Research On Synergistic Eor Mechanism Of Microbial Flooding And Air-injection Displacement

With the rapidly development of world economy and growth of population,it makes the demand for various natural resources increase day by day,especially non-renewable resource such as oil.However,the exploration and exploitation difficulty is ever increasing.The waterflood oilfield has entered high water cut stage that the water cut of produced liquid is about 80%.At the same time two-thirds of thegeological reserve of oil is far too difficult to extract.In consequence,there is an urgent need to study further enhanced oil recovery techniques and methods.Microbial flooding and air injection displacement are newly developed technology with a bright future,which used alone are effective to displacement of reservoir oil.However there are some problems with swept area for single microbial flooding,and the single air injection displacement also has some major disadvantages,such as,the hidden trouble of safety and the drawbacks of gas channeling.Therefore,a systematic study of overcoming the shortcomings of these two oil displacement styles has important practical significance and theoretical value.Firstly,this paper analyzes the effect of different dissolved oxygen concentration on the microbial metabolism.The microbial nutrition and the kinetic model of microbial growth were investigated.The basic features of microorganism used in oil recovery were studied through isolation and identification of test strains.The effect of different dissolved oxygen concentration on the gases produced by biological processes uses the mathematical expression of microbial metabolism as a guide.Taking the dissolved oxygen content as index,the rule of microbial growth in different dissolved oxygen level was discussed.Secondly,the rock wettability,oil-water interfacial tension were used to study the effect of different dissolved oxygen concentration on microbial enhanced oil recovery.Further,the oil displacement experiments of multistage alternating injection of microbes and gas were developed.Finally,the numerical simulation study based on the alternating injection of microbes and gas experiments was carried out.The results showed that insufficient oxygen content limits the growth of microorganisms,the biofilm and biomacromolecule were destroyied in the hyperoxic environment,the optimal dissolved oxygen concentration for microbial growth is 4.5mg/L~5.5mg/L.The main oxygen consumption of the reservoir happened on stationary and declining phase.The metabolism oxygen consumption is the slope of the straight line segment on the oxygen consumption curve.The reduce number of microorganisms on declining phase was supplemented by growth on account of the adequate nutrition adding in the injection water.The total oxygen consumption rate of stationary and declining phase is the sum of the metabolism oxygen consumption and growth oxygen consumption.At the same time,this paper suggests the synergistic effect of oxygen on microbial enhanced oil recovery.Microbial capacity of changing rock wettability and oil-water interfacial tension was enhanced with the increase of dissolved oxygen content in water.What' more,the increase of dissolved oxygen concentration is conducive to the foam stability of bacteria solution.After injection of air into the variable-diameter capillary branching model,bubble came across the big throat firstly to produce additional resistance,which had the profile control effect on microbial displacement fluid.The microorganisms-air-microorganisms-air displacement method has the best results of enhanced oil recovery.Taking this one step further,the permeability saturation curve of microorganisms-air displacement could calculate by the oil displacement experiment results.While water injection intensity remained unchanged,the minimum radius of microbial oxygen consumption to safe concentration was 145 m.While air injection intensity remained unchanged,the minimum radius of microbial oxygen consumption to safe concentration was 140 m.The oxygen concentration in the reservoir will even lower,if the oxygen consumption of low-temperature oxidation is taken into account,the calculated radius of safety will be even safer.The results prove that there is synergetic effect on enhanced oil recovery between microbial flooding and air injection displacement.