Tight Gas Evaluation Method Based on Fast Neutron Cross Section and Its Applications

The tight sandstone gas reservoir in a certain area of Shanxi Province is characterized by low porosity and low permeability. The relationship between pore structure, resistivity and gas and water is complex. The reservoir characteristics pose challenges to the traditional gas layer interpretation and evaluation methods mainly based on resistivity logging. Therefore, it is urgent to seek a gas layer evaluation method that is suitable for such complex reservoirs and well conditions. This paper is based on the small-diameter pulsed neutron saturation logging tool - reservoir evaluation tool (RET), and uses the Fast Neutron Cross Section (FNXS) method to evaluate gas layers.. Based on the feature that FNXS is sensitive to gas but not to non-gas, the FNXS value characterization formula is obtained through Monte Carlo numerical simulation under complex pore structure conditions. The correctness of the FNXS characterization formula is verified in the standard calibration well, and the gas saturation of the reservoir is calculated. The accuracy of this method is verified through field gas testing. Meanwhile, through the data analysis of multiple wells in the block, the FNXS value characterization formula for mudstone correction suitable for this block is established, further improving the accuracy of gas saturation calculation and forming the preliminary gas layer evaluation standard for this block. Practice has proved that the FNXS method based on the RET instrument can quickly identify gas layers under complex formation and well conditions. After slime emendation, the FNXS value characterization is more accurate and the calculation of gas saturation is more precise. This research effectively guides the exploration and evaluation of tight gas in the study block. In - depth research on the FNXS method shows that this method can also be popularized and applied in conventional gas - bearing reservoirs.