Evidences of CDG formation and possible interpretations of core flood studies

Resumen

Colloidal Dispersion Gels (CDG’s) have been successfully tested in several countries including Colombia. However, despite numerous successful field results reported in the literature, laboratory-scale experiments have generated controversy regarding the ability to inject CDG’s in large volumes without reducing injectivity while also improving sweep efficiency.

This paper summarizes the updates in microgel technologies, especially the Linked-Polymer Solutions (LPS) that have been also referred as CDG’s leading to misinterpretation of both systems. This brief review will also present the main mechanisms proposed for the formation of LPS in fluid:fluid studies and during its flow in porous media. This study also presents for the first time evidences of the possible mechanisms for the formation of CDG’s using a high molecular weight (MW) partially hydrolyzed polyacrylamide (HPAM) and Aluminum Citrate (Al(Cit)3) as a crosslinker using Dina Cretáceos Field, Colombia, synthetic brine at room temperature (25°C). The results generated during this study were used to re-interpret corefloods injecting CDG in Berea and Tello Field, Colombia, core plugs at different experimental conditions.

The main difference identified between LPS and CDG systems is the viscosity behavior in the presence of Al(Cit)3. LPS reports a decrease in viscosities while CDGs shows an increase in viscosities in the presence of crosslinker. This difference is due to the use of different high MW HPAM polymers. However, the crosslinking of the trivalent ion (Al3+) and the negatively charged carboxylic groups of the polymer of both microgels occurs through intra-and inter-molecular interactions leading to different particle size or hydrodynamic diameter distributions (HDD). The rate and type of HDD is dependent of polymer and crosslinker concentration. These results were also compared with a CDG systems using Chromium Acetate (Cr(Ac)3) as a crosslinker used in Loma Alta Sur Field, Argentina. The crosslinkers used (Al3+ y Cr3+) forming CDG suggests similar crosslinking mechanisms but shows differences in HDD. However, the difference in the experimental conditions of studies documented makes difficult developing a more detailed comparison. Finally, the re-interpretation of CDG corefloods suggests that the main operating mechanisms include viscosity effects, adsorption, straining and log-jamming as proposed for LPS systems. However, viscosity effects and the gradual blocking of pore channels (log-jamming) seem to be more dominant in CDG than LPS systems. The results of this study will contribute with the understanding of the CDG’s and also provides guidance to improve the evaluation and research of the technology at lab scale.