Effects of core structure and clay mineral on gel-forming performance of chromium polymer

Abstract

Cr3+ polymer gel flooding, an effective EOR technique, has been tested in some reservoirs (LDT-1, LDF-2 and NBTF-2) of Bohai oilfield--an offshore oilfield in China. Its performance demonstrates that this technique can significantly increase oil production and reduce water cut. However, the comprehension of this technique is still insufficient to satisfy its application requirements, which restrains its further application and improvement. As a result, this paper studies the comprehensive effects of core structure and clay mineral on gel-forming performance of chromium polymer, on the basis of reservoir and fluid properties of Bohai Oilfield. The results indicate that at static conditions, cross-linking reaction between Cr3+ and polymer molecular chain occurred at reservoir condition, and formed polymer gel with intramolecular cross-linking structure. Gel-forming performance is better with higher reservoir permeability and looser cementation, lower clay content and oil saturation. Also, clay type determines the degree of damage. From kaolinite, montmorillonite to illite, their damage gets bigger. Moreover, gel-forming performance at dynamic condition is much poorer than that at static condition. And a suspension of injection after alternate injection of Cr3+ and polymer solution could promote cross-linking reaction.