Summary
In the past few years, nanoparticle flooding has displayed significant potential for enhancing oil recovery. Among different nanoparticles, hydrophilic (functionalized) nanotubes have not been tested yet. Therefore, in this study, functionalized multiwalled carbon nanotubes (MWCNT) were used in three concentrations—0.01, 0.05, and 0.1 wt%—to conduct micromodel, interfacial–tension (IFT), wettability, viscosity, phase–behavior, and static–adsorption tests. In addition, constancy of nanofluids in the presence of sodium chloride (NaCl) was investigated qualitatively. Obtained results illustrated that by increasing the nanoparticle concentration from 0.01 to 0.1 wt%, nanofluid/oil IFT decreased, because MWCNT were placed between the surfaces of the oil and the nanofluid. Also, viscosity of the nanofluid improved slightly when the nanoparticle concentration increased. Moreover, contact angle was measured before and after coating with nanosuspensions, and the achieved data showed a change from oil–wet to water–wet. The resulting emulsion was a water–in–oil type; therefore, as MWCNT concentration increased, the size and number of water droplets in the oil also increased. This augmentation improved the effectiveness of the emulsion viscosity. Stability tests also provided evidence confirming that the nanofluids were stable for 10 days in concentrations of 0.01 and 0.1 wt% and in salinities of 1 and 0.5 wt%, respectively. Besides, the addition of 0.05 wt% sulfonated polymer to the nanofluids ensured their stability in higher salinities. Moreover, the results of the micromodel test revealed that by increasing the concentration of nanoparticles, sweep efficiency increased and the fingering phenomenon was reduced. In addition, the ultimate recovery of oil obtained by nanosuspension flooding in concentrations of 0.01, 0.05, and 0.1 wt% was, respectively, 12.6, 16.4, and 20% higher than that of waterflooding. Static adsorption on sandstone was found to be 0.575, 1.25, and 1.76 mg/m2 at 0.01, 0.05, and 0.1 wt%, respectively, and it reached its fixed amounts within 24 hours. Therefore, functionalized MWCNT might help increase heavy–oil recovery through mechanisms of reducing IFT, changing wettability from oil–wet to water–wet in oil–wet reservoirs, increasing viscosity (slightly), and developing a water–in–oil emulsion.
New Surfactant Extracted from Zizyphus Spina-Christi for Enhanced Oil Recovery: Experimental Determination of Static Adsorption Isotherm
