Abstract:
A method of microbial enhanced oil recovery from an oil-bearing formation that involves treating the water that is to be injected into the oil-bearing formation to enable microbial activity and adding oxygen to aid microbial activity. The treatment applied to the water is based, at least in part, upon establishing at least one condition in the oil-bearing formation favorable to microbial activity that enhances movement of oil from the oil-bearing formation.

Description:
TECHNICAL FIELD 
     The current invention generally relates to the field of enhanced oil recovery (EOR). Specifically, the current invention relates to systems and methods of microbial enhanced oil recovery. 
     BACKGROUND OF THE INVENTION 
     Petroleum (crude oil) is one of the world&#39;s major sources of energy. Crude oil naturally occurs in geological formations. Typically, the crude oil is recovered by simply drilling a well in an oil-bearing formation. For some wells, because the oil is under pressure in the reservoir, the oil rises to the surface unaided and recovery simply involves constructing pipelines to carry the crude oil to storage facilities such as tanks. This is known as primary recovery. Over the life of a well, however, the reservoir pressure falls and eventually becomes insufficient to cause the oil to rise to the surface. In this scenario, additional measures have to be adopted to get the oil to the surface. These additional methods are known as secondary recovery methods. Secondary oil recovery includes: pumping, water injection, natural gas reinjection, and gas lift (air injection, carbon dioxide injection or injection of other gases into the production well). 
     The primary and secondary oil recovery methods noted above usually do not result in all the oil in a formation being recovered. Indeed, it is estimated that about half to two-thirds of the oil of a formation remains in that formation after primary and secondary oil recovery. To leave that much oil—a finite resource—in each formation is undesirable. Consequently, over time, further methods have been developed to increase the proportion of oil recovered from a formation after primary and secondary methods fail to provide adequate oil production. These methods are known as tertiary or enhanced oil recovery methods. Common enhanced oil recovery methods include thermal enhanced oil recovery such as steam injection and in-situ burning, chemical flooding methods such as polymer flooding, surfactant flooding, alkaline flooding, micellar flooding and alkaline-surfactant-polymer flooding. However, in situ-combustion is hard to control, steam injection requires expensive steam generating equipment, and chemical flooding is often uneconomical because of the cost of the chemicals. Microbial enhanced oil recovery (MEOR) can be used as a secondary or tertiary enhanced oil recovery process that offers an alternative EOR method that is expected to be less costly and potentially more effective than other EOR methods. 
     MEOR involves the use of biological organisms—microbes—growing in-situ in a formation to facilitate either the production of materials to aid oil recovery or implementing a mechanism for oil recovery. MEOR has been in existence for at least 50 years and is believed to enhance oil recovery in one of or a combination of several ways. First, the microbes produce surfactants in the formation. Surfactants are wetting agents that lower the interfacial tension between fluids and/or substances. Thus, surfactants produced by microbes reduce the interfacial tension of oil droplets that would prevent the oil from moving easily through the formation. Second, the microbes can produce gases such as methane, carbon dioxide, nitrogen and hydrogen. The production of these gases can increase the pressure in the formation and reduce oil viscosity, which makes it easier to mobilize the oil (to the surface). Third, the microbes can also produce compounds, such as acids, that dissolve carbonates and make the formation more permeable so that oil will flow easily thorough the formation to the surface. Fourth, other compounds (solvents) produced by the microbes may decrease the viscosity of the oil so that it flows easier through the formation. Fifth, the microbes break down the hydrocarbons in the oil, making the oil less viscous and easier to recover. Sixth, the microbes may be used to plug certain sections of an oil-bearing formation as a method of modifying fluid flow. These are only some of the ways MEOR is believed to enhance oil recovery. 
     Microbial processes in the reservoir primarily involve anaerobic microbes, in part, because it is typical that oxygen content is low in oil-bearing formations. Nonetheless, aerobic MEOR is also practiced as is described, for example, in U.S. Pat. No. 5,163,510 entitled, “Method of Microbial Enhanced Oil Recovery,” the disclosure of which is incorporated herein in its entirety by reference. While historically there has been some success with MEOR generally, positive results are not consistent and it may be concluded that MEOR&#39;s impact overall, to date, is marginal with regards to the improvement in the proportion of oil recovered from formations. Therefore, there exists a need to make MEOR a more successful method of enhancing oil recovery. 
     BRIEF SUMMARY OF THE INVENTION 
     The current invention is directed to systems and methods of microbial enhanced oil recovery that involves adapting the environment in which microbes live in an oil-bearing formation. The adaptations of the environment facilitate microbial activity that increases oil recovery from the oil-bearing formation. 
     Certain embodiments of the invention include a method that involves introducing microbes into an oil-bearing formation. The method further includes treating water that is to be injected into the oil-bearing formation. The treatment applied to the water is based, at least in part, upon establishing at least one condition in the oil-bearing formation favorable to microbial activity that enhances movement of oil from the oil-bearing formation. The treated water is injected in the oil-bearing formation to establish the condition. Embodiments of the invention also include introducing oxygen into the oil-bearing formation. 
     Embodiments of the invention also include a method of microbial enhanced oil recovery from an oil-bearing formation that involves utilizing microbes naturally residing in the oil-bearing formation. The method further includes treating water for introduction into the oil-bearing formation. The treatment of the water is based, at least in part, upon establishing at least one condition in the oil-bearing formation favorable to microbial activity that enhances movement of oil from the oil-bearing formation. The treated water is injected into the oil-bearing formation to establish the condition. Embodiments of the invention also include introducing oxygen into the oil-bearing formation. 
     Further embodiments of the invention include a system for microbial enhanced oil recovery from an oil-bearing formation. The system includes an oxygen supply apparatus for supplying oxygen to microbes in the oil-bearing formation. The system further includes a water treatment facility for treating water for introduction into the oil-bearing formation. The water treatment performed at the water treatment facility is based, at least in part, upon establishing at least one condition in the oil-bearing formation favorable to microbial activity that enhances movement of oil from the oil-bearing formation. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a diagram of a system for implementing MEOR methods according to select embodiments of the invention; 
         FIG. 2  shows a functional block diagram according to select embodiments of the invention; and 
         FIG. 3  shows a diagram of a system according to select embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a diagram of system  10  for implementing MEOR methods according to embodiments of the invention. System  10  includes a production well  103  for recovering crude oil  109  located in oil reservoir  108 . Oil reservoir  108  is situated within oil-bearing formation  101 . Formation  101  may be any type of geological formation and may situated under overburden  102 . Although formation  101  is shown as being onshore in FIG.  1 , it should be appreciated that formation  101  may be located onshore or offshore. Injection well  105  is a well used to inject water into oil-reservoir  108 . The injected water may be used for water flooding and for providing a medium for growth of microbes used in MEOR of oil  109 . Produced water  125  may be the source of water used in water flooding and/or providing medium for microbial growth in oil reservoir  108 . Formation water  111  naturally occurs in water reservoir  110  and may be the source of water used in water flooding and/or providing a medium for microbial growth in oil-reservoir  108 . Water for system  10 , however, may also be obtained from other sources such as other formations and other bodies of water such as rivers, streams, lakes, etc. Indeed, water used in the MEOR process may be purchased, for example, from a municipal authority. Water  113  from these other sources may be stored in water storage  112 . Pumping station  106  may include one or more pumps. Pumping station  106  pumps water  111  from water reservoir  110  via water well  104  or from water storage  112 . Embodiments of the invention make adaptations to the environment in oil reservoir  108  to facilitate microbial activity that enhances oil recovery from reservoir  108 . As described further below, system  10  includes water treatment  114 , oxygen supply apparatus  116 , microbe injection apparatus  117  and nutrient supply apparatus  118  as components that may be used in MEOR processes to make these adaptations. 
       FIG. 2  shows a functional block diagram according to select embodiments of the invention. Process  20  is a MEOR process that may be applied to, for example, an oil-bearing formation  101 . Oil-bearing formation  101  includes oil reservoir  108  that has been subjected to primary or primary and secondary recovery. As is typical with most oil reservoirs, after primary or primary and secondary recovery has been applied to formation  101 , a significant amount of oil  109  remains entrapped in formation  101 . As such, process  20  may be applied to oil-bearing formation  101  to recover oil  109  that the primary or primary and secondary methods are unable to recover. It should be appreciated that MEOR process  20 , in embodiments of the invention, would yield best results if implemented at the start of the secondary recovery. Process  20  may begin at step  201 , which involves determining the microbes that are to be used in the MEOR process. In process  20 , microbes  107  have been determined to be the microbes that will be used. Microbes  107  may be microbes that naturally exist in oil reservoir  108  or oil-bearing formation  101  (as used herein, native microbes of a formation are microbes that naturally exists in that formation). Alternatively, microbes  107  may not be native to oil reservoir  108  or oil-bearing formation  101  but are introduced therein in order to achieve a desired microbial activity. Indeed, microbes  107  may be a mixture of native and non-native microbes with respect to oil-bearing formation  101 . Utilizing microbes as described herein includes determining what microbes exist in the oil-formation, determining whether these microbes can provide the microbial activity desired to recover oil  109  and, if the identified microbes are adequate, relying on these microbes for the desired microbial activity. Utilization of microbes also includes injecting microbes in the oil-bearing formation that are known to provide the desired microbial activity. 
     Microbes  107  may include one or more microbes selected from bacteria, archaea, fungi and yeast etc., or combinations thereof. In embodiments of the invention, at least some of microbes  107  may be aerobic or facultative. Further, microbes  107  may include microbes uncharacterized from natural inoculums, for example, microbes from sea water, creek water, sludge and soil. Microbes  107  may also include microbes characterized from natural inoculums, which presents a scenario where it is known that the microbes have the ability to grow with hydrocarbons as the main carbon source under reservoir-like conditions. Examples of microbes used in embodiments of the invention include microbes that degrade hydrocarbons, using oxygen, nitrates or sulphates as electron acceptors and has surfactants as a part of their membrane and/or cell wall. 
     Microbes  107  may also include genetically engineered/modified organisms (GMOs). These GMOs may be engineered to adapt to particular reservoir conditions or to enhance particular microbial activity for enhancing oil recovery such as the ability to degrade hydrocarbons, using oxygen, nitrates or sulphates as electron acceptors and to have surfactants as a part of their membrane and/or cell wall. It is to be noted that microbe  107  may include any combination of the different types of microbes described above. 
     At step  202 , the environment that best facilitates population growth of microbes  107  is determined. This determination may include control experiments that monitor microbial growth as a function of changes in the environment in which microbes  107  are placed. For example, the water conditions that best facilitate microbial population growth of microbes  107  may be identified. This may involve changing the properties of water and testing what impact these changes have on microbial growth of microbes  107 . The properties of water that may affect microbial growth and thus may be varied in control experiments include heavy metals content, pH, salinity, anion content, cation content, biochemical oxygen demand, total organic carbon, and precipitation properties. 
     Based on the determination of the water conditions that best facilitate microbial growth of microbes  107 , specifications for the water that is to be used in MEOR process  20  may be set at step  203 . It should be noted that though the control experiments may identify a particular range for ideal microbial growth with respect to a particular water property, that range may be varied because of other criteria. For example, higher salinity water may negatively affect microbial performance. If it is determined that for a particular microbe population the ideal salinity for water in which that population will grow is 5-10%, it should be appreciated that the specification of water to be used in the system may be set at, for example, 5-8% to satisfy some other criteria. The relationship between one water property and another water property may also guide the specifications set for the water overall. Moreover, it is not necessary that every aspect of the specification always meets the ideal conditions for microbial growth. There may be instances where the MEOR process can operate effectively though the specification of the water with respect to a particular property does not fall into the identified ideal range provided by the control experiments. 
     Once the specification is set for the water that will be used in the MEOR process, at step  204 , a water source is identified. Typically, the source of water will be water reservoirs in the oil-bearing formation from which the oil is being extracted. As such, injection of water into an oil-bearing formation as used herein includes removing water from the oil-bearing formation, treating the water and re-injecting the water into the oil-bearing formation. For example, in system  10 , water well  104 , which is supplied by water reservoir  110 , is a source of formation water  111  for use in the microbial enhanced oil recovery of oil  109  from oil reservoir  108 . Formation water  111 , however, may or may not meet the established specification set for the MEOR process. As such, formation water  111  may be analyzed at step  205 . Similarly, water  113  from storage  112 , which is supplied by water sources other than water reservoirs or produced waters from oil-bearing formation  101 , may be analyzed at step  205 . 
     At step  206 , a determination is made whether formation water  111  or water  113  meets the specification of the water to be used in MEOR process  20  by comparing the established specifications with the results of the analysis at step  205 . If the water does not meet established specifications then, at step  207 , the water is treated. To treat water, pumping station  106  pumps water from water reservoir  110  via water well  104  or from water storage  112  to water treatment system  114 . Valves v 1  and v 2  control the source from which pumping station  106  pumps. Indeed, pumping station  106  may pump from more than one source to water treatment system  114 . For example, valves v 1  and v 2  may be opened to allow pumping station  106  to concurrently pump from water well  104  and water storage  112  to water treatment system  114 . 
     Water treatment system  114  may have different types of equipment and systems for achieving different water properties for water used in process  20 . The water properties that may be adjusted by water treatment system  114  include biochemical oxygen demand/total organic carbon, heavy metals content, pH and salinity, anion content, cation content, precipitation properties. Each of these properties and its impact on the MEOR process is discussed in turn below. 
     Biochemical Oxygen Demand, Total Organic Carbon, Chemical Oxygen Demand 
     It is important that injection water for MEOR be free of, or contain only limited amounts of, organic carbon. Biological Oxygen Demand (BOD), Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD) are indicators of organic carbon/pollutants in water. That is, BOD, TOC and COD are known measures of water quality. BOD is a measure of the amount of oxygen used by aerobic organisms in water to break down organic material present in the water. TOC is the amount of organic carbon contained in organic matter in water. COD is the amount of organic compounds in water. Organic carbon in water may come from various sources including chemical treatment programs that are employed in the field to prevent or inhibit corrosion of or scale precipitation in oil recovery equipment. 
     Low levels of BOD, TOC and COD are important for effective MEOR for at least three reasons. First, the microbial activity in MEOR should be focused on processes involving hydrocarbons from reservoir  108  as carbon source. Second, elevated levels of BOD, TOC and COD can cause the development of rogue bacterial blooms that can consume both the injected nutrient and the injected oxygen that are intended to support the oxygen reduction processes within reservoir  108 . Removal or lowering of BOD, TOC and COD allows for MEOR oxygen reduction processes to be sustained within the reservoir. Third, naturally occurring communities of microbes are present in the injected water, inside surface flowlines, pumping equipment and wellbore tubulars. Exposing these indigenous microbial communities to nutrients, oxygen and organic carbon pollution can cause the formation and growth of biofilm that can foul and plug surface equipment, flowlines and wellbore tubulars. Removal or lowering of BOD, TOC and COD can minimize the possibility of biofouling. 
     In some embodiments of the invention, BOD of water to be used in the MEOR process is set at 0-20 milligrams per liter. BOD, TOC and COD may be reduced by any water treatment method known in the art. For example, BOD, TOC and COD reduction may be performed by sedimentation in gravity sedimentation tanks, filtration by screens, chemical oxidation, biological processes in, for example, aerobic, facultative and anaerobic lagoons, activated sludge systems, aeration systems etc. 
       FIG. 3  shows a specific system for eliminating or controlling organic pollutants in injection water  305 , according to one embodiment of the invention. System  30  involves employing a controlled nitrogen reduction process to consume organic carbon prior to the injection of nutrient and oxygen that support the MEOR process. As such, water treatment  114  may comprise system  30  and implemented prior to injection of oxygen by oxygen supply apparatus  116 , microbe injection by microbe injection apparatus  117  and nutrient injection by nutrient supply apparatus  118 . System  30  includes water holding tank  301 , which is typically employed upstream of water injection pump  302 . Nitrate and phosphate injection apparatus  304  injects nitrate, (typically sodium nitrate) and phosphate (typically monosodium phosphate or phosphoric acid) directly upstream of holding tank  301 . Alternatively, the nitrate and phosphate are pumped into holding tank  301  in sufficient quantities to support the reduction of organic content. The carbon limited denitrification process takes place within water holding tank  301  with the organic carbon being consumed in the process. The quantities of nitrate and phosphate that must be injected can be determined and controlled by monitoring the effluent water from holding tank  301  via sampling and analysis or real time with, for example, a probe such as a ultraviolet absorption probe  303  that may be deployed to measure nitrate, COD, TOC and BOD concentrations. It should be noted that in embodiments of the invention where water treatment  114  comprises system  30 , then nutrient supply by nutrient supply apparatus  118  may be eliminated from system  10 . 
     Heavy Metals 
     Heavy metals are metallic elements that can be toxic to biological activity. Examples of heavy metals include mercury, cadmium, lead, chromium, strontium, barium, copper, boron and arsenic. In some embodiments of the invention, it is desirable to keep the heavy metal content below 15 milligrams per liter. Heavy metals at high concentrations inhibit biological processes in microbes. As such, it is desirable to limit heavy metal content to tolerable levels in the water to be used in MEOR process  20 . Water treatment system  114  may use several different methods for reducing heavy metal content. These methods include precipitation, flocculation, reduction extraction, chelation, and ion exchange, etc. 
     pH 
     pH is a measure of acidity or alkalinity. The microbial activity is affected by changes in pH. In some embodiments of the invention, a preferred pH range is 5 to 9 and a more preferred range is 6 to 8.5. The pH may be altered by removing acidic or basic compounds that exist in the water being treated or by addition/formation of acids and bases. 
     Salinity 
     Salinity is the salt content of water. Different microbes may thrive in water of different salinities. Changing the salinity of water to meet the particular needs of the microbes being used may include adding salt to or removing salt from the water. Salt removal may be done by distillation and by membrane processes using reverse osmosis, etc. In some embodiments of the invention, a salinity less than 10% is preferred. In other embodiments of the invention a salinity less than 5% is preferred. 
     Anion Content 
     Anion content is a measure of the amount of anions such as nitrates, phosphates, sulfates chlorides, bicarbonates and carbonate present in the water. Anion content is related to salinity because as salinity increases, the anion content increases. Also, the anion content gives an indication of nutrients that may be available to the microbes. The anion content may be varied by addition or removal processes similar to those employed in adjusting salinity. 
     Cation Content 
     Cation content is a measure of the amount of cations such as calcium, magnesium, sodium, potassium, copper, barium, strontium and iron. Cation content also gives an indication of nutrients that may be available to the microbes. The cation content may be varied by addition or removal processes similar to those employed in adjusting salinity. 
     Precipitation Properties 
     The precipitation properties of the water indicate whether solids are likely to precipitate from the water. It is important to identify the precipitation properties of the water because if there is a high tendency for precipitation to occur in the water used in the MEOR process this can result in wells (e.g., such as injection well  105  and production well  103 ) becoming clogged over time. For example iron hydroxides tend to precipitate from formation water when increasing the level of oxygen in the water. When mixing different waters, barium and strontium compounds are known to precipitate from produced formation waters. Increasing pH from removal of CO 2  from a water may result in precipitation of calcium carbonate. The anions and cations present in the water and the pH of the water are indicators of the likelihood that precipitation problems may occur when the water is used in MEOR process. Additionally, precipitation tests may be carried out by replicating, in the laboratory, conditions that will likely exist in formation  101 , during MEOR, and measuring the level of precipitation that occurs. 
     As noted above, embodiments of the invention may utilize various types of water treatment processes including physical, chemical and biological processes. The water treatment processes may involve the removal and/or reduction of chemical oilfield treatments that have contaminated formation water  111  in the primary and secondary recovery processes. The invention is not limited to the various water treatment methods described herein as other water treatment methods may be used. Further, in addition to the treatment processes described herein, a further treatment method may involve simply blending one batch of water having certain properties with another batch of water having different properties in order to get water meeting the established specifications. For example, if formation water  111  has a salinity of 20%, the salinity may be reduced to less than 10% by blending formation water  111  with water  113  (in this example freshwater) from water storage  112 . 
     After water treatment at step  207 , the treated water is analyzed at step  205  and another determination made at process  206  whether the established specification is met. Once the established specification is met, treated water  123  is pumped from water treatment system  114  via line  115  towards injection well  105 . It should be noted that if formation water  111  and water  113  meet the established water specifications, formation water  111  and water  113  may be pumped directly from water well  104  by pumping station  106  to injection well  105  by, for example, closing valves v 3  and v 6  and opening valves v 4  and v 5 . 
     In certain embodiments of the invention, treated water  123  may not be sufficient in providing the ideal conditions for microbial growth. For example, embodiments of the invention use aerobic microbes in the MEOR process and these microbes require oxygen for survival. Enough oxygen does not exist in oil-bearing formation  101  and thus oxygen will need to be added to oil-bearing formation  101  so that microbes  107  can survive therein. As such, at step  208  a determination may be made whether the MEOR process requires the addition of oxygen for microbes  107 . It should be noted, however, that excess oxygen may negatively affect the MEOR properties of microbes  107 . If it is determined that oxygen is to be added, at step  209  a pre-determined amount of oxygen is added. Oxygen may be added by various means. For example, oxygen or air may be injected into treated water  123  by oxygen supply apparatus  116  via line  119  (as shown in  FIG. 1 ). Air introduction systems are described in U.S. Pat. No. 6,546,962 entitled “Introduction of Air into Injection Water,” the disclosure of which is incorporated herein by reference. Oxygen supply apparatus may include injection pumps, ejectors, etc. In addition to or alternative to injecting air or oxygen into treated water  123 , oxygen producing compounds may be injected into treated water  123  or may be injected directly into oil formation  101 . Oxygen producing compounds may include H 2 O 2 , NaClO 3 , KClO 4  and NaNO 3  and combinations thereof. In some embodiments of the invention, the oxygen content is adjusted to 0.2-15 ppm. 
     At step  210 , a determination is made whether microbes  107  should be added to formation  101 . It may be necessary to add microbes  107  to formation  101 , for example, when no microbes or insufficient amount of microbes exist in formation  101 . Further, a particular type of microbe may be desired in the MEOR process applied to formation  101 . If microbe addition is determined to be necessary, microbes  107  are be added at step  211  by microbe injection apparatus  117  via line  120 . Microbe injection apparatus may include, for example, pumps to pump microbes  107  dispersed in a liquid medium. 
     Apart from oxygen, microbes  107  will require nutrients to survive. The type and amount of nutrients required by microbes  107  may be known based on knowledge in the art about microbe  107 . Additionally, the type and amount of nutrients required by microbes  107  may be determined by controlled growth experiments. From this information, it may be determined, at step  212 , whether nutrients should be added to treated water  123 . If all the required nutrients are not present in treated water  123 , then nutrients are added to treated water  123  by nutrition supply apparatus  118  via line  121 , at step  213 . Alternatively, nutrients may be added to formation  101  by other methods apart from injection into treated water  123 . Examples of nutrients according to embodiments of the invention include NaNO 3 , KNO 3 , NH 4 NO 3 , Na 2 HPO 4 , K 2 HPO 4 , Ca(NO 3 ) 2  and NH 4 Cl. 
     It should be noted that whether oxygen and/or nutrient addition is required at steps  209  and  213  may depend on factors such as the type of microbes  107 , the type of oil  109 , the depth of reservoir  108 , etc. Further, in embodiments of the invention that involve blending of, for example, formation water  111  and water  113 , without further treatment at water treatment system  114 , the blending may be done at pumping station  106 . Pumping station  106  may then pump the blended water directly to oil-bearing formation  101  via water well  105 . In this scenario, oxygen, microbes and nutrients may be injected into line  124  for delivery to oil-bearing formation  101  via water well  105 . 
     At step  214 , treated water  123 , which may have been amended with oxygen, microbes, nutrients or combinations thereof, is injected in oil-bearing formation  101  via line  115  and injection well  105 . Once treated water  123 , microbes  107 , oxygen and nutrients are in place in reservoir  108 , at step  215 , microbial action is allowed to take place and the production of incremental oil monitored in production well  103 . In other words, enough time is allowed for microbes  107  to grow on residual oil (oil  109 ) by consuming the nutrients and the oxygen. By growing on oil  109 , the microbes reduce the interfacial tension between oil  109  and water in oil-bearing formation  101  (treated water  123  and water that may otherwise exist in the formation) and reduces water relative permeability in oil-bearing formation  101 . In certain embodiments of the invention, the water treatment applied at water treatment system  114  is directed to enhancing a particular one or more of microbe  107 &#39;s ability to grow on oil  109  to reduce the interfacial tension between oil  109  and the water in the oil-bearing formation and reduce water relative permeability. The reduced water relative permeability will, as a consequence, divert nutrients to areas of reservoir  108  where they will stimulate the interaction of microbes  107  with the trapped oil  109  for increased production of oil  109 . 
     After sufficient microbial activity has occurred to enhance oil recovery, the oil is recovered at step  216 . The oil recovery at step  216  may involve recovery processes, that include water flooding. Water used in water flooding at step  216  may be formation water  111 , water  113  or water from other sources. Crude oil  109  is recovered from oil well  103  via pipelines to separator/storage, such as at tank farm  122 . At tank farm  122 , production water  125  (water recovered along with oil  109 ) is separated from oil  109 . In some embodiments, production water  125  may be transported to water storage  112  or to a separate storage. Production water may then be treated by water treatment system  114  and used in the oil recovery process as described above with respect to formation water  111  and water  113 . 
     Although a preferred embodiment of the present invention has been described with reference to the steps of  FIG. 2 , it should be appreciated that operation of the present invention is not limited to the particular steps and/or the particular order of the steps illustrated in  FIG. 2 . Accordingly, alternative embodiments may provide functionality as described herein using various steps in a sequence different than that of  FIG. 2 . For example, the injection of oxygen, microbes and nutrients (steps  209 ,  211  and  213 ) may take place consecutively. Further, the injection of microbes (step  211 ) may occur before the injection of oxygen (step  209 ) or after the injection of nutrients (step  213 ). Any order of implementing steps  209 ,  211  and  213  may be used in embodiments of the invention, including implementing two or more of steps  209 ,  211  and  213  concurrently. Furthermore, the steps of  FIG. 2  may be carried in distinct batch processes or in a continuous process or as combinations thereof. For example, a batch process may involve carrying out the injection of oxygen, microbes and nutrients (steps  209 ,  211  and  213 ) consecutively and then allowing microbial activity to take place for a certain period of time before oil  109  is recovered at step  216 . On the other hand, a continuous process may involve continuously and concurrently performing the injection of oxygen, microbes and nutrients (steps  209 ,  211  and  213 ) over time and concurrently recovering oil at step  216 . 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.