New method for the determination of surfactant solubility and partitioning between CO2 and brine

Research of CO2-Soluble Surfactants for Enhanced Oil Recovery: Review and Outlook

CO2 foam injection has been shown to be effective under reservoir conditions for enhanced oil recovery. However, its application requires a certain stability and surfactant absorbability on rock surface, and it is also associated with borehole corrosion in the presence of water. Adding surfactants to CO2 can enhance the interaction between CO2 and crude oil and control the CO2 mobility, thereby improving the performance of CO2 flooding. This paper presents a review of the research of CO2-soluble surfactants and their applications. Molecular dynamics simulation is introduced as a tool for analyzing the behavior of the surfactants in supercritical CO2 (scCO2). The applications of CO2-soluble surfactants, including CO2 thickening, reducing miscibility pressure, and generating supercritical CO2 foam, are discussed in detail. Moreover, some opportunities for the research and development of CO2-soluble surfactants are proposed.

Research Progress on Displacement Mechanism of Supercritical CO2 in Low-Permeability Heavy Oil Reservoir and Improvement Mechanism of Displacement Agents

With the continuous growth of global energy demand and the late stage of conventional oilfield exploitation, the demand for developing and utilizing low-permeability heavy oil reservoirs is becoming increasingly urgent. However, the exploitation of low-permeability heavy oil reservoirs faces many challenges due to their high viscosity, low permeability, and complex geological conditions. To overcome these challenges, researchers have gradually introduced SC-CO2 as an oil displacement agent in the exploitation of heavy oil reservoirs. However, the oil displacement mechanism of SC-CO2 in low-permeability heavy oil reservoirs and its improvement mechanism are still not completely understood. The article provides a detailed study and understanding of the oil displacement mechanism of SC-CO2, which involves the expansion of heavy oil volume through SC-CO2 dissolution. This mechanism reduces the capillary resistance and flow resistance during the oil flow process. The permeation of CO2 disrupts the internal structure and arrangement of heavy oil, reducing its viscosity. CO2 extracts both light and heavy components from the heavy oil, reducing the residual oil saturation. In addition, the mechanism of improving the effect of oil displacement agents such as nanoparticles, polymers, and surfactants on SC-CO2 displacement was also explored. By further exploring the mechanisms and improvement mechanisms of SC-CO2 displacement for heavy oil, it can guide the selection and optimization of oil displacement agents. Furthermore, understanding the mechanism can also provide a theoretical basis for engineering practice and technical innovation. While the research on CO2 flooding is analyzed and evaluated, the obstacles and challenges that still exist at this stage are indicated, and future research work on CO2 in low-permeability heavy oil reservoirs is proposed.

Numerical well testing interpretation model and applications in crossflow double-layer reservoirs by polymer flooding

This work presents numerical well testing interpretation model and analysis techniques to evaluate formation by using pressure transient data acquired with logging tools in crossflow double-layer reservoirs by polymer flooding. A well testing model is established based on rheology experiments and by considering shear, diffusion, convection, inaccessible pore volume (IPV), permeability reduction, wellbore storage effect, and skin factors. The type curves were then developed based on this model, and parameter sensitivity is analyzed. Our research shows that the type curves have five segments with different flow status: (I) wellbore storage section, (II) intermediate flow section (transient section), (III) mid-radial flow section, (IV) crossflow section (from low permeability layer to high permeability layer), and (V) systematic radial flow section. The polymer flooding field tests prove that our model can accurately determine formation parameters in crossflow double-layer reservoirs by polymer flooding. Moreover, formation damage caused by polymer flooding can also be evaluated by comparison of the interpreted permeability with initial layered permeability before polymer flooding. Comparison of the analysis of numerical solution based on flow mechanism with observed polymer flooding field test data highlights the potential for the application of this interpretation method in formation evaluation and enhanced oil recovery (EOR).