate of Oman; E-mail:
[email protected] 2 Department of Biology, College of Science, Sultan Qaboos University, PO Box 33, Al-Khod, 123, Sultanate of Oman
ABSTRACT It is anticipated that over 2 trillion barrels of conventional oil will remain in reservoirs worldwide after conventional recovery methods have been exhausted. Other oil recovery methods depend on many economic and technological limitations. Microbial Enhanced Oil Recovery (MEOR), on the other hand, has been proposed for many years as a cheap and effective alternative to enhance oil recovery as its different processes generally do not depend on oil prices. Microbes offer useful metabolic products such as biosurfactants, biopolymers, biogas, biomass, in addition to bio-acids and bio-solvents for enhancing oil recovery. These bioproducts contribute to different microbial systems which tackle specific problems of oil recovery from a chosen target reservoir. The present review provides an overview of MEOR developments from its early stages until today. Basic aspects of petroleum engineering oil recovery stages and microbial characteristics suitable for MEOR are introduced to better link the two bioengineering technologies. The uses and types of different microbial bioproducts available in literature are reviewed and various recovery mechanisms are discussed. Successful MEOR field trials around the world are summarized which shows the potential of this technology as alternative oil recovery method. However, these processes have not been fully proven and did not receive large attention in the petroleum industry due to several reasons that are also discussed. One major reason is the absence of standardized field results and post trial analysis and the lack of structured research methodology. Also, the inconsistent technical performance and lack of understanding of the mechanism of oil recovery contributed to the fact that MEOR received little interest in the petroleum industry. Keywords: microbial enhanced oil recovery, microbial bioproducts, biosurfactants, biopolymers, MEOR candidate microbes, field trials
INTRODUCTION There are three stages of oil recovery process employing mechanical, physical and chemical methods [1]. The first stage is the primary recovery stage where the natural energy of the reservoir, mainly reservoir pressure, is utilized. These natural driving forces include: water drive from the aquifer, solution gas drive that results from gas evolving from oil as reservoir pressure decreases, gas cap drive, rock and fluid expansion and others [2,3]. The next oil recovery stage is the secondary stage which takes place when the reservoir pressure tends to fall and becomes insufficient to force the oil to the surface. In this stage, external fluids are injected into the reservoir either to maintain the reservoir pressure or to displace the oil in the reservoir [4]. The usual fluid injected is water; however, immiscible gases could also be injected in this stage. While primary recovery stage produces generally between 5-10% of the total oil reserves, recovery efficiencies in the secondary phase varies from 30-40% [1,5]. Based on recent world reserves statistics, nearly 2 trillion barrels of conventional oil and 5 trillion barrels of heavy oil will remain in reservoirs worldwide after !
" #$$
! %"
&
148
conventional recovery methods have been exhausted [6]. Hence, attention has been focused on the Enhanced Oil Recovery (EOR) techniques for recovering more oil from the existing and abandoned oil fields. The EOR methods may be divided to thermal, chemical and gas injection methods. The thermal methods are primarily intended for heavy oils and tar sands mainly to supply heat to the reservoir. These methods include steam or hot water injection and in situ combustion technique. Chemical flooding involves injection of certain chemicals that might change either the characteristics of the reservoir fluids or improve the recovery mechanisms. These include polymer, surfactants and alkaline flooding. Miscible flooding (either first- or multi- contact miscible) includes CO2 miscible gas injection, N2 miscible injection and others. Now, more advanced technologies are being implemented in the oil industry to recover the trapped oil. These include seismic/sonic stimulations and electromagnetic methods [1]. However, economics are the major deterrent in the commercialization of the above mentioned EOR methods [6]. Microbial Enhanced Oil Recovery (MEOR) is one of the technologies that can be potentially implemented with an exceptionally low operating cost. It has several advantages compared to conventional EOR processes where it does not consume large amounts of energy as do thermal processes, nor does it depend on the oil price as do many chemical processes [7]. MEOR is simply the process of utilizing microorganisms and their bio-products to enhance the oil recovery. Bacteria are the only microorganisms used for MEOR by researchers due to their small size, their production of useful metabolic compounds such as gases, acids, solvents, biosurfactants, biopolymers as well as their biomass [8]. Also, their ability to tolerate harsh environments similar to those in the subsurface reservoirs in terms of pressure, temperature, pH and salinity increased their attraction to be used for EOR purposes. Bacteria’s average cell size ranges between 0.5-5.0 m which makes it easier for them to penetrate through the reservoir’s porous media [9]. For MEOR processes which involve the injection of bacteria into the reservoir, it was calculated that the microbes have to be small, spherical and less than 20% of the size of the pore throat in the formation [10,11]. Most of the oil reservoirs are sedimentary basins, reservoir lithology is usually sandstone or carbonates, mostly fractured limestone for the carbonates reservoirs, with pore size being greater than 30 m for productive reservoirs and pore throat size not less than 10 m [12]. It was reported that for reservoirs having permeability higher than 0.6 Darcy (D), an area of 60,000m2 was affected by microbial treatment [13]. It is also believed that sandstone reservoirs need to have permeability greater than 0.1 D for the microbes to be able to pass through them [9]. However, for reservoirs with tight formations having permeability around 0.1 D, the effect was limited to the wellbore region. Jang et al. [13] conducted a bench scale study on the transport of three bacterial species (Bacillus subtilis, Pseudomonas putida and Clostridium acetobutylicum) in highly permeable and porous rock. They have also provided a quantitative screening criterion for selecting proper potential bacterial strains for in situ MEOR applications. Jansheka [14] compiled a partial list of some bacteria that have been used in the MEOR experiments and field studies. It was found that Bacillus and Clostridium species are the most common species used for MEOR purposes since they can form dormant, resistant endospores that can survive under stressful environmental conditions and they can produce the useful bioproducts for MEOR [14-16]. The idea of using bacteria for the production of oil was first suggested by Beckman back in 1926 [17]. However in 1946, Zobell and his co-workers were the first to perform actual experimental work to confirm Beckman’s theory. Their work continued till 1955 and they patented a process for secondary recovery of petroleum using anaerobic bacteria, hydrocarbon utilizing, and sulfate reducing bacteria [18]. Later, extensive experimental work on the potential of microbes for MEOR purposes was conducted [19-22]. Although the results were promising, the research in this area lost its interest in the 1970s due to economic reasons [23]. However, in the 1980s and 1990s, the global decline in oil prices raised the need for a cost effective process that is both technically
149
and economically feasible. Thus, considerable research in the area of MEOR was performed during that period [3,9,14,24-36]. MEOR is also considered as an inexpensive process since it can be implemented with minor modifications to existing field facilities [9]. However, despite the positive and promising experimental and field tests results, it did not receive wide spread attention in the oil industry due to several factors suggested by many researchers. Some of these reasons were the negative perception on the use of bacteria and handling them in the field for MEOR processes although it was verified by tests conducted by public health laboratories which reported that the mixed cultures of bacteria are safe to handle and pose no threat to the environment, plants, animals or human beings [15,39]. Besides, the reservoir’s environment is not favorable for the pathogenic organisms to grow. That’s why, it is recommended to perform a toxicity test for any organism to be used in the field for MEOR to assure the safety of involved parties. Another factor was the inconsistent technical performance and lack of understanding of the mechanism of oil recovery [38]. It is difficult to extrapolate the results from one microbial field trial to other reservoirs as each reservoir has its unique properties and microbial population for indigenous MEOR cases [39]. One of the major reasons for MEOR not receiving wide popularity was the absence of standardized field results and post trial analysis [16]. Most field trials were not followed for enough amount of time to determine the long term effect [2]. In addition, another reason might be that extensive laboratory tests are needed to determine the microbe to be used, its survival and competitiveness in the reservoir, feeding regime strategy and to evaluate the effectiveness of the process.
MICROBIAL CANDIDATES FOR MEOR Microbes can be classified in terms of their oxygen intake into three main classifications; aerobes where the growth depends on a plentiful supply of oxygen to make cellular energy. Strictly anaerobes, by contrast, which are sensitive to even low concentration of oxygen and are found in deep oil reservoirs. These anaerobes do not contain the appropriate complement of enzymes that are necessary for growth in an aerobic environment [40]. Lazar [41] found predominantly sporeforming bacilli and cocci in deep reservoir and non spore-forming bacilli in shallow ones [42]. The third group of bacteria is facultative microbes, which can grow either in the presence or reduced concentration of oxygen [40]. Successful field experiments mostly used the anaerobic bacteria [16]. There are many sources from which bacterial species that are MEOR candidates can be isolated. Lazar [39] suggested four main sources that are suitable for bacterial isolation. These are formation waters, sediments from formation water purification plants (gathering stations), sludge from biogas operations and effluents from sugar refineries. Oil contaminated soil could be used as a good source of microbes isolation for MEOR [43]. Isolation from hot water streams was also reported [15]. Nutrients are the largest expense in the MEOR processes where fermentation medium can represent almost 30% of the cost for a microbial fermentation [44]. The microbes require mainly three components for growth and metabolic productions: carbon, nitrogen and phosphorous sources, generally in the ratio of C, 100: N, 10: P, 1. Media optimization is very important since the types of bioproducts that are produced by different types of bacteria are highly dependent on the types, concentrations and components of the nutrients provided. Sometimes, cheap raw materials are also used as nutrients such as molasses, cheese whey, beef extract and others that contain all the necessary nutritional components. Huge varieties of raw materials are currently used for industrial fermentations which are important to the overall economy as they accommodate high percentage of the final production cost [45,46]. Joshi et al. [46] reported the possibility of using cheese whey for biosurfactant production. Cheese whey is a liquid byproduct of cheese production. It is composed of 75% of lactose and 12-14% protein in addition to organic acids, vitamins and minerals. Molasses is a byproduct of sugar production and its low price and presence of vitamins which are valuable for
150
fermentation made it an attractive carbon source used by many researches. It contains several other compounds besides sucrose which include minerals, organic compounds and vitamins. Some microbes utilize oil as the carbon source, which is excellent for heavy oil production, since it will reduce the carbon chain of heavy oil and thus increase its quality. Cooper and his co-workers [47] tested microbes using kerosene as the carbon source to release bitumen from tar sands. Moses [2] showed that the presence of crude oil in the media can significantly increase the production of methane and carbon dioxide while the growth rate was reduced [42]. Thus, it is important to carefully test the nutritional preferences of the studied microbes that would maximize the production of desired metabolites provided that cost effective supplies are assured.
MICROBIAL BIOPRODUCTS Microorganisms produce a variety of metabolites that are potentially useful for oil recovery [48]. There are six main bioproducts or metabolites produced by microbes. Table 1 shows a summary of these bioproducts and their application in oil recovery. Table 1. Microbial bioproducts and their applications in oil recovery [48]. Product Biomass
Biosurfactants
Biopolymers
Bio-solvents
Bio-acids Biogases
Microorganism Bacillus licheniformis, Leuconostoc mesenteroides, Xanthomonas campestris Acinetobacter calcoaceticus, Arthrobacter paraffineus, Bacillus sp., Clostridium sp., Pseudomonas sp. Bacillus polymyxa, Brevibacterium viscogenes, Leuconostoc mesenteroides, Xanthomonas campestris, Enterobacter sp. Clostridium acetobutylicum, Clostridium pasteurianum, Zymomonas mobilis Clostridium sp., Enterobacter aerogenes Clostridium sp., Enterobacter aerogenes, Methanobacterium sp.
Application in oil recovery MPPM, selective plugging, viscosity reduction, oil degradation, wettability alteration Emulsification, interfacial tension reduction, viscosity reduction
MPPM-Injectivity profile modification, mobility control, viscosity modification
Emulsification, viscosity reduction
Permeability increase, emulsification Increased pressure, oil swelling, interfacial tension reduction, viscosity reduction, permeability increase
Biosurfactants They are amphipatic molecules with both hydrophilic and hydrophobic parts which are produced by variety of microorganisms. They have the ability to reduce the surface and interfacial tension by accumulating at the interface of immiscible fluids and increase the solubility and mobility of hydrophobic or insoluble organic compounds [49]. There are five major types of biosurfactants, namely lipopeptides, phospholipids, glycolipids (which include rhamnolipids, trehalose lipids and sophorolipids), fatty acids and neutral lipids [42,47]. Table 2 shows the details of some of the biosurfactants along with their producing organisms [50].
151
Table 2. Types of biosurfactants and their producing organisms [50]. Biosurfactant type Lipopeptides Surfactin Lychenysin Glycolipids Rhamnolipids Trehalose Lipids Sophorolipids Phospholipids Polymeric biosurfactants Emulsan
Producing organism
References
B. subtilis B. licheniformis
[38,93] [7,46,55,94]
P. aeruginosa Pseudomonas sp., R. erythropolis Arthrobacter sp., Mycobacterium sp. Acinetobacter sp., T. thiooxidans Acinetobacter sp.
[98,99] [96,100] [47,55,95] [97] [101]
Surfactants are known to reduce the interfacial forces between oil and water and thus improve the mobilization of oil [51]. It was reported that some microbes can produce biosurfactants that reduced IFT between oil and water from typical values of 10mN/m to as low as 0.005mN/m [52,53]. In the past few years, biosurfactants have gained attention because of their biodegradability, low toxicity, and its cost effectiveness [7,45,46,54-57]. Since biosurfactants can be produced from carbohydrates by fermentation process, it is possible to produce huge amount more cheaply than the synthetic surfactants, for which they are also developed for use in the oil industry [42]. There is a wide variety of microorganisms that are reported to produce different types of biosurfactants. For instance, many Bacillus species were found to produce lipopeptides; Pseudomonas and Candida species are known to produce glycolipids while Thiobacillus thiooxidans produce phospholipids [58]. Al Araji et al. [59] reported that the type, quality and quantity of biosurfactants produced are influenced by the nature of the carbon substrate and the concentration of nitrogen, phosphorous, magnesium, ferric and manganese ions in the medium. The culture conditions such as pH, temperature, agitation and dilution rate in continuous culture are also additional factors [59]. Jenneman et al. [60] isolated a Bacillus licheniformis strain, JF-2, from oil field injection water that is reported to produce biosurfactants that are potentially useful for in situ MEOR processes. McInerney et al. [61] and Youssef et al. [58] found that the lipopeptide biosurfactant produced by JF-2 mobilized large amounts of residual hydrocarbon from sand-packed columns and it generated a low interfacial tension needed for substantial oil recovery. This strain grew and produced lipopeptide anaerobically at salinity up to 8% and temperatures up to 45 C. Furthermore, the growth of JF-2 was not inhibited by the presence of crude oil [55]. There are several other potential applications of biosurfactants such as detergents, cosmetics, pharmaceutical, sewage sludge treatments for oily wastes, pipeline transportations and many others [46]. However, the largest market for biosurfactants is the oil industry for petroleum production enhancement.
Biopolymers These are polysaccharides which are secreted by many strains of bacteria mainly to protect them against temporary desiccation and predation as well as to assist in adhesion to surfaces [1,62]. The proposed processes of biopolymers are mainly selective plugging of high-permeability zones and thus permeability modification of the reservoir to redirect the waterflood to oil rich channels [1].
152
Another important process of biopolymers is their potential as mobility control agents by increasing the viscosity of the displacing water hence improving the mobility ratio and sweep efficiency [63]. There are different types of biopolymers produced by different bacteria such as Xanthan gum produced by the Xanthomonas sp. [64], Levan produced by the Bacillus species [63], Scleroglucan produced by the Sclerotium sp. [65] and many others [1]. There are many applications where these biopolymers can be used in addition to enhancement of oil recovery. These include their use in medical field in drug delivery systems, wound closure, healing products and others. In addition to their use in food containers, waste bags, agriculture and protective clothing [66]. One of the biopolymers that is currently in commercial product and have been subjected to extensive studies is the Xanthan gum. It is produced by fermentation of carbohydrates and it is well known as a thermally stable heteropolysaccharide. In addition, its physical properties of viscosity, shear resistance, temperature and salt tolerance made it almost an ideal polymer for use in EOR [64,67]. A very successful MEOR field trial using the biopolymer process of selectively plugging the high permeable zones was reported in Fuyu oilfield, China [68]. These MEOR tests started since 1996 by using the strain CJF-002 which was identified to be an Enterobacter sp. This strain was able to produce insoluble biopolymers that formed a jelly-like substance at high molasses concentrations. Oil production was increased more than twice by regulating the water flow and reducing the channeling effects [68].
Biogases Bacteria can ferment carbohydrates to produce gases such as carbon dioxide, hydrogen and methane gas. These gases can be used for enhancing oil recovery by exploiting the mechanisms of reservoir re-pressurization and heavy oil viscosity reduction. These gases can contribute to the pressure buildup in pressure depleted reservoirs [62]. They may also dissolve in crude oil and reduce its viscosity [42,69]. Some of the reported gas-producing genera are Clostridium, Desulfovibrio, Pseudomonas and certain methanogens [70]. Methanogens produce about 60% methane and 40% carbon dioxide where the methane will partition between oil and gas phase while carbon dioxide will partition to the water phase as well and hence improve the mobility of oil [71].
Bio-Acids Some bacteria when given certain nutrients can produce acids such as lactic acid, acetic acid and butyric acid [61]. These acids can be useful in carbonate reservoirs or sandstone formations cemented by carbonates, since it can cause dissolution of the carbonate rock and hence improve its porosity and permeability [69]. Production of organic acids by bacteria is a normal phase of anaerobic fermentation of sugars. Clostridium sp., for example, can produce 0.0034 moles of acid per kilogram of molasses [71].
Bio-Solvents Sometimes solvents can also be produced as one of the metabolites of the microbes. These include ethanol, acetone and butanol. They may also help in reduction of oil viscosity and can also contribute as a co-surfactant in reducing the interfacial tension between oil and water [58].
Microbial biomass Bacteria are known to grow very fast as some are reported to multiply every 20 minutes under aerobic conditions [40]. The mechanism of the microbial biomass in MEOR involves selective
153
plugging of high permeability zones where the microbial cells will grow at the larger pore throats restricting the undesirable water flow through them [72]. This will force the displacing water to divert its path to the smaller pores and hence displacing the un-swept oil and increasing the oil recovery. Polymers, biofilms and slimes may also contribute to the selective plugging process. Several laboratory and field tests were conducted to test the feasibility of this mechanism. Jenneman [60] showed that the addition of nutrients (carbon, nitrogen and phosphate) in sufficient concentrations into Berea sandstone cores resulted in permeability reduction of 60-80%. The advantage of Microbial Permeability Profile Modification (MPPM) process is that it does not interfere with the normal waterflood operation. It is also eco-friendly and is considered as the cheapest MEOR mechanism [73].
IN SITU AND EX SITU MEOR There are two processes for MEOR depending on the site of the bioproducts production. These are namely in situ and ex situ processes. The in situ process involves producing the bacterial bioproducts inside the reservoir. This can be done either by stimulating the indigenous reservoir microbes or injecting specially selected consortia of bacteria (exogenous microbes) that will produce specific metabolic products in the reservoir which will lead to enhancement in oil recovery [72]. The ex situ process, in turn, involves the production of the bioproducts at the surface outside the reservoir then injecting them separately either with or without the separation of the bacterial cells. In this case, commercial size bio-reactors are needed to scale-up the production of the desired metabolite for field applications. For the in situ process where the exogenous microbes are introduced into the reservoir, it is important to conduct compatibility studies to determine the interaction of the injected microbes with indigenous microbes, nutrients, oil and rock [9]. As described by Jang et al. [13], the success of an in situ MEOR process depends on the selection of the candidate reservoir, the proper choice of potential bacterial species, the viability of bacteria under reservoir conditions, the amount of metabolites generated and their effects on releasing residual oil and other economic factors. However, care must be taken when nutrients or sulfate-containing waters are injected to ensure that indigenous sulfate-reducing bacteria (SRB) are not stimulated or overgrown by the injected microbes. These SRBs play a very negative role in MEOR due to the production of hydrogen sulfide [74]. The major concerns of the global oil industry with SRBs include oil souring, corrosion caused by H2S production, plugging by iron sulfide, the related financial burden and the threat to health and safety of the operators [11]. Hitzman [75] patented the concept of adding a biocide to the water in a waterflood to kill or inhibit SRB (US patent 2917428). In the laboratory scale, promising microorganisms are isolated from different sources such as water, oil and soil samples. Then they are screened for desirable metabolites for oil release, followed by bench-scale experiments showing release of oil-saturated sand packs, cores or even micro models [76].
MEOR FIELD TRIALS The first MEOR field test was carried out in Lisbon field Union County, Arkansas, in 1954 [77,78]. Since then, several field trials were performed and by 2003, more than 400 MEOR field tests have been conducted in the US alone [11], in addition to numerous other field tests carried out in the rest of the world. There are two main purposes to go for MEOR field applications as single well treatment and full field treatment. Single well treatment includes well stimulation, well bore clean-up and others. In this treatment process, improvement in oil production can result from removal of paraffinic or asphaltic deposits from the near well bore region or from mobilization of residual oil in the limited volume of the
154
reservoir that is treated [9]. This is similar to huff and puff process where the microbial effect is utilized in this case. In this process, the well is initially inoculated by the desired microbes and nutrients are injected to stimulate the indigenous microbes. Then, the well is shut-in for a while to allow microbial growth and to produce the desired metabolites around the well bore. Finally, the well is opened for production and operation [79]. Most of the reported successful field trials were single well treatments in the US, China, Romania, India, Russia and Argentina where incremental oil varied from no impact to 204% [16]. Full field treatment includes microbial enhanced water flooding, MPPM, and other processes that involve both injection and production wells. In this case, the microbes and nutrients are injected through an injector well where the metabolites will be produced in situ such as biopolymers that will help in mobility control of the water flooding. Biomass can also develop from growth of bacterial cells and block the high permeable zones which will divert the flow of displacing fluids and allow the displacement of the un-swept oil. Incremental oil is produced from the production wells in this case. The success of the full field applications has been mixed and the data from MEOR field tests is limited [42]. The main problem is that the design of the microbial system and oil production response are not well documented. Several field trials were summarized and reviewed in literature [2,3,16,17,22,39] where it was remarked that many of the field tests lacked explanation on the mechanisms of the oil recovery. Post-treatment analyses were also missing in most of the cases which might be the major reason why MEOR technology has not gained credibility in the oil industry [11]. Moses [2] stated that most field trials were not followed for a long enough time to determine the long term effects. Monitoring and follow-up of results are important factors for successful MEOR tests. Furthermore, previous work on MEOR has not been informed by a reservoir engineering perspective such as placement and propagation of biochemicals, effects of reservoir heterogeneity, mobility control and others [80]. It is important to characterize the target reservoir prior to designing the MEOR treatment. This includes structural, geological and reservoir engineering analysis of the target reservoir to better diagnose the problem that would help in selecting the appropriate microbial mechanism or process for enhancing the oil recovery for this particular reservoir. Bryant and Burchfield [9] set a minimum criteria requirement that reservoirs targeted for microbial treatment have to meet. This include reservoir’s permeability to be greater than 0.1D, temperature to be less than 160 ºF and preferably total dissolved solids in brine not exceed 100,000 ppm. On the other hand, Portwood [81] obtained a database of information collected from 322 projects all treated with the MEOR process in the US. One of the objectives was to determine if any reservoir characteristics is a dominating factor in determining the applicability of the MEOR process. He concluded that reservoir lithology neither enhances nor impedes the effectiveness of MEOR as 73% of the projects were conducted in sandstone reservoirs and the rest were in carbonate reservoirs. He also concluded that MEOR process is applicable in wide range of reservoir temperature as microorganisms can survive the temperatures present in most of the oil reservoirs. He also found that as the porosity increased, the incremental oil production decreased. However, even at highest porosity ranges (26-30%) the incremental production was nearly 20%. Thus, porosity was not considered as a limiting factor of the MEOR process. Another conclusion was that reservoirs with low oil gravity (30 °API or less which indicates heavier oil) are found suitable for MEOR applications. It is important to note that microbial EOR is not a single technology based on a common approach; rather, it is the adaptation of microbial systems to specific problems of oil recovery from a chosen target reservoir [3]. These microbial systems include wettability alteration, viscosity reduction of oil, selective plugging, scale and corrosion control and many others [82]. The technology of MEOR has advanced from a laboratory-based evaluation of microbial processes to field application internationally [53]. Many of the early field trials were conducted in
155
the US. Johnson and his co-workers [83] injected 150 stripper wells (production less than 10bbl/day) with mixed cultures of Bacillus and Clostridium species using crude molasses. Most of these wells produced, on average, 2 bbl/day of oil and reservoirs depths varied between 200-1000 ft. In successful cases, Johnson [83] reported that 20-30% of additional oil in place was recovered. Hitzman [17] reported on some preliminary field testing with 24 wells during 1977-1982. The depths varied from 300-4600 ft and he reported that 75% of the wells showed a pressure increase of 10-200 psi. Most of the wells doubled the production for a period between three to six months [8]. Hitzman patented in 1962 a process for the injection of bacterial spores along with the nutrients into a reservoir (US patent 3032472). A very successful, well documented and characterized field trial was conducted and supervised by Lewis Brown since 1994 [73]. The field was the North Blowhorn Greek Unit in Lamar, Alabama, USA. It had 20 injectors and 32 production wells. The treatment process was MPPM by adding KNO3 and NaH2PO4 to the waterflood to stimulate the indigenous microbes. Brown [11] reported in his review that the production decline rate decreased from 18.9% per year to 7-12% per year and that the field is still producing till today, although it was scheduled to be abandoned in 1998. Several field tests were conducted in other countries which include Romania [39], Argentina [84], Russia [47,85] and others. Lazar [39] reported an extensive review on MEOR field applications that was conducted in Romania during the period from 1971-1991. He emphasized on three main areas of research namely examination of the bacterial populations present in the formation water of the reservoir, adaptation of the microorganisms to field conditions prior to injection and finally, field testing of the adapted microorganisms. He concluded that the successful trials resulted in a two-fold increase in the oil production for one to five years. In Eastern Asia, some MEOR experimental and field trials were reported in China, Malaysia, India and Indonesia. Several large-scale field tests were carried out in China including Jilin, Xinjiang, Daqing, Fuyu and many others [86]. One of the successfully reported field trials was in Daqing oilfield which is the largest oilfield in China with an average effective thickness of 30ft [87]. In this application, Pseudomonas aeruginosa (P-1) and its metabolic products were used which reduced the oil viscosity by 38.5%. It was reported that 80% of the wells showed a significant increase in oil production and total enhancement of oil recovery of 11% was observed [87]. Another MEOR application in the same field was by using Brevibacillus brevis and Bacillus cereus. The mechanism suggested was petroleum hydrocarbon degradation of heavy compounds by the stated microbes and bio-oxidation process [88]. In this field trial, the microbes were injected between 2002 and 2004 in a huff and puff manner as well as microbial enhanced water flooding method which was carried out in 2004. Corresponding oil production increased from 20.8 tons per day before bacteria injection to 36.9 tons per day was reported [88]. In the Arab world, some MEOR laboratory experimental tests were conducted by Sayyouh and his co-workers since 1992 in Cairo University and in King Saud University [89]. They isolated their bacteria from the Egyptian and Saudi crude oils and brine. They tested experimentally the effects of nutrient types and its concentrations, bacterial type, salinity and permeability on oil recovery. Some other experimental work was conducted by Zekri et al. [15] in United Arab Emirates University where they studied the possibility of increasing oil recovery from UAE reservoirs using bacterial flooding. They also investigated the parameters which affected the optimization of microbial flooding in carbonate reservoirs [15,90,91]. A study was presented by Sayyouh [98] on the applicability of MEOR for recovering more oil under the Arab reservoir conditions where data was obtained from more the 300 formations from seven Arab countries (Saudi Arabia, Egypt, Kuwait, Qatar, UAE, Iraq and Syria). He anticipated that MEOR technology may recover up to 30% of the residual oil under the Arab reservoir conditions [92]. Some initiatives were taken in the Sultanate of Oman at Sultan Qaboos University to experimentally investigate the potential of MEOR in Omani oil fields [122]. Biosurfactant producing strains were isolated from oil contaminated soil samples.
156
One Bacillus subtilis strain was found to be able to produce biosurfactant that reduced the interfacial testion (IFT) from 47 mN/m to 3.28 mN/m and yielded a total of 23% of additional oil recovery in coreflooding experiment [122]. However, to our knowledge, no field trials were reported so far for testing the applicability of MEOR in the Arab region.
CONCLUSION In conclusion, MEOR is well-proven technology to enhance oil recovery from oil wells with high water cuts and also to improve it in mature oil wells, but still in order for MEOR processes to be well accepted and successful, extensive laboratory tests are required prior to field implementation to select the suitable microbes, to understand their growth requirements and production conditions. Also, optimization of nutrients and testing the microbes and their bioproducts compatible with reservoir conditions are required. During field tests, design of the microbial system and oil production response has to be well documented and results have to be monitored and followed up. Finally, it is recommended to conduct toxicity tests on the microbes that are to be used in the field to assure that it is safe to handle and pose no threat to human or to the environment.
REFERENCES [1] Sen R. Prog. Energy Comb Sci. 2008, 34:714-724. [2] Moses V. Recent Advances 1991:21-28. [3] Sheehy AJ. The APEA J. 1991, 31:386-391. [4] Singh A, Van Hamme JD, Ward OP. Microbiol. Mol. Biol. Rev. 2003, 67:503. [5] Van Hamme J, Singh A, Ward O. Energy Sources 2006, 24:52-56. [6] Thomas S. Oil Gas Sci. Tech. 2007, 1-11. [7] Youssef N, Simpson DR, Duncan KE, et al. Appl Environ Microbiol.2007, 73:1239-1247. [8] Obeida TA. PhD Thesis, The University of Oklahoma, USA, 1990. [9] Bryant RS. SPE Res Eng. 1989, 151-154. [10] Jack TR, Steheier GL. In: Proceed. Symp. Applications of Microorganisms to Petroleum Technology, Burchfield T E, Bryant RS (ed.), National Technical Information Service, Springfield, Virginia, 1988. [11] Brown L. Curr Opinion Micobiol. 2010, 13:1-5. [12] Lidsay RF. Search and Discovery, AAPG Annual Convention and Exhibition, Louisiana, 2010. [13] Jang LK, Chang PW, Findley JE, et al. App Environ Microbiol. 1983, 45:1066-1072. [14] Sarkar AK, Goursaud JC, Sharma MM, et al. In Situ. 1989, 13:207-238. [15] Zekri AY, Almehaideb RA, Chaalal O. 1999, SPE 26827. [16] Maudgalya S, Knapp RM, McInerney MJ. 2007, SPE 106978. [17] Hitzman DO. Microbial Enhancement of Oil Recovery Conference, Oklahoma, 1983. [18] Brown LR, Azdapour A, Vadie AA. USA Dept of Energy, DOE/BC/14665-8, 1992. [19] Updegraff D. International Conference on MEOR. 1954, 80-85. [20] Hitzman D. 1962, US Patent 3032472. [21] Hauser G, Karnovsky ML. J Biol Chem. 1958, 233:287-291. [22] Davis J. Petroleum Microbiology. Elsevier Science Publishers, New York, 1967. [23] Behlulgil K, Mehmetoglu MT. Energy Sources 2002, 24:413-421. [24] Lappinscott HM, Cusack F, Macleod FA, et al. ACS Symposium Series 1989, 396:651-658. [25] Momeni D, Yen TF. Microbial Enhanced Oil Recovery: Principle and Practice. CRC Press, Boca Raton, USA, 1990, 165-171. [26] Ivanov MV, Belayev SS. Microbial Enhancement of Oil Recovery Recent Advances. Elsevier, Amsterdam, 1993, 421-432. [27] Cusack F, Lappinscott H, Singh S, et al. Appl Biochem Biotechnol. 1990, 24:885-898. [28] Belyaev SS, Borzenkov IA, Glumov IF, et al. Microbiol. 1998, 67:708-714. [29] Premuzic ET, Woodhead A. Microbial Enhanced Oil Recovery Conference, Elsevier, Amsterdam, 1993.
157 [30] Ivanov MV, Belayev SS, Borzenkov IA, et al. Microbiology in the Oil Industry and Lubrication Conf. 1991, 130-136. [31] Nelson SJ, Launt PD. Oil Gas J. 1991, 89:114. [32] Adkins JP, Tanner RS, Udegbunam EO, et al. Geomicrobiol J. 1992, 10:77-86. [33] Sunde E, Beeder J, Nilsen RK, Torsvik T. SPE/DOE Symposium on EOR, 1992. [34] Matz A. SPE/DOE Symposium on EOR, 1992. [35] Islam MR, Gianetto A. J Can Pet Technol. 1993, 32:30-36. [36] Bryant RS. Chem Eng Res Design. 1994, 72:144-151. [37] Portwood JT. Production Operations Symposium, 1995, SPE 29518. [38] McInerney MJ, Han SO, Maudgalya S, et al. 2003, DOE/BC: 15113-2. [39] Lazar I. Devel. Petr. Sci. 1991, 33:365-386. [40] Pommerville J. Alcamo's Laboratory Fundamentals of Microbiology, 7th ed., Jones and Bartlett Publishers, 2005. [41] Lazar I. International MEOR workshop. 1987, 124-151. [42] Ramsay J. PhD Thesis, McGill University, Montreal, Canada, 1987. [43] Sarkar A, Georgiou G, Sharma M. Biotech Bioeng. 1994, 44:499-508. [44] Rodrigues LR, Teixeira JA, Oliveira R. Biochem Eng J. 2006, 32:135-142. [45] Makkar RS, Cameotra SC. J Surfac Deterg. 1999, 2:237-241. [46] Joshi S, Yadav S, Nerurkar A, et al. J Microbiol Biotech. 2007, 17: 313-319. [47] Cooper DG, Macdonald CR, Duff SJ, et al. Appl Environ Microbiol. 1981, 42:408-412. [48] McInerney MJ, Sublette KL. Manual Environ Microbiol. 2002, 2:777-787. [49] Singh A, Van Hamme JD, Ward OP. Biotech Adv. 2007, 25:99-121. [50] Rosenberg E. Prokaryotes 2006, 1:834-849. [51] Banat IM. Biotechnol Lett. 1993, 15:591-594. [52] Singer ME, Finnerty WR. J Bacteriol. 1988, 170:638-645. [53] Gabitto J, Barrufet M. Improved Oil Production Using Economical Biopolymer-Surfactant Blends for Profile Modification and Mobility Control, 3rd Annual Progress Report, Department of Energy, Oklahoma, 2004. [54] Desai J, Banat I. Appl Environ Microbiol. 1997, 61:47-64. [55] Yakimov MM, Amro MM, Bock M, et al. J Petrol Sci Eng, 1997, 18:147-160. [56] Yonebayashi H, Yoshida S, Ono K, et al. J Japan Petrol Inst. 2000, 43:59-69. [57] Joshi S, Bharucha C, Jha S, et al. Biores Tech. 2008, 99:195-199. [58] Youssef NH, Duncan KE, McInerney MJ. Appl Environ Microbiol. 2005, 71:7690-7695. [59] Al-Araji L, Raja RN, Basri M, et al. J. Mol. Biol. Biotech. 2007, 15:99-105. [60] Jenneman GE, Knapp RM, McInerney MJ, et al. SPEJ. 1984, 33-37. [61] McInerney MJ, Nagle, DP, Knapp RM. Petrol Microbiol. 2005, 11:215-237. [62] Brown FG. SPE Oil and Gas Recovery Conference, 1992, SPE 23955. [63] Akit RJ, Cooper DG, Neufield RJ. Geomicrobiol J. 1989, 7:115-65. [64] Pollock TJ, Thorne L. 1994, US Patent 5279961. [65] Sandford PA. Adv Carbohydrate Chem Biochem. 1979, 36:265-312. [66] Valde KV, Kiekens P. Polymer Testing. 2002, 21:433-442. [67] Salome M. 1996, US Patent 5536651. [68] Nagase K, Zhang ST, Asami H. SPE/DOE Improved Oil Recovery Symp., 2002, SPE75238. [69] McInerney MJ, Javaheri M, Nagle DP. J Ind Microbiol. 1990, 5:95-102. [70] Behlulgil K, Mehmetoglu M. Energy Sources 2003, 25:871-877. [71] Gray MR, Yeung A, Foght JM. Annual Technical Conf., 2008, SPE 114676. [72] Jack TR, Steheier GL. Symposium on Appl. of Microorganisms to Pet. Tech., 1988. [73] Brown LR, Vadie AA. SPE/DOE EOR Symp. 2000, SPE 59306. [74] Bass C. Oilfield Rev. 1997, 9:17-25. [75] Hitzman DO, Sperl GT. SPE/DOE Ninth Symp. on Imporved Oil Recovery., SPE/DOE 27752, 1994. [76] Khire JM, Khan MI. Enzyme Microbiol Technol. 1994, 16:170-172. [77] Yarbrough HF, Coty VF. Conference on Microbial Enhancement of Oil Recovery, US Department of Energy, 1983, 162-218. [78] Lazar I, Petrisor IG, Yen TF. Pet Sci Tech. 2007, 25:1353-1366.
158 [79] Bryant SL, Lindsey RP. Improved Oil Recovery Symp. SPE/DOE 35356, 1996. [80] Bryant SL, Lockhart TP. SPE Reservoir Evaluation & Eng. 2002, 5:365-374. [81] Portwood JT. Production Operations Symposium. 1995, SPE 29518. [82] Bailey SA, Kenny TM, Schneider DR, et al. SPE Asia Pacific IOR Conf. 2001, SPE 72129. [83] Johnson WP, Logan BE. Water Research 1996, 30:923-931. [84] Maure MA, Dietrich FL, Diaz VA. SPE Latin American and Caribbean Pet. Eng. Conf., SPE 53715, 1999. [85] Nazina TN, Ivanova AE, Ivoilov VS, et al. Microbiol (Moscow) 1999, 68:222-226. [86] George S, Volk H, Thill G, et al. CSIRO Petroleum Report. No. 05-051. 2005. [87] Li Q, Kang C, Wang H, et al. Biochem Eng J. 2002, 11:197-199. [88] Hou Z, Wu X, Wang Z. Int. Improved Oil Recovery Conf. 2005, SPE 97469. [89] Sayyouh MH. SPE/DOE Improved Oil Recovery Symp. 2002, SPE 75218. [90] Abdulrazag Y, Almehaideb RA, Chaalal O. 1999, SPE 56827. [91] Almehaideb RA, Zekri AY. Pet Sci Tech. 2002, 20:377-392. [92] Sayyouh MH. Emirates J Eng Research. 1998, 3:61-67. [93] Ghojavand H, Vahabzadeh F, Roayaei E, et al. J. Col. Int. Sci. 2008, 324:172-176. [94] Lin SC, Minton MA, Sharma MM, et al. Appl Environ Microbiol. 1994, 60:31-38. [95] Li ZY, Lang S, Wagner F, et al. Appl Environ Microbiol. 1984, 48:610-617. [96] Kim JS, Powalla M, Lang S, et al. J Biotechnol. 1990, 13:257-266. [97] Kaeppeli O, Finnerty WR. Biotechnol Bioeng. 1980, 22:495-501. [98] Sim L, Ward OP, Li ZY. J Ind Microbiol Biol. 1997, 19:232-238. [99] Lang S, Wullbrandt D. Appl Microbiol Biotechnol. 1999, 51:22-32. [100] Lang S, Philip JC. Anton Leeuw Int. 1998, 74:59-70. [101] Rosenberg E, Zuckerberg A., Rubinovitz C., et al. Appl Environ Microbiol. 1979, 37:402-408. [102] Aitken CM, Jones DM, Larter SR. Nature 2004, 431:291-294. [103] Al-Wahaibi Y, Al-Bemani A, Al-Bahry S, et al. Int J Oil Gas Coal Tech. 2009, 4:315-330. [104] Banat IM, Makkar RS, Cameotra SS. Appl Microbiol Biotech. 2000, 53:495-508. [105] Banat IM. Biotechnol Lett. 1993, 15:591-594. [106] Banat IM. Biores Technol. 1995, 51:1-12. [107] Bryant RS. National Institute for Petroleum Energy Research. 1987, 97-104. [108] Bryant RS. Chem Eng Res Design. 1994, 72:144-151. [109] Choi KS, Kim SH, Lee TH. J Microbiol Biotechnol. 1999, 9:32-38. [110] Gautam KK, Tyagi VK. J Oleo Sci. 2006, 55:155-166. [111] Grula EA, Russell HH, Grula MM. Biores. Technol. 1985, 99:4603-4608. [112] Hua ZZ, Chen J, Lun SY, et al. Water Res. 2003, 37:4143-4150. [113] Joshi S, Yadav S, Desai AJ. Biochem Eng J. 2008, 41:122-127. [114] Knapp RM, McInerney MJ, Coates JD, et al. SPE 24818, 1992. [115] Makkar RS, Cameotra SS. J Ind Microbiol Biotech. 1997, 18:37-42. [116] Marsh TL, Zhang X, Knapp RM, et al. CONF-9509173, 1995, 593-610. [117] Mulligan CN. Env. Poll. 2005, 133:183-198. [118] Nelson SJ, Launt PD. Oil Gas J. 1991, 89:114. [119] Portwood JT, Heibert F. Annual Technical Conference and Exhibition, SPE 24820, 1992. [120] Raiders RA, Knapp RM, McInerney MJ. J Ind Microbiol. 1989, 4:215-230. [121] Streeb LP, Brown FG. SPE Rocky Mountain Regional Meeting, SPE 24334, 1992. [122] Al-Sulaimani, H, Al-Wahaibi Y, Al-Bahry S, et al. SPE OGWA Conference, , SPE 129228, 2010.
