چكيده به لاتين
The purpose of doing this project is usage of unique properties of nanocomposites for wettability alteration of carbonate rocks from oil-wet to water-wet in such a way that causes reduction of capillary force in porous media and consequently enhancing oil recovery. For this, at first the TiO2/Al2O3 nanocomposite was synthesized in the laboratory. But since our goal was to produce environmentally friendly water-based nanofluids, and the synthesized nanocomposite was unable to be dispersed in water, it was decided to modify the nanocomposite surface by PVA that is a hydrophilic polymer. The usage of different disparsants and stabilizers along with this material, provided stable nanofluid at the water base. By performing contact angle test, it was observed that the contact angle of oil-wetted carbonate rock was changed from 157 degree (relative to heavy fluid) before coating with modified nanocomposite TiO2/Al2O3/PVA(100%wt) to sliding phase with tilting degree of 10 after coating, which revealed the wettability alteration of carbonate rock from superoleophilic to superhydrophilic state. Then, the optimum concentration of nanofluid and the optimum time for rock aging in nanofluid were determined, which was 20%wt and 7 days, respectively. It was further shown that the rock coated with this nanofluid retains its wettability at pH 2-11. The thermal stability of the nanofluid was also tested and approved to 150 °C. In addition, with increasing pressure up to 4000 psi, it was observed that the pressure did not affect the performance of the nanofluid. It was also shown that the nanofluid at moderate to high salinity (35000 ppm), well maintained its efficiency in changing the wettability of the rock to the superhydrophilic state. In all these conditions, the oil drop rolled-off on the rock surface showed that the surface wettability of the nanofluid coated surface was consistent with the Cassie model. Afterwards, the mechanical stability of the coated rocks was evaluated and verified by various methods including finger pressure, adhesive tape test and abrasion test. For example, the abrasion test of abrasive paper with different roughnesses (P400, P240 and P180) was used to abrade the coated rocks which showed that with a total of 400 reciprocating cycles of 8.4 psi pressure on these abrasive papers, the oil contact angle was 0 degree and rolled-off on the rock surface. Subsequently, interfacial tension testing was performed, which showed that the interfacial tension decreased from 31 mN/m (water and oil) to 4 mN/m (nanoFluid and oil) at ambient temperature. Imbibition test using amott cell showed that the recovery rate of oil from the saturated core changed from 6% when using saline to 14% when using nanofluids made at the saline base. TEM, XRD and FT-IR tests were performed to characterize synthesized modified nanocomposites. The TEM test revealed that the nanoparticles were 40 nm in size and their morphology was nearly spherical. The XRD test was performed to determine the type and structure of the nanoparticles and to determine the crystallite size of the nanoparticles, which was in agreement with the results of the TEM test. The FTIR test confirmed the accuracy of TiO2/Al2O3 nanocomposite synthesis and its surface modification by PVA chemical. The FESEM_EDS test was also used to characterize the the surface properties of the rocks coated with nanofluids. The results of these analyzes showed that by coating the rock with nanofluids, the surface of the rock became a micro/nanostructured surface, causing water to fall through the cavities in it and thereby repelling oil.
