Certain methods to determine wellbore relative permeability ratio from wellbore drilling data are described. A section of a wellbore is drilled in a subterranean zone including a subsurface reservoir in which hydrocarbons are entrapped. The hydrocarbons include a multiphase fluid including oil phase and water phase. A relevant suite of logs of rock in the section of the wellbore is determined. Water saturation is determined from the relevant suite of logs. A relative permeability ratio of the rock in the section to a flow of the oil phase and the water phase is determined. Using the relative permeability ratio, a flow rate of the oil phase or a flow rate of the water phase through the rock is determined.