Abstract Tight gas reservoirs have been one of the most important field of gas exploration and development, and the dynamic monitoring of gas saturation is of great significance to the adjustment of oilfield development scheme. Pulsed neutron logging technology plays an important role in the evaluation of gas saturation in cased holes. The low porosity of tight gas reservoir presents a new challenge to the application of pulsed neutron logging technology. In order to further investigate the measurement information of pulsed neutron logs to improve the performance of gas saturation measurement, the Monte Carlo numerical simulation method is used to study the gas saturation responses of different parameters obtained by the pulsed neutron-gamma logging instrument with an extra gamma-ray detector added. The results show that the capture count ratio measured by the instrument is mainly affected by changes in the hydrogen index of the formation. The ratio of pure inelastic gamma rays is more sensitive to the variation of formation density. When the porosity of the reservoir is fixed, the gas layer has a low hydrogen index and low density relative to the water layer. By combining the response characteristics of the two ratios, a new gas saturation evaluation parameter (GSEP) is proposed to evaluate gas saturation. The new method displays a higher gas sensitivity compared with the conventional ratio method and macroscopic capture cross section (Sigma) method. In addition, the response characteristics of GSEP in different well logging environments are also studied. It displays GSEP is less affected by the variation of the formation water salinity and clay contents compared with the Sigma method. At last, field examples are presented to validate the effectiveness of the proposed method.

中文翻译：

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套管井中脉冲中子测井评价含气饱和度的方法

摘要 致密气藏一直是天然气勘探开发的重要领域之一，含气饱和度动态监测对油田开发方案的调整具有重要意义。脉冲中子测井技术在套管井含气饱和度评价中具有重要作用。致密气藏的低孔隙度对脉冲中子测井技术的应用提出了新的挑战。为进一步研究脉冲中子测井的测量信息，提高含气饱和度测量性能，采用蒙特卡罗数值模拟方法，研究脉冲中子-伽马测井仪获得的不同参数对含气饱和度响应的附加值。添加了伽马射线探测器。结果表明，仪器测得的捕获计数比主要受地层氢指数变化的影响。纯非弹性伽马射线的比例对地层密度的变化更为敏感。当储层孔隙度固定时，气层相对于水层具有较低的氢指数和较低的密度。通过结合两个比率的响应特性，提出了一种新的含气饱和度评价参数（GSEP）来评价含气饱和度。与传统的比率方法和宏观捕获截面 (Sigma) 方法相比，新方法显示出更高的气体灵敏度。此外，还研究了GSEP在不同测井环境下的响应特性。表明与Sigma方法相比，GSEP受地层水盐度和粘土含量变化的影响较小。最后，通过现场实例验证了所提出方法的有效性。