Nano-Silica Hybrid Gel System for the Conformance Improvement of CO2-EOR

To take full advantage of CO_2­­-EOR_, several methods related to conformance control have been discussed as an important technical suggestion. Due to the unfavorable mobility ratio and heterogeneities of reservoirs, in-situ gel treatment combined with CO₂ WAG flooding has been developed many years to solve such problem. Bulk gel consists of acrylamide based polymer was regarded as the mainstream technique which could inject into the target fracture or high permeability zones works as plugging agents to prevent the production or channeling of CO_{2. ­}

Low toxic cross-linker PEI was introduced to obtain rudimentary 3D networks through covalent bonding with acrylamide groups. The effect of major parameters included polymer, PEI concentration, molecular weight and total dissolved solids (TDS) on the performance of gelation time, strength and thermal stability were comprehensively investigated in this thesis.

The syneresis of polyacrylamide gels were frequently reported in most fields at high temperature and high content of divalent ions condition. To overcome such problems, copolymers including AMPS moieties was considered as a thermal stable polymer used in this work. Aqueous nanoparticle silica was formulated to enhance the viscosity and viscoelasticity of the hybrid gel through the inherent additional bonding effect. And the poor long time thermal stable performance in the presence of high calcium content could be removed in advance by including a powerful chelating agent EDTA.

The viscosity was measured by gel code and viscometer and the viscoelasticity was described by rheometer. The vessel test was performed to evaluate the impact of supercritical CO₂ on hybrid gels. The plugging performance on the mixed matrix/fracture media was proceeded by core flooding test.