A new type of CO₂ responsive gel based channeling blocking system

In order to solve the gas channeling problem in the late stage of CO₂ flooding in low-permeability reservoirs, a new type of CO₂ responsive gel based channeling blocking system was prepared by using small-molecule amine compound and a kind of modified long-chain alkyl anionic surfactant. Then, the rheological property of this system before and after contacting CO₂ was tested under different temperatures (25 ℃ and 70 ℃) and different pressures (normal pressure and 8 MPa), and its microscopic structure was characterized by means of environmental scanning electron microscope (ESEM) and nuclear magnetic resonance (NMR). And in addition, its channeling blocking performance was evaluated by virtue of core physical simulation experiment. The experimental results show that before contacting CO₂, this system is a kind of solution whose viscosity is close to that of water, and after contacting CO₂, it transforms into high-viscosity gel with viscoelasticity. And after this system contacts CO₂, its internal structure is transformed into tightly-connected ordered arrangement from loosely-separated random arrangement, and a 3D network aggregation structure is formed. NMR test results prove that after this system contacts CO₂, small-molecule amine compound is protonated to form the “pseudo Gemini surfactant” and then vermicular micelle is formed through self-assembly, aggregation and winding, which leads to the sharp increase of the viscosity. High-low permeability double tubes parallel core experiment indicates that under the condition of porous medium, the blocking rate of this system to high-permeability core is higher than 90 %. The research results provide technical guidance for the gas channeling blocking in the late stage of CO₂ flooding in low-permeability reservoirs.