Study On The Change Law Of Rock Surface Characteristics Of Tight Gas Reservoirs Under The Action Of Nanofluids

Tight gas reservoirs in my country are rich in resources.In the process of gas reservoir exploitation,formation water flows along the high-permeability zone to the pores of the gas reservoir,sealing the undischarged gas in the pores,and causing water outflow from gas wells,resulting in a decline in productivity.Conventional polymer water control agents cannot meet the needs of tight gas reservoirs due to the high viscosity of the system,and bubble drainage methods are mainly aimed at wellbore fluid accumulation.Therefore,this dissertation develops a nanofluid drainage agent to study its influence on the rock surface characteristics of tight gas reservoirs to achieve"deep"drainage of tight gas reservoirs.In this paper,the formulation of nanofluid is optimized by phase inversion emulsification method,combining single factor and multi-factor uniform experiment.Under the best formulation,the median particle size can reach 5.37nm,and the distribution is uniform,and the zeta potential is 43.30m V,showing a positive charge.Sex is a stable system.Rheological experiments show that nanofluids are power-law fluids,and have good elastic characteristics and thixotropy,which can meet the needs of tight gas reservoirs;FT-IR testing characterizes the presence of hydrophilic groups and hydrophobic groups such as silyl groups in nanofluids;SEM Analysis proves that nanofluid changes the microscopic morphology of the rock surface,making the rock surface smoother and more uniform;after nanofluid treatment,the contact angle of water on the rock surface increases from 18°to 92.74°,indicating that the nanofluid passes through polar groups Acting on the rock surface,the hydrophobic group faces outward to form a hydrophobic film;using XPS,FT-IR,and zeta potential testing techniques,the mechanism of nanofluid action on the rock surface is studied,that is,the nanofluid does not chemically interact with the rock surface.It mainly acts on the rock surface through physical methods such as electrostatic interaction and hydrogen bonding to change the characteristics of the rock surface.Based on the results of dynamic core displacement experiments and using the theoretical model of the farthest particle migration distance,the migration capacity of nanofluids in porous media is analyzed.Compared with the bubble drainage method,"deep"drainage can be achieved.Two-phase flow experiments show that after the core is treated with nanofluid,the relative permeability of the water phase increases by 63.79-100%and the gas phase decreases by9.80-13.04%during the displacement process.And the saturation of bound water is reduced,the nanofluid reduces the flow resistance of water,increases the amount of free water,and achieves the purpose of drainage.Nanofluids can reduce the core static water absorption by 26.4-70.2%,indicating that nanofluids can effectively prevent the produced water from re-absorbing into the reservoir and extend the effective period of drainage gas recovery.Nanofluid has green environmental protection performance,its EC₅₀is 25554.29mg/L（>25000mg/L）,BOD₅/COD_crvalue is 29%（>25%）,indicating that it has no biological toxicity and is easily biodegradable.