Abstract: In land facies detrital reservoirs,mudstones and silty mudstones with low resistance are very common,and sometimes thinner calcareous interlayers with high resistance are also found,resulting in strong nonhomogeneity.Those interlayers are oil free or not contributive to commercial oil and gas flows,hence should be deducted when calculating the effect thickness of reservoir.The deducting method of interlayer thickness has been studied based on micro-electric-log and Laterolog 8,improving the reliability of effective thickness calculation and reserve prediction.