Development And Performance Evaluation Of High Temperature Resistant Nano-SiO₂ Oil Based Fracturing Fluid

In recent years,with the dwindling of conventional oil and gas fields,conventional oil and gas production declined year by year.For this reason,the world transfer their enhancing oil and gas production's focus on the development of low-permeability,low-pressure and strong water-sensitive reservoir and tother unconventional oil and gas resources.The reserves of such resources are very rich in our country.There are about 1.9×10¹⁴m³unconventional oil and gas reserves,is 2 times of the conventional oil and gas reserves.The oil-based fracturing system is an important way to exploit low-permeability,low-pressure and strong water-sensitive reservoirs.Oil based fracturing fluid has own advantages,however the stability and persistence of the system become worse when it encounters high temperature formation?above 100??.In this paper,modified nano-SiO₂ was added to the base solution.As SiO₂ has good thermal stability,it can significantly improve the temperature resistance of the system and the performance of oil-based fracturing fluid.The new high-temperature resistant nano-SiO₂ oil based fracturing fluid had been developed.Firstly,wettability,dispersion and particle size distribution of nano-SiO₂ were analyzed.Then we adopted the method of wet method modification.SCA-1?SCA-2?SCA-3?SCA-4?SCA-5?SCA-6 as the modifier,the nano-SiO₂ surface modification experiment was carried out.Then the type of modifier was determined by the number of hydroxyl groups on the surface of SiO₂ and the particle size distribution,and the influence of the amount of modifier,reaction temperature and reaction time on the modification effect was analyzed.Finally,the amount of modified SiO₂ was optimized.Experimental results show that the surface hydroxyl number of nano-SiO₂ modified by SCA-4 was biggest drop,and the decrease rate of SCA-4 reached80%.The number of hydroxyl groups on the surface of SiO₂ decreased to 0.24nm^-2.The result showed that size distribution of SiO₂ clearly left shift.It showed that the aggregation of modified SiO₂ in solvent can be effectively improved.Moreover,the particle size distribution of modified nano-SiO₂ was concentrated.Therefore,SCA-4 was selected as the modifier.The amount of modifier was determined to be 15%,the reaction temperature was 130?,and the reaction time was 50min.The amount of modified SiO₂ was determined to be 0.3%according to the relationship between the thermal stability and viscosity of the fluid and SiO₂ of different volume fraction.Secondly,dialkyl phosphate was prepared by microwave heating with triethyl phosphate,which greatly shortened the reaction time and increased the reaction yield,and obtained more pure products.Different kinds of alcohols were used as the raw materials in orthogonal experiment to obtain the optimum reaction conditions and 7 kinds of gelatinizer were producted.The results showed that in a certain amount of carbon number,the viscosity of fracturing fluid increased with an increasing length of the ester chain length.When the ester linkage is C₁₃viscosity growth rate is the largest,but then the growth trend of relatively flat.In terms of cost and construction difficulty,this paper selected the new C₁₄dialkyl phosphate?PE-14?as a gelling agent of fracturing fluid.Finally,three kinds of fracturing fluids which contain PE-14,PE-14nano-SiO₂ and traditional fracturing fluid were taken to do the performance evaluations.The results showed that compared with the traditional oil base fracturing fluid,the new PE-14 nano-SiO₂ oil based fracturing fluid has significantly improved the viscosity and the heat resistance.The new recipe was 500ml white oil+0.3%SCA-4-SiO₂ +1.5%PE-14+0.5%Al₂?SO₄?₃+1%Na Ac.The maximum viscosity is 233.8m Pa·s;Heat resistance reach130°C;After gel broken,the viscosity is less than or equal to 5 m Pa·s and residue is 0 mg·L^-1.