The New Micro-sol System And Application Performance Studies

After long-term waterflooding developments, most oil fields in China have entered the high water cut stage, which has strong formation heterogeneity, high water cut rate, and lower oil yield rate year by year. The profile control and water shutoff have become one of the most important measures to improve the crude oil recovery ratio. But for most complex reservoir in China, the traditional profile control agents cannot meet the requirements of production increases. This paper developed a new profile control agent—micro-gel. The micro-gel expanded with water immersion, had large expansion ratio even in high salinity water and had the performance of slightly solubility, substantially increased the waterflooding sweep efficiency, improved the water injection profile of formation, so the objective of enhancing oil recovery was achieved. Main research content of this paper was listed as follows.1) The micro-gel was prepared with a method of inverse emulsion polymerization, using the acrylamide (AM) and 2-acrylamide-2-methyl propane sulfonic acid (AMPS) as basic monomers, the compound of type I and type II as crosslinker system, Tween/Span compound as emulsifier systems, water-soluble VFT as initiator.The factors affected polymerization stability and performance of micro-gel were studied, such as monomer content, monomer ratio, initiator dosage, cross-linking agent dosage, HLB value, reaction temperature and stirring speed. The optimal reaction conditions were:monomer content,30-35%;monomer mass ratio, AM:AMPS=2:1-5:1; initiator for the monomer mass amount,0.10%～0.15%; type I crosslinker for the monomer mass amount,1.5%; HLB value 5-6;reaction temperature, 50-55℃;stirring speed,500-700rpm.2) The performances of micro-gel were evaluated. The spherical structure of the micro-gel was maintained even in high salinity water of 100000mg/L for 90 days, so the salt resistance of the micro-gel is good. Under this salinity, the particle size expanded to maximum in 7 days, swelling volume up to 151.7 times for the original size, so the water-swelling performance of the micro-gel was also good and long-term stable. The micro-gel had good strength, elastic deformation.3) The application properties of the micro-gel were studied by core flow experimental. Smaller core flow experimental showed that the drag coefficient of the micro-gel was lower in high permeability core, the injection was good, and the recovery ratio was improved 8.33% to 32.26%. Long core flow experimental showed that the closure pressure of the micro-gel particles was spread rapidly in porous media and the movement ability of the micro-gel particles was good. Double parallel cores flow experimental showed that the micro-gel system had good performance of profile control, ameliorated the conflicts between layers to some extent and enhanced oil recovery. So the applicability of this new micro-gel system was good in the high salinity, high permeability and strong heterogeneity of reservoir, it can effectively resolve the conflicts between layers and increase the recovery.