Experimental Studies On Depressurizing And Injection Enhancement Of Low Permeability Reservoirs By Nanometer Polysilicon Materials

Nanometer polysilicon material(NMPM) is a type of nanometer silicon dioxide modified by additives and activated byγ-ray. NMPM has been used as a new type of agent for depressuring and injection stimulation of low permeability wells and achieved good results. The mechanisms for depressurizing and injection stimualtion by NMPM are not clear and require further investigation. The size of NMPM particles was observed by a transmission electron microscope (TEM). The viscosities of NMPM solutions were measured by capillary viscometers and compared with that of diesel oil. The NMPM solution-water interfacial tension was measured by a automatic interfacial tensionmeter. The swelling properties of calcium clay samples pre-treated by NMPM solution with different NMPM concentration were evaluated by a shale swelling meter. The size distribution of NMPM solution and diesel oil solved by paraffin was measured by a zeta potential laser particle sizer. The flow properties of NMPM solution in low permeability cores were evaluated by using a set of core flowing equipment.Experiments show that the NMPM is in the size of nanometer and it is hydrophobic. The phenomenon of coacervation occurs when it is put into distilled water. The viscosity of NMPM solution is slightly higher than that of diesel oil. The viscosity of NMPM solutions increases with the concentration of NMPM and decreases with temperature. At the same temperature, the interfacial tension of NMPM solution and water surface is higher than that of diesel oil/water surface. The interfacial tension increases with the increase of NMPM concentration. The expansion rate of calcium clay in NMPM solution is lower than that in diesel oil, distilled water and brine. The expansion rate of swelled calcium clay is becoming a bit lower by NMPM solution treatment. The solubility of paraffin in NMPM solution is greater than that in diesel oil and the mean diameter and wax crystal size in NMPM solution are larger than those in diesel oil. The pressure across the low permeability cores with permeability between 20×10-3μm2 and 50×10-3μm2 decreases greatly by NMPM solution treatment. The pressure decrease is related to the time between the end of NMPM solution injection and the beginning of water injection. These conclusions are of great theoretical significance for the explanation of the mechanisms for depressurizing and injection stimulation and can provide useful guides for field tests.