Method of preparing sulfonated-phenoformoldehyde resin for drilling fluid

The invention discloses a kind of sulfomethylated phenolic resin for drilling fluid and its preparation. The material is prepared according to following steps and weight shares: a. it puts 3.8~4.1 of phenol, 0.9~1.1 of dihydric phenol, 1.4~1.7 of sodium pyrosulfite, 0.1~0.2 of coupling agent, into a tank, and mixes them for 2~3 hours. b. it transfers the mixture into the reactor, boosts 1mpa, keeps the pressure for an hour. c. it transfers the mixture into a microwave cycle reactor and cycles for 2 hours. d. it transfers the mixture into the next reactor, and adds another 0.3~0.6 of phenol, 2.0~2.2 of sodium pyrosulfite, 0.16~0.19 of dispersant, and cysle the mixture for two hours, and boosts 2.8mpa, and keeps the pressure for 3~4 hours, after that it transfers the mixture into a spray-dryer to remove water to achieve the products.