Abstract: This paper makes a research on extra-low permeability reservoirs in early Cretaceous Yingcheng formation of Shiwu oilfield in Songliao basin. By analyzing plenty of petrophysical measurements, extra-low permeability reservoir characteristics in this area has been revealed, and a model was built with reasonable reservoir parameters such as porosity, saturation and permeability etc. According to the analysis of logging, oil test and mercury injection data, the minimum effective thickness limit were determined to meet the requirements of the logging assessment of extra-low permeability reservoirs in oilfield, and the accuracy of logging interpretation in target reservoirs and the favorable zones prediction in this area has been enhanced.