| By adding nanomaterials and special surfactants in the common acid solution,a low-viscosity,low-resistance nanoretarded acid was prepared without increasing the viscosity of the acid solution,which can greatly reduce the acid-rock reaction rate and increase the effective distance of acid etching to achieve the purpose of improving single well production.In this paper,foam acid was used as the research object,through the study of co-stabilized bubble theory between nanoparticles and surfactant,analysis of matching rules and interaction mechanisms between solid particle characteristics and surfactant,exploration of the enhancement of solid particles on the foam liquid film,the nanoparticles were optimized and modified.Through the synthesis of the surfactant intermediate AMD of the acid system,and then the performance-matched surfactant YFP was synthesized to form the key technology of solid particle reinforcing foam acid.Finally,a new type of low-viscosity,low-resistance retarded acid system was built by means of a small amount of drag reducer to achieve effective drag reduction.The main results were as follows:(1)The intermediate AMD was prepared with fatty acid and N,N-dimethyl-propanediamine as raw materials by amidation condensation reaction.By the nucleophilic substitution reaction of AMD with sodium chloroacetate,a betaine-type amphoteric surfactant YFP with good foaming ability and foam stabilizing ability was synthesized.Infrared spectroscopy FT-IR and 1HNMR were used to confirm the structure of the intermediate AMD and surfactant YFP.The effects of reaction temperature,mole ratio of reactants,catalyst concentration and reaction time on the conversion rate of fatty acids were investigated.The results showed that the temperature was controlled at160~170°C,the optimal molar ratio of fatty acid to N,N-dimethyl-propanediamine is 1:1.1,the mass fraction of the catalyst is 0.2%,and the optimal reaction time is 8 hours.The influencing factors of acid surfactant synthesis were analyzed,and the product performance,optimumfoaming concentration,mineralization resistance and temperature resistance performance of the acid surfactant YFP were evaluated.The results showed that the optimal reaction conditions were as follows: the ratio of solvent is 1:1,the molar ratio of tertiary amine to sodium chloroacetate is 1:1.05,the optimal reaction temperature is 85°C,the reaction time is 7h,and the optimal foaming concentration is 0.3~0.5%.The surfactant YFP has the largest half-life and good thermal stability in both clean water and acid when the salinity is 150,000 mg/L.(2)After adding nano-silica,a synergistic effect is generated with the acid frothing agent YFP to form a relatively dense foam,the volume of the foam is decreased at different degree,and the half-life is prolonged.After adding 1.0%nanomaterials,the foam volume of 0.5%YFP solution with 20%HCl decreased from 500 mL to 395 mL,and the half-life increased from 8min to 14 min.(3)In order to further enhance the synergistic effect between nanomaterials and acid liquid foaming agents,the nano-silica was modified with silane coupling agents KH570,A172,A171 and A151.The experiment results showed that the nano-silica modified with KH570 had the best foam performance.The optimum reaction conditions are 0.3% KH570.After the modification,the contact angle is 46°.By adding the nano-silica modified with KH570 to the acid solution,the foam half-life can be effectively improved(8.1 min to 25 min),and the foam height is basically unchanged(400mL to 385mL).The effects of particle size and concentration of nano-particles on the stability of the foam were discussed.The actual industrial conditions are preferably a particle size of 20 nm and a concentration of 1.0%.(4)According to the above research results,the basic formula of the retarding acid is determined as 20%HCl+0.5%YFP+1.0% nano-silica.The compatibility of retarded acid with corrosion inhibitors,iron ion stabilizers,cleanup additives and drag reducers were further studied.The results showed that the retarded acid has good compatibility with all the additives,the formula of the optimal acid system is as follows: 0.5% YFP,1.0% nano-silica,20% HCl,1.5%corrosion inhibitor,1.0%iron ion stabilizer,0.5% cleanup additive and 0.2% drag reducer.The static dissolution test and dynamic erosion test were used to analyze the reaction kinetics with the acid-rock reaction.A 0.5% acid frothing agent YFP was prepared in 20%HCl,after adding 1.0% nanosilica,the average staticreaction rate of the core was decreased by 5.4 times at 90°C,and the average dynamic reaction rate was decreased by 11.9 times. |
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