Preparation method and application of modified lignin-based gel water plugging agent

The invention discloses a preparation method and application of a modified lignin-based gel water shutoff agent, and the preparation method comprises the following preparation steps: step A, putting a lignin raw material into a reaction container, uniformly stirring, adding a carboxymethylation modification reagent, and reacting for a period of time at a certain temperature; step B, adding an epoxy modification reagent, and reacting for a period of time at a certain temperature; c, adding a polyvinyl alcohol solution, uniformly stirring, and cooling; and D, adding a cross-linking agent to adjust the concentration, uniformly stirring, transferring into a high-temperature-resistant pipe or a high-temperature-resistant tank, putting into an electrothermal blowing dry box, and reacting at 100-200 DEG C to form gel, thereby obtaining the modified lignin-based gel water plugging agent. The lignin is subjected to chemical modification, the modified lignin contains carboxyl and epoxy groups at the same time and then