Abstract:Neutron technology utilizes the interaction between neutrons and matter to determine its composition and other properties, and finds wide-ranging applications in fields such as medicine, environmental science, nuclear reactor construction, metal mineral exploration, and petroleum industry. Within the oil and gas industry, neutron detection technology is primarily employed for determining crucial parameters such as porosity, density, and fluid saturation in wellbore formations. As logging technology progresses, neutron activation analysis based on prompt gamma rays has emerged to determine the content of formation elements in the well, becoming the sole method for obtaining mineral content in complex lithology and unconventional oil and gas reservoirs. This paper presents a detailed account of the gamma-ray spectrum logging method for assessing formation elements. The Monte Carlo method is used to simulate the gamma-ray spectrum under varying formation conditions, and a standard spectrum library for formation elements is constructed. Furthermore, the study explores data processing methods, including singular value decomposition and maximum likelihood estimation, to extract specific parameters from the spectrum data. The obtained element yield and oxygen closure model enable accurate determination of formation element content. Monte Carlo simulations were conducted using known formation data, and the aforementioned data processing methods yielded errors within 4% compared to the actual formation element content, with the maximum error for Si element being 2.8% and for Ca element being 3.3%. These research findings establish effective technical support for the determination of composition and content of formation elements in subsurface environments.