Search

CO2 EOR (enhanced oil recovery) will be one of main technologies of enhanced unconventional resources recovery. Understanding effect of permeability and fractures on the oil mobilization of unconventional resources, i.e. tight oil, is crucial during CO2 EOR process. Exposure experiments based on nuclear magnetic resonance (NMR) were used to study the interaction between CO2 and tight oil reservoirs in Chang 8 layer of Ordos Basin at 40 °C and 12 MPa. Effect of permeability and fractures on oil mobilization of exposure experiments were investigated for the different exposure time. The oil was mobilized from matrix to the surface of matrix and the oil recovery increased as the exposure time increased. The final oil recovery increased as the core permeability increased in these exposure experiments. Exposure area increased to 1.75 times by fractures resulting in that oil was mobilized faster in the initial stage of exposure experiment and the final oil recovery increased to 1.19 times from 28.8 to 34.2%. This study shows the quantitative results of effect of permeability and fractures on oil mobilization of unconventional resources during CO2 EOR, which will support CO2 EOR design in Chang 8 layer of Ordos Basin.

Flue-gas foam/surfactant polymer flooding is a novel technology to enhanced oil recovery for heavy oil reservoir after hot water flooding with safety and efficiency. However, high temperature and the complex composition of flue gas greatly influence the foaming ability of the foaming agent, and weaken the plugging and profile control ability of the foam. Hence, screening suitable foam agents is of great significance. Here, a typical terpolymer of N‒methyl butenone carboxylates, alkyl phenyl sulfonates and pyrrolidone was selected as an efficient foam agent. The foaming performance and stability of the foam agent remained unchanged after 300 °C aged for 72 h in the flue gas atmosphere. Foam performance and stability tests in the simulative flue gas environment, adsorption properties of oil sands, and resistance factor evaluation were carried out. It showed good foam performance and stability, low adsorption capacity (0.77 mg/g), low interfacial tension (10−2 mN/m) and high resistance factor (>418), which indicated that the terpolymer (PNCAS) can reduce the gas channeling and increase the sweep area. The results of homogeneous and heterogeneous model experiments and microscopic mechanism suggested that foam flooding can greatly improve oil recovery while the low permeable sand-pack recovery can increase almost 42% in comparison with the conventional hot water flooding.

The ultrasonic guided wave testing method is very effective in monitoring the safety of complex structures. The fundamental shear horizontal (SH) wave mode has the advantage that the propagation velocity does not change with the frequency. However, accurately recognizing the ultrasonic signal is difficult due to the SH guided wave’s bidirectional propagation characteristics generated by the Lorentz force mechanism. Therefore, it is necessary to achieve unidirectional focusing of Lorentz force-generated SH guided waves. A newly designed SH guided wave electromagnetic acoustic transducer (EMAT) is proposed with an interlaced periodic permanent magnet (PPM) and AC coils of different phases. A 3D model based on the electromagnetic mode and the solid mechanics mode using COMSOL software is calculated and compared with the bidirectional focusing EMATs. The results show that there are many influencing factors in the structural design of the transducers, and the focal radius and the angle of the individual PPMs are discussed in this work. The results indicate that the new unidirectional EMAT shows superiority in many cases, and the decrease of the focal radius with a suitable aperture angle will increase the focusing intensity of the signal.