Experiments on water flooding in fractured-vuggy cells in fractured-vuggy reservoirs
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Water flooding
Water cut
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Using the three-dimensional network model,the saturating oil,water flooding and polymer flooding processes are simulated and the residual oil distribution pattern is studied.The influences of pore size,coordination number,shape factor and wettability on the residual oil distribution are analyzed.The results show that: with the increasing of the pore size,coordination number and shape factor,the residual oil after polymer flooding decrease;the oil recovery of water wet reservoir is higher than that of oil wet reservoir.
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Fractured reservoirs contain a large fraction of the world supply of oil and imbibition is one of the dominant recovery mechanisms. For fractured reservoirs containing heavy oils or tars, oil viscosity is high and it is hard to get a good development effect at reservoir temperature. However, if thermal methods are adopted, the oil viscosity will decrease sharply as temperature goes on and the oil recovery will increase on the contrary due to capillary imbibition. In this paper, fracture is created by wrapping the core with a steel wire mesh. Before flooding, cores are let to stand at the experimental temperature to eliminate the effect of thermal expansion on oil recovery. Considering that oil volume recovered is very small, a high precision electronic balance is used to weigh the oil and then calculate the oil volume. Different factors including contact area, matrix permeability, oil viscosity, water injection rate, temperature of the injected fluid and wettability of the core are all investigated. Results of this work should be helpful for the better understanding of the capillary imbibition in the development of fractured heavy oil reservoir.
Imbibition
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In order to investigate the effect of the complex structure of fracture-vuggy oil reservoir on water flooding recovery factor,4 types(including 17 different structures) of fracture-vuggy media models were made and a series of simulation experiments of water flooding were carried out.The results show that,①to the fracture-vuggy media with single vug connecting with single fracture,the water flooding recovery factor is higher when the vug is under the fracture than when the vug is above the fracture;②to the fracture-vuggy media with single fracture and the vugs of different density,the ultimate water flooding recovery factor will decrease with the increase of the vug density;③the ultimate water flooding recovery factor will decrease with the increase of the volume fraction of vug;④fracture-vuggy network structure has a significant influence on water flooding recovery factor.Among the network structures of the same connectivity,the network structures with vugs have the lowest recovery factor.The greater the connectivity is and the more complex the network structure is,the lower the recovery factor is.These experimental results show that gravity,vug density,the volume ratio of vug to total pore and fracture-vuggy network structure have a significant influence on oil recovery factor.The study results can be used for guiding enhancing the water flooding recovery factor of the fracture-vuggy carbonate reservoir.
Water flooding
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Nitrogen gas
Water flooding
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Residual oil
Water flooding
Oil in place
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Based on the theory of scaling criteria, a physical experimental model of fractured-vuggy cell which meets the geometric similarity, kinematic similarity, dynamic similarity and characteristic parameters similarity was designed. The factors affecting fluid flow and water flooding characteristics, and the EOR features of different displacing modes were studied by experiments. The experimental results show that: Oil and water displacement effect caused by the density difference between oil and water is the main mechanism of water flooding; Injection rate has no effect on the remaining oil and water-cut; Fracture-vuggy connection is the dominant factor controlling water-free recovery, ultimate limit of remaining oil and water-cut variation in the fractured-vuggy cell; Oil-water viscosity ratio has an important effect on oil production rate, oil replacement ratio and economic limit remaining oil; When the filling degree is low, it has no effect on remaining oil, but when the filling degree is high, the remaining oil contains both "attic oil" and the oil existing in porous media; Foam flooding after water flooding enhances oil recovery by starting the attic oil at the top of vugs, and the remaining oil is in the center of the vugs after foam flooding; Polymer flooding after water flooding enhances the economic limit recovery by increasing the oil production rate and oil draining ratio, but it has no effect on the limit remaining oil of water flooding.
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Residual oil
Tight oil
Fracturing fluid
Matrix (chemical analysis)
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Residual oil
Water flooding
Oil in place
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