Chao Zhang,Zihan Gu,Zongyang Li,Meijia Wang,Pingkeng Wu,Zhaomin Li
To investigate the effect of CO 2 on the precipitation of asphaltene in oil, and verify the advantages of CO 2 flooding, this work designs interfacial tension experiments and PVT system experiments to create the experimental environment under different temperature and pressure conditions that make CO 2 contact with oil. The results indicate that CO 2 can affect the oil morphology, and the trend of oil volume increase and decrease depends on the dynamic balance between the expansion effect and the component extraction effect of CO 2 on oil. Under low pressure, the oil expansion caused by dissolved CO 2 dominates the experiments, increasing the oil volume. Under high pressure, sufficient CO 2 in the oil activates its component extraction effect, and the asphaltene in the oil precipitates and accumulates at the interface between the oil and CO 2 due to the disruption of the component equilibrium of the system, exerting a surface activity effect, leading to a decrease in oil volume. Due to the movement of asphaltene towards the system interface and the formation of an asphaltene film during this stage, which hinders the entry of CO 2 into the oil, the interfacial tension shows three linear decreasing trends with increasing pressure. This mechanism also changes the variation trend of the oil volume in CO 2 during the pressure increase. Moreover, the components of the oil extracted by CO 2 will be transferred to CO 2 , making its properties similar to oil. With the reduction of interfacial tension, this process promotes the miscibility between the two. These effects verify that CO 2 can improve the fluidity and quality of oil during reservoir development, and reduce or even eliminate the adhesion work required for the working fluid to displace the oil. These conditions are conducive to improving reservoir development efficiency, reflecting the great application value of CO 2 flooding.
Guang Zhao,Li-Hao Liang,Dong-Fang Lv,Wen-Juan Ji,Qing You,Cai-Li Dai
A novel nanofluid of modified carbon black (MCB) nanoparticles was initially developed for enhanced oil recovery (EOR) in low permeability reservoirs. The MCB nanoparticles were obtained via a three-step reaction involving modification by oxidation, acyl chlorination, and activated grafting. MCB nanoparticles were spherically dispersed, with an average size of 72.3 nm. Compared with carbon black (CB) nanoparticles, dispersed MCB nanoparticles can effectively reduce the oil–water interfacial tension (IFT) to 10 −2 mN/m and change the surface wettability of sand particles. Based on the results of core flooding experiments, the MCB nanoparticles exhibited a better EOR capacity than surfactants and CB nanoparticles, and the final oil recovery was significantly increased by 27.27%. The core scanning test showed that the MCB nanoparticles could plug high permeability channels by adsorbing onto the surfaces of sand particles and forming larger aggregates that bridge across pores or throats, resulting in a higher swept volume. The synergistic effects of improved swept volume and oil displacement efficiency were the EOR mechanisms of the MCB nanoparticles. The studies indicate that these MCB nanoparticles have excellent potential for EOR in low permeability reservoirs.
Han Jia,Jiajun Dai,Lingchun Miao,Xin Wei,Hongtao Tang,Pan Huang,Haidong Jia,Juan He,Kaihe Lv,Dexin Liu
The Janus nanoparticles stabilized Pickering emulsions showed great application potential in various fields, including enhanced oil recovery (EOR). In this study, the amphiphilic Janus-SiO 2 nanoparticles (Janus-C12) are successfully synthesized by the Pickering emulsion method and characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), ζ-potential and contact angle measurements. The phase inversion from oil-in-water (O/W), multiple oil-in-water-oil (O/W/O) emulsion, to water-in-oil (W/O) emulsions was observed with the delicate control for the modification degrees of Janus-C12. The possible emulsification mechanisms for various Janus-C12 stabilized emulsions were proposed. The multiple O/W/O emulsion stability in harsh conditions and the influence factors (nanoparticles concentration, water/oil volume ratio and NaCl concentration) were studied systematically. Moreover, the Janus-C12–79% stabilized multiple O/W/O Pickering emulsions exhibited excellent EOR performance (additional oil recovery of 27.2%) in core flooding tests, and the possible EOR mechanism was explored via microscopic visualization experiments.
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