Swelling Mechanism Investigation of Microgel with Double-Cross-Linking Structures

Microgel is a novel conformance control technology that can be injected into high permeability zones and transport into deep area through pore throats. It can efficiently plug large pores to force injection water diversion to achieve conformance control. In this paper, we synthesized the microgel with a double-cross-linking structure of non-labile and labile characteristics. Then, a polarizing microscope, laser particle analyzer, Brookfield DV-III, and atomic force microscopy (AFM) were used to investigate the swelling mechanism of the microgel in high-saline water (total dissolved solids is from 30 to 100 g/L) at 65 degrees C. Results show that the swelling ability of the double-cross-linking structure microgel is not sensitive to salinity and the solution viscosity can increase to a certain degree with the maximum value of 18 mPa s. The decomposition of labile cross-linker results in a loose and explosive structure, which seems like a mushroom cloud. Because of the high-density cross-linking sites provided by the non-labile cross-linker, the integrity of the spherical feature of the microgel was reserved after aging for 70 days. On the basis of the viscosity increase of microgel solution during the swelling process, a concept to develop a novel water shutoff agent is proposed. That is, the conventional cross-linkers, such as formaldehyde, methenamine, or phenolic or chromic salt, can be added to microgel solution during the injecting process. Thus, the cross-linker can have the potential to cross-link with the groups that released during the swelling process to form a bulk gel system, which can further improve the water shutoff performance.