Study Of Nano-fluid System Screening For Drag Reduction And Injection Enhancement In Ultra-low Permeability Reservoirs In Mahu Sag

Low-permeability reservoir reserves accounts for a large proportion of China's total oil resources,and it is the main field in oil enhancement.The most important development method for most low-permeability reservoirs including the Mahu Sag is waterflood development.However,due to its low permeability,low porosity,small pore throat radius,and large resistance to seepage,it is common that there are problems in the development of water injection such as high water injection pressure,low injection volume and insufficient water injection.Nanomaterials have achieved certain results in addressing the problem of"high pressure and low pressure" in the water injection process of low-permeability reservoirs,and have the advantages of excellent results,minor environmental pollution,and simple construction techniques.However,the simple nano-materials tend to agglomerate in the solvent and block the pore throat,causing serious problems related to "high pressure under-injection".Nano-materials and surfactants can be combined to make nano-fluids work synergistically to solve this problem.In view of the characteristics of ultra-low permeability reservoirs in Well Ma 18 in Mahu Depression,the features of nano-materials suitable for drag reduction and injection in this block are analyzed.Four kinds of nano-materials are selected and their effects of drag reduction and injection enhancement are verified by experiments such as adsorption amount determination,and two types of nanomaterials are selected.Then,a relatively suitable surfactant is selected from the four types of surfactants and the above two kinds of nanomaterials are compounded into eight nano-liquids.Three kinds of nano-liquids with relatively good effects are initially selected through experiments such as wetting contact angle measurement;then the core drag flow experiments are performed to verify the effects of drag reduction and injection enhancement of the three nano-fluids and to optimize a best nano-fluid system.Finally,the nanofluid injection parameters(concentration,slug,static adsorption time,and nanofluid formulation ratio)are optimized via core flow experiments.The four nanomaterials that are more suitable for the reservoir in the Ma 18 well area are nanometer polysilicon material(NMPM),hydrophobic nano-alumina material(a-A1203),hydrophobically modified a-zirconium phosphate(a-ZrP-1)and Hydrophobically modified graphene oxide(M-GO).The diesel-made M-GO solution and a-ZrP-1 solution have a comparetively large influence on the wetted contact angle of the core surface of Well Ma 18,which can achieve a wet contact angle of 147.1° and 138.5° respectively.Its experiment results of rapid drag reduction effect evaluation are also relatively good.Of eight resultant nanofluids generated by a mix of these two nanomaterials and Gemini surfactants,sodium dodecyl sulfate(SDS),emulsifier OP-10 and dodecyldimethyl betaine(BS-12),the three groups of nanofluid systems consisting of a-ZrP-I+OP-10,?-ZrP-I+SDS,and M-GO+Gemini surfactants embodies strong stability and wettability change capablity.By conducting core flow experiments,the average drag reduction ratios are equal to 44.85%,21.95%,and 18.8%respectively.Then,the injection parameters of ?-ZrP-I+OP-10 nanofluid system are optimized including concentration,slug,static adsorption time,and nanofluid formulation ratio.Ultimately,the following research results are obtained:(1)Compared with the other two nanomaterials,hydrophobically modified graphene oxide and hydrophobically modified a-ZrP nanomaterial solutions have better drag reduction and injection enhancement effects on ultra-low permeability reservoirs in Mahu Sag.(2)Hydrophobically modified a-ZrP and OP-10-modified nanofluids are better than the other seven nanofluids for drag reduction and injection enhancement in ultra-low permeability reservoirs in Mahu Sag.(3)The compounding ratio of OP-10 to ?-ZrP-I produces better results when it is set as 1:1 to 1:2.When concentrations are set within 90 mg/L to 110 mg/L,slugs 2 to 3 PV,and soaking time of 26 h to 30 h,each achieves good results.