Tertiary amine-grafted silica nano-plugging agent and water-based drilling fluids

A tertiary amine-grafted silica nano-plugging agent, wherein the tertiary amine-grafted silica nano-plugging agent is prepared from a hydrazine compound, a diallyl compound, an enamine compound, a silica particle, and an amino-containing silane coupling agent, wherein the silica particle has a particle size of 10-20 nm;

• the tertiary amine-grafted silica nano-plugging agent is prepared through steps of:
• (S1) adding 0.25-0.3 mol of the silica particle into 70 mL of methylbenzene followed by heating to 50-60° C. and stirring to obtain a first solution;
• introducing nitrogen for 20-30 min, and heating the first solution to 80-90° C. followed by addition of the amino-containing silane coupling agent under stirring;
• reacting the silica particle with the amino-containing silane coupling agent for 5 h followed by vacuum distillation for 2 h to obtain a first crude product;
• and subjecting the crude product to rinsing with methylbenzene and filtration to remove unreacted silica particle, and vacuum drying for 2 h to obtain a modified nano-silica;
• (S2) dissolving the modified nano-silica in 90-110 mL of tetrahydrofuran to obtain a second solution;
• adding 0.24-0.29 mol of the diallyl compound into the second solution followed by stirring at 50-60° C. for 24 h and vacuum distillation for 2 h to obtain a second crude product;
• and drying the second crude product under vacuum for 2 h followed by dissolving in 90-110 mL of tetrahydrofuran under stirring to obtain a third solution;
• introducing nitrogen for 20-30 min, and adding 0.48-0.53 mol of the hydrazine compound under stirring in the protection of nitrogen followed by heating to 30-40° C. for reaction for 8-12 h and vacuum distillation to obtain a secondary amine polymer;
• and
• (S3) dissolving the secondary amine polymer in 90-110 mL of tetrahydrofuran to obtain a fourth solution;
• adding 0.24-0.29 mol of the enamine compound into the fourth solution, followed by stirring at 60-68° C. for 36 h and vacuum distillation to obtain a third crude product;
• subjecting the third crude product to vacuum drying for 2 h to obtain a hydroxyl-containing tertiary amine polymer as the tertiary amine-grafted silica nano-plugging agent;
• and subjecting the tertiary amine-grafted silica nano-plugging agent to grinding and sealed storage;
• and
• the hydrazine compound is selected from the group consisting of 2-hydroxyl benzoyl hydrazine, 3-hydroxyl benzoyl hydrazine, 4-hydroxyl benzoyl hydrazine, 4-hydroxyl phenylacetic hydrazine, 2,4-dihydroxyl benzoyl hydrazine, 3,4-dihydroxyl benzoyl hydrazine, and 3,5-dihydroxyl benzoyl hydrazine;
• and the enamine compound is selected from the group consisting of N-methyl-N-vinyl acetamide, N,N-diethyl-2-acrylamide, and N-vinyl-N-methyl-2-acrylamide.