ADDITIVE FOR DRILLING FLUID, DRILLING FLUID COMPOSITION AND GROUND EXCAVATING METHOD

摘要

An additive for a drilling fluid, consisting of a water-soluble polyurethane which comprises repeating units (a) represented by general formula (I) and repeating units (b) represented by general formula (II) at a ratio of the molar amount of the repeating units (a) to the total molar amount of the repeating units (a) and the repeating units (b) of 0.5 to 0.99. In the general formulae, A is a divalent linking group which contains a poly(oxyalkylene) group, D is a divalent linking group which contains two or more C4-21 monovalent hydrocarbon groups in the molecule, and B is a divalent linking group.