Study On Microscopic Flow Mechanism Of Preformed Particle Gel Through Porous Media

Preformed particle gel flooding is one of the most effective displacement patterns to tapthe potential residual oil and enhance oil recovery for the eastern muture oilfields. Comparedwith polymer flooding, it is applicable to more cases, especially the reservoirs with strongheterogeneity. However, it is very difficult to describe the microscopic flow mechanism ofpreformed particle gel in porous media, which has involved the flow properties ofparticle-fluid such as swelling, migrating, depositing and straining. Therefore, it is of greatimportance to understand and describe the flow mechanism of preformed particle gelaccurately, which can be used to strengthen its reservoir adaptability and improve the fieldapplication effect.Using the morphology analysis and test experiments, the morphology of preformedparticle gel after swelling some time is obtained, and then the influence of swelling time andinitial particle size range on equivalent size distribution is discussed. Based on understandingthe swelling property, waterflooding experiments and PPG flooding experiments areperformed on a series of glass etching models with different pore throat distributioncharacteristics by the visual microscopic displacement apparatus. Then, the migrating,depositing, and straining properties of preformed particle gel are described. It demonstratesthat, compared with waterflooding, the breakthrough time of PPG flooding is greatly delayed.Meanwhile, the displacement front moves forward more evenly. On the other hand, preformedparticle gel can plug the big pore throat temporarily in the process of migrating, and then thedisplacing fluid will divert its direction which leads to a larger displacement range. Based onanalyze the shortage of the classic seepage equations to describe evolvement of the seepageboundary, the fractal dimension theory is introduced to describe the evolvement ofdisplacement front quantitatively. The industrial computed laminography system is used to carry on waterfloodingexperiment, polymer flooding experiment and PPG flooding experiment, and information offluid distribution at different displacement stages such as beginning of waterflooding,beginning of injecting chemicals, end of injecting chemicals and end of displacement, will beobtained. On the basis, the displacement image processing technology is established, which isutilized to actualize2D segmentation of pore space and fluid distribution,3D reconstructionof CT scanning images and information extraction of pore throat characteristics.By analyzing the difference of microscopic displacement characteristics, describing themicroscopic displacement oil characteristic and characterizing the fluid-pore throat spatialdistribution interaction quantitatively, the flow mechanism of preformed particle gel in porousmedia is studied deeply. The results indicate that, aspect ratio, coordination number, swellingtime and particle size have a great impact on microscopic displacement characteristics. Due tothe influence of the migrating, depositing and straining properties, both microscopic sweepefficiency and microscopic oil displacement efficiency of PPG flooding increase greater thanthat of waterflooding and polymer flooding. Besides, the shape of displaced residual oil isplumper. Compared with that of waterflooding and polymer flooding, residual oil distributionof PPG flooding is dispersible, but residual oil occurrence stage that dominates relatively haschanged from the meshy to the porous.