Experimental investigation of wettability alteration of carbonate gas-condensate reservoirs from oil-wetting to gas-wetting using Fe3O4 nanoparticles coated with Poly (vinyl alcohol), (PVA) or Hydroxyapatite (HAp)

Abstract

Wettability alteration near-wellbore region in a gas-condensate reservoir is an effective way to reduce liquid blockage. To this end, Fe3O4 NPs (nanoparticles) first synthesized by the co-precipitation method and then coated with Poly (vinyl alcohol) (PVA) and or Hydroxyapatite (HAp). Besides, the synthesized NPs and two core-shell nanostructures were characterized by the Field Emission Scanning Electron Microscopy (FE-SEM), X-ray diffraction (XRD) analysis and the Fourier-Transform Infrared spectroscopy (FTIR). The synthesized NPs coated with PVA and or HAp were then exploited to coat on the surface of carbonate rocks by the dip-coating method in the course of 48 h. Next, the contact angle on the surface of carbonate rocks in condensate/air and water/air systems was measured in a wide range of pressure from 1 to 40 bar. In contact angle measurements, the effect of different parameters including the NPs concentration, temperature and pressure was examined.Also, the spontaneous imbibition and fluid flow tests were fulfilled in the artificial core-plugs before and after the wettability alteration. The results show that the imbibition rate of water and condensate noticeably reduced after the wettability alteration by both core-shell nanostructures. Additionally, the pressure drop and breakthrough time significantly diminished after the wettability alteration by both core-shell nanostructures. Moreover, coating of the two core-shell nanostructures on the surface of carbonate rocks was confirmed by the Scanning Electron Microscope (SEM) analyses.Furthermore, based on contact angle measurements between gas-condensate and the carbonate artificial core-plug surface after the treatment with the Fe3O4-PVA and or Fe3O4-HAp nanostructures, the optimum concentrations of Fe3O4/PVA and Fe3O4-HAp nanostructures in distilled water were 0.5 wt % and 0.4 wt %, respectively, to attain the greatest wettability alteration from oil-wetting to preferentially gas-wetting. In this condition, the contact angle between gas-condensate and the treated carbonate artificial core-plug surface by the Fe3O4/PVA and or Fe3O4-HAp nanostructures shifted from 10 ͦ to 66 ͦ and or 90 ͦ, respectively. Also, the contact angle between water and the treated carbonate artificial core-plug surface using the Fe3O4/PVA and or Fe3O4-HAp NPs altered from 62 ͦ to 107 ͦ and or 116 ͦ, respectively.Generally, the iron oxide NPs coated with HAp significantly improved the wettability of the rock samples from oil-wetting to gas-wetting as compared to those coated with PVA.Finally, the spontaneous imbibition experiments were carried out in the tight rock before and after the wettability alteration. Results demonstrated that the imbibition rate of gas-condensate decreased about 63 and 64% after the wettability alteration by the Fe3O4-PVA/DW and Fe3O4-HAp/DW nanofluids with the optimum concentration of 0.5 and 0.4 wt %, in sequence. Additionally, experimental results of the fluid flow tests at high pressures showed that the pressure drop reduced 34 and 32% after the wettability alteration for both Fe3O4-PVA/DW and Fe3O4-HAp/DW nanofluids, respectively.