Evaluation of Fluid Property Changes in Different Displacement Stages of Polymer-Surfactant Binary Flooding in Conglomerate Reservoir

A polymer-surfactant binary oil displacement experiment was carried out in long-size conglomerate reservoir using spliced typical natural cores. The whole process of the experiment included four stages: pre-polymer flooding, binary main slug, post-slug and subsequent water flooding. The changes of concentration, viscosity, interfacial tension, emulsion particle size, type and variation law of produced fluid in different displacement stages were compared and analyzed. At the stage of pre-polymer flooding, the water content at the end of water flooding decreased from 98.0% to 90.3%, without the appearance of emulsion, and the viscosity and agent concentration were both low. At the initial stage of binary main slug, the water content decreased to the lowest 83.3%, the water-in-oil emulsion with a particle size of 5.80 mm appeared, the polymer concentration began to increase, the surfactant concentration changed little, and the interfacial tension reached the lowest, indicating that the solution was evenly displaced in the core. In the later stage of binary main slug, the water content slowly increased to 93.1%, the emulsion type changed to oil-in-water type, and the particle size decreased to a minimum of 4.79 mm, the concentration of the production agent increased significantly, and the viscosity of the produced fluid rose to the highest, indicating that the displacement solution began to break through in the core. In the post-slug stage, the increase of water content tended to be gentle, the particle size of oil-in-water emulsion began to increase, and the concentration of polymer production and surface production both rose to the highest, indicating that binary displacement solution completely broke through in the core, and the particle size of emulsion became the largest in the subsequent water flooding stage. The field test of in District Qizhong of Karamay Oilfield (8 injection 13 production well group) showed that, through the whole process control, especially the fine control of emulsification degree, the water cut in the peak period of binary flooding efficiency was reduced by 40 percentage points at most, and the oil recovery could be improved by 18%.