Gamma ray logging while drilling is currently one important geo-steering logging technology. Due to the influence of many formation or non-formation factors, the gamma ray pipe detection is interfered more by K40, so the environmental coefficient shall be corrected. In newly developed blocks (e.g. South Pars Block in Iran), however, on-site operators cannot correct the gamma value accurately for LWD manufacturer cannot offer accurate field correction data and charts. In this paper, optimization fitting analysis and matlab data statistics were carried out on abundant practical data obtained during the directional drilling of ?311 mm hole in four blocks of South Pars, Iran, including SPDC19-x, SPDC15-x, SPDC4-x and SPDC6-x. And a new correction method was developed and a new gamma calculation formula was established. When KCl drilling fluid system is used, the gamma ray curve plotted on the basis of the new correction method is highly accordant with the gamma value of reference exploration formation, with accordance rate of 95% and error ratio lower than 1%. Obviously, it is much superior to the traditional correction technologies. It has been widely applied to the field correction of over 20 wells in other blocks of South Pars in Iran.%随钻自然伽马测井是现代地质导向测井的主要技术手段,且受到诸多地层或者非地层因素的影响,其中K40对伽马探管的探测有着较大的干扰,需要进行环境系数校正.但是在伊朗南帕斯区块等新开发区块,LWD生产商无法提供准确的现场校正数据和图表,导致现场人员无法准确完成伽马值的校正工作.通过对伊朗南帕斯SPDC19-x、SPDC15-x、SPDC4-x、SPDC6-x四大区块中?311 mm井眼的定向井施工中得到的大量实践数据进行优化拟合分析和matlab的数据统计,得出了新的校正方法和伽马值的计算公式.在KCl钻井液体系下,通过新的校正法得到的伽马曲线与标准勘察地层伽马值吻合度高达95%,且负值错误率低于1%,远优于传统校正方式,并且在伊朗南帕斯其余区块20余口井的现场校正施工中得到了广泛的应用.
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