A dispersant and a drilling fluid containing the dispersant

A dispersant comprises the product obtained from the reaction of water, lignin, phenol, sulfonating agent, telogen and catalyst at 140-220°C, preferably at 160-180°C; the catalyst is one or more selected from the group consisting of sulfamic acid, p-toluenesulfonic acid and benzenesulfonic acid. The sulphonating agent may be a metal sulphite e.g. sodium sulfite, sodium bisulfite; the telogen is preferably an aldehyde e.g. formaldehyde, acetaldehyde, propanal, pentanal. Also shown is a drilling fluid comprising the dispersant wherein the dispersant can significantly lower the viscosity of the drilling fluid and also plays a role in reducing filtration loss.