Abstract: The present invention provides a filtration control agent and a drilling fluid containing the same. The filtration control agent comprises the product obtained from the reaction of water, lignite, aldehyde and sulfonate polymer at 180-220° C. and the units containing sulfonate groups in the molecular chains of sulfonate polymer are at least 30 wt %. The filtration control agent provided by the present invention features a good filtration loss reduction effect and a low viscosity effect and can improve the rheological behavior of the drilling fluid, thereby meeting the requirements of the drilling of deep wells, ultra-deep wells and ultra high pressure formations.

Abstract: The present invention provides a dispersant and a drilling fluid containing the dispersant. The 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 dispersant provided by the present invention not only can significantly lower the viscosity of the drilling fluid but also plays a role in reducing filtration loss.