Basic Biochemical Study On Improvement Of Reservoir Seepage By Fe(?) Reducing Functional Bacteria In Low Permeability Reservoirs

In China,the microbe enhanced oil recovery(MEOR)technology will gradually become a new research concept in oil recovery field with the development scale of low-permeability reservoirs expanding day by day.However,low-permeability reservoirs mainly contain montmorillonite,illite,mixed montmorillonite/illite,chlorite,and other irregular clay minerals.Among them,the hydration and swelling effect between montmorillonite and its mixed minerals in low permeability reservoirs is a bottleneck problem that directly leads to the decrease of reservoir porosity,permeability,and oil recovery.In the present study,we investigated the diversities and characteristics of microbial community structure in low-permeability reservoirs with different characteristics by high-throughput sequencing technology,and screened of Fe(?)reducing functional bacteria from oil well production fluid.On this basis,the interaction mechanism between functional bacteria and different clay minerals in reservoirs was studied from the perspective of biochemistry,and the new biochemical theory of improving reservoir seepage and pore drag reduction in low permeability reservoirs was established.In this study,a new MEOR strategy was proved successful in the laboratory and presented great potential application for the development of low-permeability oil reservoirs.The major findings and conclusions are shown as follows:(1)The screening conditions and evaluation methods of Fe(?)reducing functional bacteria were optimized in this study.Screening of four strains of Fe(?)reducing efficient functional bacteria from oil well production fluid,and they were identified by 16S r RNA gene analysis to exhibit a similarity of 97-99%to Enterobacter aerogenes,99%to Pseudomonas sp.,98-99%to Bacillus cereus,and 99%to Proteus sp.,respectively(Hereafter named CA,KB,TC,and TD).These functional bacteria can produce a large amount of bio-organic acids by metabolism under facultative anaerobic conditions,and efficiently reduce Fe³⁺to Fe²⁺in montmorillonite minerals and the reduction rate of Fe(?)was 47.1%,62.9%,67.1%,and 71.1%,respectively.(2)After the action of CA bacteria,KB bacteria,TC bacteria and TD bacteria,the chemical bonds strength in the crystal structure of montmorillonite changed significantly.Among them,the peak intensities of?Mg-OH,?Al-OH,and?Fe-OH were sharply weakened,which can result in an imbalance of charge between the lattices,and cause distortion of the lattice distortion and destruction of the frame structure.Meanwhile,the characteristic peak intensity of montmorillonite decreased and the value of half-width increased,and the mineral phase changes partially to form new secondary minerals such as illite etc.Finally,three mechanisms of the transformation of montmorillonite to illite were revealed.In addition,CA bacteria,KB bacteria,TC bacteria and TD bacteria had a good inhibition effect on the hydration expansion of clay minerals,and the inhibitory expansion rates were 45.65%,48.91%,35.87%and 40.22%,respectively.(3)The composite Fe(?)reducing bacteria have good hinge fixing effect on the migration and dispersion of mineral particles by itself and metabolites,and meanwhile the spacing of the mineral layers and the lattice fringe spacing were significantly reduced after the action of bacteria.Furthermore,these functional bacteria has a certain inhibitory effect on clay minerals with different types and contents,and the inhibitory expansion efficiency of montmorillonite(the content of montmorillonite in clay minerals is>95%,70-80%,and 40-50%),kaolinite,illite and chlorite were 62.81%,71.93%,82.76%,98.00%,100.00%,and 99.00%,respectively.In addition,the mechanism of synergistic action of four Fe(?)reducing bacteria on different clay minerals and the electron transfer pathway of Fe³⁺reduced by bacteria in clay minerals were revealed,as well as the formation mechanism of secondary minerals formed by using Fe²⁺as crystal nucleus growth point.(4)Developed the formulation of directional activator of indigenous channel drag reducing functional microorganism in low permeability reservoir,and the composition of the optimal activator was molasses 0.9%,NH₄Cl 0.1%,yeast powder 0.15%,Mg SO₄·7H₂O 0.3 mg/L,Na₂CO₃ 0.25 mg/L,and Fe Cl₃·6H₂O 0.6 mg/L.In addition,we was found that the functional bacteria selectively degraded the polycyclic aromatic hydrocarbons in crude oil,especially the diphenylfuran in benzenes and the1,3,5,7-tetramethylnaphthalene in naphthalenes,and the relative abundance decreased by 0.4%and 3.1%,respectively.The viscosity of crude oil decreased by 1.58 mpa·s after the effect of functional bacteria.(5)The diversity and characteristics of microbial community structure in different production modes of the Yan Chang oilfields,as well as with the different water content of the reservoirs in Chang Qing oilfields were investigated by using high-throughput sequencing technology,and found the possible mechanism and potentials of EOR by activating these functional microbes in low permeability oil reservoir.The results showed that Marinobacterium,Sulfurimonas,Thalassospira,and Pseudomonas were the dominant functional bacteria at the level of genus in the different mining methods areas(normal water flooding,air-assisted flooding,and CO₂ flooding)in the Yan Chang oilfields.Compared with the control group water sample,the microbial community structure changed obviously when the nutrients were added to the production fluids for directional activation.Bacillus,Stenotrophomonas,Pseudomonas,and Lactobacillus were the dominant channel drag reducing functional bacterial genera.In addition,Pseudomonas,Marinobacter,Vibrio,and Arcobacter were the main dominant genera in Chang Qing oilfields.After the directional activation culture,Arcobacter,Desulfobulbus,and Pseudomonas were transformed into dominant functional bacterial genera.(6)The exogenous Fe(?)reducing bacteria and indigenous channel drag reducing functional microorganism can effectively increase the permeability of 10-50m D core and reduce the injection pressure of water flooding,and the permeability increased efficiency was 49.58%and 39.3%;the reducing rate of water injection pressure was61.11%and 55.56%,respectively.Meanwhile,the effect of microbial improvement on the channel drag reduction of the core before hydration expansion was better than that after.The exogenous and indigenous functional bacteria were the effective width of the pore radius of the core after hydration expansion,and the radius values increased by2.412?m and 3.145?m,respectively.Furthermore,the core flooding tests showed that the oil recovery efficiency increased by 6.9%on the basis of water flooding by the activation of indigenous channel drag reducing functional microorganisms.