Research on recognition of gas saturation in sandstone reservoir based on capture mode

Abstract

Pulsed neutron technology has been widely used to monitor the remaining oil saturation of the formation. In order to solve the problem of the remaining oil saturation and porosity of the reservoir after casing, and to study the condition of the reservoir after water flooding, the pulsed neutron logging tool with the same technology has been recommended and used in China. Most of these instruments have many measurement modes such as inelastic, capture, carbon–oxygen ratio, and gas-view, and these can measure a large amount of stratum information. By studying the influencing factors of the capture mode in sandstone reservoirs, it can be used to research the methods of gas reservoir identification and quantitatively evaluate the gas saturation. This paper studies the detection principles, modes, advantages, and disadvantages of pulsed neutron logging tools. The principle of gas recognition is analyzed in the capture mode, and the formation model is established based on the Monte Carlo method. The common influencing factors are studied, and the sensitivity of detection is also analyzed. It realizes the identification of gas layers by the combined detector, as well as the calculation of gas saturation in comprehensive logging interpretation. The results show that the source distance of the detector affects the detection sensitivity, and the sensitivity of the near-ultra-far detector combination is better. As the porosity increases, the sensitivity of the detector increases, and the capture count ratio also increases significantly. Based on the same pore conditions, the higher the gas saturation, the lower is the capture gamma ratio. The shale content is less sensitive to the capture gamma count ratio, and it can still be concluded that the higher the mud content, the lower the capture count ratio. The conclusions can be used in the research method of gas formation identification and can also be used to accurately explain and quantitatively analyze the gas saturation of the formation.