Adaptability study and formula optimization of different gel systems under the critical temperature

In order to meet the demand of field in-depth flooding control, this paper studied the formula of gel flooding control system suitable for the critical temperature of 65-75 ℃. The adaptability of two commonly used gel systems, i.e., polyacrylamide (HPAM)-organic chromium and HPAM-phenolic resin under 70 ℃ were analyzed and evaluated by means of the laboratory experimental evaluation method. The results show that compared with organic chromium gel, phenolic resin gel has higher gelling viscosity and larger viscoelastic modulus, indicating its adhesive force and shear resistance are strong. And the lower limit of its gelling concentration is low, which can reduce the flooding control cost greatly. However, phenolic resin gel has the disadvantages of low crosslinking speed and long crosslinking time (120-140 h). To solve these problems, metallic ions were introduced to increase the types of crosslinking reaction so as to shorten the crosslinking time to 48 h. Finally, the formula of the movable gel system suitable for the critical temperature was obtained as follows: polymer concentration 1 200 mg/L, crosslinker concentration 1 300 mg/L and crosslinking promoter concentration 50 mg/L. The crosslinking time and gelling viscosity of the corresponding gel system are 48 h and 2 100 mPa · s, respectively. It is observed for 90 d under the constant temperature of 70 ℃. It is shown that the viscosity maintenance rate is over 70 %, the viscoelasticity is still kept better and no gel breaking or free water occurs, indicating the long-term stability of this system is good.