| As an important method of enhanced oil recovery technology,emulsion flooding has been widely studied by scholars at home and abroad for its adaptability,displacement mechanism and displacement effect.However,due to the limitations of experimental techniques and materials,the effect of emulsion flooding on microscopic residual oil and the mechanism of the remobilization of residual oil in three-dimensional pore space has not yet been clarified.Therefore,in this paper,with using advanced micro-CT in-situ scanning technology,we conducted three sets of micro-scale displacement experiments.By quantitatively characterizing dynamic characteristics of remaining oil,including location,particle size,volume,3D/2D shape factor and contact angle,the effect of emulsion displacement on the remaining oil was analyzed,and the displacement mechanism of emulsion flooding in microscopic pore space was obtained:Firstly,the configuration parameters and method of the emulsion were determined according to the results of the configuration experiment.On this basis,two sets of emulsion flooding experiments and one set of polymer flooding experiments were performed.The images of oil-water distribution during every displacement process were obtained.After image process,image segmentation and pore network model established,the pore structure and dynamic characteristics of oil were accurately quantified.Secondly,the effect of emulsion flooding on the residual oil was clarified by analyzing the dynamic characteristics of oil phase at different process,First,the water mainly displaces the remaining oil in the throat;the emulsion displaces the remaining oil not only in the pores but also in the throat.Second,during water flooding,oil cluster which radius was between 16 and 37?m and between 6 and 25?m was displaced during water flooding and emulsion flooding,respectively.Third,after oil saturated,the form of oil clusters was extremely irregular,and the shape factor of oil clusters was the largest;after water flooding,the shape factor of oil clusters is uniformly reduced,and its range is narrowed;after emulsion flooding,the shape factor oil clusters and range of shape factor were both further reduced,and the number of oil clusters with smaller shape factors was significantly increased.Fourth,after water flooding,the ranger of oil contact angle was from 85° to 134°,and the average contact angle is 111.7°.After emulsion flooding,the contact angle of the oil cluster distributed from 40° to 119°,and the average contact angle is 79.0°.Fifth,the second water flooding has the greatest contribution to enhanced oil recovery.Finally,combined with the pore structure characteristics,residual oil dynamic characteristics and oil classification method,it was found that the emulsion mainly has the following three mechanisms for displacing residual oil at the pore scale: First,the emulsion removes some pieces of oil droplets from large oil clusters,reducing the volume of continuous type oil and increasing the number of non-continuous oil clusters.Second,the emulsion changes the interfacial tension of the fluid system,and the remaining oil originally trapped on the wall and corners is concentrated in the center of pores.Third,emulsion changes the distribution of local capillary pressure and increases sweeping area of the displacement phase by two different ways.The displacement mechanism of emulsion flooding and polymer flooding was compared: polymer flooding has only one way to increase the sweeping area,that is,plugging the dominant channel.And polymer did not change the form of remaining oil,only affected distribution and saturation of the continuous type oil.And second water flooding contributes little to enhanced oil recovery. |
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