Coalescence Behavior of a CO2-Resistant Dispersed Particle Gel (SCDPG) in Supercritical CO2

Abstract

The reservoir heterogeneity and unfavorable oil/gas mobility ratio lead to gas channeling and low CO2 sweep efficiency during CO2 flooding in low-permeability reservoirs. A dispersed particle gel (DPG) could migrate deep into the reservoir and coalesce, which has the potential for CO2 gas channeling control. In this work, a CO2-resistant bulk gel was prepared by a cross-linking reaction of a copolymer with acid-resistant groups and catechol–hexamethylenetetramine, which exhibited excellent CO2 resistance. Subsequently, a CO2-resistant dispersed particle gel (SCDPG) used in supercritical CO2 was successfully prepared from the CO2-resistant bulk gel by a high-speed mechanical shearing method. Meanwhile, the coalescence behavior of the SCDPG particles in supercritical CO2 was systematically investigated from the microstructure, particle size, ζ potential, and mechanical strength. The results showed that the SCDPG particles were dispersed in the liquid phase as a single particle. SCDPG had good dispersion stability during storage and injection. In supercritical CO2, the dispersion stability of SCDPG decreased, and the particles coalesced with each other to form aggregates with a stereostructure instead of degradation. The SCDPG particles maintained high mechanical strength, showing the long-term effectiveness for gas channeling control during CO2 flooding. In addition, the interparticle force of SCDPG particles was measured by an AFM colloid probe based on the reservoir characteristics. The interparticle force of SCDPG particles changed from repulsion to adhesion with increasing salinity. At a salinity of 0.5 mol/L, the adhesion force increased with the increase of temperature and the decrease of the pH value. According to the type of intermolecular force, the adhesion force originated from the hydrogen bond, π–π stacking, and cation−π interaction. This work provides theoretical support for the field application of the dispersed particle gel and promotes the development of utilization of carbon dioxide in oilfields.