Laboratory Study On Enhanced Oil Recovery Process By Oil Displacement System With Adjustable Flowing Resistance

Due to the vertical and plane heterogeneity of oil layer in reservoir, it is easy to lead tothe dashing and fingering of injected water and resulting in different directional producersaround injection well respond differently and nonuniform displacement in main streamlineand distributary streamline. Chemical flooding like polymer flooding, profile control anddisplacement can improve water flooding effect greatly. But due to the reservoir heterogeneity,there are still a large number of uneven remaining oil in oil layers after these methods wereapplied. There is a paradox between oil displacing agent with certain viscosity andheterogeneous oil layers. Under this background, this paper proposes a kind of enhanced oilrecovery method of oil displacement system with adjustable flowing resistance. Someresearches are conducted on many kinds of oil displacement system with adjustable flowingresistance on the basis of water flooding, chemical flooding like polymer flooding and profilecontrol, which can be adapted to heterogeneous oil layers and uneven pressure gradientdistribution. This method not only enhances oil recovery of water flooding in middle and highpermeability reservoir, but also enhances that in low permeability reservoir.This paper explains the theory of enhanced oil recovery of variable seepage resistance oildisplacement system for enhancing regional pressure gradient and formulates differentadjustable flowing resistance oil displacement system. The possibility of enhanced oilrecovery by this method is confirmed through different experiments. In order to find out thematching relationship between adjustable flowing resistance oil displacement system and thecondition of oil layer, some laboratory tests were conducted by using polymer as arepresentative oil displacing agent. This paper takes constant speed and pressure combinationas technical route firstly, the criterion of matching relationship between oil displacing agentand the condition of oil layer were formulated by combing resistance coefficient and residualresistance factor from constant speed injection and injection speed from constant pressureinjection together. The matching relationship plate was given, which provided theoreticalguide for field application of adjustable flowing resistance oil displacement system.A kind of visual sand-packs model of plane heterogeneity was developed and some oildisplacing experiments were conducted, that can be observed directly. The results show that,in contrast to constant seepage resistance system, adjustable flowing resistance oildisplacement system with continuously reduced viscosity can achieve larger swept area.Based on above, it can be confirmed qualitatively that adjustable flowing resistance oildisplacement scenarios can obtain larger swept volume and enhance oil recovery by waterflooding or polymer flooding further.Some laboratory tests are carried on six parallel cores with polymer alternatively injectedadjustable flowing resistance oil displacement system. The permeability of these six cores are 100,300,500,700,900and1100×10-3μm2respectively. Compare with flow ratio, oil recovery,water cut and pressure of different alternate pattern and alternate cycle scenarios, a suitablealternate adjustable flowing resistance injection pattern was studied. It can be concluded thatalternate cyclic injection can increase fluid suction volume of low permeability layer to adjustprofile and can refrain unfavorable profile change to improve displacing effect ofheterogeneous oil layers. But there should be a optimal range of alternate cycle, whenalternate cycle is0.2PV, best oil displacing effect can be obtained for the heterogeneous oillayers we studied in the experiments. For the sequence of alternate injection, it can beconcluded that scenario with high molecular weight and high concentration in first is betterthan that of low molecular weight and low concentration in first. Further optimal alternatelyadjustable flowing resistance injection pattern was screened.Taking into account the good mobility control and variable seepage resistance andreducing interfacial tension of foam system, some experiments are carried out to determinethe oil displacing effect of different alternate pattern between foam system and binary systemon artificial three-layer heterogeneous cores and then a optimal alternate pattern betweenfoam system and binary system is determined. On the basis of this, some displacingexperiment were conducted by making use of microscopic etched glass model and manyimages of different variable seepage resistance oil displacement system flowing in the modelare collected. Comparing displacing effect of polymer flooding, polymer and air alternateinjection and binary system and foam system alternate injection, it can be concluded that incontrast to polymer flooding, polymer and air alternate injection and binary system and foamsystem alternate injection can enhance oil recovery and reduce the amount of polymerconsumed greatly. It was analysed of the seepage difference between polymer and air systemand polymer and foam system. Both of them can make injection seepage resistance change,but the oil displacing effect of the latter is better than the former and it can be confirmedfurther that variable seepage resistance oil displacement system can enhance oil recovery.According to the optimal molecular weight and concentration of polymer, someexperiments are carried out to determine the oil displacing effect among continuouslyreducing polymer viscosity method and alternate injection of polymer and binary system andfoam system alternate injection and ASP flooding and so on by using artificial three-layerheterogeneous cores simulating the condition of typeⅠreservoir of Daqing oilfield. Theresults show that the oil recovery by continuously reducing polymer viscosity method ishighest, which illustrates that the variable seepage resistance system of continuously reducingpolymer viscosity is suitable for typeⅠreservoir and is feasible economically.