A method for tight gas reservoir evaluation based on nuclear logging

Abstract

Tight gas reservoirs with low porosity and low permeability can encounter problems such as small dynamic range of measurement information and low log-response sensitivity, which make it difficult to accurately identify gas reservoirs and evaluate gas saturation. The purpose of this paper is to improve the accuracy of tight gas reservoirs evaluation by combining different nuclear logging methods. Slope, a parameter based on thermal neutron cross section and density, is proposed to improve the accuracy of tight gas reservoirs evaluation. The Monte Carlo method is used to analyze the sensitivity of different nuclear logging parameters to gas-bearing formations. The effects of various environmental factors on slope calculation results are analyzed. The applicability of the proposed method in synthetic models and field data is analyzed to verify its effectiveness. The results show that the sensitivity of the slope-based method to gas in low-porosity formations is much higher than that of other methods. Shale content has a minor impact on slope. Lithology and gas density affect slope calculation results. Salinity has little effect on slope in low-porosity formations. The data interpretation results from the field well show that the accuracy of gas saturation calculation of the slope-based method is much higher than that of the Archie formula-based method. The proposed method can provide strong support for the effective exploration and development of tight gas reservoirs.