Compositions with modified tannins can be used in wellbore operations. A composition can include an oil, a modified tannin, a dimer fatty acid, an aqueous liquid, and an emulsifier, where the material is injectable into a wellbore. The modified tannin may be treated with a primary amine, secondary amine, tertiary amine, or quaternary amine. The compositions may be used as drilling fluids having enhanced yield point and fluid loss control properties.