Drilling mud additive, drilling mud composition and ground drilling method

摘要

(A) represented by the following general formula (I) and a repeating unit (b) represented by the following general formula (II), wherein the total number of moles of the repeating unit (a) and the repeating unit , Wherein the ratio of the number of moles of the repeating unit (a) to the number of moles of the repeating unit (a) is from 0.5 to 0.99, the additive for drilling and muddy water comprising a water-soluble polyurethane. (In the formula, A represents a divalent linking group containing a poly (oxyalkylene) group, D represents a divalent linking group having two or more monovalent hydrocarbon groups having 4 to 21 carbon atoms in the molecule And B represents a divalent linking group.)