Injecting surfactant by means of chemical enhanced oil recovery (cEOR) has acquired predominant attention in improving oil recovery by changing either fluid/rock and/or fluid/fluid interaction due to ion-pair forming and/or surfactant adsorption on the rock surface. As the main surfactant role in EOR, IFT reduction refers to adsorbing of surfactant molecules on the residual oil/water interface, which causes an increase in capillary number; as a result, trapped oil drops in porous media get free and start to move through the pore space toward the production well. The toxic nature, excessive cost, and environmental issues are the obvious limitations in applying the chemical surfactants in EOR, hence, looking for a less-expensive and eco-friendly type of surfactant has become a significant task to researchers to study the natural surfactant as an alternative to chemical surfactants. A deep understanding about the classification of natural surfactants, fabrication methods, and the difference between each class is crucial to propose a new plant-derived natural surfactant. This study tried to review up-to-date published studies related to the natural surfactant types and prepare a comprehensive catalog respective to natural surfactant that helps researchers with regard to future work in natural surfactant application in EOR. In addition, comparisons of each class performance and the impact of nanoparticles and the salinity on them in reducing IFT, altering wettability, and improving the recovery factor have been investigated. It had been concluded that natural surfactant can be produced from different plant parts (leaf, root, steam, fruit, and seed) based on the fabrication method. Natural surfactants synthesized from seed oil are stronger, compared with those extracted from the plant part (i.e., IFT reduction by 98%). Generally, injecting natural surfactants expressed low to high performance in improving the ultimate oil recovery from 2% to 40% original oil in place (OOIP).

In this study, a green, simple and economical approach was used to synthesise the SiO 2 @ZnO@Xanthan nanocomposite (NC) to modify the rheological and filtration characteristics of the water-based drilling mud. The green synthesised NCs were identified using scanning electron microscopy, energy dispersive X-ray spectroscopy, elemental mapping, X-ray diffraction and UV-Vis analytical techniques. Additionally, the effect of SiO 2 @ZnO@Xanthan NCs on the filtration and rheological properties of mud including apparent viscosity, plastic viscosity, yield point, gel strength, mud cake and fluid loss was investigated. The obtained results confirmed that the synthesised NCs effectively improved the rheological properties of drilling mud, and considerably decreased its fluid loss and filter cake by about 54 and 92.5%, respectively. The results highly recommend the SiO 2 @ZnO@Xanthan NC as an excellent additive to improve the rheological properties, and reduce the fluid loss and the filter cake of the drilling mud.

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