Abstract: Jirgalangtu depression is one of the important exploration targets in Erlian faulted basin. The reservoirs are mainly glutenite bodies of fan delta, near-shore sub-aqueous fan and sublacustrine fan deposit. The reservoirs are mainly of lithologic and structural-lithologic reservoirs characterized by high resistivity water layers and low resistivity gas layers. Based on the analysis of well drilling, mud logging, well logging, testing and core analysis, the relationship among four properties of medium porosity and low permeability reservoir was discussed. According to the relationship, the well logging interpretation model was established and the standard lower limit for the effective thickness determined. On this basis, we used the three-porosity overlay method to effectively identify the low resistivity gas layers. The abnormal magnitude on spontaneous potential was used to effectively recognize high resistivity water layers and low resistivity gas layers. The old wells are rechecked and the layer No.1 (water layer formerly) in X4-12 well area was interpreted as oil, making the layer No.1 become a whole and the oil-bearing area broadened. Moreover, five tight layers (4.7 m) in X4 well area were interpreted as poor oil layer, seventeen poor oil layers were interpreted as oil layers, largely increasing the thickness of oil-layer.