Enhanced Oil Recovery ( EOR ) is a generic term for techniques used for increasing the sum of petroleum oil that can be extracted from an oil well. Using EOR, 30-60 % of the reservoir original oil can be extracted compared with 20-40 % utilizing primary and secondary recovery techniques.
Enhanced oil recovery is besides called improved oil recovery or third recovery. This improved extraction is achieved by gas injection, chemical injection and thermic recovery ( which includes cyclic watercourse, watercourse implosion therapy, and fire implosion therapy ) . Gas injection is the most normally used EOR technique ; here gas such as C dioxide ( CO2 ) , natural gas, or N is injected into the reservoir whereupon it expands and thereby pushes extra oil to a production wellbore, and furthermore dissolves in the oil to take down its viscousness and better the flow rate of the oil. Oil supplanting by C dioxide injection relies on the stage behavior of C dioxide and petroleum oil mixture that are strongly dependent on reservoir temperature, force per unit area and rough oil composing. These mechanisms range from oil swelling and viscousness decrease for injection of non-miscible fluids ( at low force per unit area ) to wholly mixable supplanting in high force per unit area applications. In these applications, more than half and up to two-third of the injected C dioxide returns with the produced oil and is normally re-injected into the reservoir to minimise operating cost. The balance is trapped in the oil reservoir by assorted agencies.
Other techniques include thermic recovery ( which uses heat to better flow rate ) and, more seldom, chemical injection, where polymers are injected to increase the effectivity of H2O inundations or the usage of detergent-like wetting agents such as to assist take down the capillary force per unit area that frequently prevents oil droplets from traveling through a reservoir. Surfactant enhanced H2O inundations are used for oil recovery where wetting agents are injected with polymer.
Microbial Enhanced oil Recovery ( MEOR ) is peculiarly suited for application in carbonate reservoir, after secondary oil recovery, there are still big sum of oil left in the reservoir. Some bacteriums are able to increase the oil production when injected into the oil reservoir. To excite such anaerobiotic microbial increased oil recovery, foods is injected together with the injection H2O.
Oil recovery requires two to three phases which are briefly described below
Stage1: Primary Recovery – 12 – 15 % of the oil in the well is recovered without the demand to present other substances into the well.
Phase 2: Secondary Recovery – The oil well is flooded with H2O or other substances to obtain an extra 15-20 % more oil from the well.
Phase 3: Third Recovery – This phase may be accomplished through several methods which includes MEOR to to boot retrieve up to 11 % more oil from the well.
Figure 1: Flow diagram for different enhanced oil recovery procedures
Layout for different recovery techniques are shown in figure 1. Primary and secondary recovery techniques are normally called conventional recovery. Primary recovery is done by natural flow which is normally enhanced by reservoir natural force per unit area, and unreal lift such as pumps and gas lift, etc. Secondary recovery is done by H2O folding and force per unit area care by gas reinjection. Third recovery techniques cover wide country which includes thermic recovery such as unmoved burning and steam implosion therapy, solvent recovery is done by methods such as polymer implosion therapy and wetting agent enhanced H2O inundation. Chemical enhanced recovery methods include gas injection or hydrocarbon mixable injection and N and fluke gas implosion therapy. Microbial enhanced oil recovery which is the chief focal point of this undertaking will be explained better in the following chapter, but it is fundamentally injection of bugs such as bacteriums into oil reservoir to assist retrieve oil. All these methods of oil recovery will be explained briefly.
If the belowground force per unit area in the oil reservoir is sufficient, so this force per unit area will coerce the oil out to the surface of the Earth. Gaseous fuel, natural gas or H2O is normally present, which besides supply needed belowground force per unit area. In this state of affairs, it is sufficient to put a complex agreement of valves ( Christmas tree ) on the well caput to link the well to a grapevine web for storage and processing. Normally oil is recovered by natural agencies and unreal lift like pumps and gas lift.
Over a life-time of an oil well, the force per unit area will fall and at some point there will be deficient belowground force per unit area to coerce the oil to the surface of the Earth. If economical, as frequently is, more oil in the well is extracted utilizing secondary recovery methods. Secondary oil recovery uses assorted techniques to help in retrieving oil from depleted or low force per unit area reservoir. Sometimes, pumps such as beam pumps and electric submergible pumps ( ESPs ) are used to pump the oil to the surface of the Earth. Other secondary recovery techniques increases the reservoir ‘s force per unit area by H2O injection, natural gas reinjection and gas lift, which inject air, C dioxide or some other gases into the reservoir. Together, primary and secondary recovery by and large allows 25-35 % of the reservoir oil to be recovered.
The productiveness of bing oil Wellss can be significantly increased by the usage of H2O injection. Statistics has shown that a reservoir produces merely 37 % oil in the first recovery. By utilizing H2O injection, a reservoir can bring forth more than 50 % of its oil. One of the most of import issues during oil production is to maintain the matrix/formation every bit clean as possible to keep maximal oil production. Water is injected for two grounds: foremost is for force per unit area support of the reservoir. Second is to brush or displace the oil from the reservoir, and force it outward.
Gas lift is one of a figure of procedures used to unnaturally raise oil from a well, where there is deficient reservoir force per unit area. The procedure involves shooting gas through the tube-casing ring. Injected gases aerate the fluid and cut down its denseness so the formation force per unit area is so able to raise the oil column and forces the fluid out of the wellbore. Gas may be injected continuously or intermittently, depending on the bring forthing features of the well and the agreement of the gas-lift equipment. Although the gas is recovered from the oil at a latter separation phase, the procedure requires energy to drive a compressor in order to raise the force per unit area of the gas to a degree where it can be reinjected.
Third recovery reduces the oil viscousness to increase oil production. Thermally enhanced oil recovery methods ( TEOR ) are third recovery techniques that heat the oil and do it easier to flux or pull out. Steam injection is the most common signifier of TEOR, and is frequently done with a cogeneration works. In this type of cogeneration works, a gas turbine is used to bring forth electricity and the waste heat is used to bring forth steam, which is so injected into the reservoir. In-situ combustion is another signifier of TEOR, but alternatively of steam, some of the oil is burnt to heat the encompassing oil. Occasionally, detergents are besides used to diminish oil viscousness as a third oil recovery method, another method to cut down viscousness is carbon dioxide deluging. Third recovery begins when secondary oil recovery is n’t plenty to go on equal production, but merely when the oil can still be extracted productively. ( Hitzman 1983 )
Gas injection or Hydrocarbon Miscible injection
Gas injection is the most normally used EOR technique, here, gas such as C dioxide is injected into the reservoir whereupon it expands and thereby pushes extra oil to a production wellbore, and furthermore dissolves in the oil to take down its viscousness and improves the flow rate of the oil. Oil supplanting by C dioxide injection relies on the stage behavior of C dioxide and petroleum oil mixture that are strongly dependent on reservoir temperature, force per unit area and rough oil composing. These mechanisms range from oil swelling and viscousness decrease for injection of non-miscible fluid ( at low force per unit area ) to wholly mixable supplanting in high force per unit area applications. In these applications, more than half and up to two-third of the injected C dioxide returns with the produced oil and is normally reinjected into the reservoir by assorted agencies.
Figure 2: illustration of Gas injection utilizing C dioxide
Figure 2 shows C dioxide injection in reservoir to retrieve oil, C dioxide becomes mixable with oil to cut down viscousness and increase mobility of oil return with produced oil and separated from it.
Nitrogen and gas implosion therapy
Nitrogen and fluke gas about 87 % N and 12 % C dioxide is used in topographic point of hydrocarbon gases because of economical grounds. Nitrogen competes with C dioxide because it is economical and its squeezability is much lower. For a given measure at standard status N will busy much more infinite at reservoir force per unit area than C dioxide and methane at the same status. Nitrogen has a hapless solubility and lower viscousness in oil and requires much higher force per unit area to make miscibility.
Fire implosion therapy is universe cheapest agencies of thermic recovery, nevertheless, important sum of sum of fuel must be burned, both above the land to compact the air, and below land in the burning procedure. Actually the worst portion of the petroleum oil is burnt, the lighter terminal are carried frontward in progress of the firing zone to upgrade the petroleum oil.
Stream implosion therapy
In the steam thrust, steam Is continually introduced in the injection good to cut down the viscousness of the oil and supply a drive force to travel oil towards the production good. Steam drive may work by driving H2O and oil to organize an oil bank in forepart of steamed zone. Ideally this steam bank remains n forepart, increasing in size until it is produced by the well countervailing the injector. However, in many instances the steam flows over the oil and transportation heat by conductivity. Oil at the interface will so be less syrupy and dragged along with the steam to the bring forthing good. Recoverability is increased because the steam lowers the oil viscousness and improves the oil mobility. The more nomadic oil displace the steam zone expands vertically, and the steam oil interface is maintained.
Other techniques which uses heat to better flow rates ( and more seldom ) is chemical injection, where polymers are injected to increase the effectivity of H2O inundations, or the usage of detergent like wetting agents to assist take down the capillary force per unit area that frequently prevents oil droplets from traveling through a reservoir. Alkaline implosion therapy is an effectual chemical EOR method.
Polymer implosion therapy
Both man-made polymer such as polyacrylamides and natural polymers are used for betterment of sweep efficiency. Extra polymer makes the H2O more syrupy so that oil is produced quicker. Obviously, this is non a good thought n a low permeableness reservoir or one with high clay content that absorb the polymer. However, polymer-augmented H2O inundations can be profitable
Surfactant-Enhanced Water inundation
Three types of chemical inundations exist. The first is an alkaline-augmented polymer inundation. Another is an alkaline-surfactant polymer inundation. The 3rd is a micellar or low interface tenseness inundation ( Donaldson, 1989 ) .
AIM AND OBJECTIVES
The purpose of this undertaking is to analyze the adaptability of anaerobiotic bacteriums ( Clostridium Thyrobutyricum 633 ) to different salts and look into the consequence of the microbic strain on permeableness of the Danish Nord Sea Chalk.
To accomplish this purpose, the following aim has been set:
Check adaptability of microbic strain to high salts
Microbial gas production and kineticss of metamorphosis
Carry out home base count experiment
Observation of agitation procedure and microbic analysis
To find and mensurate the volume of C dioxide gas produced by these bugs when exposed to different salts
To find the sum of acid produced during agitation procedure
Statistical analysis of consequences to derive theoretical account
Improvement of experimental process
The undertaking work is based on perusal of the microbial enhanced oil recovery method and the possibilities of utilizing this in the Danish sector of the Nord Sea. The undertaking undertaking applies experimental process and the particular to look into if these bugs can last under reservoir conditions and produce merchandises of import in oil recovery.
2.0 LITERATURE REVIEW
MICROBIAL ENHANCED OIL RECOVERY ( MEOR )
MEOR is used in the 3rd stage of oil recovery from a well, it is a third oil recovery technique. MEOR is the usage of microorganisms to recover extra oil from an bing good, thereby heightening the crude oil production of an oil reservoir. In this technique, selected natural microorganisms are introduced into oil well to bring forth harmless byproducts like C dioxide. These procedure aid to mobilise the oil and facilitate oil flow by cut downing the viscousness of the oil and doing the stone permeable, thereby leting more sum of oil to be recovered from a well. Amongst the available third oil recovery techniques, MEOR is arguably the best for many grounds. One cardinal factor in the choice of microbic enhanced oil recovery is the economical potency, by which desirable chemicals and gases are produced to heighten oil recovery. MEOR procedures are besides energy efficient and environmental friendly as compared to other recovery techniques.
History of bugs used
MEOR is a engineering that has a history based on over 60 old ages of research and field surveies. The earlier plants by ZoBell CE and Updegraff D ( USA ) , Kuznetsov SI and Shturn DL ( USSR ) , shows the international range of the work. This work was expanded in the 1950s chiefly by research workers Coty VF, Yarborough H and Hitzman DO in the major oil companies in the United States. In MEOR, the procedure that facilitates oil production is complex and may affect multiple biochemical procedures. Microbial biomass or biopolymers may stop up high permeableness zones and lead to a redirection of H2O inundation, produce wetting agents which lead to increased mobilisation of residuary oil, addition gas force per unit area by the production of C dioxide or cut down the oil viscousness due to digestion of big molecules.
Application of MEOR engineerings
MEOR engineerings have the common footing of presenting or exciting feasible micro beings in an oil well reservoir for the intent of heightening oil recovery. However, this wide generic definition of MEOR is non a individual methodological analysis but is a broader engineering which can be designed for different and selective applications. It is convenient to split the MEOR engineering into the undermentioned application groups:
Single good stimulation
MEOR H2O inundations
Paraffin ‘s remotion
Heavy oil alteration
The categorization of MEOR engineering by the proposed oil let go ofing mechanism shows the scope of microbic effects which can be identified or expected to happen to which the MEOR system can be directed.
MEOR Oil Releasing Mechanism
Gas coevals: The production of gases will help the supplanting of oil in the pore infinites.
Acerb production: Organic and inorganic acid production by bugs will fade out carbonate sedimentations, Fe sulfide and disintegration and sulphate stuffs.
Surfactant production: Biosurfactants produced by the beings consequence in the decrease of interfacial surface tenseness of the oil/water bond.
Other MEOR oil let go ofing mechanisms includes:
Physical oil supplanting
Selective plugging of high permeableness zones within a reservoir is necessary to accomplish oil recovery. This is best achieved in MEOR procedure where cells stimulated to turn profoundly in a formation where production of biomass and merchandises will hold the greatest impact. If growing occurs chiefly at the well bore, so face stop uping will ensue, and no extra oil will be recovered, go forthing the reservoir unproductive.
The Science of MEOR
The micro beings used in MEOR can be applied to a individual oil well or to an full oil reservoir. They need certain conditions to last, so foods are frequently introduced into the well certain intervals. MEOR besides requires that H2O be present. Micro organisms grow between the oil and the well ‘s stone surface to heighten oil recovery by the undermentioned methods:
Decrease of oil viscousness: Oil is a thick fluid that is rather syrupy, intending that it does non flux easy. Micro organisms assist interrupt down the molecular construction of rough oil, doing it less syrupy and easier to retrieve from the well.
Production of C dioxide gas: As a byproduct of metamorphosis, micro beings produce C dioxide gas. Over clip, these gases accumulate and displace the oil in the well, driving it up and out of the land.
Production of biomass: When micro organisms metabolise the food they need for endurance, they produce organic biomass as a byproduct. This biomass accumulates between the oil and the stone surface, physically displacing the oil and doing it easier to retrieve from the well.
Selective plugging: Some micro organisms secrete slimy substances called exopolysaccharides to protect themselves from drying out or falling quarry to other beings. The substance helps bacteriums plug the pores found in the stones within the well so that oil may travel yesteryear stone surfaces more easy. Barricading stone pores to ease the motion of oil is known as selective plugging.
Production of bio wetting agents: Micro organisms bring forth slippery substances called wetting agents as they breakdown il. Because they are of course produced by biological micro beings, they are referred to as bio wetting agents. Bio surfactants act like slippery detergents, assisting the oil move more freely off from stone and crannies so that it may go more easy out of the well.
If we make a comparing between MEOR and other enhanced oil recovery, so we can see that MEOR is much adoptable, it offers multiple recovery mechanisms, low capital and operating cost, while in other enhanced oil recovery techniques, merely a specified engineering is applicable besides has a high capital and operating cost.
TYPES OF MICROBES AND THEIR SELECTION
MEOR has gained much attending in recent times, but it is deserving observing that non all bugs can last in such conditions as found in an oil well, therefore the bug which are able to defy these conditions are discussed below:
Microbes used in MEOR
There are many types of bacteriums used in MEOR, they include aerophilic and anaerobiotic bacteriums and are divided on the footing of their demand for O. In this undertaking work, the bacteriums used were anaerobiotic from CHP-biogas works at Ribe in Denmark.
Choice of Bacteria
The choice of specific bacteriums is considered in this method. There are a batch of bacteriums available, but the normal conditions for bulk of bacteriums is 5 % Sodium chloride, optimal temperature of 37 degree Celsius, pH less than seven.
Factors impacting growing of bacteriums
There are many factors which affects the growing of bacteriums. Some of which are explained in the below:
Salt: The term salt refers to the sum of dissolved salt that are present in H2O. Sodium chloride is the prevailing ions in sea H2O, the concentration of Mg, Ca and sulfate ions are besides significant. High salt and toxic substances are responsible for restricting the growing of bugs. Halophiles are salt loving bugs which use Na chloride and besides have complex food demands. Moderate halophiles can turn anaerobically at temperature greater than 50o C. The salt in the northern portion of Danish oil field is approximately 40g/l or more. Since salt excessively high, formation H2O is diluted with sea H2O during injection in the well. In order to execute experimental and laboratory analysis, a sample of green goods H2O is taken so as to cognize how much salt can be controlled ; hence microbic gas production has been tested up to 140g/l.
Temperature: Extreme high temperature affects the growing of bacteriums, although they need mean temperature for growing. Thermopiles are bacteriums which are heat loving ; these bacteriums have an optimal growing temperature of 45 Os C – 80 o C. Their membranes are remarkably stable at this highly high temperature. Therefore many of import biotechnological procedures utilise thermophilic enzymes because of their ability to defy intense heat. So before shooting these bacteriums into the reservoir, the temperature of the reservoir should be considered, hence, choice of the right thermophilic bacteriums for high temperature is really of import.
Consequence of pH: pH is the step of sourness or alkalinity of a solution. Simply pH is the step of concentration of H ions in a solution. It is a step of the activity of dissolved H ion. In pure H2O at 25 o C, the concentration of H ion equals the concentration of hydroxide ions ; this is known as “ impersonal ” and corresponds to a pH degree of 7.0. Solutions in which the concentration of H ions exceeds that of hydroxyl ion has a pH degree lower than 7.0 and are known ad bases. The pH reading of a solution is normally obtained by comparing unknown solution to those of known pH, and there are several ways to make so. More favorable pH status for micro beings is about 7 and really few of them can turn below2 and above 10. Micro organisms capable of life at really low pH are called acidphilies and those which live at high pH are called alkaliphiles.
Pressure: Extreme force per unit area affects the growing and metamorphosis of micro beings. A force per unit area lower than 100-200 standard pressure has no consequence on microbic metamorphosis, nevertheless, force per unit area of the scope of 500-600 standard pressures have restricting consequence on growing of bacteriums. The ocean floor possesses high force per unit area. For most MEOR processes barophilic beings will non be necessary, alternatively, barotolerant bugs can turn at high force per unit areas, but do non necessitate these high force per unit areas for optimum growing. The ability to turn force per unit area depends on the energy beginnings available, inorganic salts present, pH and temperature. Adaptation of microbic civilizations to higher force per unit area therefore is possible.
Toxic elements: Chemicals which have toxic effects on micro beings are found in some reservoirs. These chemicals include co-surfactant, surfactant, biocides, ethylenediaminetetraacetate, and methylbenzene, many of which are used in assorted chemical EOR operations. Sodium and Potassium may be exchanged without impairing the growing of micro beings. Magnesium has higher toxicity than Na and K, but the most toxic formation H2O are those with high Calcium Chloride ( CaCl2 ) , so adaptability should be considered before shooting micro beings in such toxic environment.
The pick of Clostridium Tyrobutiricum
Thousands of bacteriums have been investigated for MEOR intent, but the agitation bacterium remain the most popular particularly Clostridia coinage because they produce big volume of gas which include CO2, H2 and CH4. These gases produced, diminish the oil viscousness and increase the force per unit area in the oil reservoir.
Agitation is the procedure that produces alcoholic drinks or acidic dairy merchandises. In general, agitation involves the interrupting down of complex organic substances into simpler 1s. Waste merchandises formed in this manner include gases, ethyl intoxicant, butyl intoxicant, organic acids, propanone and others. Molassess agitation generates energy rich metabolic merchandise, which may respond in the concluding decomposition line of sulphate decrease under anaerobiotic formation status. With sulphate ion in the formation H2O, sulfur decrease predominates. Hydrogen sulfide produced is really non desirable.
The organic acids are formed through agitation of the molasses by the bacteriums in the reservoir do do a stone fade outing procedure.
Dorben field ( Germany ) , 1982, Dr. Wagner
Another ground for utilizing agitation bacteriums is Dr. Wagner field trail. If we make comparing between Danish north oil field formation and Zechstein evaporates stones which are similar to the Danish North Sea formation. Dolomite is besides similar to Danish north field chalk. Formation temperature is rather similar and of class has a high salt. Clostridia tyrobutiricum was selected for Dr. Wagner ‘s experiment.
The features of Dr. Wagner ‘s experiment field are as follows:
Dolomite of Zechstein formations
Depth of 1240m
Formation temperature 53 oC
High salt formation H2O, even the crevices and breaks are partly filled with salt.
The consequence of Dr. Wagner ‘s MEOR good experiments:
Water cut decreased from 80 to 60 %
Average one-year oil production:
Before microbic intervention – 50 dozenss per month
3 months after injection – 150 dozenss per month
1 twelvemonth after injection – 300 dozenss per month
Since all these conditions are similar to Danish North Sea formation and other factors are besides same, so we can utilize agitation bacteriums for MEOR experiment.
Adaptation of bacteriums to high salts
Majority of the bacteriums can non defy high salt, from the clip of ancient civilisation ; it is known that adding 50 g/l of salt in nutrient conserves it from botching. This means that agitation bacteriums which usually populate organic substances has a challenge of version in high salt. The spore organizing bacteriums like clostridia signifier spores in utmost conditions. These conditions allow bacteriums to last but they will non be active and would non be productive. Under highly high salts, bacteriums undergo osmotic emphasis which is expressed in osmotic force per unit area. Osmotic force per unit area affects the H2O activity and production of CO2 gas during the agitation procedure.
Osmosis is the transition of H2O from part of high concentration through a semi-permeable membrane to a part of lower H2O concentration.
Semi permeable membrane are really thin beds of stuff ( cell membrane are semi-permeable ) which allow some substances to go through through them and forestall other substances from go throughing through. Cell membranes will let little molecules like O, H2O, CO2, ammonium hydroxide, glucose, amino acid, etc. to go through through ; meanwhile, cell membranes do non let transition of larger molecules like saccharose, amylum, protein, etc.
Osmotic force per unit area
Osmotic force per unit area is hydrostatic force per unit area produced by a difference in concentration between solutions on the two sides of a surface such as a semi permeable membrane. It was besides observed that the bacteriums change its morphology. For the instance of clostridium it will intend that from rod-shape it turns to cocci-form which is merely the contemplation of shrinking.
Potential osmotic force per unit area
Potential osmotic force per unit area is the maximal osmotic force per unit area that could develop in a solution if it were separated from distilled H2O by a selectively permeable membrane. It is the figure of solute atom in a unit volume of the solution that straight determines its possible osmotic force per unit area.
Osmotic belongingss of cells
The wall of bacteriums and turning works cells are non wholly stiff, and the turgor force per unit area has been proposed to supply the mechanical force for the enlargement of the cell walls during cell growing. The consumption or biogenesis of osmotically active solutes causes an addition in the cells, therefore supplying the necessary tugor force per unit area for enlargement of the cell walls. Although the suggestion that turgor force per unit area is the driving force for cell wall enlargement would connote that the mechanisms that regulate the osmotic balance of beings are cardinal to the really procedure of cell growing.
Lipid membranes allow rapid diffusion of H2O molecules into or out of cells while showing an effectual barrier to most other biological molecules. Membranes that exhibit selective permeableness for different substances are called semi permeable, and the osmotic belongingss of cells derive from this belongings of the membranes.
Thermophyllic and Halophyllic bacteriums
There are bacteriums which need high salts and high temperatures for their growing. In order to look into and enter the conditions of bugs at high salts and high temperature it is better to cognize about the bacteriums which can defy on these conditions. Important information has been given about these type of bacteriums is discussed below.
A thermopile is an extremophile being which survives at comparatively high temperatures. Thermophilic ( heat-loving ) beings are being with an optimal growing temperature of 50o C or more, a upper limit of up to 70