If equal amount of oil is distributed in reservoir rocks with different porosity

the oil packing degree in the pore is different. The porosity is larger

the packing degree is lower and the oil saturation in reservoir rock is lower whereas the saturation is higher. So a new method for distinguishing oil and water intervals can be obtained through acquiring the oil saturation in reservoir rock with rock-eval and setting up the relation between oil saturation and the porosity. The key step is to get exactly the density of reservoir oil.Test result of moderate density oil in Tarim Basin are similar to the real situation. The method is not suitable for bearing light oil because it is volatile on the ground.