Study on Matching Relationship of Polymer Hydrodynamic Size and Pore Throat Size for Stratum in Sand Reservoir

Considering the existing problems of high injection pressure and lagged oil well response during SP flooding in the low permeability Hong gang reservoir in Jilin oilfield, in this paper compatibility researches are processed between polymer hydrodynamic radius and core pore-throat size under various permeability. Traditional way of determination of polymer hydrodynamic size using the laser particle size analyser is under ordinary conditions of pressure, but this method can only determine the size of the low concentration (below 800mg/l) polymer solution, and polymer solution for ERO concentration is always high. Another method is underpressure of 0.15MPa according to the API. Through experiment under different pressures, we found that polymer hydrodynamic size decreases with increasing of pressure. Due to the pressure drop funnel between the injection and production wells, the polymer coils' patterns and flow properties vary a lot spatially. So the above two methods are not accurate determination of the polymer solution hydrodynamic size in the formation. And for the low pressure gradient in zones far from the well, compatibility has changed between polymer and the pore throats, which results in the increasing injection pressure and hysteresis effects observed in production wells. In this paper, considering the far-well zone pressure gradient and shear force during the preparation and injection of polymer, nuclepore membrane filtration experiments are developed to measure the hydrodynamic radius under different molecular weights and polymer concentration, as well as the flow properties in three cores with different permeability. The results show good matching between the polymer solutions with molecular weight of 2000×104, 1500×104, 800×104 with corresponding concentration of 1700mg/L, 1500mg/L and 1000mg/L, and the nuclear pore membrane filter of 0.49μm, 0.36μm and 0.2μm, respectively. Also, they show a relatively good compatibility to the cemented cores of 180-200×10−3μm2,60-80×10−3μm2,25–40×10−3μm2, respectively. Furthermore, the ratios of the median radium pore throats to polymer hydrodynamic size(R/Rh) are 7.01-8.9,7.28-9.12 and 6.53-8.85, respectively, and for that in the Hong gang field, the ratio as 7–9 shows goodcompatibility.