The Characteristics and Adjustment Technology of Surfactant/Polymer Binary Flooding in Conglomerate Reservoir

Abstract

Abstract The recovery factor of surfactant/polymer binary flooding field test in conglomerate reservoir is 14.6% now and it will reach to 18% by prediction. Nevertheless, it has not achieved good results in the early stage. Conglomerate reservoir is more complex and special. The method used in sandstone reservoirs can't be used directly in the conglomerate reservoir. In the early stage of SP flooding, the mature injection technique of sandstone reservoirs was adopted, but the phenomenon of high polymer concentration appeared. The reservoir and porous characteristics of conglomerate reservoir was analyzed by intrusive mercury curve and pore throat distribution. The law of SP flooding was studied by micro experiment and nuclear magnetic resonance. Comprehensive analyses of SP flooding between conglomerate reservoir and sandstone reservoir were conducted, including SP flooding water cut, injecting SP pressure, time of polymer appearing in production fluid, producing polymer speed and incremental oil recovery. In order to find out the law of different type's reservoir moving, the casing logging analyses was carried out. Due to the presence of the small grain between the large gravels, the distribution of pore and throat in conglomerate reservoir was characterized by two peaks. It was found that the remaining oil after water flooding was mainly in the pores with radius 1-5μm in the conglomerate reservoir. Because of the existence of the macro pore path, the initial chemical flooding system had a rapid advance, and the effect was obvious seen after the profile control. The molecular weight of the polymer should be appropriately reduced according to the pore and throat sizes of the reservoir after the macro pore path were blocked by large molecular weight polymers. The matching relationship between polymer and reservoir was reestablished, and the molecular weight and injection concentration of the polymer were adjusted, and the effect of oil increasing was obvious. The most significant new finding was that the SP system realized the utilization of 30-50mD reservoir by casing logging, which reduced the lower limit of SP flooding to 30mD. This is important because the reserves ratio of 30-50mD reservoir account for a large proportion in the conglomerate reservoir. The SP flooding in conglomerate reservoir is different from the conventional chemical flooding. The novelty of this paper is to find the characteristics and appropriate adjustment method, which will provide the necessary support for future applications.