The Mechanism And Practice Of MEOR By Brevibacillus Brevis And Bacillus Cereus In Daqing Oilfield

To investigate the mechanism and principle of Microbial Enhanced Oil Recovery (MEOR), thebehavior of two kinds of facultative anaerobes, HT (Brevibacillus brevis) and HP (Bacillus cereus)which are selected from Daqing produced water and use petroleum hydrocarbons as the sole carbonsource, is studied under the Physical and Chemical conditions of Daqing oil reservoir. Its potentialapplication to EOR is further confirmed by the field tests. The major conclusions are as follows:1. The regularity of oil degradation action by HP and HT(1) The group composition of oil samples before and after degradation is detected with methodof GC-MS and it indicates that both HP and HT have great capabilities to degrade saturationhydrocarbons with high carbon chain. It is interesting to note that HP is more likely to degradehydrocarbons with even carbon number than it does those with odd carbon number. HT, however, isable to degrade saturation hydrocarbons regardless of their carbon number. The saturationhydrocarbons with low carbon chain, by contrast, can hardly be degraded by both HP and HT andthere are no such compounds generated during the oil degradation process.(2) The GC-MS analysis shows that HP and HT can degrade the homologue of phenanthrenes,one kind of aromatic hydrocarbon in the oil samples, to a certain extent.(3) Micro-infrared method, together with the titration of acid number are employed to analyzethe nonhydrocarbon in oil samples before and after degradation and the study shows that differentcomponents in oil samples undertake some bio-oxidation reactions during the degradation process,which results in a production of organic acid with high carbon chain and an increase in acid numberby 8-15 times higher.2. Analysis and comparison of polar components in oil samples before and aftermicrobial degradation.(1) To study the microbial action on Daqing crude oil, the blank sample is first analyzed withGC-MS method. The result shows that there are altogether 56 kinds of polar components present inthe blank, among them, the kinds of alcohol, aldehyde/ketone and ester compounds amounts to 31,11 and 7, respectively. Furthermore, the alcohols and esters are preponderant and both of themaccount for 97.46 percent of the polar oxygen compounds. The content of another kind of oxygencompound, fatty acid, however, remains much lower in the blank.(2) The kinds of extracellular fatty acids in samples treated by HP and HT are increased fromthe original 7 to 17 and 24, respectively, and their relative content rises from the original 1.05wt%to 60.05wt% and 61.02wt%. They are composed mainly of monoatomic acids and binary acids withcarbon number between 2 and 20. The study also indicates that the alkyl acids, especially those withlinear and saturation chain preponderate in the newly-generated acids. A certain amount ofnaphthenic, alkenyl and aromatic acids are also generated in the degraded samples.(3) In the sample treated by HP, 5 kinds of alcohols are newly produced and 6 other are thesame as those present in the blank. For the sample treated by HT, 4 kinds of alcohols are the sameas those in the blank and 6 other are new. The alcohols produced from the two actions vary little instructure and molecule weight, which prove to be composed mainly of monoatomic acids withcarbon number below 20.3. The metabolite composition of the fermentation solution(1) In HP fermentation solution, there are four kinds of low carbon organic acids-acetic acid,propionic acid, butyric acid and isovaleric acid-and one alcohol (ethanol, with a concentration of16.52 mmol/L), the concentrations of total acids and acetic acid amount to 9.9158 mmol/L and9.5667mmol/L, respectively. In HT fermentation solution, the concentration of low carbon organicacids (including acetic acid, propionic acid and butyric acid) is 0.109 mmol/L.(2) Several analytical approaches such as TLC, ultraviolet absorption, infrared spectrum andelementary analysis are employed to determine the nature of the bio-surfactants in both of thefermentation solutions. The result shows that they are mixture of neutral alcohol/ester non-ionicsurfactants.4. How HP and HT degrade saturation hydrocarbons and how they ingest thosepetroleum hydrocarbons which are not water soluble are speculated based onthe metabolite analysis, the result shows that:(1) Bio-oxidation is the main pathway that HP and HT use to degrade Daqing crude oil. Thereis probably a process called unconventional subterminal oxidation through which HP and HTconvert one long-chain molecule of hydrocarbon into two short-chain molecules of fatty monoacidsor alcohols, then the resultants will undergo terminal, double-terminal and β-oxidation to producefatty monoacids, hydroxyl fatty acids and dicarboxylic acids.(2) Bio-surfactants generated from the microbial metabolism prove to be a mixture of paraffinesters and glycerides. The study demonstrates that petroleum hydrocarbons first undergobio-oxidation to produce fatty acids and fatty alcohols which, at the presence of catalyst calledextracellular esterase, will be converted into a mixture of compounds with a certain molecularweight distribution, they are paraffin esters, paraffin esters with alcoholic group or poly-paraffinesters. At the same time, the produced fatty acids or those with odd carbon number can be convertedinto acetyl-CoA or propionyl—CoA via the process of β-oxidation cycle, then the resultants willundergo the gluconeogenesis to produceα-phosphoglycerol which finally react with the fatty acylto generate mixed glycerides.(3) There are two petroleum hydrocarbon ingestion modes (mode Ⅲ and mode Ⅱ) used by thebacteria and it can be turned from one to the other depending on the specific period. At thebeginning of microbial growth, petroleum hydrocarbons are ingested mainly through the mode Ⅲ(what the bacteria contact with and ingest are the large hydrocarbon drops) resulting in a slowincrease in bacteria concentration and a production of bio-surfactants. As hydrocarbons are ingested,more and more bio-surfactants are generated and when their concentration reaches or exceeds CMCin aqueous phase, petroleum hydrocarbons will be converted from the larger ordinarily-emulsifieddrops into minute ones solubilized by micelle or micro-micelle and then these minute hydrocarbondrops will be ingested by the bacteria, the ingestion mode is also turned from the mode Ⅲ to modeⅡ (what the bacteria contact with and ingest are minute petroleum drops).5. Based on the metabolite analysis, we provide the methods and technicalstandards to select bacteria which use the petroleum hydrocarbons as the solecarbon source:Test parameters Determination methods Technical standards(compared with the blank)Ability to produce Oil acid number determination 10~20 times higherextracellular highcarbon fatty acids andability to lower oilviscosity Oil viscosity determination Viscosity decreasesby 20~30%Ability to produceextracellular lowcarbon acidsFermentation solution pHdetermination pH decreases by 2~3Ability to producebio-surfactantsDetermination of IFT betweenfermentation solution and oil IFT decreases by 50%6. Physical simulation(1) An experiment called microscopic modeling is performed to investigate the mechanism ofMEOR. When injected into the model, the bacteria HP and HT will distribute all over themicroscopic pore through migration, and then grow and propagate on the oil-aqueous interface.During their degradation on heavy components, the bacteria will alter the properties of the crude, atthe same time, they can produce metabolite which proves to be interfacial activity. Through theactions of emulsification, wettability reversal and in-suit propagation of microorganism, thenonproducing oil can be motivated and striped from the pore, then the residue oil will distribute inthe pore uniformly and later aggregate in the macrovoid. During the water post-flush period, it willbe displaced, resulting in an enhancement of oil recovery.(2) The experiments to evaluate microbial oil displacement are performed on models usinglong-tube artificial cores and natural cores under conditions resembling those in the reservoir. Thestudy shows that the bacteria U1-U6 and HP+HT can enhance 10 percent more OOIP than waterflooding on the long-tube artificial cores and this will also happen in the case with natural cores ifthe growth conditions for the bacteria are appropriate. Because a large volume of fermentationsolution is needed during the microbial flooding, much work remains to be done to shorten the oilproduction time and finally to make this process economically feasible.7. The feasibility of MEOR and its adaptability to the reservoir is verified by thehuff and puff injection of microorganism in an individual well in DaqingChaoyanggou area which is characterized by its excessively low permeability.The dynamic tracking of the test well reveals the oil-displacement mechanism.(1) When the well returns to production after the injection of microorganism, the concentrationof bacteria amounts to 105--107 per ml, the highest is 108 per ml. The period that keeps the bacteriain a high number level can last for 1 to 2 months, indicating that the bacteria can use the crude oil asthe carbon source to grow and propagate under the reservoir conditions. This also explains why thetest well can be operated effectively more than one year on average resulting in an increase of oilproduction.(2) After the microbial treatment, the passages in the near wellbore area which are blocked bythe high carbon paraffin are opened to make the content of high carbon chain normal alkaneproduced from the test well decrease relatively, on the contrary, the content of those with lowcarbon chain is relatively increased. The content of resin also decreases by 30-40 percent. Thechange of those components points out that the normal alkane with high carbon chain and the resinare first degraded by the bacteria, resulting in a viscosity decline and a flowability improvement ofthe crude oil, therefore, more oil is displaced in the individual well.(3) The content of the organic acids in produced water rises to a certain extent. These acidsgenerated from the microorganism metabolism will dissolve the scale composed of silicon as wellas the scale composed of calcium and magnesium. Consequently, the permeability of the formationand flowability of oil and water are both improved.(4) After the microorganism injection, the interfacial tension (IFT) between oil and producedwater declines from the original value 30mN/m to about 18mN/m. This tells us that a certainamount of active substances are produced by metabolism when the bacteria grow and propagate inthe area near the well. These substances can alter the wettability of the rock effectively, which alsocontributes to the oil increase.(5) Among the 13 test wells, 10 of them (5 in layer Ⅰ, 3 in layer Ⅱ and 2 in layer Ⅲ) show agood oil production response and the average input-output ratio is less than 1:9. At present, the huffand puff test can attain a considerable economic profit in layer Ⅰ (the input-output ratio below 1:15)than it does in layer Ⅱ and Ⅲ (the ratio is about 1:3). Therefore, the huff and puff test can beapplied on a large scale in layer Ⅰ whose permeability is excessively low, at the same time, itsadaptability to the layer Ⅱ and Ⅲ needs further investigation.8. A large amount of organic acids are produced and present in oil phase duringthe microbial action on Daqing crude oil by HP and HT, therefore, the acidnumber of the crude is increased dramatically. An exploratory study on theapplication of combination of Microbial and ASP flooding to EOR is made andthe result is encouraging.(1) The acid number of Daqing crude oil is so low that the alkali solution (dissolving NaOH inproduced water to prepare a 0.6 percent solution) usually can not reduce the oil-water interfacialtension (IFT) to ultralow interfacial tension, however, the IFT between the treated oil and alkalisolution can attain 10-2mN/m. The dynamic IFT between the existing ASP system and treated oil isreduced by approximately one order of magnitude and its dynamic behavior is much better than thatbefore microbial treatment. This indicates that there is a strong synergistic effect between thenewly-generated organic acids and ASP system.(2) After the formula optimizing, the composition of Microbial/ASP system is determined asfollows: the dilution multiple of the fermentation solution is 2;the concentration of the synthesizedsurfactant S1, NaOH and polymer is 0.04 wt%, 1.0 wt% and 2500 mg/L, respectively. From theabove formula, we can see that the combination of Microbial and ASP flooding will reduce theusage of expensive surfactant dramatically from 0.2 wt% to 0.04 wt%.(3) The laboratory flooding experiment on natural cores indicates that after microbial treatment,the diluted fermentation solution (the dilution multiple is 2) with addition of some sulfonate(0.04wt%) serving as the surfactant for ASP flooding, can enhance 20.25 percent more OOIP thanwater displacement, which is comparable with the existing ASP flooding. Another experimentpoints out that after the injection of bacteria, the existing ASP formula will enhance averagely 29percent more OOIP than water flooding and near 10 percent than the individual ASP flooding,respectively. This achievement provides not only the theoretical but also the practical importance inthe field of EOR.