Experimental Study on Double-Group Secondary Crosslinking System for Profile Control

For fractured reservoirs,water shutoff and profile control measures often failed and are ineffective due to serious leakage of plugging agent in formation.To address this problem,two groups of partially hydrolyzed polyacrylamide(HPAM)are reacted with two crosslinking agents to generate a high-strength polymer plugging agent.Through analysis,an optimum formula of ingredients is defined as follows:5 000-7 000 mg/L HPAM+125 mg/L organic chrome crosslinking agent+80 mg/L phenol+120 mg/L urotropine+80 mg/L intensifier.Influences of temperature,pH value and salinity on the profile control system were studied,and the gelling performance of double-group secondary crosslinking system was compared with two crosslinking agents separately.The single-barreled and double-barreled parallel cores were used in plugging test to simulate the profile control,the results show that plugging rate is over 99% and break-through pressure gradient higher than 36 MPa/m for single-barreled cores.For the double-barreled parallel cores,the plugging rate of high permeability core is over 98%,and that of low permeability core is less than 15%.It is concluded that double-group secondary crosslinking system can prevent plugging agent from leaking in the fractures,and greatly reduce possibility of plugging the passageway of oil and gas when it penetrates into the micro-fractures.This system is prospective for profile control in fractured reservoirs.