A higher viscosity needs a larger pressure gradient to push the same rate through the same rock. Oilfield calculations use centipoise. Reservoir oil viscosity depends on pressure, temperature, and how much gas is in solution: it is usually lowest near the bubble point, then rises as gas comes out of solution and the oil cools on the way to surface.
Gas viscosity is much lower than oil viscosity, which is why gas moves more easily and why the mobility ratio of a gas displacement is often unfavorable. A viscosity used in a well calculation has to be the viscosity at the pressure and temperature of that calculation, not the dead-oil viscosity measured in the stock tank.