Hydrocarbon-bearing formation identification with conventional logs faces great challenge in tight sandstone reservoirs due to the low resistivity contrast and complicated oil/water system. The conventional methods, which are applicable in normal reservoirs in oil or gas identification, such as the porosity and resistivity crossplot of the Hingle and Pickett crossplots, lose their roles. In this paper, based on the analysis of the conventional log responses in hydrocarbon-bearing formations in the Chang 8 Formation in Longdong Region of Ordos basin, the positive correlation of porosity and resistivity in oil-bearing formation, and negative correlation in water saturated layers are observed. A correlation analysis method, which can be used to express the correlation of porosity and resistivity in formations with different type of pore fluids occupied, is presented, and the corresponding model which is used to calculate the correlation coefficient is established. For reservoirs with hydrocarbon-saturated, the value of the correlation coefficient ranges from 0.0 to 1.0, in pure water layers, the correlation coefficient ranges from −1.0 to 0.0, and in oil-water bed, the correlation coefficient is salutatory between −1.0 and 1.0. By using this correlation coefficient, hydrocarbon-bearing formations can be identified from pure water layers. This correlation analysis method can also be used in tight gas sands identification by establishing the correlation coefficients of porosity versus resistivity, density and neutron logs. Field examples illustrate that this method has played an important part in hydrocarbon-bearing identification in tight sandstone reservoirs.

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