CO2-responsive agent for restraining gas channeling during CO2 flooding in low permeability reservoirs

Abstract

Hydraulic fracturing and CO2 flooding are extensively used in low-permeability reservoirs to enhance oil recovery (EOR). However, due to the serious heterogeneity of the formation, CO2 is prone to break through the oil-bearing zone prematurely, which leads to the decrease of the swept volume. Conventional blocking agents have some defects such as difficult injection, poor stability and weak sealing strength. Therefore, it is critical to developing a new type of channeling blocking agent for low-permeability fractured reservoirs. In this study, ten kinds of chemicals with tertiary amino groups are filtered for the most effective CO2-responsive agent, which turns out to be N, N-Dimethyl erucamide tertiary amine (DMETA). Subsequently, rheological properties, response performance, and microstructure of the optimum agent are researched systematically through rheological experiments, CO2-response processes and Cryo-TEM. The results show that the viscosity of the DMETA solution can increase to nearly 605,700 mPa·s by self-assembly into wormlike micelles (WLMs). And it can be reversibly circulated between low viscosity and high viscosity by alternately introducing and removing CO2, which endows it with the ability to healing its viscoelasticity under an environment full of CO2. A new method based on optical microrheology is proposed to study the viscoelastic properties of WLMs under no external force. The experiments prove that the network structure is not stable after formation, but remains in a continuous process of separation and reconstruction as “a living polymer.” Furthermore, the plugging performance and EOR capacity are evaluated using fractured tight cores. The experiments demonstrate that the optimum agent can effectively restrain gas channeling and enhance recovery factor by 21.7%. We expect our work can provide insights for the synthesis of CO2-responsive WLMs and guidance for retarding gas channeling during CO2 flooding in low permeability reservoirs.