Activator Screen, Optimization And Effect Evaluation Of Indigenous Microorganisms From Oil Reservoir

Biotechnologically enhanced oil recovery processes, known as microbial enhanced oil recovery (MEOR), has played a significant role in enhancing crude oil recovery from the depleted oil reservoirs to solve stagnant petroleum production, after a three-stage recovery process employing mechanical, physical and chemical methods. Compared with injecting specially selected consortia of natural bacteria into the reservoir to improved oil recovery, stimulating indigenous reservoir microbes has more potential. This paper essentially studied the efficient activators screen, optimization and performance evaluation of reservoir indigenous microorganisms, to provide the technical support for activating indigenous microbes in reservoirs to enhance oil recovery.According to biochemistry characteristics of reservoirs and nutritional requirements of functional bacteria, we initially established methods of activators screen, which includes basis of activators screen, components screen, determination and optimization of components content.This paper also established the methods of activators'performance evaluation, which referee to the composition and the effect of activors. Basing on the economic and technical feasibility, microbes activated, biological and chemical index, and flooding test of physical simulation, we preliminarily classified the activors and the effect.In order to activate indigenous microorganisms to enhance oil recovery, the compositions of indigenous microbial community in Zhan 3 block were investigated with the methods of MPN (Most Probable Number) and DGGE (Denatured Gradient Gel Electrophoresis). To get more information, the ionic compositions of the formation water were also analyzed by means of ion chromatography and Inductively Coupled Plasma Emission Spectrometry. To effective evaluate the effect of the activation system, the microflora dynamics of bacteria and SRB in the water sample and the effect of emulsification of crude oil were taken as evaluation indexes. The compositions and concentration ranges of the activation system were selected by means of single-factor test. On the basis of single-factor test, the mathematical regression model was established about the dependent variable [corn steep powder, (NH4)2HPO4, NaNO3] and independent variables (the absorption value at 550nm of the activated water sample) through Box-Benhnken center composite design and response surface methodology. As the final composition of the activation system were Corn steep powder 0.33%, (NH4) 2HPO40.312%, NaNO30.2%, the total bacteria concentration was up to 108cells-ml-1, HOB 107cells-ml-1, MPB 104cells-ml-1, SRB was effectively controlled, oil evenly dispersed in the culture medium, oil viscidity reduced 30% and enhanced oil recovery 6.9% in physical simulation experiment.Three crude oil-degrading bacteria, numbered N12-1, N12-2 and N12-3, were isolated from Zhan 3-N12 injected water. Through the 16S rDNA sequence analyzing, the three bacteria were identified as Geobacillus pallidus with 99% of homogenous, Bacillus thermoamylovorans with 99% of homogenous and Bacillus Jirmus with 97% of homogenous respectively. With the culture medium contained 2% of crude oil, degrading rate of crude oil was up to 50% after 7 days. Comparing with single bacteria, mixed bacteria, whose degrading rate of crude oil was up to 60%, have better degradation ability. The relative content of saturated hydrocarbons, aromatic hydrocarbons and non-hydrocarbons is changed from 17.88% to 14.29%,28.48% to 17.24% and 27.81% to 17.73% respectively. Results by gas chromatography-mass spectrometry (GC-MS), the n-alkane components with the number of carbon under 20 were preferred to degradation, the∑21-∑/C22+was decreased from 2.62 to 0.74 and the relative content of naphthalene was decreased from 42.05% to 13.31%. Using the techniques of spectrophotometer and microscope, the emulsification effect of the crude oil after degradation were appraised, which indicated the oil-water mixtures were relatively stable and the particles diameter were between 10-90um. All of the three bacteria can endure high salinity, which can degrade crude oil under 4% of salinity. Thus, it can be seen these bacteria have higher flooding potential.