Quantitatively determining gas content using pulsed neutron logging technique in closed gas reservoir

Abstract Tight gas has become an important part of unconventional petroleum exploration and development. The evaluation of gas content is of great significance for reservoir prediction and oil & gas production. Pulsed neutron technology has been widely used for gas content evaluation in cased hole. The accurate evaluation of gas content under different types of gas reservoir is a huge challenge for pulsed neutron technology. In this paper, for closed gas reservoirs, the apparent gas saturation which utilizes the captured gamma ratio of near to extra-far detector is proposed to evaluate gas content. To accurately determine gas content, the responses of apparent gas saturation under different environment conditions were studied by Monte Carlo simulation. The result shows that lithology and clay content have a great influence on the use of the captured gamma ratio to calculate the apparent gas saturation. At the same time, the gas content in the wellbore is also an important interference factor. These factors should be considered in the actual evaluation of gas content. At last, the actual measurement data and interpretation results verify the validity of the method.